Non-agricultural sources of groundwater nitrate: a review and case study

Nitrate is often seen as an agricultural pollutant of groundwater and so is expected to be at higher concentrations in the groundwaters surrounding a city than in those beneath it. However the difference between rural and urban nitrate concentrations is often small, due to the non-agricultural sources of nitrogen that are concentrated in cities. This paper illustrates the source and significance of non-agricultural nitrogen for groundwater and presents a case study of nitrate loading in the city of Nottingham. Major sources of nitrogen in urban aquifers are related to wastewater disposal (on-site systems and leaky sewers), solid waste disposal (landfills and waste tips). The major sources of nitrogen in the Nottingham area are mains leakage and contaminated land with approximately 38% each of a total load of 21 kg N ha(-1) year(-1).     

Landscape planning to reduce coastal eutrophication: agricultural practices and constructed wetlands

Southern Sweden suffers from coastal eutrophication and one reason is the high nitrogen load through rivers. The major part of this load originates from diffuse land-based sources, e.g. arable soil leaching. Effective reduction of load from such sources demand careful landscape analysis, combined with changed behaviour of the stakeholders. This study describes a chain of methods to achieve trustworthy management plans that are based on numerical modelling and stakeholders participation and acceptance. The effect of some measures was unexpected when modelling their impact on the catchment scale.Management scenarios to reduce riverine nitrogen load were constructed in an actor game (i.e. role-play) for the Genevadsån catchment in southern Sweden. The game included stakeholders for implementation of a loading standard for maximum nitrogen transport at the river mouth. Scenarios were defined after negotiation among involved actors and included changes in agricultural practices, improved wastewater treatment, and establishment of wetlands. Numerical models were used to calculate the nitrogen reduction for different measures in each scenario. An index model (STANK) calculated the root zone leaching of nitrogen from crops at four type farms. This generated input to a catchment scale model (HBV-N) and farm economics. The economic impact of different sets of remedial measures was evaluated for each type farm and then extrapolated to the catchment.The results from scenario modelling show that possible changes in agricultural practices (such as tuning, timing of fertilisation and ploughing, changed crop cultivation) could reduce the nitrogen load to the sea by some 30%, while wetland construction only reduced the original load by some 5%. In the most cost-effective scenario agricultural practices could reduce the riverine load by 86 t per year at a cost of 1.0 million SEK, while constructed wetlands only reduced the load by 14 t per year at a cost of 1.7 million SEK. Thus, changed agricultural practices can be the most effective and less expensive way to reduce nitrogen transport from land to the sea, while constructed wetlands with realistic allocations and sizes may only have small impact on riverine nitrogen transport from land to sea. The overall experience is that actor games and numerical modelling are useful tools in landscape planning for analysing stakeholders’ behaviour and the impact of measures to reduce coastal eutrophication.     

Land-use based stormwater pollutant load estimation and monitoring system design

Accurate quantification of the amount, quality and sources of urban stormwater runoff are a prerequisite for effective stormwater management. The goal of this study was to estimate city-scale stormwater pollutant export, examine the effect of data sources on export estimates, and develop an optimization method for stormwater monitoring. The results were presented for the city of Lahti in southern Finland, where site mean pollutant concentrations (SMCs), annual pollutant loads, and monitoring guidelines for specific land use types were determined for total suspended solids (TSS), nutrients (total nitrogen TN and total phosphorus TP), chemical oxygen demand (COD), and metals (Pb, Zn, Cu, Cr, and Ni). Depending on the data source, differences between estimated pollutant exports ranged from -89% to 215%. Lack of reference data for every urban land use type and differences in land use classification schemes were identified as key factors limiting the accuracy of pollutant load estimation.     

Characterisation of diffuse pollutions from forested watersheds in Japan during storm events - its association with rainfall and watershed features

Forest areas have been identified as important sources of nonpoint pollution in Japan. The managers must estimate stormwater quality and quantities from forested watersheds to develop effective management strategies. Therefore, stormwater runoff loads and concentrations of 10 constituents (total suspended solids, dissolved organic carbon, PO(4)-P, dissolved total phosphorus, total phosphorus, NH(4)-N, NO(2)-N, NO(3)-N, dissolved total nitrogen, and total nitrogen) for 72 events across five regions (Aichi, Kochi, Mie, Nagano, and Tokyo) were characterised. Most loads were significantly and positively correlated with stormwater variables (total event rainfall, event duration, and rainfall intensity), but most discharge-weighted event concentrations (DWECs) showed negative correlations with rainfall intensity. Mean water quality concentration during baseflow was correlated significantly with storm concentrations (r=0.41-0.77). Although all pollutant load equations showed high coefficients of determination (R(2)=0.55-0.80), no models predicted well pollutant concentrations, except those for the three N constituents (R(2)=0.59-0.67). Linear regressions to estimate stormwater concentrations and loads were greatly improved by regional grouping. The lower prediction capability of the concentration models for Mie, compared with the other four regions, indicated that other watershed or storm characteristics should be included in the prediction models. Significant differences among regions were found more frequently in concentrations than in loads for all constituents. Since baseflow conditions implied available pollutant sources for stormwater, the similar spatial characteristics of pollutant concentrations between baseflow and stormflow conditions were an important control for stormwater quality.     

Polyacrylamide added as a nitrogen source stimulates methanogenesis in consortia from various wastewaters

Polyacrylamides are widely used as flocculants to enhance clarification of drinking waters and domestic wastewaters, for stabilization of agricultural soils, and to aid in managing mine tailings. The flocs produced with polyacrylamide may be deposited into retention areas that become anaerobic. Although it is unlikely that the carbon backbone of these polymers would be cleaved by microbial activity, the amide group could serve as a nitrogen source for microorganisms. Previous studies have shown that aerobic bacteria utilize the nitrogen from polyacrylamide. This study assessed whether methanogenesis was stimulated when an anionic polyacrylamide (Magnafloc LT27AG) was the sole fixed nitrogen source in serum-bottle microcosms. Microorganisms from two oil sands tailings sources, and a domestic anaerobic sewage sludge were used, with benzoate or acetate provided as carbon and energy sources. In each inoculum-substrate combination, the presence of polyacrylamide-enhanced methane production, indicating that polyacrylamide may stimulate microbial activities in anaerobic environments that are rich in fermentable carbon, but lack nitrogen sources.     

Nutrient fluxes in the Po basin.

The nutrient load of the river Po needs to be reduced in order to bring the eutrophication problems in the Northwest Adriatic Sea under lasting control. In this paper we analyse the contribution of the different pollution sources to the nitrogen and phosphorus loads of the river Po (source apportionment). We also estimate the effects of measures that aim to reduce nitrogen and phosphorus pollution in the Po basin (scenario analyses). Using a model (PolFlow) that was previously applied to the Rhine and Elbe basins, we found that more than half of the nitrogen and phosphorus loads in the river Po originates from diffuse sources. The results of the scenario analyses indicate that the measures imposed by the EU Nitrates Directive and the EU Wastewater Treatment Directive may not be stringent enough to achieve a large reduction in the N and P loads in the river Po.     

Long-term changes in watershed nutrient inputs and riverine exports in the Neuse River, North Carolina

We compared patterns of historical watershed nutrient inputs with in-river nutrient loads for the Neuse River, NC. Basin-wide sources of both nitrogen and phosphorus have increased substantially during the past century, marked by a sharp increase in the last 10 years resulting from an intensification of animal production. However, this recent increase is not reflected in changes in river loading over the last 20 years. Temporal patterns in river loads more closely parallel short-term changes in point sources and cropland nutrient application despite their overall lower magnitude. Total phosphorus loads have declined at all stations considered, corresponding to a 1988 phosphate detergent ban. Nitrogen load temporal patterns vary by location and the nitrogen fraction considered. The furthest upstream station exhibited nitrogen decreases after the completion of a dam in 1983. At a station just downstream of a rapidly growing urban area, the total nitrogen load has increased since the mid-1980s, primarily as a nitrate concentration increase. This is consistent with concurrent increases in chemical fertilizer use and point source discharges, as well as increased nitrification at treatment plants. This increase in nitrate loading is not reflected at the most downstream station, where no clear nitrogen trends are discernable. The lack of clear downstream nutrient increases suggests that current water quality impairment in the lower river and estuary may result from chronic nutrient overload rather than recent changes in the watershed. If this is true, then the impact of a planned 30% nitrogen loading reduction may not be immediately apparent. We calculate that, given annual variability, detecting a load reduction of this magnitude will take at least four years, and, should nutrients accumulated in the watershed become a significant source, detecting the resulting ecological improvements is likely to take substantially longer.     

