The Egyptian Nile estuarine habitats: a review

Abstract

Estuaries are nutrient-rich environments characterized by a gradient in salinity due to the mixing of freshwater and seawater. These bodies of water play vital functions in nature and provide a wide variety of essential ecosystem services. In general, many natural and/or man-made activities have strongly stressed the Egyptian Nile estuarine habitats, as has the water shortage that was expected after the construction of the Grand Ethiopian Renaissance Dam. In recent decades, the Nile Delta has been considered to be one of the most important productive oil-producing petroleum regions due to onshore and offshore gas discoveries alongside gasoline and base oil generation. Up-to-date systematic reviews of the Egyptian estuarine habitats (Rosetta and Damietta) are missing, and the review reported here was undertaken to fill this gap. In this review, we consider the physical, chemical, geological, pollution, and biological parameters of Egyptian Nile estuaries. In this context, our aim is to contribute to a broader understanding of the Egyptian estuarine habitat; moreover, we provide potential warning signals that may aid in estuarine environmental protection. We found that most of the previous studies had focused on the two branches of the Nile or on the marine waters adjacent to these branches, and that only a few studies focused on the estuarine habitats themselves. In most of these previous studies, the salinity gradient of water was reported to be a significant factor in the distribution of the different measured parameters while, in contrast, more recent investigations confirm the importance of potential effluent sources in affecting the distribution of these parameters. We highly recommend that the data reported here be updated in future studies on different environmental aspects.

Introduction

An estaury is an area where freshwater and marine water mix (El-Gamal 2017). These types of water bodies have a vital function in nature and supply several crucial ecosystem services by crossing the boundary between rivers and the sea (Savage et al. 2012; Layman et al. 2014; Gittman et al. 2016).

Estuaries have attracted human settlements from prehistoric times because of their ecosystem services and their sheltered nature (López-Romero et al. 2023). Estuaries are one of the most important aquatic resources in the world, providing food and habitat for fish and shellfish species that are both ecologically and economically significant, as well as recreational opportunities, experiences for science and education, and other crucial ecosystem services (Costanza et al. 1997; Hobbie 2000; Yoskowitz et al. 2010). These ecosystems are extremely productive in the tropics and host a diverse population of invertebrates. These habitats can serve as spawning and nursery grounds for a range of young marine fish, crustaceans, and other planktonic organisms because of their distinctive productive features (Whitefield 1998; Sheaves et al. 2015).

Rivers and other surface waters are by far the most important mechanism for transporting solids and suspended matter into the sea (Juračić and Prohić 1986). As recently reported by Broadley et al. (2022), every year, some 36,000 km³ of freshwater enters coastal fishing locations around the world through rivers and estuarine habitats. Freshwater and sediment movement affects coastal circulation regionally, boosts marine productivity, and aids in defining the hydrologic characteristics of estuarine and oceanic waters. Additionally, on average more than 20 billion tons of both dissolved and solid sediments are added to the ocean each year. Rivers are a significant factor in defining the estuarine and coastal environment, along with tides, winds, waves, currents, and geology (Milliman and Farnsworth 2011). For example, water circulation in estuaries has a direct impact on suspended particle transport and deposition (Meade 1972). In addition, variations in flow velocity and the presence of sharp density and salinity gradients, cause fine particle aggregation and settling in the estuarine mixing zone (Wright 1977; Menon et al. 1998).

Estuaries are under a great deal of pressure from human settlements, rapid urban expansion, and related agricultural and industrial advances (Lemley et al. 2017). Other natural processes, such as global warming, also place stress on estuaries. The rapid decline of this aquatic ecosystem as a result of heavy element pollution is a focus of considerable concern worldwide. In addition, rapid fluctuations in the concentrations of heavy elements in the estuarine waters may affect rate of absorption or release of these elements by the bed sediments (James 1985).

Egypt is one of 11 African countries through which the Nile River runs before discharging into the Mediterranean Sea. Egypt’s life artery is the Nile River. Throughout recorded Egyptian history the Nile has greatly affected the culture, economy, social life, public health, and political aspects of Egypt, and remains doing so today (Abdel Hamid et al. 1992). However, the construction of the Aswan High Dam (AHD) has greatly altered the hydrodynamic regime of the Nile River and significantly altered the environmental aspects of Nile River water flowing downstream (Saad and Goma 1994; Fishar and Khalifa 2003). It is reported that 55.5 × 10⁹ m³ of water are released from the AHD each year. Over 100 million Egyptians live within the Nile's catchment, and the river receives different sources of pollution (domestic, industrial, and agricultural).

The Nile Delta was created through the deposition of nutrient-rich sediments carried down the Nile River as silt during flood seasons. After passing through Cairo, the Nile divides into two branches: the Rosetta branch in the west and the Damietta branch in the east (Fig. 1). In the historical context, originally there were seven branches, each of which created a lobe in the Mediterranean Sea. Only the Damietta and Rosetta tributaries have remained up to the present following the silting up of the other five branches (Sneh and Weissbrod 1973). Significant natural and human-caused environmental changes have recently occurred in the Nile Delta (Becker and Sultan 2009).

Fig. 1

Map of Egypt and the two remaining Nile branches: the Rosetta branch and the Damietta branch. Map is modified from Google Earth

The Rosetta branch, which flows in a north-west direction, is around 240 km long; it has an average width of 180 m and ranges in depth from 2 to 4 m. The water in this branch is controlled through the Edfina Barrage upstream and the Delta Barrage downstream. Renewal of water is regulated through the Edfina Barrage once a year, during the winter-closing period (when canals are closed to perform maintenance and constructions). Water taken from the Rosetta branch is mostly used as drinking water and for irrigation, industry, and fisheries (Dimian et al. 2014). However, massive amounts of contaminated water flow into the Rosetta branch each day from various sources, including waste from fish cages and sewage from industry, agriculture, and cities. These pollutants have a major negative influence on the aquatic ecology (Abdel-Satar and Elewa 2001; Elewa et al. 2009; Abbassy 2018).

The Damietta Branch, which has an average width of 200 m and an average depth of 12 m, travels approximately 242 km north from the Delta Barrage (20 km north of Cairo) before it enters the Mediterranean Sea in the coastal city of Damietta. The Farskour Dam, located on the Damietta Branch 20 km inland from the Mediterranean Sea, separates the branch into two distinct regions: saltwater to the north of the dam and freshwater to the south of the dam. This branch also receives contaminated water from a variety of sources, including industrial, agricultural, and municipal sewage, which has a significant negative environmental influence on its freshwater (Sayed 1998).

Ethiopia is aiming to enhance its energy production by building the Great Ethiopian Renaissance Dam (GERD), which will be powered by Nile River water. Although this project offers Ethiopia promising development potential, Egypt will face a difficult water deficit due to changes in the flow of the Nile River, which will have negative socioeconomic impacts (Heggy et al. 2021). Negm (2017) and Kansara et al. (2021) reported that Egypt's water supply will experience measurable shortages during the dam filling phase under short-term filling scenarios (3–5 years).

In general, these natural and/or man-made activities strongly stress any estuary, especially the Egyptian estuarine habitats. Consequently, the aim of this review was to summarize–in a historical context–the effects of all of these natural and/or constructed activities on the environmental conditions of the two Egyptian estuarine habitats (Damietta and Rosetta). We have analyzed the physical, chemical, geological, pollution, and biological aspects of these two Egyptian estuarines by comprehensively analyzing information from the available literature to understand past conditions and recently expected patterns of change in these habitats.

Physical parameters

Egypt’s Nile River estuaries represent a complex ecosystem that is most likely shaped by a number of physical factors. In estuarine ecosystems, some of the important physical factors that are frequently investigated include salinity, temperature, tidal range, river discharge, light penetration, and currents and water movement.

Estuaries exhibit differences in salinity due to the mixing of freshwater from rivers and saltwater from the sea or ocean. The salinity gradient greatly affects the distribution of species in estuaries (Cloern et al. 2017). Temperature fluctuations in estuarine ecosystems are frequently caused by tidal cycles, river discharge, and climate change while estuarine ecosystems are greatly influenced by tidal movements. The distribution of nutrients, the movement of silt, and the circulation of water are all impacted by tides (Daborn and Redden 2018). Additionally, the structure and functionality of estuarine ecosystems can be impacted by tidal range, although the regional tide is small in the Mediterranean Sea where the area of interface between fresh- and salt water may be limited. However, the freshwater discharged into the estuary from the Nile river strongly affects the salinity, nutrient availability, and sediment movement. Domingues et al. (2011) reported that in estuarine environments, the presence of light is essential for the establishment of submerged vegetation (phytoplankton). At the same time, light penetration may be impacted by turbidity, which is influenced by sea waves and sediment load (Dera et al. 1993).

For more than 1 million years up to the present, the annual flooding of the Nile River is the most significant environmental event in the southern Levant. The Nile releases massive amounts of biogenic salts into the coastal waters of the southeast Mediterranean every year from late summer through autumn, making them fertile and teeming with marine life (Dowidar 1984). Based on data of the Ministry of Public Works in Egypt, the estimated annual average of turbid Nile water discharging into the Mediterranean from 1956 to 1965 was approximately 46.86 × 10⁹ m³ (Ramadan 1976). This massive amount of turbid freshwater was detected in several areas of the Levantine (Dowidar 1965; Halim et al. 1967; Ramadan 1976) and reported to reduce water salinity to as low as 10 and 8 ppt a few kilometers upstream of the mouth of the Damietta and Rosetta branches, respectively (Halim 1960; Dowidar and El-Maghraby 1971). Additionally, the freshwater flows have the potential to cause physical changes in estuarine and coastal ecosystems that may have an impact on marine species either directly or indirectly (Drinkwater and Frank 1994). The building of the AHD in Egypt, however, has impacted marine life both in the coastal waters next to the Nile Delta and in the brackish water in the northern lakes due to the subsequent (after 1965) control of the release of excess Nile flood water into the Mediterranean Sea. Following the disappearance of phytoplankton blooms linked to the annual Nile floods, nutrient concentrations in these waters have significantly decreased. As a result, Sardinella catches have decreased from around 15,000 tons in 1964 to 4600 tons in 1965 and 554 tons in 1966 (Aleem 1972).

Similar to other deltaic locations around the world, the Nile Delta is liable to suffer from changes in shoreline due to accretion and erosion, land subsidence, and climate change-related sea level rise. In its fifth assessment report, the Intergovernmental Panel on Climate Change (IPCC) indicated that a range of local mechanisms unrelated to climate change influence both relative sea level rise (RSLR) and its consequences (e.g., subsidence, glacial isostatic adjustment, sediment transport, and coastal development) (IPCC 2014).

Many researchers have looked into the effects of sea level rise (SLR) on Egypt's Nile Delta coastal zones. To create a digital elevation model (DEM) for the Nile Delta coastal zones, these researchers relied on aerial survey maps and measurements of the sea level around the Delta and at the top of the Delta around Burullus Lake, which borders the Mediterranean Sea to the north. These studies found that if sea level increases by 1 m, 20–30% of the Nile Delta area would be swamped and lost due to a lack of field measurements and data to produce a DEM that depicts the true status of the Nile Delta coastal zones (El Ganzori 2012). In this same context, Hereher (2010) reported that according to digital elevation models, 18.1% of the area of the delta is below mean sea level, 12.7% is between 0 and 1 m a.s.l., and 13.1% is between 1 and 2 m a.s.l. These places are vulnerable to flooding if the sea level rises by 1 or 2 m. In a different study, Elshinnawy et al. (2017) reported that areas vulnerable to coastal flooding account for around 3.33%, 4.25%, and 11.75% of the total area of the Nile Delta according to the Coastal Research Institute (CoRI), Global Service Economy (B1), and Fossil Intensive (A1F1) scenarios, respectively; in contrast, 0.74%, 0.97%, and 3.01% off Nile Delta area are susceptible to flooding in the CoRI, B1, and A1F1 scenarios, respectively.

Temperature affects both the organisms in an aquatic ecosystem as well as the chemical and physical characteristics of the water in that ecosystem and is, consequently, an important factor in aquatic ecosystems (Delince 1992). At the mouth of the Damietta branch, water temperatures fluctuate from a low of 15.80 °C in the winter to a high of 30.30 °C in the summer. Ali (1998) reported that electrical conductivity measurements along the Mediterranean coast line were higher than those in the Damietta Estuary as a result of dilution with freshwater brought in by the Faraskour Dam. The readings for the estuary ranged from 1.62 to 9.21 mmhos/cm, a limited range, although the highest values (35.4 mmhos/cm) were noted in the summer as a result of seawater intrusion through the Boughaz entrance (Hassan et al. 2012a).

