Abstract  This study involves a process of phyco-remediation of dairy industry wastewater by algal strain Chlamydomonas polypyrenoideum. The results of selected algal strain indicated that dairy industry wastewater was good nutrient supplement for algal growth in comparable with BG-11 growth medium. Alga grown on dairy industry wastewater reduced the pollution load of nitrate (90%), nitrite (74%), phosphate (70%), chloride (61%), fluoride (58%), and ammonia (90%) on 10th day of its growth as compared to that of uninoculated wastewater. The lipid content of algal biomass grown on dairy wastewater on 10th day (1.6g) and 15th day (1.2 g) of batch experiment was found to be higher than the lipid content of algal biomass grown in BG-11 growth medium on 10th day (1.27 g) and 15th day (1.0 g) of batch experiment. The results on FTIR analysis of the extracted bio-oil through transesterification reaction was comparable with bio-oil obtained from other sources.

Abstract  Silver/alumina catalysts are known to be highly active for hydrogen-assisted selective catalytic reduction (SCR) of nitrogen oxides. A comparison of silver/alumina and pure alumina catalysts shows that hydrogen conversion occurs on the silver. Subsequently formed NO2 is crucial for NH3-SCR and in addition products from the hydrogen conversion influence nitrates on the alumina by spill-over.

Abstract  In this study, cerium oxide nano-rods were synthesized by hydrothermal method in order to develop electro-catalysts for direct ethanol fuel cells. Carbon monoxide (CO) and ethanol electro-oxidation activities of PtRuC catalyst supported onto cerium oxide prepared by hydrothermal method (CeO2(HT)) were compared with PtRuC supported onto cerium oxide prepared by direct calcination (CeO2(K)) of ammonium cerium nitrate ((NH4)(2)[Ce(NO3)(6)]). After surface analysis of (CeO2(HT)) by scanning electron microscopy, non-uniform nano-rods with approximately 1 mu m length and 200nm radius were observed. On the other hand, cerium oxide prepared by calcination has a particle structure in 400nm size approximately. According to results obtained by energy dispersive X-ray spectroscopy, CeO2(HT) has substantially higher oxygen stoichiometry than CeO2(K). After electrochemical analysis, it was seen that % 10PtRuC/(CeO2(HT)) has the highest CO and ethanol electro-oxidation activity.

Abstract  Access to safe drinking water is one of the basic human rights and essential for healthy life. The present study investigated the concentrations of various pollutants in drinking water and health risk in Charsadda district, Khyber Pakhtunkhwa, Pakistan. Water samples were collected from dug-wells, tube-wells and hand pumps which were the most common sources of drinking water and analyzed for physical parameters, anions, heavy metals and coliform bacteria using standard methods. The concentrations of nitrate (10.3-14.84 mg L-1) in 13 sites exceeded the permissible limit (10 mg L-1) set by US-EPA, while sulfate concentrations (505-555 mg L-1) in 9 sites exceeded the permissible limit (500 mg L-1) set by WHO. Similarly, the concentrations of Pb, Cd, Ni and Fe exceeded their respective permissible limits set by different organizations in some locations. Furthermore, the coliform bacterial contamination (2-5 MPN 100 mL(-1)) was also found in some sources of water, confirming the bacterial contamination of drinking water. In the study area, improper disposal of sewage and solid wastes, over application of agrochemicals (pesticides and fertilizers), deteriorating condition of piping network and transportation were the major sources responsible for contamination of drinking water. Water contamination with coliform bacteria was the main source of waterborne diseases like gastroenteritis, dysentery, diarrhea and viral hepatitis as complained by most of the respondents during questionnaire survey. In order to reduce the health risk, it is necessary to immediately stop the uses of drinking water from contaminated sources and government should supply treated/clean water with supply lines far away from solid waste, sludge and sewage sites. The farmers should be properly trained to avoid the overusing of agrochemicals responsible for drinking water contamination, while both women and men should be properly educated with water knowledge through awareness and training programs needed for sustainable use and management of drinking water. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract  Nutrient removal and recovery has received less attention during the development of bioelectrochemical systems (BES) for energy efficient wastewater treatment, but it is a critical issue for sustainable wastewater treatment. Both nitrogen and phosphorus can be removed and/or recovered in a BES through involving biological processes such as nitrification and bioelectrochemical denitrification, the NH4+/NH3 couple affected by the electrolyte pH, or precipitating phosphorus compounds in the high-pH zone adjacent a cathode electrode. This paper has reviewed the nutrients removal and recovery in various BES including microbial fuel cells and microbial electrolysis cells, discussed the influence factors and potential problems, and identified the key challenges for nitrogen and phosphorus removal/recovery in a BES. It expects to give an informative overview of the current development, and to encourage more thinking and investigation towards further development of efficient processes for nutrient removal and recovery in a BES. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract  N-butyl Pyridine Nitrate ionic liquid is prepared by the double decomposition reaction of BPC and NaNO3. The ionic liquid at room temperature used in the experiment has a significant absorption determined by UV spectrum within the range of 200-400nm, the maximum absorption wavelength of BP-NO3 ionic liquid is 259nm. The standard working curve of BP-NO3 ionic liquid is y=0.04555x+0.05604 (R=0.99922). The recovery rate of BP-NO3 ionic liquid which is between 99.8% and 103.4%, is measured by standard addition method in ethanol.

