The physical impact of the late 1980s climate regime shift on Swiss rivers and lakes

In the late 1980s, a sudden climate regime shift (CRS) occurred throughout the Northern Hemisphere that affected both marine and inland waters. In Switzerland, rivers and lakes underwent an abrupt warming. A month-by-month comparison of water temperatures before and after the late 1980s CRS shows seasonal differences in the magnitude of the warming, which was stronger in winter, spring, and summer than in autumn. In lakes, the magnitude of the increase and the abruptness of the change diminished with increasing depth. Surface temperatures showed the most consistent abrupt warming. Hypolimnetic temperatures also increased, but the change was gradual in 3 of the 4 lakes studied. The abrupt warming in the late 1980s contributed substantially to the overall increase in  temperature that has occurred in water bodies in Switzerland over the last few decades

Hypolimnetic oxygen consumption by sediment-based reduced substances in former eutrophic lakes

We quantified the areal hypolimnetic mineralization rate (AHM; total areal hypolimnetic oxygen depletion including the formation of reduced substances) in two formerly eutrophic lakes based on 20 yr of water-column data collected during oligotrophication. The upward diffusion of reduced substances originating from the decomposition of organic matter in the sediment was determined from pore-water profiles and related to the time of deposition. More than 80% of AHM was due to degradation of organic matter in the water column (including sediment surface) and diffusion of reduced substances from sediment layers younger than 10 yr. Sediments older than 10 yr, including the eutrophic past, accounted for similar to 15% of AHM. This "old'' contribution corresponds to a 20-43% fraction of the total sediment-based AHM. The contribution from old sediment layers to AHM is expected to be even lower in lakes with deeper hypolimnia (> 12 m). In summary, oxygen consumption in stratified hypolimnia is controlled mainly by the present lake productivity. As a result, technical lake management measures, such as oxygenation, artificial mixing, or sediment dredging, cannot efficiently decrease the flux of reduced substances from the sediment

A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues