The presence of heterotrophic plate count (HPC) bacteria in drinking water distribution systems is usually not considered harmful to the general consumer. However, precautions must be taken regarding the immunocompromised. All water supply authorities in South Africa are lawfully required to provide consumers with high-quality drinking water that complies with South African-and international standards. This study mainly focused on the isolation, identification and characterization of HPC and other bacteria from biofilm-and bulk water samples from two sampling points located within the Potchefstroom drinking water distribution system. Based on five main objectives set out in this study, results indicated that the bulk water at the J.S. van der Merwe building was of ideal quality fit for lifetime consumption. Application of enrichment-and selective media allowed for the isolation of 12 different bacterial morphotypes. These were identified by way of biochemical-and molecular methods as Bacillus cereus, Bacillus subtilis, Brevundimonas spp., Clostridiaceae, Corynebacterium renale, Flavobacteriaceae, Kytococcus sedentarius, Leuconostoc lactic, Lysinibacillus sphaericus, Pseudomonas spp., Staphylococcus aureus and Staphylococcus capitis. The greatest diversity of bacteria was detected early autumn 2008, while the lowest diversity occurred during mid-winter 2007. Bacillus cereus, Kytococcus sedentarius and Staphylococcus capitis displayed potential pathogenic properties on blood agar. Kytococcus sedentarius could be classified as potentially the most pathogenic among the isolates. All isolates displayed multiple-resistant patterns towards tested antibiotics. Corynebacterium renale and Staphylococcus aureus were least resistant bacterial species and Lysinibacillus sphaericus the most resistant. All isolates were susceptible to ciprofloxacin (CIP) and streptomycin (S), but most were resistant to erythromycin (E). Transmission electron microscopy (TEM) allowed for detailed examination of Brevundimonas spp., Pseudomonas spp. and Staphylococcus spp. The capability of Brevundimonas spp. to produce slime and store nutrients within inclusion bodies, suggests the ability of this bacterium to form biofilm and persist in the drinking water for prolonged periods. Despite the inhibitory or toxic effect of copper against bacterial growth, scanning electron microscopy (SEM) revealed the presence of biofilms as well as diatoms on red-copper coupons. Biofilm activity was also observed on reverse-osmosis (RO) filters. Since corrosion was evident on red-copper coupons, it is recommended that prospective studies also look into the significance of microbial induced corrosion (MIC) within the Potchefstroom drinking water distribution system. Other prospects include determining minimum inhibitory concentrations of isolates against antibiotics and the application of culture independent methods such as SSCP and DGGE to investigate biofilm development. The use of diatoms as an index of the drinking water quality is also suggested. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2010.

Source water quality plays a critical role in maintaining the quality and supply of drinking water, yet it can be negatively affected by human activities. In Pennsylvania, coal mining and treatment of conventional oil and gas drilling produced wastewaters have affected source water quality for over 100 years. The recent unconventional natural gas development in the Marcellus Shale formation produces significant volumes of wastewater containing bromide and has the potential to affect source water quality and downstream drinking water quality. Wastewater from coal-fired power plants also contains bromide that may be released into source water. Increasing source water bromide presents a challenge as even small amounts of bromide in source water can lead to carcinogenic disinfection by-products (DBPs) in chlorinated finished drinking water. However, bromide is not regulated in source water and is not removed by conventional drinking water treatment processes. The objective of this work is to evaluate the safe bromide concentration in source water to minimize the cancer risk of trihalomethanes - a group of DBPs - in treated drinking water. By evaluating three years of water sampling data from the Monongahela River in Southwestern Pennsylvania, the present analysis reached three conclusions. First, bromide monitoring for source water quality should be taken at drinking water intake points. Water sample types (river water samples vs drinking water intake samples) can lead to different water quality conclusions and thus affect regulatory compliance decision-making. Second, bromide monitoring at drinking water intake points can serve as a predictor for changes in heavily brominated trihalomethanes concentrations in finished water. Increasing bromide in source water can serve as an early warning sign of increasing formation of heavily brominated trihalomethanes and their associated cancer risks in drinking water. Finally, this work developed a statistical simulation model to evaluate the effect of source water bromide on trihalomethane formation and speciation and to analyze the changing cancer risks in water associated with these changing bromide concentrations in the Monongahela River. The statistical simulation method proposed in this work leads to the conclusion that the bromide concentration in source water must be very low to prevent the adverse health effects associated with brominated trihalomethanes in chlorinated drinking water. This method can be used by water utilities to determine the bromide concentration in their source water that might indicate a need for process changes or by regulatory agencies to evaluate source water bromide issues.

