How freshwater biomonitoring tools vary sub‐seasonally reflects temporary river flow regimes

Characterizing temporary river ecosystem responses to flow regimes is vital for conserving their biodiversity and the services they provide to society. However, freshwater biomonitoring tools rarely reflect community responses to hydrological variations or flow cessation events, and those available have not been widely tested within temporary rivers. This study examines two invertebrate biomonitoring tools characterizing community responses to different flow‐related properties: the “Drought Effect of Habitat Loss on Invertebrates” (DEHLI) and “Lotic‐invertebrate Index for Flow Evaluation” (LIFE), which, respectively reflect community responses to habitat and hydraulic properties associated with changing flow conditions. Sub‐seasonal (monthly) variations of LIFE and DEHLI were explored within two groundwater‐fed intermittent rivers, one dries sporadically (a flashy, karstic hydrology—River Lathkill) and the other dries seasonally (a highly buffered flow regime—South Winterbourne). Biomonitoring tools were highly sensitive to channel drying and also responded to reduced discharges in permanently flowing reaches. Biomonitoring tools captured ecological recovery patterns in the Lathkill following a supra‐seasonal drought. Some unexpected results were observed in the South Winterbourne where LIFE and DEHLI indicated relatively high‐flow conditions despite low discharges occurring during some summer months. This probably reflected macrophyte encroachment, which benefitted certain invertebrates (e.g., marginal‐dwelling taxa) and highlights the importance of considering instream habitat conditions when interpreting flow regime influences on biomonitoring tools. Although LIFE and DEHLI were positively correlated, the latter responded more clearly to drying events, highlighting that communities respond strongly to the disconnection of instream habitats as flows recede. The results highlighted short‐term ecological responses to hydrological variations and the value in adopting sub‐seasonal sampling strategies within temporary rivers. Findings from this study indicate the importance of establishing flow response guilds which group taxa that respond comparably to flow cessation events. Such information could be adopted within biomonitoring practices to better characterize temporary river ecosystem responses to hydrological variations

The development of a novel macroinvertebrate indexing tool for the determination of salinity effects in freshwater habitats

Salinisation is a global threat to freshwater habitats and is predicted to worsen with climate change. Increases in salinity can result in substantial modification of freshwater biotic communities through both direct toxic effects and indirect effects such as altering prey resources, competitive interactions, predator abundances, and facilitating the spread of invasive species. Traditional techniques to determine salinity, such as point sampling chemical assessment, are typically periodic and may not reveal intermittent changes in salinity concentration. Halo-stratification and a lack of standardised depth to collect chemical data further complicates using these methods. More importantly, such methods do not show the ecological impacts of salinity increases in freshwater habitats. Complementing traditional techniques with biological assessments may resolve these issues. Pressure-specific biotic indices using aquatic macroinvertebrate community data have long been used to assess aspects of aquatic habitats, although relatively few have focussed on salinity. This paper presents the Salinity Association Group Index (SAGI), a novel aquatic macroinvertebrate index to assess salinity in freshwater habitats. SAGI is compatible with data derived from established survey techniques employed by regulatory bodies and for Water Framework Directive assessments, amongst others. The method integrates taxonomic resolution beyond the family level with taxon abundance weighting in a scoring matrix to increase the efficacy of the tool and make the best use of publicly available data. Application of SAGI in case studies demonstrates a positive, moderate to strong correlation with conductivity used as a measure of salinity. The range of correlations (R2 = 0.57–0.91) compares favourably with pressure-specific, macroinvertebrate-based monitoring tools used in Europe for WFD monitoring. Furthermore, SAGI is shown to be highly effective in comparison to alternative salinity-specific biotic indices

Environmental flows from dams:the water framework directive

The Water Framework Directive (WFD) provides a template for sustainable water management across Europe. The WFD requires the development of procedures to ensure the appropriate mitigation of anthropogenic impacts on river ecosystems resulting from water abstraction and impoundments. It is widely acknowledged that alterations to the flow regime impacts on riverine ecosystems. As a result hydromorphology, which includes the hydrological regime, is embedded within the WFD as a supporting element to achieve Good Ecological Status (GES). Environmental flow releases from impoundments, such as reservoir dams, will need to be implemented to mitigate impacts caused by their construction and operation. This paper outlines the process involved in the analysis of available scientific information and the development of guidance criteria for the setting of environmental flow release regimes for UK rivers. The paper describes two methods for implementation of the WFD for rivers subject to impoundments developed by round table expert knowledge and discussions, supported by available data. First, a method for preliminary assessment of a water body to determine if it is likely to fail to achieve Good Ecological Status because of changes to the flow regime (indexed by simple flow regime statistics) in systems where appropriate biological assessment methods are limited or currently unavailable. Second, a method for defining an environmental flow regime release based on the requirements of riverine ecological communities and indicator organisms for basic elements (building blocks) of the natural flow regime

Sub-fossil Chironomidae as indicators of palaeoflow regimes: integration into the PalaeoLIFE flow index

The sub-fossil head capsules of larval Chironomidae have been widely exploited as palaeoecological indicators of lentic ecosystems but their value in the interpretation of the evolution of lotic systems has been underutilised by comparison. Recent research has demonstrated that the remains of Chironomidae are abundant within fluvial sequences and that they offer a valuable record of channel change and floodplain evolution that may complement that derived from existing biological and sedimentological techniques. This paper demonstrates the use of Chironomidae in characterising the palaeoflow regime of a large mid–late Holocene floodplain palaeochannel (5470–4960 to 1530– 1350 cal. a BP) of the River Trent (Derbyshire, UK). Using expert knowledge and published information regarding flow preferences, larval Chironomidae were incorporated into the PalaeoLIFE (Loticinvertebrate Index for Flow Evaluation) methodology. The results clearly demonstrate that the subfossil record provided by Chironomidae can be used to characterise changes in the flow regime within palaeochannel sections. At the scale of the channel section, species- and generic-level ecological associations can provide useful information regarding habitat characteristics, including the presence of instream vegetation, mineral substrates and woody debris. The ability to undertake environmental reconstruction and channel evolution history was significantly enhanced through the application of a multi-proxy approach, by incorporating other aquatic insect groups (Trichoptera and Coleoptera) into the PalaeoLIFE metric, together with sedimentological data

Using large climate ensembles to plan for the hydrological impact of climate change in the freshwater environment

We explore the use of large ensembles of climate scenarios to inform climate change adaptation in response to hydrological impacts on the freshwater environment, using a sensitive chalk river in south east England to illustrate the approach. The climateprediction.net experiment provides large ensembles of transient climate series from 1920 to 2080. We use 246 transient climate series in the CATCHMOD rainfall-run-off model to develop large ensembles of plausible river flows for the River Itchen. This transient ensemble allows the exploration of how flows may change through the twenty-first century, and demonstrates the range of possible consequences for freshwater ecosystems, based on invertebrate community impacts. Hydrological modelling of flow sequences including abstraction allows the continued effectiveness of river support from groundwater to be assessed. A new environmental impact matrix considers the response of the freshwater ecosystem in the Itchen, concentrating particularly on macro-invertebrates. Through the century increasing numbers of models fail the flow targets, with a minority of models suggesting flows that would lead to irreversible change to the invertebrate community. The large ensemble provides a richer picture of the range of possible change, allowing managers to explore a range of different responses. The approach used is illustrative, but demonstrates that large ensembles may be of great value in improving the understanding of the possible impact of climate change, provided that they can be communicated effectively to decision-makers