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The hydrochemical and physical functioning of UK river basins, estuaries and coastal waters through to the open sea are outlined in relation to British environmental research over the last ten or more years. An overview of a considerable body of published work is presented in the context of current findings and future research challenges. This is linked to this special issue of Science of the Total Environment ‘Land Ocean Interaction: processes, functioning and environmental management: a UK perspective’ for which this contribution provides a conclusion. [Copyright &y& Elsevier]

The catchment and river modelling undertaken within the UK Land Ocean Interaction Study programme represents the most extensive consistent exercise of this type undertaken in the UK. The calibrated model provides a quantitative assessment of the water and chemical fluxes transported by the rivers Derwent, Yorkshire Ouse, Wharfe, Aire, Don and Trent into the Humber estuary. These fluxes have been partitioned according to source (diffuse or point) for each basin, and a number of determinands. Total nitrogen from diffuse sources ranged from 92% on the largely agricultural Derwent to 38% from the industrial Don catchment. Even on catchments dominated by diffuse sources, point sources can contribute most during summer months. A quantitative assessment of the effect of in-stream processes suggests that denitrification can remove up to 40% of the total nitrogen entering the river system. A climate change scenario representing the 2050s revealed major changes in flow patterns, with all rivers showing a faster return to zero soil moisture deficit in the autumn and increased winter runoff, but a mixed picture of enhanced and reduced summer flows. Many associated fluxes may also increase, but long-term mean concentrations reduce because of the increased flows. The effect of the scenario on a river ecosystem classification was minor. Fertilizer reduction scenarios showed that even a large reduction in N applied as fertilizer (50%) resulted in much smaller reductions in the load delivered to the Humber estuary (6–16%). [Copyright &y& Elsevier]

The distribution of boron in rivers across European Union countries is described. The data have been collected from national and international monitoring programmes. The data show a wide range of concentrations but only in a few instances do concentrations exceed environmental quality standards. Although there is a good body of data for the analysis presented here, it is clear that there is not a full coverage of environments and for some studies there is a clear bias towards sampling of the main rivers or specific rivers where there are environmental concerns. The variations in concentration link directly to pollutant sources although assessment of the details of the spatial variations is clouded by factors such as the location of monitoring points in relation to pollutant discharges, the variation in dilution potential of the various rivers and contrasting hydrological and geological environments. The data are presented to complement more detailed studies on particular river basins as a basis for the further development of regional environmental impact water quality modelling frameworks and within the newly developing field of typological settings. [Copyright &y& Elsevier]

This review introduces the methods used to simulate the processes affecting dissolved oxygen (DO) in lowland rivers. The important processes are described and this provides a modelling framework to describe those processes in the context of a mass-balance model. The process equations that are introduced all require (reaction) rate parameters and a variety of common procedures for identifying those parameters are reviewed. This is important because there is a wide range of estimation techniques for many of the parameters. These different techniques elicit different estimates of the parameter value and so there is the potential for a significant uncertainty in the model''s inputs and therefore in the output too. Finally, the data requirements for modelling DO in lowland rivers are summarised on the basis of modelling the processes described in this review using a mass-balance model. This is reviewed with regard to what data are available and from where they might be obtained. [Copyright &y& Elsevier]

The catchment and river modelling undertaken within the UK Land Ocean Interaction Study (LOIS) programme represents the most extensive consistent exercise of this type undertaken in the UK. The calibrated model provides a quantitative assessment of the water and chemical fluxes transported by the rivers Derwent, Yorkshire Ouse, Wharfe, Aire, Don and Trent into the Humber estuary, i.e. a total drainage area of almost 18 000 km2 (almost 15% of the area of England) with 2088 km of modelled river. The model simulated flow, temperature, pH, suspended sediment, dissolved oxygen, biochemical oxygen demand, particulate organic nitrogen, ammonium, ammonia, nitrite, nitrate, zinc (dissolved and particulate), lindane and atrazine. For all rivers, except the Trent, simulations were for the period 1985–1995; the simulation period for the Trent was 1998–1995. The modelling used routine monitoring data collect by the England and Wales Environment Agency, for both calibration and validation, with other data sets mainly collated by the LOIS River-Atmosphere Coastal Study (RACS) data centre (e.g. land use, soils, river network). A stepwise model development started with a basic water quality model driven by observed in-stream water quality, and resulted in the development of a LOIS specific version of the in-stream model Quality Evaluation and Simulation Tool for River-systems that could be used to explore scenarios. The performance of the model was demonstrated by the reproduction of long-term statistics describing loads and concentrations, together with graphical output in the form of time series and distributions. The simulations were subsequently used to drive a linked catchment-river-estuary-coast-sea model covering the full domain of the RACS area. [Copyright &y& Elsevier]

