1 Introduction

The Earth predominantly consists of water, with over 97% of this precious resource residing in its vast oceans, constituting the planet’s largest ecosystem. Water, which is an indispensable element in every corner of the earth, has a great influence on every facet of life and is consumed in all the major activities on the earth. Beyond quenching our thirst, water plays pivotal roles in irrigation, agriculture, and power generation. The quality of water is of great importance, specifically if human utilization is considered. The absence of specific water characteristics makes the water unfit for human consumption.

The quality of water is greatly influenced by the surroundings because of the natural tendency of matter to move from areas of high concentration to low concentration. In the same context, the interaction of various ecosystems such as mangroves, mudflats, beaches, coral reefs, and oceans with the flowing water of the river greatly affects the quality of water in the river and its branches. Especially, the quality of river water at the deltaic streams flowing to the ocean is highly prone to be negatively affected by the ocean [1]. At the deltaic interface, the transfer of minerals takes place from the mineral-rich oceanic waters to the less concentrated river water. The influx of high nutrients from the saline water to the freshwater of the river can lead to eutrophication and the formation of seaweed in streams of deltaic regions, that is undesired [2].

Indus Delta is one of the same deltas formed at the interface of the Indus River and the Arabian Sea. River Indus is one of the major rivers in Pakistan, which has an approximate length of 3180 km and flows through India, China, and predominantly Pakistan before ending at the Arabian Sea in the South of Pakistan. Near its ending, it forms a huge delta called the Indus Delta which covers an approximate area of 17,000 km2 [3]. This is the 7th largest delta in the world which houses more than 97% of mangroves in Pakistan. It is primarily located within the Thatta and Sujawal districts of Sindh [4] and encompasses several creeks, including Korangi Creek in the North, and Sir Creek in the South [5]. Khobar is the main creek along the river that connects the Arabian Sea with the river.

Water quality degradation is a global concern, and its escalation in Pakistan’s Sindh Province is of profound interest. Approximately 41% of Sindh’s population faces severe water shortages and related problems, especially in coastal regions [6]. People in deltaic regions are compelled to use low-quality water, contaminated with minerals due to seawater intrusion, which also renders groundwater unfit for consumption. Consequently, they are left with no choice but to rely solely on surface water [7].

The absence of a reliable water supply scheme and poor groundwater quality compounded the crises for the Inhabitants of this region. The intrusion of seawater into this delta has further exacerbated the situation in the area and led to devastating health concerns [8]. However, the importance of this delta is inexorable, as the Indus Delta boasts diverse ecosystems, encompassing mangroves, coral reefs, freshwater lakes, and brackish wetlands [9], the population is confronted with formidable challenges and is heavily reliant on the surface water of the Indus River for their daily needs.

The ramifications of these changes are profound, affecting livelihoods, fishing, irrigation, livestock, and drinking water supply. The Earth’s hydrological cycle drives the movement of water from rivers to oceans and vice versa. Tides, which are the prime source of this transition, are driven by various forces including lunar attraction, wind, and gravitational force, making it a contingent variable on which several physical properties of water like pH, salinity, dissolved solids, and turbidity are reliant [1]. Furthermore, the retention of water behind hydraulic structures also weakens the fluvial regime and reduces flow towards the sea [10]. As a result, the tides of the ocean superseded the freshwater of the river leading to stunted mangrove growth, coastal erosion, and seawater inundation [5]. Mahar and Zaigham [11] also reported the narrowing of the river towards the seaside and the widened river landwards. Moreover, excessive groundwater abstraction also facilitated seawater intrusion into aquifers and water streams along the coastlines [12].

The literature reveals that seawater intrusion into the Indus Delta Pakistan, is increasing at an alarming rate which severely affects the livelihood of the people and leads to environmental degradation [13]. Furthermore, various ill effects of seawater intrusion have also been pointed out such as the engulfing of fertile land [10], stunted growth of mangrove forests [14], loss of nutrients [15], and reduced flow of freshwater [16].