One of the biggest challenges currently facing the world, and not just at a national or regional scale, is climate change. Khalil et al. (2022) in their review on the impact of climate change on the aquatic biodiversity of Egyptian waters and the general approach to adaptative action, showed that there are observable detrimental effects of climate change on biodiversity and that it is likely that these effects will modify how species and ecosystems are distributed in the future, leading to overall biodiversity loss. Climate-related variations in air temperature, precipitation, and other stressors have already had an impact on the physical, chemical, and biological properties of freshwater ecosystems. Although Khalil et al. (2022) introduced the topic of the impact of climate change on many examples of the Egyptian aquatic ecosystem (e.g., marine ecosystem, Nile River, and wetlands), there has been no study on Egyptian estuarine habitats.

Estimates of the annual discharge of agricultural drainage water fluctuate depending on a number of factors, including irrigation system management, crop patterns, and irrigation efficiency. Limiting the amount of water released from the AHD impacts on the quantity and quality of the drainage water. The drought in the Horn of Africa generated a supply constraint, which resulted in a drop in Nile water flow downstream of the AHD. In response, the Ministry of Public Works and Water Resources set rigorous restrictions regarding the release and distribution of Nile water downstream of the AHD. It has been reported that there will be a rise in salinity and a further drop in the volume of drainage water when irrigation efficiency is improved on farms as well as in conserved systems. The amount of water wasted in the Mediterranean Sea has been calculated (Abu-Zeid 1995) and estimated to be between 11 and 14 billion m³ (average annual 12.8 billion m³). This water has the potential to transform Egypt's modern future. According to a Food and Agriculture Organization of the United Nations (FAO) assessment, Egypt’s strategic water budget is 55.5 billion m³, the majority of which is utilized for agriculture in the Nile Valley and Nile Delta, with the remaining 14 billion m³ flowing out to sea (Hundertmark and Salman 2005). This so-called “official” reuse increased from 2.6 billion m³ in 1988/1989 to 5.0 billion m³ in 1998/1999 (Yousif 2011).

Dorgham et al. (2019) evaluated a number of physical parameters, phytoplankton biomass (Chlorophyll-a), and nutrients in the coastal waters of five challenging regions in the eastern part of the Nile Delta, close to the Damietta branch. Biweekly samples were taken from January to December 2007. With relatively little variation across the sampling stations, the water temperature varied from 12.5 °C in the winter (February) to 31 °C in the summer (July and August). At the point where the Mediterranean Sea and Damietta Harbor meet, west to the Damietta Branch of the River Nile, the water may be categorized as moderately or high brackish based on its annual average salinities of 16.43 ppt and 18.55 ppt, respectively. At the point where Damietta Harbor and the Mediterranean Sea meet, the weekly salinity values ranged from 17.0 to 27.7 ppt for the majority of the year, but dropped to 1.6 to 4.6 ppt from September to November (this is called the winter blockage period whenever the flow of freshwater is permitted). The Damietta Branch of the Nile, which is located in the west, typically had a salinity of 21.5–22.5 ppt. The amount of garbage dumped at the Damietta Harbor-Mediterranean Sea link, however, was not documented. These authors also found that water turbidity varied temporally across the challenged region, with the lowest values (annual average: 13.4 nephelometric turbidity units [NTU]) being found in the western direction towars the Damietta Branch of the River Nile and the highest values (annual average: 117.4 NTU) being found close to the intersection of the Mediterranean Sea and Damietta Harbor. At the confluence of the Mediterranean Sea and Damietta Harbor, turbidity varied on a monthly basis between 0.2 and 13.4 NTU, while west of the Damietta Branch of the Nile River, turbidity maintained values of 3.6–11.2 NTU from May to August, increased to 26 NTU up to 117 NTU during the rest of the year. However, to date no comparable study has been conducted in the Rosetta estuary.

In previous studies on Egyptian estuaries, most of the studied physical parameters were related to river discharge, SLR, temperature, climatic change, industrial discharge, and salinity gradient. However, the most important consideration was associated with river discharge and salinity gradient. Over time, river discharge showed a gradual decrease that always correlated with increased salinity.

A recent study of physical parameters in the two Nile estuaries (unpublished data) showed higher salinity values for longer periods than those previously reported. These results can be correlated with the construction of GERD, where the shortage of freshwater that pours into the Mediterranean Sea may increase the salinity of the water in front of the two Nile branches, dramatically impacting the quality and distribution of aquatic organisms, including microbial, phytoplankton, macrophytes, zooplankton, and benthic invertebrates.

Chemical parameters

Among the significant chemical factors in estuarine ecosystems that are regularly studied are nutrients, pH, dissolved oxygen (DO), heavy metals, organic matter, Chlorophyll-a, human activities, and persistent organic pollutants.

A variety of factors, including the presence of organic matter, biological activity (mainly phytoplankton production), and freshwater imports, can affect the pH of estuary waters (e.g., Kuliński et al. 2014; Raven et al. 2020). Additionally, as indicated by Omarjee et al. (2021), seasonality in river flow rates can alter pH levels (e.g., periods of high flow are always associated with a decrease in pH values). According to Neal et al. (1998), pH is a significant physico-chemical parameter that influences a variety of mineral and ion exchange equilibria, as well as the availability and possible toxicity of metals and other chemical compounds.

At the same time, CO₂ is the essential source for phytoplankton production. Unlike the open ocean, most estuaries are suppliers of CO₂ to the atmosphere and are heterotrophic ecosystems that convert organic matter into inorganic nutrients and CO₂. They are also oversaturated with CO₂ relative to the atmosphere (Cloern et al. 2014).

One important measure of water quality is the amount of DO, which is an essential component for the survival of organisms in aquatic habitats. DO varies seasonally, with much lower values in the summer period compared with the winter period (Sheldon et al. 2019). Simultaneously, a low level of DO in water is a sign of contamination. Large-scale bacterial decomposition of organic waste can drastically reduce the oxygen content of water, rendering it unsuitable for a variety of organisms. Moreover, runoff from different land uses or an excess of nutrients from wastewater treatment plants exacerbate the issue (U.S. Environmental Protection Agency [EPA] 2006), particularly in regions with limited water movement.

Industrial discharges, urban runoff, and natural sources are major contributors of heavy metals to estuarine habitats. Contamination of water bodies with heavy metals is becoming a global problem. According to Dane and Şişman (2020), fish can be contaminated with heavy metals via three different pathways: the gills, the body surface, and the digestive tract. Consequently, it is critical to track the concentrations of metals like lead, cadmium, and mercury in order to evaluate any possible ecological hazards. Zhang et al. (2013) indicated that some aquatic bodies may contain more than 20 different organic and inorganic chemical compounds carrying arsenic. However, numerous factors, including temperature, salinity, redox conditions, bacteria, and phytoplankton, affect the form of these chemical compounds found in water.

The amount and kind of organic matter in estuarine waters affect the ecosystem’s general health, nutrient cycling, and water clarity. Sediment organic matter (SOM) consists of organic matter from various sources. According to Hedges and Keil (1995), the primary sources of SOM in estuary ecosystems include aquatic macrophytes, microphytobenthos, phytoplankton, terrestrial plant detritus, and soils from river flow.

Pesticides and polychlorinated biphenyls (PCBs) are examples of persistent organic pollutants that may be present in estuarine habitats. These compounds have the ability to accumulate in biota and sediments, endangering aquatic life and perhaps having an impact on human health (Montano et al. 2022).

The study of Abo El-Khair (1993), was one of the first investigations that focused on the chemical parameters of the Mediterranean coastal water in front of the Rosetta mouth of the Nile River (see Fig. 2, where sampling station III represented the estuary mouth at the time of the study). The maximum amount of discharged water was found during January 1987 (1487 million m³), while the minimum discharge occurred during April to November (6 million m³). The study distinguished two regions, the estuarine area (region A; sampling stations I-III) and the marine coastal area (region B; 9 sampling stations [IV-XII]). Vertical distribution of water temperature showed a slight decrease with depth. Transparency was affected by suspended matter content of the estuarine water, with transparency increasing seaward. The average pH values showed slight seasonal variations at each location. The DO level showed irregular vertical variations, possibly due to occasional turbulence of the water column and to certain local and seasonal conditions. The DO values showed remarkable regional variations in region A, with the maximum regional average at station III coinciding with its position at the estuary mouth. Salinity distribution in the Rosetta estuary was sigmoidal due to fresh water input from the Nile source and seawater mixing. The vertical distribution of nitrate, nitrite, and ammonia varied irregularly with depth. The mean average values for nitrite in both surface and bottom waters of region A were higher than those of region B. The vertical distribution of total nitrogen (TN) values also varied irregularly with depth, with the minimum seasonal average found in the summer, coinciding with the notable increase in standing crop of autotrophic organisms. The vertical values of reactive phosphorous and total phosphorus (TP) showed irregular variations, and the annual mean value for TP for region A exceeded that for region B. The vertical silicate values showed irregular variations, while those of the suspended matter (SM) in regions A and B showed an obvious increase with depth. Moreover, variations in forms of some heavy metals (iron, manganese, copper, and zinc) were also investigated in both surface and bottom waters. The values of dissolved and particulate iron was higher in the lower water layers than in the upper layers. The vertical values of dissolved manganese decreased with depth, which is contrary to particulate manganese. At most sampling stations, the vertical values for copper decreased with depth for the dissolved form and increased for to the particulate form. The vertical concentrations for dissolved and particulate zinc fluctuated irregularly with depth, as did dissolved cadmium contents.

Fig. 2

Sampling locations in front of Rosetta Branch of the Nile River during 1987–1988. See section Chemical parameters for details. Modified from Abo El-Khair (1993)

Correlation of the hydrographic parameters with salinity showed a positive correlation with temperature, pH, and nitrite and a negative correlation with SM, silicate, phosphorus, and nitrate. These negative correlations indicate that SM and many of nutrient salts are of allochthonous origin.

The environmental characteristics and nutrient salt status of the Damietta estuary of the Nile River were studied by Shaaban-Dessouki et al. (1993). These authors showed that the electrical conductivity of water (11.6–41.8 mmhos/cm) and the chlorosity of the water (8–21.6 g/L) approximately follow the same trend. As a result of atypical inflows of different wastes, the nutrient salts levels explained a broad range of variations and changes. The major chemical contents of the water of the Damietta Branch increased as the water moved northward, with significant and unusual amounts of ammonia, nitrate, organic nitrogen, and organic phosphorus being observed (Ali 1998).

The results of chemical parameter studies conducted by Hassan et al. (2012a) on the Damietta estuary and the Mediterranean coastal shoreline stations are presented in Table 1 and Fig. 3. These authors found that pH values trended towards alkaline values of between 7.61 and 8.67 and between 7.5 and 8.67, respectively. Lower phytoplankton, bacterial, and fungus activities in the sediment, the release of methane and H₂S, as well as the creation of organic acids and other breakdown products are all possible causes of the relative reduction in pH values (Ravindra et al. 2003). In this study, the DO levels of the Damietta estuary were between 3.9 and 8.3 mg/L, while those at the Mediterranean coastal shore stations were between 4.6 and 7.8 mg/L (Electronic Supplementary Material [ESM 1]). On the other hand, due to the presence of many pollutants in the Damietta estuary, produced by various human impacts, compared to their corresponding values in the Mediterranean coastal shore water, the biological oxygen demand (BOD) and chemical oxygen demand (COD) concentrations of the Damietta estuary were higher. At the Damietta estuary and the Mediterranean shore coastal stations these values ranged between 12.6 and 22.8 mg/L and between 2.3 and 3.8 mg/L for BOD, respectively, whereas the COD equivalent ranges were between 19.5 and 34.2 mg/L and between 9.1 and 16.3 mg/L.