Abstract  Cellulose nanocrystals (CNCs) are a sustainable nanomaterial with applications spanning composites, coatings, gels, and foams. Surface modification routes to optimize CNC interfacial compatibility and functionality are required to exploit the full potential of this material in the design of new products. In this work, CNCs have been rendered pH-responsive by surface-initiated graft polymerization of 4-vinylpyridine with the initiator ceric(IV) ammonium nitrate. The polymerization is a one-pot, water-based synthesis carried out under sonication, which ensures even dispersion of the cellulose nanocrystals during the reaction. The resultant suspensions of poly(4-vinylpyridine)-grafted cellulose nanocrystals (P4VP-g-CNCs) show reversible flocculation and sedimentation with changes in pH; the loss of colloidal stability is visible by eye even at concentrations as low as 0.004 wt %. The presence of grafted polymer and the ability to tune the hydrophilic/hydrophobic properties of P4VP-g-CNCs were characterized by Fourier transform infrared spectroscopy, elemental analysis, electrophoretic mobility, mass spectrometry, transmittance spectroscopy, contact-angle measurements, thermal analysis, and various microscopies. Atomic force microscopy showed no observable changes in the CNC dimensions or degree of aggregation after polymer grafting, and a liquid crystalline nematic phase of the modified CNCs was detected by polarized light microscopy. Controlled stability and wettability of P4VP-g-CNCs is advantageous both in composite design, where cellulose nanocrystals generally have limited dispersibility in nonpolar matrices, and as biodegradable flocculants. The responsive nature of these novel nanoparticles may offer new applications for CNCs in biomedical devices, as clarifying agents, and in industrial separation processes.

Abstract  Aerosol hygroscopic growth factors and chemical properties were measured as part of the MEGAPOLI "Megacities Plume Case Study" at the urban site Laboratoire d'Hygiene de la Ville de Paris (LHVP) in the city center of Paris from June to August 2009, and from January to February 2010. Descriptive hygroscopic growth factors (DGF) were derived in the diameter range from 25 to 350 nm at relative humidities of 30, 55, 75, and 90% by applying the summation method on humidified and dry aerosol size distributions measured simultaneously with a humidified differential mobility particle sizer (HDMPS) and a twin differential mobility particle sizer (TDMPS). For 90% relative humidity, the DGF varied from 1.06 to 1.46 in summer, and from 1.06 to 1.66 in winter. Temporal variations in the observed mean DGF could be well explained with a simple growth model based on the aerosol chemical composition measured by aerosol mass spectrometry (AMS) and black carbon photometry (MAAP). In particular, good agreement was observed when sulfate was the predominant inorganic factor. A clear overestimation of the predicted growth factor was found when the nitrate mass concentration exceeded values of 10 mu gm(-3), e.g., during winter.

