Acid mine drainage impact and recovery shown by long-term monitoring of benthic macroinvertebrates in Sierra Nevada streams of the Leviathan mine watershed Dave Herbst Sierra Nevada Aquatic Research Laboratory Central Sierra Nevada South of Lake Tahoe
Superfund Site: sulfur mine operating mainly from 1952-1962 showing open pit remnant and treatment ponds BIOLOGICAL INDICATORS of AMD: STREAM INVERTEBRATES >Diversity of life present, esp. of sensitive insects = EPT >Varied sensitivity to chemical and metals pollution >Density of types present reflect response & food web function >Comparisons of AMD-exposed sites to references/controls
stoneflies
caddisflies
mayflies
midge Schematic: AMD-Exposed and Reference Monitoring Stations
• Stations located Aspen Leviathan Creek along gradient of Creek distance from mine external site source area watershed MINE • Reference stations reference Mountaineer SITE streams located above mine Creek site and adjacent Bryant drainages without Creek mining influences Elevation 1800-2200 m
East Carson River How has AMD been controlled at Leviathan? • Liming: neutralize pH, precipitate metals • Microbial bioreactor: reverse pyrite oxidation Exposure to Acid Mine Drainage: expressing [metals] as expected toxicity = CCU Cumulative Criterion Units
• Metals present: Al, Fe, Ni, Se, As, Cu, Mn, Zn
• CCU = 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 ∑𝑎𝑎𝑙𝑙𝑙𝑙 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝐸𝐸𝐸𝐸𝐸𝐸 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 • CCU = 1 is the expected chronic exposure sum of metals that would cause biological impairment • Log CCU of 1 = 0 for graphs to come….. Flows, Treatment, Load A. Hydrograph > B. Remedial Treatments C. Relative Metals Load
• High flows 2005-06 and in 2011 • Drought 2012-15 and in 2007 • Improving capture and lower loads over time except high flow (note log scale) Log Scale History of AMD control and exposure by site
3.0 06 - 2.5 11 - 2005 2.0 2010 1.5
1.0
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-0.5 Log CCU sum of metals -1.0
-1.5
-2.0 <1998-2015> <1998-2015> <1998-2015> <1998-2015> <1998-2015> <1998-2015> -2.5
source >> < downstream > << source reference Bio-monitoring Trends (reference line in red): Total but not EPT richness recovered at most sites Seasonal recovery and relapse
TOTAL Fall = filled symbols
Spring = open symbols
Reference …….. 10th percentile
EPT Pattern seen in most years unless AMD was severe (Early years or failed capture) Trophic Structure (Food Web) By Site
• Grazers most depleted group • Collector-gatherer midges dominate AMD exposed sites Similarity of communities among sites and times All Data for Leviathan above Mountaineer Relative to Grouping of all Reference Sites
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-1.5 -4 -3 -2 -1 0 1 2 Fall 1998
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-1.5 -4 -3 -2 -1 0 1 2 Spring 1999
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Take home message: fall-spring recovery-relapse and stabilization over time Summary • Remediation actions are reducing metal load • Recovery is progressing within downstream areas reaching the reference condition of health • Upstream areas (nearer mine) show signs of recovery after treatment periods but relapse after overwinter periods without capture/treatment • High flow years tend to amplify metals load • Stable communities become instable in AMD • Species composition has progressed to within the range of reference stream communities of aquatic invertebrates • Year-around capture/treatment is needed for complete recovery of ecological health at all sites
Thresholds of CCU effects depend on the metric, the analysis method, and the metals mix
• Example here is EPT Richness Diversity • 10th %tile reference is accepted as unimpaired, criterion is the 90th %tile meeting that standard • Changepoint analysis divides data to minimum variance within-groups relative to overall variance • Segmented or piece-wise regression shows change in slope Communities transition between stable and instable states with metals exposure
Ordination scores of community similarity show increased scatter as AMD metals exposure increases Community reassembly responses frame the theoretical EPA standard of CCU=1 Summary • Remediation actions are reducing metal load • Recovery is progressing within downstream areas reaching the reference condition of health • Upstream areas (nearer mine) show signs of recovery after treatment periods but relapse after overwinter periods without capture/treatment • High flow years tend to amplify metals load • Stable communities become instable in AMD • Metric sensitivity shows phased sequence of community recovery as CCUs are reduced • EPA criteria for predicting impact are consistent with the observed range of thresholds for recovery Community reassembly responses frame the theoretical EPA standard of CCU=1 Leviathan Creek – central Sierra Nevada test and reference monitoring stations