Quantitative ecotoxicological impacts of sewage treatment plant effluents on plankton productivity and assimilative capacity of rivers.

Sewage treatment plants are sources of inorganic and organic matter as well as contaminants for the receiving watercourses. We analyzed the ecological consequences of such effluents by following a holistic and synecological ecotoxicological approach based on quantifying extracellular enzyme activities (EEA), primary production and bacterial cell, and biomass production rates. Samples were obtained at three locations at the Rivers Holtemme and Elbe, Germany and Lower Jordan River, Israel and West Bank, as well as from their adjacent sewage treatment plants. Blending river samples with sewage treatment plant effluents mainly resulted in a stimulation of EEAs, which was diminished in blends with 0.2-µm filtered sewage treatment plant effluents. Stimulation for primary production and bacterial cell and biomass production of River Holtemme and Elbe samples was observed, and inhibition of these rates for Lower Jordan River samples probably linked to generally high turbidity. The quantified bacterial biomass versus cell production rates showed almost unbalanced (≫ 1) growth. Very high biomass to cell production ratios were found for sewage and sewage-containing samples, which provides a semi-quantitative indicator function for high quantities of microbial easy utilizable dissolved organic matter as nutrition source. The presented approach enables the simultaneous quantification of inhibitory and stimulating toxic responses as well as supplying ecosystem-based data for policy decision-making, and for direct incorporation in models to derive management and remediation strategies.

Agriculture, diversions, and drought shrinking Galilee Sea.

In water-limited regions worldwide, climate change and population growth threaten to desiccate lakes. As these lakes disappear, water managers have often implicated climate change-induced decreases in precipitation and higher temperature-driven evaporative demand-factors out of their control, while simultaneously constructing dams and drilling new wells into aquifers to permit agricultural expansion. One such shrinking lake is the Sea of Galilee (Lake Kinneret), whose decadal mean level has reached a record low, which has sparked heated debate regarding the causes of this shrinkage. However, the relative importance of climatic change, agricultural consumption, and increases in Lebanese water consumption, remain unknown. Here we show that the level of the Sea of Galilee would be stable, even in the face of decreasing precipitation in the Golan Heights. Climatic factors alone are inadequate to explain the record shrinkage of the Sea of Galilee. We found no decreasing trends in inflow from the headwaters of the Upper Jordan River located primarily in Lebanon. Rather, the decrease in discharge of the Upper Jordan River corresponded to a period of expanding irrigated agriculture, doubling of groundwater pumping rates within the basin, and increasing of the area of standing and impounded waters. While rising temperatures in the basin are statistically significant and may increase evapotranspiration, these temperature changes are too small to explain the magnitude of observed streamflow decreases. The results demonstrate that restoring the level of the Sea of Galilee will require reductions in groundwater pumping, surface water diversions, and water consumption by irrigated agriculture.

New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project.

The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, ~1m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments.

Challenges to estimate surface- and groundwater flow in arid regions: the Dead Sea catchment.

The overall aim of the this study, which was conducted within the framework of the multilateral IWRM project SUMAR, was to expand the scientific basement to quantify surface- and groundwater fluxes towards the hypersaline Dead Sea. The flux significance for the arid vicinity around the Dead Sea is decisive not only for a sustainable management in terms of water availability for future generations but also for the resilience of the unique ecosystems along its coast. Coping with different challenges interdisciplinary methods like (i) hydrogeochemical fingerprinting, (ii) satellite and airborne-based thermal remote sensing, (iii) direct measurement with gauging station in ephemeral wadis and a first multilateral gauging station at the river Jordan, (iv) hydro-bio-geochemical approach at submarine and shore springs along the Dead Sea and (v) hydro(geo)logical modelling contributed to the overall aim. As primary results, we deduce that the following: (i) Within the drainage basins of the Dead Sea, the total mean annual precipitation amounts to 300 mm a(−1) west and to 179 mm a(−1) east of the lake, respectively. (ii) The total mean annual runoff volumes from side wadis (except the Jordan River) entering the Dead Sea is approximately 58­66 × 10(6) m(3) a(−1) (western wadis: 7­15 × 10(6) m(3) a(−1); eastern wadis: 51 × 10(6) m(3) a(−1)). (iii) The modelled groundwater discharge from the upper Cretaceous aquifers in both flanks of the Dead Sea towards the lake amounts to 177 × 10(6) m(3) a(−1). (iv) An unexpected abundance of life in submarine springs exists, which in turn explains microbial moderated geo-bio-chemical processes in the Dead Sea sediments, affecting the highly variable chemical composition of on- and offshore spring waters.The results of this work show a promising enhancement of describing and modelling the Dead Sea basin as a whole.

Microbial and chemical characterization of underwater fresh water springs in the Dead Sea.

Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water's chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea-Dead Sea water conduit.