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Surface water storage and fluxes in rivers, lakes, reservoirs and wetlands are currently poorly observed at the global scale, even though they represent major components of the water cycle and deeply impact human societies. In situ networks are heterogeneously distributed in space, and many river basins and most lakes—especially in the developing world and in sparsely populated regions—remain unmonitored. Satellite remote sensing has provided useful complementary observations, but no past or current satellite mission has yet been specifically designed to observe, at the global scale, surface water storage change and fluxes. This is the purpose of the planned Surface Water and Ocean Topography (SWOT) satellite mission. SWOT is a collaboration between the (US) National Aeronautics and Space Administration, Centre National d’Études Spatiales (the French Spatial Agency), the Canadian Space Agency and the United Kingdom Space Agency, with launch planned in late 2020. SWOT is both a continental hydrology and oceanography mission. However, only the hydrology capabilities of SWOT are discussed here. After a description of the SWOT mission requirements and measurement capabilities, we review the SWOT-related studies concerning land hydrology published to date. Beginning in 2007, studies demonstrated the benefits of SWOT data for river hydrology, both through discharge estimation directly from SWOT measurements and through assimilation of SWOT data into hydrodynamic and hydrology models. A smaller number of studies have also addressed methods for computation of lake and reservoir storage change or have quantified improvements expected from SWOT compared with current knowledge of lake water storage variability. We also briefly review other land hydrology capabilities of SWOT, including those related to transboundary river basins, human water withdrawals and wetland environments. Finally, we discuss additional studies needed before and after the launch of the mission, along with perspectives on a potential successor to SWOT.

Concern has been raised in the scientific literature about the environmental implications of extracting natural gas from deep shale formations, and published studies suggest that shale gas development may affect local groundwater quality. The potential for surface water quality degradation has been discussed in prior work, although no empirical analysis of this issue has been published. The potential for large-scale surface water quality degradation has affected regulatory approaches to shale gas development in some US states, despite the dearth of evidence. This paper conducts a large-scale examination of the extent to which shale gas development activities affect surface water quality. Focusing on the Marcellus Shale in Pennsylvania, we estimate the effect of shale gas wells and the release of treated shale gas waste by permitted treatment facilities on observed downstream concentrations of chloride (Cl ⁻) and total suspended solids (TSS), controlling for other factors. Results suggest that (i) the treatment of shale gas waste by treatment plants in a watershed raises downstream Cl ⁻ concentrations but not TSS concentrations, and (ii) the presence of shale gas wells in a watershed raises downstream TSS concentrations but not Cl ⁻ concentrations. These results can inform future voluntary measures taken by shale gas operators and policy approaches taken by regulators to protect surface water quality as the scale of this economically important activity increases.

Brown waters There have been widespread reports of surface waters in many remote glaciated regions of North America and Northern Europe becoming browner as levels of dissolved organic carbon have increased. Several hypotheses have been proposed to explain the effect, including recent climate change, but the question remains controversial. A new survey of time series data from more than 500 remote lakes and streams, combined with a simple model, now shows that dissolved organic carbon concentrations are in fact closely related to the decline in the sulphate and seasalt content of atmospheric deposition. Dissolved organic carbon concentrations may therefore be returning towards levels that would have been typical prior to the first onset of acid rain during the nineteenth century. The use of time series data from 522 remote lakes and streams in North America and northern Europe and a simple model shows that dissolved organic carbon concentrations between 1990– 2004 have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. It is suggested that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in dissolved organic carbon is integral to recovery from acidification. Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe 1 , 2 , 3 . Some invoke anthropogenic forcing through mechanisms related to climate change 3 , 4 , 5 , nitrogen deposition 6 or changes in land use 7 , and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition 8 , 9 , 10 . Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances 11 . The increase in DOC concentrations in these regions appears unrelated to other climatic factors.

