Evaluating the performance of taxonomic and trait-based biomonitoring approaches for fine sediment in the UK

Fine sediment is a leading cause for the decline of aquatic biodiversity globally. There is an urgent need for targeted monitoring to identify where management methods are required in order to reduce the delivery of fine sediment to aquatic environments. Existing sediment-specific biomonitoring indices and indices for general ecological health (taxonomic and trait-based) developed for use in the UK were tested in a representative set of lowland rivers in England that consisted of a gradient of fine sediment pressures (deposited and suspended, organic and inorganic). Index performance was modelled against environmental variables collected during sampling and hydrological and antecedent flow variables calculated from daily flow data. Sediment-specific indices were indicative of surface sediment deposits, whereas indices for general ecological health were more closely associated with the organic content of fine sediment. The performance of biotic indices along fine sediment gradients was predominantly dependent on hydrological variability. Functional diversity indices were poorly related to different measures of fine sediment, and further development of traits-based indices and trait databases are recommended. In summary, the results suggest that sediment-specific biomonitoring tools are suitable for evaluating fine sediment stress in UK rivers when index scores are viewed within the context of local hydrolog

Abiotic predictors of fine sediment accumulation in lowland rivers

The delivery of excessive fine sediment (particles <2 mm in diameter) to rivers can cause serious deleterious effects to aquatic ecosystems and is widely acknowledged to be one of the leading contributors to the degradation of rivers globally. Despite advances in using biological methods as a proxy, physical measures remain an important method through which fine sediment can be quantified. The aim of this study was to provide further insights into the environmental variables controlling sediment accumulation in lowland gravel bed rivers. We sampled 21 sites, during spring and autumn, selected to cover a gradient of excess fine sediment. Fine sediment was sampled using a range of methods including visual assessments, the disturbance method and suspended sediment concentrations. A range of abiotic predictors were measured during sampling, and hydrological and antecedent flow indices were derived from local flow gauging station data. The results show reach scale visual estimates of fine sediment to be significantly and highly correlated with fully quantitative estimates of total surface sediment. Multivariate regression analysis showed that flow variables (regime, antecedent and local flow characteristics) were strong predictors of deposited sediment metrics but poor predictors of suspended sediment. Organic content was shown to be relatively independent of total sediment quantity and is likely driven by other factors which influence the supply and breakdown of organic matte

Back to the future: Exploring riverine macroinvertebrate communities' invasibility

Riverine communities have been subject to numerous biological invasion events, with crustaceans among the most successful group of invasive animals worldwide. Understanding what makes a river system prone to invasion is of considerable interest to environmental regulators, resource managers, scientists and wider society globally. The Ponto-Caspian amphipod, Dikerogammarus haemobaphes (Crustacea: Gammaridae), is a hyper-successful invasive species that was first recorded in the UK in 2012. The use of contemporary distribution data for D. haemobaphes (2009–2020) from England provided a unique opportunity to study faunal community patterns and differences between sites that experienced invasion compared to those that have not. Macroinvertebrate community taxonomic, functional and phylogenetic features, as well as the presence of co-occurrent invaders and abiotic features of the river systems, were examined from sites before the invasion and compared to control sites that were not invaded during the study period. Sites that would later experience invasion by D. haemobaphes were characterized by higher abundances of other invaders (e.g., especially Ponto Caspian taxa), lower abundances of crustaceans and typically had greater channel width and water depth. These basic characteristics may help identify sites at risk of future invasion by D. haemobaphes. Most biomonitoring tools examined displayed no difference between control and pre-invaded samples, while both taxonomic and functional richness displayed higher values at sites that were subsequently invaded, questioning classic biological invasion hypotheses. Recognizing specific community characteristics that may be a precondition for subsequent invasion is essential for understanding and better predicting their future trajectories of change

Biological metrics from 202 UK lotic sites

Biological metrics: data from 202 UK lotic sites used in the analysis for the study: Multiple co-occurrent alien invaders constrain aquatic biodiversity in rivers. Ecological ApplicationsThe following explain the column headings in the spreadsheet:SITE_ID =Site ID of the lotic site; WATER_BODY= Water body name, SAMPLE_DATE=Date of Sampling, WHPT_TOTAL= WHPT index score, N_TAXA-WHPT=Total number of taxa used to calculate the WHPT score, Frich=Functional Richness value, FRed= Functional Redundancy value, ACI=Abundance Contamination Index, RCI=Richness Contamination Index, Invaders= Number of invaders (5 = ≥5)</div

