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.

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

“…Both microcosm experiments exposed benthic communities to an equitoxic mixture of Cd, Cu, and Zn at six target concentrations bracketing levels previously measured in the Arkansas River [15,19]. Target concentrations of these metals ranged from 0.0 (control) to 10.0 μg Cd/L, 36 μg Cu/L, and 1,200 μg Zn/L in the highest‐treated streams.…”

“…Benthic macroinvertebrate communities for both in situ and stream microcosm experiments (described later) were obtained using methods previously published [6,19,20]. Communities were established on plastic trays (10 × 10 × 6 cm) filled with cobble and pebble substrate and placed at a reference site (AR1; Fig.…”

“…Natural food sources in the streams included seston from Horse‐tooth Reservoir and periphyton and detritus associated with the trays. Previous experiments conducted at the Stream Research Laboratory have examined effects of heavy metals [6,19], acidification [20], ultraviolet‐B radiation [23,24], and stonefly predation [21] on benthic macroinvertebrate communities.…”

Ecological evidence links adverse biological effects to pesticide and metal contamination in an urban Australian watershed

“…There are numerous eco‐epidemiological studies that have investigated causation of altered biological condition in aquatic fauna (Clements et al . ; Haake et al . ; Cormier et al .…”

Prediction of taxon occurrence: a test on taxon‐specific change point values of stream benthic invertebrates

“…life‐cycle time, generation periods or even longer). This is assumed for several groups of riverine organisms, including benthic algae (Fairchild & Lowe, ), macrophytes (Tremp & Kohler, ), fish (Karr et al ., ) and benthic invertebrates (Clements et al ., ). The chemical concentration over certain periods of time is often approximated, e.g.…”