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Community structure and water quality in the Mediterranean streams of a natural park (St. Llorenç del Munt, NE Spain)

Abstract:

The macroinvertebrate community in the streams of the Natural Park of Sant Llorenç del Munt and Serra de l'Obac (Barcelona, NE Spain) and its relationships with the stream flow were studied twice in one year, in winter and summer 1996. 78 localities were visited for flow examination, although samples of macroinvertebrates were taken in only 26 of them. While in winter, 63% of the stream's length had continuous flow, and the rest had at least pools, in summer only 26% had continuous flow, 20% was totally dry and the rest maintained permanent pools. Despite this, the total number of macroinvertebrate families increased from 54 in winter to 94 in summer. Trichoptera and Plecoptera lost relative importance from winter to summer, while Heteroptera, Coleoptera, Odonata and Diptera were dominant in summer. In general, collector-gatherers were the most abundant, although, in summer, an increase in the number of scrapers and predators was observed. The study of the abundance of the different families in the two periods, using canonical correspondence analysis, revealed that flow and temperature, together with those factors related to the increase in primary production in summer (pH, oxygen) explained most of the community change between wet and dry seasons, while other physicochemical-factors were unimportant. The biotic index BMWP' did not show significant changes between periods. High values of BMWP' in summer can be explained by the high diversity of the macroinvertebrate community during this season, despite individual scores of families being smaller than in the wet period. © Asociación Española de Limnología.