Multiple co‐occurrent alien invaders constrain aquatic biodiversity in rivers

A greater understanding and effective management of biological invasions is a priority for biodiversity conservation globally. Many freshwater ecosystems are experiencing the colonisation and spread of multiple co-occurrent alien species. Here the implications of both the relative abundance and richness of alien invaders on aquatic macroinvertebrate taxonomic and functional richness, ecosystem quality and functional redundancy are assessed using long-term data from rivers in England. Based on the most common aquatic invaders, results indicated that their richness rather than abundance was the most important factor negatively affecting aquatic macroinvertebrate biodiversity. However, the response of functional redundancy was negatively affected by invader abundance at the river basin scale. The response of communities varied as the number of invading taxa increased, with the most marked reductions following the colonisation of the first few invaders. Results indicate that different facets of multiple biological invasions influence distinct aspects of aquatic biodiversity. Preventing the establishment of new invaders and limiting invader taxa richness within a community should therefore be a conservation priority. These findings will assist river scientists in understanding mechanisms driving changes in biodiversity and facilitate the testing of ecological theories while also ensuring environmental managers and regulators can prioritize conservation / management opportunities

Invasive species influence macroinvertebrate biomonitoring tools and functional diversity in British rivers

Biological invasions could have major implications for the management and conservation of freshwater systems if they lead to a misclassification of waterbodies. However, there is limited understanding of the sensitivity of existing biomonitoring tools to invasive species in rivers; and even less known regarding how they influence community taxonomic and functional measures. This research explores the response of freshwater macroinvertebrate communities to biological invasion using taxonomic and functional indices. Utilising a long-term dataset (spanning 2000–2019, 5,988 samples) from rivers in England, the performance of four biomonitoring tools (WHPT, WHPT-ASPT, LIFE and PSI) and two community functional indices (functional richness and redundancy) was examined before and after the colonisation of the invasive species, Dikerogammarus haemobaphes (Eichwald, 1841; Crustacea: Gammaridae). This species represents a recent (first record 2012) and highly successful invader, allowing its range expansion within waterbodies to be examined in detail. Spatial (national and basin level) and seasonal (spring and autumn) effects were investigated using a before–after control–impact (BACI) experimental framework and linear mixed effects models. Results indicated that invasion by D. haemobaphes resulted in significant reductions to the WHPT index and functional diversity metrics (richness and redundancy) while more subtle patterns were observed for other metrics. Analysis of seasonal and individual river basins (River Trent and R. Thames) identified largely consistent responses. The establishment of D. haemobaphes also resulted in some modifications to the functional composition of aquatic communities primarily associated with voltinism and resistance features. Synthesis and applications. Our findings indicate that Dikerogammarus haemobaphes should be considered a significant pressure to riverine communities. These results have implications for biomonitoring, which informs managerial actions as effects may not be detected using a single taxonomic index. Community functional measures are useful in characterising the effects of invasive species and may form a valuable part of the ‘toolbox’ used for studying biological invasions in rivers. The research illustrates the need to consider the wider threats posed by invasive species on the long-term integrity of freshwaters and the efficacy of freshwater biomonitoring tools

Using invertebrate functional traits to improve flow variability assessment within European rivers

Rivers are among the most threatened ecosystems worldwide and are experiencing rapid biodiversity loss. Flow alteration due to climate change, water abstraction and augmentation is a severe stressor on many aquatic communities. Macroinvertebrates are widely used for biomonitoring river ecosystems although current taxonomic approaches used to characterise ecological responses to flow have limitations in terms of generalisation across biogeographical regions. A new macroinvertebrate trait-based index, Flow-T, derived from ecological functional information (flow velocity preferences) currently available for almost 500 invertebrate taxa at the European scale is presented. The index was tested using data from rivers spanning different biogeographic and hydro-climatic regions from the UK, Cyprus and Italy. The performance of Flow-T at different spatial scales and its relationship with an established UK flow assessment tool, the Lotic-invertebrate Index for Flow Evaluation (LIFE), was assessed to determine the transferability of the approach internationally. Flow-T was strongly correlated with the LIFE index using both presence-absence and abundance weighted data from all study areas (r varying from 0.46 to 0.96). When applied at the river reach scale, Flow-T was effective in identifying communities associated with distinct mesohabitats characterised by their hydraulic characteristics (e.g., pools, riffles, glides). Flow-T can be derived using both presence/absence and abundance data and can be easily adapted to varying taxonomic resolutions. The trait-based approach facilitates research using the entire European invertebrate fauna and can potentially be applied in regions where information on taxa-specific flow velocity preferences is not currently available. The inter-regional and continental scale transferability of Flow-T may help water resource managers gauge the effects of changes in flow regime on instream communities at varying spatial scales

