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<br />SAN BERNARDINO NATIONAL WILDLIFE REFUGE, <br />A CASE STUDY OF ACID RAIN IN THE SOUTHWEST <br />William G. Kepner <br />Environmental Contaminant Specialist <br />U.S. Fish and Wildlife Service, 3616 West Thomas Rd. <br />Suite 6, Phoenix, Arizona 85019. <br />Abstract -- The San Bernardino National Wildlife Refuge was <br />established in 1982 for the protection and management of endangered <br />desert fishes which are indigenous to the Rio Yaqui drainage. The <br />2,309-acre refuge is located on the United States-Mexico border 16 <br />miles east of Douglas, Arizona. Collectively, copper smelter <br />emissions in southern Arizona and northern Sonora have created a <br />regional atmospheric condition where mean annual precipitation pH <br />is 4.7 to 5.0. Background chemistries are largely unavailable and <br />influence of both nonferrous smelter emissions and current <br />agriculture practices and pesticide use remain unexplored. During <br />May through June 1987, water chemistry was determined on-site at <br />each of 13 locations within the refuge (including Leslie Creek) and <br />sediment and selected tissue samples were collected for trace <br />metals and pesticide analysis. Overall, refuge waters were <br />virtually absent of dissolved trace metals and spring chemistries <br />were relatively consistent due to their presumable origin from a <br />common aquifer. Alkalinity exceeded the EPA recommended minimum <br />of 20 mg/l for freshwater aquatic life by a factor of 10 to 18 and <br />appears to be the mitigating factor which disallows acidic <br />deposition to adversely manifest itself in the aquatic ecosystem. <br />Biota are probably the best integrative indicator of watershed <br />quality, and its ability to neutralize acid. Trace metal residues <br />in tissue matrices were mixed in their occurrence, especially for <br />frogs. However, no evidence of acid-stress in resident organisms <br />on the refuge was observed. Native fish populations exhibited no <br />symptoms of lack of recruitment, incident of morphological <br />abnormalities, or subnormal growth. Likewise, bullfrogs flourish <br />through the refuge and exhibited little in regard to trace metal <br />body burdens. Periodic biological and chemical monitoring is the <br />recommended course of action to evaluate refuge condition and trend <br />relative to environmental quality. <br />63