Table 1 Geographical coordinates of the sampling stations investigated in the study of Hassan et al. (2012a)

Fig. 3

Google map showing the sampling locations in the Damietta estuary and Mediterranean coastal line. Adapted from Hassan et al. (2012a). See Table 1 for more details

At the Damietta estuary and along the Mediterranean coast, the alkalinity levels of the water varied between 149 and 197 mg/L and between 131 and 201 mg/L, respectively. The acquired data revealed small variations between the two analyzed sectors; however, alkalinity values consistently increased over the extent of the Damietta estuary as a result of organic matter bacterial decomposition, with bicarbonate and ammonia byproducts (Metawea 2009). In contrast, at the Mediterranean shore and Damietta estuary, the concentrations of chloride ranged from 3.05 to 4.43 mg/L and from 3.81 to 4.43 m/L, respectively, and the concentrations of sulfate ranged from 22.1 to 24.6 mg/L and from 22.5 to 25.1) mg/L, respectively (Table 2); chloride and sulfate levels throughout both sectors exhibited the same pattern. The concentrations of Na, K, Ca, and Mg throughout the Mediterranean coast showed a similar pattern to that of Damietta estuary, with their levels gradually increasing from the Damietta estuary to the Mediterranean Sea, indicating their dependency on seawater penetration. The mixing of estuary water with seawater resulted in major control of the dynamic distribution of dissolved nutrient salts in the Damietta estuary. The collected data demonstrated that nitrite levels peaked in the winter, ranging from 4.2 to 141.2 g/L. The nitrification of ammonia (NH₃) and nitrite (NO₂⁻), caused by the biological decomposition of falling dead plankton, proteins, and their derivatives, producing nitrate, may have increased evaporation rates and contributed to the noticeable increase in nitrate levels over the summer (Munawar 1970). The acquired data also demonstrated a clear increase in ammonia values during warmer seasons (summer and spring) due to the action of heterotrophic bacteria in the ammonification process of organic matter producing ammonia (Barat and Jana 1987). The high levels of domestic sewage input and agricultural runoff from nearby cultivated fields and neighboring settlements are also considered to be responsible for the elevation of ammonia values in the Damietta estuary; as a result, ammonia content gradually decreased as with water flow from the estuary to the Mediterranean Sea.

In marked contrast to the Mediterranean Sea, the dispersion pattern of nutrient salts in the Damietta estuary was very different. The high levels of domestic sewage inflow from the nearby communities and cultivated lands were considered to be responsible for the elevation of nutrient salt values in the estuary. The concentrations of nutrient salts were found to steadily decrease with increasing distance from the Damietta estuary, demonstrating that the distribution of nutrient salts in the Mediterranean Sea depends on the concentrations in the Damietta estuary.

El-Gamal (2017) studied the water quality in both the Rosetta and Damietta estuaries. Samples were collected during different periods from 2009 to 2014. DO concentration in the Rosetta estuary fluctuated between 6.4 and 7.02 mg/L, with the DO average value exceeding the permitted limit in 2014. In 2014, average concentrations of NH₃, NO₃, TN, and TP (all in mg/L) were lower in the Rosetta estuary than in the Damietta estuary. The average COD in the Rosetta estuary between 2010 and 2011 was lower than the allowed amount (10 mg/L), while in 2012 it was slightly above the permitted level, ranging from 9.2 to 13.2 mg/L; the average BOD concentration in the Rosetta estuary was below the allowed level (6 mg/L). The BOD of the Rosetta branch varied from 2.6 to 2.9 mg/L. Comparing concentrations between 2009 and 2012 revealed a progressive decline, beginning in 2009 and continuing through 2011, despite a rise present towards the end of the period in 2012. During 2014 coliform bacteria was studied at the Rosetta estuary, and the recorded values compared to those from studies conducted in 2007, 2009, and 2011. The findings showed that coliform bacteria were more abundant in 2014 than in 2007 and 2011.

In contrast, El-Gamal (2017) found that DO concentration in the Damietta Estuary ranged between 6.5 and 7.08 mg/L during 2009–2014, exceeding the minimum permissible standard for water quality set by the Egyptian Ministry of Health (5 mg/L). In 2014, the average concentrations of key nutrients in the Damietta estuary were higher than those in the Rosetta estuary. The ammonia content along Damietta branch throughout 2012 and in prior years was lower than the permitted limit (0.5 mg/L), representing significant betterment at the branch’s estuary compared to the prior year.

The COD levels in the Damietta branch typically ranged from 11.5 to 13.2 mg/L. Despite a minor increase in the average concentration beyond the permitted limit (10 mg/L) during the course of the 4 monitoring years (2009–2012), 2012 showed an improvement over the prior years. The mean BOD concentration during 2012 and prior years varied from 2.7 to 3.1 mg/L, which is lower than permissible level for water quality in the Nile River (6 mg/L) and a remarkable improvement during 2012 compared to previous years, but all recorded levels were still lower than the permissible limits.

The incidence of coliform bacteria increased from 2009 to 2012, based on a comparison of data through the years 2007, 2009, 2011, and 2014. However, during the course of the 4 years of the study, the Damietta estuary had fewer coliform bacteria than Rosetta estuary.

The quantities of several dissolved trace metals (Fe, Mn, Zn, Cu, and Pb) along the coastal area of the Mediterranean Sea to the north of the Nile Delta Region, Egypt, were estimated by Okbah and Nasr (2006). Eight surface-water specimens were taken in 2003 from the research area’s mixing and coastal zones on a seasonal basis. Along Egypt's Mediterranean Sea coast, samples were taken from eight sites, including the Rosetta Estuary (stations I and V) and the Damietta Estuary (stations III and VII). The metal concentrations for Fe, Mn, Zn, Cu, and Pb in the coastal zone ranged from 11.92 to 30.45 μg L⁻¹ for Fe, from 5.79 to 17.36 μg L⁻¹ for Mn, from 0.87 to 7.80 μg L⁻¹ for Zn, from 0.40 to 1.87 μg L⁻¹ for Cu, and from 1.53–10.31 μg L⁻¹ for Pb. The findings revealed a striking reduction in the concentrations of various metals in water entering the coastal sea areas from the higher values of the estuaries and outflows. On average, the ambient values in the area free of pollution were lower than the amounts of metals in the two estuaries. When the least risk concentration reported by the Committee on Water Quality Criteria (WQC) [1972] were compared with the trace metal concentrations in the Mediterranean Sea's coastal zone north of the Nile Delta, the Mediterranean Sea's coastal zone of Egypt had much lower levels of the metals. This study also showed that the distribution of the metals was not significantly impacted by anthropogenic inputs, with the exception that the Pb content in the mixing zone was somewhat higher than that of the WQC.

In April 2007, Faragallah et al. (2009) estimated the physicochemical features, some heavy metals, and chlorophyll-a levels in six vertical stations (Fig. 4; Table 2) of the open Mediterranean Sea water, approximately 60 km from Damietta harbor in Egypt (ESM 2, 3). Their study included assessment of the weather due to the loss of vegetation from stream banks, which provide shade, and storm water, which also has an impact on temperature. The lowest pH was recorded in the bottom water layer. Toxic materials may be more readily absorbed by aquatic plants and animals at low pH, possibly resulting in toxic situations for aquatic life. These authors found that the surface water had the maximum DO concentration which gradually declined with depth.

Fig. 4

Sampling stations in front of the Damietta harbor. Adapted from Faragallah et al. (2009)

Table 2 Geographic coordinates of the sampling locations investigated in the study of Faragallah et al. (2009)

The levels of the majority of nutrients and heavy metals were higher in the surface layer and decreased with depth. The region is primarily N-limited, as evidenced by the N/P ratio and abundance of N ions. The low values for the enrichment factor (EF) of the metals (< 1) indicate that the enrichment and advection of heavy metals are both being counted. The distribution of nutrients and heavy metals was not significantly impacted by anthropogenic inputs, and metal concentrations were comparable to/or lower than those reported by the Committee on Water Quality Criteria [1972], with the exception of a marginally higher Zn content. Based on the BOD/COD ratio data, the water in the study area is biodegradable. Chlorophyll-a concentrations in the surface layer were rather high over the course of the investigation; moreover, a negative relationship between Chlorophyll-a and NO₃-N, PO₄-P, and SiO₄²⁻ was calculated (r = − 0.58, − 0.38, and − 0.58, respectively).

Total suspended solids (TSS) in the water and the concentration of dissolved phosphate were significantly inversely correlated (r = – 0.37; p 0.05; n = 24). Sanders et al. (1997) demonstrated that between 30% and 80% of the phosphate input was removed as PO₄-P by TSS. Many investigations have shown that one of the most significant processes influencing the behavior of phosphorus is the interaction of dissolved inorganic phosphorus (DIP) with TSS (Pratska et al. 1998). At the same time, COD and chlorophyll-a concentration, a marker of phytoplankton biomass, are strongly correlated (r = 0.559, p < 0.05) (Ogawa and Ogura 1990). Moreover, the water flow and re-suspension of particles in the study area resulted in a rather high concentration of phosphorus and nitrogen compounds, particularly in the bottom water at a depth of 75 m. Indirect correlations were found between increasing reactive silicate concentrations and diatom death as well as faster generation rates from subsurface sediments. The fact that there was a substantial positive association found between ammonia and chlorophyll-a content (r = 0.5) suggests that ammonia plays a role in the biological processes and the growth of phytoplankton. Moreover, the highest trace metal concentrations were always found in the surface layers. This pattern is consistent with what many researchers have claimed, namely that because local sources are close by and the region is oligotrophic, there is no noticeable surface depletion of trace metals in the Mediterranean. The obtained data set suggests that factors other than biogenic activity are more relevant in the dispersion of heavy metals in seawater. The greatest serious threat to water quality, however, is organic contamination brought on by the growth in both human populations and industrial activities. Heavy contamination results in oxygen deficiency due to the breakdown of organic matter.

In four subsequent marine surveys, Moustafa et al. (2010) examined the features of water quality and levels of certain heavy metals (Fe, Mn, Zn, Cu, and Pb) in the Rosetta and Damietta branches during various sampling periods (spring 2008 to winter 2009). Fourteen sites were selected from the two branches, with eight sites at the Rosetta branch and six sites at the Damietta branch. The highest concentrations of the major cations and anions were recorded in the cold season and the lowest concentrations during the hot high-flow period. DO was found to be depleted completely at the discharge point of El-Rahawy Drain, while COD, BOD, HCO₃⁻ and total dissolved solids (TDS) levels increased sharply at this site. According to the study, the water quality at the Damietta branch was superior to that at the Rosetta branch due to the existence of numerous polluting sources along length of the Rosetta Branch, particularly El Rahawy Drain, Sobol Drain, and several factories in Kafr El-Zayat City. These sources are heavily loaded with domestic, industrial, and agricultural wastes containing high amounts of inorganic and organic constituents. The concentration of heavy metals in water samples were in the order of Fe > Mn > Pb > Zn > Cu. The concentrations of Fe, Mn, and Pb exceeded the permissible limits in the two branches, especially in winter (ESM 4a, b).

El-Amier et al. (2015a) evaluated the physical and chemical analyses of 60 hydro-soil and water samples collected from four locations along the Damietta branch from its source to its furthest northern point and discovered significant geographical differences in these parameters features. The progressive increase in pollution content was extremely obvious. The northeast area (downstream location IV) has been shown to have relatively higher amounts of soluble salts, electrical conductivity (EC), and other chemical qualities than the three upstream locations (I–III). The hydro-soil and water variables had positive relationships that were statistically significant (p ≤ 0.05).

In reference to earlier research conducted in Egyptian estuaries, most of the studied chemical parameters were associated with nutrient salts, pH, DO, BOD, COD, heavy metals in water, organic matter, and human activities. However, a large number of these investigations were performed in the two Nile branches or in the Mediterranean waters near estuaries, and only a few studies were conducted in the two localized estuaries. It is evident that the levels of most of the nutrient contents, BOD, COD, and heavy metals increased as the water flowed northward along the branch, compared to their corresponding values in the Mediterranean shore. Moreover, the water of Rosetta branch is more polluted than that of Damietta because of the existence of numerous polluting sources, particularly El Rahawy Drain, Sobol Drain, and several factories in Kafr El-Zayat City.

A recent study on chemical parameters in the two Nile estuaries has shown a deficiency in the nutrient salts in both branches, while with respect to the trace metals, the Rosetta branch is the more polluted and is becoming a collecting system for various types of wastes (unpublished data). However, this deficiency in nutrient salts can be attributed to the low rate of river flow into the Mediterranean Sea.

Geological parameters

The geology of the area where an estuary is located determines the characteristics of that estuary, with addition influencing factors, such as climatic, chemical, and physical factors.

Among the significant geological parameters in estuarine ecosystems that are regularly studied are: sediment composition, coastal geomorphology, erosion and sedimentation, tidal dynamics, heavy metals in sediment, and land use changes. The geochemical study of bed sediment is defined as the study of the mechanisms that govern the distribution, quantity, and composition of chemical compounds and isotopes in sediments. Such studies may include many types of analyses, such as total organic carbon (TOC), total organic phosphorus, total organic nitrogen, as well as the concentration and distribution of heavy metals and/or pollutants in the sediment.

The habitat is greatly influenced by the geological features of estuarine sediments. The distribution of benthic organisms, habitat structure, and nutrient cycling are all impacted by the composition, size, and mineralogy of sediments (Coblentz et al. 2015). Sediment organic matter (SOM) consists of organic matter from various sources, with the main sources of SOM in estuary ecosystems being terrestrial plant detritus, soils from river flow, aquatic macrophytes, microphytobenthos, and phytoplankton (Hedges and Keil 1995). Wu et al. (2023) found a negative correlation between sediment grain size and SOM, suggesting that tiny particles, such as silt and clay, are the main transporters of organic matter.

