Exploitation and destabilization of a warm, freshwater ecosystem through engineered hydrological change

Exploitation of freshwater resources is having catastrophic effects on the ecological dynamics, stability, and quality of those water resources on a global scale, especially in arid and semiarid regions. Lake Kinneret, Israel (the Biblical Sea of Galilee), the only major natural freshwater lake in the Middle East, has been transformed functionally into a reservoir over the course of ∼70 years of hydrological alterations aimed mostly at producing electrical power and increasing domestic and agricultural water supply. Historical changes in lake chemistry and biology were reconstructed using analysis of sedimentary nutrient content, stable and radioisotope composition, biochemical and morphological fossils from algae, remains of aquatic invertebrates, and chemical indices of past light regimes. Together, these paleolimnological analyses of the lake's bottom sediments revealed that this transformation has been accompanied by acceleration in the rate of eutrophication, as indicated by increased accumulation rates of phosphorus, nitrogen, organic matter, phytoplankton and bacterial pigments, and remains of phytoplankton and zooplankton. Substantial increases in these indices of eutrophication coincide with periods of increased water‐level fluctuations and drainage of a major upstream wetland in the early to middle 20th century and suggest that management of the lake for increased water supply has degraded water quality to the point that ecosystem stability and sustainability are threatened. Such destabilization may be a model for eutrophication of freshwater lakes in other arid regions of the world in which management emphasizes water quantity over quality.Peer reviewedZoolog

Remote Sensing Observations of the Phytoplankton Distribution in Lake Kinneret

Reflectance spectra from 400 to 750 nm were measured in Lake Kinneret, when low phytoplankton stock prevailed, with chlorophyll concentrations from 3.1 to 7.3 μg/l. Algorithms for estimation of chlorophyll (CHL) concentration were devised using reflectances in the blue and green region of the spectrum and natural solar induced fluorescence. The fluorescence was calculated either from the reflectance height above a baseline drawn between 650 and 715 nm or between 670 and 730 nm, and also from the sum of reflectance above the base line through 670 and 730 nm. This paper presents experimental evidence showing that fluorescence can be successfully used as indicator of CHL content

Food web effects of titanium dioxide nanoparticles in an outdoor freshwater mesocosm experiment

<p>Over the course of 78 days, nine outdoor mesocosms, each with 1350 L capacity, were situated on a pontoon platform in the middle of a lake and exposed to 0 μg L⁻¹ TiO₂, 25 μg L⁻¹ TiO₂ or 250 μg L⁻¹ TiO₂ nanoparticles in the form of E171 TiO₂ human food additive five times a week. Mesocosms were inoculated with sediment, phytoplankton, zooplankton, macroinvertebrates, macrophytes and fish before exposure, ensuring a complete food web. Physicochemical parameters of the water, nutrient concentrations, and biomass of the taxa were monitored. Concentrations of 25 μg L⁻¹ TiO₂ and 250 μg L⁻¹ TiO₂ caused a reduction in available soluble reactive phosphorus in the mesocosms by 15 and 23%, respectively, but not in the amount of total phosphorus. The biomass of Rotifera was significantly reduced by 32 and 57% in the TiO₂ 25 μg L⁻¹ and TiO₂ 250 μg L⁻¹ treatments, respectively, when compared to the control; however, the biomass of the other monitored groups—Cladocera, Copepoda, phytoplankton, macrophytes, chironomids and fish—remained unaffected. In conclusion, environmentally relevant concentrations of TiO₂ nanoparticles may negatively affect certain parameters and taxa of the freshwater lentic aquatic ecosystem. However, these negative effects are not significant enough to affect the overall function of the ecosystem, as there were no cascade effects leading to a major change in its trophic state or primary production.</p