Wir untersuchen sowohl einzelne Prozesse in aquatischen Systemen als auch ganze Systeme natürlicher Gewässer. Neben der Grundlagenforschung und der interdisziplinären Systemanalyse stehen anwendungsnahe Projekte besonders im Fokus.
«The power of the small» am Global Science Filmfestival uraufgeführt
20. November 2019 Das Global Science Film Festival fand vom 15. bis 17. November in Zürich statt. Neben Filmen und Kurzfilmen wurden auch von Wissenschaftlerinnen und Wissenschaftlern in einem speziellen Workshop produzierte Videos gezeigt. Darunter war auch einer von Helmut Bürgmann und Davide Ciccarese. Weiterlesen
Oxygen consumption in seasonally stratified lakes decreases only below a marginal phosphorus threshold
Areal oxygen (O2) consumption in deeper layers of stratified lakes and reservoirs depends on the amount of settling organic matter. As phosphorus (P) limits primary production in most lakes, protective and remediation efforts often seek to reduce P input. However, lower P concentrations do not always lead to lower O2 consumption rates. This study used a large hydrochemical dataset to show that hypolimnetic O2 consumption rates in seasonally stratified European lakes remain consistently elevated within a narrow range (1.06 ± 0.08 g O2 m−2 d−1) as long as areal P supply (APS) exceeded 0.54 ± 0.06 g P m−2 during the productive season. APS consists of the sum of total P present in the productive top 15 m of the water column after winter mixing plus the load of total dissolved P imported during the stratified season, normalized to the lake area. Only when APS sank below this threshold, the areal hypolimnetic mineralization rate (AHM) decreased in proportion to APS. Sediment trap material showed increasing carbon:phosphorus (C:P) ratios in settling particulate matter when APS declined. This suggests that a decreasing P load results in lower P concentration but not necessarily in lower AHM rates because the phytoplankton community is able to maintain maximum biomass production by counteracting the decreasing P supply by a more efficient P utilization. In other words, in-lake organic matter production depends only on APS if the latter falls below the threshold of 0.54 g P m−2 and correspondingly, the atomic C:P ratio of the settling material exceeds ~155.
Müller, B.; Steinsberger, T.; Schwefel, R.; Gächter, R.; Sturm, M.; Wüest, A. (2019) Oxygen consumption in seasonally stratified lakes decreases only below a marginal phosphorus threshold, Scientific Reports, 9, 18054 (7 pp.), doi:10.1038/s41598-019-54486-3, Institutional Repository
Impact of human activities and climate on Lake Morenito, Northern Patagonia, Argentina
Lake Morenito located in the Argentinean Patagonia has been exposed to climatic, volcanic, and anthropogenic impacts for the last decades. In particular, the damming of the lake and the eruption of the Calbuco/Puyehue Volcanoes in AD 1960 played an important role in the lake’s history. A 80-cm-long sediment core from Lake Morenito spanning more than 100 years was studied for chironomids, stable isotopes, and organic geochemistry to investigate how natural and anthropogenic stressors impacted the lake. Chironomid assemblages display large changes around AD 1950, with the appearance of the warm-adapted Chironomus and the replacement of Apsectrotanypus by Ablabesmyia, indicating a shift to warmer conditions. By that time and up to the present, an increasing trend of δ15N coupled with a decrease of δ13C points to shifts in the carbon and nitrogen cycles associated with human activities. It is evident that the onset of human activities during the 1950s following by the lake damming in AD 1960 had significant effects on the chironomid assemblages and the geochemical composition of sediments which is reflected in the progressive deterioration of the lake ecosystem.