Keywords

1 Rivers as Hydrological Objects

“It’s not the river that flows – it’s the water.

It’s not the time that passes – it’s us!”

Ivo Andrić, Yugoslav novelist, the Nobel Prize winner in literature (1961)

The network of rivers in Montenegro (Fig. 1) is strongly affected by the latitudinal arrangements of the landforms. The mountain chain of the Dinarides (the Dinaric Alps) that extends in a southeast-northwest direction, parallel to the current shore of the Adriatic Sea coast, dominates in the relief of Montenegro [2, 3]. The direction of the mountain chains in Montenegro and a strong altitudinal gradient in a southwest to northeast direction are the major barriers to surface runoff that modify the direction of the flows. In the Adriatic basin, groundwater flow, which generally mirrors the surface water flow, flows to the south and southwest, while the groundwater regime in the Danube basin flows to the north and northwest [4].

Fig. 1
figure 1

Map of Montenegro with its main river basins. Modified from [1]

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In the landscape of Montenegro, three main geomorphological units can be distinguished, (1) the Mediterranean coastal area (Coastal Montenegro), (2) the sub-Mediterranean central area (Central Montenegro), and (3) the mountainous northern – northeastern area (Northern Montenegro) [5]. The main rock type in the Dinarides is karst, which dominates the majority of the Montenegrin landscape. Dinaric karst is distinguished by a complex tectonic set of diverse formations from the Paleozoic, Mesozoic, and Cenozoic ages, dominated by limestones and dolomite sedimentary rocks in which, due to tectonic activity, folding, faulting, and overthrusting, the process of karstification has come to full expression [2]. Typical Dinaric karst forms a diverse array of landforms of which karren fields, sinkholes (dolines), uvalas, fields, and caves are particularly well developed in Montenegro [3].

According to the geological map of Montenegro [6], four geotectonic units exist in Montenegro: (1) the Durmitor tectonic unit, which is in the northeast, (2) the Visoki Krš tectonic zone that includes two tectonic units: Starocrnogorska Kraljušt and Kučka Kraljušt, (3) toward the southwest we find the Budva-Cukali zone, and (4) the Paraautohton (Adriatic-Ionian) zone extends along the Adriatic coast. The chain of high coastal mountains (NW–SE oriented) composed of Mts. Orjen, Lovćen, Sutorman, and Rumija run toward the northeast and encounters the High Karst zone. This zone, characterized by diverse underground karst forms, at its southeastern limit runs into the Zeta-Skadar depression, while toward the northeast, it descends into Nikšić polje (field) and the valley of the River Zeta (the Bjelopavlići Valley) [7]. From this area, karst terrains rapidly expand to the central part of Montenegro forming a large number of high mountains (e.g., Njegoš, Žijevo, Prokletije, Komovi, Visitor, Pivske Planine, Sinjajevina, Durmitor, and others), which are bisected by river valleys and impressive canyons such as those of the rivers Morača, Piva (Fig. 2), Tara (Fig. 3), Čehotina, Lim, and Ibar [7].

Fig. 2
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The confluence of the river Tara and the river Piva at Šćepan Polje at the border between Montenegro and Bosnia and Herzegovina. The Montenegrin rivers (the Piva, the Tara, the Lim, and the Ćehotina) represent about one third of the entire basin of the River Drina, but they provide more than 52.9% of the mean annual river flow [4]. Photo by D. Marić

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Fig. 3
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The canyon of the River Tara, 78 km long and 1,350 m deep, is the deepest canyon in Europe and the second deepest in the world after the Colorado River Canyon [7]. In Montenegro the canyon is protected as a part of the Durmitor National Park, and since 1977 it has been a UNESCO World Heritage Site. Photo by S. Popović

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Geological processes in the karst have had a decisive influence on hydrology and the formation of the hydrographic network [8]. From the territory of Montenegro, surface and groundwater flow into both the Black and Adriatic Seas, with approximately 45.4% (about 6,268 km2) of its surface belong the Adriatic basin and around 54.6% (about 7,545 km2) to the Black Sea (Danube) basin (Fig. 1) [9].

