A systematic approach to understand hydrogeochemical dynamics in large river systems: Development and application to the River Ganges (Ganga) in India

Large river systems, such as the River Ganges (Ganga), provide crucial water resources for the environment and society, yet often face significant challenges associated with cumulative impacts arising from upstream environmental and anthropogenic influences. Understanding the complex dynamics of such systems remains a major challenge, especially given accelerating environmental stressors including climate change and urbanization, and due to limitations in data and process understanding across scales. An integrated approach is required which robustly enables the hydrogeochemical dynamics and underpinning processes impacting water quality in large river systems to be explored. Here we develop a systematic approach for improving the understanding of hydrogeochemical dynamics and processes in large river systems, and apply this to a longitudinal survey (> 2500 km) of the River Ganges (Ganga) and key tributaries in the Indo-Gangetic basin. This framework enables us to succinctly interpret downstream water quality trends in response to the underpinning processes controlling major element hydrogeochemistry across the basin, based on conceptual water source signatures and dynamics. Informed by a 2019 post-monsoonal survey of 81 river bank-side sampling locations, the spatial distribution of a suite of selected physico-chemical and inorganic parameters, combined with segmented linear regression, reveals minor and major downstream hydrogeochemical transitions. We use this information to identify five major hydrogeochemical zones, characterized, in part, by the inputs of key tributaries, urban and agricultural areas, and estuarine inputs near the Bay of Bengal. Dominant trends are further explored by investigating geochemical relationships (e.g. Na:Cl, Ca:Na, Mg:Na, Sr:Ca and NO₃:Cl), and how water source signatures and dynamics are modified by key processes, to assess the relative importance of controls such as dilution, evaporation, water-rock interactions (including carbonate and silicate weathering) and anthropogenic inputs. Mixing/dilution between sources and water-rock interactions explain most regional trends in major ion chemistry, although localized controls plausibly linked to anthropogenic activities are also evident in some locations. Temporal and spatial representativeness of river bank-side sampling are considered by supplementary sampling across the river at selected locations and via comparison to historical records. Limitations of such large-scale longitudinal sampling programs are discussed, as well as approaches to address some of these inherent challenges. This approach brings new, systematic insight into the basin-wide controls on the dominant geochemistry of the River Ganga, and provides a framework for characterising dominant hydrogeochemical zones, processes and controls, with utility to be transferable to other large river systems.

The Time Machine framework: monitoring and prediction of biodiversity loss

Transdisciplinary solutions are needed to achieve the sustainability of ecosystem services for future generations. We propose a framework to identify the causes of ecosystem function loss and to forecast the future of ecosystem services under different climate and pollution scenarios. The framework (i) applies an artificial intelligence (AI) time-series analysis to identify relationships among environmental change, biodiversity dynamics and ecosystem functions; (ii) validates relationships between loss of biodiversity and environmental change in fabricated ecosystems; and (iii) forecasts the likely future of ecosystem services and their socioeconomic impact under different pollution and climate scenarios. We illustrate the framework by applying it to watersheds, and provide system-level approaches that enable natural capital restoration by associating multidecadal biodiversity changes to chemical pollution.

Estimation of river flow using CubeSats remote sensing

River flow characterizes the integrated response from watersheds, so it is essential to quantify to understand the changing water cycle and underpin the sustainable management of freshwaters. However, river gauging stations are in decline with ground-based observation networks shrinking. This study proposes a novel approach of estimating river flows using the Planet CubeSats constellation with the possibility to monitor on a daily basis at the sub-catchment scale through remote sensing. The methodology relates the river discharge to the water area that is extracted from the satellite image analysis. As a testbed, a series of Surface Reflectance PlanetScope images and observed streamflow data in Araguaia River (Brazil) were selected to develop and validate the methodology. The study involved the following steps: (1) survey of measurements of water level and river discharge using in-situ data from gauge-based Conventional Station (CS) and measurements of altimetry using remote data from JASON-2 Virtual Station (JVS); (2) survey of Planet CubeSat images for dates in step 1 and without cloud cover; (3) image preparation including clipping based on different buffer areas and calculation of the Normalized Difference Vegetation Index (NDVI) per image; (4) water bodies areas calculation inside buffers in the Planet CubeSat images; and (5) correlation analysis of CubeSat water bodies areas with JVS and CS data. Significant correlations between the water bodies areas with JVS (R² = 88.83%) and CS (R² = 96.49%) were found, indicating that CubeSat images can be used as a CubeSat Virtual Station (CVS) to estimate the river flow. This newly proposed methodology using CubeSats allows for more accurate results than the JVS-based method used by the Brazilian National Water Agency (ANA) at present. Moreover, CVS requires small areas of remote sensing data to estimate with high accuracy the river flow and the height variation of the water in different timeframes. This method can be used to monitor sub-basin scale discharge and to improve water management, particularly in developing countries where the presence of conventional stations is often very limited.