The factors influencing sediment transport in coastal locations are site-specific environmental variables, including sediment characteristics, wind, currents, waves, tides, and the exchange activities between estuaries and nearshore regions (e.g., Wang et al. 2014; Fitri et al. 2015; Joshi and Xu 2017). The hydrodynamics and sedimentation patterns in estuarine environments are also influenced by the physical characteristics of the coastal area, such as the existence of deltas, sandbars, and mudflats. An estuary's overall ecological dynamics may be impacted by all of these geomorphological factors. Additionally, the geological context of the estuarine habitats under review in this article is influenced by processes linked to the discharge of the Nile River and the formation of the Nile Delta. The distribution of nutrients and sediment can be affected by the size, shape, and historical evolution of the Nile Delta (Darwish 2023).

Due to their dependence on the interplay of several factors, the patterns and rates of sedimentation and erosion in estuaries are typically complex. Accretion occurs when the flow velocity is not strong enough for the local conditions, and erosion takes place when the flow velocity is too strong. Changes to the environment, whether caused by human activities (such as building a pier) or natural events (like a strong storm), can alter the sediment-erosion patterns and hydrodynamics (Ferreira and Santos 2018). Simultaneously, a rise in the frequency and intensity of rainfall may result in increased stormwater runoff, as well as heightened erosion and sedimentation. The introduction of higher levels of nutrients, pollution, or sediment into an estuary poses a potential threat to the overall functioning of the estuarine ecosystem.

The tidal dynamics in estuarine environments are influenced by geological features such tidal channels, flats, and bars. The intricacy of the habitat, nutrient distribution, and sediment transport are all impacted by tidal motions (Daidu 2013).

The concentrations of heavy metals in the surface sediment of many estuaries have been investigated (e.g., Niu et al. 2021; Yi et al. 2021; Zhang et al. 2022). Various factors governing the bioavailability, bioaccumulation, and biological effects of heavy metals in sediment-dominated estuaries have been reviewed (Bryan and Langston 1992).

Modifications in land use, urbanization, and infrastructure development are examples of human-caused geological changes that can affect the geological characteristics of estuarine environments (e.g., Poff et al. 2006; Price et al. 2011). Degradation of the environment and changed patterns of sedimentation could result from these changes.

El-Fiky et al. (2002) used the numerical model “GENEralized model for SImulating Shoreline change” (GENESIS) to analyze and record the sediment transport rate and coastline modification and to predict the shoreline position along the Rosetta promontory. El-Asmar and White (2002) investigated how the development of the New Damietta Harbor altered the processes of sediment transport along the shore. The findings of these studies show that sedimentological changes brought on by the harbor construction have affected 10.5 km of shoreline, which is far more than anticipated by Sogreah (1982) at the time the harbor was built. Comparable changes are taking place in the nearshore environment, which is why the harbor access channel is silting up and the bathymetric contours west of the western jetty are prograding. The beach sands on each side of the port provide a sedimentological record of the changes in the process domain. West of the western jetty, sediments from the accretionary beach have a tendency to have a finer grain size and to be abundant in assemblages of non-opaque, low-density heavy minerals. However, the beach sediments along the shoreline that has been eroded away to the east of the eastern jetty are rich in heavy minerals, with opaque and high-density non-opaque heavy metals predominating. They also have a coarser mean grain size, and frequently sort better when skewed toward the coarser fraction.

Hamouda et al. (2014) examined the distinctive characteristics of seafloor fluvial marine sediments in front of the Damietta promontory in Egypt’s Nile Delta. They found that fine sediments (clay and silt) cover the front portion of Damietta outflow cut across the region under investigation, which is primarily composed of fluvial sediments. In contrast, little patches of sandy material were found to the east and west. The Nile Delta fan is predominantly made up of mud sediments, and the river deposits that make up the fan correspond to the predominance of the microscopic mean size (fine fractions); indeed, sediment discharge at the Nile promontories has decreased to nearly zero since the construction of the AHD in 1964, and the contemporary state of seabed features is mostly influenced by the oceanic circulation regime that dominates the area of study.

The shoreline of the Nile Delta and its geomorphologic alterations were examined between 1945 and 2015 (Darwish et al. 2017) using the Egyptian Geological Survey's topographic maps from 1945 and Landsat satellite images from 1973 to 2015. The study discovered that the geomorphology of the shoreline underwent significant change throughout this time, particularly at the Damietta and Rosetta promontories, which underwent significant erosion during and since the building of the AHD. Other areas of the shoreline also experienced erosion, while some accretion did happen along the coastline downdrift from the promontories. As a result of how beach erosion has occurred along the Nile promontories and the accretion that has occurred in the embayment between the promontories, the coastline has typically gotten smoother. Near the inlets, some of the eroded material has accumulated as spits or shoals. The effects of the AHD, sea level rise, land subsidence, storms, and coastal protection structures were considered by the authors of the study to be the main causes of coastline modification. Results of efforts to pause erosion have been inconsistent. While other coastal protection measures have failed to stop erosion, seawalls constructed around Alexandria's coastline have preserved the coastline. A great deal of the Nile Delta is at or near sea level, making large portions of cultivated land extremely vulnerable to saltwater intrusion.

The bottom sediments of the northern part of the Damiettabranch were investigated by El-Fawal et al. (2018), who aimed to examine the distribution and assessment of the geochemical parameters. The distribution of sediment type is variable among different regions, with the composition being mostly clay > silt in the northern regions, muddy in the center, and silt > clay in the southern regions. The predominant hydrodynamic depositional regime within the river branch is reflected in the general distribution pattern in the bottom sediments. The mixture of cations and anions in the bottom sediments of the river branch demonstrate the geochemical environment that supports multivalency conditions. However, the concentrations of the trace elements (Cu, Cd, Pb, Zn, Cr, and Co) in the bottom sediments varied, indicating inappropriate river branch treatments. Important environmental awareness and critical environmental repair are needed. A recent study on the geochemical properties of bed sediment in the two estuaries demonstrated a higher percentage of sand fraction in Rosetta than in Damietta, showing different percentages of water content, TOC, total organic matter, total carbonate, total silicate, and organic phosphorus in sediment (unpublished data).

El-Sherif et al. (2020) studied the grain size distribution along Rosetta beach of the Nile River. The study demonstrated the high sensitivity of grain size characteristics to even minute changes in the chemical formulation of the sediment mixture. The results of this study showed that unimodal pure sand sediments, primarily from Nile River sand sources, predominated. The primary factors of transportation for sediments that have been deposited and reworked by turbidity and marine processes in a shallow, agitated marine environment are both graded suspension and suspension with rolling mode (saltation).

Sedimentation is a major issue affecting Egypt’s northeastern Nile Delta coastline, and the navigation channel of Damietta harbor is seen as a prime example of this challenge. The effects of the Damietta harbor and its navigation channel on the coastline were investigated and monitored over the course of 45 years by Ezzeldin et al. (2020) using remote sensing techniques. During this 45-year period, the average sedimentation rate was 2.13 m/year, resulting in the Damietta harbor generating an accretion region on the western side. Conversely, over the past 45 years, the shoreline on the eastern side of the harbor has receded by an average of 92 m.

Recently, Abd-Elhamid et al. (2023) attempted to forecast shoreline changes along the shores of the Nile Delta by performing a historical trend analysis (HTA). Using a variety of statistical techniques, the Digital Shoreline Analysis System (DSAS) software was used in conjunction with the geographic information system (GIS) environment to monitor shoreline changes. Coastal erosion caused the Nile Delta’s shoreline to shift inland in diverse directions between 1974 and 2022; this erosion is projected to continue between 2033 and 2043, primarily damaging the Rosetta and Damietta areas. At Damietta and Rosetta, the erosion rates were 10–25 m/year and 30–60 m/year, respectively. If the shoreline of the Nile Delta continues to erode, there could be dire repercussions for the local population, economy, infrastructure, ports, buildings, and railroads.

In conclusion, most of the previous studies on geological parameters focused on sediment composition and distribution, geomorphologic changes of the shoreline based on sediment erosion and accretion, and land use. However, the primary concern is that of geomorphologic changes in the shoreline associated with sediment erosion and accretion. These studies showed that sediment discharge at the Nile promontories has decreased to nearly zero since the construction of the AHD in 1964. Moreover, the geomorphology of the shoreline has undergone significant change from 1945 and from 1973 to 2015, particularly at the Damietta and Rosetta promontories, which have suffered significant erosion during the construction of the AHD. Additionally, the authors of a recent study reported that coastal erosion caused the Nile Delta’s shoreline to shift inland in diverse directions, and that this erosion will continue between 2033 and 2043, primarily damaging the Rosetta and Damietta areas. So, precautionary measures should be taken.

Pollution parameters

Pollution refers to the introduction of contaminants into the natural environment that cause adverse change and may ultimately have negative effects on human health. Air pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, and water pollution are the major types of pollution. The chemical nature of a pollutant, its concentration, the region it affects, and its persistence, are the four elements of pollution that define how harmful it is. The different pollution parameters that are frequently investigated in estuarine environments are: water quality parameters, chemical contaminants, sediment quality, biological indicators, and land-based sources of pollution.

Abundant influxes of nutrients (nutrient pollution), such as nitrogen and phosphorus, stemming from runoff in agriculture and discharges in urban areas can result in eutrophication, leading to algal blooms and adverse effects on the quality of water. Various pollution sources, including the decomposition of organic matter and the enrichment of nutrients, can result in diminished levels of DO in estuarine waters. This poses a threat to aquatic life (Smith et al. 1999; Heisler et al. 2008).

Heavy metals (e.g., mercury, lead, cadmium) may be introduced into estuarine habitats via industrial discharges and urban runoff. Such introductions into estuarine waters present hazards to aquatic organisms and may have potential implications for human health. Moreover, estuarine ecosystems have the potential for exposure to persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs) and pesticides. These substances can accumulate in sediments and biota within the estuarine environment (Barletta et al. 2019).

Within estuarine environments, sediments may act as pollutant repositories, and the presence of such contaminants in these sediments can impact benthic organisms and the general health of the ecosystem. Simultaneously, the composition of sediments in estuarine areas plays a role in determining the movement and destiny of pollutants. Fine sediments, in particular, exhibit a greater ability to retain contaminants (Rodgers et al. 2020).

On the other hand, assessing the health of indicative species, such as bivalves and fish, can provide valuable information on the overall levels of pollution, as well as on the ecological consequences within estuarine environments (e.g., Puente and Diaz 2008; O’Brien et al. 2016).

Contamination stemming from urban regions, including from runoff carrying chemicals, heavy metals, and various pollutants, has the potential to influence the quality of water in estuarine environments (Willis et al. 2017). Additionally, the release of pesticides, fertilizers, and other pollutants from upstream areas can have consequences for estuarine ecosystems (Bashir et al. 2020).

Numerous issues over contamination in the Rosetta branch of the Nile River, particularly in the area downstream of El Rahawy Drain, have been reported. For example, tons of fish were discovered floating in the water during the summer of 2012 due to water pollution in this area (Dimian et al. 2014). These authors used the Duflow model to calculate the variations in DO, BOD, and ammonia over time along the study region.

Measurements of various metals in water, sediments, and living resources are required for the assessment of environmental quality in terms of heavy metals in aquatic systems (see Samecka-Cymerman and Kempers 2001; Sánchez López et al. 2004). However, according to biochemistry studies, certain heavy metals are essential components of living plants and animals, but at high concentrations, they become poisonous (Kotickhoff 1983).

In this review, previous studies on the Northern Delta region of Egypt are presented. These studies focus primarily on pesticides in water, heavy metals in water, heavy metals and PAHs in sediment and/or biota, as well as on fluoride in water and biota in addition to fish cages.

Pesticides in water

Abbassy et al. (1999) studied the seasonal presence of pesticide residues and other organic pollutants, such as PCBs, in the water of the estuaries of Egypt's Nile River Rosetta and Damietta branches from the summer of 1995 to the summer of 1997. The findings of this study demonstrated the presence of organochlorine compounds (OCs) in all water samples, including hexachlorobenzene (range: 0.195–0.240 µg/L), aroclor 1260 (range: 0.166–0.330 µg/L), aroclor 1254 (range: 0.39–0.70 µg/L), lindane (range: 0.286–0.352 µg/L), p,p′-DDD (range: 0.019–0.033 µg/L), p,p′-DDE (range: 0.035–0.067 µg/L), and p,p′-DDT (range: 0.024–0.031 µg/L). These levels of these compounds were higher in the water of the Damietta branch than in the water of the Rosetta branch. However, three chemicals, namely, dieldrin, aldrin, and endrin, were not present in any of the water samples. Only four of the 36 organophosphorus fungicides, insecticides, and s-triazine herbicides found in water samples obtained from the Rosetta branch during the summer and autumn were present and evaluated. All of the identified compounds, namely, dimethoate, captan, malathion, and ametryne, were found in amounts ranging from 0.011 to 0.340 g/L. The same chemicals that were found in the water of the Rosetta branch during the same seasons, with the exception of ametryne, were also found in the water of the Damietta branch. Dimethoate, malathion, and captan were all detected at concentrations ranging from 0.030 to 0.330 g/L. The relative levels of the identified fungicides, organophosphorus insecticides, and s-triazine herbicides were as follows: ametrine < captan < malathion < dimethoate.

