River Nitrate Research Articles

Factor affecting nitrate in a mixed land-use watershed of southern China based on dual nitrate isotopes, sources or transformations?

River nitrate (NO3–) pollution is ubiquitous and has attracted worldwide attention. The continuous increase nitrate flux in the river system is mainly caused by inputs of exogenous nitrate sources or nitrogen transformations. In this study, coupled nitrogen and oxygen isotopes of nitrate were used to identify sources and transformations of nitrate in a mixed land use watershed of southern China (the Beijiang River basin), aimed at evaluating the impacts of sources or transformations on nitrate pollution and provide guidance for aquatic environment management. The results showed that the NO3–-N flux in the Beijiang River Basin was 9.37 × 104 tons in 2015; isotopic evidence indicated that the impacts of nitrogen transformations in the river on the removal and production of nitrate were not significant, and the increased NO3–-N concentration along the river was caused by inputs of exogenous nitrate sources. The isotope-based source apportionment revealed that approximately 52% of the influx NO3–-N was contributed by synthetic fertilizer, 27% by soil nitrogen and 21% by domestic sewage. There was no significant temporal variations in source apportionment; however, significant spatial variations were found across the study area. The spatial variations were mainly affected by the different land use patterns. With the increasing percentage of urbanized areas, the proportional contributions of domestic sewage have increased, which has resulted in an increased NO3–-N concentration. In addition, the relationships between the land use index and proportional contributions of different nitrate sources suggested that the effect of urbanized area might be more pronounced on nitrate pollution in a mixed land use watershed. Therefore, the results of this study suggested that land use should be considered in nitrate pollution management strategies and reducing inputs of nitrate sources to river water is crucial to reducing nitrate pollution in mixed land use watersheds.

The effects of clean energy production and urbanization on sources and transformation processes of nitrate in a subtropical river system: Insights from the dual isotopes of nitrate and Bayesian model

Source appointment and control of water pollution caused by nitrate in river are the key to water quality management as well as the basis for achieving aquatic environment sustainability. However, the effects of clean energy production (hydropower generation) and urbanization on the nitrate accumulation and transformation remain unclear. For that, this study quantified and identified the nitrate sources and key processes in a subtropical river, which has been impounded and urbanized in varying degree. The variations of dual isotopes and water chemistry indicated that NO3− in agriculture and forest land mainly from the chemical fertilizer and soil N, while manure and sewage were the main riverine NO3− sources. Nitrification was the dominate process while influenced greatly by inputs of manure and sewage, especially in urban area. Progressive denitrification has been found in the upper reaches of the Beixi River where the river impounded by dams for hydropower generation, with an estimated contribution of 36% (1%–68%). Results from Bayesian model showed that fertilizer and soil N contributed more than half of the NO3− in the wet season as a result of rainfall and surface runoff; while manure and sewage were the dominate NO3− sources in the dry season due to the urbanization. Land use including agriculture, dam construction, and urbanization have characterized the nitrate sources and pollution in the Jiulong River, and cascade dam impoundment could enlarge nitrate retention. We concluded that the combined use of dual isotopes of NO3−, hydrochemicals and the SIAR model offers an efficient approach to understand the nitrogen transformation and quantify the contributions of nitrogen source in river waters.

Effects of Land Use on Nutrient Concentrations in the Inflow River of Lake Taihu, China

Land use is an important factor affecting non-point nutrient loading. Here, the Wuxi River basin was selected to analyze the influence of sub-basin land use on nutrient concentrations using remotely sensed land use data and monthly river water quality variables from October 2019 to September 2020. The results showed that the water quality of the river was closely related to land-use type. Specifically, dryland farmland, villages, and building land have a strong promoting influence on nitrogen, phosphorus, organic carbon, and phytoplankton chlorophyll a. The proportion of orchard land was also positively correlated with river nutrient concentrations. A negative correlation was observed between the proportion of forest land and nutrient concentrations. Moreover, the proportion of the water area in rivers and reservoirs was negatively correlated with the total dissolved nitrogen and nitrate concentrations in the river, and the proportion of the water area in natural pits and fishponds was negatively correlated with river nitrate and ammonia concentrations. Furthermore, the proportion of river and fishpond areas was positively correlated with the concentration of dissolved total phosphorus, dissolved organic carbon, and the permanganate index, while the proportion of the natural pond area was positively correlated with the concentration of particulate phosphorus and phytoplankton chlorophyll a. The influence of land-use types on water quality was also affected by distance from the river. This research indicates that the appropriate utilization of land and wetlands is key to controlling non-point nutrient loading in the river network, including Lake Taihu. Specifically, the self-purification capacity of wetland waters should be incorporated into nutrient control schemes, and special attention should be paid to the reduction of non-point source pollution in the drylands along the downstream riverbanks and urbanized areas.