Abstract  Northern peatlands are increasingly threatened by climate change and industrial activities. This study examined the impact of simulated droughts on pore water chemistry at six peatlands in Sudbury, Ontario, that differ in copper (Cu), nickel (Ni) and cobalt (Co) contamination, including a site that had been previously limed. All sites responded similarly to simulated drought: pore water pH declined significantly following the 30 day drought and the decline was greater following the 60 day drought treatment. The decline in pore water pH was due to increasing sulphate concentrations, whereas nitrate increased more in the 60 day drought treatment. Decreases in pH were accompanied by large increases in Ni and Co that greatly exceeded provincial water quality guidelines. In contrast, dissolved organic carbon (DOC) concentrations decreased significantly following drought, along with concentrations of Cu and Al, which are strongly complexed by organic acids.

Abstract  The ability of plants to compete effectively for nitrogen (N) resources is critical to plant survival. However, controversy surrounds the importance of organic and inorganic sources of N in plant nutrition because of our poor ability to visualize and understand processes happening at the root-microbial-soil interface. Using high-resolution nano-scale secondary ion mass spectrometry stable isotope imaging (NanoSIMS-SII), we quantified the fate of ¹⁵N over both space and time within the rhizosphere. We pulse-labelled the soil surrounding wheat (Triticum aestivum) roots with either ¹⁵NH₄⁺ or ¹⁵N-glutamate and traced the movement of ¹⁵N over 24 h. Imaging revealed that glutamate was rapidly depleted from the rhizosphere and that most ¹⁵N was captured by rhizobacteria, leading to very high ¹⁵N microbial enrichment. After microbial capture, approximately half of the ¹⁵N-glutamate was rapidly mineralized, leading to the excretion of NH₄⁺, which became available for plant capture. Roots proved to be poor competitors for ¹⁵N-glutamate and took up N mainly as ¹⁵NH₄⁺. Spatial mapping of ¹⁵N revealed differential patterns of ¹⁵N uptake within bacteria and the rapid uptake and redistribution of ¹⁵N within roots. In conclusion, we demonstrate the rapid cycling and transformation of N at the soil-root interface and that wheat capture of organic N is low in comparison to inorganic N under the conditions tested.

Abstract  Concerns about the environmental effect and the economic burden of methane (CH4) emissions from ruminants are driving the search for ways to mitigate rumen methanogenesis. The use of direct-fed microbials (DFM) is one possible option to decrease CH4 emission from ruminants. Direct-fed microbials are already used in ruminants mainly to increase productivity and to improve health, and are readily accepted by producers and consumers alike. However, studies on the use of DFM as rumen CH4 mitigants are scarce. A few studies using Saccharomyces cerevisiae have shown a CH4-decreasing effect but, to date, there has not been a systematic exploration of DFM as modulators of rumen methanogenesis. In this review, we explored biochemical pathways competing with methanogenesis that, potentially, could be modulated by the use of DFM. Pathways involving the redirection of H-2 away from methanogenesis and pathways producing less H-2 during feed fermentation are the preferred options. Propionate formation is an example of the latter option that in addition to decrease CH4 formation increases the retention of energy from the diet. Homoacetogenesis is a pathway using H-2 to produce acetate, however up to now no acetogen has been shown to efficiently compete with methanogens in the rumen. Nitrate and sulphate reduction are pathways competing with methanogenesis, but the availability of these substances in the rumen is limited. Although there were studies using nitrate and sulphate as chemical additives, use of DFM for improving these processes and decrease the accumulation of toxic metabolites needs to be explored more. There are some other pathways such as methanotrophy and capnophily or modes of action such as inhibition of methanogens that theoretically could be provided by DFM and affect methanogenesis. We conclude that DFM is a promising alternative for rumen methane mitigation that should be further explored for their practical usage.

