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Estimating the attenuation of nutrients (e.g., nitrogen, phosphorus) in groundwater from onsite wastewater treatment systems (OWTS) is difficult due to the costs and uncertainty associated with determining site-specific degradation rates, groundwater flow paths, and aquifer hydraulic properties. Some available methods allow users to specify natural degradation rates for nutrients from OWTS but provide inadequate guidance on how to determine those rates. Other methods use a mechanistic approach with numerous variables and equations that are known to affect nutrient attenuation but are necessarily complex and difficult to use for assessing hundreds or thousands of septic systems, as is often needed for regulatory applications. A spreadsheet analysis, the Method for Estimating Attenuation of Nutrients from Septic Systems (MEANSS), has been developed within the Montana Department of Environmental Quality to provide a relatively simple method of estimation with minimal data requirements. MEANSS is an empirical method designed to estimate the load of nutrients that will migrate to groundwater and surface water from OWTS sources. MEANSS provided comparable estimates of nitrogen and ortho-phosphorus attenuation below and downgradient of OWTS when evaluated against several field studies, a GIS-based nitrogen loading model, a mechanistic model, and a watershed model. Keywords: wastewater, nitrogen attenuation, phosphorus attenuation, septic system, nutrients, Introduction In 1990, approximately 25% of the U.S. population used onsite wastewater systems (commonly known as septic systems) to dispose of household wastewater; 1990 was the last year this information [...]

Policy measures resulted in reductions in acidic emission of sulfur and nitrogen in North America. Here, we conducted trend analyses on a 37-year database for atmospheric depositions and lake (n = 78) chemistry in the provinces of Nova Scotia, New Brunswick, and Newfoundland and Labrador, in Canada. Sulfate, and particularly nitrate deposition, began to decrease strongly around the year 2000, resulting in strong pH increases in precipitation. Recovery was observed in most lakes with significant increases in pH and Gran alkalinity (AlcG). A piecewise regression approach detected coherent breaks and overlapping confidence intervals in the break years for precipitation pH and lake AlcG (to a lesser extent for lake pH), suggesting a rapid lake response to the sudden changes in acidic inputs. However, an increase in organic acid after 2000 decreases the rate of acid neutralizing capacity recovery nearly by half in about a third of the studied lakes. Despite the positive pH and AlcG trends, a significant proportion of lakes still have pH and calcium values below the recommended thresholds for aquatic life. Key words: atmospheric deposition, lake recovery, catchment, long-term trend, Atlantic Canada Differentes politiques ont mene a des baisses des emissions acides de soufre et d'azote en Amerique du Nord. Nous avons realise des analyses de tendances en utilisant une base de donnees de 37 ans sur la chimie des depots atmospheriques et des lacs (n = 78) dans les provinces de la Nouvelle-Ecosse, du Nouveau-Brunswick et de Terre-Neuve-et-Labrador (Canada). Le depot de sulfates et, particulierement, de nitrates a commence a diminuer fortement autour de l'annee 2000, entrainant de fortes hausses du pH dans les precipitations. Un retablissement a ete observe dans la plupart des lacs presentant des hausses significatives du pH et de l'alcalinite de Gran (AlcG). Une approche de regression par morceaux a fait ressortir des changements brusques coherents et le chevauchement d'intervalles de confiance dans les annees de changements pour le pH des precipitations et l'AlcG des lacs (et pour le pH des lacs dans une moindre mesure), ce qui indiquerait une reponse rapide des lacs a des variations soudaines des apports acides. Une hausse des acides organiques apres l'annee 2000 a toutefois entraine une baisse de presque 50 % du taux de retablissement du capacite de neutralisation de l'acide dans environ un tiers des lacs etudies. Malgre les tendances positives du pH et de l'AlcG, une proportion significative des lacs presente toujours un pH et des teneurs en calcium inferieurs aux seuils recommandes pour la vie aquatique. Mots-cles : depot atmospherique, retablissement des lacs, bassin versant, tendance a long terme, Canada atlantique, 1. Introduction Surface water acidification resulting from anthropogenic deposition has been reported in Europe and North America as early as the 1950s (Gorham 1957; Gorham and Gordon 1960). Due to [...]