The terrain along the drainage boundaries is mainly formed by the Mesozoic carbonate sediment that builds the famous karst terrains of the Dinarides, which leads that the hydrological drainage boundaries between the Adriatic and Black Sea’s basins are mostly underground [7]. This makes it difficult to define the drainage boundaries between individual catchments, especially between smaller basins in the holokarstic terrain (e.g., between Trebišnjica and Boka Kotorska Bay on the one hand and the basin of the Nikšić polje on the other) [7].

The Adriatic basin generally experiences a “Mediterranean” type climate, with a predominantly hot and dry summer with average temperature of >22°C in the warmest month, and much lower temperatures in the winter, although they still remain above freezing point [10]. A moderately warm climate with a dry summer but without a pronounced dry period over the year is present in the northwestern, western, and southwestern part of the Adriatic basin at altitudes ≥650 m [7]. On the other hand, the Black Sea basin experiences a “continental” type climate without a dry period over the year, with relatively cool and humid summers and long and harsh winters.

The amount of precipitation rapidly increases from the southwest toward the northeast [7]. The greatest annual amount of precipitation of 8,063 mm was registered at Crkvine on Mt. Orjen in 1938, which is still the European record [7]. The average annual amount of precipitation as well as the mean annual number of days with precipitation strongly varies both between the river basins and across the year. November and December are the rainiest months, while July and August are the driest months [7].

Montenegrin rivers are characterized by a complex flow regime that depends on the climatic conditions and morphogenetic zones from where these rivers flow. Most of the rivers of the Black Sea basin are characterized by large flows in the spring (April and May) and late autumn (November and December) with their minimum flows coming between August and September [7]. The rivers in the Adriatic basin, which are closer to the sea, exhibit their highest flows in November and December. On the upper part of the Morača and the Zeta, the greatest water flow was recorded in the spring [7].

There is considerable variability in the flow between different basins. The River Ćehotina has the most stable average annual flow, while the Ibar exhibits the greatest variability [7]. On the temporal scale, the variability of monthly flows is greatest in the autumn [7]. Moreover, a considerable difference in the river density between the basins was found, in that the river network is denser in the Black Sea basin and less dense in the Adriatic one (Fig. 4).

Fig. 4
figure 4

Most rivers found in coastal Montenegro such as the river Ljuta (between the towns of Kotor and Perast) are short and do not have floodplain habitats; usually they rise from strong karstic springs and descend abruptly into the sea after short stretches. Photo by V. Pešić

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The contribution of surface runoff to the river basin discharge varies both spatially and temporally. Underground water drainage is the main factor that affects the stability of the water in the karstic terrain. Most rivers and streams in the Adriatic basin dry up in the summer months as a result of the fact that field evaporation exceeds precipitation in this period of the year. In general, it can be noticed that there is a tendency toward decreasing precipitation moving from the northwest toward the southeast, in the direction of Cetinje-Ostros, as well in toward Nikšić-Podgorica [7], consequently leading to a denser network of intermittent rivers and ephemeral streams (IRES) along those gradients. Intermittent rivers that have been often neglected in limnological studies dominate in the river network of South Montenegro, and they are analyzed here in a special chapter in this book.

2 The Rivers of Montenegro as Scientific Objects: Challenges and Perspectives

The first systematic limnological and hydrobiological research of Montenegro began in the second half of the nineteenth century and was mostly performed by foreign researchers (e.g., for hydrogeology, see [3]; for ichthyology and fisheries, see [11]; for limnological research in the Lake Skadar basin, see [12]).

