Functional measures as potential indicators of down‐the‐drain chemical stress in freshwater ecological risk assessment

Abstract

Conventional ecological risk assessment (ERA) predominately evaluates the impact of individual chemical stressors on a limited range of taxa, which are assumed to act as proxies to predict impacts on freshwater ecosystem function. However, it is recognized that this approach has limited ecological relevance. We reviewed the published literature to identify measures that are potential functional indicators of down-the-drain chemical stress, as an approach to building more ecological relevance into ERA. We found wide variation in the use of the term "ecosystem function," and concluded it is important to distinguish between measures of processes and measures of the capacity for processes (i.e., species' functional traits). Here, we present a classification of potential functional indicators and suggest that including indicators more directly connected with processes will improve the detection of impacts on ecosystem functioning. The rate of leaf litter breakdown, oxygen production, carbon dioxide consumption, and biomass production have great potential to be used as functional indicators. However, the limited supporting evidence means that further study is needed before these measures can be fully implemented and interpreted within an ERA and regulatory context. Sensitivity to chemical stress is likely to vary among functional indicators depending on the stressor and ecosystem context. Therefore, we recommend that ERA incorporates a variety of indicators relevant to each aspect of the function of interest, such as a direct measure of a process (e.g., rate of leaf litter breakdown) and a capacity for a process (e.g., functional composition of macroinvertebrates), alongside structural indicators (e.g., taxonomic diversity of macroinvertebrates). Overall, we believe that the consideration of functional indicators can add value to ERA by providing greater ecological relevance, particularly in relation to indirect effects, functional compensation (Box 1), interactions of multiple stressors, and the importance of ecosystem context.

Linking freshwater ecotoxicity to damage on ecosystem services in life cycle assessment

“…Processes at the ecosystem level emerge from species' interaction with each other in their food web and with the environment, which often involves transformation of nutrients and energy, generation of the species habitat structures, and maintenance of the species populations ( Truchy et al, 2015 , Faber et al, 2019 , Maltby et al, 2017a , Maltby et al, 2017b ). Dominant processes associated with freshwater ecosystem functioning are nutrient cycling, organic matter transformation, primary productivity, secondary productivity, and ecosystem metabolism ( Harrison et al, 2022 ). A specific process consists of the option of sequestration or detoxification of pollutants influencing water quality in the ecosystem ( Maltby et al, 2021 ).…”

“…Exploiting the relationship between potential functional indicators that are more directly connected to mechanistic processes can help link species loss to ecosystem function loss by assessing how a change in the state related to processes impact rates of processes within the food web. However, changes in multiple interacting functions at the food web level and across different trophic levels are indicated by processes measured at the food web level, such as the flow of energy through the food web ( Harrison et al, 2022 ).…”

“…Combining different functional diversity components, FSD, and functional indicators ( Posthuma and de Zwart, 2014 , Carmona et al, 2016 , Harrison et al, 2022 ) can hence provide a possible starting point in translating species loss to damage on functional diversity. Furthermore, eDNA and sRNA measurements may provide a direct way of measuring species diversity, in addition to getting an insight into the community function dynamics from direct observation of species (biomonitoring data).…”