A hillslope-scale aquifer-model to determine past agricultural legacy and future nitrate concentrations in rivers

The long-term fate of agricultural nitrate depends on rapid subsurface transfer, denitrification and storage in aquifers. Quantifying these processes remains an issue due to time varying subsurface contribution, unknown aquifer storage and heterogeneous denitrification potential. Here, we develop a parsimonious modelling approach that uses long-term discharge and river nitrate concentration time-series combined with groundwater age data determined from chlorofluorocarbons in springs and boreholes. To leverage their informational content, we use a Boussinesq-type equivalent hillslope model to capture the dynamics of aquifer flows and evolving surface and subsurface contribution to rivers. Nitrate transport was modelled with a depth-resolved high-order finite-difference method and denitrification by a first-order law. We applied the method to three heavily nitrate loaded catchments of a crystalline temperate region of France (Brittany). We found that mean water transit time ranged 10–32 years and Damköhler ratio (transit time/denitrification time) ranged 0.12–0.55, leading to limited denitrification in the aquifer (10–20%). The long-term trajectory of nitrate concentration in rivers appears determined by flows stratification in the aquifer. The results suggest that autotrophic denitrification is controlled by the accessibility of reduced minerals which occurs at the base of the aquifer where flows decrease. One interpretation is that denitrification might be an interfacial process in zones that are weathered enough to transmit flows and not too weathered to have remaining accessible reduced minerals. Consequently, denitrification would not be controlled by the total aquifer volume and related mean transit time but by the proximity of the active weathered interface with the water table. This should be confirmed by complementary studies to which the developed methodology might be further deployed.

Application of ANN and SVM for prediction nutrients in rivers

This paper presents the results of predicting nutrients in rivers on national level by the use of two artificial intelligence methodologies. Artificial neural network (ANN) and support vector machine (SVM) were used to predict annual concentration of nitrate and phosphate in rivers of eleven European countries. For creation of an optimal model of prediction, 23 industrial, economical and agricultural parameters were used for the period from 2000 to 2011. The data from 2000 to 2010 was used for training, while the data for 2011 was used for model validation. Optimization of different parameters of ANN and SVM was conducted in order to obtain the model with the best performances. Results of created models were evaluated by using statistical performances indicator named coefficient of determination (R2). The obtained results showed that ANN has better results in predicting nitrate and phosphate compared to SVM models. These results suggest that ANN model is a promising tool for prediction of nutrients in rivers.

Nutrient chemistry and eutrophication risk assessment of the Ghaghara river, India

AbstractThis study was carried out to evaluate the eutrophication risk associated with the nutrient flux from the Ghaghara river by using nutrient molar ratios and indicators for coastal eutrophication potential values. The concentration of ammonium (3–8 times), nitrate (3–10 times), and phosphate (3–4.5 times) in the Ghaghara river were higher than the reported value for the unpolluted rivers, indicating the contribution from the anthropogenic sources. The dissolved nutrients concentration showed significant seasonal variations in the Ghaghara river system. The specific yield of nitrate-N, phosphate-P, and dissolved silica-Si from the Ghaghara river were 0.49, 0.03 and 0.96 tons km−2 yr−1 respectively. The average molar ratio for dissolved inorganic nitrogen (DIN)/Dissolved inorganic Phosphate (DIP) was above 16:1, which indicated phosphate limitation in biological productivity. In contrast, an average molar ratio of Dissolved inorganic Silica (DSi)/DIN of 4.6 ± 4.4 favored the diatom growth in the Ghaghara river. The negative value of P-ICEP (-2.93 kg C. km−2day−1) indicated phosphate limitation in the Ghaghara river. The positive value of N-ICEP (1.71 kg C·km−2day−1) indicates an excess of nitrogen over silica transport from the Ghaghara river to the Ganga river, which can create an eutrophication problem in the Ganga river.