Delays between soil sampling and processing for analysis are common in both research and agronomy, but the effects of storage conditions on measurements of plant-available nitrogen (N) are rarely considered. With increasing recognition of organic N pools in soils, such as amino acids and peptides, it is necessary to determine how sample handling impacts the outcomes of soil N quantification. In this study, we used in situ microdialysis to approximate plant availability of amino acids, ammonium and nitrate, then compared to both potassium chloride (KCl) extract and microdialysis samples taken from excavated soil samples when in the field, after 24 h refrigerated storage, and after storage for I month, either refrigerated or air-dried. Nitrate levels measured with microdialysis and KCl extracts increased immediately after soil sampling and continued to accumulate in the next day and I month stored samples. Amino acid and ammonium measurements remained more constant; however, microdialysis showed a decline in amino acid-N between in situ and next day samples. The proportional representation of N pools in the in-field extracts was most similar to in situ microdialysis. Soil samples should be processed for N analysis as close to sampling as possible, and the storage duration and conditions reported. The influence of storage must be considered in interpreting soil test results. Keywords: air-dry, amino acids, ammonium, in situ soil sampling, microdialysis, nitrogen flux, organic nitrogen, refrigerated storage, soil testing., Introduction Nitrogen (N) in soils is a highly dynamic nutrient, rapidly converting between different forms and moving through the soil profile. Nitrogen pool dynamics are driven by the chemical, physical [...]

The importance of oxalic acid for tree seedling growth and the competition for inorganic nitrogen (N) by plants and soil microorganisms under warming was investigated using [sup.15]N tracer techniques in Picea brachytyla (Franch.) E. Pritz. Results showed that warming combined with oxalic acid application induced growth enhancements in seedlings primarily through increases in fine root length and fine root surface area. Moreover, soil N[H.sub.4.sup.+], N[O.sub.3. sup.-], P[O.sub.4.sup.3-], N mineralization, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were significantly higher or tended to be higher with oxalic acid application. However, warming with oxalic acid application altered the partitioning of N between plants and soil microorganisms by increasing microbial [sup.15]N recovery to a lesser extent than it increased plant [sup.15]N recovery. While plants showed no specific preferences between N forms under normal conditions or warming alone, under warming and oxalic acid, plants showed a preference for [sup.15]N[O.sub.3] . Microorganisms showed a stronger preference for [sup.15]N[H.sub.4] especially under warming and oxalic acid treatments. These findings suggest that plasticity in resource use could be an important mechanism in alleviating competition for soil N between plants and microbes under warming and oxalic acid addition. Key words: ammonium, plant preference, N partitioning, nitrate, microbial activity., Resume : L'importance de l'acide oxalique pour la croissance des semis d'arbre et la competition pour l'azote (N) inorganique entre les plantes et les microorganismes du sol dans le contexte [...]

Growing populations and agricultural intensification have led to raised riverine nitrogen (N) loads, widespread oxygen depletion in coastal zones (coastal hypoxia).sup.1 and increases in the incidence of algal blooms.Although recent work has suggested that individual wetlands have the potential to improve water quality.sup.2-9, little is known about the current magnitude of wetland N removal at the landscape scale. Here we use National Wetland Inventory data and 5-kilometre grid-scale estimates of N inputs and outputs to demonstrate that current N removal by US wetlands (about 860 [plus or minus] 160 kilotonnes of nitrogen per year) is limited by a spatial disconnect between high-density wetland areas and N hotspots. Our model simulations suggest that a spatially targeted increase in US wetland area by 10 per cent (5.1 million hectares) would double wetland N removal. This increase would provide an estimated 54 per cent decrease in N loading in nitrate-affected watersheds such as the Mississippi River Basin. The costs of this increase in area would be approximately 3.3 billion US dollars annually across the USA--nearly twice the cost of wetland restoration on non-agricultural, undeveloped land--but would provide approximately 40 times more N removal. These results suggest that water quality improvements, as well as other types of ecosystem services such as flood control and fish and wildlife habitat, should be considered when creating policy regarding wetland restoration and protection. Analysis of US continental wetland inventory data combined with model simulations indicate that a spatially targeted 10% increase in wetland area could double wetland nitrogen removal., Author(s): F. Y. Cheng [sup.1] , K. J. Van Meter [sup.2] , D. K. Byrnes [sup.1] , N. B. Basu [sup.1] [sup.3] [sup.4] Author Affiliations: (1) Department of Civil and [...]

