Response of stream ecosystem function and structure to sediment metal: Context-dependency and variation among endpoints

Abstract

Physicochemical and ecological attributes of ecosystems (i.e., environmental context) can modify the exposure and effects of metals, which presents a challenge for ecosystem management. Furthermore, the functional and structural attributes of an ecosystem may not respond equally to metals or be uniformly responsive to environmental context. We explored how physicochemical and ecological context modified sediment metal dose-response for a suite of functional and structural measures. Two sediments with high (HB) and low (LB) acid volatile sulfide and organic carbon content (i.e., physicochemical context) were amended with copper and nickel to establish a gradient of treatments from non-toxic to potentially toxic. Sediments were deployed in each of two streams (i.e., ecological context), incubated for four weeks, and measured for sediment microbe, biofilm, and macroinvertebrate dose-response to metal. The dose-response of microbial function was affected by physicochemical context, with cotton decomposition negatively related to sediment metal only on LB sediments. The abundance of invertebrates from the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) responded negatively to sediment metal only on LB sediments; however, this dose-response was only observed in one stream, likely because of greater abundance of sensitive EPT taxa (i.e., Baetidae and Ephemerellidae). Biofilm structure was negatively affected by sediment metal in only one stream and there was no difference in dose-response between the two sediment types. Biofilm function was affected by sediment type and stream; production by biofilms exposed to HB sediment was negatively related to sediment metal in only one stream. In all, the majority of our endpoints exhibited responses that were modified by environmental context; however, each component of the ecosystem exhibited unique context dependency. For management of sediment metals, an understanding of context dependency is useful for informed decision-making, but the application of simple contextual filters are unlikely to protect all elements of an ecosystem.

Macroinvertebrate responses to nickel in multisystem exposures

“…The GCsed experienced the most Ni loss over time, followed by WDsed and BCsed. Nickel flux and other sediment chemical results were similar to those observed in previous Ni studies [12,[38][39][40]. The WDsed experienced some of the highest Ni concentrations but the lowest Ni loss over time.…”

“…In addition, several studies have demonstrated that benthic invertebrates respond negatively to increasing Ni in sediments. These Ni effects have suggested that loss of populations and community structure changes can alter ecosystem function . In the present streamside mesocosm study, several benthic macroinvertebrate community indices and metrics responded negatively to increasing bioavailable Ni (SEM Ni /AVS models).…”

Recovery of a mining-damaged stream ecosystem

“…While only a fraction of the metal present in sediments is bioavailable at any one given time due to binding to particulate organic carbon and iron and manganese oxyhydroxides and sediment burial (Costello and Burton, 2014), trace contaminants associated with sediments will remain in the riverfloodplain system and be subject to remobilization until stored deposits become depleted (Hamilton, 2012;Moore and Langner, 2012).…”

A novel method to assess effects of chemical stressors on natural biofilm structure and function

“…The exponential decline in biomass and primary production was confirmed with a likelihood ratio test comparing the regression model to an ANOVA model (χ 2 < 2.2, P > 0.09). These data suggest that the current understanding of sediment metal toxicity, which is based on macroinvertebrate and fish responses, may not be appropriate for predicting biofilm responses (Costello & Burton, ). Snail feeding rates were highly variable and showed marginally significant response to metal dose.…”