Fluoride concentrations in eastern UK rivers (the Humber, Tweed, Wear, Great Ouse and Thames) are described based on information collected within the Land–Ocean Interaction Study (LOIS) and by the Environment Agency (EA) of England and Wales. The results show varied fluoride concentrations across the region, with a range from <0.01 to >10 mg l−1; and mean, median and range in mean concentrations of 0.30, 0.21 and 0.05–3.38 mg l−1 (excluding one outlier point), respectively. Within the main rivers and tributaries, the mean fluoride concentration varied from approximately 0.5 to over 2 mg l−1 and the highest values occurred within the Don basin (Don, Dearne and Rother) and parts of the Trent basin (upper Tame and mid–upper Derbyshire Derwent) in highly industrialised and urbanised areas (Sheffield and Rotherham in the Don basin; Birmingham and Derby on the Trent). For localised inputs to the rivers, fluoride concentrations were slightly higher, and considerably higher in one outlier case. Correspondingly, the other rivers examined typically had mean fluoride concentrations between approximately 0.2 and 0.5 mg l−1, but fluoride concentrations were lower in the headwater areas. As there is much less information on fluoride levels in upland areas, extensive data collected as part of an acid waters survey are used to show that fluoride concentrations are generally less than 0.1 mg l−1 for the upland UK. The data are summarised in terms of both fluoride concentrations and flux, and the values are cross-referenced to other determinands collected within LOIS. The high positive correlation with boron and negative correlation with flow show the importance of point source (sewage) inputs of fluoride, while strong positive correlations between fluoride and barium indicate the relative importance of vein mineralisation in the bedrock in supplying fluoride to the waters of the Yorkshire Ouse and its tributaries. There seems to be some process that limits the fluoride concentrations within the more contaminated rivers, and this is indicated by a negative upper bound between fluoride and calcium. The waters are undersaturated with respect to fluorite and oversaturated with respect to calcium fluoro-phosphates. This upper bound may reflect either physical controls, such as the availability and size of point and diffuse sources for fluoride coupled to mixing of these sources with rain and soil runoff of low concentration, or solubility controls for a pure or mixed-phase mineral that cannot be specified here. [Copyright &y& Elsevier]

This paper provides a foreword to a special edition of Science of the Total Environment concerned with land–ocean interaction from a UK perspective as linked to processes, functioning and environmental management. The volume structure is presented together with an outline of the nature of the individual papers. The areas covered are: (1) freshwater chemistry, (2) riverine sedimentology, (3) tidal river, estuarine and coastal chemistry, (4) estuarine and coastal sediments and (5) shelf-sea-ocean linkages. The foreword provides as an introductory link to the broader perspectives of contemporary UK research in this area, which comes in a conclusions paper at the end of the volume. [Copyright &y& Elsevier]

Changes in phosphorus concentration and form along 110 km of the River Swale in Northern England were examined over a 2-year period during 1998–2000. This study aimed to use these data to identify the importance of within-channel storage on phosphorus dynamics and to determine the changes in longitudinal transport of phosphorus along a river continuum. The catchment was divided into three contrasting zones: the upland, dominated by sheep farming; a transitional zone, and an intensively-farmed lowland, impacted by sewage inputs. Samples, taken at the downstream extent of each zone at approximately 2-day intervals, were analysed for total phosphorus (TP), total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP), all of which increased in concentration downstream. SRP concentrations were highest in summer and during low flows, although 92% of phosphorus was exported between autumn and spring. The TDP in the upper and transitional zones consisted of both soluble reactive and un-reactive phosphorus, but in marked contrast was almost entirely in soluble reactive form in the lowland. The majority (85%) of phosphorus exported from the catchment was generated within the lowland, due to sewage inputs and losses from intensive agricultural land. It was predominantly particulate-bound, due to interactions of dissolved phosphorus with suspended sediment. The upland contributed less than 5% to the TP annual budget. Intensive river water monitoring highlighted that the lowland dominated phosphorus export during the rising stage of storms (indicating a rapid mobilisation of fine phosphorus-rich sediment), whereas the transitional zone became dominant on the falling stage (due to greater diffuse phosphorus input). [Copyright &y& Elsevier]

We investigated long-term variations in dissolved chemical species in water sampled from the Sagami River and its tributaries, Japan. The samples were taken monthly from May 1993 to April 2000 at 28 sampling sites in the Sagami River system. In this paper, we concentrate on 17 sites in the upper catchment. Twenty-four major to trace elements (Li, Mg, Al, Ca, V, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, W, Tl, Pb, U) were determined by using conventional Q-pole ICP-MS with direct nebulizalion. Water flux was measured from 1995. The data for most species were subjected to fast Fourier transformation (FFT) to extract dominant periodicities, their magnitudes, and their phases. Clear seasonal variations were observed for Al, V, As, Rb and Cs at some sampling points, especially in the tributaries. The seasonal variations may be due to either anthropogenic causes, such as irrigation or wastewater discharge, or natural causes, such as water temperature, pH, redox condition, water flux, or activity of microorganisms. We found no correlation with pH. Water temperature may not be a main controlling factor, although the seasonal variability would be correlated with it. Hydrologic factors may have only minor effects. We suggest that most of the seasonal variation might be correlated with the irrigation of rice paddies. It was difficult to identify all the causes of the seasonal variability. To investigate interannual trends, we used centered 12-month moving averages to eliminate seasonal variations. The water quality of the uppermost streams was generally constant, being controlled by springs on Mt. Fuji. However, in 1993 and 1998, V, As, Rb, Cs and U were depleted briefly, possibly by dilution by overflow from Lakes Kawaguchi and Yamanaka. Hydrologic factors may be more important for interannual variability than seasonal variability. Some heavy trace elements (Zn, Ni, Cd and Sb) showed very irregular variations with high concentration peaks. These elements were discharged from either factories or abandoned mine tailings. [Copyright &y& Elsevier]