Dual-isotope-based source apportionment of nitrate in 30 rivers draining into the Bohai Sea, north China

Excessive nitrate (NO3−) in rivers can lead to water quality deterioration, and can also be directly input into estuaries and oceans, thus posing a serious threat to the stability of their ecosystems. In this study, the concentration, isotopes and sources of NO3− in 30 rivers discharging into the Bohai Sea were comprehensively investigated. The mean concentration of NO3−-N was 2.24 ± 2.11 mg L−1, with obvious seasonal and spatial variations. In total, 104.24 kt of NO3−-N was discharged into the Bohai Sea annually, to which the Yellow River Basin and Liao River Basin made the largest contributions. The range of δ15N–NO3− was −1.1‰ to +33.2‰ (mean value, +11.4 ± 5.0‰), with no significant seasonal or spatial differences; the mean value of δ18O–NO3− was +9.4 ± 7.2‰, with much higher values seen in June. Based on the MixSIAR model, manure (24.3 ± 7.5%) and sewage (19.1 ± 14.5%) were the primary sources of NO3− in the 30 rivers, followed by NO3− fertilizers (16.3 ± 12.5%), soil N (15.5 ± 11.9%), atmospheric deposition of NO3− (13.5 ± 5.7%) and NH4+ fertilizers (11.4 ± 8.9%). This finding highlights the vital roles of sewage and manure management in riverine NO3−. Using a mathematical method, the contributions of various sources to each river were simulated. The results indicated that management of the Yellow River, Daliao River, Liao River, and Xiaoqing River is more urgently needed than that of other rivers to control Bohai NO3− pollution. We believe that this finding will provide guidance for scientific management of NO3− pollution in these 30 rivers and the Bohai Sea.

Feasibility of Nitrate Removal using Hydroxylamine Hydrochloride from Sundarijal River Water through a Laboratory Scale

Sundarijal River supply drinking water in Kathmandu city, Nepal and to study the nitrate concentration, 10 different sample from different locations of the Sundarijal River was taken. The method for the removal of presence nitrate in River was tested using hydroxylamine hydrochloride dose at 25±20C with 35 minutes contact time. Samples was tested for different dose of hydroxylamine hydrochloride and reduction of nitrate increase with increasing hydroxylamine hydrochloride dosages, up to certain limit. That mean with 0.5g, 0.6g and 0.8g dosages of hydroxylamine hydrochloride, reduction of nitrate was not observed when tested with 10mg/L, 50mg/L and 100mg/L river water, orderly. This tested samples shows the feasibility of nitrate removal from River water, Sundarijal.

Identifying the sources of nitrate contamination using a combined dual isotope, chemical and Bayesian model approach in a tropical agricultural river: Case study in the Mun River, Thailand

Environmental issues triggered by increasing nitrate in agricultural river has become global concern. Identifying nitrate sources and transformation are crucial for water sources protection and eliminating nitrate contamination in an agricultural watershed. In this study, chemical and dual isotopic compositions of nitrate were employed to trace the nitrate sources and transformation processes, and proportional contribution of NO3− source were estimated by SIAR based on Bayesian model. NH4+ concentrations in middle Mun and lower Mun in wet season were significantly higher than NO3−, suggesting enhanced runoff processes by flood promote agricultural fertilized NH4+ leaching into the river. Higher Cl− concentration and NO3−/Cl− indicated that manure and sewage was the dominate nitrate source in the Lam Takhong River and the upper Mun. The overall values of δ15N-NO3− and δ18O-NO3− ranged from −3.9‰ to +16.6‰ and from −5.2‰ to +40.0‰, respectively. The results of nitrate isotopes indicated that NO3− mainly originated from soil N nitrogen, chemical fertilizer, and manure and sewage wastes. Spatially, soil N and chemical fertilizer contributed the most nitrate in the mainstream of lower Mun, middle Mun, and the Lam Takhong River; whereas over 60% of nitrate was derived from manure and sewage in the upper Mun. The spatial variation of water discharge and rainfall, together with the nitrate concentration and isotopes inferred that the nitrate sources and transformations in rain-fed river in tropical zone were distinguished from other rivers. High water discharge driven by rainfall events accelerated the nitrate export and the contribution of atmospheric deposition in wet season, and enlarged the contribution of manure and sewage in dry season. This study provided an example for further researches and approaches to assess the effects of tropical climate and agriculture on nitrate accumulation in watershed.

