Search

Abstract: Lake Tegel (Berlin, Germany) is controlled by two main inflows: inflow #1 (River Havel) is heavily phosphorus-laden, whereas inflow #2 is an artificial confluence that includes discharge from a municipal wastewater treatment plant distinguished by high levels of phosphorus and pharmaceuticals. To reduce the phosphorus load on the lake, a phosphorus elimination plant (PEP) is situated at inflow #2. Moreover, the two inflows are short-circuited by a pipeline that transfers part of the inflow #1 water to the PEP and finally releases it into inflow #2. The pipeline and the PEP have contributed to a continuous reduction in the total phosphorus concentration of Lake Tegel in the past 25 years. We investigate the question of whether the existing lake pipeline can also be used to reduce the amount of pharmaceuticals in Lake Tegel originating from inflow #2 by dilution with water from River Havel, by diverting part of inflow #2 around the lake, or by a combination of both strategies. The circulation pattern of Lake Tegel is complicated by complex bathymetry and numerous islands and is therefore highly sensitive to winds. We tested seven different management scenarios by hydrodynamic modeling for a period of 16 years with the two-dimensional version of the Princeton Ocean Model (POM). None of the scenarios provided a strategy optimal for both pharmaceuticals and phosphorus. Nonetheless, compound regimes, such as alternating the pipe flow direction or adding another pipeline, allowed the most abundant pharmaceutical (carbamazepine) to be reduced while maintaining the current phosphorus level. This study demonstrates the ability of immediate lake regulation measures to maintain water quality. In the case of Lake Tegel, the pipeline can be fully effective with regard to pharmaceuticals only in combination with additional efforts such as advanced pharmaceutical treatment of wastewater and/or phosphorus reduction in the River Havel catchment. [Copyright &y& Elsevier]

Abstract: A model of seasonal heat storage by lake sediments is proposed oriented at applications in climate modeling and at lake parameterization in numerical weather prediction. The computational efficiency is achieved by reformulating of the heat transfer problem as a set of ordinary differential equations for evolution of the temperature wave inside the upper sediment layer. Arising temperature and depth scales completely replace the conductivity of the sediment in the heat transfer equation and can be easily achieved from the lake water temperature observations without any data on the sediment thermal properties. The method is proposed for the scales estimation from the inverse solution of the model equations in special case of the constant water-sediment heat flux in ice-covered lakes. The method is tested on data from sediments of Lake Krasnoye, North-Western Russia. The long-term (1961–2002) modeling of temperature in German lakes Müggelsee and Heiligensee with a coupled one-dimensional model of lake water column and sediments has demonstrated an appreciable effect of the sediment heat storage on near-bottom temperatures in both lakes. Thus, incorporation of the sediment layer into lake temperature models can essentially improve, at low computational costs, the model performance, especially for shallow lakes. In addition, a better forecast of near-bottom temperature evolution on climatic scales can provide a better understanding of the response of lake benthic communities to global warming. [Copyright &y& Elsevier]

Abstract: Although lacustrine groundwater discharge (LGD) might be important in water and nutrient budgets, it has often been neglected due to the required effort to measure LGD and due to intense spatial heterogeneity of LGD limiting the validity of measurements. Therefore, fast, easy applicable methods for a first snapshot of the LGD pattern are required and might be the basis for choosing relevant and representative sampling sites. In the present case study, which is actually the first application of an airborne measurement of thermal infrared radiation (TIR) to identify LGD pattern for entire deep freshwater lakes, the measurement was substantiated with thermal profiles in sediments and a water-table map. We found that measurement of TIR is a powerful tool to identify LGD pattern in lake-related studies provided that there is a lack of warm surface inflows. A TIR image taken in March 2012 shows that warm groundwater entering the relatively colder lake water in some near-shore areas is visible as a plume floating on top of the lake water. Prerequisites for the application of TIR to detect LGD pattern are the positive buoyancy of the groundwater relative to lake water and weak mixing in the water column. We propose a dimensionless scale for identifying groundwater floating conditions based on weather conditions. Attributing a surface thermal anomaly to LGD depends on careful consideration of other factors that could produce similar patterns and careful consideration of lake physics. [Copyright &y& Elsevier]