Limnetica 32

Paleolimnological techniques permit the reconstruction of past environmental and biological conditions in aquatic ecosystems. However, more studies that include comparisons with historical and limnological records are needed, particularly in subtropical and tropical regions, to validate the links between extant and subfossil indicator communities. We performed a paleolimnological study to reconstruct environmental changes over the last 11 years in Lake Rodó, a subtropical, hypereutrophic shallow lake located in Uruguay (34◦ 54’ 45’’ S, 56◦ 10’ 01’’ W), which was subjected to rehabilitation measures and from which limnological data were available. Analyses of the composition and abundance of fossil diatoms divided the record into three time periods that coincided with events during the history of Lake Rodó and its rehabilitation. The most abundant species were Aulacoseira granulata, Synedra acus, Aulacoseira granulata var. angustissima, Achnanthidium minutissimum, Stephanodiscus hantzschii and Fragilaria crotonensis. Indices of planktonic/benthic subfossil diatoms and of diversity reflected changes in the transparency of lake water and in the diversity of habitats available for growth. Records of diatom abundances from phytoplankton and sediment samples were highly correlated; these results highlight the value of diatoms as bioindicators for reconstructing environmental conditions even on short time scales (sub-decadal). Our results also show important differences between temperate and subtropical systems and highlight the need for caution when attempting to apply ecological data determined in other regions.