前置反硝化BAF工艺处理景观水体

为了提高曝气生物滤池(BAF)对景观水体的脱氮效果,开发了前置反硝化BAF工艺,考察了其对景观水体的处理效果及影响因素,并与传统BAF工艺作比较。结果表明,前置反硝化BAF工艺对TN和浊度的去除效果明显优于传统BAF工艺,前者对TN和浊度的平均去除率分别为45%和88%,而后者的分别为30%和47%;两种工艺对COD和氨氮的去除效果相近,但前置反硝化BAF工艺的出水水质更稳定;对于前置反硝化BAF工艺,当水力负荷为1.42~4.95 m/h时,对COD、氨氮和TN的去除率均随水力负荷的增加而降低;在水力负荷为2.12 m/h的条件下,回流比对COD和氨氮的去除效果影响不大,但对TN的去除率随回流比的增加呈先升高后降低的趋势,最佳回流比为1.5∶1;另外,对TN的去除率随进水C/N值的增加而升高,当C/N6时,系统的脱氮效果较好。     

Wastewater treatment by reed beds: An experimental approach

The present study consists of assessing the efficiency of a macrophyte (Phragmites australis) system in wastewater purification in an arid climate. The experimental system is made up of three beds differing in length (30, 40 and 50 m) and implanted with Phragmites australis. Wastewater inflow through these beds is horizontal with a flow of 10 l.s⁻¹. Retention time varies between 1 and 4 h. The frequency of irrigation is weekly. The studied parameters are: the organic load (COD and TSS), nutrients (total Kjeldhal nitrogen: TKN and total phosphorus: TP) and the parasitical load (helminth eggs). Water, soil and plants are the three components of the experimental system we analyzed.Results reveal that in the output, the decrease in organic load, nutrients and parasitical load is very sharp in the large bed (COD: 62%, TKN: 43%, TP: 14%, helminth eggs: 93%). However, in the small bed (30 m), the decrease is slight (COD: 48%, TKN: 23%, TP: 5%, helminth eggs: 88%). Concerning parasitical load, the study shows that the three beds are effective in eliminating helminth eggs, even with a very short retention time (1–4 h). The quality of the effluent of the reed bed system should be classified within category B according to WHO guidelines (1989) for crops irrigation.Soil sample analysis from entrance to exit shows a decreasing gradient of nitrogen (N), phosphorus (P), organic carbon (Org.C), organic matter (OM) and parasitical helmith eggs. The gradient becomes more significant in the largest bed with decreasing rate, reaching respectively 49%, 44%, 37%, 40% and 100% for TKN, TP, Org.C, OM and helminth eggs.As for the plant material, the composition of major elements (nitrogen and phosphorus) of Phragmites aerial parts shows the same evolution. While the decreasing rate of nitrogen in the leaves reaches 50% in the largest bed, it does not exceed 8% in the smallest bed. Mean aerial productivity of the studied reed beds was estimated at 134 tons dry weight.ha⁻¹. The aerial biomass exported contains only 5–6% of nitrogen and 10–12% of phosphorus with regard to their load at the influent.     

深圳河水体污染特征分析及整治措施

为提高深圳河的水环境,在水体污染特征分析及污染源解析的基础上,对污染物削减目标进行了估算,并提出了最大日负荷总量(TMDL)水质改善措施。结果表明,水体中DO浓度较低,71%的断面水体中氨氮和总氮浓度超出地表Ⅴ类水质标准,且氨氮和总氮浓度均沿河流方向升高。各行政区中生活和工业废水及河道底泥是水体污染的主要来源,福田区污染贡献占比最大,生活污水排放占比为33%,工业废水排放对河道COD、氨氮的贡献率分别达到42%、44%,是溯源截污的重点区域。通过截污清淤、海绵调蓄、生态修复及景观营造等措施,可以实现2020年全面消黑及2025年水质达到Ⅴ类水的目标。     

Biological Cr(VI) removal coupled with biomass growth, biomass decay, and multiple substrate limitation

In this work, a mathematical model for the biological reduction of Cr(VI), carbon and nitrogen sources consumption, and biomass growth under fully aerobic conditions was developed. The model comprises three types of aerobic heterotrophic cells (non-growing cells, growing cells with chromate reductase activity, and growing cells that have lost the chromate reductase activity), and five soluble compounds (organic substrate, ammonia nitrogen, non-metabolizable soluble products, dissolved oxygen, and hexavalent chromium). Two processes are considered responsible for the reduction of Cr(VI). The first one is the reduction of Cr(VI) coupled with growth, the second process is coupled with the endogenous decay of the biomass. The model was calibrated using the results obtained in batch cultures in the absence of carbon and nitrogen sources, using different initial Cr(VI) concentrations (0-100 mgCr L⁻¹), two carbon sources (cheese whey and lactose), and different initial nitrogen to carbon ratio (0-50 mgN gCOD⁻¹). The calibrated model was used to calculate steady-state values of TSS, soluble COD, TAN and Cr(VI) in continuous systems, obtaining a good agreement with the experimental data. The model also accurately predicted the transient concentration of Cr(VI) as a function of time in response to step changes of the inlet Cr(VI) concentration in continuous systems.     