Magister Public Health - MPH / Introduction: In-house contamination of drinking water stored in wide-mouthed buckets (even with lids) has been widely reported in epidemiologic investigations as vehicles for diarrhoea disease transmission. The long handled mukombe cup (LHM cup), recently developed by the National Institute of Health Research (NIHR), a department of the Ministry of Health and Child Care (MoHCC) in Zimbabwe, is a promising low cost dipping devise for extraction of water from wide-mouthed containers. Aim: The study aim was to assess the effectiveness and household acceptability of the long handled mukombe cup in reducing bacteriological contamination of drinking water stored in wide-mouthed vessels in the home in a peri urban settlement in Harare, Zimbabwe. Methodology: A randomised controlled trial of a long handled mukombe cup was conducted in Hatcliffe, Harare. After collecting baseline data on demographics, household water quality, and other sanitation and water handling practices, households were given basic health education before the two selected communities were randomly assigned to one of the two groups of 119 households each. The intervention group received the LHM cup while the control group received no intervention. Households were followed up after two months and assessed effectiveness and user acceptability of the intervention. Data Analysis: Data analysis was conducted using STATA 11. Descriptive statistics were calculated and reported as percentages, proportions, frequencies and measures of central tendency. Bivariate statistics were carried out to test independent associations between use of the LHM cup and E. coli. All analyses were conducted in an intention-to-intervene analysis. Results: A total of 230 households were analysed during follow-up. Samples of stored drinking water from intervention households were significantly lower in E. coli levels than those of control households (geometric mean E. coli of 0.8/100 ml vs 13.0/100 ml, p <0.0001). Overall, 78.4% (987/111) of samples from the intervention households met World Health Organization (WHO) guideline value of 0 cfu/100ml sample, while 52.1% of the 119 samples from control households met such a benchmark (p < 0.0001). In addition, 94.6% of intervention household samples were in compliance with this intervention or presented low risk, 27.7% of samples from control group households presented intermediate or high risk. There was a statistically significant association between LHM cup use and reduced E. coli bacterial contamination in stored drinking water (p < 0.05). There was no statistically significant difference in turbidity in both intervention and control groups, both for turbidity <5 and >5 (p = 0.071). Acceptability of the LHM cup was very high (100%). Conclusion: To our knowledge, this is the first study on the evaluation and acceptability of the LHM cup in the Sub-Saharan Africa. Positive results were recorded that showed that the LHM cup was effective in minimising E. coli contamination in the intervention group as compared to the control group. It is postulated that this is because the LHM cup reduces hand contact with stored water during scooping, thus maintaining improved water quality in communities in Zimbabwe that collect and store drinking water in wide-mouthed containers with lids where extraction is by scooping. However, more research is required to document the LHM cup's continued and effective use, durability and overall sustainability in the absence of any serious sampling or monitoring.

