NO3-N Concentrations In Groundwater Research Articles

Identification of surface water - groundwater nitrate governing factors in Jianghuai hilly area based on coupled SWAT-MODFLOW-RT3D modeling approach

A comprehensive understanding of the key controlling factors on NO3-N spatiotemporal distribution in surface and groundwater is of great significance to nitrogen pollution control and water resources management in watershed. Hence, the coupled SWAT-MODFLOW-RT3D model was employed to simulate nitrate (NO3−) fate and transport in Huashan watershed system. The model was calibrated using a combination of stream discharge, groundwater levels, NO3-N in-stream loading and groundwater NO3-N concentrations. The simulation revealed the significant spatiotemporal variations in surface water-groundwater nitrate interactions. The annual average percolation of NO3− from rivers to groundwater was 171.5 kg/km2 and the annual average discharge NO3− content from groundwater into rivers was 451.9 kg/km2 over the simulation period. The highest percolation of NO3− from rivers to groundwater occurred in April and the highest discharge NO3− content from groundwater into rivers occurred in July. Grassland and agriculture land contributed more nitrate contents in river water and groundwater compared to bare land and forest in the study area and the water exchange was the primary driving force for nitrate interactions in the surface water-groundwater system. Sensitivity analysis indicated that river runoff and groundwater levels were most influenced by the SCS runoff curve number f (CN2) and aquifer hydraulic conductivity (K), which, in turn, significantly affected nitrate transport. Regarding water quality parameters, the denitrification exponential rate coefficient (CDN) had the most pronounced impact on NO3-N in-stream loading and groundwater NO3-N concentrations. This study underscores the central role of surface-groundwater (SW-GW) interactions in watershed-scale nitrate research and suggests that parameters with higher sensitivity should be prioritized in analogous watershed modeling.

Crop Field Level Estimation of Nitrogen Input from Fertilizer Use in Jeju Island, South Korea: Management Methods to Prevent Groundwater NO3-N Contamination

The application of synthetic nitrogen (N) fertilizers has boosted crop yields globally. However, it has also imposed on environmental pollution problems. An estimation of actual fertilizer N inputs at the crop field level is needed to establish effective N management plans to control groundwater NO3-N contamination. Here, a survey to collect the types of cultivated crop and fertilizer application rate was conducted during 2016–2018, covering 44,253 small crop fields (7730 ha) in the western part (Hanrim and Hankyung regions) of Jeju Island, South Korea. Foreign vegetables, citrus fruits, and bulb vegetables are the major crop types grown in the total cultivated areas of 2165.6 ha, 1718.7 ha, and 944.9 ha, respectively. For several crops (green garlic, potato, and chives), the over-use of N fertilizers is observed, the amount of which is 1.73–4.95 times greater than the standard fertilizer application rate. The highest level of fertilizer N input is observed for bulb vegetables in both the regions (Hanrim: 500.5 kg/ha, Hankyung: 487.1 kg/ha), with nearly 80% of the N fertilizer input turned into surplus N loading. A comparison between a spatial interpolation map of the fertilizer N input and that of the groundwater NO3-N concentration implies that the excessive use of synthetic fertilizer results in the degradation of groundwater quality by NO3-N. N management plans for the study area are suggested based on the N fertilizer input at the crop field level. This study highlights that sustainable N management plans should be arranged at the crop field level, considering the spatial heterogeneity of N fertilizer use.

Riparian Zone Nitrogen Management through the Development of the Riparian Ecosystem Management Model (REMM) in a Formerly Glaciated Watershed of the US Northeast

The Riparian Ecosystem Management Model (REMM) was developed, calibrated and validated for both hydrologic and water quality data for eight riparian buffers located in a formerly glaciated watershed (upper Pawcatuck River Watershed, Rhode Island) of the US Northeast. The Annualized AGricultural Non-Point Source model (AnnAGNPS) was used to predict the runoff and sediment loading to the riparian buffer. Overall, results showed REMM simulated water table depths (WTDs) and groundwater NO3-N concentrations at the stream edge (Zone 1) in good agreement with measured values. The model evaluation statistics showed that, hydrologically REMM performed better for site 1, site 4, and site 8 among the eight buffers, whereas REMM simulated better groundwater NO3-N concentrations in the case of site 1, site 5, and site 7 when compared to the other five sites. The interquartile range of mean absolute error for WTDs was 3.5 cm for both the calibration and validation periods. In the case of NO3-N concentrations prediction, the interquartile range of the root mean square error was 0.25 mg/L and 0.69 mg/L for the calibration and validation periods, respectively, whereas the interquartile range of d for NO3-N concentrations was 0.20 and 0.48 for the calibration and validation period, respectively. Moreover, REMM estimation of % N-removal from Zone 3 to Zone 1 was 19.7%, and 19.8% of N against actual measured 19.1%, and 26.6% of N at site 7 and site 8, respectively. The sensitivity analyses showed that changes in the volumetric water content between field capacity and saturation (soil porosity) were driving water table and denitrification.

