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Derivation of a benchmark for freshwater ionic strength
Susan M Cormier1, Glenn W Suter, Lei Zheng
1National Center for Environmental Assessment, U.S. Environmental Protection Agency, Cincinnati, Ohio, USA.
Environmental Toxicology and Chemistry
|November 20, 2012
Summary
Establishing aquatic life benchmarks for specific conductance is crucial for managing freshwater streams impacted by increased ionic strength from surface coal mining. A new benchmark of 300 µS/cm aims to prevent species extirpation in affected waters.
Area of Science:
- Environmental Science
- Aquatic Ecology
- Ecotoxicology
Background:
- Increased ionic strength in freshwater streams, often from surface coal mining effluents, causes ecological harm.
- Resource management requires clear thresholds to mitigate these deleterious effects.
Purpose of the Study:
- Develop an aquatic life benchmark for specific conductance to protect benthic invertebrates in neutral to alkaline waters.
- Establish a threshold to prevent the local extirpation of 95% of species.
Main Methods:
- Estimated extirpation concentrations of specific conductance using presence/absence data of benthic invertebrate genera from 2,210 West Virginia stream samples.
- Calculated the 95th percentile of genus occurrence probability relative to specific conductance.
- Determined the 5th percentile of the species sensitivity distribution for 163 genera.
Main Results:
- The proposed benchmark for specific conductance is 300 µS/cm in regions with a background conductivity of 116 µS/cm.
- This benchmark represents the 5th percentile of extirpation concentrations for 163 benthic invertebrate genera.
Conclusions:
- The 300 µS/cm benchmark may not fully protect all genera, particularly sensitive species or those in exceptional waters.
- The benchmark focuses on preventing extirpation, not just abundance reduction, offering a critical but not absolute level of protection.
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