Abstract
Streams and rivers provide important services to humans, and therefore, their ecological integrity should be a societal goal. Although ecological integrity encompasses structural and functional integrity, stream bioassessment rarely considers ecosystem functioning. Organic matter decomposition and ecosystem metabolism are prime candidate indicators of stream functional integrity, and here we review each of these functions, the methods used for their determination, and their strengths and limitations for bioassessment. We also provide a systematic review of studies that have addressed organic matter decomposition (88 studies) and ecosystem metabolism (50 studies) for stream bioassessment since the year 2000. Most studies were conducted in temperate regions. Bioassessment based on organic matter decomposition mostly used leaf litter in coarse-mesh bags, but fine-mesh bags were also common, and cotton strips and wood were frequent in New Zealand. Ecosystem metabolism was most often based on the open-channel method and used a single-station approach. Organic matter decomposition and ecosystem metabolism performed well at detecting environmental change (≈75% studies), with performances varying between 50 and 100% depending on the type of environmental change; both functions were sensitive to restoration practices in 100% of the studies examined. Finally, we provide examples where functional tools are used to complement the assessments of stream ecological integrity. With this review, we hope to facilitate the widespread incorporation of ecosystem processes into bioassessment programs with the broader aim of more effectively managing stream and river ecosystems.
Highlights
Streams and rivers provide important services to humans, and their ecological integrity should be a societal goal
Studies), with performances varying between 50 and 100% depending on the type of environmental change; both functions were sensitive to restoration practices in 100% of the studies examined
Ecosystem structure refers to the physical characteristics of the ecosystem and the composition of biological communities, while ecosystem functioning refers to the processes, such as those that control energy and matter fluxes in the ecosystem, including organic matter decomposition and ecosystem metabolism [1]
Summary
Streams and rivers can be characterized by both their structure and function. Organic matter decomposition connects riparian vegetation and aquatic communities via the instream cycling of energy and nutrients of terrestrial origin, while ecosystem metabolism is an integrative measure of organic carbon production and consumption Both functions integrate environmental conditions over time, and across multiple trophic levels and multiple levels of biological organization, such that changes in a single level may be reflected in altered process rates [1,13]. Organic matter decomposition and ecosystem metabolism do not depend on the presence of a specific taxon, but rather on functional groups (e.g., invertebrate shredders), potentially allowing for large spatial scale comparisons that are not complicated by biogeography [10] These functions will only be useful bioassessment tools if they respond predictably and sensitively to environmental change and anthropogenic stressors and can discriminate between different types of human impacts [14]
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