How the structure of a phytophilous chironomid assemblage responds to a lake level drawdown for submerged macrophyte control in a tropical reservoir

Abstract

In hydropower reservoirs, lakes permanently connected to the river present high temporal and spatial stability, what favors the occurrence of macrophytes and a diverse Chironomidae fauna. However, the rapid proliferation of macrophytes causes problems for the diverse uses of the reservoir, being common the application of induced drought to expose the plants to desiccation. In a lake connected to Paranapanema River and under the influence of Salto Grande reservoir, the structure of the Chironomidae fauna associated with the submerged macrophyte Egeria densa was analyzed during an induced drought management to verify its consequences on the fauna structure. One sample was taken before starting the management (Control-C), three during the drought disturbance (1st, 7th and 11th days-DD) and one on the 49th day after the reservoir refilling (flood disturbance-FD). A Principal Coordinates analysis applied to density data of 28 Chironomidae taxa (nine replicates per date) indicated a temporal variation. Eight taxa had high correlation with the ordination, but only three with significant temporal difference in density (higher for Caladomyia in C, Dicrotendipes in FD and Thienemanniella in DD11). A temporal difference was also found for richness and diversity (lower at DD1). The higher values of diversity in the peak of the induced drought and after the refilling emphasize the strong effect on this fauna, with reduction of Caladomyia and increase of Dicrotendipes and Thienemanniella densities. Forty-nine days after refilling (FD), the richness and density did not return to pre-management values, with a distribution of abundance among diferent genera and none expressing dominance.