Heavy metals in water

Heavy metals are one of the most prevalent type of environmental pollutants. Biota and waterways are affected by their presence and independent of whether their sources are anthropogenic or naturally occurring. Chemical weathering of minerals and soil leaching are the two primary natural sources of metals in water. The majority of the anthropogenic sources are associated to home and industrial discharges, urban storms, water runoff, and inputs from rural areas. Water contamination induced by trace metals has significant impacts on both metal geochemical cycling and environmental health. The impact of heavy metals on plant and animal life due to their presence in aquatic environments is worrying (Hassan et al. 2012a). The ideal concentration ranges for elements (Cu, Zn, etc.) are often small, and the nutritional needs vary greatly depending on the species or element. Even at trace quantities, given elements (Pb, Cd, etc.) demonstrate severe toxicity (El-Bouraie 2010). Data showing the findings of the investigation by Hassan et al. (2012a) on heavy metals in water are given in ESM 5. The Damietta estuary and the Mediterranean coastal coastline, respectively, had iron concentrations in the ranges of 219 to 312 g/L) and 174 to 406 g/L, respectively. The lowest iron levels were detected during the summer, which could be linked to the iron that suspended debris, clayey minerals, surface microorganisms, and metal oxides, such as iron oxide absorbed under the effect of high temperatures. The impact of flooding events, which resulted in iron leaching from the banks of the Nile River into the water and significant quantities of small grains and suspended particles containing elemental iron being imputed into the water, may also be responsible for the elevated iron concentrations observed during autumn. Manganese concentrations varied between 32 g/L and 72 g/L at the Mediterranean coastline shore, whereas they ranged between 38 and 72 g/L at the Damietta estuary. At the Damietta estuary and the Mediterranean coastal shore, copper concentrations, however, varied from 3.9 to 11.3 g/L and from 2.4 to 5.6 g/L, respectively. At station VI in the summer, the zinc concentration was found to be at its lowest level (65 g/L), while at station I in the winter near the Damietta Estuary, it was found to be at its highest level (152 g/L). The release of elements into the surface water during a dry period, when the water scale was reduced, and microbial activity accelerated the degradation of aquatic life and organic debris, and may explain the proportionally higher level of zinc concentrations during the winter (Osman et al. 2010; Hassan et al. 2012a). The lead dispersion pattern in sea water followed a comparable trend to that of the Damietta estuary. This discovery demonstrated that the levels of lead in the sea were associated with those in the Damietta estuary. Due to lead adsorption onto organic materials that dropped to the bottom sediment, particularly at high temperatures, lead concentrations rose in the colder months and decreased in the warmer ones. The highest lead concentration (23.36 g/L) was found at station I in the winter, and the lowest value (7.28 g/L) was recorded at station VI in the summer. Cadmium concentrations followed a similar pattern to lead levels, but the lowest level of cadmium was found at station V during the springtime (0.65 g/L). Due to cadmium's adsorption onto organic matter, cadmium concentrations decreased during the spring (Tessier et al. 1993); the maximum concentration of cadmium was found in the summertime (2.34 g/L).

Heavy metals in sediment and biota

Many investigations have focused on the distribution of heavy metals in sediments. El-Bouraie et al. (2010) investigated the distribution of heavy metals (Al, Cd, Ba, Co, Cu, Cr, Fe, Ni, Mn, Zn, and Pb) in the surface water and sediments of the Rosetta Branch. These authors also monitored how these metals affected water quality. The results of their study indicated that while the quantities of heavy metals in the water were mostly within allowable levels, the concentrations in the river sediments were extremely high but varied among sampling stations. The concentration of heavy metals in the bed sediment was at its maximum at the end of the winter period.

Using X-ray diffraction, optical microscopy, electron-microprobe analysis, scanning electron microscopy, and inductively coupled plasma-mass spectrometry, El-Kammar et al. (2011) looked at the possible heavy mineral composition of the black sand resources in Rosetta.

The concentrations of certain heavy metals (Pb, Cu, Cr, Zn, Mn, Hg, Cd, Fe) in the water and sediments of the Egyptian Nile River and in the tissues of the African Catfish Clarias gariepinus of the Egyptian Nile River were evaluated by Osman and Kloas (2010). These authors selected 18 separate sampling points at six sites along the whole length of the Nile River, from its source in Aswan to its estuary in Rosetta and Damietta (3 locations for each site). Higher mean values of conductivity, COD, alkalinity, TOC, nitrate (NO₃), NH₃, total solids (TS), chloride (Cl), sulfate (SO₄), and orthophosphate (OP) were recorded in the waters of both the Damietta and Rosetta branches. By moving from Aswan to the two branches, the concentration of heavy metals levels in the water, sediments, and tissues of Clarias gariepinus was lowest at the AHD, rising significantly as the water flowed towards the two branches (p < 0.05). Additionally, the liver and gills of the fish showed the highest levels of metal accumulation, whereas muscle had the lowest levels overall.

The concentrations of trace metals measured in sediments from the Rosetta and Damietta estuaries are shown in (ESM 6). These levels reflect the water system's current quality and can be used to determine those contaminants that do not stay soluble after being released into the water. In comparison to the concentration of the selected heavy metals in water samples from the different sites, the concentration of the chosen heavy metals in sediment samples was considerably high at these sites. While short-term, low-level contamination discharges might satisfy water quality regulations, long-term discharges may result in large loads of contaminants accumulating in sediments (Binning and Baird 2001). Hassan et al. (2012b) studied the distributional pattern of specific heavy metals, namely, Fe, Zn, Mn, Cu, Cd, Pb, Ni, Co, Cr, Mo, Al, As, and Hg, in sediment of Damietta estuary and along the Mediterranean coast (ESM 7, 8). Four subsequent surveys (from February to November 2008) were performed. The findings showed that the concentrations of heavy metals were higher in the Damietta estuary than along the Mediterranean coastline. This is due to the return flow of agricultural drainage water and the discharge of domestic and industrial wastes. Furthermore, as the water moved further from the Damietta Estuary to the Mediterranean coastline, the concentrations of heavy metals gradually decreased, demonstrating that heavy metal dispersion in the Damietta estuary affects the content of heavy metals along the Mediterranean shoreline.

El-Sorog et al. (2016) assessed the concentrations of hazardous metals in the coastal sediments of Abu Khashaba beach, on the Egyptian Mediterranean Sea, located approximately 37 km east of Rosetta branch. Results of the coastal stations (1–10) revealed that iron was the most abundant major element in the sediment (189,800–198,100 μg/g), followed by cerium (1670–1750 μg/g), barium (1580–2140 μg/g), phosphorus (1310–2370 μg/g), nickel (706.91–894.17 μg/g), manganese (600–640 μg/g), magnesium (530–590 μg/g), vanadium (512.4–652.32 μg/g), lead (388.22–476.45 μg/g), titanium (330–430 lg/g), zinc (298.5–387.91 μg/g), arsenic (234.32–399.16 μg/g), strontium (118.81–175.01 μg/g), cobalt (80.95–89.40 μg/g), uranium (41.05–47.49 μg/g), cadmium (29.43–36.97 μg/g), copper (25.41–42.66 μg/g), hafnium (1.759–2.03 μg/g), zirconium (0.214–0.349 μg/g), and chromium (0.233–0.290 μg/g).

Abou El-Anwar et al. (2018) assessed the degree of contamination in the sediments of the Rosetta branch of the Nile River by measuring the concentrations of a number of heavy metals. These metals can impact adversely on the quality of the sediment of the area. The results showed that bottom sediments of the Rosetta branch were subjected to moderate levels of pollution with Cu, Co, Ni, and Fe; moderate to strong pollution with Cr and Zn; and strong pollution with Pb and Cd. These authors proposed stopping the use of wastewater for irrigation when it has not been properly treated and stopping the dumping of industrial effluent into the Nile, as both actions have increased the levels of heavy metals in the freshwater sources.

El-Alfy et al. (2019) evaluated the amounts of hazardous heavy metals and organochlorine pesticides (OCPs) in the water, sediments, and Phragmites australis in freshwater and marine ecosystems in the Rosetta estuary. According to metal index (MI) values for the water, the study area is moderately affected by heavy metal pollution. OCP residues in the water and sediment were determined to be below the detection limits (5 μg/L and 5 μg/kg), respectively.

Metal pollution in sediments of the Nile Delta was evaluated by Abdelhady et al. (2021) during a survey of 20 locations on the Damietta and Rosetta branches. The majority of heavy metal measurments exceeded the standards for sediment quality. The pollution load index (PLI), geo-accumulation index (I_geo), and contamination factor (CF) all showed that Ni, Cr, Cd, Cu, Zn, and Pb contamination levels in the sediments ranged from moderate to highly polluted.

Redwan and Elhaddad (2020) examined harmful elements (Fe, Cd, Mn, Co, Ni, Cu, Zn, and Pb) in sediments of the Damietta branch. The amounts of metals and organic materials were estimated using inductively coupled plasma mass spectrometry and loss-on-ignition methods, respectively. The main causes of metal accumulations in Damietta branch sediments, according to the study, were varied, from sources such as wastewater discharge, agricultural discharge, industrial activities, and fisheries, as well as due to the impact of dilution/concentration throughout the winter and summer.

Abdelhady et al. (2021) evaluated metal contamination in the Nile Delta along both the Rosetta and Damietta branches. According to the results of this study, the sediments are moderately to severely contaminated by Ni, Cr, Cd, Cu, Zn, and Pb. The historical sinking of heavy metals into the sediment, where many agricultural drains were carrying mixed wastewater, was shown to be the cause of the observed trend of rising metal concentration towards the Mediterranean Sea.

Polycyclic aromatic hydrocarbons in sediment

Persistent organic pollutants are composed of hundreds of polycyclic aromatic hydrocarbons (PAHs) resulting from pyrolysis of organic materials or incomplete combustion (FAO/WHO 2005). PAHs are found in atmospheric, terrestrial, and aquatic environments worldwide, with sources that are mainly pyrogenic and petrogenic in nature (Nawaz et al. 2014; Zhang et al. 2015). When introduced into aquatic environments, PAHs bind with suspended particles and bottom sediments due to their hydrophobic nature (Readman et al. 1984; Ko and Baker 1995).

Monitoring pollutants in the Rosetta Nile branch is crucial for identifying abundant organic micropollutants, their origins and environmental fate, determining compliance with regulations, and improving treatment technology targeting (Eissa et al. 2020). Moreover, contamination sources, including industrial (thermal pollution from cooling the condensers of Kafr Saad Electrical station and Talkha fertilizer factory), municipal (El-Serw City and numerous villages without sanitation facilities), and agricultural drains, have impacted the Damietta Nile branch (Agricultural Policy Reform Program, Water Policy Program [APRP] 2002; Authman et al. 2009; EL-Bady and Metwally 2016; Abdel-Satar et al. 2017).

In the aquatic environment, sediments are thought to act as a sink for hydrocarbons, and numerous studies have underlined the significance of sediments in the monitoring of pollution (e.g., Wakeham et al. 1980; Witt 1995). However, samples containing hydrocarbon levels several folds of magnitude greater than those found in the water column can be obtained from sediments (Witt 1995).

PAHs that are discharged into the water environment can bioaccumulate in aquatic organisms and travel through the food chain. POPs are a major problem in environmental monitoring due to their impacts on animals, which include teratogenicity, mutation, and cancer (Perera 1997). Due to their known carcinogenicity, the U.S. Environmental Protection Agency (U.S. EPA 2014) has registered 16 PAHs as priority pollutants that require periodic environmental monitoring.

Few studies have been conducted on the concentrations of PAHs in the sediments of the Rosetta and Damietta branches. Moreover, data on the levels of these compounds in the two estuarine habitats of the Damietta and Rosetta branches are very scarce. Therefore, it is advisable and necessary to monitor and assess the current concentrations of PAHs in the surface sediments of these estuarine habitats to identify where the high concentrations of these potentially hazardous contaminants are found, as well as to perform an ecological risk assessment for aquatic organisms exposed to the PAHs estimated in sediments.