Long-term changes in pollutant load outflows and purification function in a paddy field watershed using a circular irrigation system

A long-term investigation on the water quality and hydrology was carried out for 8 years and 7 months (from October 1991 to April 2000) in a paddy field watershed using a circular irrigation system. The annual amount of rainfall ranged from 1270 to 2226 mm and it was found that the amount of irrigation water tended to decrease as rainfall increased. Phosphorus and chemical oxygen demand (COD) concentrations tended to decrease with the river flowing down, whereas nitrogen concentrations showed no significant difference. The annual outflow loads (sum of the net-outflow load during irrigation periods and the outflow load during non-irrigation periods) of total nitrogen (T-N), total phosphorus (T-P), and COD ranged from 13.6 to 75.3 kg ha(-1)yr(-1), -3.55 to 2.21 kg ha(-1)yr(-1), and -24.7 to 48.5 kg ha(-1)yr(-1), respectively. The negative values for T-P and COD loads indicated that the study watershed performed a purification function. The change in annual pollutant loads was primarily attributed to the amount of hydrological water volumes (the annual amount of rainfall or that of rainfall plus irrigation water) for T-N and COD loads and partially for T-P load. In addition, the purification function was related to the hydraulic retention time, and the study watershed allows sufficient retention for pollutant purification for phosphorus and COD contents and partially for nitrogen content.     

Comparison of different critical load approaches for assessing streamwater acid-sensitivity to broadleaf woodland expansion

Due to its potential adverse effects on freshwater acidification, risk assessments of the impacts of forest expansion on surface waters are required. The critical load methodology is the standard way of assessing these risks and the two most widely used models are the Steady-State Water Chemistry (SSWC) and First-order Acidity Balance (FAB) models. In the UK the recommended risk assessment procedure for assessing the impact of forest expansion on freshwater acidification uses the SSWC model, whilst the FAB model is used for guiding emission policy. This study compared the two models for assessing the sensitivity of streamwater to acidification in 14 catchments with different proportions of broadleaf woodland cover in acid-sensitive areas in the UK. Both models predicted the exceedance of streamwater critical loads in the same catchments, but the magnitudes of exceedance varied due to the different treatment of nitrogen processes. The FAB model failed to account for high nitrogen leaching to streamwater, attributed to nitrogen deposition and/or fixation of nitrogen by alder trees in some study catchments, while both models underestimated the influence of high seasalt deposition. Critical load exceedance in most catchments was not sensitive to the use of different acid neutralising capacity thresholds or runoff estimates, probably due to the large difference between critical load values and acidic deposition loadings. However, the assessments were more sensitive to differences in calculation procedure in catchments where nitrogen deposition was similar to the availability of base cations from weathering and/or where critical load exceedance values were < 1 keq H⁺ ha^− 1 yr^− 1. Critical load exceedance values from both models agreed with assessments of acid-sensitivity based on indicator macroinvertebrates sampled from the study catchments. Thus the methodology currently used in the UK appears to be robust for assessing the risk of broadleaf woodland expansion on surface water acidification and ecological status.     

