Integrating Observational and Experimental Approaches to Demonstrate Causation in Stream Biomonitoring Studies

Abstract

Routine biomonitoring of aquatic ecosystems generally is performed with the intent of demonstrating a causal relationship between stressors and responses. However, because it is impossible to eliminate other potential explanations for observed spatiotemporal correlation between stressors and responses, demonstrating causal relationships is highly tenuous in descriptive studies. In this research we show how results of descriptive and experimental approaches can be integrated to demonstrate a causal relationship between heavy metals and benthic community responses in a Rocky Mountain stream (CO, USA). By using a stressor identification process, we show that effects and exposure data collected from a contaminated site (Arkansas River, CO, USA) can be integrated with experimental data to support causal arguments. Analysis of the spatial co-occurrence of metals and benthic community responses in the Arkansas River provided support for the hypothesis that metals caused alterations in benthic community structure. Exposure pathways were quantified by measuring metal bioaccumulation in caddisflies (Trichoptera) collected upstream and downstream from metal inputs. A long-term (10-year) monitoring study showed that reductions in metal concentrations corresponded with improvements in benthic communities. These results were supported by microcosm and field experiments that quantified concentration-response relationships between heavy metals and benthic community composition. Consistency of these responses was demonstrated by comparing results to a spatially extensive survey of metal-polluted streams in Colorado. Our study demonstrates the power of integrating descriptive and experimental approaches for developing causal arguments in ecological assessments.

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.…”

Environmental and spatial processes determining Ephemeroptera (Insecta) structures in tropical streams

“…The higher percentage of variation in Ephemeroptera community structures explained by environmental factors could be due to the high sensitivity of the taxa to many contaminants (Clements et al, 2002) and to physical changes of the system (Buss et al, 2002;Shimano et al, 2010). In addition, there are also reports of the influence of temperature, substrate type and speed of water flow on Ephemeroptera (Brittain, 1982).…”

Assessing contaminated sediments in the context of multiple stressors

“…This includes a greater focus on ecologically relevant endpoints not traditionally used in ecotoxicology, such as predator-prey interactions, drift, preference-avoidance, and other behavioral measures. These endpoints have been shown to be more sensitive than mortality, growth, or reproduction measures of sediment toxicity and habitat degradation due to uncontaminated fine sediments [3,6,181,[239][240][241][242]. In food webs with organisms interacting strongly through predatory or competitive relationships, indirect effects of contamination will arise [6,243].…”