Effect of shifts in habitats and flow regime associated to water diversion for agriculture on the macroinvertebrate community of a small watershed

Abstract

Water abstraction for irrigation has an important effect on stream organisms in general and aquatic macroinvertebrates in particular. The alteration of flow modifies the habitat conditions and creates important ecological constraints for many of these animals, so shaping the communities and affecting their diversity. With the aim to assess the impact of flow and habitat changes due to water abstraction for agriculture on the macroinvertebrate community of a Mediterranean stream, we characterized physicochemically three sampling sites representing three habitat types and collected the macroinvertebrate assemblage of each one. The three sites were a spring, an irrigation ditch 90 m downstream from the spring that diverge all the water from the natural channel and return it downstream, and a site after an area of agriculture 500 m downstream of the spring. Our hypothesis was that the highest diversity would be found in the irrigation ditch, where conditions were more constant along the year and that could act as a refuge for some organisms, followed by the spring and, afterwards, the downstream site, which would have a very poor community. Nonetheless, although our results showed that the irrigation ditch had the highest values of diversity, the spring and the downstream site did not differ significantly. When analysing the effect of the measured physicochemical parameters on macroinvertebrate communities, the most important was discharge. Thus, our study underlines the effect that water diversion may have on the macroinvertebrate communities even at a small watershed scale.