UK Rivers Research Articles

Physically-based modelling of UK river flows under climate change

This study presents the model setup and results from the first calibrated, physically-based, spatially-distributed hydrological modelling of combined land cover and climate change impacts on a large sample of UK river catchments. The SHETRAN hydrological model was automatically calibrated for 698 UK catchments then driven by the 12 regional climate model projections from UKCP18, combined with urban development and natural flood management scenarios. The automatic calibration of SHETRAN produces a median Nash-Sutcliffe efficiency value of 0.82 with 581 catchments having a value greater than 0.7. 24 summary metrics were calculated to capture changes to important aspects of the flow regime. The UKCP18 realisations in SHETRAN indicate that a warming climate will cause river flows, on average, to decrease. These decreases are simulated to be greatest in the south and east of the UK, with droughts becoming longer and more severe. While high flows also decrease on average, an increased number of extremes are exhibited, implying a greater number of extreme flood events in the future, particularly in the north and west of the UK. In the urban development scenarios, for flood events there is an increase in flow with the increased urbanization, with the 1 in 3-year peak flow event showing the greatest increase. The natural flood management scenarios consider the effect of increasing woodland and adding surface water storage ponds. The inclusion of these features produces a complex response but overall, the modelling shows a reduction in low, median, and high flows, although the more extreme the flow event the smaller the percentage change in flow. Simulated timeseries and summary metric datasets are freely available on the CEDA archive.

The effect of downstream translocation on Atlantic salmon Salmo salar smolt outmigration success.

Trap and transport, the capture and subsequent translocation of fish during the freshwater phase of their migration, is becoming more common as a management intervention. Although the technique can be successful, it is costly and can have unintended effects on the fish being transported. This study investigates whether trap and transport can be used to increase the migration success of Atlantic salmon, Salmo salar, smolts in naturally flowing rivers. Seaward-migrating S. salar (n = 294) from two UK rivers were tracked using acoustic telemetric techniques. Outmigration success and timing were compared between non-transported (released at the original in-river capture site) and transported (released ca. 23 km downstream of the capture site) individuals. Downstream translocation increased the proportion of fish that successfully migrated to marine waters, and there was no indication that transport reduced post-release survival. The post-release migration speed of transported fish was slower than expected but this was likely a function of their advanced migration timing rather than an inhibition of their capacity to migrate. These results suggest that trap and transport can increase the outmigration success of S. salar smolts, but the earlier river exit dates of transported fish could negatively affect their survival at sea.

The effects of drought on biodiversity in UK river ecosystems: Drying rivers in a wet country

AbstractClimate change is interacting with water resource pressures to alter the frequency, severity and spatial extent of drought, which can thus no longer be considered a purely natural hazard. Although particularly severe ecological impacts of drought have occurred in drylands, its effects on temperate ecosystems, including rivers, are also considerable. Extensive research spanning a diverse range of UK rivers offers an opportunity to place the effects of past drought in the context of intensifying climate change and to examine the likely effects of future drought in a typically cool, wet country. Here, drought manifests instream as deficits in surface water, modified flow velocities, and—increasingly—partial or complete drying of previously perennial and naturally non‐perennial reaches. As a result, drought causes declines in the taxonomic and functional biodiversity of freshwater communities including microorganisms, algae, plants, invertebrates and fish, altering ecological processes and associated benefits to people. Although freshwater communities have typically recovered quickly after previous UK droughts, an increase in drought extremity may compromise recovery following future events. The risk of droughts that push ecosystems beyond thresholds to persistent, species‐poor, functionally simplified states is increasing. Research and monitoring are needed to enable timely identification of rivers approaching such thresholds and thus to inform interventions that pull these ecosystems back from the brink. Management actions that support natural flow regimes and promote natural processes that diversify instream habitats, including drought refuges, are also crucial to support biodiversity within functional river ecosystems as they adapt to a changing world.This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

When unlocking rivers results in building more infrastructure: A group mental model shares lessons from weir remediation in the United Kingdom

