Long term record (1933-2014) of Water Level (WL), nutrient concentrations, plankton densities, and temperatures in the epilimnion of Lake Kinneret was analyzed. The aim is to identify if water quality is deteriorated ...Long term record (1933-2014) of Water Level (WL), nutrient concentrations, plankton densities, and temperatures in the epilimnion of Lake Kinneret was analyzed. The aim is to identify if water quality is deteriorated when the WL is low. It was found that water temperature increased and the composition and biomass of plankton communities were modified. Nitrogen and TDP decreased but TP slightly increased in the epilimnion during low WL conditions. The quality of epilimnetic water was not deteriorated and followed by a slight oligotrophism trend.展开更多
Until the late 1950s the Hula Valley, located between altitude of 170 masl in the northern part and 61 masl in the southern part, was covered by the old shallow Lake Hula (1.5 m mean depth;1400 ha water surface);and 4...Until the late 1950s the Hula Valley, located between altitude of 170 masl in the northern part and 61 masl in the southern part, was covered by the old shallow Lake Hula (1.5 m mean depth;1400 ha water surface);and 4500 ha of swamps partly or permanently were water covered. During 1950-1957 the old Lake Hula and the wetlands were drained and converted into agricultural usage. As a result of inappropriate agricultural management, a reclamation project (Hula Project, HP, 1990-1997) was implemented. A vertical plastic sheet (4.5 m deep) was placed along 2.8 km across the valley aimed at reduction of pollutants migration. This plastic barrier divided the valley into northern, organic, and southern mineral soil blocks. The HP was aimed at agricultural renovation together with prevention of water quality deterioration in the downstream Lake Kinneret. The chemical composition of the underground waters was monitored on a monthly basis in 14 drills and ground water table observation wells over the valley during 14 months. The Ground Water Table (GWT) in the northern part of the valley was shallower than in the south and seasonal fluctuation amplitudes were smaller in the north. Higher levels of TP, TDP, P-Ortho and particulate Phosphorus, TN and ammonium were documented in the southern underground waters. The level of nutrient concentrations in the south was probably enhanced by three factors: 1) accumulation by underground water migration;2) eroded substances from the southern mineral soil;3) intensive Evapo-Transpiration in the south. Due to the lower level of organic content in the south and in spite of possible underground accumulation no significant difference between southern and northern blocks was indicated for Nitrate (NO3) concentrations. Not like nitrates, the reduced nitrogen form of ammonium concentration in the undergrounds was higher in the south. It was suggested that the nutrient concentrations (dissolved and suspended) in the Southern underground waters were higher than those in the North as a result of water migration, which took over the plastic barrier underneath and/or aside while moving from north to south was resulted by the hydraulic gradient. This gradient was partly due to the topographic slope and partly to the intensive Evapo-Transpiration in this part of the valley, which also contributed to the decline of GWT.展开更多
An ecological project is proposed for the system of Lake Agmon (Hula Valley, Israel). The project indicates a change of the original concept of the Hula Project construction. Practically Lake Agmon system was found to...An ecological project is proposed for the system of Lake Agmon (Hula Valley, Israel). The project indicates a change of the original concept of the Hula Project construction. Practically Lake Agmon system was found to remove negligible amounts of Nitrogen and Phosphorus from the Lake Kinneret budget. Moreover, Lake Kinneret ecosystem has undergone limnological changes. The P limited Kinneret system is currently N limited. Therefore reduction of P and enhancement of N from the Hula Valley outflow might be beneficial to the Kinneret ecosystem. Currently, the TN concentration in the Agmon outflow is lower than in its inflow and vice versa for P. Consequently, this paper recommends conveying peat soil drained waters, the Agmon inflow, directly to Lake Kinneret instead of letting the waters flow through Lake Agmon. Nitrogen reduction in Lake Agmon is due to de-nitrification and sedimentation and P increase is due to degradation of aquatic vegetation. Additional benefit of this change is the predicted improvement of the new infrastructure for the activity of aquatic birds aimed at eco-tourism improvement.展开更多
In this work, the thermal response of Mesocyclops ogunnus was experimentally studied. Temperature was the only one parameter that was tested. Other parameters, such as food quality and availability, light conditions, ...In this work, the thermal response of Mesocyclops ogunnus was experimentally studied. Temperature was the only one parameter that was tested. Other parameters, such as food quality and availability, light conditions, predation pressure, and water mass motions were not included in the study. Organisms were collected in Lake Kinneret and the experiments were carried out under diffused light, 12/12 hours light/dark conditions. In the experimental system, the organisms were exposed to different temperatures of 15℃, 25℃, 27℃, and 30℃ with open pathway to migrate according to temperature preference. The preference of upper thermal range (25℃, 27℃, 30℃) by copepodite and adult stages was documented.展开更多
