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Lead corrosion in premise plumbing systems from materials, such as lead pipes, soldered joints, and brass, can cause elevated lead in drinking water. This work examined mechanisms by which galvanic corrosion of lead solder:copper joints is accelerated by high chloride, low sulfate, and high nitrate in the water. Galvanic corrosion studies conducted using simulated copper plumbing joints showed lowered pH and concentrated anions at the lead solder surface. A combination of low pH and high chloride can prevent passivation of the solder surface, indefinitely sustaining high corrosion rates and lead contamination of potable water supplies. The mass of lead leached to water correlated with predictions based on Faraday's law, although a portion of the oxidized lead remained attached to solder in a scale layer. When the level of sulfate in water increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced. The impact of chloride-to-sulfate mass ratio (CSMR) on lead leaching from 50:50 lead:tin solder galvanically coupled to copper was examined at the bench scale.The CSMR can be affected by coagulant changeover, use of desalinated water, anion exchange, brine leaks, and other treatment changes. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from this source. Above this range, while lead leaching was generally very high, there was little correlation between lead release and CSMR. The impact of nitrate was tested at the bench scale using synthesized water. Results consistently showed that increasing nitrate in the range of 0 to 10 mg/L NO??N, could dramatically increase lead leaching from simulated soldered pipe joints. Although higher nitrate slightly increased the galvanic current, the main factor affecting lead release appears to be initiation of non-uniform corrosion, with small pieces of solder detaching into the water. Under some circumstances, the decay of chloramine after it leaves the treatment plant, and formation of nitrate via nitrification, can markedly increase corrosivity of distributed water to lead solder. The bench scale experiments conducted in this work illuminated many issues related to accelerated lead corrosion of solder. However, future research is necessary to further elucidate the mechanisms behind nitrate-accelerated corrosion, as well as methods for inhibition of corrosion due to chloride and nitrate. / Master of Science

The sediment-water interface is an active biogeochemical zone within streams, where solutes come in contact with mineral surfaces, biota, and reducing conditions. Here, we sought to examine the influence of light, the sediment water interface, and algae on dissolved organic carbon (DOC), nitrogen, and phosphorus within Maple Creek, an agriculturally impacted stream located in Fremont, Nebraska. Simultaneous continuous injection experiments into replicate open- and closed-bottom chambers were used to control the hydrologic residence time. A bromide tracer was injected, and samples were taken for nutrient analysis in the surface and subsurface water at depths up to 8 cm. Dissolved oxygen (DO) and temperature were recorded in order to monitor biotic production. Experiments were conducted over 10 hours, encompassing both light and dark conditions. Results show a strong biotic influence at the sediment-water interface causing nutrient uptake and changes in carbon quality. Changes are especially pronounced during peak photosynthesis hours. The open-bottom mesocosms consistently showed removal of N and P from the surface water to the subsurface. An increase in DOC flux was observed in the open-bottom mesocosms and the organic matter pool exhibited evidence of microbial reduction. The closed-bottom mesocosm showed NH?⁺ increased likely due to photochemical oxidation. These results show the importance of promoting exchange through the subsurface and across the sediment-water interface due to the positive impact it has on nutrient retention. / Master of Science

The CE-QUAL-W2 model has been selected as a tool for use in water quality management studies of the Occoquan Reservoir. In order for the model to achieve its best possible predictive capability, additional quantitative information on denitrification rates in the reservoir was required. A microcosm operating protocol was developed to obtain such information and also to enhance the understanding of complex nitrate-sediment-phosphorus interactions. The microcosm system developed was a biphasic system, consisting of a single continuous stirred tank reactor (CSTR), or a series of CSTRs containing representative sediment and water samples from the reservoir. The system was configured to simulate the bottom waters in the upper reaches of the reservoir during anoxic conditions. Nitrate concentrations in the microcosm system were monitored, and first-order denitrification-rate constants calculated to be used as an input to the reservoir water quality model CE-QUAL-W2. Other water chemistries were also monitored to investigate the nitrate effects on water quality. From the investigation results, it appears that the first-order denitrification-rate constant of the model should be set at 0.22 day-1 instead of the model default value. Nitrate was also observed to be removed by chemical and/or biologically mediated reduction by reduced forms of manganese. Once the nitrate was depleted, soluble manganese was released from the sediment first, followed by soluble iron. The release of phosphorus was not observed in this study after the depletion of nitrate, but nevertheless, was believed to occur. The absence of the release was attributed to phosphorus adsorption to the Plexiglas reactor walls. / Master of Science