AbstractThe last several decades have seen a rise in efforts to remove weirs, but there is little research investigating how projects are carried out, potential areas for improvement, or sharing of lessons to facilitate reconnection of more rivers. The aim of the study presented here was to explore how people involved in weir remediation perceive project processes, factors that facilitate or hinder action implementation, and possible ways processes could be improved to reconnect more rivers. We carried out semi‐structured interviews with people (n = 11) who had been actively involved in weir remediation processes in the Severn River Catchment, United Kingdom, and used their responses to create a group mental model. The group mental model was created to support learning and communication about weir remediation projects between individuals and groups. We found broad agreement from those involved in creating the group mental model about weir remediation project processes and potential areas for improvement. One of the only points of divergence within the group mental model was associated with the impact of different weir remediation actions, particularly weir removal. Based on the group mental model, we set out three calls to action to reconnect more rivers in the UK. First, move beyond opportunistic projects and establish national goals and catchment‐scale plans for weir remediation. Second, reform fish passage legislation and legislate weir ownership. Doing so would support more effective remediation solutions by recognizing the diversity of fish species that reside in UK rivers and help mitigate risks from hazardous weirs through owner accountability. Third, build cross‐sector and public partnerships to encourage removal or improved fish pass designs. We direct the three calls to action to policy makers and anyone already engaged in or envisioning weir remediation projects in the UK. The calls also have potential implications and relevance to people in other countries in Europe and beyond.

Divergent future drought projections in UK river flows and groundwater levels

Abstract. Hydrological drought is a serious issue globally, which is likely to be amplified by 21st century climate change. In the UK, the impacts of changes in river flow and groundwater drought severity in a future of climate change and higher water demand are potentially severe. Recent publication of a new nationally consistent set of river flow and groundwater level projections (the eFLaG dataset), based on state-of-the-art UKCP18 climate projections, offers a unique opportunity to quantitatively assess future UK hydrological drought susceptibility. The dataset includes a transient, multi-model ensemble of hydrological projections driven by a single regional climate model (RCM), with a 12-member perturbed-parameter ensemble, for 200 catchments and 54 boreholes spanning a period from 1961 to 2080. Assessment of a baseline period (1989–2018) shows that the RCM-driven projections adequately reproduce observed river flow and groundwater level regimes, improving our confidence in using these models for assessment of future drought. Across all hydrological models and most catchments, future low river flows are projected to decline consistently out to 2080. Drought durations, intensities and severities are all projected to increase in most (over 90 %, pooling across different drought characteristics) UK catchments. However, the trajectory of low groundwater levels and groundwater drought characteristics diverges from that of river flows. Whilst groundwater levels at most (> 85 %) boreholes are projected to decline (consistent with river flows), these declines are relatively modest (< 10 % reduction) in transient low groundwater levels by 2080, and, in fact, six show moderate increases. Groundwater drought characteristics in the far future (2050–2079) are often similar to those of the baseline (1989–2018), with only 33 % of boreholes showing an increase (towards worsening drought) of more than 10 % for drought severity (48 % of boreholes for drought intensity). Interestingly, for some boreholes, droughts are projected to be more prolonged and severe in the near future (2020–2049) before returning to shorter durations and lower severity in the far future. A number of explanatory factors for this divergence between river flow and groundwater are discussed. The sensitivity to seasonal changes in precipitation and potential evapotranspiration is proposed as a principal driver of divergence because low river flows are more influenced by shorter-term rainfall deficits in the summer half-year, whilst groundwater drought appears to be offset somewhat by the wetter winter signal in the RCM projections. Our results have important implications for water management, demonstrating a widespread increase in river flow drought severity and diminishing low flows that could have profound societal and environmental impacts unless mitigated. Furthermore, the divergence in projections of drought in river flows and groundwater levels brings into question the balance between surface and subsurface water resources. The projected contrast in fortunes of surface and subsurface water resources identified for the UK may be replicated in other parts of the world where climate projections suggest a shift towards drier summers and wetter winters.

