Environmental changes in Wigry Lake during the Late Glacial and Holocene were studied on the basis of subfossil Cladocera analysis. Cladocera are present in a long core WZS/03 (Słupiańska Bay), and a surface sediments. The sediment contains remains of twenty-seven species belonging to 5 families. Species composition of plankton and the variability in the frequency of specimens of Cladocera made possible to distinguish five phases of their development, which well correlated with palynological phases. The correlation proves that the biological development of Wigry Lake was determined mainly by climatic changes. During the history of the lake, planktonic forms were dominant and represented by Bosminidae. It indicates that the lake was (excluding the initial part) deep and oligo- or mesotrophic. The mesotrophic state has been noted during the Atlantic chronozone and temporary. Taking into consideration the size and the depth as well as the rare human population around the lake it can be stated that the trophy rise was the result of the warm climate. It is also possible that during the last few decades the natural and anthropogenic factors could add. Probably mild winters, warm and long summers, increased tourists number were partly responsible for changes of water state.

Cladocera are one of the most important freshwater biological indicators for a wide range of environmental variables. They show strong responses to several environmental factors (e.g., trophic state, water depth, temperature) and are very sensitive to changes in water pH. The main interest of this study was to evaluate the relationship between subfossil Cladocera community composition and environmental properties of dystrophic lakes (pH, water transparency, conductivity, dissolved oxygen, depth and area). We hypothesize that Cladocera species composition depends on a dystrophication index (HDI); thus, Cladocera assemblages change with the degree of dystrophication. For the study, we selected a group of dystrophic lakes located in Wigry National Park (WNP), NE Poland, where we found subfossil remains of 24 Cladocera species belonging to four families (Chydoridae, Bosminidae, Daphniidae, and Sididae). A non-metric multidimensional scaling (NMDS) was used to elaborate on the similarities among samples in cladoceran-community composition and structure. Statistical analyses showed that Cladocera assemblages in all the studied lakes were similar, and individual Cladocera species respond to the measured environmental parameters (e.g., pH, lake size and depth). Our results suggest that in dystrophic lakes, Cladocera community composition is an emerging characteristic of individual species responses to the environment.

Knowledge and management of aquatic ecosystems (formerly Bulletin Français de la Pèche et de la Pisciculture), an international journal on freshwater ecosystem

Lake Jelonek is a small lake located in central northern Poland, in the Tuchola Forest. The sediments of the lake represent a natural archive that offers insights into the natural history of the region from the Late Glacial to present. In winter 2002, a 1330 cm long sediment core was recovered from the deepest part of lake. Using a multiproxy approach (cladocerans, pollen and basic geochemistry), we reconstructed trophic status changes through the last ~15,000 years. Special attention was devoted to the evaluation of nutrient contributions to the lake from natural and anthropogenic sources. The Cladocera analyses yielded a total of 29 species belonging to five families (Bosminidae, Daphniidae, Leptodoridae, Chydoridae, Sididae), with planktonic species representing more than 60% of Cladocera relative abundance throughout the core. The pollen results suggested four periods of increased human activity, so-called settlement phases. The first traces of human activity in the basin of Lake Jelonek appeared in the Atlantic period and were related with Mesolithic and Neolithic settlements. The second (Bronze Age) and the third (Iron Age) settlement phases are well marked by the paleolimnological proxies studied. This time period clearly manifested on the lake waters as an increasing trophy level probably caused by human-associated discharges of nutrients to the lake. After the third settlement phase cladoceran data indicated a significant decrease in the lake trophic level and the pollen data showed a recovery of forest cover. The fourth period of human economic activity during the early Middle Age was characterized by deforestation associated with land reclamation for grazing and cultivation of cereals, and the subsequent nutrient enrichment of lake waters. According to our results, the biological development of Lake Jelonek was determined by climate changes from Late Glacial up to the Atlantic period. Contrastingly, the most important driver for the lake development though the middle and late Holocene has been human activity within the lake catchment. The recovery of the lake trophic level during the last century, which is primarily related to extensive afforestation of the lake catchment, highlighted the importance of land use in the conservation of healthy water bodies.

Environmental changes during the last millennium recorded in subfossil Cladocera, diatoms and sediments geochemistry from Lake El Sol (Central Mexico)