A Model Analysis of the Tidal Engine That Drives Nitrogen Cycling in Coastal Riparian Aquifers

AbstractIn coastal rivers, tides facilitate surface water‐groundwater exchange and strongly coupled nitrification‐denitrification near the fluctuating water table. We used numerical fluid flow and reactive transport models to explore hydrogeologic and biogeochemical controls on nitrogen transport along an idealized tidal freshwater zone based on field observations from White Clay Creek, Delaware, USA. The capacity of the riparian aquifer to remove nitrate depends largely on nitrate transport rates, which initially increase with increasing tidal range but then decline as sediments become muddier and permeability decreases. Over the entire model reach, local nitrification provides a similar amount of nitrate as surface and groundwater contributions combined. More than half (~66%) of nitrate removed via denitrification is produced in situ, while the vast majority of remaining nitrate removed comes from groundwater sources. In contrast, average nitrate removal from surface water due to tidal pumping amounts to only ~1% of the average daily in‐channel riverine nitrate load or 1.77 kg of nitrate along the reach each day. As a result, tidal bank storage zones may not be major sinks for nitrate in coastal rivers but can act as effective sinks for groundwater nitrate. By extension, tidal bank storage zones provide a critical ecosystem service, reducing contributions of groundwater nitrate, which is often derived from septic tanks and fertilizers, to coastal rivers.

Beyond the trends: The need to understand multiannual dynamics in aquatic ecosystems

Beyond the trends: The need to understand multiannual dynamics in aquatic ecosystems

Patterns of Denitrification Potential in Tidal Freshwater Forested Wetlands

Limited evidence for spatial patterns of denitrification in tidal freshwater forested wetlands (TFFWs), seemingly due to high spatial variability in the process, is surprising considering the various spatial gradients of its biogeochemical and hydrogeomorphic controls in these ecosystems. Because certain physical environmental gradients may be useful for the prediction of denitrification in TFFWs, we measured denitrification and ecosystem attributes in hummock-hollow microtopography of TFFWs along longitudinal riverine positions (upper, middle, and lower tidal river sites, and nearby upstream nontidal forested floodplains) of the adjoining Pamunkey and Mattaponi Rivers, Virginia. We tested differences by river, site, and plot in denitrification enzyme activity (DEA) and substrate limitations of denitrification potential (DP). The Pamunkey River carries greater river nitrate concentrations, and we found less nitrate limitation of DP and greater soil nitrate in hollows of this river. DEA in tidal hummocks was positively correlated with soil organic matter, nitrogen, and carbon, with the highest rates in lower tidal sites. Hummocks also promoted greater oxygen-controlled substrate limitation of DP, whereby experimental aeration stimulated DP under subsequent inundation more in hummocks than hollows. Additionally, tidal sites had greater DEA than nontidal sites, inferred to be caused by a combination of higher moisture, organic, and nutrient content. Our results indicate that the increasing nitrogen concentrations in these rivers will increase denitrification more on the Mattaponi River by alleviating its greater nitrogen limitation compared to the Pamunkey River, and modification to sedimentation, inundation, or microtopography from sea level rise may alter denitrification gradients in TFFWs and upstream low-elevation nontidal floodplains.

