No abstract

A former meander of the Upper Rh6ne River, France, is completely filled with silt and occurs as a forested wetland. Bosminidae and Chydoridae (Crustacea, Cladocera) remains are analysed from a 6-m sediment core that reaches coarse sand and gravel layers deposited by running water.The lower layer of fine sediment, deposited by still water after the meander had been cut off, was dated at 1666 + 211 BC. The likely end of aquatic succession was dated at 800 _+ 150 AD. The results, processed using Factorial Correspondence Analysis, suggest 3 phases during the aquatic succession. Phase I, corresponding to open water conditions, is very short. The following phases, indicating the development of macrophyte stands, then a decrease in depth, extend much longer. The unexpectedly long duration (1000-2000 years) of these macrophyte-dominated and marshy phases may be explained by a progressive rise in the mean water level of the Rh6ne River. The causes of this water level rise may be related to climatic and/or fluvial dynamics changes.

In a reservoir tailwater of the large, lowland Warta River, perch and ruffe coexist in a macrophyte habitat, which develops as a result of low water discharge in the late spring and summer. At the beginning of each year the diet of both percids, when shorter than 100 mm, is dominated by large, benthic Hydropsyche. Later in the year, epiphytic Chironomidae and Simuliidae replace these trichopterans in the perch diet, and benthic Chironomidae replace them in the ruffe diet. Large cladoceran species then become accessory food items for perch. Consequently, the food niche overlap of these two percids during the research period is only marginal.

Ponds are common and abundant features in nearly all landscapes typical of European lowland landscapes yet research on freshwater biodiversity has traditionally focussed on larger waterbodies such as lakes and rivers. This has led to an increased need to understand and quantify the biodiversity associated with pond habitats to better inform the active conservation and management of these small waterbodies. This thesis examines the aquatic macroinvertebrate biodiversity (alpha, beta and gamma) and conservation value of 95 ponds in Leicestershire, UK, across a variety of urban and rural landscape types and at a range of spatial scales. In addition, the relative importance of local (physicochemical and biological) and spatial (connectivity) variables in structuring macroinvertebrate communities within ponds is investigated. At a regional scale, the greatest macroinvertebrate biodiversity and conservation value was recorded within meadow ponds compared to urban, agricultural and forest ponds. Spatially, ponds were highly physically and biologically heterogeneous. Temporally (seasonally), invertebrate communities were most dissimilar in meadow and agricultural ponds but assemblages were similar in urban and forest ponds. In urban landscapes, park ponds supported a greater diversity of invertebrates than 'other' urban or garden ponds and typically had a greater conservation value. Garden ponds were the most taxon poor of those investigated. Perennial floodplain meadow ponds supported a greater biodiversity of invertebrates compared to ephemeral meadow ponds although conservation value was similar. Despite regular inundation from the River Soar, ephemeral ponds supported distinct communities compared to perennial meadow ponds. Aquatic macrophytes supported a higher diversity of taxa than other pond mesohabitats across all landscapes studied. Physicochemical factors were identified to be the dominant influence on macroinvertebrate assemblages although, a combination of local and spatial factors best explained the variation in community composition at a regional scale and for meadow ponds. Spatial factors were not identified to significantly influence urban pond communities. This study highlights the ecological importance and conservation value of ponds in rural and anthropogenically disturbed landscapes. Recognition of the significant contribution of ponds to freshwater biodiversity at regional and landscape scales is important for future conservation of pond habitats and will help focus and direct conservation strategies to where they are needed most.iv

W o j c i e c h J u r a s z Wioślarki (Cladocera) Roztocza Środkowego [Z 1 tab elą i 1 ry su n k ie m w tekście] A bstract. W ater-fleas from th e C en tral Roztocze U pland were exam ined. 54 species w ere found i. e. 60% of th e Polish fresh-w ater clad o ceran fau n a. Eleven species am ong th e m w ere ra re in Poland.