Ensuring access to safe drinking water to protect public health in many communities underserved or unserved by centralized water systems in the US requires regular water quality testing and reporting. Following testing, access to easy-to-comprehend water quality information may be challenging. Households served by water utilities have access to water quality information. However, households depending on unregulated water systems like wells and springs are often unaware of their water quality. Therefore, this study utilized multiple water quality parameters to determine the quality of karst spring water using two Water Quality Index (WQI) methods. In-situ measurements of physico-chemical parameters (pH, dissolved oxygen, temperature, turbidity, conductivity, specific conductance, total dissolved solids, oxidation reduction potential were taken at 50 karst springs in east Tennessee during Summer 2021. Water samples were analyzed for microbial (fecal coliform, and E. coli), nutrients (nitrate and nitrite), and radiological (radon) constituents using standard analytical methods. Springs generally met federal and state water quality safe limits for physicochemical parameters, but 100% of water samples contained fecal coliform and 90% contained E. coli revealing widespread fecal contamination; 60% of springs exceeded radon concentrations of 300 pCi/L. WQI method 1 (Brown et al. 1972) rated 12 % of springs as very poor water quality and 88% as unfit for drinking. WQI method 2 (NSFWQI) rated 4% of the sampled springs as good, 92% as moderate and 4 % as bad. Water treatment procedures for microbial pollution purification are advised before the studied springs are used as a drinking water source.

Karst springs are an essential source of private water supply for about 10% of households in Tennessee. However, these springs, which can be easily polluted, are unregulated. This study, therefore, assesses water quality spatial patterns and water quality rating of roadside springs in northeast Tennessee. Karst spring water samples collected from 50 springs were assessed using EPA Standard methods for pathogens, nutrients, radon, and physicochemical parameters. Springs generally met federal and state standards for physicochemical parameters, 90% of samples contained E. coli, and all samples contained fecal coliform. High E. coli was spatially clustered causing a fecal contamination hot spot on the border of Washington and Sullivan Counties, Tennessee. 60% of springs exceeded radon concentrations of 300 pCi/L. Water quality ratings were very poor or unfit for drinking, with 4% of springs ranked “good”. Therefore, microbial pollution purification procedures are advised before using these springs as a drinking water source.

No description available.

This dissertation consists of three essays that examine consumer behavior with respect to drinking water quality issues. The first essay uses contingent valuation method to explore consumers' willingness to pay (WTP) for a hypothetical material in home drinking water infrastructure that will remain leak free. Willingness to pay is investigated using both dichotomous choice and dichotomous choice with follow-up formats using a national telephone survey of consumers. Our results indicate that consumers' concerns about future system failures and income positively affect their WTP for an improved material while satisfaction with the water quality, education and the bid amount asked negatively affect their WTP for an improved material. There are no significant differences in the determinants of WTP between respondents who have experienced problems with home water infrastructure and respondents who have not. Furthermore, the estimated mean WTP does not change significantly between the dichotomous choice questioning format and the dichotomous choice with follow-up format The second essay investigates the determinants of consumers' willingness to accept improvement programs for three drinking water issues: water quality, pinhole leaks in home plumbing infrastructure and aging public infrastructure. The research is based on a mail survey of consumers in Northern Virginia and the Maryland suburbs of Washington D.C. The analysis focuses on the relationship between information, risk perceptions and willingness to pay. Results indicate that the choice to support any of the programs is negatively affected by the cost of the proposed improvement. Consumers' risk perceptions, the external information provided in the survey and whether they read the annual report from their water utility affect their choices for investment in improvement programs. The third essay examines the effect of risk perceptions about tap water, general risk aversion and consumers' characteristics on their decision to avert drinking water risks and related expenditures. Results are based on the same survey data from the second study. The risk aversion measure is elicited using the sequence of questions employed in the National Panel Study of Income Dynamics. Results indicate that consumers' risk perceptions affect both the decision to avert and the amount spent on averting activities. However, we do not find a significant impact of risk aversion on averting behavior. In addition we find that respondents were more likely to use water treatments if they were unsatisfied with their tap water or had problems or concerns with water odor and particles. / Ph. D.

