Crop landscapes reduced taxonomic and functional richness but increased evenness of aquatic macroinvertebrates in subtropical rivers.

Abstract

Human activities altering ecosystems structure and function worldwide strongly affect rivers. We studied aquatic macroinvertebrate communities (taxonomic and functional diversity) from rivers immersed in a forest matrix and rivers flowing through croplands. As rivers of the region experience a monsoon climate, high and low water seasons were also considered and their effect tested. We expected lower taxonomic and functional diversity in rivers flowing through croplands, and also during high water periods. We selected five Piedmont forest and three sugarcane crop rivers in Austral Yungas piedmont forests (Argentina), where marginal vegetation, land use, and hydromorphological variables were studied. Samplings were performed in these 8 sites during high and low water seasons of three consecutive years, totaling 32 samples. We analyzed differences between categories through nonparametric analyses of variance and SIMPER analysis. We studied taxonomic diversity through effective number of species and functional diversity using feeding groups with a factorial ANOVA. We calculated different biotic indices to test differences in water quality. We identified 11,034 specimens from 58 families of aquatic macroinvertebrates. Piedmont forest rivers showed higher richness (order 0) than crop rivers, but diversities of orders 1 and 2 showed the opposite pattern. Functional feeding groups were different between both situations. Season greatly influenced the assemblages, with reduced diversity and abundances during high water periods. Biotic indices showed good water quality, except during high water season for crop sites. A complex response of aquatic communities was found, but generally crop sites were more markedly affected during high water season.