Calibration of an in-situ fluorescence-based sensor platform for reliable BOD5 measurement in wastewater

Reliance on biochemical oxygen demand (BOD₅) as an indicator of wastewater quality has hindered the development of efficient process control due to the associated uncertainty and lag-times. Surrogate measurements have been proposed, with fluorescence spectroscopy a promising technique. Yet, assessment of in-situ fluorescence sensors across multiple wastewater treatment plants (WwTPs), and at different treatment stages, is limited. In this study a multi-parameter sonde (two fluorescence peaks, turbidity, temperature and electrical conductivity) was used to provide a BOD₅ surrogate measurement. The sonde was deployed at three WwTPs, on post primary settlement tanks (PST) and final effluent (FE). Triplicate laboratory measurements of BOD₅, from independent laboratories were used to calibrate the sensor, with high variability apparent for FE samples. Site and process specific sensor calibrations yielded the best results (R²_cv = 0.76-0.86; 10-fold cross-validation) and mean BOD₅ of the three laboratory measurements improved FE calibration. When combining PST sites a reasonable calibration was still achieved (R²_cv = 0.67) suggesting transfer of sensors between WwTPs may be possible. This study highlights the potential to use online optical sensors as robust BOD₅ surrogates in WwTPs. However, careful calibration (i.e. replicated BOD₅ measurements) is required for FE as laboratory measurements can be associated with high uncertainty.

Macrophyte Controls on Urban Stream Microbial Metabolic Activity

Urban rivers worldwide are affected directly by macrophyte growth, causing reduced flow velocity and risks of flooding. Therefore, cutting macrophytes is a common management practice to ensure free drainage. The impacts of macrophyte removal on transient storage dynamics and microbial metabolic activity of wastewater-fed urban streams are unknown, preventing any assessment of the hydrodynamic and biogeochemical consequences of this management practice. Slug tracer injections were performed with the conservative tracer uranine and the reactive tracer resazurin to quantify the implications of macrophyte cutting on stream flow dynamics and metabolism. Macrophyte cutting reduced mean tracer arrival times in managed stream reaches but did not significantly decrease whole-stream microbial metabolic activity. In fact, transient storage indices were found to have increased after cutting, suggesting that macrophyte removal and the resulting increase in flow velocity may have enhanced hyporheic exchange flow through streambed sediments. Our results evidence that macrophyte cutting in nutrient-rich urban streams does not necessarily lead to lower in-stream storage and metabolism but that the gain in hyporheic exchange and streambed microbial metabolic activity can compensate for reduced in-stream storage. Increased stream flow resulting from macrophyte removal may therefore even enhance nutrient and pollutant attenuation capacity of streambed sediments.

Combining in-situ fluorometry and distributed rainfall data provides new insights into natural organic matter transport dynamics in an urban river

Urbanization alters the quality and quantity of Dissolved Organic Matter (DOM) fluxes to rivers potentially leading to water quality problems and impaired ecosystem function. Traditional synoptic and point sampling approaches are generally inadequate for monitoring DOM source dynamics. To identify links between spatial heterogeneity in precipitation and DOM dynamics, we used a unique approach combining high spatial and temporal resolution precipitation datasets featuring point, catchment, and land-cover weighted precipitation to characterise catchment transport dynamics. These datasets were linked to fluorescence records from an urban stream (Bourn Brook, Birmingham, UK). Humic-like fluorescence (HLF: Ex. 365 nm, Em. 490 nm) and Tryptophan-like fluorescence (TLF: Ex. 285 nm, Em. 340 nm) were measured, (plus river flow and turbidity) at 5 min intervals for 10 weeks during Autumn 2017. The relationship between discharge (Q) and concentration (C) for TLF and HLF were strongly chemodynamic at low Q (<Q50) but TLF was chemostatic when Q exceeded this threshold. Figure of eight hysteresis was the most common response type for both HLF and TLF, indicating that DOM sources shift within and between events. Key drivers of DOM dynamics were identified using regression analysis and model outputs using point, catchment-averaged, and land-use weighted precipitation were compared. Antecedent rainfall was identified as the most important predictor (negative relationship) of TLF and HLF change suggesting DOM source exhaustion. Precipitation weighted by land cover showed that urbanization metrics were linked to increased TLF:HLF ratios and changes in hysteresis index. This study presents a novel approach of using land-cover weighted rainfall to enhance mechanistic understanding of DOM controls and sources. In contrast, catchment-average rainfall data have the potential to yield stronger understanding of TLF dynamics. This technique could be integrated with existing high resolution in-situ datasets to enhance our understanding of DOM dynamics in urban rivers.

