Cladocera Analysis Research Articles

Human impact on lakes recorded in the remains of Cladocera (Crustacea)

Subfossil Cladocera analysis allows discussion of the influence of human activity on the lake environments from Neolithic times up to the present. Three lakes were chosen for the analysis: two in northern Poland and the third on Cres Island, Adriatic Sea (Croatia). During the Holocene the species composition and the specimen abundance often changed, resulting mainly from climate changes, and also from human activity. This phenomenon is recognized on the diagrams of absolute abundance and percentage ratio of specimens of the pelagic species to the littoral ones. The data from Cladocera analysis were compared with the abundance of some plants reflecting human activity. A large degree of correlation was noted between the increased presence of these plants and the occurrence of the Cladocera species preferring more trophic water. Some phases of increased lake eutrophication were distinguished on the basis of Cladocera species preferring nutrient rich water. According to the comparative palynological and archaeological studies, these phases are correlated with the periods of settler groups’ activity beginning in Neolithic times. The most distinct changes in the species composition of Cladocera have been noted in the lake sediment from the Medieval Period. They were brought on by the agricultural revolution, which has lasted uninterruptedly up to now. It was observed that the intensity of the expressed abundance of index species in sediments is dependent on the size (area and depth) of the lake. The smaller the lake is, the greater is the change in species composition of zooplankton. The smaller water bodies react faster to an excessive supply of eutrophic compounds, and therefore the change is more clearly evident in the sediment record. Considerable secondary influence of these changes on the species composition of plankton was noted in the large lakes: Lednickie Lake (Poland) and Vrana Lake (Adriatic).

Palaeolimnological investigations in Poland based on Cladocera (Crustacea)

The results of subfossil Cladocera analysis obtained from deposits of 26 lakes throughout Poland have been presented. For years throughout Poland a broad range of palaeolimnological studies have been conducted. Their aim is to discover the historical development of water basins and climatic changes in the course of the last 13,000 years and also to investigate the gradual influence of man on the ecosystem with particular emphasis on the last few decades. The hitherto obtained results of palaeolimnological studies, including the results of Cladocera analysis, have yielded information about the development of lakes and provided the basis for plans of certain reservoirs and their basins. Over the past years, analysis of subfossil Cladocera has become one of the leading palaeolimnological methods. The results of detailed qualitative and quantitative analysis of Cladocera remains from sediments of 15 lakes allowed for a reconstruction of the lakes' development. The littoral and limnetic regions, changing trophy, from oligotrophy to advanced eutrophication, changes in pH and fluctuation of water levels, as well as changes resulting from settlement — from Mesolithic and Neolithic through Medieval times until the present — have been reconstructed. For individual lakes, phases of Cladocera development and periods of eutrophication were indicated which partially correlated with certain pollen zones as well as periods of human impact and geochemical effects.

The Litorina transgression in the Helsinki region, southern Finland: new evidence from coastal mire deposits

Sediment profiles were obtained, from the basal sections of two mire basins located above the highest Litorina shore in the Helsinki region, for pollen, diatom and Cladocera analyses and radiocarbon dating with the aim of exploring the relative sea‐level changes during the Litorina stage of the Baltic Sea. Both profiles provided indications of ‘long‐distance effects’ of the Litorina transgression around 7500–6100 BP, in the form of eutrophication, inundation, increased Pediastrum abundances, declined chydorid diversity and the presence of saline water diatoms. The results support the idea that sea level rose during the Litorina stage in the Helsinki region and suggest that this transgressive event had considerable effects on natural conditions in the coastal ecosystems. The findings contradict earlier accounts of a shore level stillstand during the Littorina stage in the Helsinki district.