When well water becomes contaminated to the extent that is does not meet EPA drinking water quality standards, it is considered unsafe for consumption. Nitrate and total coliform bacteria are both health contaminants and are both regulated in public water systems. A nitrate concentration of 10 mg/L or higher is considered unsafe, as is the presence of total coliform bacteria. Well degradation, inadequate well construction, and aquifer contamination can all result in contamination of well water. Factors such as well type, well age, well depth, treatment devices, population density, household plumbing pipe materials, and nearby pollution sources may affect household water quality. The specific objective of this study was to determine which factors influence nitrate levels and total coliform presence/absence of household well water. If possible, these influencing factors would be used to develop a relationship that would allow household residents to predict the nitrate level and total coliform presence/absence of their well water. As a result, a means of predicting the contamination risk to a specific well water supply under a given set of conditions, in addition to increasing awareness, could provide the homeowner with a rationale for further investigating the possibility of contamination. Existing data from the Virginia Cooperative Extension Household Water Quality Testing and Information Program were assembled for analyses in this project. The data consisted of 9,697 private household water supplies sampled from 1989-1999 in 65 Virginia counties. Initially, the entire state of Virginia was analyzed, followed by the five physiographic provinces of Virginia: the Blue Ridge, Coastal Plain, Cumberland Plateau, Ridge & Valley, and Piedmont. Ultimately, Louisa County was investigated to evaluate the possibility that better models could be developed using smaller land areas and, consequently, less geological variation. Least squares regression, both parametrically and non-parametrically, was used to determine the influence of various factors on nitrate levels. Similarly, logistic regression was used to determine the influence of the same parameters on nitrate categories, presence/absence of total coliform, and risk categories. Using stepwise model-building techniques, based primarily on statistical significance (p-values) and partial coefficient of determination (partial-R2), first and second-order linear models were evaluated. The best-fitting model only explained 58.5% of the variation in nitrate and none of the models fit well enough to be used for prediction purposes. However, the models did identify which factors were, in a statistical sense, significantly related to nitrate levels and total coliform presence/absence and quantified the strength of these relationships in terms of the percent of variation explained. / Master of Science

Aquatic ecosystems are especially vulnerable to human impacts associated with agricultural land-use, which provide multiple stressors altering community composition, important ecosystem functions and human valued properties of freshwaters. However, the increased occurrence of excessive levels of nitrate-nitrogen has raised major concerns about toxicity and stress on aquatic life, especially in regions such as the Canterbury Plains, New Zealand. The aims of this thesis were to identify nitrate-nitrogen effects on stream communities, and additionally provide field data to inform proposed national bottom lines for nutrients in New Zealand streams. A field survey was conducted on 41 small streams on the Canterbury Plains spanning a nitrate-nitrogen gradient (mean 0.4 – 11.3 mg/L). Spot nitrate-nitrogen was collected during and after the field survey to measure temporal variation in stream nitrate-nitrogen concentration for six months. This showed nitrate-nitrogen concentration varied between season and sub-region, where concentrations increased in winter and Ashburton had higher nitrate-nitrogen than Rangiora and Lincoln, respectively. These regimes of nitrate-nitrogen showed similar patterns in mean, median and maximum concentrations. To be confident my spot nitrate-nitrogen provided a true representation of long-term water chemistry, I compared Environment Canterbury 12 monthly data with my six monthly data in a sub-set of 15 sites. This comparison showed similar nitrate-nitrogen patterns and range of values between the two datasets. I then compared 12 common benthic invertebrate biotic metrics with my nitrate-nitrogen data and found none were correlated with this contaminant. For example, the Macroinvertebrate Community Index and quantitative variant (QMCI) derived to measure the response to organic pollution provided inconsistent results when applied to my streams. Nevertheless, gut content stoichiometry of the common mayfly grazer Deleatidium spp. indicated improvement in food quality (lower C:N ratio) with higher nitrate-nitrogen concentrations. These results indicated either nitrate-nitrogen does not alter invertebrate structural metrics across this nitrate-nitrogen gradient, or that these biotic metrics measure community structure aspects not affected by nitrate-nitrogen. I then investigated possible community composition patterns across the nitrate-nitrogen gradient. Unconstrained ordination (on presence/absence data) showed invertebrate communities at my sites were influenced primarily by discharge and shade, with the next most important driver being nitrate-nitrogen. A constrained ordination (on the same data) testing the singular effect of nitrate-nitrogen showed a marginally non-significant change in composition, with higher variability in community composition at higher nitrate-nitrogen concentrations. A further aim of my study was to test the draft nitrate-nitrogen bands proposed by Hickey (2013). These nitrate-nitrogen bands may advise guidelines to protect aquatic organisms as required by the National Policy Statement on Freshwater. Analysis of my invertebrate communities showed differences in composition, particularly at < 1 and > 6.9 mg/L bands. Several predatory caddisfly taxa: Triplectides, Neurochorema and Oeconesus were identified as potential indicator species of communities associated with low nitrate-nitrogen. These findings show that nitrate-nitrogen effects are difficult to detect, and that it is not the main driver of community composition in Canterbury streams. However, nitrate-nitrogen may be an important stressor for sensitive benthic invertebrate communities, as effects were observed on pollution tolerant organisms in this study. Therefore, this research has implications for freshwater ecologists and environmental managers striving to improve the health of streams on the Canterbury Plains.