Thesis (MBA)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: South Africa’s efforts to ensure safe drinking-water provision to all have resulted in an admirable reduction in the backlog in drinking-water provision since 1994. However, in the non-metro areas of South Africa poor drinking-water quality is common and, combined with inadequate sanitation, results in a significant and deleterious primary health impact. Given the South African government’s commitment to co-operative government and good governance, and a willingness to both mobilize government funds and to involve the private sector in addressing poor water services delivery by local government, it can be expected that a significant opportunity exists for a “service/product” combination that assists local, provincial and national government in both, (i), the progressive realization of suitable drinking-water quality via a consultative audit, and (ii), an environmental governance function to ensure that acute and chronic issues are timeously identified and resolved. Drinking-Water Quality Management (DWQM) procedures developed and operated by the government research organization, CSIR, have been shown to be effective in achieving (i) and (ii) above. However, CSIR is not the appropriate business environment from which to roll out a commercialized service. This study assesses the prospects of a start-up Small, Medium and Micro Enterprise (SMME) to access and develop the DWQM market in South Africa. A thorough review of the role of governance in the delivery of water services in South Africa is provided, and it is confirmed that DWQM procedures can be expected to contribute towards improvement in drinking-water quality in non-metro South Africa and satisfy government’s requirement of demonstrated good governance (co-operative and regulatory governance) and co-operative government. A situational analysis of the internal (CSIR) and external business environment confirms that a win-win opportunity exists for entrepreneurs from within CSIR to “spin-out” the DWQM services, and thereby fulfill CSIR’s mandate of supporting SMME’s and Black Economic Empowerment (BEE). A summary of considerations for a start-up SMME in South Africa emphasizes the importance of some key factors. A key factor for a SMME selling services to government is the satisfaction of BEE requirements. Additional key factors include the business marketing factors of customer relationship management, delivering value and ongoing evolvement of marketing strategy. A case study involving Stellenbosch Municipality is used to demonstrate the customer centric nature of DWQM, and the positive Value Impact delivered to the client. The above are used to critically consider a Business Action Plan (which has a focus on the first year of operation) and to identify amendments required for the future and separate preparation of a full Business Plan. The short term focused Business Action Plan (BAP) confirms that market forces and opportunities combine with the skills and the background of the start-up team to provide a positive prospect for the startup SMME. Conversion of the BAP to a fully fledged Business Plan will require the development of a full business strategy, and supportive marketing strategy, as the short term focus strategies are inadequate. Importantly, adjustments to the black equity holding should be brought in line with the requirements of the Broad-Based BEE Act. / AFRIKAANSE OPSOMMING: Suid-Afrika se deurlopende pogings om veilige drinkwater te verskaf het gesorg vir ‘n benydenswaardige vermindering in die agterstand in verskaffing van drinkwater sedert 1994. In die nie-metropolitaanse areas van Suid-Afrika is swak drinkwater gehalte egter steeds algemeen en is verantwoordelik, saam met ontoereikende sanitêre infrastruktuur, vir beduidende en dodelike primêre gesondheidsrisikos. Die Suid-Afrikaanse regering is toegewyd tot samewerking met die private sektor en die toepassing van goeie besigheidsbeginsels. Dit is ook gewillig om regeringsfondse beskikbaar te stel indien die betrokkenheid van die privaat sektor kan help om swak waterdienste lewering deur die regering aan te spreek. Daar kan dus verwag word dat ‘n daadwerklike geleentheid bestaan om ‘n “diens/produk” kombinasie daar te stel wat plaaslike, provinsiale en nasionale regering sal bystaan in beide die: (i), progressiewe verwesenliking van geskikte gehalte drinkwater deur middel van ‘n konsultatiewe oudit, en (ii), ‘n omgewings oorsig funksie om te verseker dat akute en kroniese probleme tydig geidentifiseer en opgelos word. Drinkwater Gehalte Bestuur (DWGB) prosedures ontwikkel en toegepas deur die regeringsnavorsingseenheid, die WNNR, is bewys as effektief in die bereiking van (i) en (ii) soos hierbo gemeld. Die WNNR is egter nie ‘n geskikte besigheids-omgewing vir die wyer kommersiële toepassing en