Testing the Performance of Macroinvertebrate Metrics as Indicators of Changes in Biodiversity After Pasture Conversion in Patagonian Mountain Streams

摘要

Conversion of native forest to pastures is a common practice worldwide; it has complex effects on river biota that are related to activity type and intensity. This work was conducted in order to evaluate the effects of cattle grazing on environmental features and to select the most appropriate measures based on the macroinvertebrate community as indicators of ecological changes. Physicochemical features, riparian ecosystem quality, habitat condition, and benthic macroinvertebrates were investigated in streams draining pastures and were compared to reference streams located in nonimpacted native forested catchments. Strong evidence of sediment deposition was observed at pasture streams, which had higher percentage of sand in the streambed but also increased levels of suspended solids. Pasture sites had significantly higher water temperature and conductivity as well as lower dissolved oxygen concentrations than did forested sites. Both riparian quality and in-stream habitat condition were degraded at pasture sites. Among metrics, total richness, Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness, Plecoptera richness, Shannon diversity, percentage of dominant taxon, percentage of Chironomidae species, shredder richness, and percentage of predator resulted to be the most consistent measures by displaying stronger responses to impairment. Our results suggest that forest conversion to pasture for livestock practices is diminishing macroinvertebrate biodiversity and potentially changing functioning and dynamics of Patagonian mountain streams as well. Damage prevention on riverine landscapes by restoring riparian ecosystems, replanting missing vegetation in buffer areas, and limiting livestock access to the riverbanks could contribute to enhance the ecological integrity at converted areas. A more extended and comprehensive use of macroinvertebrate metrics could contribute to better understand and evaluate impact effects of these extended land use activities and to promote conservation strategies.