The period after World War II was characterized by the formation of institutions involved in the fundamental and applied research of the aquatic resources of Montenegro. The Geological Survey of Montenegro, the main public institution responsible for regional hydrogeological investigations, was founded in 1945. The Hydrometeorological Institute (Montenegrin: Hidrometeorološki zavod Crne Gore or RHMZ), the main national hydrological and the meteorological service in the country involved in the monitoring of meteorological, hydrological, and ecological parameters, began working in 1947. The first hydrobiological institution, the Fishing Station of the People’s Republic of Montenegro, was founded in 1952 and worked until 1965 when it was transformed into the biological station, which worked within the Institute for Biological and Medical Research (from 1973) as part of the state University in Titograd (the modern Podgorica) [13].

Regardless of the large amount of disciplinary-specific knowledge acquired, most of the data that are crucial for understanding the history of the Montenegrin river basins and their living world [14] remain highly fragmented, and a comprehensive meta-analysis is long overdue. An analysis of the comprehensive bibliography on the Lake Shkodra/Skadar basin [12] revealed the difference in the amount of data of discipline-specific knowledge and variation of the number of publications over the time [15]. For example, in most disciplines, relatively few studies were reported prior to the 1940s, with most publications occurring from 2000 up to the present (e.g., see [15] and references cited therein).

The largest number of limnological and hydrobiological studies done so far are related to the Lake Skadar basin which is paleo- and phylogeographically the best and most widely studied hydrological area of Montenegro (see [14] for an overview). Phylogeographic studies have confirmed that the lake itself cannot be referred to as an ancient lake but is rather a very recent water body that some 1,200 years ago took over a former freshwater marshlands [16]. However, regardless of the recent formation of this lacustrine system, the Lake Skadar basin with its large system of karst springs is definitely ancient, having originated more than 2.5 million years ago and being isolated for most of its history, with a high number of crenal and fluvial endemics, at both the morphospecies level and potentially also at the level of lineage (cryptic or pseudocryptic species) [14].

While employing an integrative methodology based on comparative phylogeographic studies on the biota of Montenegrin rivers, this also needs to be complemented by geological evidence with the aim of building up reliable knowledge on the changes throughout which the river basins (Fig. 5) of Montenegro and their living world pass [14]. This would help to more accurately forecast even those changes that are likely to occur, which is particularly important because, for many rhitrobiontic species, there is enough evidence that they are being altered by ongoing climate change.

Fig. 5
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The canyon of the river Cemi/Cijevna that flows through Albania and Montenegro, situated at the fifth kilometer from Podgorica; in places, it is less than 1 m wide. Photo by S. Popović

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Climate change, which has markedly increased since the early 1990s, has had a particularly significant impact on the frequency, duration, and intensity of extreme hydrologic events in Montenegro [10]. For example, in the last decade, Montenegro has experienced severe droughts (in 2000, 2003, 2007, and 2012) and has suffered losses from damaging floods, most notably in 2010. The increased frequency and duration of drought period affects the river ecosystems by increasing the share of IRES in the regional hydrological network, by reducing the flow in the lotic and increasing the water temperature in the lentic parts of the perennial rivers. On the other hand, the higher frequency and abundance of floods accelerate bank erosion, increasing suspended sediment load into the rivers, which leads to reduced diversity among aquatic biota and their communities. In addition, the changes in local hydrology as the result of regional warming may also reduce the hydropower capacity of exposed rivers.

The rivers in Montenegro are not only exposed to climate change but also to various types of anthropogenic activities. The impacts of land-use changes, urbanization, deforestation, agriculture, industry, sand and gravel extraction, fisheries, mining, hydropower development, and hazardous weather events are recognized as the main pressures threatening the integrity of the rivers and their basins in Montenegro. Some of the above-mentioned factors have had a serious impact on the economy, especially in the agricultural and livestock production sectors, due to their dependence on the water conditions.