Removal of nutrients in various types of constructed wetlands

The processes that affect removal and retention of nitrogen during wastewater treatment in constructed wetlands (CWs) are manifold and include NH(3) volatilization, nitrification, denitrification, nitrogen fixation, plant and microbial uptake, mineralization (ammonification), nitrate reduction to ammonium (nitrate-ammonification), anaerobic ammonia oxidation (ANAMMOX), fragmentation, sorption, desorption, burial, and leaching. However, only few processes ultimately remove total nitrogen from the wastewater while most processes just convert nitrogen to its various forms. Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 55% with removed load ranging between 250 and 630 g N m(-2) yr(-1) depending on CWs type and inflow loading. However, the processes responsible for the removal differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical flow constructed wetlands remove successfully ammonia-N but very limited denitrification takes place in these systems. On the other hand, horizontal-flow constructed wetlands provide good conditions for denitrification but the ability of these system to nitrify ammonia is very limited. Therefore, various types of constructed wetlands may be combined with each other in order to exploit the specific advantages of the individual systems. The soil phosphorus cycle is fundamentally different from the N cycle. There are no valency changes during biotic assimilation of inorganic P or during decomposition of organic P by microorganisms. Phosphorus transformations during wastewater treatment in CWs include adsorption, desorption, precipitation, dissolution, plant and microbial uptake, fragmentation, leaching, mineralization, sedimentation (peat accretion) and burial. The major phosphorus removal processes are sorption, precipitation, plant uptake (with subsequent harvest) and peat/soil accretion. However, the first three processes are saturable and soil accretion occurs only in FWS CWs. Removal of phosphorus in all types of constructed wetlands is low unless special substrates with high sorption capacity are used. Removal of total phosphorus varied between 40 and 60% in all types of constructed wetlands with removed load ranging between 45 and 75 g N m(-2) yr(-1) depending on CWs type and inflow loading. Removal of both nitrogen and phosphorus via harvesting of aboveground biomass of emergent vegetation is low but it could be substantial for lightly loaded systems (cca 100-200 g N m(-2) yr(-1) and 10-20 g P m(-2) yr(-1)). Systems with free-floating plants may achieve higher removal of nitrogen via harvesting due to multiple harvesting schedule.     

An assessment of anthropogenic source impacts on mercury cycling in the Willamette Basin, Oregon, USA

In Oregon's Willamette River Basin (Basin), methylmercury levels in fish triggered health advisories and required development of a mercury Total Maximum Daily Load (TMDL) for the Willamette River. A seasonally-responsive dynamic systems model is used to identify the principal sources of natural and anthropogenic mercury, the relative contributions of these sources to the river, the impact of hypothetical reductions in specific natural and anthropogenic sources on mercury levels in surface water, sediment, and fish tissue, and the degree to which any such changes would be clearly discernible to environmental managers and Basin stakeholders. Two scenarios are modeled: "PRES", which considered all currently known natural and anthropogenic mercury sources and "LEEM", which (hypothetically) eliminated all local, but not global, anthropogenic sources and greatly lowered native soil erosion rates. Elimination of local air emissions reduces runoff of air-deposited mercury by approximately 34% and advection from the Basin by approximately 12%, while lowering erosion rates reduces particulate runoff by approximately 57%, deposition from the water column to surficial sediment by approximately 33%, and fluvial load by approximately 24%; for a net reduction of 25.6% in the total mercury load to the river. Such hypothetical reductions bring methylmercury concentrations in predatory fish to levels that would allow restoration of fish consumption as a beneficial use. However, several factors, primarily technical feasibility and global sources, may impede attempts to attain this beneficial use. Actualizing the hypothetical 100% elimination of local anthropogenic sources and a >50% reduction in erosion could pose significant technical challenges. Because local anthropogenic emissions make relatively smaller contributions to the Basin than do persistent global sources (sources over which there is little, if any, possibility of local control), localized environmental management actions alone may not be adequate to address mercury impacts within the Basin.     

Modeling the contribution of point sources and non-point sources to Thachin River water pollution

Major rivers in developing and emerging countries suffer increasingly of severe degradation of water quality. The current study uses a mathematical Material Flow Analysis (MMFA) as a complementary approach to address the degradation of river water quality due to nutrient pollution in the Thachin River Basin in Central Thailand. This paper gives an overview of the origins and flow paths of the various point- and non-point pollution sources in the Thachin River Basin (in terms of nitrogen and phosphorus) and quantifies their relative importance within the system. The key parameters influencing the main nutrient flows are determined and possible mitigation measures discussed.The results show that aquaculture (as a point source) and rice farming (as a non-point source) are the key nutrient sources in the Thachin River Basin. Other point sources such as pig farms, households and industries, which were previously cited as the most relevant pollution sources in terms of organic pollution, play less significant roles in comparison. This order of importance shifts when considering the model results for the provincial level. Crosschecks with secondary data and field studies confirm the plausibility of our simulations. Specific nutrient loads for the pollution sources are derived; these can be used for a first broad quantification of nutrient pollution in comparable river basins. Based on an identification of the sensitive model parameters, possible mitigation scenarios are determined and their potential to reduce the nutrient load evaluated.A comparison of simulated nutrient loads with measured nutrient concentrations shows that nutrient retention in the river system may be significant. Sedimentation in the slow flowing surface water network as well as nitrogen emission to the air from the warm oxygen deficient waters are certainly partly responsible, but also wetlands along the river banks could play an important role as nutrient sinks.     