Urban pesticide use has a direct impact on surface water quality. To determine the extent of pesticide contamination, the California Department of Pesticide Regulation initiated a multi-area urban monitoring program in 2008. Water and sediment samples were collected at sites unaffected by agricultural inputs in three areas: Sacramento (SAC), San Francisco Bay (SFB), and Orange County (OC). Samples were analyzed for up to 64 pesticides or degradates. Multiple detections were common; 50 % of the water samples contained five or more pesticides. Statewide, the most frequently detected insecticides in water were bifenthrin, imidacloprid, fipronil, fipronil sulfone, fipronil desulfinyl, carbaryl, and malathion. Bifenthrin was the most common contaminant in sediment samples. Key differences by area: OC had more pesticides detected than SAC or SFB with higher concentrations of fipronil, whereas SAC had higher concentrations of bifenthrin. The most frequently detected herbicides were 2,4- D , triclopyr, dicamba, diuron, and pendimethalin. Key differences by area: OC and SFB had higher concentrations of triclopyr, whereas SAC had higher concentrations of 2,4-D and dicamba. Detection frequency, number of pesticides per sample, and pesticide concentration increased during rainstorm events. In water samples, all of the bifenthrin, malathion, fipronil, permethrin, and λ-cyhalothrin detections, and most of the fipronil sulfone and cyfluthrin detections were above their lowest US EPA aquatic benchmark. Diuron was the only herbicide that was detected above its lowest benchmark. Based on the number of pesticides and exceedances of aquatic benchmarks or the high number of sediment toxicity units, pesticides are abundant in California surface waters.

Trenbolone acetate (TBA) is a high-value steroidal growth promoter often administered to beef cattle, whose metabolites are potent endocrine-disrupting compounds. We performed laboratory and field phototransformation experiments to assess the fate of TBA metabolites and their photoproducts. Unexpectedly, we observed that the rapid photohydration of TBA metabolites is reversible under conditions representative of those in surface waters (pH 7, 25°C). This product-toparent reversion mechanism results in diurnal cycling and substantial regeneration of TBA metabolites at rates that are strongly temperature-and pH-dependent. Photoproducts can also react to produce structural analogs of TBA metabolites. These reactions also occur in structurally similar steroids, including human Pharmaceuticals, which suggests that predictive fate models and regulatory risk assessment paradigms must account for transformation products of high-risk environmental contaminants such as endocrine-disrupting steroids.

The usefulness of water quality indices, as the indicators of water pollution, for assessment of spatial-temporal changes and classification of river water qualities was verified. Four water quality indices were investigated: WQI (considering 18 water quality parameters), WQI(min) and WQI(m) (considering five water quality parameters: temperature, pH, DO, EC and TSS) and WQI(DO) (considering a single parameter, DO). The water quality indices WQI(min), WQI(m) and WQI(DO) could be of particular interest for the developing countries because of the minimum analytical cost involved. As a case study, water quality indices were used to evaluate spatial and temporal changes of the water quality in the Bagmati river basin (Nepal) for the study period 1999-2003. The results allowed us to determine the serious negative effects of the city urban activity on the river water quality. In the studied section of the river, the water quality index (WQI) was 71 units (classified as good) at the entry station and 47.6 units (classified as bad) at the outlet station. For the studied period, a significant decrease in water quality (mean WQI decrease = 11.6%, p = 0.042) was observed in the rural areas. A comparative analysis revealed that the urban water quality was significantly bad as compared with rural. The analysis enabled to classify the water quality stations into three groups: good water quality, medium water quality and bad water quality. WQI(min) resulted in overestimation of the water quality but with similar trend as with WQI and is useful for the periodic routine monitoring program. The correlation of WQI with WQI(min) and DO resulted two new indices WQI(m) and WQI(DO), respectively. The classification of waters based on WQI(m) and WQI(DO) coincided in 90 and 93% of the samples, respectively.

