Lakes Hula and Agmon: destruction and creation of wetland ecosystems in northern Israel

A portion of the former Lake Hula wetland (northern Israel) was re-flooded in spring 1994 and the physical, chemical and biological developments within the resulting new lake and wetland complex (Agmon) was followed closely by a multi-disciplinary scientific team. The first three years of study relating to Lake Agmon are reported in this issue of Wetlands Ecology & Management. We provide in this paper a general background on the Lake Hula Draining Project in the 1950s and the recent re-flooding and creation of the Agmon wetland.     

Strontium isotopes in Melanopsis sp. as indicators of variation in hydrology and climate in the Upper Jordan Valley during the Early-Middle Pleistocene, and wider implications

Aquifers dominated by Pleistocene basalts and Jurassic to Cretaceous calcareous rocks feed the Hula basin which is drained by the Jordan River into Lake Kinneret. The sedimentary sequence of Lower-Middle Pleistocene Benot Ya‘akov Formation (BYF) exposed by excavations of the 0.78 Ma lake-side site of Gesher Benot Ya‘aqov (GBY) consists of six cycles representing ca. 100 ka history of the Hula basin. This study characterizes the types of water sources in the catchment, tests the use of the Strontium (Sr) isotopes in the common extant snail Melanopsis sp. as a tracer for water in its habitat, and uses this tracer in the fossil specimens from GBY to investigate the palaeohydrology of the Hula paleolake during the corresponding period.The Sr isotope composition (⁸⁷Sr/⁸⁶Sr) of extant Melanopsis shells in the Hula catchment range widely (0.7046-0.7079). These analyses define distinct groups of water sources and aquifers, while the Jordan River at the GBY site has values around 0.70685. The values for fossil Melanopsis from GBY vary along stratigraphy; they are highest around 0.70710 in Cycles 1 and 2, decrease to around 0.70685 in Cycle 3, and exhibit upward trending fluctuations in the subsequent cycles to 0.70703 in Cycle 6. This trend reveals the dominance of the Hermon Jurassic aquifer during the earlier, colder periods before the Matuyama-Brunhes Boundary (MBB) and enhanced influence of the Golan basaltic aquifers, in subsequent warmer periods, indicating that the MBB coincides with climate warming as supported by other indicators. Hence, this global geochronological indicator of 0.78 Ma is also potentially a global palaeoclimatic marker. The similarity between the Sr isotope composition of the Jordan River waters and Melanopsis and those from Cycle 3 suggests that the current climate corresponds to that of the warmest period within the record of GBY, clarifying the comparative interpretation of this 100 k.yr. climate record.     

A palynological study of the Acheulian site of Gesher Benot Ya’aqov, Israel

The results are discussed of the palynological (pollen-analytical) examination of a sediment section in the Hula Valley of northern Israel, with evidence of Acheulian occupation dated to 700,000–800,000 b.p. In general there is a fair agreement between the palynological data and the wood remains identified from the site, but there are also discrepancies, some of which can be explained and others not. Although relatively well represented in the pollen record, Pinus (pine) most probably did not occur in the Hula area. Some pollen types are thought to have been carried in from hundreds of kilometres away (long-distance transport). Together the pollen and wood evidence suggests that Quercus ithaburensis–Pistacia atlantica (Tabor oak–Atlantic terebinth) woodland (open forest) was found in the Hula Valley (other than the lake and marshes) and on the lower reaches of the mountains flanking the valley on both sides. In addition to deciduous Tabor oak, evergreen Kermes oak (Quercus calliprinos) must have been an important component of this woodland. Wild olive (Olea europaea var. oleaster) may also have been quite common here. The suggestion of open forest, with fairly widely spaced trees, is based upon the high non-arboreal pollen frequencies and indicates fairly dry climatic conditions. Various stream-bank trees and shrubs are represented in the pollen and/or wood records, such as Fraxinus (ash), Ulmus (elm), Salix (willow) and Platanus (plane tree). During the period represented by the upper section of the pollen diagram, Cedrus (cedar) must have reached the Hula area, indicating increased humidity. In the steppe-like field layer (undergrowth of the woodland) grasses (Gramineae) must have played a prominent role in addition to a great number of other species. In particular Compositae and Umbelliferae include a large variety of species (many different pollen types). Two Chenopodiaceae maxima, coinciding with Gramineae minima, are thought to be indicative of periods of increased climatic dryness. The local lake and marsh vegetation is fairly well represented in the pollen record, but interpretation in terms of vegetation succession is only possible to some degree. Mention is made here of Trapa natans (water chestnut), the nuts of which were consumed by the Acheulian inhabitants. Sytze Bottema: Deceased in 2005.     

