Organic Matter Decomposition and Ecosystem Metabolism as Tools to Assess the Functional Integrity of Streams and Rivers–A Systematic Review

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.

In Situ Monitoring of a Eutrophicated Pond Revealed Complex Dynamics of Nitrogen and Phosphorus Triggered by Decomposition of Floating-Leaved Macrophytes

“…At present, methods to research the decomposition of aquatic plants mainly include indoor simulation [15] and litterbags [16,17]. The former is mainly used to explore the effects of certain quantitative factors on plant decomposition, and most of them are smallscale simulation experiments [18] in which the water volume is normally limited.…”

Quantifying the response of a functional indicator of ecosystem health to disturbance gradients in New Zealand riverine environments: a meta-analysis

“…Process-based indicators also may have utility for discriminating low levels of impairment, have lower variability, and higher sensitivity than conventional structural indicators (Niemi et al, 1993;Young et al, 2006;Mckie & Malmqvist, 2009;Riipinen et al, 2009;Clapcott & Barmuta, 2010;Ferreira et al, 2020;Cargill et al, 2021). This ability to detect early signs of degradation could allow for more rapid management intervention , and allow small-scale improvements to be observed in the early stages following restoration (Palmer et al, 2005;, all ultimately improving managers' response time to degrading conditions.…”

“…Breakdown is predominantly mediated by a combination of macroinvertebrate and microbial derived activity, though the relative dominance of one over the other can change dependent on the material and environmental conditions (Suberkropp & Chauvet, 1995;Ostrofsky, 1997;Grattan & Suberkropp, 2001;Hieber & Gessner, 2002;Pascoal & Cássio, 2004;Gonçalves et al, 2006;Bergfur, 2007;Lecerf & Chauvet, 2008a;Dang et al, 2009;Taylor & Chauvet, 2014;Tonin et al, 2018). Many previous studies have concluded that OM breakdown can be used to detect changes in environmental condition (Ferreira et al, 2020) promoting its use in riverine bioassessment.…”

“…Sedimentation rate has been negatively correlated with breakdown, likely due to the impacts it has on light penetration, primary production, habitat homogenisation, and smothering effect on biota (Imberger et al, 2010;Piggott et al, 2015). Included in the point above, it is recommended that measures of OM breakdown be taken in riffles or areas of constant flow, as this also minimises sedimentation build up on materials and avoids potential anoxic conditions (Ferreira et al, 2020).…”

“…Although the measure of cotton strip material breakdown does not measure the same attributes of decomposition as natural leaf-litter, they are composed of ~95% cellulose, the predominant composite in leaf-litter (Tiegs et al, 2013). Further, the cotton strip assay is consistent, relatively cheap, easy to source, and a repeatable method for monitoring freshwater ecosystem function (Boulton & Quinn, 2000;Imberger et al, 2010;Tiegs et al, 2013;Piggott et al, 2015;Colas et al, 2019;Ferreira et al, 2020;Pingram et al, 2020), all of which are desirable traits of a successful indicator (Bonada et al, 2005). Different breakdown metrics have been considered, with cotton tensile strength loss (CTSL) found to be the most effective at distinguishing differences of conditions than the mass loss (as largely used in leaf litter studies) (Tiegs et al, 2007), and so has been studied more thoroughly.…”