The deteriorated groundwater quality near coastal areas has been reported in Pakistan highlighting the effect of seawater intrusion [17]. The surface water of many regions has also been studied for the same menace as the Yangtze River in China has been studied by He et al. [18] and Hau River by Ni et al.[19]. Physicochemical parameters for various lakes, ponds, streams, and natural depressions located in the Indus Delta have been studied by Siyal [16], who has quantified the area taken away by the sea. In the same way, Ahmed et al. [20] have explored this spatiotemporal variation of various dissolved organic nutrients and chlorophyll-a across the various creeks of the Indus Delta including the Khobar Creek. Moreover, Sediment concentration has been quantified from Kotri Barrage to Khobar Creek [15]. The longitudinal variation in various physicochemical parameters of the river Indus with respect to the sea is still undiscovered.

Considering the immensity and gravity of the problem, the current work has been targeted to evaluate the water quality in terms of physiochemical parameters and the longitudinal variation of these parameters from the mouth of the river at the ocean to the upstream side to highlight the zone of high salinity inundation and determine safe zones for accessing surface water in the Indus Delta for drinking purpose in the Sujawal district. To accomplish the objectives, representative samples from the river from the various locations along the length were analyzed for basic physiochemical parameters to establish a relation between the distance and properties.

1.1 Study area

Indus Delta stretches along the South-Eastern coast of Pakistan laying between 20° E and 24° N [20]. Pakistan contains about 1046 km of the total coast, out of which 270 km falls in the boundaries of Sindh [21]. River Indus joins the Sea through an active creek, the Khobar Creek, which presently is the only functional creek that joins the two water bodies [15, 22, 23]. This creek lies within the administrative jurisdiction of District Sujawal which is one of the four coastal districts of Sindh, the Southward province of Pakistan. The geographical location of the study area and sampling points are  shown in Fig. 1 and Fig. 2.

Fig. 1
figure 1

Geographical location of the study area

Full size image
Fig. 2
figure 2

Map indicating the tail of River Indus marked with sampling locations

Full size image

2 Material and methods

Ten Water samples of surface water at an approximate interval of about 5 km from the mouth of the creek were collected in triplicate in 1.5 L prewashed clean water bottles and carried out to the laboratory for testing. Composite samples were prepared by mixing water collected from various depths to have a representative sample of the sampling point ensuring a true representation of the site. Standard surface water sampling protocols were followed for sample collection and preservation. These protocols are widely recognized and accepted in scientific studies to maintain the integrity of the samples and minimize any potential biases. Sampling bottles were sealed immediately to prevent any possible contamination and brought to the laboratory for further analysis.

In the laboratory, water samples were tested for pH, total dissolved solids (TDS), electrical conductivity (EC), hardness, chloride concentration, turbidity, and acidity. Each test was conducted separately in duplicate to obtain specific and accurate data for each physiochemical parameter. An average of three readings are taken to have a representative value of the site that can reflect the overall properties and composition of the water sample at that site. The procedure for each test is described in succeeding sections.

2.1 Total dissolved solids (TDS)

An electronic TDS meter was used to find out the total dissolved solids concentration. For measuring TDS, pre-calibration of the instrument with reference salutation was made. The meter was washed with deionized water to remove any traces of the reference solution. After each measurement, the probe was rinsed with distilled water to remove any residue from the previous sample, and the same procedure was repeated for all other samples. All the samples are tested twice to ensure data integrity and overcome the possibility of any error.

2.2 Electrical conductivity (EC)

The electrical conductivity was measured through a digital EC meter. The meter was initially calibrated with standard solutions of known EC and the probe was washed with distilled water to remove the traces of reference solution. The meter was turned on and the probe was submerged in the sample and readings were recorded after stabilization.

2.3 pH

An electronic pH meter was used to find out the existing value of pH for the sampled water. The standard procedure of pH determination was followed through an electronic pH meter. The meter was first calibrated using standard buffer solutions of a known pH. The probe of the meter was then washed with distilled water and then immersed in the sample until a stable reading appeared on the screen. Reading was recorded and the test was repeated after washing the probe again.

