Efectos directos e indirectos de la de la alteración hidrológica en un arroyo del Mediterráneo

Abstract

A study was conducted to demonstrate the effect of an hydrological alteration caused by drought (due both to the Mediterranean climate and human action) and the presence of fish on a given ecosystem. It was held in Llémena stream, a eutrophic one, where it will differentiated two sites (site 1 with a permanent water regime and site 2, with an intermittent regime). Cages or enclosures were built, each of which was used for a different treatment: one in which the fish were excluded (FE), one that maintained the basal conditions (Ctrl) and one in which fish were added (BM). The study lasted fifteen days, and ammonia excretion by the fish, the stoichiometry of fish, macroinvertebrates and epilithon, and nutrient uptake by the epilithon were evaluated, taking samples at the end of the experiment. The comparison between sites and treatments showed a higher amount of biomass in the permanent site, but this was less active, due to the accumulation of accessory pigments and of degradation products of chlorophyll, whereas intermittent site epilithon was lower but richer in photosynthetic organisms. Algal biomass loss was found associated with the presence of macroinvertebrates, these being higher in the intermittent site due to the lower density of fish. Finally, the results of this study suggest a negative effect generated by the presence of fish, preventing epilithon rejuvenation and causing the saturation of the milieu