4 pp. / This fact sheet is to be taken from research conducted by Uhlman and Rahman and published on the WRRC web site as: "Predicting Ground Water Vulnerability to Nitrate in Arizona". Funded by TRIF and peer reviewed by ADEQ. It also follows on "Arizona Well Owner's Guide to Water Supply" and also "Arizona Drinking Water Well Contaminants" (part 1 already submitted, part 2 in process). / Arizona's arid environment and aquifer types allow for the persistence of nitrate contamination in ground water. Agricultural practices and the prevalence of septic systems contributes to this water quality concern, resulting in nitrate exceeding the EPA Maximum Contaminant Level (MCL) in several locations across the state. Working with known nitrate concentrations in 6,800 wells across the state, this fact sheet presents maps showing the probability of nitrate contamination of ground water exceeding the MCL. The importance of monitoring your domestic water supply well for nitrate is emphasized.

Les systèmes de sécrétion de NO3– de la membrane plasmique des cellules végétales jouent un rôle important dans l'activité stomatique et la réponse des plantes à des stress biotiques et abiotiques. Malgré quelques avancées récentes, ces systèmes restent mal connus sur le plan moléculaire. Mon travail de thèse a consisté à caractériser le rôle physiologique de NAXT2, un membre du sous-groupe NAXT (NitrAte eXcretion Transporter) de la famille des transporteurs NRT1/PTR chez Arabidopsis thaliana. Mes résultats montrent que NAXT2 est un transporteur de NO3– et qu'il est principalement exprimé dans les cellules du péricycle de la racine, au voisinage des vaisseaux xylémiens. Sous contrainte saline et comparativement aux plantes sauvages (WT), un mutant knock-out pour NAXT2 (naxt2-1) présente un défaut de distribution du NO3– vers les feuilles et de sécrétion du NO3– dans la sève xylémienne, qui se traduisent par une diminution des teneurs en NO3– foliaires. NAXT2 est donc impliqué dans la charge du xylème en NO3– sous contrainte saline. Aucune des différences phénotypiques mises en évidence entre le mutant et WT sous contrainte saline n'a été observée sous stress osmotique ou en condition standard, suggérant que NAXT2 est essentiellement impliqué dans la réponse à la composante ionique du stress salin. Enfin, après un traitement salin prolongé, la biomasse foliaire de naxt2-1 est inférieure à celle de WT, ce qui indique que NAXT2 joue un rôle important dans l'adaptation des plantes aux contraintes salines modérées. Dans l'ensemble, ce travail suggère que NAXT2 est impliqué dans une fonction physiologique majeure, la translocation du NO3–, point de contrôle de la distribution du nitrate, et dans l'adaptation de la plante aux contraintes salines. / NO3– secretion systems at the plasma membrane of plant cells play an important role in stomata activity and plant response to biotic and abiotic stresses. Despite of few recent advances, these systems are still poorly known at the molecular level. During my thesis, I worked on the characterization of the physiological role of NAXT2, a member of the NAXT (NitrAte eXcretion Transporter) sub-group from the large NRT1/PTR transporters family in Arabidopsis thaliana. The results presented here show that NAXT2 is a NO3– transporter and that it is mainly expressed in root pericycle cells, close to the xylem vessels. Under salinity constraint and relatively to wild type plants (WT), a NAXT2 knock-out mutant (naxt2-1) displayed a defect in NO3– distribution towards the shoots and in NO3– secretion into the xylem sap, which lead to a decrease in shoot NO3– content. Thus, NAXT2 is involved in NO3– xylem loading under salinity constraint. None of the phenotypic differences described in this work between WT and mutant was observed under osmotic stress or standard culture conditions, suggesting that NAXT2 is specifically involved in response to the ionic component of salt stress. Finally, after a prolonged salt treatment, naxt2-1 shoot biomass was lower than that of WT, indicating that NAXT2 plays an important role in plant adaptation to mild salinity constraint. Altogether, this work suggests that NAXT2 is involved in a major physiological function, the NO3– translocation, control point of nitrate distribution and in plant adaptation to salinity constraint.

