Macroinvertebrates drift on two stations with different degree of disturbance, Gaira river, Santa Marta – Colombia

Abstract

The aim of this work was to evaluate the spatial variation of the macroinvertebrate biomass and density drift on two stations with different degree of disturbance (flow regulated and higher sediment amount in one of them) in the lower basin of Gaira River (Santa Marta, Colombia). We carried out three surveys per station using drift nets during 24-hour periods, collecting samples each four hours. We found differences on abundance-, biomass- and drift density between sites and samples, where the less disturbed station had the higher values. The daily variation of drift was highest at night. Leptohyphidae, Chironomidae, Hydropsychidae and Elmidae were the most abundant drifting taxa. The differences can be related to river flow variability and sediment transport, in spite of the marginal value of both magnitude and frequency of the disturbance.