Sea-level rise and saline water intrusion have caused a shortage of fresh water and affected agricultural areas globally. Besides inundation, the salinity could alter soil nitrogen and carbon cycling in coastal soils. To examine the effect of salinity, an incubation experiment was used to investigate soil nitrogen and carbon cycling from an acid sulfate soil and an alluvial soil with and without additional nitrogen and carbon sources. Four levels of saline solution of 0.03, 10, 16 and 21 dS [m.sup.-1] were used to submerge acid sulfate and alluvial soil samples in a 125-mL jar. The experimental jars were incubated in the dark at 25[degrees]C. Gas samples were collected over 4 weeks and analysed for nitrous oxide ([N.sub.2]O), carbon dioxide (C[O.sub.2]) and methane (C[H.sub.4]). The results showed that salinity significantly decreased [N.sub.2]O emissions from the acid sulfate soil but did not affect emissions from the alluvial soil. Addition of glucose and nitrate enhanced [N.sub.2]O production in both salt-affected soils. Emissions of C[O.sub.2] were not different among the salinity treatments, whereas available carbon and nitrate promoted soil respiration. Changes in C[H.sub.4] fluxes over the 4-week incubation were the same for both soils, and substrate addition did not affect emissions in either soil. The findings indicate that salinity has altered carbon and nitrogen cycles in the acid sulfate soil, and future fertiliser and crop management will need to account for the changed nutrient cycling caused by saline water intrusion and climate change. Additional keywords: denitrification, electron donor, methanogenesis, osmotic potential, submergence., Introduction Sea-level rise caused by global climate change is an issue for many coastal and agricultural areas worldwide. Church et al. (2013) indicated that sea-level rise could range from 0.52 [...]

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Nitrate (N[O.sub.3.sup.-]-N) lost through leaching contaminates the groundwater in many agricultural areas. Understanding the relationship between leaching and climate is an important consideration for developing nutrient management strategies. Soil water was sampled for 11 yr under plots with summer vegetables grown in the Willamette Valley, Oregon, with and without winter cover crops. A randomized complete-block, split-plot design was employed with three N fertilizer application rates (N0 for no fertilizer, N1 for an intermediate input, and N2 for a full, recommended N input). Fall-seeded cover crops included cereal rye (Secale cereale L. var. Wheeler), triticale (Triticosecale X L. vat. Celia), and a common vetch (Vicia sativa)/triticale mix. Twenty-six, 0.26-[m.sup.2] passive capillary samplers (PCAPS), which are capable of sampling in unsaturated and saturated conditions, allowed for the uninterrupted measurement of soil water and solute flux at a depth of 1.2 m. Eleven-year flow-weighted average N[O.sub.3.sup.-]-N concentrations (mg [L.sup.-1]) for fallow (F) and cover cropped (CC) treatments were 16.7 and 11.9 for the N2 fertilizer treatment, 9.9 and 6.4 for the N1 fertilizer treatment, and 7.0 and 4.1 for the NO treatment. Annual average N[O.sub.3.sup.-]-N mass losses (kg [ha.sup.-1]) for F and CC treatments were 76 and 46 for the N2 fertilizer treatment, 40 and 30 for the N1 fertilizer treatment, and 29 and 17 for the NO treatment. Fully fertilized CC and F treatments consistently exceeded the EPA's 10 mg [L.sup.-1] drinking water standard set for N[O.sub.3.sup.-]-N. The timing and quantity of yearly rainfall, particularly from October to December, was a dominant contributor to the fluctuations of N[O.sub.3.sup.-]-N concentrations and mass losses. Soil N[O.sub.3.sup.-]-N and bromide soil concentration profiles suggested that high leaching losses in leaching Year 2001 were related to the previous drier-than-average winter and the early arrival of rainfall following the vegetable harvest. The long-term water quality benefits observed under the CC treatments suggest that an increase in organically bound N is occurring. doi:10.2136/sssaj2008.0178