Agmon is a small, shallow man-made lake (area: 1.1 km2;mean depth 0.45 m), excavated in the peat soils of the Hula Valley in northern Israel, that was filled with water in August 1994. We followed the seasonal variati...Agmon is a small, shallow man-made lake (area: 1.1 km2;mean depth 0.45 m), excavated in the peat soils of the Hula Valley in northern Israel, that was filled with water in August 1994. We followed the seasonal variations in phytoplankton and metaphyton biomass, primary production and related environmental conditions between December 1995 and July 1997. Water temperature ranged between 9.5°C - 30.8°C;pH ranged between 7.2 - 8.6. The algae in Lake Agmon were characterized by seasonal alterations between summer-fall phytoplankton blooms and spring proliferation of benthic algal mats, with a winter clear-water phase. Chlorophyll a content in the water, as a measure of planktonic algal biomass, was low in winter (1.75 - 5 μg·L-1) and high in summer (>100 μg·L-1), when planktonic cyanobacteria (Microcystis spp.) bloomed. Metaphyton biomass varied between 3.5 and 970 g·dry·wt·m-2, with chlorophyll a content ranging from 5 - 701 mg·m-2. The dominant benthic algal genera were Spirogyra and Oedogonium in 1996 and Cladophora in 1997. Phytoplankton primary production was high in summer-fall, with a maximum of 1200 mg·O2·m-2·h-1. Benthic primary production was high from March till May, with a peak of 2173 mg·O2·m-2·h-1 in April 1997. The rate of benthic algal primary production was positively correlated to benthic chlorophyll a (r2 = 0.90). Diel measurements of water column dissolved oxygen (DO) concentration, conducted monthly from January to May 1997, revealed that DO concentration ranged from a nighttime minimum of 5.3 to a noon peak of 15.3 mg·L-1. Only during January to February, no significant changes in DO with depth were found, suggesting that at that time the water column was well mixed. The most salient feature of primary production in the lake was the seasonal partitioning between its benthic and planktonic components. This was most evident in the significant inverse relationship between benthic and planktonic primary productivity rates (r2 = 0.78).展开更多
文摘Long term record (1933-2014) of Water Level (WL), nutrient concentrations, plankton densities, and temperatures in the epilimnion of Lake Kinneret was analyzed. The aim is to identify if water quality is deteriorated when the WL is low. It was found that water temperature increased and the composition and biomass of plankton communities were modified. Nitrogen and TDP decreased but TP slightly increased in the epilimnion during low WL conditions. The quality of epilimnetic water was not deteriorated and followed by a slight oligotrophism trend.
文摘Until the late 1950s the Hula Valley, located between altitude of 170 masl in the northern part and 61 masl in the southern part, was covered by the old shallow Lake Hula (1.5 m mean depth;1400 ha water surface);and 4500 ha of swamps partly or permanently were water covered. During 1950-1957 the old Lake Hula and the wetlands were drained and converted into agricultural usage. As a result of inappropriate agricultural management, a reclamation project (Hula Project, HP, 1990-1997) was implemented. A vertical plastic sheet (4.5 m deep) was placed along 2.8 km across the valley aimed at reduction of pollutants migration. This plastic barrier divided the valley into northern, organic, and southern mineral soil blocks. The HP was aimed at agricultural renovation together with prevention of water quality deterioration in the downstream Lake Kinneret. The chemical composition of the underground waters was monitored on a monthly basis in 14 drills and ground water table observation wells over the valley during 14 months. The Ground Water Table (GWT) in the northern part of the valley was shallower than in the south and seasonal fluctuation amplitudes were smaller in the north. Higher levels of TP, TDP, P-Ortho and particulate Phosphorus, TN and ammonium were documented in the southern underground waters. The level of nutrient concentrations in the south was probably enhanced by three factors: 1) accumulation by underground water migration;2) eroded substances from the southern mineral soil;3) intensive Evapo-Transpiration in the south. Due to the lower level of organic content in the south and in spite of possible underground accumulation no significant difference between southern and northern blocks was indicated for Nitrate (NO3) concentrations. Not like nitrates, the reduced nitrogen form of ammonium concentration in the undergrounds was higher in the south. It was suggested that the nutrient concentrations (dissolved and suspended) in the Southern underground waters were higher than those in the North as a result of water migration, which took over the plastic barrier underneath and/or aside while moving from north to south was resulted by the hydraulic gradient. This gradient was partly due to the topographic slope and partly to the intensive Evapo-Transpiration in this part of the valley, which also contributed to the decline of GWT.
