The mixing regime of Lake Ammersee

Climate change affects the circulation of lakes and has already induced mixing regime shifts for 9 several sites. The pre-alpine Lake Ammersee, Germany, is usually dimictic, but exhibits rarely a 10 complete ice cover. Furthermore, it has potentially shown some monomictic years in the past. Based 11 on vertical profile data of water temperatures (WT) and dissolved oxygen (DO) the mixing behavior 12 of the lake is visualized and analyzed for the period of 1986 – 2014. The classification of mixing 13 depicts 22 dimictic years and eight monomictic years, which approves the assumption of of 14 occasional monomixis in the lake. No significance of a trend of shift in mixing pattern can be found. 15 By also deriving also the mixing depths from the vertical DO distribution, one year without complete 16 overturn (meromictic) is detected. The results show that no regime shift has set in for Lake 17 Ammersee until 2014. Considering the high percentage of monomictic years and the potential 18 occurrence of meromixis, it can be assumed that the lake’s mixing pattern will alter due to predicted 19 climate change in the future

glmGUI v1.0: an R-based graphical user interface and toolbox for GLM (General Lake Model) simulations

Abstract. Numerical modeling provides an opportunity to quantify the reaction of lakes to alterations in their environment, such as changes in climate or hydrological conditions. The one-dimensional hydrodynamic General Lake Model (GLM) is an open-source software and widely used within the limnological research community. Nevertheless, no interface to process the input data and run the model and no tools for an automatic parameter calibration yet exist. Hence, we developed glmGUI, a graphical user interface (GUI) including a toolbox for an autocalibration, parameter sensitivity analysis, and several plot options. The tool is provided as a package for the freely available scientific code language R. The model parameters can be analyzed and calibrated for the simulation output variables water temperature and lake level. The glmGUI package is tested for two sites (lake Ammersee, Germany, and lake Baratz, Italy), distinguishing size, mixing regime, hydrology of the catchment area (i.e., the number of inflows and their runoff seasonality), and climatic conditions. A robust simulation of water temperature for both lakes (Ammersee: RMSE =1.17 ∘C; Baratz: RMSE =1.30 ∘C) is achieved by a quick automatic calibration. The quality of a water temperature simulation can be assessed immediately by means of a difference plot provided by glmGUI, which displays the distribution of the spatial (vertical) and temporal deviations. The calibration of the lake-level simulations of lake Ammersee for multiple hydrological inputs including also unknown inflows yielded a satisfactory model fit (RMSE =0.20 m). This shows that GLM can also be used to estimate the water balance of lakes correctly. The tools provided by glmGUI enable a less time-consuming and simplified parameter optimization within the calibration process. Due to this, i.e., the free availability and the implementation in a GUI, the presented R package expands the application of GLM to a broader field of lake modeling research and even beyond limnological experts

Bacterial communities in trace metal contaminated lake sediments are dominated by endospore-forming bacteria

Lake sediments in areas close to the outlet of wastewater treatment plants are sinks for pollutants. Bacterial communities in sediments are likely affected by the released effluents, but in turn they might modify the distribution and bioavailability of pollutants. On the shore of Lake Geneva, Switzerland, wastewater from the City of Lausanne is treated and discharged into the lake via an outlet pipe in the Vidy Bay. The objectives of this study were to assess (1) the impact of the treated wastewater release on the bacterial communities in the Vidy Bay sediments and (2) the potential link between bacterial communities and trace metal sediment content. Bacterial community composition and abundance were assessed in sediments collected in three areas with different levels of contamination. The main factors affecting bacterial communities were inferred by linking biological data with chemical analyses on these sediments. Near to the outlet pipe, large quantities of bacterial cells were detected in the three upper most cm (3.2 × 109 cells assessed by microscopy and 1.7 × 1010 copies of the 16S rRNA gene assessed by quantitative PCR, per gram of wet sediment), and the dominant bacterial groups were those typically found in activated sludge (e.g. Acidovorax defluivii and Hydrogenophaga caeni). Three samples in an area further away from the outlet and one sample close to it were characterized by 50 % of endospore-forming Firmicutes (Clostridium spp.) and a clear enrichment in trace metal content. These results highlight the potential role of endospore-forming Firmicutes on transport and deposition of trace metals in sediments

Endospore-forming bacteria as new proxies to assess impact of eutrophication in Lake Geneva (Switzerland-France)

Measurements of chemical composition and biological parameters of sediment cores are used as proxies for changes in past environmental conditions and more recently the human impact on ecosystem health. In this study, endospore-forming bacteria are proposed as a new biological proxy for such paleoecological reconstructions. A sediment core providing a record for the past 90years (137Cs and magnetic susceptibility dating) was retrieved from the Rhone Delta of Lake Geneva. X-ray fluorescence was analyzed at a 0.2-cm resolution, while DNA extracts, elemental geochemistry and grain size were obtained at 4-cm intervals. The total number of bacteria and endospore-forming bacteria were quantified by qPCR using the 16S rRNA gene and the endosporulation-specific spo0A gene. Furthermore, a spo0A fragment was subjected to amplicon sequencing to define OTUs (operational taxonomic units) and the phylogenetic affiliation of the endospore formers. The results showed that despite the fact that the quantity of extracted DNA decreased with the age of the sediment, the abundance of endospore-forming bacteria remained constant. However, the diversity of this group of bacteria changed significantly, reflecting the eutrophication of the lake from 1960 to 1990. The shift in community composition was linked to the dominance of anaerobic clostridia-like endospore formers. This trend has reversed in the last 10years of the record, suggesting a recovery after perturbation. This study shows that the abundance and diversity of endospore-forming bacteria can be used as proxies to reconstruct lake history. We hereby successfully introduce a new strategy for paleoecology that could also be applied to ocean sediments and long sediment cores

Bacterial communities in trace metal contaminated lake sediments are dominated by endospore-forming bacteria

Lake sediments in areas close to the outlet of wastewater treatment plants are sinks for pollutants. Bacterial communities in sediments are likely affected by the released effluents, but in turn they might modify the distribution and bioavailability of pollutants. On the shore of Lake Geneva, Switzerland, wastewater from the City of Lausanne is treated and discharged into the lake via an outlet pipe in the Vidy Bay. The objectives of this study were to assess (1) the impact of the treated wastewater release on the bacterial communities in the Vidy Bay sediments and (2) the potential link between bacterial communities and trace metal sediment content. Bacterial community composition and abundance were assessed in sediments collected in three areas with different levels of contamination. The main factors affecting bacterial communities were inferred by linking biological data with chemical analyses on these sediments. Near to the outlet pipe, large quantities of bacterial cells were detected in the three upper most cm (3.2×109 cells assessed by microscopy and 1.7×1010 copies of the 16S rRNA gene assessed by quantitative PCR, per gram of wet sediment), and the dominant bacterial groups were those typically found in activated sludge (e.g. Acidovorax defluivii and Hydrogenophaga caeni). Three samples in an area further away from the outlet and one sample close to it were characterized by 50% of endospore-forming Firmicutes (Clostridium spp.) and a clear enrichment in trace metal content. These results highlight the potential role of endospore-forming Firmicutes on transport and deposition of trace metals in sediments