2.4 Acidity

The total acidity of the collected water samples is found by titrating the water sample against NaOH until the appearance of the pink color of the phenolphthalein indicator. The amount of the titrant was recorded, and the acidity was calculated using standard molecular weights. Equation 1 was used to calculate acidity. Where C is the molar concentration of NaOH solution.

$$Acidity = C \cdot \frac{{Volume\;of\;titrant\, \left( {ml} \right)}}{{Volume\;of\;Sample\,\left( {ml} \right)}} \cdot 1000\, \left( {mg/L} \right)$$
(1)

2.5 Hardness

Hardness was determined by titrating the collected water sample against Ethylene-diamine-Tetra-Acetic-Acid (EDTA) in the presence of ammonium buffer and Eriochrome Black T (EBT) indicator until the EDTA complex was formed and indicated by a color change of the solution to blue. Calculations have been made using Eq. 2 to find hardness.

$$Hardness = C \cdot \frac{{Volume\;of\;EDTA\,\left( {ml} \right)}}{{Volume\;of\;Sample\,\left( {ml} \right)}} \cdot 1000\,\left( {mg/L} \right)$$
(2)

2.6 Chloride Concentration

Chloride Concentration was found by titrating the collected water sample against Silver Nitrate (AgNO3) in the presence of K2CrO4 until the appearance of red precipitates. The amount of titrant was recorded, and chloride concentration was calculated using Eq. 3.

$$Chloride\;Concentration = C \cdot \frac{{Volume\;of\;AgNO_{3}\,\left( {ml} \right)}}{{Volume\;of\;Sample\,\left( {ml} \right)}} \cdot 1000\,\left( {mg/L} \right)$$
(3)

2.7 Turbidity

The measurement of turbidity was performed using Jackson’s method. Two sets of Jackson’s turbidity tubes were washed with decontaminated water. The sample was shaken vigorously to obtain a homogenous mixture and then poured into the Jackson’s turbidity tube gradually until the disappearance of the Secchi disc attached at the bottom of the tube. Turbidity readings were noted from the graduations on the tube. The obtained readings were in the unit of (Jackson’s Turbidity Unit (JTU) which was converted to the Nephelometric Turbidity Unit (NTU) by using a conversion factor of 0.4.

3 Results and discussion

Samples were named SW1 through SW10 indicating the first location to the tenth location respectively. These sites were selected based on accessibility. Their respective distances were calculated from the mouth of the creek to the ocean providing comprehensive coverage of the study area.

Samples were analyzed for turbidity, which ranged between 21 and 57 NTU, indicating increasing degrees of cloudiness or haziness in the water from the mouth toward the landside. The other key parameters of the samples collected are documented and presented in Table 1, providing an overview of the different physicochemical characteristics including TDS, EC, pH, Acidity, hardness, and chloride concentration.

Table 1 Observed water quality parameters of the samples
Full size table

To comprehend the results of drinking water quality, results are compared with WHO-recommended values, which are established to ensure the safety and quality of drinking water. World Health Organization (WHO) has established specific recommendations and guidelines regarding the acceptable limits for various parameters. To facilitate easy reference and compare the obtained values with these standards, its relevant portion is tabulated in Table 2. This table serves as a valuable resource for water quality management, enabling regulatory bodies, water treatment facilities, and individuals to compare and monitor the measured values against the recommended limits set by WHO. By adhering to these guidelines, it becomes possible to safeguard public health and ensure the provision of clean and safe drinking water to communities worldwide.

Table 2 WHO limiting values for the selected parameters
Full size table

Results from this study underscore the critical significance of freshwater flow towards the sea, which in contrast can cause the engulfing of fertile land by the sea. The literature extensively documents a surge in seawater intrusion within the aquifers of the Indus Delta, presenting an alarming escalation. Infrastructure development in the basin has notably impacted sediment and water discharge downstream of the Kotri Barrage [25]. This reduction in discharge contributes to coastal erosion in the Indus deltaic and coastal regions, concurrently elevating sea water turbidity to levels unsuitable for diverse marine organisms.

A detailed analysis and interpretation of the obtained results are presented in subsequent sections. This analysis aims to elucidate the relationships, trends, and potential implications of measured parameters for shedding light on the water quality and overall environmental conditions in the studied area. The findings will contribute to a comprehensive understanding of the state of the water samples and assist in assessing their suitability for Drinking Purposes.

3.1 Total dissolved solids (TDS)

It is revealed that the TDS concentration of samples, that are collected from near to seashore, was observed very high, and a decreasing trend was observed for the TDS values along the longitudinal distance along the creek. Samples upto 15 km exhibited values upto 9000 mg/L, which is nine times more than the limits. This finding aligns with the observations made by Shahab et al. [24], who reported that the highest TDS values in Pakistan are typically found in the lower part of Sindh, which corroborates the results of this study. Siyal [16] has also reported that 64% of water bodies of the Indus Delta do not satisfy WHO standards for drinking water in terms of TDS, which is in accordance with the results of this study. Data depicted that at about 57 km from the ocean, the river water maps with the limit of WHO in terms of TDS and EC. The longitudinal variation of TDS is displayed in Fig. 3.