Concentrations of six phenolic endocrine-disrupting chemicals [4- tert -octylphenol (OP), 4-t-nonylphenol (4-t-NP), 4-n-nonylphenol (4-n-NP), nonylphenol mono- to di-ethoxylates (NP1EO, NP2EO), and bisphenol A (BPA)] and five estrogens [estrone (E1), β-estradiol (E2), estriol (E3) 17α-ethynylestradiol (EE2), and diethylstilbestrol (DES)] were determined in surface water and sediment samples collected from the Songhua River in northeast China. Concentrations of sum of five alkylphenols and alkylphenol ethoxylates (ΣOP, 4-n-NP, 4-t-NP, NP1EO, NP2EO) were 117–1,030 ng L −1 (mean 296) in water samples and 25.5–386 ng g −1 (mean 67.3 ng g −1 dry weight (dw)) in sediments. Concentrations of BPA in water and sediments were 8.24–263 ng L −1 (mean 52.0) and 1.60–17.3 ng g −1  dw (mean 4.90 dw), respectively. Concentrations in water were 0.840–20.8 ng L −1 (mean 5.03) for the sum of three natural steroidal estrogens (ΣE1, E2, E3) and below detection limit (BDL) at −1.38 ng L −1 (average 0.200) for the sum of two synthetic estrogens (EE2, ΣDES). Among estrogens, only E1 was detected in all of the sediment samples in the range of 0.100–3.00 ng g −1  dw. Concentrations of Σphenolic EDCs and Σestrogens in water and sediments and their correlations with total organic carbon indicated that these contaminants originate from similar sources, such as municipal wastewater. In situ log K o c ′ values and sediment–water fugacity fraction were calculated for the target chemicals, and the results indicated that these chemicals were, in general, supersaturated in sediments relative to those in water.

The occurrence of 15 pharmaceuticals and personal care products in the influent and effluent from the wastewater treatment plant (WWTP) and its receiving water in Beijing, China were determined. Results from the present study confirmed that caffeine, N,N-diethyl-m-toluamide and chloramphenicol were removed at a high rate (>70 % efficiency). In contrast, removal efficiency of the other 12 compounds was quite poor (ranged from −40 % to 58 %). Some compounds in the receiving river were present at higher concentrations compared to those in the WWTP effluent, indicating that sources other than treated effluents are present. The risk to the aquatic environment was estimated by a ratio of measured environmental concentration and predicted no-effect concentration. For those compounds found in the effluent and surface water, mefenamic acid, trimethoprim and gemfibrozil may pose a medium risk to aquatic environment.

This study presents concentrations of iron, manganese, zinc, and copper in selected tissues of two fish species: pike ( Esox lucius L.) and bream ( Abramis brama L.) living in lakes Ińsko and Wisola, Northwestern Poland. The lakes differ in their trophic status. The effect of gender and environmental conditions on metals accumulation was also investigated. Metal analyses were performed using inductively coupled plasma atomic emission spectroscopy. Considering all studied fish species and tissues, the average metal concentrations (micrograms per gram wet weight) in both lakes occurred in the following ranges: Fe 0.8–240.6, Mn 0.2–8.4, Zn 3.0–185.9, and Cu 0.14–7.76. The lowest levels of the studied metals were always detected in the muscles. The spleen, kidneys, and liver were found to accumulate the highest amounts of Fe. In the case of the other metals, the highest levels were found, as follows: Mn in skin, gills, and gonads, Zn in digestive tract and gills, Cu in liver. Heavy metal content in fish gonads was observed to be sex dependent.

Assessment of the water quality can enhance understanding of the hydrochemical system and effective management of water resources. To this end, an assessment of water quality was conducted in the Messolonghi–Etoliko and Neochorio region. Surface water and groundwater samples have been collected, treated, and subjected to chemical analysis for the following parameters: Br  −  , Cl  −  , F  −  , NO , NO , PO , SO , Li  +  , Na  +  , NH , K  +  , Mg  2+  , Ca  2+  , HCO , Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. A characterization has been carried out using the Piper trilinear diagram, the United States Salinity Laboratory diagram, and the Wilcox diagram. Assessment of water samples by comparing the recorded values of the water quality parameters with the parametric values established by European Community indicated that the 50% of the surface water samples and 67% of the groundwater samples in the study area are chemically suitable for drinking use. Assessment of water samples from calculation of chemical indexes like sodium adsorption ratio, sodium percentage, residual sodium carbonate, and by comparing the values of the water quality parameters with the water quality limits established by Canadian Council of Minister of the Environment indicated that 75% of the surface water and that all the groundwater samples are chemically suitable for irrigation use.