GIS based evaluation of fluoride contamination and assessment of fluoride exposure dose in groundwater of a district in Uttar Pradesh,India

Groundwater is the main source of drinking water in both rural and urban areas of the Pratapgarh district in the eastern Uttar Pradesh. Fifty-five groundwater samples were collected from 17 blocks of the Pratapgarh district and analyzed for fluoride (F^?) and other water quality parameters (pH, EC, TDS, turbidity, Cl^?, HCO₃^?, SO₄^2?, NO₃^?, Ca²⁺, Mg²⁺, Na⁺, K⁺, silica and total hardness) to assess its suitability for drinking uses. The fluoride concentration in the analyzed groundwater of the Pratapgarh district varied between 0.41 and 3.99 mg/L. Fluoride concentration in about 78% of the groundwater samples exceeded the acceptable level of 1.0 mg/L, while in 70% samples it exceeded the maximum permissible limit of 1.5 mg/L. A geographic information system (GIS) tool was used to study the spatial variation of fluoride concentrations in the groundwater of the Pratapgarh district. Fluoride is positively correlated with pH (0.36) and HCO₃^? (0.22) and negatively with Ca²⁺ (?0.23) and Mg²⁺ (?0.08), suggesting dissolution of fluoride-bearing minerals with the precipitation of Ca/Mg carbonate in the alkaline environment. The maximum exposure dose to fluoride for adults in the study area was found to be 6.8 times higher than the minimum risk level (MRL) of 0.05 mg kg^?1 day^?1 estimated by the Agency for Toxic Substances and Disease Registry (ATSDR).     

Source apportionment of pollution in groundwater source area using factor analysis and positive matrix factorization methods

By means of factor analysis (FA) and positive matrix factorization (PMF) methods, groundwater pollution sources were identified in the Jinji groundwater source area, which is beside the Yellow River and is the only urban water supply source for the city of Wuzhong in Northwestern China. The sources of groundwater were quantified based on 16 samples of shallow groundwater from the source area. The source apportionment with the PMF model identified three dominant groundwater pollution sources. These were anthropogenic activities of agricultural and industrial pollution with a pollution contribution of 53.0%, water–rock interaction of 24.6%, and evaporation and concentration of 22.4%. The source apportionment with the FA model identified four sources which were evaporation and concentration, with the largest contribution (42.6%), followed by anthropogenic activities (29.2%), mineral dissolution and industrial pollution (22.4%), and natural effects (5.8%). Specific attention should be paid to these natural (fluoride, TH, etc.) and anthropogenic sources (NH₄⁺, NO₂^?, turbidity, total bacterial count, etc.), and pertinent measures should be taken to control local groundwater pollution. The most significant trait of the PMF is its scientific interpretation and physical explanation of the results, depending on non-negative restriction of the pollution source profiles and contributions.     

Denitrification as a major regional nitrogen sink in subtropical forest catchments: Evidence from multi‐site dual nitrate isotopes

Increasing nitrogen (N) deposition in subtropical forests in south China causes N saturation, associated with significant nitrate (NO₃^?) leaching. Strong N attenuation may occur in groundwater discharge zones hydrologically connected to well‐drained hillslopes, as has been shown for the subtropical headwater catchment “TieShanPing”, where dual NO₃^? isotopes indicated that groundwater discharge zones act as an important N sink and hotspot for denitrification. Here, we present a regional study reporting inorganic N fluxes over two years together with dual NO₃^? isotope signatures obtained in two summer campaigns from seven forested catchments in China, representing a gradient in climate and atmospheric N input. In all catchments, fluxes of dissolved inorganic N indicated efficient conversion of NH₄⁺ to NO₃^? on well‐drained hillslopes, and subsequent interflow of NO₃^? over the argic B‐horizons to groundwater discharge zones. Depletion of ¹⁵N‐ and ¹⁸O–NO₃^? on hillslopes suggested nitrification as the main source of NO₃^?. In all catchments, except one of the northern sites, which had low N deposition rates, NO₃^? attenuation by denitrification occurred in groundwater discharge zones, as indicated by simultaneous ¹⁵N and ¹⁸O enrichment in residual NO₃^?. By contrast to the southern sites, the northern catchments lack continuous and well‐developed groundwater discharge zones, explaining less efficient N removal. Using a model based on ¹⁵NO₃^? signatures, we estimated denitrification fluxes from 2.4 to 21.7 kg N ha^?1 year^?1 for the southern sites, accounting for more than half of the observed N removal. Across the southern catchments, estimated denitrification scaled proportionally with N deposition. Together, this indicates that N removal by denitrification is an important component of the N budget of southern Chinese forests and that natural NO₃^? attenuation may increase with increasing N input, thus partly counteracting further aggravation of N contamination of surface waters in the region.     

