Effects of Water Use on Biodiversity in the Study Area
The Yarkon And Other Coastal Rivers
The Yarkon River once was the largest perennial river flowing to the Mediterranean in the study area. Its biodiversity has been rich, including fish of recreational and commercial value. Though the river has been infected with schistosomiasis, it has been used for recreation (hiking, boating, and angling) by the inhabitants of the highest density urban center of the study area—Tel Aviv. Increasing discharges of urban and industrial pollution into the river at first encouraged an invasion of hyacinth floating plant cover, but eventually eradicated most of the biota (including the schistosomiasis vectors). Finally, the impoundment of Ein Afek Spring reduced the river to a sewage stream at its upper reaches, and to a marine tidal stream at its lower reaches. Rather than providing aesthetic and recreational opportunities, the river ecosystem generated unpleasant smells and mosquito outbreaks.
The Taninim River has an annual flow of 50 million m3/yr. Half of this flow is provided by a large mountain watershed to the east of the river, and the other half by Timsah springs in the foothills of the watershed. Nature reserves along the course of the coastal section conserve the river's biodiversity, and they attract some quarter of a million visitors each year. However, water quantity and quality still steadily decline. Pumping from the aquifer feeding Timsah springs reduces its discharge. In flows into the river include untreated sewage of local townships, irrigation drainage water enriched with fertilizers and pesticides from agricultural
fields and drainage aquaculture ponds. In addition, prior to reaching the nature reserve, half of the flow is diverted to feed fish ponds. As a result, the river is stressed by pollutants and increasing salinity, especially toward the end of summer.
The high concentration of pollutants and the low and slow flow promotes the spread of duckweed—a distinct signal of severe ecosystem change, and many aquatic species typical to this river have already disappeared. Yet, the Taninim River, with protected areas along its course, is the only perennially flowing coastal river in Israel because the natural low salinity of the Timsah springs, 1,200 mg Cl/l, is suitable for aquaculture but not for agriculture. However, the economic feasibility of desalinating this relatively low salinity water makes the 25 million m3/y discharge of Timsah springs attractive for closing the water supply "gap" of exactly the same amount, forecasted for the city of Haifa by year 2000. If this project of impounding, desalinating, and transporting all the Timsah discharge is to be implemented, it is estimated that the Taninim River's current flow of 50 million m3/yr will be reduced to 18 million m3/yr of highly polluted water. This project will obstruct the outlet of the river to the sea, such that estuarine biodiversity will disappear (Ben-David, 1987). Thus, the Taninim River may become a case in which implementing desalination technology for domestic water supplies will kill the only functioning coastal river ecosystem west of the Jordan River.
The Jordan River Basin
The basin elevation ranges from 90 m above sea level to 400 m below sea level and includes three source streams, which create the northern section of the Jordan River. Most important of these three headwaters is River Dan, the only Israeli river that has a seasonally stable output. It has also a stable temperature, a year-round high oxygen saturation and a high number of species (156 aquatic animal species). The three streams cross the Hula Project region as a canal, then descend in the Jordan River's natural course to Lake Kinneret.1 The Kinneret drains to the lower Jordan River, which discharges to the Dead Sea, which is a dead-end lake.
The major water management activities in the basin are the drainage of the Hula wetland and its subsequent management (See Box 4.2), and the management of Lake Kinneret, which is the major surface water storage of the State of Israel. The Hula project affected and is still affecting Lake Kinneret's water quality, the management of Lake Kinneret affects
the Lower Jordan River ecosystem, and both affect the economy, environment and biodiversity of the Dead Sea region. Each section of the Jordan River basin is described below, from north to south.