Microplastics in commercial marine fish species in the UK – A case study in the River Thames and the River Stour (East Anglia) estuaries

The aim of this study was to assess the abundance of microplastics in the gastro-intestinal tracts of three commercially important fish species in the UK, to determine whether catch location, feeding habits and fish size influence the amount of microplastics within fish. Fish were collected from two rivers in the UK: the River Thames and the River Stour (East Anglia). Fish were collected from two sites in the River Thames and one site in the River Stour. Species selected were European flounder (Platichthys flesus), whiting (Merlangius merlangus), and Atlantic herring (Clupea harengus), and were chosen to represent benthic and pelagic feeding habits. Across all locations, 41.5 % of fish had ingested at least one microplastic particle (37.5 % of European flounder, 52.2 % of whiting, and 28.6 % of Atlantic herring). The average number by species was 1.98 (±3.50) microplastics/fish in European flounder, 2.46 (±3.10) microplastics/fish in whiting and 1.47 (±3.17) microplastics/fish in herring. There were no significant differences in the number or mass of microplastics in fish based on river, site, species or habitat. However, the number and mass of microplastics within benthic fish (European flounder) in the River Stour were significantly higher than in benthic fish from the River Thames. By number of microplastics, larger and heavier fish were more highly contaminated. This study enhances our understanding of microplastics in commercially important fish but highlights that fish contamination is not easily predicted by feeding habits or catch location alone. Exposure and uptake is likely to vary with changing environmental conditions. Fish size tends to be a good predictor of contamination, with larger fish generally containing more microplastics. This is the first study to directly compare concentrations of microplastics in fish from different UK rivers and the first evidence of microplastics in the River Stour.

PFAS permitted to enter UK river

The chemical maker AGC Chemicals Europe is discharging almost 800 kg of ammonium difluoro[1,1,2,2-tetrafluoro- 2-(pentafluoroethoxy)ethoxy]acetate (EEA-NH 4 ) annually into the UK’s Wyre River from its facility near Blackpool and is doing so legally, according to the UK’s Department for Environment, Food, and Rural Affairs (DEFRA). The discharge was identified by the Guardian newspaper and journalists at Watershed Investigations. Some per- and polyfluoroalkyl substances (PFAS) like EEA-NH 4 are known to be persistent in the environment, can accumulate in the human body, and have the potential to be hazardous. UK legislation currently restricts the release of only a handful of specific PFAS—such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—from among thousands of PFAS molecules. PFOA and PFOS have been largely phased out, and some chemical companies have replaced them with similar PFAS that are unregulated. EEA-NH 4 is an alternative to PFOA as a processing aid in fluoropolymer production.

Concentrations, spatial and seasonal variations of Organophosphate esters in UK freshwater Sediment

This study provides the first report of organophosphate esters (OPEs) in UK freshwater sediments with a focus on the possible impact of factors such as spatial/seasonal variation and wastewater treatment plants (WWTPs) on the measured OPE concentrations in surficial sediment from 3 UK rivers and 1 canal. Detection frequencies of: (tris (chloroethyl) phosphate (TCEP), tris (2-chloroisopropyl) phosphate (TClPP), tris (1,3-dichloro-2 propyl) phosphate (TDClPP), tri-n-butyl phosphate (TNBP), tris (2-butoxyethyl) phosphate (TBOEP), 2-ethylhexyl diphenyl phosphate (EHDPP), tris (phenyl) phosphate (TPHP), and tri-m-tolyl phosphate (TmTP)) ranged from 58% to 100%. The concentration of Σ8OPEs ranged from 107 ng g−1 (dry weight - dw) (in the Worcester-Birmingham canal) to 52 ng g−1 (dw) in both Rivers Severn and Sowe). The highest ∑8OPE concentration for all study locations was recorded during the autumn months (September, October, and November), and concentrations of ∑8OPEs in sediment samples from the River Severn, River Tame, and River Sowe all varied inversely with the river level and flow rate. The average concentrations of each target OPE in each study location were lower than those reported elsewhere but fell broadly within the range of concentrations reported from other countries. The potential risk posed by target OPEs in all study locations was found to be low, except for a moderate risk identified for EHDPP in the Worcester - Birmingham canal.