Fig. 3
figure 3

Pattern of TDS and EC variation with respect to the distance from the sea

Full size image

3.2 Electrical conductivity (EC)

High EC values of surface water samples were exhibited close to the sea, which was decreased longitudinally with the increase in distance. The EC values of collected samples ranged between 33,000 µS/cm to 1385 µS/cm, while WHO specifies a limiting value of 1500 µS/cm for drinking water. These findings indicate that the water quality in Khobar Creek, particularly at greater distances from the sea belt, is deteriorating due to factors such as the scarcity of freshwater, tidal influence, and rapid deforestation of mangroves. These factors can have adverse effects on the ecosystem of the Indus Delta. The elevated levels of total dissolved solids (TDS) and EC can be attributed to the influence of seawater along the streams, highlighting the impact of saline intrusion in the region. 78% of the natural surface water bodies have been reported to be saline in the delta which is because of the seawater inundation. Siyal [16] reports that 66% of the surface water samples from the delta do not meet the standards of drinking water. Figure 3. Further illustrates the variation pattern of EC along the length of the river from the mouth.

3.3 Chloride concentration

Among the several minerals transported through seawater, chlorides of sodium, calcium, and magnesium are some of the most concerned minerals. Like other factors, chloride concentration has also been observed to vary spatially along the length of the river. Data revealed that this parameter is within the allowed limits till a distance of 32 km from the sea towards the river. Lower values after this distance clearly indicate the reduced influence of the oceanic water. Overall values varied between 1421 to 96 mg/L at 3 km away to 57 km away from the mouth of the creek. WHO limiting value for this parameter is reported to be 250 mg/L, which shows lesser concerns after 32 km. The graphical variation of chloride concentration is displayed in Fig. 4.

Fig. 4
figure 4

Fluctuation Patterns of Chloride Concentration, Hardness, and Acidity with respect to the Sea

Full size image

3.4 Total hardness

A range of 3654 to 1475 mg/L of the total hardness has been witnessed till the distance of 21 km, which is three to seven times more than the WHO limiting values. This zone within 21 km from the ocean raises concerns due to the presence of hard water, which is known to have adverse effects on human health. Hard water can lead to skin diseases and an increase in the levels of bicarbonates of calcium and magnesium. However, as the distance from the sea increased beyond 21 km, the hardness values gradually decreased to 192 mg/L. The visual representation of the spatial variation is shown in Fig. 4, highlighting the significant fluctuations in water hardness along the studied coastline.

3.5 Acidity

When examining the acidity parameter in terms of water quality, it was observed that the acidity levels consistently decreased as the distance from the sea increased. The acidity levels fluctuated depending on the presence of other contaminants in the water as well. This finding indicates that the water quality in this location may be affected by acidic substances or contaminants. However, it is important to note that the acidity levels in the collected surface water samples varied between 400 and 860 mg/L, reflecting a significant range of acidity across the studied area, which was not depicted by the pH value and was in an almost neutral range instead. Figure 4 allows readers to visualize the changes in acidity levels along the coastline, highlighting a smooth pattern or trend. By analyzing the graph, one can observe the fluctuations in acidity levels at different locations.

3.6 Turbidity

The turbidity of the collected samples showed a surprising trend, which was just in reverse to other observed parameters. Interestingly, the turbidity values were increasing while going away from the sea. Turbidity, which measures the cloudiness or haziness of water, is an important parameter in assessing water quality. According to the World Health Organization (WHO), turbidity should ideally not exceed 5 NTU. The observed values were varying from 21 to 57 NTU. It is noteworthy that lower turbidity levels were observed near the sea, suggesting relatively clearer water in those areas. However, as the distance from the sea increased, the turbidity levels exhibited an upward trend, indicating increased cloudiness or haziness in the surface water. High turbidity levels can indicate the presence of suspended particles, sediments, or other impurities that may affect the clarity and quality of the water, which may settle down with the flow of river water and might be the reason for these results. Figure 5 provides a visual representation of changes in turbidity levels as we move away from the seashore, providing valuable insights into the turbidity values in the studied region.