The Hula Wetland
The Hula was a large wetland at the north end of Lake Kinneret. It is now reduced in size by drainage and most of the wetland has been replaced by cropland. A nature reserve was reconstructed on a part of the drained wetland and a section of the newly created cropland area is flooded seasonally, until recently part of that section was intentionally flooded. These vicissitudes had dramatic effects on the species richness and composition of the Hula region. Dimentmann et al. (1992) showed that 585 (612, if doubted or insufficiently described records are included) aquatic animal species, excluding unicellular and parasitic species, were recorded in the wetland prior to drainage. Of these, 19 were represented by peripheral populations (for 14 and 5 species the Hula constituted the southern and northern limit of the species' global distributions, respectively), and 12 were endemic to the Hula wetland (6 beetles, 2 dragonflies, a flatworm, a fly, a frog, and a fish). The reconstructed nature reserve lacks, 119 (20 percent) of the native species, including 11 of the 19 species represented in the Hula by peripheral populations, and 7 of the 12 Hula endemic ones. Seven species, among them a frog and a fish, have become globally extinct. Furthermore, since the drainage of the Hula, 36 of the species lost to the Hula have not been recorded anywhere else in Israel. The birds are the best known group of the Hula, and the information about this group is highly reliable. Of the 36 species breeding prior to drainage, 10 ceased to breed after the drainage, but 5 were replaced by species that had not bred there prior to drainage.
To summarize, the drainage of the Hula, a wetland that is relatively small in global terms, resulted in a local loss of 119 species (plus 10 birds species that ceased to breed there), the national loss of 36 species, and the global loss of 7 animal species. On the other hand, 212 aquatic animal species new to the Hula have been recorded after the drainage. Some of these might have existed in the Hula prior to the drainage but escaped attention. However, most of them are probably new colonizers, indicative of the changes in habitat extent and diversity, and in the quality of the water, following the drainage and subsequent reconstruction efforts.
The Hula formerly supported a unique community of species. From the north (Europe), west (Mediterranean basin), east (Iraq, Iran), and south (Egypt, tropical Africa) of the Hula many species assembled into a unique community in the Hula. Thus, although most of the species also exist elsewhere, their combination, and hence their interactions, existed nowhere
else. The ability of northern and tropical species to live together in the Hula developed from the high diversity of aquatic habitats in the Hula and the year-round discharge of springs with year-round stable moderate temperatures, thus providing the Hula with a refuge from extreme high summer and low winter water temperatures. Species belonging to each of these biogeographic categories were lost by the drainage, and hence, unique species interactions, probably related to unique ecosystem functions, were lost. Also, some dramatic natural phenomena, such as the upstream spawning migration into the Dishon stream of Lake Hula's three cyprinid species, are forever lost, though the species themselves have not become extinct.
The management of the Hula wetland is a clear case of water resource development raising conflicts between agriculture and the ecosystem services provided to society by biodiversity. Agricultural development in the reclaimed Hula lands potentially conflicts with water quality downstream in Lake Kinneret.
There is also local conflict between the economic benefit to the farmers now cropping the Hula land, and the economic benefit of the "aesthetic services" provided by a recreation in the Hula wetland. A similar though not identical conflict has developed in the other large wetland of the region. The Azraq oasis in Jordan drew international attention in the 1960s (Mountford, 1965; Nelson, 1973) as a hotspot of desert biodiversity, with cultural and aesthetic values. Recently, however, the functioning of this oasis as a wetland declined, due to exploitation of its water source to supply the increasing demands of the urban population of Jordan, notably that of Amman. The oasis of Azraq now has lost most of its aesthetic value.
Lake Kinneret/Lake Tiberias/Sea of Galilee
The structure and function of the Lake Kinneret ecosystem, described by Gophen (1995), are relevant to the ways in which the lake's biodiversity and water quality are affected by the management of the watershed and the water level of the lake itself.
The Effect of the Watershed
Lake Kinneret stores between 3,903 and 4,301 million m3 of water, depending on the water level, and the mean annual natural in flow is 940 million m3. The lake's water turn over on average once in every 4.4 years, a relatively short residence time for lakes. The area of Kinneret's watershed is 2,730 km2, and the ratio of this area to the lake's volume is 0.68, a relatively high value for lakes. The two indices mean that, first, the watershed,
mostly agricultural land, introduces high quantities of fertilizers and other pollutants relative to the lake's volume; and second, that water use prior to discharge to the lake and the use of the lake's water jointly reduce the lake's volume and shorten the turnover time of the lake's water, thus increasing the salinity and the nutrient contents of the lake. The Jordan River, which drains large parts of the watershed, annually discharges to the lake 1,610 tons of nitrogenous compounds and 130 tons of phosphorous compounds annually. Much of the nitrogen is denitrified in the Kinneret and released to the atmosphere. Much of the phosphorus discharge is deposited at the lake bottom in an inert form, not available to algae.