Regulations permit PFAS to be discharged into UK river

Regulations permit PFAS to be discharged into UK river

Using acoustic tracking of an anadromous lamprey in a heavily fragmented river to assess current and historic passage opportunities and prioritise remediation

AbstractAnthropogenic structures extensively fragment riverine systems, reducing longitudinal connectivity, inhibiting migration and leading to severe declines in many fish populations, especially for diadromous species. This study investigated the upstream spawning migration of anadromous river lamprey (Lampetra fluviatilis) in a heavily fragmented tributary of the Humber Estuary, the location of one of the largest UK river lamprey populations. Overall, this study quantified river lamprey migration, spawning habitat distribution and historic river levels to develop a novel empirical index to understand the impact of man‐made barriers and prioritise their remediation. Passage at all weirs only occurred during episodic high river levels, often after prolonged delays with no lamprey passing below average levels for the time of year or utilising the fish pass at the first weir (T1) at the tidal limit. Barrier passage opportunities at the first four weirs were only possible for 30.3%, 38.7%, 52.1% and 6.7% of the migration period, but were lower and severely limited in 15 of the last 21 years. In addition, more lamprey (60%, n = 18) were last detected in reaches with no spawning habitat than in spawning habitat (40%, n = 12). Given the impassibility of, and lack of retreat from, T1 to other Humber tributaries, the River Trent is currently considered an ecological trap for a large proportion of lamprey that enter from the Humber Estuary. This passage should be urgently remediated, per the prioritisation index presented here, to aid river lamprey conservation, especially given their status as a designated feature of the Humber SAC.

Implications of the Riverine Response to Enhanced Weathering for CO2 removal in the UK

Enhanced silicate weathering, the application of crushed calcium and magnesium-rich rocks to arable cropland, has been proposed as a potential negative emissions technology for the drawdown of atmospheric CO2. Previous estimates have suggested that enhanced silicate weathering (EW) has the potential to remove significant quantities of CO2, as much as 6–30 Mt CO2 yr−1 for the UK. However, if secondary carbonates are precipitated during the riverine transport of the products of EW, a portion of this CO2 will be re-released, lowering the net carbon dioxide removal (CDR) potential of the mitigation strategy. Here, we assess the fluvial response to EW in the UK by calculating the expected riverine carbonate precipitation due to the dissolution of 10–50 t ha−1 yr−1 of silicate rock on available arable cropland in major UK catchments.Increases in calcite saturation due to the export of soluble cations sourced from EW from soil to rivers are simulated to cross thresholds for spontaneous carbonate precipitation in several major UK river catchments (e.g. the Great Ouse, Thames). Catchments most susceptible to potential secondary carbonate precipitation are those with a high ratio of cropland to water discharge. On average, carbonate precipitation for major UK catchments is expected to make EW 16% (10 t ha−1), 21% (20 t ha−1) or 27% (50 t ha−1) less effective at removing CO2 than that predicted in the absence of such precipitation. Furthermore, when placing strict silica limitations on weathering reactions within soils, the CDR potential of EW is reduced considerably, to 0.23 Mt CO2 yr−1.Although reducing the CDR potential of EW, we suggest that under rapid weathering conditions, carbonate precipitation in UK rivers will prevent pH increases over the safe level for freshwater ecosystems (pH > 9). Together, the simulations suggest that ambient hydrological conditions may make certain UK agricultural areas less effective for CDR by EW and call for methods to quantify secondary carbonate precipitation in response to EW treatments and to further investigate the role of silica saturation in suppressing weathering reactions.

Stream power indices correspond poorly with observations of alluvial river channel adjustment

AbstractA variety of stream power‐based approaches for predicting catchment‐scale alluvial channel adjustment have been developed. There is an international interest in applying these to inform river catchment management. However, there is some uncertainty regarding their ability to make consistently accurate predictions. This study evaluates the performance of a range of stream power indices for predicting observed channel adjustment. Remotely sensed data were used to generate 33 different stream power indices every 50 m across the networks of five test catchments. The performances of the indices were evaluated by comparing them against observations of erosion and deposition‐dominated channels extracted from the UK's River Habitat Survey (RHS) database. A selection of metrics for evaluating the performance of the indices were calculated. The key finding from this study is that the stream power indices were poorly associated with the observations of alluvial channel adjustment. It is not clear whether this poor association is due to limitations with stream power indices or the suitability of the RHS observations. However, this is not the first study to find a weak association between stream power and observed adjustment. Therefore, caution is recommended to anyone hoping to take advantage of the practicability of stream power indices until further testing is applied using alternative observation datasets. An additional finding from this study is the inconsistency of outcomes between different measures of model performance. It is recommended that future studies also employ multiple model performance measures rather than relying on accuracy alone.