Landscape-level nitrogen import and export in an ecosystem with complex terrain, Colorado Front Range

Knowledge of import, export, and transport of nitrogen (N) in headwater catchments is essential for understanding ecosystem function and water quality in mountain ecosystems, especially as these ecosystems experience increased anthropogenic N deposition. In this study, we link spatially explicit soil and stream data at the landscape scale to investigate import, export and transport of N in a 0.89?km² site at the alpine-subalpine ecotone in the Front Range of the Rocky Mountains, Colorado, U.S.A. For two of the major N inputs to our site, N deposition in the snowpack and N fixation, a complementary relationship was found across the study site, with greater abundance of N-fixing plants in areas with less snow and substantial snow inputs in areas with low N fixer abundance. During the initial phases of snowmelt, mixing model end members for oxygen isotopes in nitrate (NO₃ ^?) indicated that a substantial quantity of NO₃ ^? is transported downhill into the forested subalpine without being assimilated by soil microbes. After this initial pulse, much less NO₃ ^? entered the stream and most but not all of it was microbial in origin. Rising δ¹⁵N in stream NO₃ ^? indicated greater influence of fractionating processes such as denitrification later in the season. NO₃ ^? from both atmospheric and microbial sources was not exported from our site because it was consumed within the first several hundred meters of the stream; ultimately, N exports were in the form of dissolved organic nitrogen (DON) and particulate N (PN). The results of this study suggest that the highest elevation dry alpine meadows rely more heavily on N fixation as an N source and experience less of the effects of anthropogenic N deposition than mid and lower elevation areas that have more snow. Our data also suggest that mid-elevation krummholz, moist meadows, and talus slopes are exporting N as NO₃ ^? shortly after the onset of snowmelt, but that this NO₃ ^? is rapidly consumed as the stream flows through the subalpine forest. This consumption by assimilation and/or denitrification currently provides a buffer against increased inorganic N availability downstream.     

Cooperation of Three Denitrifying Bacteria in Nitrate Removal of Acidic Nitrate- and Uranium-Contaminated Groundwater

In uranium-contaminated aquifers co-contaminated with nitrate, denitrifiers play a critical role in bioremediation. Six strains of denitrifying bacteria belonging to Rhizobium, Pseudomonas, and Castellaniella were isolated from the Oak Ridge Integrated Field Research Challenge Site (OR-IFRC), where biostimulation of acidic (pH 3.5–6.5), nitrate-contaminated (up to 140 mM) groundwater occurred. Three isolates were characterized in regards to nitrite tolerance, denitrification kinetic parameters, and growth on different denitrification intermediates. Kinetic and growth experiments showed that Pseudomonas str. GN33#1 reduced NO^? ₃ most rapidly (V_max = 15.8 μmol e^?·min^?1·mg protein^?1) and had the fastest generation time (gt) on NO^? ₃ (2.6 h). Castellaniella str. 4.5A2 was the most low pH and NO^? ₂ tolerant and grew rapidly on NO^? ₂ (gt = 4.0 h). Rhizobium str. GN32#2 was also tolerant of low pH values and reduced NO^? ₂ rapidly (V_max = 10.6 μmol e^?·min^?1·mg protein^?1) but was far less NO^? ₂ tolerant than Castellaniella str. 4.5A2. Growth of and denitrification by these three strains incubated together and individually were measured in OR-IFRC groundwater at pHs 5 and 7 to determine whether they cooperate or compete during denitrification. Mixed assemblages reduced NO^? ₃ more rapidly and more completely than any individual isolate over the course of the experiment. The results described in this article demonstrate 1) that this synthetic assemblage comprised of three physiologically distinct denitrifying bacterial isolates cooperate to achieve more complete levels of denitrification and 2) the importance of pH- and nitrite-tolerant bacteria such as Castellaniella str. 4.5A2 in minimizing NO^? ₂ accumulation in high-NO^? ₃ groundwater during bioremediation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.     