Supplementary information files for Using invertebrate functional traits to improve flow variability assessment within European rivers

Supplementary files for article Using invertebrate functional traits to improve flow variability assessment within European rivers. Rivers are among the most threatened ecosystems worldwide and are experiencing rapid biodiversity loss. Flow alteration due to climate change, water abstraction and augmentation is a severe stressor on many aquatic communities. Macroinvertebrates are widely used for biomonitoring river ecosystems although current taxonomic approaches used to characterise ecological responses to flow have limitations in terms of generalisation across biogeographical regions. A new macroinvertebrate trait-based index, Flow-T, derived from ecological functional information (flow velocity preferences) currently available for almost 500 invertebrate taxa at the European scale is presented. The index was tested using data from rivers spanning different biogeographic and hydro-climatic regions from the UK, Cyprus and Italy. The performance of Flow-T at different spatial scales and its relationship with an established UK flow assessment tool, the Lotic-invertebrate Index for Flow Evaluation (LIFE), was assessed to determine the transferability of the approach internationally. Flow-T was strongly correlated with the LIFE index using both presence-absence and abundance weighted data from all study areas (r varying from 0.46 to 0.96). When applied at the river reach scale, Flow-T was effective in identifying communities associated with distinct mesohabitats characterised by their hydraulic characteristics (e.g., pools, riffles, glides). Flow-T can be derived using both presence/absence and abundance data and can be easily adapted to varying taxonomic resolutions. The trait-based approach facilitates research using the entire European invertebrate fauna and can potentially be applied in regions where information on taxa-specific flow velocity preferences is not currently available. The inter-regional and continental scale transferability of Flow-T may help water resource managers gauge the effects of changes in flow regime on instream communities at varying spatial scales.</p

The role of rewilding in mitigating hydrological extremes: State of the evidence

Landscape rewilding has the potential to help mitigate hydrological extremes by allowing natural processes to function. Our systematic review assessed the evidence base for rewilding-driven mitigation of high and low flows. The review uncovers a lack of research directly addressing rewilding, but highlights research in analogue contexts which can, with caution, indicate the nature of change. There is a lack of before-after studies that enable deeper examination of temporal trajectories and legacy effects, and a lack of research on the scrub and shrubland habitats common in rewilding projects. Over twice as much evidence is available for high flows compared to low flows, and fewer than one third of studies address high and low flows simultaneously, limiting our understanding of co-benefits and contrasting effects. Flow magnitude variables are better represented within the literature than flow timing variables, and there is greater emphasis on modeling for high flows, and on direct measurement for low flows. Most high flow studies report a mitigating effect, but with variability in the magnitude of effect, and some exceptions. The nature of change for low flows is more complex and suggests a higher potential for increased low flow risks associated with certain trajectories but is based on a very narrow evidence base. We recommend that future research aims to: capture effects on both high and low flow extremes for a given type of change; analyze both magnitude and timing characteristics of flow extremes; and examine temporal trajectories (before and after data) ideally using a full before-after-control-impact design. This article is categorized under: Human Water > Value of Water Science of Water > Hydrological Processes Science of Water > Water Extremes Water and Life > Conservation, Management, and Awareness.</p

Defining recovery potential in river restoration: a biological data-driven approach

Scientists and practitioners working on river restoration have made progress on understanding the recovery potential of rivers from geomorphological and engineering perspectives. We now need to build on this work to gain a better understanding of the biological processes involved in river restoration. Environmental policy agendas are focusing on nature recovery, reigniting debates about the use of “natural” reference conditions as benchmarks for ecosystem restoration. We argue that the search for natural or semi-natural analogues to guide restoration planning is inappropriate due to the absence of contemporary reference conditions. With a catchment-scale case study on the invertebrate communities of the Warwickshire Avon, a fifth-order river system in England, we demonstrate an alternative to the reference condition approach. Under our model, recovery potential is quantified based on the gap between observed biodiversity at a site and the biodiversity predicted to occur in that location under alternative management scenarios. We predict that commonly applied restoration measures such as reduced nutrient inputs and the removal of channel resectioning could be detrimental to invertebrate diversity, if applied indiscriminately and without other complementary measures. Instead, our results suggest considerable potential for increases in biodiversity when restoration measures are combined in a way that maximises biodiversity within each water body