Examining the influence of human stressors on benthic algae, macroinvertebrate, and fish assemblages in Mediterranean streams of Chile.

Changes in land-uses and cover are strong drivers of stream degradation worldwide. In Mediterranean ecoregions, land conversion from forest with native species to tree plantations, agricultural, and urban areas have drastically increased in recent years. Here, we examined the influence of land-use types on water quality (physical and chemical variables) and biota (benthic algae, macroinvertebrates, and fishes). We conducted field surveys between December-March 2016 (dry season) in 24 sites located across four land-use types including native vegetation (NV), tree plantation (TP), agriculture (Ag), and urban (Ur) within the Chilean Mediterranean ecoregion. We calculated metrics and multivariate statistics to assess correlations between biological and environmental variables. Significant differences between land-uses were found for environmental/physicochemical variables and the three biotic groups (i.e., benthic algae, macroinvertebrates, and fishes). We found higher chlorophyll-a biomass for TP, Ag, and Ur compared to NV streams. The macroinvertebrate diversity of sensitive taxa (i.e., Ephemeroptera, Plecoptera, and Trichoptera) and water quality were lower in land draining streams with human uses, other than NV, with the most evident impact found in Ag and Ur streams. NV and TP streams had a lower Diptera density and lower percentage of non-insect taxa. Fish richness and diversity were not affected by land-use. However, cold-water fishes (both native and introduced) were closely associated with NV and TP streams whereas warm-water fishes (mostly introduced) were closely associated with Ag and Ur streams. Multivariate analysis revealed that both local habitat and catchment-scale variables influenced each biological assemblage. Our findings suggest that benthic algae, macroinvertebrates, and fish populations are good indicators of human land-use disturbances, with Ag and Ur areas being the most detrimental for freshwater biota.

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