In summer 2003 central Europe suffered an unusually severe heat wave, with air temperatures similar to those predicted for an average summer during the late 21st century. We use a unique set of over half a century of lake data from two lakes in Switzerland to determine the effect of the 2003 heat wave on water temperature and oxygen conditions in order to assess how temperate lakes will react when exposed to the increased ambient summer air temperatures that will be encountered in a generally warmer world and to test the predictions of relevant simulation models. In both lakes, surface temperature and thermal stability in summer 2003 were the highest ever recorded, exceeding the long-term mean by more than 2.5 standard deviations. The extremely high degree of thermal stability resulted in extraordinarily strong hypolimnetic oxygen depletion. These results are consistent with the predictions of the simulation models. Additionally, the results indicate that climatic warming will increase the risk of occurrence of deep-water anoxia, thus counteracting long-term efforts that have been undertaken to ameliorate the effects of anthropogenic eutrophication.

1. Periphyton chlorophyll a was measured at weekly or 2 weekly intervals from October 1992 to March 1994 at four sites in a Swiss prealpine gravel bed river that was frequently disturbed by unpredictable spates. 2. To evaluate the dominant processes that control periphyton biomass, measured data were compared with a set of simulations from an empirical dynamic periphyton model. Different combinations of process hypotheses were systematically activated and deactivated in order to assess their importance. 3. The simplest model leading to an acceptable agreement with measured data employs a biomass‐dependent growth rate, a detachment rate directly proportional to discharge and biomass, and a catastrophic loss rate during bed moving spates. Terms describing light or temperature dependence had a minor effect on the model fit. 4. The model describes the temporal pattern of the periphyton biomass as a series of growth curves periodically truncated by spates. Within the uncertainties of the measurements, mainly caused by the spatial heterogeneity of periphyton, the biomass recovered along deterministic trajectories. 5. Sensitivity analyses with respect to model parameters and model structure showed that site‐specific model parameters could not be unequivocally determined, and that the model yields similar results with slightly different formulations of processes. This indicates that the data base with respect to periphyton biomass was too small for a unique identification of model details but that the main conclusions on the significance of processes did not depend on arbitrary choices of the model formulation.

Phosphorus and nitrogen concentrations, phytoplankton, bacteria, detritus, primary production, and sedimentation have been investigated over a year in two Swiss lakes of different trophic state. Inflow and outflow of the lakes were calculated, as well as the eddy diffusion of P and N from the metalimnion into the epilimnion, and from these data a balance of the cpilimnetic phosphorus and nitrogen cycle was drawn up. Different methods of calculation all suggested a high intensity of the internal nutrient cycle in the epilimnion. By means of autolysis, destruction, and excretion, about 35-75s of the nitrogen and 55-85s of the phosphorus needed for the measured primary production can thus be regenerated.

In 1982 -1984 eight limnocorral (LC) experiments, each lasting for two weeks, were performed in mesotrophic Lake Lucerne, Switzerland, to study the effects of biomanipulation (removal of crustaceans by 95 /~m filter nets) on zooplankton -phytoplankton relationships and epilimnetic carbon and phosphorus fluxes. Seston concentrations and to a lesser extent primary production rates were reduced in control LCs through zooplankton grazing, and settling flux increased through fecal pellet production. But C and P regeneration were not significantly affected.We found several indications that the LCs, despite of their large size (-70 m 3 , 3 m in diameter and 11 m long) were artificial systems when compared to the surrounding lake: The eddy diffusion was diminished by about one order of magnitude, nutrients depleted (but phosphorus was supplied to the LCs), the phyto-and zooplankton showed lower standing crops in the control LCs than in the lake, the phytoplankton showed a shift from nannoplankton to netplankton, the crustacean zooplankton was mostly limited in their vertical migration, and the POC and PP sedimentation rates were increased. Moreover, in our set of experiments we always found outliers, which may have been caused by the different in situ conditions at the beginning of the experiments, and further enhanced by the complexity of the enclosed system.The problems of the LC-technique, such as replicability, scaling (size and time) and data extrapolation are discussed. The impact of crustacean zooplankton on particulate matter, i.e. seston reduction and sedimentation enhancement, can be extrapolated on a qualitative rather than on a quantitative basis for the Lake Lucerne ecosystem.