Abstract  ZnAl2O4:Cr3+, Tb3+ powders with different dopant contents have been synthesized by sol-gel method using the following precursors: zinc nitrate (Zn(NO3)(2)), aluminum nitrate (Al(NO3)(3)), terbium nitrate (Tb(NO3)(3)), chrome nitrate (Cr(NO3)(3)), and citric acid. The effect of the Cr3+, Tb3+ concentration and heat-treating temperature on structural and optical properties of the synthesized samples has been studied.

Abstract  Atmospheric particulate matter is composed of inorganic and organic components of natural and anthropogenic origin. Wind-transport is probably the most important process responsible for the emission of solid particulate matter into the troposphere, but there are also important contributions from chemical reactions due to the interaction of different atmospheric components in presence of water and solar radiation. Sulfate, nitrate and carbonate salts can be both reactants and products in this complex dynamic system, and there is no doubt about their important impact on the climate. Both simple and mixed salts can be produced in atmosphere by dissolution-crystallization processes. The Raman spectra of 45 representative salts of the atmospheric environment were recorded and the bands assigned. The chemometric analysis of the spectroscopic data of these 45 salts demonstrates the suitability of Raman spectroscopy to classify and identify sulfate, nitrate and carbonate salts of atmospheric importance. Salts were classified into three groups: "sulfates", "nitrates or carbonates" and "sulfate-nitrates or sulfate-carbonate". This kind of information is relevant in atmospheric studies because specific characteristics of the salts can provide valuable information about the origin of the salts, the atmospheric chemistry and climate forcing, thus contributing to the evaluation of environmental impacts.

Abstract  Various nitration systems comprising nitric acid, acid anhydride and zeolite H beta in the absence of solvent are described. Direct double nitration of toluene with a nitric acid, propanoic anhydride and zeolite H beta system has been developed to give 2,4-dinitrotoluene in 98% yield, with a 2,4-:2,6-dinitrotoluene ratio of 123:1. This system also nitrates activated mono-substituted benzenes (anisole and phenetole) and moderately activated mono-substituted benzenes (ethylbenzene and propylbenzene) to give mainly 2,4-dinitro derivatives. The zeolite can be recovered, regenerated and reused to give almost the same yield as that given when fresh zeolite is used.

Abstract  Purpose: Ischemia-reperfusion injury can cause testicular damage and phosphodiesterase inhibitors are reported to regulate antioxidant activity. We investigated the prevention of ipsilateral and contralateral testicular damage using 2 phosphodiesterase inhibitors after testicular detorsion in rats.

Materials and Methods: A total of 28 adult male rats were randomly divided into 4 groups of 7 each, including group 1-sham operation, group 2-testicular torsion and detorsion, group 3- testicular torsion and detorsion with sildenafil administration before detorsion and group 4- testicular torsion and detorsion with udenafil administration before detorsion. Tissue levels of malondialdehyde, total sulfhydryl and nitrite were evaluated, and histopathological changes in the groups were examined.

Results: Compared to group 1 significantly increased tissue malondialdehyde (p = 0.001), significantly decreased total sulfhydryl (p = 0.038) and insignificantly increased nitrite were found in group 2. Compared to group 2 malondialdehyde decreased significantly and total sulfhydryl increased significantly in groups 3 and 4. The decrease in nitrite was insignificant in the latter 2 groups. Histopathology revealed increased hemorrhage, congestion and edema in group 2 rats. The testicular injury score was lower in groups 3 and 4. In group 2 grades II to IV injury was detected while most specimens in treated groups showed grade II injury.

Conclusions: This study indicates that intraperitoneal administration of sildenafil and udenafil efficiently suppresses radical production while decreasing histological changes after testicular ischemia-reperfusion injury.