Long-term river invertebrate community responses to groundwater and surface water management operations

River flow regimes have been transformed by groundwater and surface water management operations globally, prompting widespread ecological responses. Yet, empirical evidence quantifying the simultaneous effects of groundwater and surface water management operations on freshwater ecosystems remains limited. This study combines a multi-decadal freshwater invertebrate dataset (1995-2016) with groundwater model outputs simulating the effects of different anthropogenic flow alterations (e.g. groundwater abstraction, effluent water returns) and river discharges. A suite of flow alteration- and flow-ecology relationships were modelled that tested different invertebrate community responses (taxonomic, functional, flow response guilds, individual taxa). Most flow alteration-ecology relationships were not statistically significant, highlighting the absence of consistent, detectable ecological responses to long-term water management operations. A small number of significant statistical models provided insights into how flow alterations transformed specific ecological assets; including Ephemeroptera, Plecoptera and Trichoptera taxa which are rheophilic in nature being positively associated with groundwater abstraction effects reducing river discharges by 0-15%. This represents a key finding from a water resource management operation perspective given that such flow alteration conditions were observed on average in over two-thirds of the study sites examined. In a small number of instances, specific invertebrate responses displayed relative declines associated with the most severe groundwater abstraction effects and artificial hydrological inputs (predominantly effluent water returns). The strongest flow-ecology relationships were recorded during spring months, when invertebrate communities were most responsive to antecedent minimum and maximum discharges, and average flow conditions in the preceding summer months. Results from this study provide new evidence indicating how groundwater and surface water resources can be managed to conserve riverine ecological assets. Moreover, the ensemble of flow alteration- and flow-ecology relationships established in this study could be used to guide environmental flow strategies. Such findings are of global importance given that future climatic change and rising societal water demands are likely to further transform river flow regimes and threaten freshwater ecosystems.

River temperature research and practice: Recent challenges and emerging opportunities for managing thermal habitat conditions in stream ecosystems

There is growing evidence that river temperatures are increasing under climate change, which is expected to be exacerbated by increased abstractions to satisfy human water demands. Water temperature research has experienced crucial advances, both in terms of developing new monitoring and modelling tools, as well as understanding the mechanisms of temperature feedbacks with biogeochemical and ecological processes. However, water practitioners and regulators are challenged with translating the widespread and complex technological, modelling and conceptual advances made in river temperature research into improvements in management practice. This critical review provides a comprehensive overview of recent advances in the state-of-the-art monitoring and modelling tools available to inform ecological research and practice. In so doing, we identify pressing research gaps and suggest paths forward to address practical research and management challenges. The proposed research directions aim to provide new insights into spatio-temporal stream temperature dynamics and unravel drivers and controls of thermal river regimes, including the impacts of changing temperature on metabolism and aquatic biogeochemistry, as well as aquatic organisms. The findings of this review inform future research into ecosystem resilience in the face of thermal degradation and support the development of new management strategies cutting across spatial and temporal scales.

Moving beyond the Technology: A Socio-technical Roadmap for Low-Cost Water Sensor Network Applications

In this paper, we critically review the current state-of-the-art for sensor network applications and approaches that have developed in response to the recent rise of low-cost technologies. We specifically focus on water-related low-cost sensor networks, and conceptualize them as socio-technical systems that can address resource management challenges and opportunities at three scales of resolution: (1) technologies, (2) users and scenarios, and (3) society and communities. Building this argument, first we identify a general structure for building low-cost sensor networks by assembling technical components across configuration levels. Second, we identify four application categories, namely operational monitoring, scientific research, system optimization, and community development, each of which has different technical and nontechnical configurations that determine how, where, by whom, and for what purpose low-cost sensor networks are used. Third, we discuss the governance factors (e.g., stakeholders and users, networks sustainability and maintenance, application scenarios, and integrated design) and emerging technical opportunities that we argue need to be considered to maximize the added value and long-term societal impact of the next generation of sensor network applications. We conclude that consideration of the full range of socio-technical issues is essential to realize the full potential of sensor network technologies for society and the environment.

High frequency fluorescence monitoring reveals new insights into organic matter dynamics of an urban river, Birmingham, UK

Natural organic matter (NOM) is fundamental to many biogeochemical processes in river ecosystems. Currently, however, we have limited knowledge of NOM dynamics across the spectrum of flow conditions as previous studies have focused largely on storm events. Field deployable fluorescence technology offers new opportunities to explore both stochastic and predictable diel NOM dynamics at finer time-steps and for longer periods than was hitherto possible, thus yielding new insight into NOM sources, processing, and pathways. Hourly fluorescence data (humic-like fluorescence [Peak C] and tryptophan-like fluorescence [Peak T]) and a suite of hydro-climatological variables were collected from an urban river (Birmingham, UK). We explored monthly concentration-discharge (C-Q) patterns using segmented regression and assessed hysteretic and flushing behaviour for Peak C, T and turbidity to infer source zone activation. Diel patterns were assessed during low flow periods. Wavelet analysis identified strong diurnal variations in Peak C with early morning peaks while no diel dynamics were apparent for Peak T. Using generalised linear modelling relationships between Peak C periodicity and both solar radiation and time since previous storm/scouring event were identified. Breakpoints and positive slopes for C-Q relationship highlighted chemodynamic behaviour for NOM over most of the monitoring period, with Peak T mobilised more relative to Peak C during high Q. Hysteresis patterns were highly variable but flushing behaviour of Peak T and C suggested exhaustion of humic compounds during long duration events and following successive rainfall events. Peak T flushing was correlated with Q magnitude highlighting the potential for combined sewer overflows to act as important NOM sources despite significant dilution potential. This research highlights the potential of real-time, field deployable fluorescence spectroscopy as a viable method for providing insight into diel and transport driven NOM dynamics.