文摘An ecological project is proposed for the system of Lake Agmon (Hula Valley, Israel). The project indicates a change of the original concept of the Hula Project construction. Practically Lake Agmon system was found to remove negligible amounts of Nitrogen and Phosphorus from the Lake Kinneret budget. Moreover, Lake Kinneret ecosystem has undergone limnological changes. The P limited Kinneret system is currently N limited. Therefore reduction of P and enhancement of N from the Hula Valley outflow might be beneficial to the Kinneret ecosystem. Currently, the TN concentration in the Agmon outflow is lower than in its inflow and vice versa for P. Consequently, this paper recommends conveying peat soil drained waters, the Agmon inflow, directly to Lake Kinneret instead of letting the waters flow through Lake Agmon. Nitrogen reduction in Lake Agmon is due to de-nitrification and sedimentation and P increase is due to degradation of aquatic vegetation. Additional benefit of this change is the predicted improvement of the new infrastructure for the activity of aquatic birds aimed at eco-tourism improvement.
文摘In this work, the thermal response of Mesocyclops ogunnus was experimentally studied. Temperature was the only one parameter that was tested. Other parameters, such as food quality and availability, light conditions, predation pressure, and water mass motions were not included in the study. Organisms were collected in Lake Kinneret and the experiments were carried out under diffused light, 12/12 hours light/dark conditions. In the experimental system, the organisms were exposed to different temperatures of 15℃, 25℃, 27℃, and 30℃ with open pathway to migrate according to temperature preference. The preference of upper thermal range (25℃, 27℃, 30℃) by copepodite and adult stages was documented.
文摘Agmon is a small, shallow man-made lake (area: 1.1 km2;mean depth 0.45 m), excavated in the peat soils of the Hula Valley in northern Israel, that was filled with water in August 1994. We followed the seasonal variations in phytoplankton and metaphyton biomass, primary production and related environmental conditions between December 1995 and July 1997. Water temperature ranged between 9.5°C - 30.8°C;pH ranged between 7.2 - 8.6. The algae in Lake Agmon were characterized by seasonal alterations between summer-fall phytoplankton blooms and spring proliferation of benthic algal mats, with a winter clear-water phase. Chlorophyll a content in the water, as a measure of planktonic algal biomass, was low in winter (1.75 - 5 μg·L-1) and high in summer (>100 μg·L-1), when planktonic cyanobacteria (Microcystis spp.) bloomed. Metaphyton biomass varied between 3.5 and 970 g·dry·wt·m-2, with chlorophyll a content ranging from 5 - 701 mg·m-2. The dominant benthic algal genera were Spirogyra and Oedogonium in 1996 and Cladophora in 1997. Phytoplankton primary production was high in summer-fall, with a maximum of 1200 mg·O2·m-2·h-1. Benthic primary production was high from March till May, with a peak of 2173 mg·O2·m-2·h-1 in April 1997. The rate of benthic algal primary production was positively correlated to benthic chlorophyll a (r2 = 0.90). Diel measurements of water column dissolved oxygen (DO) concentration, conducted monthly from January to May 1997, revealed that DO concentration ranged from a nighttime minimum of 5.3 to a noon peak of 15.3 mg·L-1. Only during January to February, no significant changes in DO with depth were found, suggesting that at that time the water column was well mixed. The most salient feature of primary production in the lake was the seasonal partitioning between its benthic and planktonic components. This was most evident in the significant inverse relationship between benthic and planktonic primary productivity rates (r2 = 0.78).
