Dataset for: Long-term effects and recovery of streams from acid mine drainage and evaluation of toxic metals threshold ranges for community re-assembly

Monitoring of benthic invertebrates in streams receiving acidic metal-contaminated water over 18-years revealed both degraded conditions and recovery along a network of downstream locations. Compared to reference streams, and over the course of clean-up remediation efforts below an abandoned open-pit sulfur mine in the central Sierra Nevada (California), improving water quality was accompanied by recovery of benthic communities at some sites. Years of high flow resulted in degraded biological status when acid mine drainage capture was incomplete and metals loading had increased with runoff. Seasonal patterns of recovery evident in fall after the summer treatment season, reverted in the following spring after overwinter periods when sources were not captured. As the metals load has been reduced, phased recovery of community structure, function, and similarity progressed toward that of reference assemblage taxonomic composition. From impacted communities dominated by relatively tolerant midges, reassembly involved an increase in density, return of long-lived taxa, an increased ratio of sensitive/tolerant forms, followed by overall diversity and community composition, and eventually large predators and grazers reappear along with mayfly, stonefly, and caddisfly richness. Threshold effect levels defined using various analysis methods showed the response range of biological indicators corresponds to EPA guidelines of predicted effects using cumulative criterion units of metals toxicity (i.e., CCU ~1). All sites have shown improved function as increased density of some or all trophic groups over time. Although recovery is progressing, year-around treatment may be necessary to fully restore biological integrity in streams nearest the mine.