Abstract  We present a description of the algorithm used to retrieve peroxyacetyl nitrate (PAN) concentrations from the Aura Tropospheric Emission Spectrometer (TES). We describe the spectral microwindows, error analysis, and the utilization of a priori and initial guess information provided by the GEOS-Chem global chemical transport model. The TES PAN retrievals contain up to one degree of freedom for signal. In general, the retrievals are most sensitive to PAN in the mid-troposphere. Estimated single-measurement uncertainties are on the order of 30 to 50 %. The detection limit for a single TES measurement is dependent on the atmospheric and surface conditions as well as on the instrument noise. For observations where the cloud optical depth is less than 0.5, we find that the TES detection limit for PAN is in the region of 200 to 300 pptv. We show that PAN retrievals capture plumes associated with boreal burning. Retrievals over the Northern Hemisphere Pacific in springtime show spatial features that are qualitatively consistent with the expected distribution of PAN in outflow of Asian pollution.

Abstract  In microaerophilic or anaerobic environments, Pseudomonas aeruginosa utilizes nitrate reduction for energy production, a process dependent on the availability of the oxyanionic form of molybdenum, molybdate (MoO42-). Here, we show that molybdate acquisition in P. aeruginosa occurs via a high-affinity ATP-binding cassette permease (ModABC). ModA is a cluster D-III solute binding protein capable of interacting with molybdate or tungstate oxyanions. Deletion of the modA gene reduces cellular molybdate concentrations and results in inhibition of anaerobic growth and nitrate reduction. Further, we show that conditions that permit nitrate reduction also cause inhibition of biofilm formation and an alteration in fatty acid composition of P. aeruginosa. Collectively, these data highlight the importance of molybdate for anaerobic growth of P. aeruginosa and reveal novel consequences of nitrate reduction on biofilm formation and cell membrane composition.

Abstract  A series of 3,4-dihydropyrimidin-2(1H)-one(thione) derivatives was synthesized using Co(NO3)(2)center dot 6H(2)O in solvent-free condition. Avoiding organic solvents during the chemical reactions leading to an economic approach is effective. The reaction is characterized by high efficiency, short reaction time, high yields, simple experimental procedure, availability of catalyst and environmentally friendly reaction conditions.

Abstract  The influence of long-term land application of stockpiled feedlot manure (SM) containing either wood-chip (SM-WD) or straw (SM-ST) bedding on soil properties during the barley (Hordeum vulgare L.) silage growing season is unknown. The main objective of our study was determine the effect of bedding material in stockpiled manure (i.e., SM-WD vs. SM-ST) on certain soil properties. A secondary objective was to determine if organic amendments affected certain soil properties compared with unamended soil. Stockpiled feedlot manure with SM-WD or SM-ST bedding at 77 Mg (dry wt) ha(-1) yr(-1) was annually applied for 13 to 14 yr to a clay loam soil in a replicated field experiment in southern Alberta. There was also an unamended control. Soil properties were measured every 2 wk during the 2011 and 2012 growing season. Properties included water-filled pore space (WFPS), total organic C and total N, NH4-N and NO3-N, water-soluble non-purgeable organic C (NPOC), water-soluble total N (WSTN), denitrification (acetylene inhibition method), and CO2 flux. The most consistent and significant (P <= 0.05) bedding effects on soil properties in both years occurred for total organic C, C:N ratio, and WSTN. Total organic C and C:N ratio were generally greater for SM-WD than SM-ST, and the reverse trend occurred for WSTN. Bedding effects on other soil properties (WFPS, NH4-N, NO3-N, NPOC) occurred in 2012, but not in 2011. Total N, daily denitrification, and daily CO2 flux were generally unaffected by bedding material. Mean daily denitrification fluxes ranged from 0.9 to 1078 g N2O-N ha(-1) d(-1) for SM-ST, 0.8 to 326 g N2O-N ha(-1) d(-1) for SM-WD, and 0.6 to 250 g N2O-N ha(-1) d(-1) for the CON. Mean daily CO2 fluxes ranged from 5.3 to 43.4 kg CO2-C ha(-1) d(-1) for SM-WD, 5.5 to 26.0 kg CO2-C ha(-1) d(-1) for SM-ST, and from 0.5 to 6.8 kg CO2-C ha(-1) d(-1) for the CON. The findings from our study suggest that bedding material in feedlot manure may be a possible method to manage certain soil properties.