Effects of Managing the Lake Water Levels
The lake is the major operational reservoir for water supply to Israel. Ecosystem functions of the lake are involved in determining the quality of its water for domestic and agricultural use. A high density of microalgae and high salinity reduce the quality of the lake as a provider of potable water and irrigation water, respectively. Microalgae cause undesirable odor and taste and secrete toxic compounds and materials that interfere with the disinfecting process of potable water. The density of microalgae is regulated by various factors, among them grazing microcrustaceans, which in turn are controlled by predatory fish. Salinity derives from discharge of saline springs at the bottom and the edges of the lake and from the discharge of the Jordan River. The volume of the lake, expressed by its water level, affects the two water quality attributes, microalgae and salinity. With respect to salinity, hydrostatic pressure may control the saline discharge from the springs at the bottom of the lake. The microalgae are limited at times by mineral resources, mainly dissolved phosphates. The lake's bottom is rich in particulate phosphorous compounds, and their dissolution, hence their availability as a resource for microalgal growth, is controlled by the concentration of CO2 in the lower water strata (the hypolimnion). Prior to human intervention, the water level was determined by variations in inflows (rainfall, storm runoff, river discharge) and outflows (evaporation and the outlet discharge to the lower Jordan River). The level fluctuated within a range of 1.3 m with the high bound determined by winter floods and the low bound by the depth of the bottom of the outlet to the Jordan River.
The management of the lake involves manipulations of both inflow and outflow. Extraction from sources (impoundments of springs discharging to the Jordan River, damming of stormwater in the watershed) affect the inflow. Pumping into the National Carrier, damming the outlet to the lower Jordan River and manipulating the dam all affect the out-flow.
Legislation currently determines the upper and lower bounds of the water level and prevents damage to shore installations (pumps, piers, recreation facilities) and their operation. The motivation for lowering the level as much as possible is the need to free space for storage of the winter inflow, even if this is at the expense of "losing" water to the Dead Sea. Currently the fluctuation range of the managed lake is 4.1 m and the mean water level is 0.5-1 m lower than the natural mean level of the lake.
These managed low levels may lower water quality. With respect to salinity, there is a risk of increased discharge of the saline springs at the bottom of the lake. Countering this risk is the "salty carrier." This is a diversion which captures saline spring water flowing in the Kinneret and transports it directly to the lower Jordan River, thus bypassing the lake and freeing it from a third of its annual salt input.
Low water levels, which reduce the volume of water in the lake, affect the biota of the lake by changing the concentrations of dissolved chemicals. Microalgae increase in response, and at first are controlled by plank-tonic small crustaceans. But soon the numbers of crustaceans and reduced fish increase their predation on the crustaceans, thus releasing the microalgae from their control. Fertilizers transported from the watershed also enrich the lake with nutrients, contributing to the increase of microalgae. Low water levels also affect the littoral and shallow estuaries (Gasith and Gafny, 1990). The turbidity associated with low water levels deposits muddy sediments on pebbles and other hard substrates, thus reducing their quality for fish reproduction. Abrupt fluctuations of the water level also reduce the quality of stones for egg attachment (due to development of microalgal mat). Altogether, the lowering of the lake level increased the proportion of sandy bottom of the littoral from 10 percent to 60 percent, thus reducing the extent of pebbles required for fish reproduction. Lengthy exposures encourages colonization of riparian and terrestrial vegetation, and reflooding of these areas in years of high runoff increases the organic load of the lake, through the death and decomposition of this vegetation. Low levels add to the management problems for wetland nature reserves along the northern and eastern coasts.