Les oxydes d’azote atmosphériques (NOx=NO+NO2) sont des composés clefs en chimie de l’environnement, jouant un rôle central pour la capacité oxydante de l’atmosphère et le cycle de l’azote. La composition isotopique du nitrate atmosphérique (NO?3 particulaire et HNO3 gazeux), constituant leur puits ultime, renseigne sur leur bilan chimique. Le rapport 15N/14N donne une indication de leurs sources, alors que l’anomalie isotopique en oxygène (?17O=d17O-0.52×d18O) révèle la nature de leurs mécanismes d’oxydation. Des études couplées de d15N et ?17O d’échantillons de nitrate atmosphérique collectés dans l’Arctique, en Antarctique et dans l’atmosphère marine au dessus de l’Océan Atlantique, où le bilan des NOx est souvent mal connu ont été effectuées. À ces fins, le défi que constitue la mesure simultanée des trois rapports isotopiques du nitrate (17O/16O, 18O/16O et 15N/14N) dans le même échantillon représentant moins d’une micromole a été relevé. La solution adoptée tire avantage des propriétés d’une bactérie dénitrifiante, utilisée pour convertir le nitrate en N2O, dont la composition isotopique totale a été mesurée en utilisant un système automatisé de chromatographie en phase gazeuse et spectrométrie de masse de rapport isotopique. Les principaux résultats obtenus via les isotopes de l’oxygène permettent l’identification claire de transitions saisonnières entre voies d’oxydation des NOx, y compris le rôle majeur des composés halogénés réactifs au printemps polaire en régions côtières. Les isotopes de l’azote ont quant à eux permis d’apporter de nouvelles contraintes sur le cycle de l’azote dans les régions polaires, grâce au fractionnement significatif induit par les phénomènes de remobilisation post-dépôt affectant le nitrate dans le manteau neigeux, et l’émission de NOx qui en découle / Atmospheric nitrogen oxides (NOx=NO+NO2) are central to the chemistry of the environment, as they play a pivotal role in the cycling of reactive nitrogen and the oxidative capacity of the atmosphere. The stable isotopes of atmospheric nitrate (in the form of particulate NO?3 or gaseous HNO3), their main ultimate sinks, provide insights in chemical budget of NOx : its nitrogen isotopes are almost conservative tracers of their sources, whereas NOx sinks are revealed by its triple oxygen isotopic composition. The long-awaited challenge of measuring all three stable isotope ratios of nitrate (17O/16O, 18O/16O and 15N/14N) in a single sample at sub-micromolar levels has been resolved. The newly developed method makes use of denitrifying bacteria to quantitatively convert nitrate to a stable species (N2O), whose isotope ratios are measured using an automated gas chromatography/isotope ratio mass spectrometry analytical system. Dual measurements of d15N and the isotope anomaly (?17O=d17O-0.52×d18O) of atmospheric nitrate samples collected in the Arctic, the Antarctic and in the marine boundary layer of the Atlantic Ocean, have been used to derive the chemical budget of NOx and atmospheric nitrate in these remote regions. Main results from oxygen isotope measurements pertain to the identification of seasonal and latitudinal shifts in NOx oxidative pathways in these environments (including the role of halogen oxides chemistry in polar regions during springtime), as a function of particle sizes. Nitrogen isotopes are found to provide strong constraints on the budget of reactive nitrogen in polar regions, due to the strong fractionation associated with snowpack photochemical loss of nitrate and its conversion to NOx