We analyzed the concentration of 129I in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4×109 atoms l−1), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The 129I concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the 129I in the studied rivers is atmospheric fallout of 129I emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the 129I concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue. [Copyright &y& Elsevier]

Total mercury (THg) concentrations in streams draining cultivated watersheds in Minnesota, USA are strongly correlated with total suspended sediment (TSS) concentrations, varying widely in response to precipitation-driven inputs of soil-derived suspended sediments. Methylmercury (MeHg) concentrations in these waterways have not been studied, and little is known about mercury uptake mechanisms in resident fish populations. To begin to identify factors influencing MeHg concentrations and loadings in these streams, we measured THg and MeHg concentrations in unfiltered whole water samples from the Minnesota River and two of its major tributaries, the Blue Earth and Le Sueur Rivers. Land use in the watersheds of these rivers is over 90% row-crop agriculture, and extensive artificial drainage systems deliver runoff and associated solids quickly to local streams and rivers. THg concentrations were elevated (>10 ng/l) during much of Spring 2000 and part of the summer when runoff from precipitation events increased stream discharge and carried soil materials into the streams. Reduced precipitation resulted in low flow conditions from August through October, and THg concentrations decreased to <4.0 ng/l in all three rivers. MeHg concentrations in the Le Sueur River ranged from 0.07 to 0.42 ng/l between June and December. Higher MeHg concentrations (>0.2 ng/l) were measured during summer months when THg and TSS concentrations were high after precipitation events. Elevated MeHg concentrations were also observed in late October after leaf litter inputs. Conditions on the Blue Earth River were different, with elevated MeHg concentrations (>0.5 ng/l) observed during low flow in August and September. These higher concentrations coincided with a period of enhanced microbial growth stimulated by high late-summer temperatures. A late-October increase in MeHg concentration attributed to leaf litter inputs was also observed in this river. MeHg concentration trends in the Minnesota River were similar to those in the Blue Earth River. Indicators of biological productivity (chlorophyll a, volatile suspended solids, and total Kjeldahl nitrogen) were higher in the Blue Earth and Minnesota Rivers compared to the Le Sueur River, which may signal a connection between higher biological activity and increased MeHg concentrations. [Copyright &y& Elsevier]

Here we present original data on the geochemical composition of fluvial particulate matter transported by the rivers of the Adour/Garonne basin, which drains one-fifth of the French land surface. Suspended particulate matter from the six main rivers in the basin, sampled at ‘normal’ flow and during a flood, is compared in terms of: grain size; particulate organic carbon; Fe; Mn; and trace element concentrations (e.g. Zn, Cd, Pb, Cu, Mo, Sn, Ni, Co, Cr, V, As, Hg, U, Th, W, Au, Ag, Ta). Three of the six studied rivers (Garonne, Dordogne and Isle Rivers) are the main tributaries of the Gironde estuary (southwest France), known for Cd pollution. The Adour and Gaves Rivers enter the Adour Estuary and the Charente River reaches the ocean by the Charente Estuary. Our data show, that Cd (and Zn) are not the only trace elements of eco-toxicological relevance transported into the Gulf of Biscay by these six rivers. Potentially toxic elements (e.g. As, Sn, U, Cu, Ag) show elevated concentrations in river particulates entering the estuaries, compared to world average concentrations [Martin and Whitfield, 1983, The significance of the river input of chemical elements to the oceans. In: C.S. Wong, E. Boyle, K.W. Bruland, J.D. Burton, E.D. Goldberg (editors), Trace Metals in Sea Water, Plenum, New York: pp. 265–296]. Comparing SPM sampled during ‘normal’ discharge and flood, the basin shows a distinct trace element composition of SPM mostly related to ore deposits in the upper basins (Massif Central and Pyreneans). This geochemical signal is partly masked during floods due to changes in grain size, but also due to increased erosion of the lower parts of the basins. This study proves pumping/centrifugation to be the most appropriate sampling/separation technique (recovery, representativity, contamination) by comparing different methods of SPM recovery. [Copyright &y& Elsevier]

A new in-stream model of phosphorus (P) and macrophyte dynamics, the Kennet Model, was applied to a reach of the River Kennet to investigate the impacts of changing flow conditions on macrophyte growth. The investigation was based on the assessment of two flow change scenarios, which both included the simulation of decreasing total phosphorus concentrations from a sewage treatment works due to improved effluent treatment. In the first scenario, the precipitation and potential evaporation outputs from a climate change model (HadCM2 GGx) where input into the catchment model INCA to predict the mean daily flows in the reach. In the second scenario, the mean daily flows observed in a historically dry year were repeated as input to the in-stream model to simulate an extended low flow period over 2 years. The simulation results suggest that changes in the seasonal distribution of flow were not detrimental to macrophyte growth. However, the simulation of extended periods of low flow suggests that a proliferation of epiphytic algae occurs, even when the in-stream phosphorus concentrations are reduced due to effluent treatment. This epiphytic growth was predicted to reduce the macrophyte peak biomass within the reach by approximately 80%. Thus, the model simulations suggest that flow was more important in controlling the macrophyte biomass in the River Kennet, than the in-stream phosphorus concentrations, which are elevated due to agricultural diffuse sources. [Copyright &y& Elsevier]

