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RESEARCH PRODUCT

Multivariate-Analysis of Phytoplankton and Related Environmental-Factors, in a Shallow Hypertrophic Lake

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Data on some relevant environmental variables and phytoplankton species composition, collected from the hypertrophic shallow lake Albufera of Valencia (Spain) during 1980-88, were examined using Redundancy Analysis (RDA). The hydrological cycle of the lake is manipulated for rice cultivation in the area. Seasonality and the particular hydrological cycle of the lake were the principal factors influencing long-term phytoplankton dynamics. Annual or horizontal differences were less important than the seasonal factor. However, a trend of phosphate increase and underwater illumination decrease was observed between 1980 and 1988. These changes might be related to some species year-to-year variations, although in general interannual phytoplankton changes were scarce. Spatial phytoplankton differences were much smaller than physical and chemical differences, which were mainly related to loading and residence times at the different sampling zones. Shallowness, hypertrophy and the regular hydrological cycle of the Albufera for rice yield, seem to contribute to the maintenance of an almost stable and homogeneous algal community, mainly composed of filamentous cyanophytes. RDA analysis has proved to be an efficient method in yielding valuable information on phytoplankton-environment interactions and trends over a long series of data. It seems also a feasible technique to monitor the results of lake management and restoration in the future. [KEYWORDS: Phytoplankton; lake; shallowness; hypertrophy; rice fields area; long-term study; redundancy analysis; spain Periodicity]