verskaffing van sodanige dienste nie. Hierdie studie evalueer die vooruitsigte van Klein, Medium en Mikro Ondernemings (SMME) om die DWGB mark in Suid-Afrika te betree en te ontwikkel. ‘n Deeglike oorsig van die rol van etiese bestuur in die verskaffing van waterdienste in Suid-Afrika word gedoen. Daar word bevestig dat DWGB prosedures na verwagting sal bydra tot die verbetering van drinkwater gehalte in die nie-metropolitaanse Suid-Afrika, maar ook sal voldoen aan die regering se vereistes van daadwerklike en sigbare etiese bestuur (samewerkings en regulatoriese etiese bestuur) en samewerking van die regering en derde partye. ‘n Omgewingsondersoek van die interne (WNNR) en eksterne sake omgewing bevestig dat ‘n wen-wen geleentheid bestaan vir entrepreneurs binne die WNNR om DWGB dienste af te stig, en sodoende ook vir die WNNR om sy mandaat te vervul, by name die ondersteuning van SMME’s en Swart Ekonomiese Bemagtiging (SEB). ‘n Opsomming van die saaklike kwessies vir die stigting van ‘n SMME in Suid-Afrika lei tot die identifisering van ‘n aantal sleutel suksesfaktore se belangrikheid. ‘n Sleutel suksesfaktor vir ‘n SMME, wat dienste aan die regering verkoop, is die voldoening aan SEB vereistes. Verdere sleutel suksesfaktore sluit in die sake bemarkingsfaktor van kliënte verhoudingsbestuur, die lewering van waarde en die volgehoue evolusie van bemarkingstrategie. ‘n Gevallestudie waarin Stellenbosch Munisipaliteit betrokke was word gebruik om die kliënt-gesentreerde toepassing van DWGB te demonstreer, en die positiewe waarde wat aan die kliënt gelewer is, word uitgelig. Laastens word die bogenoemde gebruik om ‘n kritiese evaluering te doen van ‘n Besigheids Aksie Plan (met ‘n fokus op die eerste jaar se bedrywighede). Veranderinge wat vereis sou word vir die voorbereiding van ‘n toekomstige en afsonderlike volledige Besigheids Plan word geidentifiseer. Die korttermyn gefokusde Besigheids Aksie Plan (BAP) bevestig dat marktendense en geleenthede tesame met die vaardighede en agtergrond van die Kleinsake-span ‘n positiewe verwagting skep vir die voornemende kleinsake-bedryf. Die omskakeling van die BAP na ‘n volledige Besigheids Plan vereis ‘n volle Sakestrategie en ‘n ondersteunende Bemarkingsplan, aangesien die korttermyn gefokusde strategieë ontoereikend is. Verdere aanpassings tot die swart aandeelhouding moet gedoen word om te voldoen aan die vereistes van die breëbasis SEB-wetgewing.

The aim of this thesis is to determine the sources, controls and risk aspects of fluoride in surface water and groundwater in a region of southeastern Sweden where the fluorine-rich 1.45 Ga circular Götemar granite (5 km in diameter) crops out in the surrounding 1.8 Ga granites and quartz monzodiorites (TIB rocks). The materials of this thesis include both primary data, collected for the purpose of this thesis, and a large set of secondary data, retrieved from the Swedish Nuclear Fuel and Waste Management Co., the Swedish Geological Survey and the Kalmar County Council. A characteristic feature of the area is high fluoride concentrations in all kinds of natural waters, including surface waters (such as streams) and groundwater in both the Quaternary deposits (regolith groundwater) and bedrock fractures (fracture groundwater). A number of potential sources and controls of the high fluoride concentrations were investigated, including a variety of geological, mineralogical, mineral-chemical and hydrological features and processes. For the stream waters and regolith groundwater, high fluoride concentrations were correlated with the location of the Götemar granite. This finding is explained by the discharge of fluoride-rich groundwater from fractures in the bedrock and/or the release of fluoride due to the weathering of fluorine-bearing minerals in the Quaternary deposits; however, the Quaternary deposits had considerably lower fluoride concentrations than the underlying bedrock. The high fluoride concentrations in the fresh fracture groundwater (up to 7.4 mg/L) in the TIB-rocks are proposed to be the result of long residence times and the alteration/dissolution of fluorine-bearing primary and secondary minerals along the fracture walls. In terms of risk aspects, this thesis shows that fluoride can add to the transport and inorganic complexation of aluminium in humic-rich, acidic streams. Additionally, 24 % of the children in households with private wells in Kalmar County were assessed to be at risk of excess fluoride intake based on the WHO drinking water guideline value (1.5 mg/L). However, the risk increased significantly when instead the US EPA reference dose (0.06 mg/kg-day) was used, both when all relevant exposure pathways were taken into account as well as water consumption alone. Hence, it is shown that the risk of an excess intake of fluoride is strongly dependent on the basis for evaluation.