Several marine phytoplankton species, primarily diatoms, were examined for the accumulation of iodide (10 species) and iodate (9 species) using radioactive iodine-125 in f/2 artificial seawater, a nitrate-enriched medium. Iodide accumulation (net uptake) rates were variable, and diatoms exhibited the highest rates. Emiliania huxleyi and Synechococcus sp. did not accumulate iodide. Accumulation rates ranged from 0 to 1.7 fmol [cell.sup.-1] [d.sup.-1]. The diatom Porosira glacialis accumulated the greatest amount of iodide and was used to determine efflux rates of iodide. Iodide efflux was characterized by two distinct phases of iodide release: an initial rapid release rate of 10 amol [cell.sup.-1] [min.sup.-1] from the free space and a subsequent cellular release rate of 0.13 amol [cell.sup.-1] [min.sup.-1], which corresponds to a daily cellular release rate of 0.19 fmol [cell.sup.-1] [d.sup.-1]. Accumulation of iodate ranged from 0 to 19 amol [cell.sup.-1] [d.sup.-1], with P. glacialis displaying the highest rate. Emiliania, Synechococcus, and Chaetoceros did not show significant iodate accumulation. Iodide is the preferred chemical species of iodine for uptake under nitrate-replete conditions: iodide accumulation rates ranged from 3 to 90 times larger than those for iodate for the species studied. If the iodate accumulated is tightly coupled to its reduction to iodide, the accumulation rates suggest that phytoplankton-mediated iodate reduction is not environmentally significant. If diatoms can reduce iodate to iodide, their overall contribution to surface-water iodide, while living, would be further reduced because of their ability to reassimilate released iodide.

Nitrate losses through leaching were studied in a crop field in the central Sichuan Basin, southwestern China, during 2003 to 2006. Nitrate accumulations and losses via leaching were measured using two methods: a simulation with sampled soil profiles and field monitoring in situ at a 7% slope. The results showed that [NO.sub.3] was accumulated in the dry season and leached in the rainy season. No spatial dependence of soil [NO.sub.3] distribution could be distinguished along the hillslope due to complex water flow. The soil interflow was the major driver of [NO.sub.3] leaching losses from the experimental plots. The average annual discharge of the interflows was 148 mm, accounting for 63% of total runoff in the rainy season in 2003 to 2006. The interflow water contained high [NO.sub.3]-N concentrations. The highest [NO.sub.3]-N concentration and loss flux were detected in storm runoff after a long drought in 2006. The [NO.sub.3]-N leaching through interflow showed clear annual and seasonal patterns, and largely occurred in the stages from stamen elongation to maturity of maize (Zea mays L.) with a flux of 2.2 g [m.sup.-2], about 69% of the total annual loss flux. Annual estimated losses of [NO.sub.3]-N through interflow ranged from 20 to 53, with an average of 36 kg [ha.sup.-1] [yr.sup.-1]. This study indicates that croplands on hillslopes with regosols are vulnerable to [NO.sub.3] leaching. The interflow discharge monitoring method together with effluent [NO.sub.3] content analysis used in this study proved to be useful and effective for quantifying [NO.sub.3] leaching losses at the field scale in hillslope areas. Abbreviations: TGR, Three Gorges Reservoir.