English

Rivers Wouri and Meme are surrounded by streams and wells and serve for irrigation, fishing, domestic purposes and transportation. Water samples were collected from the rivers in February (dry season) and August (wet season) of 2012 at different sites and at different depths and analyzed for some physicochemical properties. This was to study the effect of seasonal changes on the properties and also infer the possible sources of pollution. Water from the other sources was also analyzed. All analyses were done using standard methods. The properties were generally higher during the dry season. Both rivers were acidic. The Electrical conductivities (E.Cs) of River Wouri were generally much lower than those of River Meme with mean values of 2943.0 and 5703.0 μS/cm respectively during the dry season. Ca2+/Mg2+ ratios for upstream in River Meme were greater than 3 during the dry season. During the dry season, in Wouri at site WO1, Cations and anions decreased with depth, while at site WO7, the same properties increased with depth. For River Meme at site ME1, there was no significant (p<0.01) variation of cations and anions with depth. On the contrary, at site ME8, the anions increased with depth while the cations decreased significantly (p<0.01) with depth. The streams were weakly basic with average pH of 8.3 for those of Wouri and 9.0 for those around River Meme. The streams around River Wouri generally had higher physicochemical properties. Physicochemical properties of the wells of Wouri were generally higher than those of the streams during both seasons. There was a very significant correlation (p < 0.01) between nitrate and choride ions in both rivers during the dry season. Most of the properties were within the levels set by World Health Organization and Environmental Protection Agency (EPA). The water sources are exposed to increases in anthropogenic activities, such as industrial and municipal waste disposal and farming practices. A more stringent legislation about water management, as well as studies about the biological content of the water sources is recommended.   Key words: Physicochemical, properties, Meme, Wouri, rivers, dry season, wet season.

Water-quality issues facing dairy farming: potential natural and built attenuation of nitrate losses in sensitive agricultural catchments

Context Dairy farming will be increasingly scrutinised for its environmental impacts, in particular for its impacts on freshwater quality in New Zealand and elsewhere. Management and mitigation of high nitrate losses is one of the greatest water-quality challenges facing dairy farming in New Zealand and other countries. Management of critical flow pathways and nitrate-attenuation capacity could offer potential solutions to this problem and help maintain dairy-farming productivity, while reducing its water-quality impacts. Aims The present paper reviewed the key water-quality issues faced by dairy farming and assessed potential of emerging edge-of-paddock technologies, and catchment-scale nutrient-attenuation practices, to reduce nitrate losses from dairy farming to receiving water bodies. Methods We developed a conceptual catchment-scale modelling analysis assessing potential natural and built attenuation of nitrate losses from dairy farming in the Tararua and Rangitikei catchments (located in the lower part of the North Island, New Zealand). Key results This exploratory analysis suggests that a reduction of greater than 25% in the river nitrate loads from dairy-farming areas could potentially be achieved by spatially aligning dairy land with areas of high subsurface nitrate-attenuation capacity, and by managing critical flow pathways using innovative edge-of-field technologies such as controlled drainage, drainage-water harvesting for supplemental irrigation, woodchip bioreactors, and constructed wetlands in the study catchments. Conclusions The research findings highlighted the potential to better understand, map and effectively utilise existing natural and new built-in nitrate-attenuation capacity to significantly reduce water-quality impacts from dairy farming across environmentally sensitive agricultural catchments. This knowledge and tools could help farmers close the gap between what can be achieved with current, in-field mitigation practises and the nitrogen-loss allocation imposed by regulatory authorities. Implications However, the research findings presented here are based on a coarse-scale, conceptual modelling analysis, and therefore further research is recommended to develop tools and practices to better understand, map and effectively utilise existing natural and new built-in nitrogen attenuation capacity at farm-scale to achieve productive and environmentally friendly pastoral dairy farming across agricultural landscapes.