Fig. 5
figure 5

Variation in turbidity values with respect to distance from the sea

Full size image

The presence of colloids and suspended matter in creeks, distracting light penetration and causing turbidity, has also been highlighted by Inam et al. [15]. The reduced turbidity near the tail of the creek is associated with abridged water flows because of the infrastructure development upstream of the river [25]. Deprived light penetration in Khobar Creek is also reported by Inam et al. [15], which is related to the strong tidal influence during ebb tides.

The results of this study are closely aligned with the studies conducted by [5, 10, 20], which have established the maximum length of salinity. The distance of salinity intrusion in the estuaries of river Indus has been reported to be around 30 km [10, 20] in the dry season, while the same has been reported to be 58 km [10] and 84 km [5]in wet seasons respectively.

The consequences of this menace are far-reaching, with the loss of fertile land, environmental degradation, salinity, waterlogging, and a significant decline in freshwater flows characterizing the Indus River delta [13]. Furthermore, the expanded intrusion of saline seawater in the Indus Delta profoundly impacts coastal agriculture, mangroves, and fisheries, as highlighted in the comprehensive study by Jamali et al. [13]. This intricate scenario necessitates urgent attention and strategic interventions to mitigate the adverse ecological and socio-economic effects on the Indus Delta region.

4 Conclusion and recommendations

The study focused on assessing the water quality parameters in the river Indus ending at the Arabian Sea in the district Sujawal. This area is among one of the most unprivileged underdeveloped areas of the Indus Delta region of Pakistan. Various physiochemical parameters, including total dissolved solids (TDS), electrical conductivity (EC), hardness, acidity, and turbidity, were analyzed to evaluate the suitability of the surface water for different purposes, particularly drinking water.

The study primarily focused on water quality assessment for drinking purposes which was evaluated with respect to varying longitudinal distances from the sea. It is concluded that chemical and physical parameters tend to change with respect to the distance from the sea. Physicochemical analysis revealed that most of the samples from the study area contained water that is unsafe for drinking as well as for irrigation purposes. From the analysis, it has been pointed out that till 14.7 km from the ocean, not a single parameter was complying with WHO limits for drinking water completely, except pH. In between 15 and 32 km from the mouth, some parameters like, Hardness and chloride concentrations were satisfying WHO standards, while others were still beyond the acceptable limits. TDS and EC values were quite high and were not in the range of standard values until 57 km from the mouth to the ocean. The turbidity of the surface water also displayed a spatial variation, with higher values observed at greater distances from the seashore. These findings underscore the importance of considering turbidity as a critical parameter in assessing water quality, particularly for drinking purposes.

Out of ten collected samples, not a single sample was found to completely satisfy the WHO standards for drinking water. Higher TDS and EC values in closer proximity to the sea belt indicate the influence of seawater intrusion. It has been noticed that a huge population is reliant on this water for domestic and agricultural purposes. However, the presence of minerals upto various levels in the water samples underscores the importance of considering multiple factors when assessing water quality. It emphasizes the need for comprehensive monitoring and evaluation to ensure the maintenance of appropriate TDS and EC levels that are conducive to the well-being of aquatic ecosystems and the safety of human consumption.

Overall, the study highlights the need for careful monitoring and management of water quality parameters in the study. The observed variations in TDS, EC, hardness, acidity, and turbidity emphasize the influence of seawater intrusion, freshwater scarcity, and other factors on the deteriorating water quality in certain areas. It is crucial to develop effective strategies for the conservation and protection of water resources, including the prevention of pollution and the sustainable management of freshwater inputs.

It is recommended to use water from the river adhering to the WHO recommendations and implementing appropriate water treatment processes in case of non-compliance with WHO standards. Authorities can ensure the provision of safe and potable water to the local communities. Furthermore, ongoing research and monitoring efforts are necessary to continually assess and address the evolving water quality challenges in the Indus Delta region, ultimately supporting the well-being and sustainable development of the affected communities and the ecosystem. Furthermore, it is recommended that coastal development authorities should take energetic measures regarding structural development which can mitigate this effect and environmental deterioration can be safeguarded.