Perspectives on the context‐dependency of stream community responses to contaminants

Abstract

SUMMARY1. Natural variation in the structure and function of aquatic communities along environmental or spatiotemporal gradients can influence how systems respond to biotic and abiotic disturbances. Although these context-dependent responses are a well-established element of basic ecology, they have received little attention from an ecotoxicological perspective. 2. As the scope of freshwater bioassessment expands from single catchments to broad-scale, regional surveys, it has become apparent that community responses to contaminants can vary significantly among locations. This variability is generally considered a nuisance and an impediment to recognising ecological patterns; however, natural spatiotemporal variation in communities also provides opportunities to test hypotheses about context-dependent responses to contaminants in aquatic ecosystems. 3. This study presents three examples of context-dependent responses of benthic stream communities to contaminants. We show how longitudinal variation in community composition, the development of tolerance to contaminants and exposure to multiple stressors influence the historical context of a community and hence may determine community responses to contaminants. 4. Aquatic ecotoxicologists have made significant progress identifying abiotic factors that influence contaminant bioavailability and toxicity. A similar effort could be undertaken to identify specific ecological factors (e.g. community composition, natural disturbance regimes and life-history characteristics) that contribute to variation in susceptibility of communities to contaminants. Understanding the nature of context-dependent responses and the mechanisms responsible for variation among communities should be a key element of ecological risk assessment and a research priority in ecotoxicology.

Fostering integration of freshwater ecology with ecotoxicology

“…Yet, the idea of context-dependent responses has received little attention in ecotoxicology (Merriam et al, 2013;Dinh Van et al, 2013). Clements et al (2016) provide a fresh perspective on the importance of context-dependency of stream communities to predict impacts of chemical contaminants. The three examples they present highlight how longitudinal variation in community composition, the development of community tolerance and exposure to multiple stressors influence stream invertebrate communities and thus community responses to contaminants.…”

Humic acid can mitigate the toxicity of small copper oxide nanoparticles to microbial decomposers and leaf decomposition in streams

“…Exposure to ionic copper (Duarte, Pascoal & C assio, 2009) or nanoCuO (Pradhan et al, 2011) reduces rates of microbial leaf decomposition and fungal species richness in stream microcosms, but no information is available on how effects may vary with nanoparticle size and the presence of DOM. This context dependency is an important factor to consider in assessments of contaminant effects on ecosystems (Clements et al, 2015).…”

Are drivers of microbial diatom distributions context dependent in human‐impacted and pristine environments?

“…Stream diatoms are simultaneously affected by abiotic and biotic forcing, the relative importance of which differ among sites and regions (Clements et al. ). For instance, the occurrence of Frustulia rhomboides , a species often classified as acidophilus, that is occurring at pH < 7 (Van Dam et al.…”

“…Recently, growing evidence of context dependency in species responses toward environmental and spatial factors have been documented among stream organisms (for example, diatoms [Heino et al 2012], bryophytes [Heino et al 2012], and macroinvertebrates [Heino et al 2012, Hawkins et al 2015, Tonkin et al 2016). Stream diatoms are simultaneously affected by abiotic and biotic forcing, the relative importance of which differ among sites and regions (Clements et al 2015). For instance, the occurrence of Frustulia rhomboides, a species often classified as acidophilus, that is occurring at pH < 7 (Van Dam et al 1994, Weckstr€ om et al 1997b, was affected mainly by pH in pristine sites (relative importance = 32%).…”