短程硝化反硝化工艺处理养猪场废水的厌氧消化液

许多规模化养猪场的厌氧消化液直接外排,造成了严重的二次污染.难降解有机物含量高且碳氮比失调是造成养猪场废水厌氧消化液难于处理的主要原因.采用水解/生物接触氧化(O_1)/厌氧生物膜/生物接触氧化(O_2)组合工艺处理养猪场废水的厌氧消化液,在常温、不添加任何药剂的条件下,实现了稳定的短程硝化反硝化;在水力负荷约为0.45 m~3/(m~2·d)的条件下,其对COD和氨氮的总去除率分别为(78%～85%)、(79%～87%),亚硝化率>99%,为高氨氮、低碳氮比废水的生物处理提供了一条有效途径.     

Nitrogen Removal from Returned Liquors

During recent years it has become clear that, particularly to protect the quality of sea waters, nitrogen and phosphorus discharges have to be substantially reduced. Nitrogen reduction can take place by conventional biological treatment. However, the problem can be partly, or perhaps completely, resolved by treating the returned liquors resulting from sludge dewatering. These normally create a substantial load on sewagetreatment works; in fact the nitrogen in the returned liquors can contribute 15–25% of the total nitrogen load entering the works. It therefore seems appropriate, particularly with a view to future nitrogenreduction requirements, to treat the returned liquors before they are returned to the works'inlet. Since 1987, Watergroup has been working on these problems, and the company now has full-scale plants at Frederikshavn, Denmark (population equivalent 130 000) and Eslöv, Sweden (population equivalent 250 000). Normally this treatment can be carried out at a considerably lower cost, per kg nitrogen removed, than when applying traditional methods. An additional advantage is that the method makes it possible to reuse the nitrogen content of the returned liquor, e.g. in the form of ammonium sulphate which is an excellent fertilizer.     

CASS工艺处理高校生活污水的试验研究

为了优化CASS工艺的运行参数,通过正交试验重点研究了污泥负荷、污泥沉降比(SV)、DO浓度、曝气时间等对COD、氨氮和TP去除效果的影响。结果表明,CASS工艺对有机物的去除效果较好,且抗冲击负荷能力较强;污泥负荷和SV值对COD、氨氮和TP去除效果的影响较大,而曝气时间和DO浓度的影响相对较小;试验条件下,CASS工艺的最佳运行参数如下:污泥负荷为0.50 kgCOD/(kgMLSS·d)、SV值为32%、曝气时间为2.5～3.0 h、DO为2.0～2.5 mg/L。     

Water quality, nutrients and the European union's Water Framework Directive in a lowland agricultural region: Suffolk, south-east England

The water quality of 13 rivers in the lowland, agricultural county of Suffolk is investigated using routine monitoring data for the period 1981 to 2006 collected by the Environment Agency of England and Wales (EA), and its predecessors, with particular emphasis on phosphorus (as total reactive phosphorus, TRP) and total (dissolved and particulate) oxidised nitrogen (TOxN — predominantly nitrate NO₃). Major ion and flow data are used to outline fundamental hydrochemical characteristics related to the groundwater provenance of base-flow waters. Relative load contributions from point and diffuse sources are approximated using Load Apportionment Modelling for both TRP and TOxN where concurrent flow and concentration data are available. Analyses indicate a mixture of point and diffuse sources of TRP, with the former being dominant during low flow periods, while for TOxN diffuse sources dominate.Out of 59 sites considered, 53 (90%) were found to have annual average TRP concentrations greater than 0.05 mg P l^− 1, and 36 (61%) had average concentrations over 0.120 mg P l^− 1, the upper thresholds for ‘High’ and ‘Good’ ecological status, respectively. Correspondingly, for TOxN, most of the rivers are already within 70% of the 11.3 mg N l^− 1 threshold, with two rivers (Wang and Ore) being consistently greater than this.It is suggested that the major challenge is to characterise and control point-source TRP inputs which, being predominant during the late spring and summer low-flow period, coincide with the peak of primary biological production, thus presenting the major challenge to achieving ‘good’ ecological status under the Water Framework Directive. Results show that considerable effort is still required to ensure appropriate management and develop tools for decision-support.