Indirect N2O emissions from shallow groundwater in an agricultural catchment (Seine Basin, France)

Production and accumulation of nitrous oxide (N₂O), a major greenhouse gas, in shallow groundwater might contribute to indirect N₂O emissions to the atmosphere (e.g., when groundwater flows into a stream or a river). The Intergovernmental Panel on Climate Change (IPCC) has attributed an emission factor (EF_5g) for N₂O, associated with nitrate leaching in groundwater and drainage ditches—0.0025 (corresponding to 0.25% of N leached which is emitted as N₂O)—although this is the subject of considerable uncertainty. We investigated and quantified the transport and fate of nitrate (NO₃ ^?) and dissolved nitrous oxide from crop fields to groundwater and surface water over a 2-year period (monitoring from April 2008 to April 2010) in a transect from a plateau to the river with three piezometers. In groundwater, nitrate concentrations ranged from 1.0 to 22.7 mg NO₃ ^?–N l^?1 (from 2.8 to 37.5 mg NO₃ ^?–N l^?1 in the river) and dissolved N₂O from 0.2 to 101.0 μg N₂O–N l^?1 (and from 0.2 to 2.9 μg N₂O–N l^?1 in the river). From these measurements, we estimated an emission factor of EF_5g = 0.0026 (similar to the value currently used by the IPCC) and an annual indirect N₂O flux from groundwater of 0.035 kg N₂O–N ha^?1 year^?1, i.e., 1.8% of the previously measured direct N₂O flux from agricultural soils.     

The effects of land use change and irrigation water resource on nitrate contamination in shallow groundwater at county scale

The objective of this study was to assess the impacts of land use changes and irrigation water resource on the nitrate contamination in shallow groundwater. 394 water samples were sampled from the same irrigation wells during a period of five years (from 2002 to 2007) in Huantai County in the North China Plain. NO₃-N concentration in irrigation wells was measured. Geostatistical method combined with GIS technique was used to analyze the spatio-temporal distribution of groundwater NO₃-N concentrations in Huantai County. Land use type and irrigation water resource were combined with the variation of NO₃-N concentrations by statistical approach to investigate the relationship between them. The distribution map showed that the percentages of area increased by 13.06%, 14.37%, 12.23% and 3.85% for that had nitrate concentrations of 10–15, 15–20, 20–30 mg L^?1 and greater than 30 mg L^?1 for shallow groundwater, respectively, while decreased by 28.87% and 14.63% for 0–5 and 5–10 mg L^?1. In the well-irrigated field, the NO₃-N concentrations in shallow groundwater had increased for vegetables, wheat–vegetables and wheat–maize rotations. In contrast, fast-growing tree system could act as a buffer to retain shallow groundwater nitrate content which resulted in reduced NO₃-N concentrations. Under the same land use condition, irrigation with sewage, or well and sewage by turns would both enormously add nitrate to groundwater.     