Effects of Further Lowering the Lake's Water Level
Increasing water level fluctuations from the natural 1-2 m to 4 m during 1969 to 1993 did not cause apparent deterioration in the functioning of the lake's ecosystem. This observation has been interpreted as indicating the high resilience of this ecosystem and has encouraged considering further lowering of the Lake Kinneret level. However, as of 1994, hitherto unknown blooms of nitrogen-fixing cyanobacteria (blue-green algae) have occurred. Besides indicating a reduction in the quality of the
water, and the fact that these blooming algae are known to produce chemicals toxic to aquatic animals and humans, this change indicates that the Kinneret ecosystem has an unpredictable potential for change. Further lowering of the level may generate further instability in the structure and function of the Kinneret ecosystem.
Besides increasing the risk of urban wastewater pollution of pumped water (since by lowering the level, pumping points will become closer to coastal pollution sources), further lowering of the water by one meter may result in the following ecosystem effects (Zohary and Hambright, 1995): (1) reduced water quality due to increased suspended materials and algal productivity brought about by further decrease in the summer volume of the lake's lower strata, hence faster rate of prevalence of anaerobic conditions, earlier accumulation of sulfides, earlier release of phosphate from the lake's bottom, and additional 33 percent increase in dissolved phosphate; and (2) reduced ecosystem stability, via food chain fluctuations brought about by changes in the food chain of littoral dependent fish-zooplankton-phytoplankton.
The Lower Jordan River and the Dead Sea
The "Salty Carrier," which discharges the coastal saline springs' water to the lower Jordan River, significantly reduces the salinity of the lake's water, thus counteracting the salinization trend associated with lowering the level of the lake. But this arrangement, as well as the overall reduction of the inflow from the Kinneret to the lower Jordan River, increases the salinity of the river to the point of losing significant components of its aquatic and riparian biodiversity and changing the structure of its biotic community and ecosystem functions. The discharge of Lake Kinneret water through the lower Jordan River to the Dead Sea is a "loss" to the water budget of the region, minimized by the prescribed low levels of Lake Kinneret. But this is not necessarily the only loss.
The reduced discharge lowers the level of the Dead Sea, and this low level and the resulting receding coastline negatively affect Dead Sea coastal installations—industrial, mining, health (spas), and recreational. Also, the low level and receding coastline of the Dead Sea affect the freshwater oases along the coast: Ein Fashkha and Ein Tureiba on the western coast are wetland nature reserves used both for recreation and for conservation of a unique biodiversity. They suffer from management problems due to constant changes in their water budget. Furthermore, not many plants are able to colonize the large expanses of the exposed, highly saline former littoral now surrounding the Dead Sea. There is a potential risk of an "Aral Sea effect" developing there, in which wind-blown minerals of the exposed lake surface affect biodiversity at a distance from the coast.
Ben-David, Z. 1987. Taninim River—nearly the end of the road. Society for the Protection of Nature in Israel, report (in Hebrew).
Dimentman, Ch, H. J. Bromley, and F. D. Por. 1992. Lake Hula. Reconstruction the fauna and hydrobiology of a lost lake. Jerusalem: Israel Academy of Sciences and Humanities.
Gasith, A., and S. Gafny. 1990. Effect of water level fluctuation on the structure and function of the littoral zone. In Large Lakes, Ecological Structure and Function, M. M. Tilzer and C. Serruya, eds. New York, N.Y.: Springer-Verlag.
Gophen, M. 1995. Whole lake biomanipulation experience: Case study of Lake Kinneret (Israel). In Lake/Reservoir Management by Food Chain Manipulation, R. De Bernardi and G. Giussani, eds. ILEC-UNEP 7,171-184.
Mountford, G. 1965. Portrait of a Desert. London, U.K.: Collins.
Nelson, J. B. 1973. Azraq: Desert Oasis. London, U.K.: Allen Lane.
Zohary, T., and K. D. Hambright. 1995. State of knowledge relevant to effects of further lowering of the Kinneret's minimal level. Kinneret News 18,2-6 (in Hebrew).