Shifts in present-day and pre-eutrophic diatom assemblages in reservoirs of different trophic status (Upper Tietê River and surrounding drainage basins)

Abstract

Freshwater ecosystems may be biodiversity hotspots. Yet, they are highly threatened by human activities that affect biodiversity, ecological quality, and also the knowledge of their natural conditions. Paleolimnology has proved to be a valuable tool for the study of aquatic ecosystems and, among several indicators of past conditions, diatoms emerge as one of the most suitable groups for studies on eutrophication. Based on the paleolimnological top-bottom approach, our main objectives are: (a) characterize and analyze diatom assemblages shifts in pre- and post-eutrophication conditions; (b) characterize indicator species associations of oligotrophic and eutrophic environments, considering the spatial (between reservoirs) and temporal (same reservoir) scales; and (c) analyze the impact of eutrophication on the diatom biodiversity shift. Six reservoirs were selected based on four criteria (age, maximum depth, non-dredged sediment and trophic state). Reservoirs are located at the Upper Tietê River and surrounding drainage basins, and have different trophic states (2 oligotrophic, 1 mesotrophic and 3 eutrophic). At most two cores will be sampled per reservoir, and the subsamples will be sectioned at 2 cm intervals along the core. Detailed analysis will be carried out for the top (first 10 cm) and the base of the core (final 10 cm). Analysis will include lithology, granulometry, geochronology and diatom assemblages (taxonomic and quantitative analysis), associated with other paleoenvironmental markers, mainly total phosphorus, organic geochemistry and stable isotopes (COT, NT, C/N, ´13C e ´15N). Some water physical and chemical characteristics will be also analyzed to assess the reservoirs recent trophic status. Data will be analyzed using cluster (similarity and distance) and ordination (PCA, PCoA, CCA) multivariate analyses, as well as indicator species analysis (INDVAL). The present proposal is innovative in the country and contributes to the understanding the diatoms' biodiversity patterns and their changes due to the cultural eutrophication in reservoirs, thus contributing to conservation and management strategies.Key words: bioindication, diatoms, ecological shift, eutrophication, organic geochemistry, paleolimnology