In utero congenital chylothorax treatment with fetal thoracoamniotic shunt: Case report

BACKGROUND

Fetal pleural effusions are a rare fetal anomaly that may result from congenital chylothorax. Severe cases lead to chest compression with resulting pulmonary hypoplasia and possible neonatal demise. Fetal thoracoamiontic shunt (TAS) placement may decrease the amount of pleural effusion and improve lung expansion.

CASE

A 30-year-old primigravida at 29 2/7 weeks' gestation presented with fetal bilateral pleural effusions with no identifiable genetic or structural abnormalities. TAS placement accomplished decompression of the left fetal chest. The neonate was delivered at 33 3/7 weeks and required minimal respiratory support with no apparent long term complications at discharge.

CONCLUSION

This case demonstrated that fetal intervention with TAS placement can improve neonatal outcomes. Referral to an MFM specialist capable of TAS should be considered for isolated fetal bilateral pleural effusion.

Diatoms as indicators of the effects of river impoundment at multiple spatial scales

River impoundment constitutes one of the most important anthropogenic impacts on the World's rivers. An increasing number of studies have tried to quantify the effects of river impoundment on riverine ecosystems over the past two decades, often focusing on the effects of individual large reservoirs. This study is one of the first to use a large-scale, multi-year diatom dataset from a routine biomonitoring network to analyse sample sites downstream of a large number of water supply reservoirs (n = 77) and to compare them with paired unregulated control sites. We analysed benthic diatom assemblage structure and a set of derived indices, including ecological guilds, in tandem with multiple spatio-temporal variables to disclose patterns of ecological responses to reservoirs beyond the site-specific scale. Diatom assemblage structure at sites downstream of water supply reservoirs was significantly different to control sites, with the effect being most evident at the regional scale. We found that regional influences were important drivers of differences in assemblage structure at the national scale, although this effect was weaker at downstream sites, indicating the homogenising effect of river impoundment on diatom assemblages. Sites downstream of reservoirs typically exhibited a higher taxonomic richness, with the strongest increases found within the motile guild. In addition, Trophic Diatom Index (TDI) values were typically higher at downstream sites. Water quality gradients appeared to be an important driver of diatom assemblages, but the influence of other abiotic factors could not be ruled out and should be investigated further. Our results demonstrate the value of diatom assemblage data from national-scale biomonitoring networks to detect the effects of water supply reservoirs on instream communities at large spatial scales. This information may assist water resource managers with the future implementation of mitigation measures such as setting environmental flow targets.

Drone-based Structure-from-Motion provides accurate forest canopy data to assess shading effects in river temperature models

Climatic warming will increase river temperature globally, with consequences for cold water-adapted organisms. In regions with low forest cover, elevated river temperature is often associated with a lack of bankside shading. Consequently, river managers have advocated riparian tree planting as a strategy to reduce temperature extremes. However, the effect of riparian shading on river temperature varies substantially between locations. Process-based models can elucidate the relative importance of woodland and other factors driving river temperature and thus improve understanding of spatial variability of the effect of shading, but characterising the spatial distribution and height of riparian tree cover necessary to parameterise these models remains a significant challenge. Here, we document a novel approach that combines Structure-from-Motion (SfM) photogrammetry acquired from a drone to characterise the riparian canopy with a process based temperature model (Heat Source) to simulate the effects of tree shading on river temperature. Our approach was applied in the Girnock Burn, a tributary of the Aberdeenshire Dee, Scotland. Results show that SfM approximates true canopy elevation with a good degree of accuracy (R² = 0.96) and reveals notable spatial heterogeneity in shading. When these data were incorporated into a process-based temperature model, it was possible to simulate river temperatures with a similarly-high level of accuracy (RMSE <0.7 °C) to a model parameterised using 'conventional' LiDAR tree height data. We subsequently demonstrate the utility of our approach for quantifying the magnitude of shading effects on stream temperature by comparing simulated temperatures against another model from which all riparian woodland has been removed. Our findings highlight drone-based SfM as an effective tool for characterising riparian shading and improving river temperature models. This research provides valuable insights into the effects of riparian woodland on river temperature and the potential of bankside tree planting for climate change adaptation.

Streambed Organic Matter Controls on Carbon Dioxide and Methane Emissions from Streams

Greenhouse gas (GHG) emissions of carbon dioxide (CO₂) and methane (CH₄) from streambeds are currently understudied. There is a paucity of research exploring organic matter (OM) controls on GHG production by microbial metabolic activity in streambeds, which is a major knowledge gap given the increased inputs of allochthonous carbon to streams, especially in agricultural catchments. This study aims to contribute to closing this knowledge gap by quantifying how contrasting OM contents in different sediments affect streambed GHG production and associated microbial metabolic activity. We demonstrate, by means of an incubation experiment, that streambed sediments have the potential to produce substantial amounts of GHG, controlled by sediment OM quantity and quality. We observed streambed CO₂ production rates that can account for 35% of total stream evasion estimated in previous studies, ranging between 1.4 and 86% under optimal conditions. Methane production varied stronger than CO₂ between different geologic backgrounds, suggesting OM quality controls between streambed sediments. Moreover, our results indicate that streambed sediments may produce much more CO₂ than quantified to date, depending on the quantity and quality of the organic matter, which has direct implications for global estimates of C fluxes in stream ecosystems.

