Das Projekt "Daphnia hybrids" wird vom Umweltbundesamt gefördert und von Universität Konstanz, Limnologisches Institut durchgeführt. Hybrids of the water flea Daphnia occur in many lakes. However, little is known about the factors that cause the success of Daphnia hybrids. In a joint project of two laboratories we study the possible role of biotic interactions in the maintenance of a Daphnia hybrid complex. Daphnia hyalina, D. galeata and their hybrids occur in Bodensee and in Greifensee. The parent species are more abundant in Lake Constance, while hybrids dominate in Greifensee. Both lakes differ in important aspects (morphometry, trophic state), which is reflected by different biotic influences con Daphnia. Compared to Lake Constance, Daphnia in Greifensee are more often exposed to low quality food (toxic blue-greens) and have less of a refuge from fish predation (due the anoxic hypolimnion). Differences between both lakes in the invertebrate predation regime and in the parasite load of Daphnia are very probable. Besides field sampling programmes, we want to establish a collection of about 50 Daphnia clones from both lakes (parent species and hybrids, recent clones and old clones hatched from sediment cores). These clones will be used for life history experiments in the laboratory to test the influences of low quality food, of fish kairomones, of invertebrate predator kairomones and of a protozoan parasite. Food quality and invertebrate predator experiments will be done in Konstanz; parasite and fish experiments will be done in Dübendorf.
Das Projekt "Geochemische Indikatoren fuer die Produktivitaet in einem entrophierten See - Greifensee (Kanton Zuerich)" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Geologisches Institut, Stabil Isotopen Labor durchgeführt. Greifensee is a small lake in north-eastern switzerland which has become progressively eutrophic during the last 100 years, as a consequence of higher rates of organic productivity facilitated by an increased nutrient supply. Mckenzie (1982) demonstrated that annual changes in the surface water productivity of greifensee could be followed using the carbon-isotop signal of the desorbed bicarbonate. This integrated study allows us to evaluate the significance of our geochemical signals (i.e. How do the signals respond to productivity changes), to quantitatively model the carbon cycle in a highly productive lake, hence to extrapolate our results to ancient anoxic basins.
Das Projekt "LAMODATE: Lakustrische Ablagerungen als Monitoren von Dynamik im Grenzbereich Atmosphaere-Erdoberflaeche - 1. Projektphase: Kalibration chemisch-physikalischer Tracer, Testgebietstudien" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Geologisches Institut durchgeführt. Leading Questions: Variations in the stable-isotope composition of Alpine and peri-Alpine surface waters are expected to ultimately reflect the different origins of the air masses (Atlantic vs. Mediterranean) - with superimposed factors such as seasonality- and altitude effects. Questions: - Is it possible, through calibration of the recent isotope patterns (and their extensions into the past via lacustrine proxy data) to reconstruct past changes in atmospheric circulation? - Is it possible through the calibration of annual varve deposits (thickness and grain-size parameters) to quantify local drainage characteristics (precipitation and ice-melt) and to follow them back beyond measured meteorological and hydrological records? Abstract: The project consists of two parts: I. Mittelland-lake sediments: their geochemical signal of climate change Oxygen isotope signatures in lake sediments provide information on past rainfall and atmospheric circulation pattern. Oxygen isotope curves from Baldeggersee and from Greifensee record distinct changes in precipitation since the end of the Little Ice Age. II. Alpine-lake sediments: their clastic response to climate change Sediments from the Engadine lakes store the Holocene erosion history of an alpine valley and the clastic sediment record documents the impact of glacial erosional activity on the alpine landscape evolution. Low sedimentation rates offer the opportunity to trace the erosional history throughout the Holocene. Complementary information: Water cycle processes leave characteristic signals in lacustrine sediments. However, more detailed information on the present natural variability is needed to obtain quantitative interpretations of climatic variations in the past. The scope of this project is to calibrate proxy-data in the present and to apply them to the interpretation of past climate changes. In the first phase of this project we will sample surface waters (rivers and lakes) and measure oxygen- and hydrogen isotopic compositions in order to obtain an insight into integration processes and patterns for the different climatic regions of Switzerland. We will also collect short sediment cores from selected lakes in order link modern proxy data to their environmental controls and to follow the most recent evolutionary trends. This calibration should then enable the objective interpretation of stable-isotope records preserved in sedimented lacustrine carbonates in terms of past climatic conditions. Clastic varves from lakes in the Engadine test-region will be used to determine variations of catchment runoff rates caused by changes in precipitation and/or temperature.