Multiyear dual nitrate isotope signatures suggest that N‐saturated subtropical forested catchments can act as robust N sinks

In forests of the humid subtropics of China, chronically elevated nitrogen (N) deposition, predominantly as ammonium (NH₄⁺), causes significant nitrate (NO₃^?) leaching from well‐drained acid forest soils on hill slopes (HS), whereas significant retention of NO₃^? occurs in near‐stream environments (groundwater discharge zones, GDZ). To aid our understanding of N transformations on the catchment level, we studied spatial and temporal variabilities of concentration and natural abundance (δ¹⁵N and δ¹⁸O) of nitrate (NO₃^?) in soil pore water along a hydrological continuum in the N‐saturated Tieshanping (TSP) catchment, southwest China. Our data show that effective removal of atmogenic NH₄⁺ and production of NO₃^? in soils on HS were associated with a significant decrease in δ¹⁵N‐NO₃^?, suggesting efficient nitrification despite low soil pH. The concentration of NO₃^? declined sharply along the hydrological flow path in the GDZ. This decline was associated with a significant increase in both δ¹⁵N and δ¹⁸O of residual NO₃^?, providing evidence that the GDZ acts as an N sink due to denitrification. The observed apparent ¹⁵N enrichment factor (ε) of NO₃^? of about ?5‰ in the GDZ is similar to values previously reported for efficient denitrification in riparian and groundwater systems. Episode studies in the summers of 2009, 2010 and 2013 revealed that the spatial pattern of δ¹⁵N and δ¹⁸O‐NO₃^? in soil water was remarkably similar from year to year. The importance of denitrification as a major N sink was also seen at the catchment scale, as largest δ¹⁵N‐NO₃^? values in stream water were observed at lowest discharge, confirming the importance of the relatively small GDZ for N removal under base flow conditions. This study, explicitly recognizing hydrologically connected landscape elements, reveals an overlooked but robust N sink in N‐saturated, subtropical forests with important implications for regional N budgets.     

An assessment of karstic submarine groundwater and associated nutrient discharge to a Mediterranean coastal area (Balearic Islands, Spain) using radium isotopes

Short and long-lived radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra, ²²⁸Ra) were used to quantify submarine groundwater discharge (SGD) and its associated input of inorganic nitrogen (NO₃ ^?), phosphorus (PO₄ ^3?) and silica (SiO₄ ^4?) into the karstic Alcalfar Cove, a coastal region of Minorca Island (Western Mediterranean Sea). Cove water, seawater and groundwater (wells and karstic springs) samples were collected in May 2005 and February 2006 for radium isotopes and in November 2007 for dissolved inorganic nutrients. Salinity profiles in cove waters suggested that SGD is derived from shallow brackish springs that formed a buoyant surface fresh layer of only 0.3 m depth. A binary mixing model that considers the distribution of radium activities was used to determine the cove water composition. Results showed that cove waters contained 20% brackish groundwater; of which 6% was recirculated seawater and 14% corresponded to freshwater discharge. Using a radium-derived residence time of 2.4 days, a total SGD flux of 150,000 m³ year^?1 was calculated, consisting of 45,000 m³ year^?1 recirculated seawater and 105,000 m³ year^?1 fresh groundwater. Fresh SGD fluxes of NO₃ ^?, SiO₄ ^4? and PO₄ ^3? were estimated to be on the order of 18,000, 1,140 and 4 μmol m^?2 day^?1, respectively, and presumably sustain the high phytoplankton biomass observed in the cove during summer. The total amount of NO₃ ^? and SiO₄ ^4? supplied by SGD was higher than the measured inventories in the cove, while the reverse was true for PO₄ ^3?. These discrepancies are likely due to non-conservative biogeochemical processes that occur within the subterranean estuary and Alcalfar Cove waters.     

Assessment of shallow groundwater quality and its suitability for drinking purpose near the Béni-Mellal wastewater treatment lagoon (Morocco)