The relationship between calcium carbonate saturation and phosphorus concentrations for seven sites on the upper reaches of the River Kennet are examined. The findings are related to issues of groundwater supplies and the introduction of phosphorus treatment of effluent from the Marlborough sewage treatment works (STW) at part of the way along the study reach. Being supplied from a Cretaceous Chalk aquifer, the Kennet is mainly of a calcium-bicarbonate type and has a relatively constant composition of many major water quality determinands. Typically, the waters average a pH of approximately eight (range approx. 7.5–8.5) during the day with the lowest values occurring at the upstream site. Dissolved carbon dioxide varies from approximately 5 to 35 times atmospheric pressure during the late morning with the highest values occurring at the upstream site. However, in-stream biological activity gives rise to marked diurnal fluctuations in pH and dissolved carbon dioxide concentrations and during the summer months, by mid to late afternoon, pH is at its maximum and dissolved carbon dioxide is at its lowest: this is shown by continuous measurements at one of the river sites. Alkalinity and calcium concentrations remain relatively constant at approximately 4700 μEq/l (range 3500–6000 μEq/l) and 120 mg/l (range 85–150 mg/l), respectively, and the waters are oversaturated with respect to calcium carbonate (calcite) typically by a factor of six (range 2–25). Along the reach, soluble reactive phosphate (SRP) increases from the first to the second site with the introduction of sewage supplies from the Marlborough STW, and then declines further downstream as sewage dilution and uptake by the river bed/aquatic plants increases. The differences in concentration decrease after phosphorus removal from Marlborough STW. Despite this change, there is no clear indication of any calcite solubility control except perhaps at times of extreme baseflow during the growing season when within-stream photosynthesis is maximal and within-stream residence times are longer. A comparison of river and groundwater data shows that the groundwaters have similar alkalinities and calcium concentrations. However, the groundwaters have (a) higher carbon dioxide saturations (a factor of 2–5 times the value for the river), (b) lower pHs (0.5–1.5 units), (c) lower SRP concentrations (a quarter or less of the river values) and (d) waters near calcite saturation (unlike the surface waters which are oversaturated). The findings indicate a river system dominated by the input carbon dioxide laden groundwaters in approximate equilibrium with calcite attenuated by within-channel biological and physical processes. Within the river: (a) the waters degas carbon dioxide increasing the pH, producing oversaturated conditions; and (b) oscillating pH-dissolved carbon dioxide levels occur between day and night due to changing balances between photosynthesis and respiration. It seems that lowering the phosphorus levels have not resulted in calcite precipitation within the water column and that no significant within-stream self-cleansing mechanisms are occurring that might be predicted from theory: other components in the water such as dissolved organic carbon may inhibit calcite nucleation. However, the low SRP levels in the groundwater coupled with calcite saturation, may well indicate that phosphorous concentrations within the groundwater are regulated by such processes: the number of calcite nucleating sites are orders of magnitude higher and the calcite inhibitors may be less prevalent. [Copyright &y& Elsevier]

In 1974–1976, baseline studies were carried out on the flora and macroinvertebrate fauna of the R. Kennet at two sites downstream of Marlborough (Savernake Upper and Lower) and at one site upstream of Hungerford (Littlecote). Simplified maps of each site, showing the cover of macrophytes, were obtained monthly between April 1974 and April/June 1976, and replicated quantitative samples of the macroinvertebrates were collected on the dominant macrophyte and on gravel in June 1974, and also in June and December 1975. As a consequence of two major droughts and increasing concern over water quality in the Upper Kennet in the 1990s, the studies recommenced in the summer of 1997 using the same sites and methodologies. Maps and macroinvertebrate samples were obtained in early July and December 1997 and in June of both 1998 and 1999. At the Savernake sites, mapping in summer 1997 confirmed what had been apparent for some years. That is, macrophyte cover (both Ranunculus and Schoenoplectus) was much lower than in the 1970s. In contrast, the site downstream at Littlecote retained a relatively high cover of Ranunculus, despite the drought. In late autumn 1997, phosphate stripping commenced at Marlborough Sewage Treatment Works, the drought ended and in addition, the spring of 1998 was unusually wet. Ranunculus recolonised both Savernake sites with remarkable speed by summer 1998 and retained this dominant position in 1999. Quantitative samples of macroinvertebrates collected on gravel and the dominant macrophyte at each of the three study sites indicated that there was no evidence of major loss of family richness between the 1970s and 1990s as a result of the low flows or enrichment. However, at Savernake (but not Littlecote) in summer 1997, the macroinvertebrate assemblage was affected by low flows and/or enrichment. This took the form of changes in the abundance of some families, with lentic forms being favoured in relation to some lotic families. Following the end of the drought, many macroinvertebrate families at Savernake showed a rapid response to the new conditions and the assemblages reverted to those expected in a fast-flowing cretaceous chalk stream. Continued monitoring through the next drought is advisable to provide a greater understanding of the interplay between water quality, the discharge regime, habitat quality (including macrophyte growth) and the response of the macroinvertebrate fauna. [Copyright &y& Elsevier]