Heavy metal and antibiotic resistance in four Indian and UK rivers with different levels and types of water pollution.

Heavy metal pollution can enhance the level of antibiotic resistance, posing concerns to ecosystem and public health. Here, we investigated heavy metal concentrations, heavy metal resistant bacteria and antibiotic resistant bacteria and their corresponding resistant genes, and integrons in four different river environments, i.e., low heavy metals and low wastewater, high heavy metals and low wastewater, low heavy metals and high wastewater, and high heavy metals and high wastewater levels. Heavy metals were found to show positive and significant correlations with heavy metal resistance and antibiotic resistance and integrons (r > 0.60, p < 0.05), indicating that heavy metal selective pressure can cause heavy metal and antibiotic resistance to be transmitted simultaneously via integrons, which can result in the development of multi-resistant bacteria in the heavy metal-polluted environments. Moreover, there were significant associations between heavy metal resistance and antibiotic resistance (r > 0.60, p < 0.05), demonstrating heavy metal and antibiotic resistance are connected via a same or related mechanism. Class 1 integrons were found to have strong correlations with heavy metals and heavy metal resistance and antibiotic resistance (r > 0.60, p < 0.05), indicating a higher occurrence of antibiotic resistance co-selection in the heavy metal-polluted environments.

In-situ multi-mode extraction (iMME) sampler for a wide-scope analysis of chemical and biological targets in water in urbanized and remote (off-the-grid) locations

Chemical pollution (including chemicals of emerging concern – CECs) continues to gain increasing attention as a global threat to human health and the environment, with numerous reports on the adverse and sometimes devastating effects upon ecosystems the presence of these chemicals can have. Whilst many studies have investigated presence of CECs in aquatic environments, these studies have been often focused on higher income countries, leaving significant knowledge gaps for many low-middle income countries. This study proposes a new integrated powerless, in-situ multi-mode extraction (iMME) sampler for the analysis of chemicals (105 CECs) and biological (5 genes) markers in water in contrasting settings: an urbanized Avon River in the UK and remote Olifants River in Kruger National Park in South Africa. The overarching goal was to develop a sampling device that maintains integrity of a diverse range of analytes via analyte immobilization using polymeric and glass fibre materials, without access to power supply or cold chain (continuous chilled storage) for sample transportation. Chemical analysis was achieved using ultra-performance liquid chromatography coupled with tandem mass spectrometry. Several mobile CECs showed low stability in river water, at room temperature and typical 24 h sampling/transport time. It is therefore recommended that, in the absence of cooling, environmental water samples are spiked with internal standards on site, immediately after collection and analyte immobilization option is considered, in order to allow fully quantitative analysis. iMME has proven effective in immobilization, concentration and increased stability of CECs at room temperature (and at least 7 days storage) allowing for sample collection at remote locations. The results from the River Avon and Olifants River sampling indicate that the pristine environment of Olifants catchment is largely unaffected by CECs common in the urbanized River Avon in the UK with a few exceptions: lifestyle chemicals (e.g., caffeine, nicotine and their metabolites), paracetamol and UV filters due to tourism and carbamazepine due to its persistent nature. iMME equipped with an additional gene extraction capability provides an exciting new opportunity of comprehensive biochemical profiling of aqueous samples with one powerless in-situ device. Further work is required to provide full integration of the device and comprehensive assessment of performance in both chemical and biological targets.

Exploring the impacts of physicochemical characteristics and heavy metals fractions on bacterial communities in four rivers

Heavy metals contamination in sediment poses serious threats to bacterial communities that play critical roles in sediment biogeochemical processes. However, the physicochemical factors and the major heavy metals fractions that affect sediment bacterial communities are still unclear. Here, we performed heatmap and redundancy analyses to examine the effects of physico-chemical characteristics and heavy metals fractions on the sediment bacterial community from rivers in the UK (River Tyne and Ouseburn) and India (River Ganga and Yamuna). The results revealed that physicochemical characteristics and heavy metals fractions altered the diversity, richness, and structures of the bacterial community. Moreover, the fractions of Co, Zn, Pb, Cr, and Cu played significant roles in shaping the bacterial community structure, and physicochemical variables, particularly NH4+-N and NO2−-N, also influenced the bacterial diversity and structure. Firmicutes showed strong associations with both physicochemical factors and heavy metals fractions. Chloroflexi and Actinobacteriota can be used as biomarkers for Zn contamination. Overall, our study identified the significance of sediment chemical characteristics and heavy metals fractions in determining the bacterial community structure as well as bioremediation and environmental management of metals contaminated sites.

