Summary

Description

The San Bernardino National Wildlife Refuge was established in 1982 for the protection and management of endangered desert fishes which are indigenous to the Rio Yaqui drainage. The 2,309acre refuge is located on the United StatesMexico border 16 miles east of Douglas, Arizona. Collectively, copper smelter emissions in southern Arizona and northern Sonora have a created a regional atmospheric condition where mean annual precipitation pH is 4.7 to 5.0. Background chemistries are largely unavailable and influence of both nonferrous smelter emissions and current agricultural practices and pesticide use remain unexplored. During May and June 1987 water chemistry was determined onsite at each of 13 locations within the refuge including Leslie Creek and sediment and selected tissue samples were collected for trace metals and pesticide analysis. Overall, refuge waters were virtually absent of dissolved trace metals and spring chemistries were relatively consistent due to their presumable origin from a common aquifer. Alkalinity exceeded the EPA recommended minimum of 20 mg1 for freshwater aquatic life by a factor of 10 to 18 and appears to be the mitigating factor which allows acidic deposition to adversely manifest itself in the aquatic ecosystem. Biota are probably the best integrative indicator of water shed quality, and its ability to neutralize acid. Trace metal residues in tissue matrices were mixed in their occurrence, especially for frogs. However, no evidence of acidstress in resident organisms on the refuge was observed. Native fish populations exhibited no symptoms of lack of recruitment, incidence of morphological abnormalities, or subnormal growth. Likewise, bullfrogs flourish throughout the refuge and exhibited little in regard to trace metal body burdens. Periodic biological and chemical monitoring is the recommended course of action to evaluate refuge condition and trend relative to environmental quality.