Barakat et al. (2011) reported that the total PAH concentrations of the 16 high-priority PAHs (U.S. EPA 2014) in sediments of two sites of the Rosetta branch were 3.49 and 42.8 ng/g, respectively, in comparison to 139 ng/g for the sediments of one site in the Damietta branch. El Nemr (2008) demonstrated that the Damietta branch had high PAH content (44,490 ng/g). Shereet (2009) evaluated the levels of hydrocarbon pollution in sediments of the Damietta Harbor and found that total petroleum hydrocarbons in the bottom sediments ranged between 156 and 4163 ng/g, with an average of 1443 ng/g, which is relatively higher than that recommended in the regulations (500 ng/g) of the Egyptian law of Environment ( No.4/1994). A recent study by El-Maradny et al. (2023) indicated that the distribution of PAHs is affected by the riverine inputs from the Nile River in front of the Rosetta branch, which varied from 30,476 to 34,852 ng/g dw (average: 32,472 ± 2213 ng/g dw) and Damietta branch which fluctuated between 23,064 and 31,555 ng/g dw (average: 26,309 ± 4585 ng/g dw).

Polycyclic aromatic hydrocarbons in biota

El-Sikaily et al. (2002) evaluated the concentrations of hydrocarbons in bivalves collected from 20 locations along the Mediterranean coast of Egypt. Two bivalve species were collected from these areas: Modiolus auriculatus from 15 sites and Donax sp. From five sites. Two locations were surveyed in the Rosetta area (sites 7, 8 = Rashid) as well as two locations in the Damietta area (sites 10, 11 = New Damietta, Ras El-Bar). The concentrations of total aromatic hydrocarbons amounted to 88.4, 391.9, 365.2 and 849.8 ng/g wet weight in locations 7, 8, 10, and 11, respectively; the concentrations of total PAHs were 6159, 5424, 1562 and 1219 ng/g wet weight in the same respective locations. According to the findings of these authors, the majority of mussel samples contained PAHs primarily from pyrolytic sources, such as grass fires (6 million tons annually) and car exhaust, whereas other stations, including El Borg, Ras El Bar, El Jamil (west), and Rommana, had PAHs primarily from petrogenic sources. However, additional sources of pollution are present.

Fluoride

Fluorides are naturally released from minerals, volcanoes, and marine aerosols through dissolution, weathering, and emissions. Human activities also contribute to their production. Fluorides can be released into the environment via coal combustion and water processes. They are found in various wastes produced from several industrial activities, released as byproducts from a variety of industries, including the production of steel, primary production of aluminum, copper and nickel, the processing of phosphate ore, the production of phosphate fertilizer, the manufacture of glass, brick, ceramics, and glue, and the production of adhesive (Masoud and El-Said 2011).

Fluoride in fluoride-containing pesticides and fluoridated drinking water is released into the environment as pollutants (Masoud and El-Said 2011). However, fluoride releases into the environment are mostly caused by the production of phosphate and aluminum manufacture (Liteplo et al. 2002; Masoud and El-Said 2011; El-Said et al. 2018). Exposure to fluoride in the aluminum smelting industry increases the risk of bladder and lung cancer, as well as other cancers in the liver, stomach, bladder, esophagus, lymphatic system, pancreas, and brain (Liteplo et al. 2002; El-Said et al. 2019).

Fluoride is a major seawater constituent (El-Said et al. 2016a), and the concentration of fluoride in unpolluted seawater ranges from 1.2 to 1.5 mg/l (El-Said 2013; El-Said et al. 2023). Fluorine is crucial for marine life, but the presence of fluorine at levels exceeding designated safety levels can be an indicator of current pollution or potential pollution in regions (El-Said and Youssef 2009; El-Said et al. 2016a; El Zokm et al. 2021). El-Said and Sallam (2008) found slight differences in percentage growth increases in the muscles and exoskeleton of shrimps found in the different fluoridated seawaters (0.5, 1, 2, 4, 8, 16, and 32 ppm), as well as fluoride accumulation in these organisms that did not release to surrounding seawater. El-Said et al. (2016a) looked at the distribution of fluoride and phosphorus forms in surface sediments along the eastern Egyptian Mediterranean Sea coast in a survey of six perpendicular sectors (Rosetta, El-Burullus, Damietta, Port Said, El-Bardaweel, and El-Arish) during 2013. The geochemical properties and textures of 30 samples of superficial sediment from the different regions were studied. TOC, total carbonates (TCO₃), iron, and aluminum-associated phosphorus (P_OH), TP, exchangeable and carbonate-associated phosphorus (Pex), calcium-associated phosphate/apatite (P_HCl), residual phosphorus (P_R), calcium (Ca_s), magnesium (Mg_s), and fluoride (F_s) were among the examined parameters. These parameters all had variable values. It is interesting to note that the variation in phosphorus and fluoride levels in the studied area seems to be related to the nature of the sediment in addition to its proximity to potential effluent sources. The level of fluoride in the sediment varied from 0.08 to 0.64 mg/g in front of the Rosetta branch, and from 0.03 to 0.77 mg/g in the Damietta sector. The fluoride concentration of seawater across the study area was different from the published levels for unpolluted seawaters (1.2–1.5 mg/l; El-Said and Sallam 2008), except in the Rosetta and Damietta regions, where the range was 0.57 to 1.83 mg/l and 0.97 to 1.97 mg/l, respectively (El-Said et al. 2016a) due to the freshwater discharge from the Nile River through these branches containing the contaminated wastes. Most types of soil contain fluoride, and in places lacking naturally occurring phosphate, total fluoride concentrations can range from 20 to 1000 μg/g. However, mineral soils contain thousands of micrograms of fluoride per gram (Liteplo et al. 2002), and this contribute to the amount of fluoride released into the sediment–water interface (El-Said 2016a, b).

Fish cages

El-Ezaby et al. (2010) reported that the Damietta region had been drastically affected by increasing levels of pollution from different sources, including domestic, industrial, and agricultural sources, as well as the from wastes from the extensive use of fish cages in the region. More recently, a comparable situation was also observed in the Rosetta region, but with more highly polluted waters (El Sayed et al. 2020). Fewer fish cages are still working in both regions.

As is well known, studies of environmental pollution are very variable. It is evident from the previous studies on pollution parameters that contamination by heavy metals in both the water and sediment of the two Nile branches was the most relevant parameter, with only a few of these studies carried out in estuarine habitats. In conclusion, the results indicated that estuaries have higher concentrations of heavy metals than the Mediterranean coastline; moreover, the dispersion of heavy metals in estuaries affects the heavy metal content of the Mediterranean shoreline.

A recent study on heavy metals in the sediments of both estuaries has shown that the concentrations are comparable with those of previous studies. These, in turn, are affected by the rate of river flow into the Mediterranean Sea (unpublished data).

Biological parameters

The biological parameters that are usually studied in estuarine environments include many communities such as the microbial, phytoplankton, protozoan and zooplankton, macrophyte, and macro-benthic invertebrate communities.

The growth, distribution, and metabolic rates of aquatic organisms are all significantly impacted by the temperature of the estuarine water (Delince 1992) while the distribution of species and transportation of nutrients are significantly influenced by the physical dynamics of water circulation patterns in the estuary (Chilton et al. 2021). The physiology of aquatic species and the solubility of specific compounds can both be impacted by pH changes. Moreover, aquatic species that are not in their ideal pH range may undergo physiological stress due to changes in ionic balance, which is regulated by pH (Davies and Day 1998). It is also well known that the distribution of most aquatic organisms in the estuary habitat is influenced by a number of factors, including salinity, turbidity, DO, BOD, nutrients, food availability, and contamination (National Oceanic and Atmospheric Administration [NOAA] 2021).

The best studied group in previous studies on the biological parameters of habitats in the Egyptian estuaries is the phytoplankton community. However, most of these earlier studies focused on the two branches of the Nile River or on the marine waters adjacent to these branches; only a very few studies focused on the communities in estuaries. The same hold true for the zooplankton, macrophyte, and macro-benthic communities, although even fewer studies investigated these communities in the estuaries. Thus, the findings we present here may highlight the importance of studying the current status of these biological communities in Egyptian estuarine habitats.

Microbial

The spatiotemporal distribution of microbial communities in the estuarine habitat is influenced by environmental parameters such as temperature, salinity, nutrient availability, levels of both DO and pH, and substrate availability (Zou et al. 2020).

Most of the previous studies on microbial communities in Egypt concentrated on the two Nile branches. To investigate bacterial contamination of the Rossetta branch of the River Nile, Sabae (1999) selected four sampling stations. Their results indicated that the El-Rahawy drain was one of the primary sources of pollution in the Rossetta branch. Bacterial populations and water turbidity both rose downstream of the drain's discharge point. At incubation temperatures of 22 °C 37 °C, respectively, viable bacterial counts exceeded those at the drain's discharge point by 250 × 10⁶ counts/mL and 383 × l0⁶ counts/mL, respectively. The total and fecal coliform levels were 350 × 10⁴ coliforms/100 mL and 90 × 10⁴ coliforms/100 mL water, respectively. A count of 450 fecal streptococci per 100 mL water was detected downstream of the drain's discharge point. This leads to the conclusion that El-Rahawy drain sewage effluents should undergo extensive treatment prior to being released into the Rossetta branch.

Sabae and Rabeh (2007) evaluated the microbial quality of the Damietta branch. Water samples, as well as some enivironmental parameters, were collected from the Damietta branch from autumn 2005 until summer 2006. Seven sampling sites were selected along the branch, with the first being an upstream sampling site (El Qanater) and the last being the furthest downstream site (Damietta). The maximum total viable bacterial counts were recorded during summer and the minimal were detected in the winter. Fecal indicator counts showed that bacterial counts rose from upstream to downstream. Eleven genera of pathogenic bacterial isolates were identified down to the species level: Esherichia coli (16%), Klebsiella pneumoniae (14%), Pseudomonas aeruginosa (12%), Pseudomonas flourcsence (4%), Salmonella colerasuis (11%), Shigella sp. (9%), Serratia liquefaciens (8%), Proteus vulgaris (8%), Acinetobacter sp. (7%), Brenneria nigrifluens (5%), Flavimonas oryzihabitans (3%), and Chryseomonas lutecla (3%). This investigation showed that during the research period sewage pollution was present in the Damietta Branch of the Nile River.

All previous bacteriological studies were conducted in the two Nile branches without inclusion of a specific study on the localized estuarine habitats. However, a recent study was conducted in the Damietta estuary and will be published in the near future.

Phytoplankton

Phytoplankton play a vital role in both the oxygen cycle and the food web and are, consequently, regarded as one of the primary indicators of the health of an estuarine ecosystem. Ammonium, phosphate, and nitrite are some of the nutrients that affect phytoplankton abundance. The river provides the freshwater input that allows these nutrients to enter the estuaries (O’Boyle and Silke 2010; Dijkstra et al. 2019).

It has been proven that the cessation of the annual Nile River floods due to human intervention, namely, the building of the AHD dam in 1965, has led to major decreases in the flow of nutrient-rich water to the eastern Mediterranean and thereby dramatically affected the structure of trophic relations in local communities. The massive phytoplankton blooms, which were once a hallmark effect of the flooding river, no longer take place. Simultaneously, the catastrophic reduction in the commercial marine fish catch, especially planktivorous pelagic fish, is a direct indicator of the impact of the AHD on the fishery. According to Aleem (1972), Halim (1976) and Dowidar (1984), the sardine fish catch sharply declined from 18,000 tons in 1962 to only 460 tons in 1968.

Phytoplankton are important organisms that form a vital part of an ecosytem, occupying a fundamental position in the food chain by supplying organic matter, accounting for at least half of the ecosystem’s primary producers (Sridhar et al. 2006). They are essential for understanding the dynamics of entire ecosystems and are major drivers of biogeochemical cycling. Members of some phytoplankton groups (diatoms, dinoflagellates, cryptophytes, and cyanobacteria) can reproduce explosively, generating dense “blooms,” which can color impacted waters (Red Tide) and damage water quality, largely because phytoplankton have high growth rates (approx. a doubling of denisity per day) Hallegraeff 1993; Richardson 1997; Anderson et al. 1998; Paerl et al. 1998). Nowadays, it is understood that phytoplankton blooms are one of the most significant situations that can endanger the majority of aquatic habitat functions. Rey et al. (2004) proposed that phytoplankton species can serve as helpful indicators of water quality in addition to their significance as the primary producers in food webs and maintaining ecological balance.

