Heavy Metals Structure Benthic Communities in Colorado Mountain Streams

Abstract

The development of field sampling designs that employ multiple reference and polluted sites has been proposed as an alternative to the traditional upstream vs. downstream approach used in most biomonitoring studies. Spatially extensive monitoring programs can characterize ecological conditions within an ecoregion and provide the necessary background information to evaluate future changes in water quality. We measured physicochemical characteristics, heavy‐metal concentrations, and benthic macroinvertebrate community structure at 95 sites in the Southern Rocky Mountain ecoregion in Colorado, USA. Most sites (82%) were selected using a systematic, randomized sampling design. Each site was placed into one of four metal categories (background, low, medium, and high metals), based on the cumulative criterion unit (CCU), which we defined as the ratio of the instream metal concentration to the U.S. Environmental Protection Agency criterion concentration, summed for all metals measured. A CCU of 1.0 represents a conservative estimate of the total metal concentration that, when exceeded, is likely to cause harm to aquatic organisms. Although the CCU was less than 2.0 at most (66.3%) of the sites, values exceeded 10.0 at 13 highly polluted stations. Differences among metal categories were highly significant for most measures of macroinvertebrate abundance and all measures of species richness. We observed the greatest effects on several species of heptageniid mayflies (Ephemeroptera: Heptageniidae), which were highly sensitive to heavy metals and were reduced by >75% at moderately polluted stations. The influence of taxonomic aggregation on responses to metals was also greatest for mayflies. In general, total abundance of mayflies and abundance of heptageniids were better indicators of metal pollution than abundance of dominant mayfly taxa. We used stepwise multiple‐regression analyses to investigate the relationship between benthic community measures and physicochemical characteristics at the 78 randomly selected sites. Heavy‐metal concentration was the most important predictor of benthic community structure at these sites. Because of the ubiquitous distribution of heavy‐metal pollution in the Southern Rocky Mountain ecoregion, we conclude that potential effects of heavy metals should be considered when investigating large‐scale spatial patterns of benthic macroinvertebrate communities in Colorado's mountain streams.

An integrative assessment of environmental degradation of Caveira abandoned mine area (Southern Portugal)

“…Thus, exceeding the conservative estimation of the total metal concentration likely to cause harm to aquatic organisms (Clements et al, 2000). The CCU scores decreased from upstream to downstream in the three sampling seasons (Table 4; Fig.…”

“…As the criterion values are only available for individual elements, alternative models are necessary to estimate toxic effects of metal mixtures, hence the derivation of the CCU was used (Clements et al, 2000). The EPA metal thresholds considered are based on toxicity tests of species from different trophic levels, including macroinvertebrates (Hirst et al, 2002).…”

“…This criterion has been already applied to analyse the response of different organisms to metals in streams (Clements et al, 2000;Hickey and Golding, 2002;Hirst et al, 2002). The authors have followed the USEPA chronic criterion values for Al (87 μg L −1 ), Fe and Mn (1000 μg L −1 ), whilst the criterion values for Ag (1.…”

Impacts of Copper on a Lotic Benthic Invertebrate Community: Response and Recovery

“…Reductions in mayfly taxa (Clements et al 2000), shifts in community dominance from intolerant taxa to Chironomidae (Winner et al 1980), and community changes such as reduction in species richness or abundance (Clements et al 1992, Schultheis et al 1997) have been reported. Studies have looked at impacts from multiple heavy metals (Clements and Rees 1997), as well as specific contaminants such as copper (Leland, et al 1989).…”

“…Because of this, many of these systems studied had been impacted by metals for decades prior to sampling, preventing comparisons to a preimpact community. A few researchers have dosed experimental streams to examine effects, and some studies have examined recovery using upstream reference sites (Nelson and Roline 1996) or reference streams within the watershed (Clements et al 2000). Wallace (1990) suggested that many studies looking at recovery take place only after the impact has occurred and that manipulating individual streams might address pretreatment or reference comparisons.…”