Analysis of clinical diagnosis for all patients receiving antenatal betamethasone in a community hospital

OBJECTIVE

Identify which obstetrical diagnoses are associated with suboptimal antenatal betamethasone administration.

METHODS

We present a retrospective, cohort study of patients who received betamethasone due to a risk for preterm delivery, between 7/2013 and 9/2016 at our institution. Details of betamethasone administration were recorded including the diagnosis leading to betamethasone. Optimal administration was defined as two doses of betamethasone given 24 hours apart, with delivery occurring at greater than 24 hours but less than seven days after completion of the second dose of betamethasone. Suboptimal administration included any betamethasone dosing that did not meet the optimal criteria.

RESULTS

428 patients were identified for the study with 20.1% of patients receiving optimal betamethasone. Patients presenting with hypertensive disorders of pregnancy (36.1%) and preterm premature rupture of membranes (PPROM) (22.1%) were more likely to receive optimal betamethasone, while patients presenting with preterm labor (PTL) (41.8%) and placental abruption (24.6%) were more likely to receive suboptimal betamethasone (p-value < 0.0001). Among PTL patients, those presenting with contractions and cervical dilation/short cervix (19.15%) were more likely to receive optimal betamethasone (p-value 0.0349). Optimal betamethasone decreased the incidence of respiratory distress syndrome (RDS) among 32.1 to 34 week neonates.

CONCLUSION

Hypertensive disorders of pregnancy and PPROM are associated with optimal betamethasone, whereas PTL and placental abruption are associated with suboptimal betamethasone.

Macroinvertebrate community responses to river impoundment at multiple spatial scales

River impoundment by the construction of dams potentially modifies a wide range of abiotic and biotic factors in lotic ecosystems and is considered one of the most significant anthropogenic impacts on rivers globally. The past two decades have witnessed a growing body of research centred on quantifying the effects of river impoundment, with a focus on mitigating and managing the effects of individual large dams. This study presents a novel multi-scale comparison of paired downstream and control sites associated with multiple water supply reservoirs (n = 80) using a spatially extensive multi-year dataset. Macroinvertebrate community structure and indices were analysed in direct association with spatial (e.g. region) and temporal variables (e.g. season) to identify consistent patterns in ecological responses to impoundment. Macroinvertebrate communities at monitoring sites downstream of water supply reservoirs differed significantly from those at control sites at larger spatial scales, both in terms of community structure and taxa richness. The effect was most significant at the regional scale, while biogeographical factors appeared to be important drivers of community differences at the national scale. Water supply reservoirs dampened natural seasonal patterns in community structure at sites downstream of impoundments. Generally, taxonomic richness was higher and %EPT richness lower at downstream sites. Biomonitoring indices used for river management purposes were able to detect community differences, demonstrating their sensitivity to river regulation activities. The results presented improve our understanding of the spatially extensive and long-term effects of water supply reservoirs on instream communities and provide a basis for the future implementation of mitigation measures on impounded rivers and heavily modified waterbodies.

Improving representation of riparian vegetation shading in a regional stream temperature model using LiDAR data

Modelling river temperature at the catchment scale is needed to understand how aquatic communities may adapt to current and projected climate change. In small and medium rivers, riparian vegetation can greatly reduce maximum water temperature by providing shade. It is thus important that river temperature models are able to correctly characterise the impact of this riparian shading. In this study, we describe the use of a spatially-explicit method using LiDAR-derived data for computing the riparian shading on direct and diffuse solar radiation. The resulting data are used in the T-NET one-dimensional stream temperature model to simulate water temperature from August 2007 to July 2014 for 270km of the Loir River, an indirect tributary of the Loire River (France). Validation is achieved with 4 temperature monitoring stations spread along the Loir River. The vegetation characterised with the LiDAR approach provides a cooling effect on maximum daily temperature (T_max) ranging from 3.0°C (upstream) to 1.3°C (downstream) in late August 2009. Compared to two other riparian shading routines that are less computationally-intensive, the use of our LiDAR-based methodology improves the bias of T_max simulated by the T-NET model by 0.62°C on average between April and September. However, difference between the shading routines reaches up to 2°C (monthly average) at the upstream-most station. Standard deviation of errors on T_max is not improved. Computing the impact of riparian vegetation at the hourly timescale using reach-averaged parameters provides results close to the LiDAR-based approach, as long as it is supplied with accurate vegetation cover data. Improving the quality of riparian vegetation data should therefore be a priority to increase the accuracy of stream temperature modelling at the regional scale.