This paper examines the nature of the risk to riverine ecosystems from artificially enhanced loads of phosphorus, considers the key sources of phosphorus enrichment and ways of controlling them, and provides a framework for developing control strategies. The aquatic plant community is the foundation for a healthy and diverse riverine ecosystem, providing food, shelter and breeding habitats for a wide range of animal species. Phosphorus enrichment in rivers can degrade the plant community by altering the competitive balance between different aquatic plant species, including both higher plants and algae. This has consequences for the whole ecosystem. To promote healthy riverine plant communities and the wide range of animal species dependent on them, phosphorus concentrations need to be reduced to as near to background levels as possible. The risk of adverse effects declines as phosphorus concentrations approach background levels, such that any incremental reduction should be seen as a positive step towards trophic restoration. Pragmatic management targets vary between 0.02 and 0.1 mg l−1 soluble reactive phosphorus, depending on river type, with an interim target of 0.2 mg l−1 for heavily enriched rivers. Continuous point sources of phosphorus, dominated by sewage treatment works, have a highly important influence on levels of bioavailable phosphorus in the water column through the growing season. It is important to tackle point sources comprehensively so that reductions in phosphorus concentrations are maximised during this critical time of year. Diffuse sources of phosphorus, particularly from agriculture, are a major contributor to phosphorus levels in riverine sediments, where it can be utilised by benthic algae and rooted plants. This phosphorus can also be released into the water column by a variety of processes. As point sources are brought under control, the relative contribution from diffuse sources becomes increasingly important. An integrated programme of control, involving proactive action on both point and diffuse sources, will be required in most circumstances to bring phosphorus levels in the water column and sediment down to near background levels. [Copyright &y& Elsevier]

Worldwide, multiple stressors affect stream ecosystems and frequently lead to complex and non-linear biological responses. These combined stressor effects on ecologically diverse and functionally important macroinvertebrate communities are often difficult to assess, in particular species-specific responses across many species and effects of different stressors and stressor levels in concert. A central limitation in many studies is the taxonomic resolution applied for specimen identification. DNA metabarcoding can resolve taxonomy and provide greater insights into multiple stressor effects. This was detailed by results of a recent multiple stressor mesocosm experiment, where only for the dipteran family Chironomidae 183 Operational Taxonomic Units (OTUs) could be distinguished. Numerous OTUs showed very different response patterns to multiple stressors. In this study, we applied DNA metabarcoding to assess multiple stressor effects on all non-chironomid invertebrates from the same experiment. In the experiment, we applied three stressors (increased salinity, deposited fine sediment, reduced flow velocity) in a full-factorial design. We compared stressor responses inferred through DNA metabarcoding of the mitochondrial COI gene to responses based on morphotaxonomic taxa lists. We identified 435 OTUs, of which 122 OTUs were assigned to EPT (Ephemeroptera, Plecoptera, Trichoptera) taxa. The most common 35 OTUs alone showed 15 different response patterns to the experimental manipulation, ranging from insensitivity to any applied stressor to sensitivity to single and multiple stressors. These response patterns even comprised differences within one family. The species-specific taxonomic resolution and the inferred response patterns to stressors highlights the potential of DNA metabarcoding in the context of multiple stressor research, even for well-known taxa such as EPT species. Unlabelled Image • Multiple stressor responses of stream invertebrate species are often complex. • Replicated mesocosm experiments are ideal to disentangle multiple stressor effects. • DNA metabarcoding was used to obtain high taxonomic resolution. • 435 macroinvertebrate OTUs with different stressor responses were assessed. • DNA metabarcoding holds great promise to improve multiple stressor inferences. [ABSTRACT FROM AUTHOR]