Repopulation and colonization by birds in the Agmon Wetland,Israel

Lake Hula and its surrounding wetland in northern Israel were drained in the late 1950s and the dried wetlands were transformed into a diverse agricultural region with a 0.3 km2 nature reserve. A portion of the extinct Hula wetland was re-flooded in April 1994 by constructing a small lake, Agmon, and 90 km of canals. The purposes of this study were (a) to document the re-population and colonization of the new Agmon wetland by birds after its flooding, (b) to evaluate bird species richness in this new wetland in comparison to that in a nearby mature Hula Nature Reserve, and, (c) to investigate if the species originally present in the Hula Valley before the drainage had been re-established. The new lake has succeeded in attracting a large variety of water birds to the newly formed habitats, especially ducks, egrets and herons, plovers, waders and snipes. The distribution of bird species among the different habitats was not random. The northern section of the lake, which is shallow and has an open shore, had the largest number of species during 1995 and 1996 and was preferred by plovers, waders and snipes. A large roosting and breeding colony of thousands of egrets and herons was formed in the dense cattails ( Typha domingensis) in the southern section of the lake. Unlike the nearby Hula Nature Reserve, the new wetland lacks a large seasonally flooded area and is less attractive for feeding and breeding plovers, waders and stilts. The new wetland also has very little muddy area without vegetation and attracts few of the species that regularly feed in this habitat in the reserve. The new wetland enlarges the area of only a few of the habitats found in the nearby reserve and therefore attracts fewer species than it might otherwise. Recommendations for management of the new wetland include increased diversity of habitats, restriction of human activities and optimization of conflicts that have arisen between the needs of the wetland and those of nearby agriculture.     

Nutrient and plant dynamics in Lake Agmon Wetlands (Hula Valley,Israel): a review with emphasis on Typha domingensis (1994–1999)

Shallow lake Agmon is a newly created subtropical wetland in north-eastern Israel. The lake is part of the Hula Project aimed at slowing down deterioration processes of the peat soils, to establish infrastructure for ecotourism as an income for the land owners, and nutrient removal from Lake Kinneret inputs. An onset of benthic filamentous macro-green algae during late winter–spring season, followed by submerged macrophytes vegetation during spring–summer was documented. The phosphorus summer loads are mostly plant–mediated internal fluxes and nitrogen intensively removed from lake waters by sedimentation and denitrification. The summer phytoplankton, mostly colonial cyanobacteria, are P limited. During 1995 and early 1996, dense Typha domingensisstands were developed in the southern half of the Lake (chalk-marl bottom sediments). The P-limited Typhavegetation collapsed within less than half a year and reappeared in the south-eastern part of the lake where sediments were exposed and oxidized. It is hypothesized that phosphorus cycle is a strong dependant of macrophyte mediation, and P deficiency in the sediments predominantly affected Typhadecline and an increase of P availability later enabled the reappearance of the Typhastands.     

Foraging,roosting, and nesting habitats of the avian fauna of the Agmon wetland,northern Israel

The foraging, nesting and roosting habitats of the avian fauna of a newly created Agmon wetland and surrounding cultivated peat land (5 km2) in the Hula Valley, northern Israel, were evaluated (January 1996–February 1997) to assess the value as a habitat and for wildlife tourism. We recorded 180 bird species (herons, dabbling ducks, kingfishers, waders, wagtails and raptors) in different habitats (the lake, shores, cattail and reed-bed stands, trees, temporary inundated areas). The most heavily used habitat for foraging, breeding, and roosting was a large cattail stand in the southern third of the lake. The foraging habitat and diet data of 97 avian species were determined. The most intensively used foraging habitats were cultivated fields, lake shore reed-beds, shallow canals and the cattail stand. Forty six species nested in the wetland during March-October, with 2,040 colonial and solitary nests mostly in the cattail stand, near-shore reed-beds and young trees. Roosts, also mostly in the cattail and reed-bed stands and in trees, were used by 55 species. Based on this survey of available habitats, we identified several key habitats that are either missing or require further development (e.g., temporarily inundated mud flats, reed-beds and bare islands). We also provide suggestions for improving the delicate balance between requirements of this developing wetland ecosystem and of the adjacent agricultural areas.     