Structural changes of the microplankton community following a pulse of inorganic nitrogen in a eutrophic river

AbstractGlobal change will increase the number and severity of extreme events resulting in strongly pulsed nutrient loading to rivers. Recent studies indicate the potential for rapid plankton shifts as short‐term response to storm events and highlight the need for high‐frequency methods to understand these complex processes. Here, we studied the effects of a strong short‐term pulse of ammonium nitrate in a eutrophic temperate river that elevated nitrate‐N concentrations from 3.1 to 10–55 mg L−1. An intense phytoplankton bloom increased chlorophyll a concentrations from below 10 μg L−1 to over 140 μg L−1 despite of high background N concentrations and followed the N‐pulse downstream. High‐throughput sequencing revealed the temporal dynamics of the bacterial (16S rRNA gene) and microeukaryotic (18S rRNA gene) community throughout the event. Bacterial and microeukaryotic community richness was reduced, and community composition changed significantly during the bloom. Few microeukaryote taxa (e.g., Cyclotella meneghiniana, Chlamydomonas) dominated the bloom and replaced the rich summer phytoplankton community. Long‐term monitoring data (2008–2016) using classical microscope analyses showed that seasonal shifts in phytoplankton community composition were linked to physical parameters and nutrient availability with P‐limitation observed in spring but not in summer. We conclude that a disturbance in abiotic and biotic control factors, such as caused by a nutrient pulse, can induce structural shifts in the microplankton community leading to a phytoplankton bloom, even in eutrophic waters.

Fluxes of nutrients and primary production between the main channel and floodplain backwaters of the Lower Mississippi River—Development of a simulation model

AbstractConnection between rivers and their floodplain is critical to the function of fluvial systems; however, there has been little research quantitatively examining the dynamics of this interaction for large, alluvial rivers. Critical questions include the following: What are the rates and mechanisms of materials and energy exchange, and in what ways does the exchange impact ecosystem functioning? To address these questions, we built a simple model of a hypothetical reach of the Lower Mississippi River (LMR) containing a single backwater. The model is based on empirical data obtained from the LMR system. Our primary objectives for the model were to assess potential backwater impacts on river nitrate transport and in subsidizing phytoplankton biomass to the main channel. Simulations run over a 10‐year period suggest that on an annual basis, (a) LMR backwaters remove NO3–N, and it would require a temporal mean of 34,400 ha functioning like the model backwater, or 2.8 times the current area of oxbow lakes, to eliminate 100% of the river flux of NO3–N of our study region; (b) it would require inputs of phytoplankton from a mean of 5,242 ha of sites functioning like the model backwater to produce observed river flux of phytoplankton biomass; and (c) backwater function is sensitive to the controlling elevation in linking channels hence subject to management. Although simple, this model is a useful first step in quantifying the significance of river–backwater connectivity on ecological processes of the LMR system.

Triple oxygen isotopic evidence for atmospheric nitrate and its application in source identification for river systems in the Qinghai-Tibetan Plateau

Nitrate source identification in river systems is important for water quality management. Recently, the oxygen isotopic anomaly of nitrate in atmospheric deposition (Δ17Oatm) is used to identify unprocessed atmospheric nitrate in river systems to reduce the uncertainty caused by the wide range of δ18O. In high-elevation regions, such as the Qinghai-Tibetan Plateau (QTP) featured with lower temperature and pressure as well as strong radiation, the Δ17Oatm might be different from that in low-elevation regions, but no relevant studies have been reported. In this work, Δ17Oatm in the QTP was studied, and the fingerprints of nitrate isotopes in synthetic fertilizer, livestock manure, domestic sewage, and soil organic nitrogen (SON) were identified and used to quantify various source contributions to riverine nitrate in the Yellow River and Changjiang River source regions located in the QTP during 2016–2017. The results showed that the average of Δ17Oatm in the QTP was 16.4‰, lower than the range (19–30‰) reported for the low-elevation regions. The possible mechanism is decreased O3 as well as increased hydroxyl and peroxy radical levels in the troposphere caused by the climate condition and ozone valley in the QTP will affect the production pathways of atmospheric nitrate. By combining the sewage discharge data with the output results of the SIAR (stable isotope analysis in R) model based on the stable isotope data, manure was determined to be one of the major sources to riverine nitrate for both rivers. The contributions of various sources to riverine nitrate were 47 ± 10% for manure, 30 ± 5% for SON, 10 ± 4% for atmospheric precipitation, 9 ± 2% for synthetic fertilizer, and 4 ± 0% for sewage in the Yellow River source region. This study indicates that the unique atmospheric conditions in the QTP have led to a lower Δ17Oatm value, and atmospheric source makes a considerable contribution to riverine nitrate in the QTP.