Abstract  Nitrogen fixation can be a dominant flux of nitrogen (N) input providing up to 97 % of new N into some terrestrial and up to 82 % into some aquatic ecosystems, yet N-2 fixation is rarely considered in the context of other N cycling fluxes. We compared N-2 fixation with dissolved inorganic N (DIN) uptake fluxes in several streams. We measured N-2 fixation in nine streams in Grand Teton National Park, Wyoming, USA and surrounding areas and we compared our estimates to the ammonium (NH4+) uptake, nitrate (NO3) uptake, and denitrification estimates from the literature for those streams. N-2 fixation was negligible or below detection in the four streams with NO3- concentrations >20 mu g NO3--N L-1 center dot N-2 fixation exceeded NO3- uptake in two of the nine streams and NH4+ uptake in one stream. To further examine the relationship between N-2 fixation and DIN uptake, we chose Ditch Creek, which is a low-N stream (<5 mu g DIN-N L-1) with high rates of N-2 fixation. We measured N-2 fixation, NH4+ uptake, and NO3+ uptake biweekly throughout one summer. In Ditch Creek, DIN uptake exceeded N-2 fixation at the beginning and end of the summer, but from July to the beginning of September N-2 fixation was up to eight times greater than DIN uptake. The epilithic biofilm in Ditch Creek accumulated 1.5 g N m(-2) throughout the summer, and N-2 fixation may have contributed up to 73 % of that accumulation. Ditch Creek N2 fixation surpassed denitrification for both Ditch Creek and many streams. N-2 fixation can be a dominant flux in low-N stream ecosystems.

Abstract  Geochemistry is a key tool in identifying sources of elements for both mineral exploration and environmental purposes. This study evaluates the first systematic regional hydrogeochemical survey for environmental assessments of the classic Andean copper mineral province and the Andina-Los Bronces mining district of Central Chile. One hundred and forty-five water samples were collected systematically in the Valparaiso and Metropolitana Regions of Central Chile, including the capital, Santiago. The concentrations of more than 70 elements and compounds were determined using inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC) along with the stable isotopes (delta D, delta O-18, delta S-34, delta O-18(SO4), delta N-15 and delta O-18(NO3)) and used to define the geochemical baselines in the area and distinguish between different sources. The geochemistry demonstrates the potential to distinguish between natural (bedrock, hydrothermal alteration and mineralization) and anthropogenic (agriculture, sewage and urban) sources of elements. The distribution patterns of many chemicals show a strong correlation with the presence of evaporitic components (Ca, SO42-, Sr, K, Rb, total dissolved solids (TDS)), hydrothermal alteration and sulphide mineralization (Cu, Zn, Ni, Cd, Co and REEs). High concentrations of nitrate, phosphate and alkalinity occur downstream of agricultural areas and reflect pollution from fertilizers. Overall, the catchment areas affected by mining activities are relatively small and highly localized compared to those affected by agriculture and urban centres.

Abstract  Postmenopausal osteoporosis due to estrogen deficiency is a major health problem, and available therapies rely largely on the inhibition of bone resorption, because estrogen replacement is associated with risks. Estrogen promotes bone health in large part by increasing osteocyte survival, but the molecular mechanisms involved are only partly understood. We showed that estradiol stimulates nitric oxide (NO) production in osteocytes, leading to increased cGMP synthesis and activation of cGMP-dependent protein kinases (PKGs). Moreover, we found that 17 beta-estradiol protects osteocytes against apoptosis via the NO/cGMP signaling pathway: type II PKG mediates estradiol-induced activation of the prosurvival kinases Erk and Akt, whereas type I PKG contributes to prosurvival signaling by directly phosphorylating and inactivating the cell death protein BAD. Preclinical data support an important role of NO in bone biology, and clinical trials suggest that NO donors may prevent bone loss in postmenopausal women. Our data provide novel insights into estrogen signaling through the NO/cGMP/PKG pathway and a rationale for using NO donors and other cGMP-elevating agents for treating postmenopausal osteoporosis.