The role of phytoplankton in estuarine production is determined by a number of variables, including salinity, temperature, light (which is impacted by turbidity), nutrients, water dynamics, and the configuration of the water basin. Additionally, the composition of phytoplankton affects a number of processes, including the recycling of nutrients, grazing, particle sinking, and food webs (Cetinić et al. 2006). Indicators the quantity, quality, and seasonal patterns of phytoplankton have been successfully used to evaluate the quality of water and its ability to sustain heterotrophic communities (Hulyal and Kaliwal 2009).

Zaghloul (1988) investigated phytoplankton production and composition at six sampling stations located in the area of the Edfina Barrage, Rosetta estuary, during the period 1986–1987. These six sampling stations were located at some distance from the localized estuary site. The phytoplankton community was composed mainly of Bacillariophyceae (constituting 58.6% of the total standing crop), Cyanophyceae (or Cyanobacteriota; 23.6%), and Chlorophyceae (17.6%). The maximum density of Bacillariophyceae was recorded during periods of high temperatures and low freshwater discharge.

Shaaban et al. (2012) reported that more than 260 algal taxas, belonging to seven algal divisions, were represented in the Rosetta branch, based on their sampling between August 2006 and April 2008. In qualitative terms, the dominant algal division was Bacillariophyta (112 taxa) followed by Chlorophyta (97 taxa) and Cyanophyta (28 taxa), Euglenophyta (14 taxa), Pyrrophyta (7 taxa), Rhodophyta, and Xanthophyta (each of the last groups represented by 1 taxon). These results are in agreement with those of Saad and Abbas (1985), Zaghloul (1988), Shehata et al. (2008), and Elewa et al. (2009), who noted that genera of the Bacillariophyta and Chlorophyta divisions dominated the majority of the phytoplankton populations in the Rosetta branch, with the divisions Pyrrophyta and Euglenophyta persisting as sporadic forms.

Ali and El Shehawy (2017) examined the phytoplankton communities in five Nile River segments along the Damietta branch, distributed along the Nile River between Aga Town (31°03′41.34″N, 31°34′84.45″E) to the south and Mansoura City (30°92′33.15″N, 31°22′25.57″E) to the north. Samples were collected from March 2011 to February 2012. These authors reported that 213 planktonic taxa from 51 genera, including 96 species of Chlorophyta, 59 species of Bacillariophyta, and 29 species of Cyanophyta, constituted the phytoplankton community along the Nile segments in this study. Chlorophyta was the dominating group in terms of species number. In terms of cell number, Cyanophyta was the abundant category across all sites, followed by Chlorophyta. Charophyta (14 species) and Euglenophyta (15 species) represented the smallest percentage of the total number of species (213 species). At Nawsa El-Bahr in April 2011, the phytoplankton total standing crop reached its apex, peaking at 106.9 × 10⁶ cells/L. Anabaena flos-aquae, Chroococcus minutus, Microcystis incerta, Nostoc sp., Merismopedia gluaca, and Gloeocapsa sanguinea were the main cyanophycean species, contributing > 50% to the total standing crop at all locations. A highly diverse community of Chlorophyta was associated with significant differences between sites. For example, certain taxa were only present at one (or 2) sites and absent from others, while numerous taxa, including Eudorina elegans, Kirchneriella obesa, Lagerheimia ciliata, Lagerheimia sp., Monoraphidium nanoselene, Pandorina charkoviensis, Pandorina morum, Scenedesmus arcutus, Tetraedron muticum, and Tetrastrum triangulare, were simultaneously and exclusively found at certain locations.

It is well known that salinity, which helps to explain the spatial and temporal distribution of phytoplankton along a gradient, is an indicator of freshwater intrusion into the estuary during the monsoon season (Madhavi et al. 2015). The observations of Shaaban et al. (2012) on phytoplankton composition in the Rosetta branch revealed that the salinity gradient has a significant impact on the distribution and composition of freshwater phytoplankton groups.

It is evident that most phytoplankton studies were conducted in the two Nile branches, with only one study in the Rosetta estuary. In conclusion, the absence of flood streams after the construction of the AHD (completed 1965) has resulted in the disappearance of massive phytoplankton blooms. In the Rosetta estuary, the community was composed mainly of Bacillariophyceae (constituting 58.6% of the total standing crop), Cyanophyceae (23.6%), and Chlorophyceae (17.6%). The maximum density of Bacillariophyceae was recorded during periods of high temperatures and low freshwater discharge.

A recent study was conducted on phytoplankton communities in the two estuaries. At the sampling stations located at the mouth of the Damietta branch, 19 taxa were identified, represented by Bacillariophyta, Dinophyta and Chlorophyta, including 11 marine, two freshwater, and six brackish species The marine species Skeletonema costatum formed a semi-bloom phenomenon at this location, possibly due to a shortage of freshwater pouring into the Mediterranean Sea and/or the intrusion of salt water into the branch mouth. At the sampling stations located at the mouth of the Rosetta branch mouth, 27 taxa were identified, represented by Bacillariophyta, Dinophyta Cyanophyta, Euglenophyceae, and Chlorophyta, including 14 fresh, 11 marine, and two brackish species (unpublished data).

Protozoa and zooplankton

Zooplankton play a vital role in the carbon cycle and act as a bridge between tiny organisms such as phytoplankton and fish larvae. Zooplankton are among the most significant organisms in an ecosystem as most zooplankton are a favorite diet for numerous fish species of major economic importance. Zooplankton are highly affected by changes in the surrounding environment and, consequently, the zooplankton reserve is a good indicator of water changes and pollutants (Alzeny 2018). Almost all studies in Egyptian waters considered protozoa to be a part of the zooplankton community.

The distribution of protozoa and zooplankton in estuary habitats is affected by several factors, such as nutrient availability, salinity, pH, and water depth, with salinity found to be a leading factor influencing rotifera and copepods. pH, however, can either promote or prevent the growth or existence of particular species and, therefore, pH is considered to be a crucial component in the management of protozoa. For example, a pH of 9.5 would encourage protozoa to fully colonize the environment, whereas a pH of 8.5–9.5 might inhibit their proliferation (Sun et al. 2023).

Only a limited number of studies have focused on surveying the protozoan community. Dorgham et al. (2009) studied the protozoan community in Damietta Harbor, Egypt, and found that protozoa comprised the second important zooplankton group (26.3%). Dorgham et al. (2013) studied protozoa in a stressed area of the Egyptian Mediterranean coast (Damietta) and identified 69 protozoan species, including eight species of Amoebozoa, 12 species of Foraminifera, 22 species of non-tintinnid ciliates, and 27 species of tintinnids.

In contrast, a relatively larger number of investigations have focused on the zooplankton community. At Damietta Harbor in Egypt, EL-Ghobashy et al. (2006) investigated the impact of maritime activities and Nile discharge on the dispersion of the zooplankton community. These authors noted that west of the estuary of the Damietta branch, a semi-closed basin known as Damietta Harbor was constructed in 1987. This port is used to import and export a large variety of goods. However, some of these product’s spill into the water while being stored in large piles on quays or when being loaded or unloaded, which, along with other maritime activities and Nile discharge, alters the physical and chemical composition of the water in the harbor. EL-Ghobashy et al. (2006) noted that some biological parameters of the harbor, particularly the phytoplankton and zooplankton communities, were affected by these changes. This study was designed to cover the cycle of zooplankton abundance, phytoplankton biomass, and water characteristics since the harbor opened to international marine trade. From May 2003 to April 2004, various parameters were monitored each month at numerous sites in the harbor, representing various ecological units. In comparison to other Egyptian Coastal Mediterranean waters, the results showed significant ecological and biological changes due to allochthonous stress. The strong seasonal and geographic changes in salinity (33.8% and 39.4%, respectively), with an annual average salinity of 33.8%, clearly demonstrated the impact of the Rive Nile discharge. The results revealed that the phytoplankton biomass in the harbor water appeared to be abnormally high, whereas the levels of chlorophyll a fluctuated between 1.2 and 19.6 μg/L. These values indicate that the port is clearly a highly eutrophic area because of the abundant fertilizer supply from both the Nile discharge and human activities. As a result, the zooplankton community was abundant, with an annual average of 82 × 10³ individuals/m³. It is also reasonable to assume that the water quality of the harbor will be more susceptible to deteriorations with time, which needs an adequate solution.

Saad et al. (2013) evaluated in impact of sewage pollution in the Rosetta branch of the Nile River on the quantity and diversity of zooplankton. Their findings showed that zooplankton function as an effective tool to measure sewage pollution, eutrophication, and heavy metal contamination and also act as a good descriptor of water quality. Abo-Taleb (2014) examined the dynamics of the zooplankton community at the Rosetta branch. In their study, water and zooplankton samples were collected at monthly intervals throughout the course of 1 year, from April 2007 to April 2008. Eight locations were selected, including three stations within the estuary mouth and five stations in the Rosetta branch. A total of 108 species were recorded, representing ten phyla. The major phyla included Arthropod Crustacea (41 species), Protozoa (23 species), Rotifera (22 species), and Annelida (6 species). The zooplankton community was found to be mainly composed of 64 marine species and 35 freshwater species, with Rotifera being most abundant, followed by Copepoda > Cirripedia > Protozoa > Annelida > Cladocera > Mollusca. Moreover, the typical estuary species comprise the majority of the zooplankton community. Nine genera and 22 species made up the Rotifera, with Keratella (3 species), Brachionus (6 species), Synchaeta (4 species), and Polyarthra (one species) being the dominant genera. The results of this study indicated that the distribution and diversity of the estuary's zooplankton community are primarily influenced by salinity and freshwater outflow volume.

In Egypt’s Damietta Nile branch, Elfeky and Sayed (2014) investigated the prevalence and distribution of Rotifers. A total of 56 species, belonging to 25 genera, were discovered in the Nile River from 28 seasonal water samples collected in 2009 from 28 places along the river, from Chema in the south to Faraskour in the north. The most common rotifer genera and species were Keratella, Brachionus, Polyarthra, Conchilus, Synchaeta, Collotheca, Philodina, Filina, Asplanchna, and Anuraeopsis. Rotifers were observed at different concentrations along the Nile River, with densities increasing downstream.

El-Tohamy (2015) investigated the hydrography and the Crustacean Zooplankton as determinants of Rotifer distribution and density in Damietta Coast. He indicated that distribution of Rotifer species was substantially correlated with salinity fluctuation, chlorophyll-a, and their defense against planktonic crustaceans from possible predators and competition. The environmental factors influencing the zooplankton community in the Damietta estuary of the Nile River, Egypt, were investigated by Tohamy et al. (2018). Most zooplankton abundance, or 39.4%, was made up of meroplanktonic larvae. Copepods and their larval stages constituted about 36.2% of the total. The third most abundant group (12.6%) was rotifers. A total of 10.6% of the community was made up of protozoa. The results of this study indicated that the main spatial gradients along the estuary were associated with salinity.

El-Tohamy and Abdel-Baki (2019) studied mesozooplankton along 78 km of the Damietta branch of the Nile River to evaluate the effects of human activities (water plant stations, drainages from a fertilizer factory, and domestic sewage) on the number and distribution of mesozooplankton in the study area. Samples were collected each month at seven stations from October 2013 to September 2014. To eliminate the bias towards the gathering of smaller mesozooplanktons, such as rotifers and copepod larvae, a plankton net with a mesh size of 180 μm was utilized. Thirty-six mesozooplankton taxa were identified, of which Cladocera (CLA; 41.6%) were the most abundant, followed by Copepods (COP; 29.9%), Rotifera (ROT; 14.8%), and Ostracoda (13.2%). The shift in the ROT:CLA:COP ratio from rotifers to copepods and cladocerans suggests that the area is becoming more eutrophicated. Based on SIMPER analysis, Bosmina longirostris, Ceriodaphnia reticulate, Moina micrura, Acanthocyclops americanus, Brachionus calyciflorus, and Candona subgibba were the most significant taxa. The results indicated that water temperature, conductivity, and nitrate levels were linked to differences in species distribution. The quality and quantity of plankton in the studied area were depend on the level of anthropogenic disturbance. The results also indicated that controlling the release of post-cooling fluids is important to protect the planktivorous fish in the study area as well as the zooplankton fauna. This is especially important for stations close to the hot water outlet of the thermal power generation plant.

Fishar et al. (2019) studied the community composition of zooplankton in El-Rayah El-Behery (connected to the Rosetta branch), Egypt in relation to a number of environmental variables. During this survey, the authors identified 61 species of zooplankton, including 42 Rotifera, nine Protozoa, seven Cladocera, and three Copepoda. Data from zooplankton populations were recently employed by Hegab and Khalifa (2021) to evaluate the water quality of numerous water bodies in the two Nile Branches (Damietta and Rosetta branches).

