Water level variability and trends in Lake Constance in the light of the 1999 centennial flood

AbstractThe extreme flood of Lake Constance in 1999 focused attention on the variability of annual lake levels. The year 1999 not only brought one of the highest floods of the last 180 years but also one of the earliest in the season. The 1999 extreme event was caused by heavy rainfall in the alpine and pre-alpine regions. The influence of precipitation in the two distinct regional catchments on lake level variations can be quantified by correlation analysis. The long-term variations in lake level and precipitation show similar patterns. This is seen through the use of spectral analysis, which gives similar bands of spectral densities for precipitation and lake level time series. It can be concluded from the comparison of these results with the analysis of climate change patterns in northern Europe, i.e. the index of the North Atlantic Oscillation, that the regional effects on lake level variations are more pronounced than those of global climate change

Simulation of surface energy fluxes and stratification of a small boreal lake by a set of one-dimensional models

Peer reviewe

Exploring, exploiting and evolving diversity of aquatic ecosystem models: A community perspective

Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5–10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary

Climate change drives widespread shifts in lake thermal habitat

Lake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we use 32 million temperature measurements from 139 lakes to quantify thermal habitat change (percentage of non-overlap) and assess how this change is exacerbated by potential habitat constraints. Long-term temperature change resulted in an average 6.2% non-overlap between thermal habitats in baseline (1978–1995) and recent (1996–2013) time periods, with non-overlap increasing to 19.4% on average when habitats were restricted by season and depth. Tropical lakes exhibited substantially higher thermal non-overlap compared with lakes at other latitudes. Lakes with high thermal habitat change coincided with those having numerous endemic species, suggesting that conservation actions should consider thermal habitat change to preserve lake biodiversity

Jahrhunderthochwasser 1999 Jahrhundertniedrigwasser 2003 : Seespiegeltrends und Extremwasserstände am Bodensee

Extremereignisse in der Wasserführung der Flüsse und Seen und im Witterungsverlauf waren in der Geschichte des Menschen häufig ein Anlass zum Innehalten und zum Nachdenken, ganz besonders, wenn sie für ihn existenzbedrohende Ausmasse annahmen. Solche Ausmasse haben das Hochwasser von 1999 und das extreme Niedrigwasser von 2003 am Bodensee glücklicherweise nicht angenommen

Assessment of human pressures and their hydromorphological impacts on lakeshores in Europe

Europe has a large number of lakes, many of them lie in densely settled areas. For instance, Germany has 1073 lakes with a surface area greater than 0.5 km2, surrounded by lakeshore habitats of appr. 11 000 km. The lakeshore habitats are of outstanding significance for biodiversity, ecosystem function as well as a variety of human uses. In this paper we give an operational definition of the lakeshore zone (i.e. the littoral zone, the shoreline and the riparian zone). We list significant human pressures directly on the lakeshores or coming from the catchment, and we describe the most important impacts resulting from such pressures. For illustration, we present some examples (eutrophication, morphological modications, hydrological changes) from Lake Constance. Generally, many of these pressures are related to changes to the hydrological regime of the lake and/or to morphological modifications of the shore zone, but knowledge about the links between pressures and specific impacts is poor. We briefly discuss four approaches, which have recently been developed to assess the hydromorphological quality of lakeshores. These procedures are designed to fulfil the requirements of the European Water Framework Directive (WFD), as well as the requirements of regional planning and nature conservation

Complex effects of winter warming on the physicochemical characteristics of a deep lake

Recent winter warming over Central Europe associated with a positive phase of the North Atlantic Oscillation (NAO) strongly influenced the thermal and water column stability properties of deep Lake Constance (zmean = 101 m).Volumet- rically weighted average water temperatures have increased since the 1960s by an average of 0.017 degree C yr-1, and its interannual variability was strongly related to the variability in winter air temperature and the NAO winter index (NAOW). The influence of NAOw on water temperature was more persistent than its influence on air temperature. The seasonal persistence of the NAOw signal increased with water depth. Deep-water temperatures were related to the NAOw from one spring mixing period to the next. This caused a time lag of 1 yr in the response of deep-water winter temperatures to the NAOw. Reduced winter cooling during high-NAOw years resulted in the persistence of small temperature gradients that possibly resisted complete mixing. This, in turn, resulted in less upward mixing of nutrients (total phosphorus and total silica), which accumulated in the hypolimnion during the previous stratification period. A second effect of incomplete mixing was the lack of the replenishment of deepwater oxygen during high-NAOw years. Hence, besides its strong impact on the thermal regime, climate variability influenced both the causes (nutrient supply for phytoplankton growth) and symptoms (the degree of hypolimnetic oxygen deficiency) of trophic changes in Lake Constance

Assessment of ecosystem health of tropical shallow waterbodies in eastern India using turbulence model

In the present study, a numerical model of the hydrodynamic and thermal structure of artificial shallow lakes in eastern India has been developed as a tool to assess the ecological water quality, driven by the meteorological forcings. It allows quantification of the vertical mixing processes that govern not only the thermal structure but also nutrient exchanges and the distribution of dissolved and particulate matter among water layers. Vertical temperature profiles were calculated by solving coupled partial differential equations for temperature (heat energy balance equation), one-dimensional momentum equation and a second order closure scheme for small-scale turbulence effects, i.e. turbulent kinetic energy and turbulent dissipation rates numerically using an implicit time integration method. The effect of advection due to the inflow and outflow is not taken into consideration as these shallow waterbodies are assumed to behave as a closed lake. The oxygen level measured at different layers during the simulation period in these waterbodies reflects hypolimnetic oxygen depletion due to the thermal stratification in the aquatic environment. The changes in the stratification regime in these waterbodies are expected to affect the water quality and the health of the ecosystem, primarily based on temperature and dissolved oxygen parameter and in particular, the certain features of the oxygen resources of the hypolimnion

Local and continental-scale controls of the onset of spring phytoplankton blooms: Conclusions from a proxy-based model

A key phenological event in the annual cycle of many pelagic ecosystems is the onset of the spring algal bloom (OAB). Descriptions of the factors controlling the OAB in temperate to polar lakes have been limited to isolated studies of single systems and conceptual models. Here we present a validated modelling approach that, for the first time, enables a quantitative prediction of the OAB and a systematic assessment of the processes controlling its timing on a continental scale. We used a weather-driven, one-dimensional lake model to simulate the seasonal dynamics of the underwater light climate in 16 lake types characterized by the factorial combination of four lake depths with four levels of water transparency. We did so at 1962 locations across Western Europe and over 31 years (1979–2009). Assuming that phytoplankton production is light-limited in winter, we identified four patterns of OAB control across lake types and climate zones. OAB timing is controlled by (i) the timing of ice-off in ice-covered clear or shallow lakes, (ii) the onset of thermal stratification in sufficiently deep and turbid lakes and (iii) the seasonal increase in incident radiation in all other lakes, except for (iv) ice-free, shallow and clear lakes in the south, where phytoplankton is not light-limited. The model predicts that OAB timing should respond to two pervasive environmental changes, global warming and browning, in opposite ways. OAB timing should be highly sensitive to warming in lakes where it is controlled by either ice-off or the onset of stratification, but resilient to warming in lakes where it is controlled by incident radiation. Conversely, OAB timing should be most sensitive to browning where it is controlled by incident radiation, but resilient to browning where it is controlled by ice-off or the onset of stratification. Available lake data are consistent with our findings