The use of in situ and stream microcosm experiments to assess population‐ and community‐level responses to metals

Abstract

We conducted field and stream microcosm experiments to assess population-level (density, size distribution) and community-level (species richness metrics, multivariate analysis of community composition) responses of macroinvertebrates to heavy metals in the Arkansas River, a mining-polluted stream in Colorado, USA. Experiments were conducted in spring and summer to coincide with early and late developmental stages (i.e., instars) of the mayfly Rhithrogena hageni. Results of field experiments showed significant mortality at metal-contaminated sites during summer when mayfly populations were dominated by small, early instars (mean dry wt = 0.13 mg). In contrast, no significant mortality was observed in spring when organisms were larger (mean dry wt = 1.78 mg). Multivariate analyses based on abundance of dominant taxa clearly separated reference and metal-impacted stations in summer experiments but showed little separation in spring. We observed no significant effects of metals on species richness, number of mayfly species, or EPT (species richness of Ephemeroptera, Plecoptera, and Trichoptera) in.either field experiment. Using stream microcosms, we established concentration-response relationships between heavy metals and R. hageni density, species richness, mayfly richness, and EPT. Density of R. hageni was generally more sensitive to metals than measures of species richness, and summer populations of R. hageni were more sensitive to metals than spring populations. Because the presence of large, relatively tolerant individuals in spring coincided with periods of higher metal concentrations, R. hageni was protected from toxic effects in this system. We conclude that phenology and developmental stage are important factors influencing responses of some aquatic macroinvertebrates to metals. Thus, timing bioassessments to coincide with the presence of these sensitive life stages can improve our ability to detect subtle contaminant effects.

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.…”

How do aquatic communities respond to contaminants? It depends on the ecological context

“…Winner et al [44] observed seasonal variation in the sensitivity of zooplankton communities to Cu exposure. Similarly, mesocosm experiments conducted with macroinvertebrate communities showed that summer communities, which were dominated by smaller, early instars of aquatic insects, were more sensitive to metals than communities collected in late spring [45], which were dominated by larger individuals. These investigators suggested that phenology and life history characteristics of sensitive resident species should be considered when designing biomonitoring programs and establishing water quality criteria.…”

Biomonitoring: An appealing tool for assessment of metal pollution in the aquatic ecosystem

“…The concentration-response relationships between heavy metals and R. hageni density, species richness, mayfly richness and EPT were established, wherein different sensitivities might exist due to the phenology and developmental stage influencing responses of some aquatic macroinvertebrates to metals. Timing bioassessments to coincide with the presence of these sensitive life stages can improve the ability to detect subtle contaminant effects [122]. The taxa richness for aquatic benthic insect community can be used to indicate the impact of acid mine drainage in a tropical Asia stream [123].…”