Small‐scale Experiments Support Causal Relationships Between Metal Contamination and Macroinvertebrate Community Responses

Abstract

Routine biomonitoring studies that compare abundance of benthic macroinvertebrates upstream and downstream from contaminant discharges generally cannot be used to demonstrate causal relationships between stressors and biological responses. In this study I describe stream microcosm and field experiments designed to support results of a 12-year monitoring project in the metal-polluted Arkansas River, Colorado. Microcosm experiments established concentration-response relationships between heavy metals and several structural (abundance, richness) and functional (macroinvertebrate drift, community respiration) endpoints. EC 10 values, the metal concentration that reduced abundance or richness by 10%, were generally lowest for mayflies and stoneflies, indicating greater metal sensitivity for these groups. Macroinvertebrate drift and community respiration showed highly significant concentration-response relationships with heavy metals and were generally more sensitive than structural measures. Potential interactions among metals were investigated by comparing community-level responses to Zn alone, ZnϩCd, and ZnϩCuϩCd. Results showed that macroinvertebrate responses to a mixture of three metals were generally greater than responses to either Zn alone or ZnϩCd. Long-term monitoring in the Arkansas River (Colorado) before and after remediation of metal inputs provided correlative evidence that elevated heavy metal concentrations altered community composition and reduced abundance of metal-sensitive organisms. However, these field data were not especially useful for estimating safe concentrations of heavy metals that would be protective of benthic communities. Microcosm and field experiments provided further support for the hypothesis that metals caused alterations in benthic community structure and provided more precise estimates of safe metal concentrations.

Aquatic insect ecophysiological traits reveal phylogenetically based differences in dissolved cadmium susceptibility

“…Our studies identified the genus Ephemerella and two heptanegiid mayflies as being particularly susceptible to dissolved Cd. These findings give mechanistic support to observations that these taxa are consistently absent from metal-contaminated habitats in nature (40) and are consistently more sensitive to metals in sophisticated toxicity tests (39)(40)(41). The presence of a relatively strong phylogenetic signal associated with the integrated trait of ''sensitivity to dissolved Cd'' suggests that sensitivity to metals may eventually be predictable on the basis of phylogenetic position, as described above.…”

The use of invertebrate body burdens to predict ecological effects of metal mixtures in mining-impacted waters

“…The present study used metrics of invertebrate taxa richness which are generally considered to be sensitive indicators of metal pollution (Hickey andClements, 1998 andClements, 2004).…”

The Cost of Tolerance: Sensitivity of Stream Benthic Communities to Uv-B and Metals

“…Long-term exposure to heavy metals in the Arkansas River has significantly altered composition of benthic macroinvertebrate communities (Clements 2004). Although the Arkansas River system is open to immigration from non-polluted sites such as the West Tennessee Creek, there are differences in the occurrence of metaltolerant and metal-sensitive species between sites.…”