In the more rural parts of Montenegro, especially in its northern regions, more and more pristine rivers have become dammed, which significantly affects their functionality and biodiversity. The construction of dams and reservoirs for hydroelectricity has transformed some rivers into standing waters (e.g., the accumulation on the river Piva), changing the pattern of the water flows, with a direct influence on the depth and the substrate contents consequently leading to changes in fish and macrozoobenthic communities and their interaction with environmental parameters [17]. In the last decade, the building of small hydropower plants (<1 MW) (Fig. 6) has significantly increased, causing a number of conflicts with local community and their interests.

Fig. 6
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The small hydropower plant at Bistrica river in Bijelo Polje Municipality The loss of the small streams in a rural regions, the loss of a fish and biodiversity, as well as the degradation of other environmental services such as using the water for irrigation but also for recreation have been recognized by the local community as the main threats caused by building small hydro power plants in the rural regions of Montenegro. Photos by S.Višnjić

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The main problem that appears here is that on the largest number of small rivers and streams in Montenegro where small hydro power plants were built, the watercourses do not have enough water in the summer months to meet the prescribed minimum for them to function (and each power plant without its own accumulations cannot provide such a flow). The result is that the streams which have installed small hydropower plants completely or partially dry up in the summer months, destroying the habitats for aquatic biota and preventing the local community from exploiting the water. Poor management of aquatic resources and the absence of an established set of equitable sharing principles among the contending parties have led to an increase in the number of conflicts over these facilities.

In urban areas, rivers are often used as a sewage recipient, degrading water quality and its capacity for self-purification. The increase in industrial and transportation activities in the major urban centers, such as Podgorica and Nikšić, has caused increasingly degraded water quality in the lower part of the rivers Morača and Zeta, where the impact of sewage effluents is often accompanied by reduced biotic diversity, changes in the trophic status, and the greater toxicity of the sediment (see [15] and references therein). In the agricultural landscapes of the Zeta-Skadar valley, the watercourses have become threatened by the accelerated process of eutrophication as a result of human activities, most especially through fertilizers that are washed out from the soil.

Montenegro is rich in water resources, but as with many other countries, it needs to comply with national and international targets for the protection and sustainable management of those water resources. Due to increased demand for water resources and in the face of ongoing climate change (for example, variation in rainfall), it can be expected that tensions will become more frequent and intensive in the future. The conflicts that mostly occur between biodiversity conservation on the one hand and general human activity on the other are in most cases complex and can severely affect both socioeconomic and biological parameters [18].

As one of the last remaining strongholds of largely unvalorized resources, the rivers have become a point of possible conflict as they become the focus of social, ecological, political, and economic changes. Recent practices in protecting water resources in Montenegro (e.g., the hydroelectric dam controversy on the River Tara), as well as in other countries in the Balkans, reveal that only ensuring political commitment can provide the institutional and legal basis for the sustainable development of water resources in this region.

The central role of researchers and scientific institutions in the conservation of water resources has often been emphasized by governmental and nongovernmental institutions in Montenegro, but, in reality, they have been rarely involved in the management of those resources. The absence of comprehensive in-depth meta-analysis between and/or within river basins impedes the estimation of conservation needs and the planning of the proper conservation strategy for the area. A scientifically based approach should ensure the development of methods that need to provide mechanisms to identify the threats to the river ecosystem and propose measures to ensure the protection of these valuable ecosystems. Collaboration between all the contending parties, from scientists to decision-makers and resource managers, and defining the obligations and responsibilities of the key stakeholders involved in the implementation of the measures planned for the protection of the riverine environment, is seen as the main factor that will prevent potential conflict and guarantee the sustainable use of water resources. The usefulness of such a comprehensive approach has recently been demonstrated by the publishing of a holistic study, “The Skadar/Shkodra Lake Environment,” [19] devoted to the environment of the unique but threatened Lake Skadar which is the largest freshwater hydrological object in both Montenegro and the Balkans. The purpose of the current book is to provide an extensive overview of the various aspects of the riverine environment that should stimulate a science-based management approach in the use of water resources in Montenegro.