Effects of Agriculture and Hydrological Changes on Macrophyte and Macroinvertebrate Assemblages: a Case Study in Lowland Riverine Wetlands of Argentina

The aim of this study was to investigate the effects of agricultural land use and periods of hydrological variability on the environmental variables, as well as macrophyte and macroinvertebrate assemblages in lowland riverine wetlands. As a case study, we compared two periurban wetlands with intensive agricultural land use against two others with extensive livestock, considered references for the region during a normal and a dry flow period. Nutrient concentrations were significantly higher in agricultural riverine wetlands (total phosphorus and total nitrogen 30% higher). These wetlands exhibited higher relative coverage of floating anchored macrophytes and the absence of submerged vegetation. They showed significantly lower taxonomic richness and 40% lower density of macroinvertebrates, and a higher relative abundance of scrapers and predators. Wetlands of both land uses had a lower total density of macroinvertebrates and a higher abundance of tolerant desiccation taxa in the dry period. Particular differences between land uses, such as lower dissolved oxygen concentrations and lower macroinvertebrate diversity in agricultural wetlands, were found during the dry period. These findings indicate that the differences between land uses seemed to increase during the aforementioned period. Further studies in riverine wetlands of both land uses must be carried on to generalize the results found. Despite this limitation, this study provides evidence of the effects of the surrounding landscape and hydrologic periods in the environmental characteristics, as well as the macrophyte and macroinvertebrate assemblages of the riverine wetlands studied.