The increased use of synthetic nitrogen fertilizers since the early 1900s has resulted in greater food production but also problems with nitrogen pollution in freshwaters. Nitrate (NO3-) is a common pollutant in rivers and groundwater in agricultural watersheds; the drinking water limit in Canada is 10 mg N/L. Microbial processing of NO3- and ammonium (NH4+) can produce nitrous oxide (N2O), a potent greenhouse gas responsible for about 5% of the greenhouse effect. Rivers provide a complex environment, where a variety of redox conditions, available substrates and microbial populations can co-exist on small spatial and temporal scales. Therefore, many questions remain about N cycling in river environments. N2O is produced during anoxic microbial NO3- or NO2- reduction to N2 (denitrification) and oxic microbial NH4+ oxidation to NO3- (nitrification). A significant portion (~25%) of global anthropogenic N2O is produced in rivers and estuaries, but mechanisms are not clear and predictability is poor. The United Nations Intergovernmental Panel on Climate Change (IPCC) provides default equations for calculating N2O emission estimates, in which annual NO3- loading to rivers is positively linearly related to N2O emissions. However, it is unclear how sound these linear relationships are and if measured N2O emissions are similar to IPCC estimates. The Grand River watershed is the largest in southern Ontario. Nutrient discharge to the Grand River is high due to extensive agriculture and high urban populations. The river often has a hypoxic water column due to high community respiration in summer. However, although nitrogen pollution is significant, N cycling is not well understood in the river. This thesis shows that NO3- and NH4+ do not typically change on the diel scale, with the exception of two sites downstream of wastewater treatment plants (WWTPs). However, N2O concentration changes dramatically. N2O concentrations are higher at night and lower during the day for most sites, but are reversed at very low-nutrient sites. N2O is therefore a sensitive indicator of changes in N cycling that may not be evident from NO3- and NH4+ concentrations or stable isotope ratios. Additionally, this work shows the importance of having a sampling design that captures diel variability in N2O. Previous work in rivers and streams worldwide focused on the appropriate N2O:NO3- ratio used to predict N2O emissions. In contrast, this thesis shows that there is a significant but very weak relationship between instantaneous N2O emissions and NO3- concentrations. However, there is a much stronger negative exponential relationship between DO and N2O. Annual N2O emissions tripled between 2006 and 2007 but NO3- masses in the river were only 10% higher, likely because river levels were lower and anoxia more prevalent in 2007. This research suggests that the IPCC needs a new conceptual model for N2O-NO3- relationships in rivers. N2O is produced in rivers, partially due to microbial processing of NO3- and NH4+ from WWTP effluent. However, WWTP effluent may also include dissolved N2O and CH4 but this previously had not been directly quantified. It was also unclear if stable isotopic ratios of NH4+, NO3-, N2O and CH4 in WWTP effluent were distinct from river sources and could be used for effluent tracing. N2O emissions from three WWTPs in the Grand River Watershed were measured over 24 hours in summer and winter. N2O emissions were similar to direct emissions from WWTPs but CH4 emissions were about an order of magnitude lower than direct WWTP emissions. This is a previously-ignored source of N2O and CH4 to the atmosphere. While stable isotopic ranges of NO3- and NH4+ were not always distinct from river sources, ??15N-N2O, ??18O-N2O and ??13C-CH4 were distinct, making them potentially useful tracers of WWTP effluent in rivers. N2O isotopic signatures may help determine production and removal processes in rivers, but isotopic effects of the major production pathway, denitrification, have not been characterized