Wednesday, May 28, 2008 - 9:30 AM
375

Effect of underlying hydrothermally altered bedrock on aquatic invertebrate community structure and function in Cabresto Creek, New Mexico, USA

Grant De Jong and Lee Bergstedt. GEI Consultants, Inc., Chadwick Ecological Division, 5575 S. Sycamore St., Ste. 100, Littleton, CO 80120

Hydrothermally altered bedrock underlies the Red River watershed in northern New Mexico.  On the mainstem, weathering and natural erosion have exposed denuded scars on the mountain faces, which erode with precipitation and affect the water quality and fauna of the Red River through natural acid rock drainage.  Cabresto Creek, tributary to the Red River, also traverses hydrothermally altered bedrock but has no eroded scars in its basin obviously impacting water quality.  From 2005–2007, aquatic invertebrates were sampled at sites bracketing the altered bedrock to determine if there is an effect on the community in the absence of hydrothermal scarring.  The data indicate that the altered bedrock impacts total benthic invertebrate density, taxa richness, and functional group composition.  Analysis of the hyporheic community, water quality samples, and sediment grain size indicated that slight acidification of the hyporheic water and a higher proportion of fine sediments appear to affect the density and taxa richness of the hyporheic community and may further play a part in the effects on the epibenthic community in Cabresto Creek.  These results suggest that aquatic invertebrate communities in the Red River might have been affected by hydrothermally altered bedrock even if erosion had not exposed the scars.


Web Page: epibenthic community, hyporheic community, acid rock drainage

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