A large number of diatom-based classification systems have been developed worldwide in recent years. These new systems, together with the oldest, emerged on the need to assess the water quality of rivers, but knowledge on possible divergences resulting from their simultaneous application within a territory is limited. This study aimed to compare the ecological status classification provided by conceptually different methodological approaches, of use or potential use within the same region. 402 monitoring samples were collected from Atlantic siliceous streams (NW-Iberian Peninsula) and temporary Mediterranean streams (Balearic Islands, Spain). Two multimetric indices specifically developed for these areas (MDIAT and DIATMIB, respectively) were calculated, as well as the Specific Polluosensitivity Index (IPS). Multimetric indices were more sensitive methods at diagnosing degradation than IPS since they took directly account of abundance (i.e. chlorophyll a in DIATMIB) or indirectly by its proved inverse relationship with Chl a (MDIAT), together with their use of the regional reference diatom community. Alteration gradients were identified in both studied regions based on the distribution of diatoms, with the first axis of distance-based redundancy analyses (dbRDA) being related to nutrient enrichment and organic loads. Threshold Indicator Taxa ANalysis (TITAN) performed on diatoms sampled along environmental (dbRDA axis 1 and phosphate) and biological gradients (as Ecological Quality Ratio scores of classifications), pointed to lower than current Good/Moderate boundaries for phosphate maximum values (e.g. 22.5 and 71.6 μg L−1 for Galicia and the Balearic Islands, respectively) as well as for higher Good/Moderate boundaries for the MDIAT and IPS classifications. A 'transition group' of species was classified as sensitive or as tolerant depending on the regional nutrients range. Findings of the present study highlight the need to perform auto-ecological studies to increase the knowledge on regional diatoms and their optimal survival ranges across regions prior to adopt other non-regional diatom indices. Unlabelled Image • Three diatom-based classification systems in two geo-climatic regions were compared. • Ecological thresholds were identified at lower phosphate levels than officially accepted. • IPS gave high sensitivity scores to species identified as tolerant by multimetric indices. • Good/Moderate boundaries identified by classification systems seem to need revision. • The Tolerant/Sensitive species character varied with geo-climatic conditions [ABSTRACT FROM AUTHOR]

In Canada's oil sands region, classic boreal hydrology (i.e., winter low flow followed by peaks during spring freshet and then summer flow recession) combined with erosion of both natural and anthropogenically-exposed bitumen results in seasonal and inter-annual variability in stream water chemistry. Using data collected from all seasons over three years (2012–2015), we investigated the mechanisms driving spatial and temporal change in the concentration of 26 water quality parameters for six rivers draining Canada's oil sands region. Mantel tests showed a strong spatial aggregation of climatic drivers (average daily precipitation, accumulated precipitation, snow water equivalent) associated with west versus east discharge patterns. Wavelet analysis highlighted unique watershed attributes, in particular the importance of developed area in lowering responsiveness to seasonal precipitation. Concentrations of most chemical parameters (20 of 23) showed distinct temporal patterns that were correlated with seasonal changes in hydrology which, in turn, were related to changes in weather. Comparison of concentrations observed in this study with those reported in the scientific literature for the same watersheds showed 81% of comparisons differed significantly. This was likely due to the short duration of previous field campaigns and thus the sampling of a very narrow window of the annual streamflow regime. Unlabelled Image • Mechanisms driving changes in river chemistry were assessed in oil sands region. • Rivers with developed areas were less responsive to changes in climate drivers. • Suggests hydrological controls have failed to fully reduce industrial impacts. • River concentration often correlated to major weather events such as snowmelt. • Weaknesses of previous studies evident when compared to this long-term dataset. [ABSTRACT FROM AUTHOR]

The Rhone River is one of the most nuclearized river in the world. Radionuclide concentrations in water and suspended sediments transferred to the marine environment were intensively monitored in this river over the last decades (2002–2018). Over this period of time, >12 and 25 time integrating samples were collected each year in filtered waters and suspended sediments, respectively, and analyzed for their radionuclide contents at ultra-trace levels by using top performance analytical tools. While >60% of plutonium, americium, cesium, cobalt, silver, beryllium and actinium radioisotopes are carried by sedimentary particles, sodium, tritium, antimony and strontium are mainly exported as dissolved species (>90%) due to their low affinity with particles. Most natural radionuclides contents show low seasonal variation. No significant trends are observed over the last two decades for these elements, even for 40K widely used in fertilizers after the middle of the last century, indicating that the basin has currently converged towards geochemical equilibrium for all of them. In contrast, the concentrations of numerous anthropogenic radionuclides originating from nuclear industries significantly declined since the beginning of the 2000s. Assuming no change of the current anthropic and climatic pressures over the next decades, apparent periods, i.e. the time required for a reduction by half the concentrations in the downstream part of the Rhône River, would be close to 6 years for most artificial radionuclides, except for tritium and other artificial radionuclides conveyed to the river by soil leaching and erosion (90Sr, 241Am, plutonium isotopes) which would be far longer. Referring to regional referential backgrounds, only few anthropogenic radionuclides specifically produced by nuclear industries are still detectable at the downstream part of the Rhone River and excess contents of tritium, 238Pu and 241Am are observed in filtered waters. Unlabelled Image • Contents of natural and anthropogenic radionuclides were monitored over the two last decades. • In filtered waters tritium contents are significantly higher than those of all other radionuclides. • Naturally occurring radionuclides contents show seasonal variation. • Most anthropogenic radionuclides contents declined over the two last decades, except for tritium, OBT, 90Sr and transuranium elements. • Resiliency of the river regarding this family of contaminant is going on for most of them. [ABSTRACT FROM AUTHOR]