Functional diversity and community assembly of river invertebrates show globally consistent responses to decreasing glacier cover

Global change threatens invertebrate biodiversity and its central role in numerous ecosystem functions and services. Functional trait analyses have been advocated to uncover global mechanisms behind biodiversity responses to environmental change, but the application of this approach for invertebrates is underdeveloped relative to other organism groups. From an evaluation of 363 records comprising >1.23 million invertebrates collected from rivers across nine biogeographic regions on three continents, consistent responses of community trait composition and diversity to replicated gradients of reduced glacier cover are demonstrated. After accounting for a systematic regional effect of latitude, the processes shaping river invertebrate functional diversity are globally consistent. Analyses nested within individual regions identified an increase in functional diversity as glacier cover decreases. Community assembly models demonstrated that dispersal limitation was the dominant process underlying these patterns, although environmental filtering was also evident in highly glacierized basins. These findings indicate that predictable mechanisms govern river invertebrate community responses to decreasing glacier cover globally.

A spatio-temporal statistical model of maximum daily river temperatures to inform the management of Scotland's Atlantic salmon rivers under climate change

The thermal suitability of riverine habitats for cold water adapted species may be reduced under climate change. Riparian tree planting is a practical climate change mitigation measure, but it is often unclear where to focus effort for maximum benefit. Recent developments in data collection, monitoring and statistical methods have facilitated the development of increasingly sophisticated river temperature models capable of predicting spatial variability at large scales appropriate to management. In parallel, improvements in temporal river temperature models have increased the accuracy of temperature predictions at individual sites. This study developed a novel large scale spatio-temporal model of maximum daily river temperature (Tw_max) for Scotland that predicts variability in both river temperature and climate sensitivity. Tw_max was modelled as a linear function of maximum daily air temperature (Ta_max), with the slope and intercept allowed to vary as a smooth function of day of the year (DoY) and further modified by landscape covariates including elevation, channel orientation and riparian woodland. Spatial correlation in Tw_max was modelled at two scales; (1) river network (2) regional. Temporal correlation was addressed through an autoregressive (AR1) error structure for observations within sites. Additional site level variability was modelled with random effects. The resulting model was used to map (1) spatial variability in predicted Tw_max under current (but extreme) climate conditions (2) the sensitivity of rivers to climate variability and (3) the effects of riparian tree planting. These visualisations provide innovative tools for informing fisheries and land-use management under current and future climate.

Macroinvertebrate community responses to hydrological controls and groundwater abstraction effects across intermittent and perennial headwater streams

Intermittent rivers comprise a significant proportion of river networks globally and their spatial extent is predicted to increase with rising water abstraction pressures. Despite this, the ecological implications of hydrological modifications within intermittent rivers have received limited research attention. This paper examines macroinvertebrate assemblages across intermittent and perennial sections of headwater streams within the Hampshire Avon catchment (United Kingdom) over a five-year period. The composition of faunal assemblages was quantified in relation to four hydrological metrics: the duration of flowing conditions, the geographical proximity to the nearest perennial source along each watercourse (two observed flow parameters) and two modelled groundwater abstraction influences. The results highlight that macroinvertebrate communities inhabiting sites which dry periodically and are positioned at greater distances (>c. 2.5km) above the perennial source (the most upstream point of permanent flow within a given year) possessed the highest conservation values. These sites supported species that are rare in many areas of Europe (e.g. Ephemeroptera: Paraletophlebia werneri) or with limited geographical distribution across the United Kingdom (e.g. Trichoptera: Limnephilus bipunctatus). A range of faunal community diversity indices were found to be more sensitive to the antecedent flow duration and distance from the perennial source, rather than any effects of groundwater abstraction. Taxonomic richness responded most strongly to these observed flow parameters and varied more markedly with the distance from the perennial source compared to the antecedent flow duration. Several taxa were significantly associated with the observed flow parameters, particularly those predominantly inhabiting perennially flowing systems. However, the distance that such fauna could migrate into intermittent reaches varied between taxa. This research demonstrates the overriding importance of antecedent flow durations and the geographical proximity to perennial sources on macroinvertebrate communities within intermittent and perennial headwater streams.

Stream temperature under contrasting riparian forest cover: Understanding thermal dynamics and heat exchange processes

Climate change is likely to increase summer temperatures in many river environments, raising concerns that this will reduce their thermal suitability for a range of freshwater fish species. As a result, river managers have pursued riparian tree planting due to its ability to moderate stream temperatures by providing shading. However, little is known about the relative ability of different riparian forest types to moderate stream temperatures. Further research is therefore necessary to inform best-practise riparian tree planting strategies. This article contrasts stream temperature and energy fluxes under three riparian vegetation types common to Europe: open grassland terrain (OS), semi-natural deciduous woodland (SNS), and commercial conifer plantation (CS). Data was recorded over the course of a year by weather stations installed in each of the vegetation types. Mean daily stream temperature was generally warmest at OS and coolest at CS. Energy gains at all sites were dominated by shortwave radiation, whereas losses where principally due to longwave and latent heat flux. The magnitude of shortwave radiation received at the water surface was strongly dependent upon vegetation type, with OS and SNS woodland sites receiving approximately 6× and 4× (respectively) the incoming solar radiation of CS. Although CS lost less energy through longwave or latent fluxes than the other sites, net surface heat flux was ordered OS>SNS>CS, mirroring the stream temperature results. These findings demonstrate that energy fluxes at the air-water interface vary substantially between different riparian forest types and that stream temperature response to bankside vegetation depends upon the type of vegetation present. These results present new insights into the conditions under which riparian vegetation shading is optimal for the reduction of surface heat fluxes and have important implications for the development of 'best-practice' tree planting strategies to moderate summer temperature extremes in rivers.

