SPATIAL VARIATION OF PERIPHYTON BIOMASS IN A MEDITERRANEAN TEMPORARY STREAM.

M. Álvarez¹, I. Pardo¹, and G. Moyá². ¹Área de Ecología, Universidad de Vigo, 36200 Vigo, Spain, ²Departament de Biología Ambiental, Universitat de les Illes Balears, 07071 Palma de Mallorca, Spain

Periphyton samples were taken every two weeks between November 2000 and July 2001 from a temporary stream (torrent) of the Mediterranean island Majorca (Spain). The study was conduced at two sites, above and below a confluence with a small spring-fed stream. Values of cholorophyll-a ranged from 2.6 to 135.1 mg m^-2 at the upstream station (T4) and from 10.8 to 339.1 mg m^-2 at the downstream station (T5). AFDM followed a similar pattern, ranging from 2.8 to 79.1 g m^-2 in T4 and from 2.9 to 167.3 g m^-2 in T5. Salt concentration and substrate composition were the most important factors distinguishing samples from the sites according to Principal Component analysis. Higher degree of substrate consolidation and lower water temperatures seemed to determine higher chl-a values in T5, both variables explaining 56% of total chl-a variance between the sites in the multiple regression model. A similar temporal chlorophyll-a pattern was found at both sites in relation to flow. In November after water returned to the torrent, high chlorophyll-a values were greatly reduced by flooding, whereafter values increased to their maximum in spring, however, lightly reduced by spring flooding. Natural flow reduction from late April motivated a gradual decline in biomass.