General water chemistry and quality in newly-created subtropical wetland lake

Sixty km2 of the southern Hula Valley (northern Israel) peat lands were flooded in 1994 as part of the Hula Valley Restoration Project. The small, shallow lake (110 ha, mean depth < 1 m) and network of ca. 90 km of canals created were designed to ameliorate problems (e.g., underground fires, soil subsidence, increased nutrient loading downstream to Lake Kinneret) resulting from drying the Lake Hula wetlands in the 1950s. This new wetland area now serves as the focus for developing eco-tourism in northern Israel. The initial development of this new ecosystem has been followed closely by a multi-disciplinary team of researchers, with an emphasis on water quality in the new lake and the potential impact of the project on Lake Kinneret. Here we report an overview of developments in general water chemistry of Lake Agmon during its first three years (1994–1996). Water quality in Agmon was within general expectations for a shallow lake situated on peat. The first year of Agmon was characterized by the heavy influence of stream and drainage inflows with high pH, alkalinity, turbidity and electrical conductivity and high concentrations of sulfate and total dissolved solids. By the third year, however, many in lake processes (e.g., nutrient cycling and algal and macrophytic production) were well-developed and thus strongly affected lake water quality. Excessive phosphorus and nitrogen concentrations in the lake have led to hypertrophy, characterized by low dissolved oxygen concentrations and prolific blooms of nuisance algae. The management of this new ecosystem in the near future will require persistent, and innovative measures.     

Phytoplankton-metaphyton seasonal dynamics in a newly-created subtropical wetland lake

The dynamics of the algal populations of Lake Agmon, a newly created shallow lake in the Hula Valley, Israel, were monitored following its filling in April 1994 through 1996. Additional limited field observations and measurements were taken throughout 1997. Following an initial establishment period, the dynamics of the algal populations showed a repetitive annual pattern comprised of three phases: I. a clear water phase in January–February, with low phytoplankton biomass and no metaphyton; II. a metaphyton dominance phase during March–June when mats of filamentous chlorophytes covered most of the lake's sediments while phytoplankton biomass remained low; and III. an intense phytoplankton bloom phase from June till December. The shifts from phase I to II and from phase II to III were gradual, resulting from interplay between phosphorus availability, the underwater light climate, temperature effects and zooplankton grazing pressure. The shift from phase III back to phase I was abrupt, due to winter flushing of Lake Agmon. The summer phytoplankton blooms intensified from 1994 to 1996 and shifted from chlorophyte dominance in 1994 and 1995 to cyanobacteria-dominance in 1996 and 1997. These observations, jointly with the nutrient chemistry of Lake Agmon, suggest intense eutrophication. Criteria based on phytoplankton taxonomy also indicate that Lake Agmon is eutrophic to hypertrophic. Due to the typical unstable nature of hypertrophic systems, careful management is essential to maintain the delicate ecological balance needed to ensure that the lake will fulfill its intended role as a center for eco-tourism.     

Temporal variation in fish community structure in a newly created wetland lake (Lake Agmon) in Israel

Lake Agmon was constructed in summer 1994 in the northern part of the drained Lake Hula swamp, as part of the Hula Reclamation Project. One of the main goals of the project was to attract aquatic and semi- aquatic birds to the area as a basis for planned eco-tourism and one of the main concerns of the project was the potential for increased proliferation of mosquitoes (including vector species of malarial parasites). There was a perceived need, therefore, to establish and maintain a suitable fish community. This present study documents the developments in the fish community in Lake Agmon between May 1995 and December 1996. The lake was initially stocked with two fish species, Tilapia zillii and Gambusia affinis, to control mosquitoes and to provide suitable small- bodied forage species for piscivorous birds. Subsequent stocking also included Oreochromis aureus, and Cyprinus carpio. Additional species were established by immigration from the Jordan River. Relatively large species ( e.g., Clarias gariepinus and C. carpio) flowed into the lake as eggs or juveniles, whereas the smaller species ( e.g., Hemigrammocapoeta nana, Pseudophoxinus kervillei and Aphanius mento) entered the lake as adults. In the first year, eight fish species were found in Lake Agmon: T. zillii, G. affinis, C. gariepinus, C. carpio, Capoeta damascina, P. kervillei, Acanthobrama lissneri and H. nana. Of these, T. zillii, G. affinis and H. nana were dominant, though the relative abundance of H. nana was very low in spring, and increased during summer. In the second year, O. aureus, A. mento and Anguilla anguilla also occurred in the lake. The density of P. kervillei increased, in comparison with the previous year. The relative proportions of juvenile and adult fish also changed in the second year. A high percentage of young T. zillii was found during the first spring, decreasing in the summer and autumn. The proportion of juveniles of both G. affinnis and H. nana was very low during the first year, but increased during the second. These results indicate that the fish community of Lake Agmon had not stabilized by the end of 1996 and that further changes in relative abundances, and species, age and sex compositions should be expected.