Glacier shrinkage driving global changes in downstream systems

Glaciers cover ∼10% of the Earth's land surface, but they are shrinking rapidly across most parts of the world, leading to cascading impacts on downstream systems. Glaciers impart unique footprints on river flow at times when other water sources are low. Changes in river hydrology and morphology caused by climate-induced glacier loss are projected to be the greatest of any hydrological system, with major implications for riverine and near-shore marine environments. Here, we synthesize current evidence of how glacier shrinkage will alter hydrological regimes, sediment transport, and biogeochemical and contaminant fluxes from rivers to oceans. This will profoundly influence the natural environment, including many facets of biodiversity, and the ecosystem services that glacier-fed rivers provide to humans, particularly provision of water for agriculture, hydropower, and consumption. We conclude that human society must plan adaptation and mitigation measures for the full breadth of impacts in all affected regions caused by glacier shrinkage.

In situ tryptophan-like fluorometers: assessing turbidity and temperature effects for freshwater applications

Tryptophan-like fluorescence (TLF) is an indicator of human influence on water quality as TLF peaks are associated with the input of labile organic carbon (e.g. sewage or farm waste) and its microbial breakdown. Hence, real-time measurement of TLF could be particularly useful for monitoring water quality at a higher temporal resolution than available hitherto. However, current understanding of TLF quenching/interference is limited for field deployable sensors. We present results from a rigorous test of two commercially available submersible tryptophan fluorometers (ex ∼ 285, em ∼ 350). Temperature quenching and turbidity interference were quantified in the laboratory and compensation algorithms developed. Field trials were then undertaken involving: (i) an extended deployment (28 days) in a small urban stream; and, (ii) depth profiling of an urban multi-level borehole. TLF was inversely related to water temperature (regression slope range: -1.57 to -2.50). Sediment particle size was identified as an important control on the turbidity specific TLF response, with signal amplification apparent <150 NTU for clay particles and <650 NTU for silt particles. Signal attenuation was only observed >200 NTU for clay particles. Compensation algorithms significantly improved agreement between in situ and laboratory readings for baseflow and storm conditions in the stream. For the groundwater trial, there was an excellent agreement between laboratory and raw in situ TLF; temperature compensation provided only a marginal improvement, and turbidity corrections were unnecessary. These findings highlight the potential utility of real time TLF monitoring for a range of environmental applications (e.g. tracing polluting sources and monitoring groundwater contamination). However, in situations where high/variable suspended sediment loads or rapid changes in temperature are anticipated concurrent monitoring of turbidity and temperature is required and site specific calibration is recommended for long term, surface water monitoring.

The use of invertebrates as indicators of environmental change in alpine rivers and lakes

In alpine regions climatic change will alter the balance between water sources (rainfall, ice-melt, snowmelt, and groundwater) for aquatic systems, particularly modifying the relative contributions of meltwater, groundwater and rain to both rivers and lakes. While these changes are expected to have implications for alpine aquatic ecosystems, little is known about potential ecological tipping points and associated indicator taxa. We examined changes in biotic communities along a gradient of glacier influence for two study systems: (1) a stream network in the French Pyrénées; and (2) a network of lakes in the Italian Alps, with the aim of identifying potential indicator taxa (macroinvertebrates and zooplankton) of glacier retreat in these environments. To assess parallels in biotic responses across streams and lakes, both primary data and findings from other publications were synthesised. Using TITAN (Threshold Indicator Taxa ANalysis) changes in community composition of river taxa were identified at thresholds of <5.1% glacier cover and <66.6% meltwater contribution. Below these thresholds the loss of cold stenothermic benthic invertebrate taxa, Diamesa spp. and the Pyrenean endemic Rhyacophila angelieri was apparent. Some generalist taxa including Protonemura sp., Perla grandis, Baetis alpinus, Rhithrogena loyolaea and Microspectra sp. increased when glacier cover was <2.7% and <52% meltwater. Patterns were not as distinct for the alpine lakes, due to fewer sampling sites; however, Daphnia longispina grp. and the benthic invertebrate groups Plectopera and Planaria were identified as potential indicator taxa. While further work is required to assess potential indicator taxa for alpine lake systems, findings from alpine river systems were consistent between methods for assessing glacier influence (meltwater contribution/glacier cover). Hence, it is clear that TITAN could become a useful management tool, enabling: (i) the identification of taxa particularly sensitive to glacier retreat; and (ii) conservation efforts/resources to be better directed in alpine aquatic systems.