for river sediments. This was addressed by preparing anoxic laboratory incubations of river sediment from two sites (non-urban and urban) in the Grand River and measuring stable isotopic effects of N2O production via denitrification. Stable isotopic fractionations were similar to published values but, surprisingly, strongly negatively correlated to production rate, even though NO3- substrate was plentiful. This novel finding suggests that N2O reduction resulting in isotopic effects is more prevalent in high-substrate systems than previously thought, and that N2O reduction may be inhibited by high NO3- or NO2- or by lags in N2O reductase activity in high N2O-production incubations. This could explain why N2O emissions from the Grand River are lower than predicted by IPCC equations, which assume that N2O:(N2O+N2) ratios produced by denitrification are constant. Concern about NO3- export to freshwater lakes and to oceans is growing, but the role of large, eutrophic rivers in removing watershed NO3- loading via denitrification and biotic assimilation is not clear. To understand how much NO3- the Grand River receives, and how much it removes annually, a NO3- isotope mass balance for the Grand River was created. The river denitrified between 0.5% and 17% of incoming NO3-, less than the 50% suggested by the IPCC. This is surprising, as the river is well mixed, has moderate to high NO3- concentrations, experiences hypoxia (promoting denitrification), and has extensive biomass (biofilm and macrophytes) that assimilate N. However, the river???s short residence time (~3 days not counting reservoirs), organic carbon-poor sediment and mineralization of organic matter could contribute to low denitrification rates. These findings suggest that denitrification rates in rivers worldwide could be lower than previously estimated. Although error was high, most ??15N-NO3- values for losses were in the expected range for denitrification and most ??15N-NO3- values for gains were within ranges from tributaries, WWTP effluent and groundwater measured in the watershed. The model suggests that 68% to 83% of N loads to the watershed are lost before entering the Grand River, and 13% is exported to Lake Erie, leaving 5 to 19% lost in the Grand River from a combination of denitrification, assimilation and storage. These findings suggest that large rivers are much less efficient in denitrification than other locations in watersheds such as small streams, ponds, groundwater and riparian zones. They also indicate that agricultural NO3- loading is much higher than WWTP effluent, suggesting that N management strategies should focus on agricultural runoff and groundwater. Given that N2O:NO3- relationships are weak and non-linear in the Grand River, a new conceptual model for N2O:NO3- relationships is presented. First, the Grand River dataset was supplemented with data from high-oxygen streams in southern Ontario. Regression tree analysis shows a weak relationship between NO3- and N2O in these streams with no other factors (temperature, DO, NH4+, TP, DOC, etc.) improving fit. A conceptual model was then created, which posits that N2O emission variability (between and within sites) increases with NO3- concentration when NO3- concentrations are above the threshold for NO3- limitation. The global dataset does not dispute this model, though a NO3- threshold was not clear. The lack of sites with both high NO3- and high N2O may indicate a paucity of research on eutrophic sites. Alternatively, high NO3- may indicate oxic conditions (i.e. little to no denitrification to remove it) which are incompatible with very high N2O emissions. In this case, the conceptual model can be modified such that N2O variability decreases when NO3- > ~ 4 mg N/L. The work also shows that low DO consistently results in high N2O emissions but high temperatures result in a very large range of N2O emissions. This approach allows N2O emissions, which have very high variability and are difficult to predict, to be constrained to likely ranges.