Effects of land-use activities in the Ayuquila river´s fauna

Land use change is an important human force causing modifications in the structure and quality of freshwater ecosystems worldwide. Multiple stressors have affected the Ayuquila-Armeria River in Jalisco, the third largest rivers and second in biodiversity in that Mexican state. Despite an on-going monitoring program focused on water quality, no evidence exists on how land use activities have affected its aquatic communities. I characterized the invertebrate and fish communities using the functional feeding group approach. Abundance, functional diversity, richness, and pollution tolerance were compared spatially and temporally using various multivariate metrics and were related to water chemical variables. Stable carbon and nitrogen analyses, and trace metal characterization were performed to biological and sediment samples from 17 sites in this River to determine sources of organic matter and to look for associations with surrounding land uses. Filter and gatherer collector invertebrates and fish omnivores dominated the community composition, which reflected the amount of suspended sediments in the water column. The presence of exotic species, fecal coliforms and total nitrogen above Mexican guidelines, were additional evidence of disturbance that contrasts the quality given by biotic indices. Spatial differences in diversity and composition were significant between agricultural and forested sites. Surrounding agricultural vegetation did not influence the d13C values in river components which were influenced by either riparian vegetation or autochthonous carbon sources, while d15N values in sediment and animal tissues confirmed the influence sewage and animal-derived organic matter has in the river's structure. Metal concentrations were site and season dependent; concentrations in invertebrates were higher than those from forested sites. Concentrations of Cd, Cu, Pb, and Mn were associated to urban and mine runoff.