EFFECT OF UNDERLYING HYDROTHERMALLY ALTERED BEDROCK ON THE BENTHIC AND HYPORHEIC INVERTEBRATE COMMUNITY STRUCTURE IN CABRESTO CREEK, NEW MEXICO

摘要

The Red River watershed of Taos County, New Mexico, is underlaid in part by hydrothermally altered granitic bedrock, including stockwork veins of metal sulfide deposits. Erosion has exposed ``scars'' of this weathered, altered material along the watershed ridges above the mainstem Red River. Precipitation brings acid rock drainage (high sediment loads and toxic by-products of metal sulfide decomposition) into the Red River, negatively impacting the water quality, substrate, and aquatic community of the stream. A tributary to the Red River, Cabresto Creek, is also underlaid in part by hydrothermally altered granitic bedrock but has little erosion. I collected data on water quality, sediment, and the benthic and hyporheic invertebrate communities from 2005 to 2009 at sites along Cabresto Creek to assess the potential effect of the underlying geology in the absence of erosion. Statistically significant differences in both density and taxa richness existed among sites in both communities; however, values for density and taxa richness recovered to upstream levels at sites downstream of the zone of hydrothermal alteration in the hyporheic community, but only to a limited extent in the benthic community. Smaller sediment grain sizes and lower dissolved oxygen concentrations in the hyporheic within the zone of hydrothermal alteration may have restricted recruitment to the benthic community. These effects continued downstream, possibly due to drift. The results suggest that the underlying geology might affect the benthic and hyporheic invertebrate communities in Cabresto Creek even in the absence of eroded hydrothermal scars in the watershed.