Diatoms are a compulsory biological quality element in the ecological assessment of rivers according to the Water Framework Directive. The application of current official indices requires the identification of individuals to species or lower rank under a microscope based on the valve morphology. This is a highly time-consuming task, often susceptible of disagreements among analysts. In alternative, the use of DNA metabarcoding combined with High-Throughput Sequencing (HTS) has been proposed. The sequences obtained from environmental DNA are clustered into Operational Taxonomic Units (OTUs), which can be assigned to a taxon using reference databases, and from there calculate biotic indices. However, there is still a high percentage of unassigned OTUs to species due to the incompleteness of reference libraries. Alternatively, we tested a new taxonomy-free approach based on diatom community samples to assess rivers. A combination of three machine learning techniques is used to build models that predict diatom OTUs expected in test sites, under reference conditions, from environmental data. The Observed/Expected OTUs ratio indicates the deviation from reference condition and is converted into a quality class. This approach was never used with diatoms neither with OTUs data. To evaluate its efficiency, we built a model based on OTUs lists (HYDGEN) and another based on taxa lists from morphological identification (HYDMORPH), and also calculated a biotic index (IPS). The models were trained and tested with data from 81 sites (44 reference sites) from central Portugal. Both models were considered accurate (linear regression for Observed and Expected richness: R2 ≈ 0.7, interception ≈ 0.8) and sensitive to global anthropogenic disturbance (Rs2 > 0.30 p < 0.006 for global disturbance). Yet, the HYDGEN model based on molecular data was sensitive to more types of pressures (such as, changes in land use and habitat quality), which gives promising insights to its use for bioassessment of rivers. Unlabelled Image • A combined Machine Learning (ML) approach is tested for the bioassessment of rivers with diatoms • OTUs were predicted (E) from environmental data for each river site • Observed/Expected (OE) OTUs at a site indicate the deviation to reference condition • More types of disturbances were detected with OTUs than with species-based methods • The OTU ML model overcomes the problem of incomplete data-bases to convert OTUs to taxa [ABSTRACT FROM AUTHOR]

Many studies have been conducted to quantify microplastic contamination, but only a few of them have actually the sampling methodology and associated uncertainties. This study seeks to examine the influence of sampling strategy on the confidence interval of river microplastic estimates. 16 samples are collected in the Gave de Pau River (southwestern France) during a three-hour window with a 330-μm mesh size net. Three different exposure times (3, 5 and 7 min) allow for a respective filtration rate by the net of 35.6 m3 (3 samples), 59.4 m3 (10 samples), and 83.2 m3 (3 samples) of water. Organic matter contained in samples is removed by hydrogen peroxide oxidation. The plastic particles are then counted and classified under a binocular microscope. The microplastic concentrations vary between 2.64 and 4.24 microplastics/m3, with a median value of 3.26 microplastics/m3. Statistical analysis does not show differences in microplastic concentrations for the three exposure times. This result seems to demonstrate that a filtration of approx. 35 m3 of water is sufficient under similar conditions (similar flow condition and degree of microplastic contamination) and can help reduce sampling and sample processing time. Other analyses, based on 10 filtrations of 59.4 m3, show that the higher the number of samples, the lower the confidence interval. For triplicates, the mean confidence interval reaches 15% of the median value. Thus, collecting triplicates would seem to offer a reasonable optimum, in combining an acceptable error percentage and time efficiency. These results might depend on the microplastic load of the river, therefore making it necessary to conduct similar analyses on other rivers. This study reports for the first time uncertainties related to microplastic sampling in rivers. Such findings will serve to set up long term monitoring, highlight spatial differences between sites and improve the accuracy of annual microplastic fluxes in rivers. Unlabelled Image • This paper helps design sampling strategy to monitor microplastics in rivers. • Mean MP concentration recorded is 3.34 ± 0.20 microplastics/m3. • Results do not statistically differ for the three volumes of filtered water. • The collection of triplicates seems to offer a reasonable optimum. • For triplicates, the mean confidence interval reaches 13% of the median value. [ABSTRACT FROM AUTHOR]

Biological communities change in response to human alteration. The response of individual taxa and the community can be used to establish preventive criteria to halt further biodiversity deterioration. Here we explore how consistent are the boundaries between Good and Moderate ecological status derived from classification systems used in North-NW Spain: NORThern Spain Indicators system (NORTI), River type specific multimetric (METI) and Iberian Bio-monitoring Working Party (IBMWP), by using common interpretation of normative definitions of Water Framework Directive. We applied the three classifications to a monitoring dataset of Nalón River basin, comprising samples from different stream types and reference conditions. We applied Threshold Indicator Taxa ANalysis to the invertebrate community along the most relevant environmental pressures and biological impairment gradients represented by the Ecological Quality Ratio (EQR) scores of the classification systems. Only NORTI provided a true community ecological threshold and the change point (cp) 95% quantile (Q95%) range of 0.760 was assumed to be the boundary from Good to Moderate (G/M) status, used to standardize the number of taxa loss in all systems. Since the average number of taxa at reference sites was 34, the estimated loss of sensitive taxa was up to 97.1% in IBMWP, 73.5% in METI and 52.9% in NORTI when passing from Good to Moderate status, revealing very permissive boundaries. The loss of common sensitive taxa in NORTI at Q95% was used as G/M threshold and applied to the other classifications, resulting all in a common biodiversity loss of 21% of sensitive taxa richness at values of NORTI-EQR = 0.760, METI-EQR = 0.818 and IBMWP-EQR = 0.753. Results indicate that significant community changes along pressure gradients allow for establishing quantitative criteria consistent with normative definitions. This understanding derived from Directive monitoring programs can assess the risk that invertebrate communities face in terms of species loss derived from anthropogenic pressures. Unlabelled Image • Biodiversity loss is in the Directive normative definitions of Moderate status. • Three classification systems based on invertebrates were compared in a river basin. • Ecological thresholds at lower than accepted impairment levels were identified. • The threshold allowed for consistent interpretation of biodiversity loss. • New proposed Good/Moderate boundaries assume a common loss of 21% of sensitive taxa. [ABSTRACT FROM AUTHOR]