Abstract

The present study aimed to evaluate the suitability for drinking purpose of shallow groundwater near the Béni-Mellal wastewater treatment lagoon based on various physicochemical, heavy metals, and bacteriological parameter analyses. The physicochemical results revealed that some of the samples do not comply with the Moroccan and/or WHO standards for drinking water. Parameters including turbidity, TH, Na⁺, Li⁺, Ba²⁺, Ca²⁺ (～47.1% of samples), Cd (～52.9% of samples), Fe (～82.4% of samples), Pb (～58.8% of samples), T. coliforms, and E. coli exceeded the drinking limits. The statistical analyses revealed that the shallow groundwater chemistry is mainly controlled by geogenic and anthropogenic sources. For quality assessment, using the Moroccan groundwater assessment grid, the values of EC and Cl^–, NO₃^–, NH₄⁺, oxidability, and E. coli, fixed as pollution indicators, showed that most of the wells showed medium-to-poor quality, 14% of them have a very poor water quality, and 20% of them belong to the bad water quality. According to geometric and arithmetic DWQI values, the groundwater quality was frequently fair to good, needing treatment or at least disinfection before public consumption. A sensitivity analysis results indicated that Fe, Cd, Cr, Pb, and E. coli have an important impact on the DWQI computing.     

Further Analysis of Anammox Bacterial Community Structures Along an Anthropogenic Nitrogen-Input Gradient from the Riparian Sediments of the Pearl River Delta to the Deep-Ocean Sediments of the South China Sea

The community structures of anammox bacteria in sediments along an anthropogenic inorganic nitrogen input gradient were further delineated with the newly available information incorporated. Anammox bacterial 16S rRNA gene-amplified sequences retrieved from riparian sediments of the Pearl River, Mai Po coastal wetland, and the South China Sea (SCS) sediments were compiled, compared and analyzed. Results indicated that the community structures of anammox bacteria varied from the upstream of the Pearl River to deep-ocean sediment of the SCS along the anthropogenic input grandient. Mai Po wetland had the most diverse anammox bacteria, followed by the shallow SCS, deep SCS and the Pearl River. Genera of the anammox bacteria Kuenenia and Brocadia showed higher proportion in the riparian sediments of the Pearl River, while those of Kuenenia and Scalindua dominated the Mai Po coastal wetland. The Scalindua subclusters showed apparent segregation in coastal wetland (S. zhenghei-III and S. wagneri), shallow SCS (S. zhenghei-I and S3) and deep SCS (S. zhenghei-I, S2 and S. arabica). Pearson correlation analysis indicated nitrogen species [NH₄⁺ and ∑(NO₂^?+NO₃^? )] negatively correlated with the diversity indices of anammox bacteria. Canonical correspondence analysis (CCA) showed that salinity, inorganic nitrogen [NH₄+, ∑(NO₂^?+NO₃^?)], and ratio of NH₄⁺/∑(NO₂^? +NO₃^?) significantly affected the bacterial community compositions. Results collectively support that the community composition of anammox bacteria can serve as a bio-indicator to the anthropogenic terrestrial N input or pollution.     

Major Ion Chemistry of Soil Solution of Mountainous Soils,Alvand, Hamedan,Western Iran

Soil solution chemistry reflects the most dynamic processes occurring in soils and is responsible for their current status. This study was undertaken to determine the soil solution status in 25 mountainous soils. The major cations in the studied soil solutions are in the decreasing order of Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The anions are also arranged in decreasing order as HCO^? ₃ > Cl^? > NO^? ₃ > SO ^2? ₄ . Concentrations of NO^? ₃ , P, and K⁺ in soil solutions were in the range of 12–364 mg l^?1, 1.75–34.8 mg l^?1, and 0.78– 198 mg l^?1, respectively. Results suggest that the concentration of P in the soil solutions could be primarily controlled by of the solubility of octacalcium phosphate and ß-tricalcium phosphate. In general, the greater the dissolved P concentration in the soil solution, the closer the solution was to equilibrium with respect to the more soluble Ca²⁺ phosphate minerals. Surface soil accumulations of P, NO^? ₃ , and K⁺ have occurred in these soils to such an extent that loss of these nutrients in surface runoff and the high risk for nutrient transfer into groundwater in concentrations exceeding the groundwater quality standard has become a priority management concern.     