In conclusion, most zooplankton investigations to date have been concentrated in the two branches of the Nile River or close to seawater areas, with a few exceptions that were performed in estuarine habitats. The absence of massive phytoplankton blooms after the construction of the AHD (completed 1965) contributed to a decrease in the abundance of zooplankton communities. In the Rosetta estuary, 108 species were recorded, representing ten taxa, with the major taxa including arthropod crustacea (41 species), protozoa (23 species), rotifers (22 species), and Annelida (6 species). In the Damietta branch the zooplankton community consisted of meroplanktonic larvae (39.4% of total abundance), copepods and their larval stages (36.2%), rotifers (12.6%), and protozoa (10.6%). These studies confirmed that the main spatial gradients along the estuary were associated with salinity.

A recent study conducted on zooplankton communities in the two estuaries demonstrated a higher total standing crop and number of taxa in the Damietta estuary than in the Rosetta estuary. The main dominant taxa in the Damietta estuary include crustacea, mollusca, and protozoa, whereas in Rosetta estuary, they include crustacea, protozoa, and mollusca (unpublished data).

Macrophytes

Macrophytes are a major constituent of aquatic ecosystems (Albay and Akcaalan 2003) and perform many ecosystem functions and contribute to the general fitness and diversity of a healthy aquatic ecosystem (Madsen et al. 2001). They also function as bioindicators of environmental conditions and provide suitable habitats for macroinvertebrates such as insects, fish, and other aquatic or semiaquatic organisms.

The most significant factors governing the abundance and distribution of macrophytes have been found to include variations in water temperature, light, nutrient enrichment, changes in water quality, sediment composition, and water level fluctuations. Water depth, season, and latitude as well as light and temperature play a major role in determining the distribution of macrophytes, which in turn affects productivity and species composition. The growth rates of macrophytes are significantly impacted by the composition of the sediment, which also has a significant impact on the dispersion of aquatic macrophytes. Significant differences can occur in species richness, composition, and density of aquatic vegetation due to nutrient enrichment and changes in water quality. The distribution and species composition of macrophytes may undergo significant changes as a result of falling dropping water levels. The distribution and community structure of macrophytes are also significantly shaped by variables related to competition, herbivory, and changes in land use and cover, among others (Dar et al. 2014).

Only a limited number of investigations have been carried out on vegetation succession in the Damietta and Rosetta estuaries, and most of these studies concentrated on the two branches (Zahran 2009; El-Amier et al. 2015b; Hussian and Haroon 2019). This review provides baseline data on currently available information on vegetation zonation around the Damietta and Rosetta estuaries.

Prior to the construction of the AHD, seagrasses were present along the Deltaic region between Rosetta and Damietta. While Posidonia oceanica was rare, Cymodocea nodosa was common (Aleem 1955). During this time, the Mediterranean Sea received a substantial influx of freshwater, which was packed with dissolved and particulate nutrients from the Nile River.

The vascular freshwater weeds of the Nile River in Egypt are represented by 87 species of flowering plants, which are classified into 25 families and 45 genera. Thirteen of these families are monocots, and 12 are dicots. Additional pteridophytes include Azolla filiculoides, Marsilea aegyptiaca, and M. capensis. Nineteen species of the family Cyperaceae are present, followed in abundance by 15 species in the Gramineae, six species each in Lemnaceae and Potamogetonaceae, four species in the Najadaceae, three species in each of six families, and two species in each of three families. Other families contain only one species each (Zahran 2009). El-Amier et al. (2015b) recorded only three submerged macrophytes in the Damietta branch. Five submerged macrophyte species belonging to three genera were identified by Hussian and Haroon (2019) in the Nile River. The variation in sampling sites, environmental circumstances, and the impact of human activity on water bodies could all be factors contributing to this variation in the number of recorded species. However, numerous variables affect the abundance and dispersal of aquatic plants, including nutrients, physicochemical characteristics of the water and sediment, water velocity, grazing animals, water depth, and allelopathic interactions between macrophytes, phytoplankton, and epiphytes (Van Donk and Otte 1996; Middelboe and Markager 1997; Armengol et al. 2003).

In this review we present basic information regarding current data on the distribution of vegetation in the vicinity of the Damietta Estuary. Aboellil (1987) carried out ecological studies on a number of hydrophytes growing in the Dakahleya and Damietta districts. Khedr (1998) examined the zonation of the vegetation along the saline and freshwater marshes of the Damietta estuary (Nile River), from close to the river’s mouth to 20 km upstream. The estuary water downstream was nearly stagnant and very salty and contained significant nutrient concentrations. Khedr (1998) demonstrated that the estuary vegetation of the Damietta branch of the Nile River is comparable to that of other deltas in the Mediterranean region, based on floristic and soil characteristics. However, in the Damietta estuary, the prominent species, such as Polygonum equisetiforme and Suaeda vera, have distinctive features. This author also added that Phragmites australis, Tamarix nilotica, Arthrocnemum macrostachyum, Zygophyllum aegyptium, Polygonum equisetiforme, Cynodon dactylon, and Suaeda vera were among the prominent species in the salty marshes. The most common species in the freshwater marshes, however, were Ludwigia stolonifera, Persicaria lapathifolia, Typha domingensis, Eichhornia crassipes, and Ceratophyllum demersum.

In the northern Nile Delta, close to Damietta City, Serag (2000) recorded the presence of Cyperus papyrus close to Mit Ghamr City, which is located in the Dakahleya Governorate. Amer and Serag (2003) discovered a flourishing community of C. papyrus in August 2000 near Damietta along the bank of the main branch of the Nile. More recently, Abu Ahmed et al. (2021) detected Ulva lactuca bloom at Damietta Nile Estuary during early spring 2019.

Three submerged macrophytes Myriophyllum spicatum, Ceratophyllum demersum L., and Potamogeton crispus were recently discovered by Haroon et al. (2020). These species were noted with significant seasonal and spatial variations. Myriophyllum spicatum was the most prevalent macrophyte in various seasons. While a high value of P. crispus may point to the presence of an industrial source of pollution, the presence of C. demersum and M. spicatum may suggest the presence of agricultural drainage sources of pollution.

Recent observations (Abd El-Ghani and El-Garf, unpublished data) on the Rosetta branch of the Nile River have confirmed the vigorous spread of other new scattered patches of Cyperus papyrus at the same latitude. Azolla had grown rapidly and spread in the form of dense mats to cover stagnant water in ditches and in irrigation and drainage canals of Rosetta district (Shaltout and Al-Sodany 2000). These findings indicate the importance of studying this community in the future.

As noted from previous studies, there is a lack of macrophyte biodiversity and abundance. Therefore, we need a better understanding of the physico-chemical parameters, particularly of water, temperature, salinity, and nutrients, as these promote the flourishing of aquatic plants in the Egyptian estuaries and will improve our understanding of how ecosystems will respond to challenging global issues such as global warming and climate change. It is also necessary to monitor and conserve these species due to the region's declining habitat degradation and potential for plant extinction.

Macro-benthic invertebrates

Animals referred to as benthos or benthic macroinvertebrates live in the bottom substrates of ecosystems, such as mud, sand, gravel, rock, shells, or even the bodies of other organisms. They are typically creatures that move slowly or are sedentary and have a close association with sediments. During all or a portion of their life cycle, they can build attached cases, tubes, or nets that they can dwell in or on, or they can move freely over rocks, organic matter, and other substrates.

In estuarine ecosystems, macrobenthos are important elements that contribute significantly to the dynamics of the system (Herman et al. 1999). van Oevelen et al. (2006) indicated that they play a key role in the process of nutrient cycling. Moreover, they have a crucial role in estuarine food webs as a major source of food for fish, birds, and large crustaceans (Day et al. 1989). However, numerous species of crabs and shellfish are also harvested by humans.

The distribution of macro-benthic invertebrates in the estuary habitat is influenced by various factors, including streambed topography, food resources, water quality parameters (such as salinity, turbidity, DO, BOD, and nutrients), contaminants in the sediment, and sediment composition itself (Rai et al. 2019; Min and Kong 2020). Other earlier studies have shown that contaminants and sediment can significantly impact estuaries (Bissoli and Bernardino 2018; Morrisey et al. 2003).

One of the most crucial ecological elements of coastal and estuarine ecosystems is sediment, which provides significant carbon storage (Donato et al. 2011) as well as habitat resources for the benthic community, which is main consumer group of an estuary ecosystem (Kristensen et al. 2008). Simultaneously, the salinity and sediment composition of an estuary gradient are used to explain the geographic variability of macrobenthos (e.g., Schlacher and Wooldridge 1996; Mannino and Montagna 1997). Other studies have focused on the effects of various anthropogenic activities (e.g., navigation, overfishing, recreational activities, industrial effluents, and sewage discharges) on the loss of macrobenthos biodiversity and habitats (Wolanski and Elliott 2015; Feebarani et al. 2016; Mulik et al. 2017). Additionally, the number of publications on estuary ecology has quickly expanded during the last 10 years (Duarte et al. 2015).

However, previous studies on macro-benthic invertebrate communities in the localized Egyptian estuarine habitats are conspicuously almost absent. El Sayed et al. (2020) performed the only study on macroinvertebrates and different chemical parameters, with the aim to conduct an integrated water quality assessment of the Damietta and Rosetta branches. These authors collected benthic fauna from five and six locations in the Damietta and Rosetta branches, respectively. All of the surveyed stations were separated from the estuarine habitats. The community composition included six species of Annelida, 12 species of Mollusca, and seven species of Arthropoda, which are found only in the freshwater environment. Simultaneously, other similar studies were previously conducted in both branches, also without reaching the estuarine habitats.

In summary, a recent study on the biodiversity of macro-benthic invertebrate communities in localized estuarine habitats of the Damietta and Rosetta branches revealed 112 and 103 taxa in the respective estuaries. All recorded taxa have a marine origin (unpublished data). This finding may highlight the influence of freshwater shortages discharging into the Mediterranean Sea on the structure of benthic communities in the two Nile estuary habitats, possibly due to the construction of the GERD.

Conclusion

This is the first systematic review of Egyptian Nile estuarine habitats and their natural and/or man-made activities.

It is evident from this review that most previous studies focused on the two Nile branches or on marine waters adjacent to these branches, and that only a few studies looked at pollution or plankton in the estuarine habitats. During most of these previous studies, the salinity gradient of water was found to be a significant factor in the distribution of the different measured parameters. However, more recent investigations confirm the importance of potential effluent sources affecting the distribution of these parameters.

Following the disappearance of phytoplankton blooms linked to the Nile flooding after the building of the AHD in Egypt (since 1965), nutrient concentrations in these waters have significantly decreased. As a result, Sardinella catches have decreased from around 15,000 tons in 1964 to 4600 tons in 1965 and 554 tons in 1966. Other previous studies on plankton, especially zooplankton, demonstrated the strong effect of seasonal and geographic changes in salinity on their distribution. More recent investigations on plankton communities have indicated that the quality and quantity of plankton in the studied areas depend on the level of anthropogenic disturbance.

Based on the available data on macrophytes and macro-benthic invertebrate communities in the two estuaries, studying the distribution and biodiversity of these flora and fauna in the localized estuarine habitats of Damietta and Rosetta is a priority.

In the current situation, following the construction of the GERD, the amount of freshwater discharged into the Mediterranean Sea should be kept to a minimum for freshwater conservation. This is associated with higher salinity values because of saltwater intrusion into the branches, which in turn dramatically affects the structure of different biological communities (microbial, phytoplankton, zooplankton, and benthic invertebrates). Other chemical and pollution parameters will, of course, be affected by this increase in salinity. Moreover, it should also be kept in mind that decreasing the amount of freshwater discharged into the Mediterranean Sea renders cultivated lands extremely vulnerable to saltwater intrusion and more susceptible to deterioration effects.

On the other hand, the preservation of Nile River water and planning for sustainable usage to prevent or minimize Nile River water quality issues and maintain the Nile ecosystem’s balance by overexploiting renewable water resources are two of Egypt’s ultimate national development goals. It is important to implement activities of the integrated water resources management and forecasting component.

At the same time, monitoring the Nile River is extremely important for all the 11 countries along its banks, and not just for Egypt. However, the availability of a sizable dataset that documents trends of change in both geographical and time dimensions depend on the ability to accurately assess progress toward minimizing impacts on natural habitats and improving human access to safe water. It is highly recommended to update these data based on more recent studies on different environmental aspects in these localized estuarine habitats under the current circumstances.

Generally, on a global scale, as people use these estuarine habitats for the provision of food and raw materials, transportation, waste treatment, and recreation, among other things, these habitats are vulnerable to threats from a variety of human activities, including domestic, industrial, agricultural, and fish cages. Therefore, some precautionary measures should be taken to save these environments.