Vertical reworking of sediment by the cased caddisfly Glossosomatidae (Agapetus fuscipes) increases sand exposure and availability in armoured gravel-bed rivers

Landscapes and ecosystems are the result of two-way interactions between hydro-geomorphic and biological processes. Many animals, particularly those that build structures or transport sediment, are important biogeomorphic agents. Glossosomatidae caddisfly larvae (Insecta, Trichoptera) are globally widespread and abundant inhabitants of gravel-bed rivers. Glossosomatidae build mobile cases from sand that they transport over the river bed. However, there is limited understanding on how Glossosomatidae bioconstructions may influence sand distribution in rivers or how their zoogeomorphic behaviours are influenced by hydraulics or characteristics of the river bed. First, we conducted surveys to quantify the magnitude of sand incorporated into Glossosomatidae (Agapetus fuscipes) cases within a UK river. Second, we studied A. fuscipes movement behaviour and quantified the direction and magnitude of sediment reworking, in a flume, under differing flow velocity and gravel size treatments. We found that 99 % of A. fuscipes larvae transported sediment vertically upwards. This resulted in an average conveyance per larvae of 0.06 g sand upwards by 25 mm (maximum of 50 mm). In gravel beds with a coarse surface layer, this resulted in displacement of sand from sheltered interstices onto the surface of exposed gravel particles. In the flume, this behaviour was maintained even at high flows, sufficient to entrain empty cases from these locations. Whilst the mass of sediment moved by individual larvae is small, dense populations of Glossosomatidae larvae may have important consequences for the vertical distribution of sand in rivers. At our field site, A. fuscipes case density averaged 2192 cases m−2, equivalent to 1.4 t km−1. This finding is important because in gravel-bed rivers frequented by Glossosomatidae larvae, sediment transport is typically limited by the availability of entrainable fine grain sediment at the surface. We discuss the implications of this sediment movement for river bed sedimentary structure, the transport of sand and gravel, and the possible role of Glossosomatidae larvae as ecosystem engineers.

Are UK Rivers Getting Saltier and More Alkaline?

River salinisation and alkalinisation have become one of the major environmental problems threatening the safety of global freshwater resources. With the accelerated climate change and aggravating anthropogenic influences, it is important to identify the trends and causes of river salinisation and alkalinisation so that better mitigation measures could be taken. This study has focused on the UK rivers because there has been insufficient investigation on this topic. To understand the salinisation and alkalinisation trends and causes of rivers in the UK over the past 20 years from a vertical (analysis of each river) and horizontal (comparison of all rivers) perspective, this study uses the Theil-Sen regression and Mann-Kendall test to deal with the trends of conductivity (proxy on salinisation) and pH (proxy on alkalinisation), obtains outliers of conductivity and pH by boxplot, and calculates the Pearson’s and the Kendall’s Tau correlation coefficients (α = 0.05) between the water quality data and the potential factors (potential road salting, normalized difference vegetation index (NDVI), river discharge, agricultural and urban lands). The results show that the UK rivers are becoming more alkaline with a median pH increase of 0.05 to 0.40, but less salty with a median conductivity decrease of 0.06 to 0.11 mS/cm. And the changes in conductivity and pH have seasonality and regionality, which shows that there are usually greater changes in trends and medians of them in winter or through reaches with more anthropogenic disturbance. Furthermore, from a vertical perspective, the conductivity of more than 50% of rivers in this study is negatively correlated with NDVI and river discharge, and positively correlated with potential road salting, and the pH of that is positively correlated with agricultural lands. While from a horizontal perspective, NDVI and agricultural lands are positively correlated with pH, and potential road salting and urban lands are positively correlated with conductivity. Therefore, road salting, urbanisation, agricultural lands, river discharge and vegetation cover can be considered to affect river salinisation and alkalinisation in the UK.