Photosynthetic energy supply for NO3− assimilation in Scenedesmus

NO₃^?-dependent O₂ in synchronous Scenedesmus obtusiusculus Chod. in the absence of CO₂ is stoichiometric with NH₄⁺ excretion, indicating a close coupling of NO₃^? reduction to non-cyclic electron flow. Also in the presence of CO₂, NO₃^? stimulates O₂ evolution as manifested by an increase in the O₂/CO₂ ratio from 0.96 to 1.11. This quotient was increased to 1.36 by addition of NO₂^?, without competitive interaction with CO₂ fixation, indicating that the capacity for non-cyclic electron transport at saturating light is non-limiting for simultaneous reduction of NO₃^? and CO₂ at high rates. During incubation with NO₃^?+ CO₂, no NH₄⁺ is released to the outer medium, whereas during incubation with NO₂^?+ CO₂, excess NH₄⁺ is formed and excreted. NO₃^? uptake is stimulated by CO₂, and this stimulation is also significant when the cellular energy metabolism is restricted by moderate concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, whereas NO₃^? uptake in the absence of CO₂ is severely inhibited by the uncoupler. Also under energy-restricted conditions NO₃^? uptake is not competitive with CO₂ fixation. Antimycin A is inhibitory for NO₃^? uptake in the absence of CO₂, and there is no enhancement of NO₃^? uptake by CO₂ in the presence of antimycin A. It is assumed that the energy demand for NO₃^? uptake is met by energy fixed as triosephosphates in the Calvin cycle. Antimycin A possibly affects the transfer of reduced triose phosphates from the chloroplast to the cytoplasm. Active carbon metabolism also seems to exert a control effect on NO₃^? assimilation, inducing complete incorporation of all NO₃^? taken up into amino acids. This control effect is not functional when NO₂^? is the nitrogen source. Active carbon metabolism thus seems to be essential both for provision of energy for NO₃^? uptake and for regulation of the process.     

Simultaneous Removal of Mn(II) and Nitrate by the Manganese-Oxidizing Bacterium Acinetobacter sp. SZ28 in Anaerobic Conditions

A novel bacterium, strain SZ28, identified as Acinetobacter sp., showed anaerobic denitrification ability using Mn(II) as the electron donor. Nitrate-nitrogen concentration decreased from nearly 16.52–mg L^?1 to 4.4–mg L^?1, without accumulation of nitrite as an intermediate, with a maximum of 0.063–mg NO₃^?-N L^?1 h^?1, reaching a peak of 0.085–mg NO₃^?-N L^?1 h^?1 in sodium acetate. The nitrate removal rate reached 0.067–mg NO₃^?-N L^?1 h^?1, 0.059–mg NO₃^?-N L^?1 h^?1, and 0.078 mg NO₃^?-N L^?1 h^?1 using Mn(II), S(II), and Fe(II) as electron donors, respectively. The optimum pH was 6.0, with a removal rate of 0.063–mg NO₃^?-N L^?1 h^?1     

Taking the pulse of snowmelt: in situ sensors reveal seasonal, event and diurnal patterns of nitrate and dissolved organic matter variability in an upland forest stream