Discharge o] Treated Wastewater in LakesTreated wastewater discharged into a lake should be introduced below the trophogenic layer. Tracing the marked wastewater by echosounding revealed that the usual discharge method is unsuitable. The wastewater flows more or less to the depth of its own density, which is usually in the trophogenic layer. If there is no movement, that is, current in the water body, the wastewater accumulates at the pipe's mouth. A continuous current is therefore an indispensable prerequisite for a wastewater discharge site. It is only when wastewater is mixed with at least five parts of lake water that it does not rise more than two meters. INHALTSVERZEICHNIS

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The influence of irradiation and grafting on the crystallinity of three base polymers has been investigated with differential scanning calorimetry. Grafting has the largest effect on the base polymer crystallinity and results in a reduction of the crystallinity. The thermal degradation of the base polymers and grafted films has been investigated with thermogravimetric analysis. The extent of the fluorination of the base polymer, the irradiation method, and the graft level all influence the thermal degradation and its activation energy. It is proposed that the variation of the chain lengths of the grafted polystyrene chains is actually a primary underlying factor responsible for the influence of these various parameters on the degradation process. The first results of a comparative thermal analysis of some fuel‐cell membranes are also presented, and the promise and shortcomings of this method are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2612–2624, 2004

Lake Greifensee, a dimictic lake situated near Zürich, Switzerland, has been monitored chemically and biologically since 1971, a period during which total phosphorus concentration changed dramatically. Based on analysis of cores of the lake sediment, this lake was oligotrophic 120 years ago. Due to a rapid increase in population in the catchment area to about 100,000 inhabitants, the phosphorus input from sewer systems eventually exceeded the tolerable P-load of 2.3 t y−1. In the early 1970s, this lake was hypertrophic (ca. 600 mg m−3 total phosphorus). Due to P-elimination in sewage treatment plants and a ban of P-containing detergents, phosphorus concentrations declined to less than 50 mg m−3 in spring 2000 (overturn value). Currently we observe growth-limiting phosphorus concentrations in the trophogenic layer from May to November. Therefore, primary productivity dropped from >700 g C m−2 y−1 at the beginning of our investigations (1971) to approximately 400 g C m−2 y−1 in 2000, which is still in the eutrophic range. Ammonia concentrations in the hypolimnion decreased significantly over this period. However, anaerobic conditions still regularly occur in the hypolimnion during May/June. Although total biomass values of phytoplankton or zooplankton did not show any correlation with the long-term decline of phosphorus concentrations, the composition of different systematic groups showed clear trends. During the period with Ptotal concentrations of >250 mg m−3 phytoplankton biomass was dominated by chlorophytes and cryptomonads, with lesser amounts of diatoms and dinoflagellates. Cyanobacteria and chrysomonads were of minor importance. With declining P load cyanobacteria biomass increased while chlorophytes and dinoflagellates decreased. Chrysomonads and pennate diatoms attained substantial portions, Zooplankton community did not change markedly. Main fraction was contributed by the herbivorous crustaceans, about 20% of total zooplankton biomass was carnivorous. Functional properties of phytoplankton showed closer relationship with P decline than biomass of systematic groups of algae. Under hypertrophic conditions r-strategists were dominant, especially during spring and early summer. K-strategists were more abundant under moderate eutrophic conditions in the second half of the year. Motility and buoyancy are very important in lakes with thin trophogenic layer (5 m in Lake Greifensee). Nonmotile plankton could survive during overturn (enhanced turbulence) and during clear water periods, whereas motile plankton groups dominated during thermal stratification. The best criteria for measuring resilience of Lake Greifensee are species richness, biomass-based diversity and evenness indices of phytoplankton and the strength of coupling between different trophic levels. With declining phosphorus content, species richness and diversity indices of phytoplankton increased.