Avian community responses to variability in river hydrology

River flow is a major driver of morphological structure and community dynamics in riverine-floodplain ecosystems. Flow influences in-stream communities through changes in water velocity, depth, temperature, turbidity and nutrient fluxes, and perturbations in the organisation of lower trophic levels are cascaded through the food web, resulting in shifts in food availability for consumer species. River birds are sensitive to spatial and phenological mismatches with aquatic prey following flow disturbances; however, the role of flow as a determinant of riparian ecological structure remains poorly known. This knowledge is crucial to help to predict if, and how, riparian communities will be influenced by climate-induced changes in river flow characterised by more extreme high (i.e. flood) and/or low (i.e. drought) flow events. Here, we combine national-scale datasets of river bird surveys and river flow archives to understand how hydrological disturbance has affected the distribution of riparian species at higher trophic levels. Data were analysed for 71 river locations using a Generalized Additive Model framework and a model averaging procedure. Species had complex but biologically interpretable associations with hydrological indices, with species' responses consistent with their ecology, indicating that hydrological-disturbance has implications for higher trophic levels in riparian food webs. Our quantitative analysis of river flow-bird relationships demonstrates the potential vulnerability of riparian species to the impacts of changing flow variability and represents an important contribution in helping to understand how bird communities might respond to a climate change-induced increase in the intensity of floods and droughts. Moreover, the success in relating parameters of river flow variability to species' distributions highlights the need to include river flow data in climate change impact models of species' distributions.

Responses to river inundation pressures control prey selection of riparian beetles

Background

Riparian habitats are subjected to frequent inundation (flooding) and are characterised by food webs that exhibit variability in aquatic/terrestrial subsidies across the ecotone. The strength of this subsidy in active riparian floodplains is thought to underpin local biodiversity. Terrestrial invertebrates dominate the fauna, exhibiting traits that allow exploitation of variable aquatic subsidies while reducing inundation pressures, leading to inter-species micro-spatial positioning. The effect these strategies have on prey selection is not known. This study hypothesised that plasticity in prey choice from either aquatic or terrestrial sources is an important trait linked to inundation tolerance and avoidance.

Method/Principal Findings

We used hydrological, isotopic and habitat analyses to investigate the diet of riparian Coleoptera in relation to inundation risk and relative spatial positioning in the floodplain. The study examined patch scale and longitudinal changes in utilisation of the aquatic subsidy according to species traits. Prey sourced from terrestrial or emerging/stranded aquatic invertebrates varied in relation to traits for inundation avoidance or tolerance strategies. Traits that favoured rapid dispersal corresponded with highest proportions of aquatic prey, with behavioural traits further predicting uptake. Less able dispersers showed minimal use of aquatic subsidy and switched to a terrestrial diet under moderate inundation pressures. All trait groups showed a seasonal shift in diet towards terrestrial prey in the early spring. Prey selection became exaggerated towards aquatic prey in downstream samples.

Conclusions/Significance

Our results suggest that partitioning of resources and habitat creates overlapping niches that increase the processing of external subsidies in riparian habitats. By demonstrating functional complexity, this work advances understanding of floodplain ecosystem processes and highlights the importance of hydrological variability. With an increasing interest in reconnecting rivers to their floodplains, these invertebrates represent a key functional element in ensuring that such reconnections have demonstrable ecological value.

Evidence needed to manage freshwater ecosystems in a changing climate: turning adaptation principles into practice

It is widely accepted that climate change poses severe threats to freshwater ecosystems. Here we examine the scientific basis for adaptively managing vulnerable habitats and species. Our views are shaped by a literature survey of adaptation in practice, and by expert opinion. We assert that adaptation planning is constrained by uncertainty about evolving climatic and non-climatic pressures, by difficulties in predicting species- and ecosystem-level responses to these forces, and by the plasticity of management goals. This implies that adaptation measures will have greatest acceptance when they deliver multiple benefits, including, but not limited to, the amelioration of climate impacts. We suggest that many principles for biodiversity management under climate change are intuitively correct but hard to apply in practice. This view is tested using two commonly assumed doctrines: "increase shading of vulnerable reaches through tree planting" (to reduce water temperatures); and "set hands off flows" (to halt potentially harmful abstractions during low flow episodes). We show that the value of riparian trees for shading, water cooling and other functions is partially understood, but extension of this knowledge to water temperature management is so far lacking. Likewise, there is a long history of environmental flow assessment for allocating water to competing uses, but more research is needed into the effectiveness of ecological objectives based on target flows. We therefore advocate more multi-disciplinary field and model experimentation to test the cost-effectiveness and efficacy of adaptation measures applied at different scales. In particular, there is a need for a major collaborative programme to: examine natural adaptation to climatic variation in freshwater species; identify where existing environmental practice may be insufficient; review the fitness of monitoring networks to detect change; translate existing knowledge into guidance; and implement best practice within existing regulatory frameworks.