Even though the occurrence of pharmaceuticals in the water environment is thought to be a potential problem for human health and aquatic organisms, the level of knowledge of their sources and presence in the marine ecosystem is still insufficient. Therefore, this study was designed to determine the emergence of sixteen pharmaceuticals and caffeine in groundwater, submarine groundwater discharge (SGD), rivers and coastal seawater in the southern Baltic Sea. It has been recognized that chemical substances load associated with SGD can affect coastal ecosystems equally or even greater than surface runoff. Hence, the Bay of Puck, which is an active groundwater discharge area, has been chosen as a model study site to assess the preliminary risk of pharmaceutical and caffeine residues supply in coastal ecosystem. A special focus was placed on tracing the possible sources of pollution for groundwater and SGD based on the composition of collected samples. Five pharmaceuticals (carbamazepine, sulfapyridine, sulfamethoxazole, ketoprofen and diclofenac) and caffeine were detected in varying concentrations from below the detection limit to 1528.2 ng L−1. Caffeine and diclofenac were the most widespread compounds. Groundwater was mostly enriched in the analysed compounds and consequently SGD has been recognized as an important source of identified pharmaceutical and caffeine residues to the Bay of Puck. A predicted no-effect concentration (PNEC) was determined in order to perform an environmental risk assessment of five pharmaceuticals and caffeine detected in water samples. Finally, future challenges and potential amendments in monitoring strategies are discussed. Unlabelled Image • Groundwater, SGD, seawater and river water samples were collected. • 16 pharmaceutical and caffeine residues were analysed in all (61) collected samples. • 3 of 17 measured residues were quantified in at least 7 samples. • Among all residues, caffeine and diclofenac, were the most widespread. • SGD is an important source of pharmaceutical and caffeine residues to the Bay of Puck. [ABSTRACT FROM AUTHOR]

Unlabelled Image • Plastic fibres and particles could be confirmed in freshwater mussels. • Higher concentrations of microplastics in urban areas compared to a rural location. • Higher concentrations of microplastics in areas with wastewater treatment plants. • All mussels contained microfibers. Alarming amounts of microplastics have recently been shown to accumulate in the environment. Recent focus has been on synthetic material contaminating the marine environment, while effects on freshwater habitats and organisms have received less attention. We here confirm and analyse occurrence of microplastics in the duck mussel, Anodonta anatina, in a Swedish river. All analysed mussels contained microplastics, and the number of microplastic debris found in the mussels increased with mussel size. In addition, we demonstrate higher concentrations of microplastics downstream urban areas with wastewater treatment plants compared to a rural upstream location. Both fibres and particles were found in the mussels, indicating that the emissions of these pollutants may have varying origin. Our study indicates that microplastics can be suspended in the water column in streams and that concentrations are higher downstream anthropogenic activity. We discuss our results in light of potential pathways in rural versus surrounding arable land, and highlight a number of required research directions in the aquatic system. [ABSTRACT FROM AUTHOR]

European countries have defined >1000 national river types and >400 national lake types to implement the EU Water Framework Directive (WFD). In addition, common river and lake types have been defined within regions of Europe for intercalibrating the national classification systems for ecological status of water bodies. However, only a low proportion of national types correspond to these common intercalibration types. This causes uncertainty concerning whether the classification of ecological status is consistent across countries. Therefore, through an extensive dialogue with and data provision from all EU countries, we have developed a generic typology for European rivers and lakes. This new broad typology reflects the natural variability in the most commonly used environmental type descriptors: altitude, size and geology, as well as mean depth for lakes. These broad types capture 60–70% of all national WFD types including almost 80% of all European river and lake water bodies in almost all EU countries and can also be linked to all the common intercalibration types. The typology provides a new framework for large-scale assessments across country borders, as demonstrated with an assessment of ecological status and pressures based on European data from the 2nd set of river basin management plans. The typology can also be used for a variety of other large-scale assessments, such as reviewing and linking the water body types to habitat types under the Habitats Directive and the European Nature Information System (EUNIS), as well as comparing type-specific limit values for nutrients and other supporting quality elements across countries. Thus, the broad typology can build the basis for all scientific outputs of managerial relevance related to water body types. Unlabelled Image • A large number of national types prevent cross country comparison of rivers and lakes. • Data on type descriptors was compiled to allow similarity analysis of national types. • Clusters of similar national types provided 20 broad river types and 15 broad lake types. • The ecological status is best in highland types and worst in lowland calcareous types. • Broad types facilitate nutrient targets comparison and revision of EUNIS freshwater habitats. [ABSTRACT FROM AUTHOR]