THE STREAM ENVIRONMENT 185 



dissolved solids in Trout Creek (Table 2). Increases in hardness and 

 soluble salts may, within limits, result in increased productivity, 

 especially in western streams, which often originate in mountainous 

 regions of insoluble crystalline rock. Downstream increases in 

 specific conductance in Trout Creek were correlated with increases in 

 the density (r = 0.9) and biomass (r = 0.8) of macroinvertebrates. 



Sedimentation and Macroinvertebrates 



Coal-mine drainage often results in the production of ferric 

 hydroxide, which is insoluble and forms a yellow— orange precipitate 

 on the stream substrate (Wentz, 1974). This did not occur in Trout 

 Creek, which had relatively low iron concentrations. Inorganic 

 sediment from erosion of surfaces exposed by mining may also cover 

 the substrate. Apart from any toxic effects, sedimentation decreases 

 substrate heterogeneity, fills interstices with silt, may severely reduce 

 algal populations, and directly affects the benthos (Ward, 1976). The 

 presence of a strip of unmined land between the mine spoils and 

 Trout Creek, in combination with the semiarid climate of the region, 

 is apparently largely responsible for the maintenance of a heteroge- 

 neous and relatively silt-free substrate. 



Climate, Groundwater, and Stream Flow 



Climatic differences between western and eastern mining regions 

 undoubtedly modify effects on stream ecosystems. Differences in 

 leaching efficiency between xeric and mesic regions have already 

 been referred to. Herricks and Cairns (1974) stressed the importance 

 of relationships between stream flow and mine drainage. The 

 apparent lack of adverse effects of Edna Mine drainage on Trout 

 Creek macroinvertebrates may result in part from a hydrologic 

 situation in which most substances enter the stream during a 

 relatively short period associated with high stream flow. For 

 example, over 80% of the total salt input from the mine occurs 

 during April, May, and early June. 



In summary, effects of mining on stream ecosystems in the 

 western United States are different in many ways from those in 

 eastern states. Acid mine drainage and ferric hydroxide precipitates 

 are rarely associated with coal mines in western energy-development 

 areas, partly because of the low sulfate content of western coal. 

 Alkaline, highly buffered waters prevent the formation of acid 

 conditions, even where sulfate values 2ire high, and reduce the 

 solubihty of heavy metals. Water depletion, sedimentation, and 

 increased salinity are the major potential problems associated with 

 western mining. 