Predicting the dispersal of SARS-CoV-2 RNA from the wastewater treatment plant to the coast

Viral pathogens including SARS-CoV-2 RNA have been detected in wastewater treatment effluent, and untreated sewage overflows, that pose an exposure hazard to humans. We assessed whether SARS-CoV-2 RNA was likely to have been present in detectable quantities in UK rivers and estuaries during the first wave of the Covid-19 pandemic. We simulated realistic viral concentrations parameterised on the Camel and Conwy catchments (UK) and their populations, showing detectable SARS-CoV-2 RNA concentrations for untreated but not for treated loading, but also being contingent on viral decay, hydrology, catchment type/shape, and location. Under mean or low river flow conditions, viral RNA concentrated within the estuaries allowing for viral build-up and caused a lag by up to several weeks between the peak in community infections and the viral peak in the environment. There was an increased hazard posed by SARS-CoV-2 RNA with a T90 decay rate >24 h, as the estuarine build-up effect increased. High discharge events transported the viral RNA downstream and offshore, increasing the exposure risk to coastal bathing waters and shellfisheries – although dilution in this case reduced viral concentrations well below detectable levels. Our results highlight the sensitivity of exposure to viral pathogens downstream of wastewater treatment, across a range of viral loadings and catchment characteristics – with implications to environmental surveillance.

EURO-CORDEX: A Multi-Model Ensemble Fit for Assessing Future Hydrological Change?

Human-induced changes in climatic behavior and variations in future river flows has been at the fore-front of recent academic and political discourse. Future climate projections are a vital tool in tackling climate change and supporting future adaptation, however until recently models have been viewed individually with a lack of uncertainty quantification. A multi-model ensemble (MME) with a wide range of general circulation models, regional climate models and emissions scenarios, EURO-CORDEX provides climate projections as well as flow series projections across the European domain from 1950 to 2100. This paper explores the validity of the 68 chain MME flow projections by investigating its ability to match observed flow records in the UK over the period 1975–2004. The work explores magnitude through quantile matching and seasonality matching by time-series decomposition of trends. Two statistical tests [Mann-Whitney, and Mean Average Arctangent Percentage Error (MAAPE)] were used to compare EURO-CORDEX flow projections to observed river flows recorded by the National River Flow Archive (NRFA) across 1,436 UK river catchments. Results indicate a high degree of similarity justifying the application of this dataset for assessing future hydrological changes across a regional scale. Discretizing the flow projections into regional and hydrometric areas highlights the variability in performance between neighboring domains and the strong influence local features may have on climate model performance. The validation of EURO-CORDEX flow projection data regionally enables a wide range of applications including the exploration of future changes in local and national river flows.

Tracking the methodological evolution of climate change projections for UK river flows

Much research has been carried out on the possible impacts of climate change for UK river flows. Catchment and national-scale studies since the early 1990s are here categorized into four modelling approaches: “top-down” GCM (Global Climate Model)-driven and probabilistic approaches and “bottom-up” stylised and scenario-neutral approaches. Early studies followed a stylised approach with a small number of model experiments focused on system sensitivity. GCM-driven approaches dominate since the mid-1990s and are scenario-led and “top-down”, but which incur the cascade of uncertainty which results in a large amount of information that may not be conducive to decision-making. The emergence of probabilistic projections aims to incorporate probabilistic information in navigating climate model uncertainty but remained “top-down” with challenges over its practical use for water resources planning. The scenario-neutral approach has clear roots in the early stylised approach with the aim to explore plausible futures beyond climate model projections and system sensitivity. A synthesis of studies employing each approach shows that the magnitude and sign of change in different hydrological variables remain uncertain between different regions of the UK. Comparison between studies is difficult due to their methodological differences and consequently different choices along the impact modelling chain, and with a notable geographic bias in catchment selection in southeast England. Major limitations for each approach include barriers to decision-making from wide uncertainty ranges, limited consideration of high-impact outcomes, and challenges in their application in water resources planning. These challenges represent priorities for future research using new “hybrid” approaches to produce complementary information to “top down” projections within a more “bottom-up” framework. Exploratory modelling, robust decision-making and storylines are examples of new approaches that have emerged. Key to the emerging approaches identified is a need to combine different modelling approaches to tackle different sources of uncertainty according to the intended aims of individual applications.