Highly resolved time series data are useful to accurately identify the timing, rate, and magnitude of solute transport in streams during hydrologically dynamic periods such as snowmelt. We used in situ optical sensors for nitrate (NO₃ ^?) and chromophoric dissolved organic matter fluorescence (FDOM) to measure surface water concentrations at 30?min intervals over the snowmelt period (March 21–May 13, 2009) at a 40.5 hectare forested watershed at Sleepers River, Vermont. We also collected discrete samples for laboratory absorbance and fluorescence as well as δ¹⁸O–NO₃ ^? isotopes to help interpret the drivers of variable NO₃ ^? and FDOM concentrations measured in situ. In situ data revealed seasonal, event and diurnal patterns associated with hydrological and biogeochemical processes regulating stream NO₃ ^? and FDOM concentrations. An observed decrease in NO₃ ^? concentrations after peak snowmelt runoff and muted response to spring rainfall was consistent with the flushing of a limited supply of NO₃ ^? (mainly from nitrification) from source areas in surficial soils. Stream FDOM concentrations were coupled with flow throughout the study period, suggesting a strong hydrologic control on DOM concentrations in the stream. However, higher FDOM concentrations per unit streamflow after snowmelt likely reflected a greater hydraulic connectivity of the stream to leachable DOM sources in upland soils. We also observed diurnal NO₃ ^? variability of 1–2?μmol?l^?1 after snowpack ablation, presumably due to in-stream uptake prior to leafout. A comparison of NO₃ ^? and dissolved organic carbon yields (DOC, measured by FDOM proxy) calculated from weekly discrete samples and in situ data sub-sampled daily resulted in small to moderate differences over the entire study period (?4 to 1% for NO₃ ^? and ?3 to ?14% for DOC), but resulted in much larger differences for daily yields (?66 to +27% for NO₃ ^? and ?88 to +47% for DOC, respectively). Despite challenges inherent in in situ sensor deployments in harsh seasonal conditions, these data provide important insights into processes controlling NO₃ ^? and FDOM in streams, and will be critical for evaluating the effects of climate change on snowmelt delivery to downstream ecosystems.     

Impact of seasonal changes in stream metabolism on nitrate concentrations in an urban stream

Nitrate (NO₃ ^?) dynamics in urban streams differ from many natural streams due to stormwater runoff, sewage inputs, decreased groundwater discharge, often limited hyporheic exchange, increased primary productivity, and limited carbon input. We investigated NO₃ ^? dynamics in a first-order urban stream in Syracuse, NY, which has urbanized headwaters and a geomorphologically natural downstream section. Twice-monthly water sampling, NO₃ ^? injection tests, NO₃ ^? isotopic analysis, filamentous algae mat density, and riparian shading were used to identify processes regulating NO₃ ^? dynamics in the stream over a 12-month period. The urban headwater reach had low NO₃ ^? (0.006–0.2 mg N/L) in the spring through fall, with a minimum uptake length of 900 m, no canopy cover, and high algae mat density. The downstream natural reach (100% canopy cover during the summer and low algae mat density) had nitrate concentrations between 0.6 and 1.2 mg N/L from winter to summer, which decreased during autumn leaf-off. In the urban reach, autotrophic uptake by filamentous green algae is a major NO₃ ^? sink in summer. In the natural reach, the addition of organic matter to the stream at leaf-off led to a decrease in NO₃ ^? concentration followed by an increase in NO₃ ^? concentration in winter as gross primary productivity decreased. This study shows that the balance between autotrophy and heterotrophy in urban streams is variable and depends on an interplay of drivers such as temperature, light, and carbon inputs that are mediated by the riparian ecosystem.     

Biomarker assessment of organic matter sources and degradation in Canadian High Arctic littoral sediments

This paper presents an uncomplicated approach to improve estimates of groundwater nutrient load to a marine embayment. A two-dimensional chemical profile of shallow groundwater was analysed in a sandy beach in three seasons (early summer, late summer and mid winter) and an adjusted estimate of groundwater nutrient discharge was derived that accounts for a complex biogeochemical environment and non-conservative behaviour of nutrients in the pre-discharge beach groundwater. The study was conducted at Cockburn Sound, Western Australia, where there has been significant groundwater contamination and associated marine ecological degradation. Losses in nitrogen and increases in phosphorus were observed along the discharge pathway beyond that expected from mixing with marine water, and the changes were attributed to chemically and biologically mediated reactions. A slow groundwater velocity (0.14–0.18 m day^?1), high organic carbon (TOC = 0.35–4.9 mmol l^?1, DOC = 0.28–4.6 mmol l^?1) and low to sub-oxic conditions (DO = 0.4–24% saturation) were deemed suitable for chemically and biologically mediated reactions to occur and subsequently alter regional estimates of groundwater nutrient concentration. Accounting for this environment, groundwater loads were calculated that were 1–2 orders of magnitude less than previous regional-based estimates: 0.4–13 kg NO _x ^?  day^?1, 0.2–24 kg NH₄ ⁺ day^?1 and 0.004–0.8 kg FRP day^?1. This paper applies knowledge of recent research and presents scope to marine managers or modellers to account for groundwater inputs to the marine environment.     