Agricultural ecosystems are the primary source of nitrate ([NO.sub.3.sup.-]) pollution in many watersheds. We used a laboratory [.sup.15]N tracer study with live and gamma irradiated soils to examine the role of land management in abiotic retention of [NO.sub.3.sup.-] in three agroecosytems and a forest soil. Nitrogen retention was defined as the quantity of [.sup.15]N that remained in soil following salt extractions. Land management only affected N retention after 15 min of incubation, with forested soils retaining ~4% of the added [.sup.15]N and agricultural soils retaining < 1%. In all four ecosystems, abiotic retention (retention in gamma irradiated soils) occurred after 1 d (15-20% of the [.sup.15]N) and 21 d (up to 60% of [.sup.15]N) of incubation. After 1 and 21 d, [.sup.15]N retention in irradiated soils was larger than in live soils, revealing a methodological artifact associated with gamma irradiation. While our results show that abiotic reactions can occur in the laboratory, it is unlikely that such high rates of abiotic [.sup.15]N retention occur in the field. Gamma irradiation appears to impart methodological artifacts that limit its use in partitioning microbial and abiotic N retention in soils. Abbreviations: l-d, one day incubations; 21-d, 21 day incubations; 15-min, 15 minute incubations; conventional, conventionally managed agroecosystem according to Penn State recommendations; DON, dissolved organic nitrogen; FST, Farming Systems Trial; legume, organically managed agroecosystem with leguminous cover crops for N source; manure, organically managed system with composted dairy manure for N source; TSP, Tryptic Soy Broth.

Septic systems can present a risk to human health by releasing highly soluble nitrate--nitrogen into the groundwater. A research and demonstration study undertaken in Black River Falls, Wisconsin, evaluated several promising biofilter technologies for on-site nitrogen removal. Duplicate recirculating sand filter-upflow anaerobic systems with a design hydraulic loading rate of 954 L/day (250 gal/day) were used to treat septic tank effluent from a correctional institution and produced a treated wastewater with a total nitrogen concentration of 15.2 mg/L for System 1 and 18.2 mg/L for System 2, or 72.0 and 63.0% nitrogen removal, respectively. The differences between the two systems appear to have been the result of process configuration changes made over the duration of the study. This paper evaluates the nitrogen removal performance of the recirculating sand filter-upflow anaerobic systems and the effect of operational and environmental factors, including the recirculation ratio, BO[D.sub.5] / N[O.sub.3], and temperature. Nitrogen removal was limited by the recirculation ratio with the maximum total nitrogen removal of 70.1% when the recirculation ratio=3. Improved performance was also noted for temperatures [greater than or equal to] 20 [degrees]C and BO[D.sub.5] / N[O.sup.-.sub.3] [greater than or equal to 8. Low temperatures adversely affected nitrification and low BO[D.sub. 5] / N[O.sup.-.sub.3] adversely affected denitrification. The relationships among nitrogen removal, recirculation ratio, BO[D.sub.5]/ N[O.sup.-.sub.3], and temperature are also discussed. DOI: 10.1061/(ASCE)0733-9372(2007)133:5(464) CE Database subject headings: Sand; Recirculation; Anaerobic treatment; Denitrification; Nitrification; Temperature effects; Filtration.

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-atmosphere simulation model, RyeGro, was developed to quantify the influence of a winter cereal rye cover crop on nitrate-N losses given climatic variability in the region. This paper describes the hydrology and nitrogen cycle submodels of RyeGro, which was developed with a low level of complexity and conceptualizes the soil profile as three soil layers. The model was calibrated with data from a three-year rye cover crop field study conducted at Lamberton, Minnesota, and validated with data from a previous study. During model calibration, field subsurface drainage nitrate-N loadings were predicted within 0.2, 0, and 1.6 kg N [ha.sup.-1] (1, 0, and -3%) of measured loadings for the corn-soybean treatment and within 1.2, 0, and 1.6 kg N [ha.sup.-1] (11, 0, and 3%) of measured loadings for the corn-rye-soybean treatment. The model validation showed nitrate-N loading differences of ? and 1 k gN [ha.sup.1] (-22 and 4%) for the two years tested. DOI: 10.1061/(ASCE)0733-9437(2007)133:2(90) CE Database subject headings: Subsurface drainage; Nitrogen; Nitrates; Nutrient loads; Computer models; Soil water storage; Crops; Agriculture.