Cladocera paleocommunity to disentangle the impact of anthropogenic and climatic stressors on a deep subalpine lake ecosystem (Lake Iseo, Italy)

In big lakes with strong anthropogenic pressure, it is usually difficult to disentangle the impacts of climate variability from those driven by eutrophication. The present work aimed at the reconstruction of change in the species distribution and density of subfossil Cladocera in Lake Iseo (Italy) in relation to climate and anthropogenic pressure. We related subfossil Cladocera species composition and density in an 80-cm sediment core collected in the pelagic zone of Lake Iseo to long-term temperature trends and phosphorus concentration inferred by diatoms frustules. The Cladocera remains detected in Lake Iseo sediment reflected the species composition and density of modern pelagic Cladocera assemblages. Cladocera rapidly respond to environmental change, and that climate change combined with eutrophication can induce changes in community composition and species density. At the beginning of twentieth century, when global warming was not yet so accentuated, the nutrient increase in water resulted as the principal driver in determining the long-term development of plankton communities and pelagic food web structure. Moreover, catchment-related processes may decisively affect both species composition and density of the lake planktonic communities due to the decrease of lake water transparency induced by input of inorganic material from the catchment area to the lake. The paleolimnological investigation, through the combined study of biotic and abiotic factor, allowed clarifying the synergic effects of the most important drivers of change in lake ecosystems, suggesting that climatic factors should be considered with nutrient availability as determinant element in controlling the temporal development of plankton communities and pelagic food web structure.

Eemian environmental changes recorded in the north located lakes (N Poland and Germany) - subfossil Cladocera data

<p>In the current study the result of subfossil Cladocera analysis of the lake sediments from tree sites: Hinterste Mühle (H-M) (NE Germany), Rzecino (NW Poland) and Łęczyce (N Poland) of the Eemian Interglacial and the inferred environmental alterations are presented. The aim of the study was to reconstruct and compare the development of Eemian lakes located within the north of Poland and Germany as determined on the basis of the changes in subfossil Cladocera composition in the context of local conditions, climate change and natural evolutionary processes.</p><p>The studied reservoirs, fully developed during the Eemian Interglacial, were formed at the end of Late Saalian (MIS 6) and Early Eemian. The Hinterste Mühle profile is located in Mecklenburg-Western Pomerania. The site lies in the southeastern edge of the gravel pit, at about 48 m a.s.l. The Rzecino paleolake is located in the West Pomerania Lakeland (NW Poland), at an elevation of 104.5 m a.s.l. The Łęczyce palaeolake is located in northern Poland, on the northern slope of the Łeba river valley.</p><p>The subfossil Cladocera fauna from the H-M palaeolake is represented by 14 species belonging to three families. Three of them belong to a benthic group inhabiting mainly the bottom sediments, one to the open water zone, while the remaining species the dominant group occur among aquatic plants. Such a species composition marks a shallow water body or the littoral, macrophyte zone of a deeper lake. The Cladoceran fauna of deposits from the Rzecino paleolake are represented by 22 species that belong to four families. The majority of the remains consist of Chydoridae and Bosminidae. In the deposits, the ephippial eggs of the <em>Daphnia longispina</em> group, <em>Ceriodaphnia</em> spp., <em>Chydorus spp</em>., and <em>Bosmina</em> spp. are also identified. The subfossil cladoceran fauna of sediments in the Łęczyce profile is represented by 18 species that belong to four families. Most of the remains belong to the family of Chydoridae (13). Such species composition points to a deeper reservoir with a developed littoral zone with macrophytes.</p><p>Summing up, a similar pattern was observed in the research paleolakes related to the beginning of the existing of the lakes, their full development and ending time, different from the paleolakes found in the south, related to the location and more intense contact with cool air masses from Northern Europe.</p>

Community Response of Cladocera to Trophic Stress by Biomanipulation in a Shallow Oxbow Lake

Studying contemporary and subfossil Cladocera (Crustacea) communities, we explored the effect of top-down stressors on the cladoceran communities; we are also interested in the coherence of the contemporary and subfossil communities. The studied Cibakháza oxbow lake is in E Hungary, on the left-floodplain of the River Tisza; it is a large, long, and shallow oxbow lake. Three areas of the oxbow lake were distinguished based on the strength of top-down stress: protected area with low top-down stress, biomanipulated area with high top-down stress, and recreational area with moderate top-down stress. Altogether, we identified 28 taxa in the contemporary and subfossil communities in the oxbow lake. We found that the species number of the contemporary Cladocera communities was lower (protected area: 13; biomanipulated area: 9, and recreational area: 14) than in the subfossil communities (protected area: 20; biomanipulated area: 16, and recreational area: 14). Among the environmental variables, we observed differences between the protected and biomanipulated area, while the recreational area showed a transition. Species number, abundances, and Simpson diversity also showed the effect of the fish introduction. There were no differences in beta-diversity among the contemporary and subfossil Cladocera community. The non-metric multidimensional scaling (NMDS) ordination showed that the biomanipulated area in the case of the contemporary communities was separated from the other areas, while in the case of the subfossil communities, there was no separation according to top-down stress. Our results showed that the number of species of contemporary Cladocera communities was lower in each area (3–10; 3–9; 5–9) compared to the subfossil communities (6–17; 7–12; 8–12). However, the highest abundances were found in the biomanipulated area due to the appearance of small-sized Cladocera species. Our findings suggest that the effect of a short-time fish introduction is restorable when the oxbow lake has a protected part.

Postglacial evolution of a small lake in the South Baltic coastal zone based on geochemical, pollen and subfossil Cladocera analysis

The paper presents sedimentary records acquired as part of the research on the coastal cliff located between 221.3 and 221.4 km of the Slovincian (Słowinskie) Coast near Debina. Palynological and subfossil Cladocera analysis of sediments combined with geochemical data proves the existence of varying environmental conditions that occurred depending on the climate fluctuation. The Debina reservoir was formed in the Late Glacial period. Mud and gyttja were deposited in an initially cold proglacial lake. Species of Cladocera identified in this period indicate a deeper oligotrophic reservoir. The end of the Late Glacial cooling inhibited the development of fauna in the reservoir. Climate change at the beginning of the Holocene improved the habitat conditions in the Debina paleolake, which is reflected in the growth of zooplankton biodiversity and enrichment of the aquatic pollen content. We distinguished three phases that illustrate the evolution of the studied aquatic-mire ecosystem. In the following periods, the trophic level in the reservoir increased and significant water-level fluctuations led to periodic transformations of reservoirs into peat bogs. Gradually, the water-level lowering and the intensification of eolian processes led to terrestrialization of the paleolake.