Ecological relationships between phytoplankton communities at different spatial scales in European reservoirs: implications at catchment level monitoring programmes.

Phytoplankton communities are structured by factors acting over temporal and spatial scales. Identifying which factors are driving spatial patterns in aquatic communities is the central aim of ecology. In this study, data sets of phytoplankton communities and environmental data of two Portuguese reservoirs types (lowland "riverine reservoirs" and higher altitude "artificial lake reservoirs") were used to determine the importance of environmental variables at different spatial (geographical, regional and local) and time scales (seasons, years) on the community structure. In all the data sets, the multivariate ordination technique Canonical Correspondence Analysis (CCA) showed that regional and local scales explained the majority (9¿18% and 13-19%, respectively) of the taxa variance. However, for "riverine reservoirs", time variables were more important, explaining 27% of the variability in phytoplankton assemblages. Variance partitioning was used to assess the individual importance of the three spatial scales and time for the community structure of the two reservoir types. The majority of among-site variability (5.9-21.4%) was accounted for by time variables, with local, regional, and geographical scale variables accounting for 3.3-5.6%, 3.7-4.5% and 2.6-2.9%, respectively. The effects of different spatial scales on phytoplankton communities were clearly interrelated; thus, implying that phytoplankton assemblages are capable of detecting stress from catchment to site scales.