Assessing the Mechanistic Basis for Fine Sediment Biomonitoring: Inconsistencies among the Literature, Traits and Indices

Abstract

Classification of species sensitivity for biomonitoring has been approached under two different frameworks, using either empirical data or expert opinion. Two tools for fine sediment (i.e. clogging and colmation) biomonitoring in the UK tend towards these contrasting approaches. The Proportion of Sediment-sensitive Invertebrates (PSI) index was developed using expert judgement. Empirical weightings were subsequently added at genus or species (EPSI) and mixed (EPSI mixed ) taxonomic levels, but scores remain constrained by the original categories. In contrast, the Combined Fine Sediment Index, composed of separate taxon scores along organic matter and total fine sediment gradients, was developed using a purely empirical approach. We tested the mechanistic bases for these indices by relating taxon scores to species traits. We compared the results with those for the well-established Whalley Hawkes Paisley Trigg index of organic pollution. After controlling for varying sample sizes, Whalley Hawkes Paisley Trigg could be better predicted by a linear combination of all available traits (mean R 2 = 0.92) than any of the fine sediment indices (0.68 < mean R 2 < 0.76). When only traits expected to respond to fine sediment were offered as independent variables, the goodness of fit was substantially reduced for all fine sediment indices (0.27 < mean R 2 < 0.46). Our findings demonstrate the lack of integration between the literature on macroinvertebrate responses to fine sediment, the available trait data and taxon scores. Refinement of the trait database is recommended to build on the valuable work performed to date. As the UK has taken the lead in embedding fine sediment into routine biomonitoring programmes, these findings have important international implications.The test evaluates the null hypothesis that the fit of the global 'all traits' model is no better than the fit of the more parsimonious model ('pruned', 'literature').

Flow velocity–ecology thresholds in Canadian rivers: A comparison of trait and taxonomy‐based approaches

“…Others have observed a similar phenomenon for a different trait database (i.e. Tachet, Richoux, Bournaud, & Usseglio-Polatera, 2010) related to fine sediment, namely that some traits occur at a range of substratum types (Wilkes, Mckenzie, Murphy, & Chadd, 2017). Thus, selection of potential indicator trait modalities that are responsive to flow velocity gradients should identify high z-score loadings paired with the knowledge of phylogenetically independent trait modalities and trait variability for labile traits.…”

The role of fine sediment characteristics and body size on the vertical movement of a freshwater amphipod

“…There have been recent calls for an improved mechanistic understanding of the effects of fine sediment on macroinvertebrates (Wilkes, McKenzie, Murphy, & Chadd, ), with some studies documenting variable responses of benthic invertebrates to sedimentation (Descloux et al., ; Mathers, Rice, & Wood, ; Murphy et al., ). The results from these experiments provide the first direct evidence that the effects of sedimentation vary as a function of sediment characteristics (particle size, heterogeneity and loading) and the body size of fauna.…”

Sediment deposition from eroding peatlands alters headwater invertebrate biodiversity

“…This highlights the benefit of mesocosms for experimentally controlling confounding variables to enable a direct analysis of trait‐sedimentation responses. Mesocosm results suggested invertebrate community changes can be partially attributed to species‐sorting processes acting on whole suites of traits that each organism possesses, reflecting the selection of disturbance‐tolerant “life strategies” under increasing levels of fine organic sediment deposition (Verberk et al, ) as expected for H 2 , rather than through a trait–environment relationship characterized by simple or additive associations (Wilkes et al, ). While the overall suite of traits responding to organic sedimentation was not directly comparable to those observed in previous studies (in part due to different profiles of traits used for analyses within different studies), some of our key findings are supported by previous studies from different geographical locations.…”

“…Analyses were undertaken at four levels of organization: (A) Benthic macroinvertebrate community , based upon the following metrics: (i) total macroinvertebrate density (per m 2 ), (ii) richness (n taxa), (iii) beta diversity (Sørensen index) amongst replicate samples (i.e. mesocosms for each experimental treatment, Surber samples for each headwater river), with partitioning analysis to consider elements of turnover (species replacements between sites) and nestedness (species loss from site to site; Baselga & Orme, ); (B) Order level , with densities calculated for the Chironomidae, Ephemeroptera, Plecoptera and Coleoptera, which are typically the most common macroinvertebrate orders in peatland river systems; (C) Species level : densities were calculated for Leuctra inermis , typically the most common Plecoptera species found in peatland rivers but which is known to be sensitive to sedimentation effects in rivers (Turley et al, ); and (D) Traits and functional diversity : we used the same traits from previous assessments of fine sediment effects on river invertebrates (Wilkes et al, ) to enable a clearer understanding of their links with organic sediments. Traits were assigned to invertebrate genera using the fuzzy codes (Chevenet, Dolédec, & Chessel, ) from the database developed by Tachet, Richoux, Bournaud, and Usseglio‐Polatera () (see Supporting Information Table S2 for traits used, their modalities and codes).…”

“…Lat/Long (Turley et al, 2016); and (D) Traits and functional diversity: we used the same traits from previous assessments of fine sediment effects on river invertebrates (Wilkes et al, 2017) to enable a clearer understanding of their links with organic sediments.…”