Long-term ecological changes in Mediterranean mountain lakes linked to recent climate change and Saharan dust deposition revealed by diatom analyses

Anthropogenic climate change and the recent increase of Saharan dust deposition has had substantial effects on Mediterranean alpine regions. We examined changes in diatom assemblage composition over the past ~180 years from high-resolution, dated sediment cores retrieved from six remote lakes in the Sierra Nevada Mountains of Southern Spain. In all lakes, changes in diatom composition began over a century ago, but were more pronounced after ~1970 CE, concurrent with trends in rising regional air temperature, declining precipitation, and increased Saharan dust deposition. Temperature was identified as the main predictor of diatom assemblage changes, whereas both Saharan dust deposition drivers, the Sahel precipitation index and the winter North Atlantic Oscillation, were secondary explanatory variables. Diatom compositional shifts are indicative of lake alkalinization (linked to heightened evapoconcentration and an increase in calcium-rich Saharan dust input) and reduced lake water turbulence (linked to lower water levels and reduced inflows to the lakes). Moreover, decreases in epiphytic diatom species were indicative of increasing aridity and the drying of catchment meadows. Our results support the conclusions of previous chlorophyll-a and cladoceran-based paleolimnological analyses of these same dated sedimentary records which show a regional-scale response to climate change and Saharan dust deposition in Sierra Nevada lakes and their catchments during the 20th century. However, diatom assemblages seem to respond to different atmospheric and climate-related effects than cladoceran assemblages and chlorophyll-a concentrations. The recent impact of climate change and atmospheric Saharan deposition on lake biota assemblages and water chemistry, as well as catchment water availability, will have important implications for the valuable ecosystem services that the Sierra Nevada provides

Regulation of rotifer species by invertebrate predators in a hypertrophic lake: Selective predation on egg-bearing females and induction of morphological defences.

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The relevance of size efficiency to biomanipulation theory: a field test under hypertrophic conditions

The superiority of large zooplankton in suppressing phytoplankton growth has often been inferred from the Size Efficiency Hypothesis (S.E.H.). The S.E.H. has originally been formulated to account for the competitive superiority of large to small zooplankton under food limiting conditions. Extrapolation of its predictions to the suppression of phytoplankton by zooplankton under high food availability, should be done with care. In an attempt to assess the relevance of the S.E.H. to biomanipulation theory in hypertrophic systems, a fish exclosure experiment was carried out in which the efficiency of two differently structured zooplankton communities in reducing phytoplankton biomass was examined. By inoculating part of the enclosures with laboratory grown Daphnia magna, a community dominated by this large cladoceran species could be compared with a community mainly consisting of Bosmina and smaller Daphnia species. After the exclusion of fish, there was an exponential increase of total. zooplankton biomass. Phytoplankton growth was efficiently suppressed to equal levels in both treatments, though there was a difference in timing: chlorophyll-a levels in the enclosures inoculated with D. magna dropped one week earlier than in non-inoculated enclosures. The time-lag was even more pronounced when large phytoplankton was considered. In accordance with the S.E.H., the time lags could be explained by differences in population growth potential as well as by differences in zooplankton grazing rates (indirectly measured as the minimal zooplankton biomass needed to suppress phytoplankton growth) and food particle size range

Gas transport in porous electrodes of solid oxide fuel cells

Abstract. This study aimed at unraveling the structure underlying the taxon-richness matrix of shallow lakes. We assessed taxon richness of a large variety of food-web components at different trophic levels (bacteria, ciliates, phytoplankton, zooplankton, fish, macro-invertebrates, and water plants) in 98 shallow lakes from three European geographic regions: Denmark (DK), Belgium/The Netherlands (BNL), and southern Spain (SP). Lakes were selected along four mutually independent gradients of total phosphorus (TP), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional phenomenon. Different PCA axes showed associations with richness in different subsets of organism groups, and differences between eigenvalues were low. Redundancy analysis showed a unique significant contribution to total richness variation of SUBMCOV in all three regions, of TP in DK and SP, and of AREA in DK and BNL. In DK, several organism groups tended to show curvilinear responses to TP, but only one was significantly hump shaped. We postulate that the unimodal richness responses to TP that are frequently reported in the literature for many organism groups may be partly mediated by the unimodal response of macrophyte vegetation to lake productivity

Rotifer communities under variable predation-turbulence combinations

The effects of water turbulence on rotifer communities were experimentally studied under different predation pressures. When the larvae of the phantom midge (Chaoborus flavicans) were present in turbulent water, the abundance of most rotifer taxa was enhanced. Especially the genera Chromogaster, Keratella, Polyarthra, and Trichocerca, increased in abundance. In calm water, chaoborids did not affect the rotifer community. In turbulent water predation by chaoborids was targeted more towards cladocerans (Bosmina sp.) and predation pressure on rotifers was relaxed. Additionally, reduced competition with cladocerans probably contributed to the increase of rotifer abundance. Turbulence alone had no significant effect on rotifer abundance because their individual size was small compared with the diameter of the turbulent eddies. The study suggested that the effects of turbulence on rotifers is not direct but takes place through changed predator-prey relations, i.e., the effect depends on the abundance of invertebrate predators. In aquatic ecosystems with a high density of chaoborids, increasing turbulence can considerably increase the abundance of rotifers.Peer reviewe