Abstract  Photooxidation of (CH3)(3)CCHO in the presence of NO2 leads to the formation of CO, CO2, (CH3)(3)CC(O) OONO2 (DMPPN), and (CH3)(3)CONO2. The synthesis of DMPPN and thermal decomposition studies were carried out. Pressure dependence was studied at 293 K from 6.0 to 1000 mbar. Kinetic parameters for DMPPN were determined between 293 and 308K, at total pressures of 9.0 and 1000 mbar. The values found for the activation energy and pre-exponential factor were (109 +/- 3)kJ/mol, 1.7 x 10(15)s(-1), and (117 +/- 3) kJ/mol, 5.2 x 10(16)s(-1) at these pressures, respectively. Thermal stability for DMPPN is similar to peroxyacyl nitrates already identified in the atmosphere, such as peroxyacetyl and peroxypropionyl nitrates. The quantum yield for photolysis at 254 nm of (CH3)(3)CCHO was determined to be 0.60 +/- 0.05. (C) 2014 Published by Elsevier B.V.

Abstract  Denitrification in the groundwater systems of agricultural catchments can provide a substantial 'ecosystem service' by attenuating leached nitrate (NO3-) before it reaches surface water bodies. Samples along a groundwater flow path with low dissolved oxygen and declining NO3- concentrations can indicate the occurrence of denitrification. Isotopic analysis of this NO3- can potentially identify and quantify denitrification activity. In this study, shallow groundwater samples (maximum 5 m below ground surface) were taken from three locations within a small agricultural catchment in the Waikato region of New Zealand. The delta N-15 and delta O-18 values of NO3- were analysed to try to determine where denitrification was occurring and at what rate. Results indicated that denitrification rates varied spatially, but interpretation was confounded by insufficiently understood flow paths and extremely low concentrations of NO3- in reduced groundwater. Seasonal denitrification was observed at a Gley soil site where the soil profile was periodically saturated to near the ground surface and delta N-15-NO3- values reached +28.5 parts per thousand and delta O-18-NO3- values up to +19.6 parts per thousand. In contrast to expectations, NO3- in well-oxidised groundwater samples showed substantial variability in its delta N-15 and delta O-18 isotopic signature. This indicated that the NO3- originated from multiple sources, which restricted the quantification of denitrification. (C) 2015 Elsevier B.V. All rights reserved.

Abstract  Hydrological conditions are among the most important factors influencing nutrient concentrations in rivers and their fluxes out of the catchments. In the boreal area extreme hydrological conditions are typical with intense floods during the snow-melt period in spring and the base-flow conditions during winter and summer.

In this study we compared nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N) and dissolved organic nitrogen (DON) concentrations and fluxes among summer seasons (June-August) with contrasting hydrology in four small boreal rivers with differing land-use in southern Finland.

For the analysis we selected 3 years of the lowest summer discharge (1999, 2010, 2011) and 3 years of the highest summer discharge (1996, 1998, 2004).

During high discharge summers NH4-N and DON concentrations were on average 187 and 240 % higher than during low discharge summers. Because of large differences in discharge between the summers the flux values of the different N fractions were at maximum 10-20 times higher during high discharge summers. The effect of heavy rains on N loading was clearly demonstrated in summer 2004 when two consecutive floods transported 42 % of the annual NO3-N flux, 44 % of the NH4-N flux and 57 % of the DON flux out of the catchment.

Available nitrogen storages in the studied catchment areas were probably in excess especially during the wet summers when the plant uptake was presumably lower compared to dryer and warmer summers. When the hydrological conditions were suitable for surface and subsurface runoff, the concentrations and fluxes of NO3-N, NH4-N and DON increased substantially.