Contributions of commercial fertilizer, mineralized soil nitrate, and animal and human waste to the nitrate load in the Upper Elbe River Basin, Czech Republic

Nitrate contamination in the upper Elbe River basin in the Czech Republic is high and has remained relatively constant since monitoring began in the 1960's. Long-term NO3− and discharge data for 138 locations in the Labe, Berounka, Ohře, and Vltava sub-basins has been analyzed. Fifty nine of the locations were sampled for δ15N during low flow conditions. The nitrate, flow, and stable isotopic data were used to evaluate the source term contributions associated with commercial fertilizer, mineralized soil nitrate, and animal and human waste. The relationship between city size and nitrate loading was also examined. The stable isotopic data indicate that about 76% of the nitrate load is from animal and human waste and that human waste water is the major source of river nitrate.

Monitoring the riverine pulse: Applying high‐frequency nitrate data to advance integrative understanding of biogeochemical and hydrological processes

AbstractWidespread deployment of sensors that measure river nitrate (NO3−) concentrations has led to many recent publications in water resources journals including review papers focused on data quality assurance, improved load calculations, and better nutrient management. The principal objective of this study is to review and synthesize studies of high‐frequency NO3− data that have aimed to improve understanding of the hydrologic and biogeochemical processes underlying episodic, diel, and long‐term stream NO3− dynamics. Investigations have provided unprecedented detail on hysteresis and flushing patterns during high flow, seasonal variation during baseflow, and responses to multiyear climate variation. Analyses of high‐frequency data have led to notable advances in understanding how climate variation affects spatial and temporal NO3− patterns, especially dry–wet cycles and antecedent moisture. Further advances have been limited by few investigations that include high‐frequency measurements outside the channel and the short duration of many records. High‐frequency data for multiple constituents have provided new insight to the relative roles of hydrology and biogeochemistry as highlighted by studies of the roles of autotrophic uptake, denitrification, riparian evapotranspiration, and temperature‐driven changes in viscosity as drivers of diel patterns. Comparisons of short duration high‐frequency data with long duration low‐frequency data have described similarities and differences in concentration–discharge patterns and highlighted the role of legacy stores. Investigators have applied innovative analysis approaches not previously possible with low‐frequency or temporally irregular data. Future availability of long duration high‐frequency data will provide new insight to processes, resulting in improved conceptual models and a deeper understanding of the role of climate variation.This article is categorized under: Science of Water > Water Quality Science of Water > Methods Water and Life > Nature of Freshwater Ecosystems

Spatio-temporal variation of nitrate sources to Lake Winnipeg using N and O isotope (δ15N, δ18O) analyses

Anthropogenic nitrogen inputs into Lake Winnipeg, Canada, from watershed sources have increased during the last decades, contributing to eutrophication. These nutrient N inputs include loadings from agriculture (inorganic fertilizer and animal waste) and urban sources (wastewater discharge from sewage treatment plants). The aim of this study was to evaluate the sources and seasonal patterns of dissolved nitrates in two major contributors to Lake Winnipeg; the Assiniboine and Red rivers. The relative contribution of nitrate sources was estimated using Bayesian isotope mixing models incorporating δ15N and δ18O values of dissolved nitrate. Overall, δ15N values of nitrate in the rivers ranged from −2 ‰ to +20 ‰, and δ18O values ranged from −20 ‰ to +20 ‰, which indicated variable contribution of nitrate sources, depending on the river reach and seasonal period of sampling. The results indicated that nitrate in the Assiniboine River originated up to 62 % from waste or municipal sources (i.e. manure and/or waste water discharge), whereas ca. 40 % of nitrate in the Red River originated predominantly from inorganic agricultural fertilizers. These different source contributions were temporally variable, with a decrease in fertilizer loading following spring snowmelt. We found higher proportions of inorganic fertilizers in the Assiniboine River watershed during flooding, which has relevant implications for water nutrient management in response to stochastic flooding events.