Bacterial Perchlorate Reduction in Simulated Reverse Osmosis Rejectate

Reverse osmosis (RO) is capable of removing perchlorate (ClO₄ ^?) from contaminated groundwater and producing potable effluent; however, RO does not destroy ClO₄ ^?, but collects it in a concentrated waste stream (rejectate) that must be treated or disposed of appropriately. A packed bed bioreactor, inoculated with the pure culture perclace, was tested for its ability to remove ClO₄ ^? from a simulated RO rejectate. Perchlorate concentrations were lowered from 5 mg/L to <0.004 mg/L with a residence time of 0.8 h. In addition, this system removed 98% of ClO₄ ^? from a twice-concentrated rejectate with an influent ClO₄ ^? concentration of 8 mg/L and a residence time of 2.0 h. In both experiments, nitrate (NO₃ ^?) was removed simultaneously with ClO₄ ^? from an initial concentration as high as 900 mg/L NO₃ to below 4 mg/L. Despite the efficiency of ClO₄ ^? removal, the system suffered from clogging due to the high total dissolved solids (TDS) of the twice-concentrated rejectate.     

Nitrate retention in a sand plains stream and the importance of groundwater discharge

We measured net nitrate retention by mass balance in a 700-m upwelling reach of a third-order sand plains stream, Emmons Creek, from January 2007 to November 2008. Surface water and groundwater fluxes of nitrate were determined from continuous records of discharge and from nitrate concentrations based on weekly and biweekly sampling at three surface water stations and in 23 in-stream piezometers, respectively. Surface water nitrate concentration in Emmons Creek was relatively high (mean of 2.25 mg NO₃?CN l^?1) and exhibited strong seasonal variation. Net nitrate retention averaged 429 mg NO₃?CN m^?2 d^?1 and about 2% of nitrate inputs to the reach. Net nitrate retention was highest during the spring and autumn when groundwater discharge was elevated. Groundwater discharge explained 57?C65% of the variation in areal net nitrate retention. Specific discharge and groundwater nitrate concentration varied spatially. Weighting groundwater solute concentrations by specific discharge improved the water balance and resulted in higher estimates of nitrate retention. Our results suggest that groundwater inputs of nitrate can drive nitrate retention in streams with high groundwater discharge.     

Seasonal and geomorphic controls on N and P removal in riparian zones of the US Midwest

Riparian zones are an important strategy to mitigate N and P export to streams. However, their efficiency with respect to nitrate (NO₃ ^?), ammonium (NH₄ ⁺), or soluble reactive phosphorus (SRP) in groundwater remains uncertain in the US Midwest. This study investigates water table fluctuations and NO₃ ^?, NH₄ ⁺, and SRP concentration dynamics in two riparian zone types (outwash vs. glacial till) common in the upper US Midwest. During low water table periods, NO₃ ^? removal was 93 % at WR (outwash site), and 75 % at LWD (glacial till site); but during high water table periods, NO₃ ^? removal efficiencies dropped to 50 % at WR, and 14 % at LWD. Median seasonal mass fluxes of NO₃ ^? removed at WR (9.4–21.7 mg N day^?1 m^?1 of stream length) and LWD (0.4–1.9 mg N day^?1 m^?1) were small compared to other riparian zones in glaciated landscapes. The WR site was a small SRP sink (0.114 and 0.118 mg day^?1 m^?1 during the dry period and wet period, respectively), while LWD acted as a small SRP source to the stream (0.004 mg day^?1 m^?1 during the dry period; 0.075 mg day^?1 m^?1 during the wet period). Both LWD and WR acted as sources of NH₄ ⁺ to the stream with mass fluxes ranging from 0.17 to 7.75 mg N day^?1 m^?1. Although riparian zones in the US Midwest provide many ecosystem services, results suggest they are unlikely to efficiently mitigate N and P pollution in subsurface flow.