Subsurface nutrient processing capacity in agricultural roadside ditches

Roadside ditches located throughout urban and rural landscapes are integral components of watershed-scale hydrologic processes but their capacity to reduce nutrients in the subsurface environment has not been investigated. In this study, vegetation, soil and groundwater conditions were characterized in six roadside ditches in the 66 km2 Lime Creek watershed in eastern Iowa. Shallow water table wells were installed at 17 locations in six transects and sampled monthly in 2017 to evaluate spatial and temporal patterns. Vegetation characteristics were surprisingly diverse but was not found to be a significant factor in water quality patterns. Groundwater NO3-N concentrations were <1 mg/L in wells at two transects and were observed to decrease from upgradient to downgradient positions at four locations (average 60% reduction). Water table levels were very shallow (<0.3 m) at nearly all sites, and the loamy and organic rich ditch soils appeared sufficiently anaerobic for subsurface processing of NO3-N via denitrification to occur. Groundwater dissolved reactive phosphorus concentrations did not vary systematically among the sites whereas two of the roadside ditches had Cl concentrations indicative of road salt encroachment. With estimated NO3-N reductions equivalent to typical wetland N reductions we recommend consideration of roadside ditches to serve as “linear wetlands” for watershed-scale treatment of nonpoint source pollution.

Changes in groundwater quality and agriculture in forty years on the Twin Falls irrigation tract in southern Idaho

Understanding long-term impacts of agricultural landscapes on shallow groundwater quality is needed to improve soil and water management in the Twin Falls irrigation tract in southern Idaho. In 1999 and 2002 through 2007, we resampled 10 of the 15 tunnel drains monitored in a late-1960s study to determine how nutrient concentrations and flow rates of outflows have changed over time in response to changes in land management or climate. Since the late 1960s, an 8-fold increase in the dairy herd has driven shifts toward increased feed cropping, which, along with improved hybrids and production, increased inorganic and manure fertilizer use. The late-1960s to early-2000s period saw a consistent 1.4-fold increase in mean tunnel-drain outflow nitrate-nitrogen (NO3-N) concentrations (from 3.06 to 5.06 mg L−1 [ppm]), a 10% decrease in mean chloride (Cl) (from 49.2 to 44.2 mg L−1 [ppm]), and an overall 14% decrease in dissolved reactive phosphorus (DRP) (14 to 12 μg L−1 [ppb]). However, 3 of the 10 tunnels exhibited increased DRP concentrations during the period, and the rate of DRP increase was positively related to increasing encroachment of confined animal feeding operations or residential development. Decreases in tunnel flow between sampling periods were linearly related to corresponding increases in the fraction of sprinkler irrigation employed on lands drained by the tunnels (p = 0.01). However, further conversion from furrow to sprinkler irrigation is unlikely to reduce tunnel drain NO3-N concentrations since the latter were unrelated to changes in sprinkler coverage. The amount and timing of applied N and availability for crop uptake or leaching should be more carefully managed in these soils to prevent continued increases in groundwater NO3-N concentrations. It is recommended that alfalfa (Medicago sativa L.) rotations be followed by deep-rooted crops with large N requirements to better utilize N mineralized from killed alfalfa roots.

Integrated assessment of agricultural nutrient pressures and legacies in karst landscapes

Landscapes typically deemed at risk from leached losses of nitrogen (N) and phosphorus (P) are those with short subsurface hydrologic time lags. Due to the short time it takes nutrients to move from a source to an area of concern, such sites are deemed perfect to test the efficacy of programmes of measures as management changes. However, a small subset of these sites can retain nutrients in soil/subsoil layers, which in turn are leached and can be either attenuated (e.g. nitrate converted to gaseous forms or immobilised in soil and P can be mineralised) or mobilised over time. This biogeochemical time lag can have long lasting effects on water quality. In an intensive agricultural karst oxidised aquifer setting, the aim of this study was to improve understanding of P and N inputs, retention, attenuation and subsurface pathway distribution and to inform how similar sites can be managed in the future. This was undertaken for the present site by integrating existing secondary and new primary datasets for both N and P. Results showed that in the years pre-2000 slurry from an on-site integrated pig production unit had been applied at rates of 33tha−1 annually, which supplied approximately 136kgha−1 total N and approximately 26kgha−1 total P annually. This practice contributed to large quantities of N (TotalN and NH4-N) and elevated soil test P (Morgan extractable P), present to a depth of 1m. This store was augmented by recent surpluses of 263kgNha−1, with leached N to groundwater of 82.5kgNha−1 with only 2.5kgNha−1 denitrified in the aquifer thereafter. High resolution spring data showed greatest percentage loss in terms of N load from small (54–88%) and medium fissure pathways (7–21%) with longer hydrologic time lags, with smallest loads from either large fissure (1–13%) or conduit (1–10%) pathways with short hydrologic time lags (reaction time at the spring from onset of a rainfall event is within hours). Although soils were saturated in P and in mobile forms to 0.5m, dissolved reactive P concentrations in groundwater remained low due to Ca and Mg limestone chemistry. Depletion of the legacy store with no further inputs (taking 25% of available mass of soil organic N as available in 1m of soil/subsoil to be 75kgNha−1) would take approximately 50 years, with NO3-N concentrations in the source area dropping to levels that could sustain groundwater NO3-N concentrations below admissible levels within 9 years. Biogeochemical time lags (decades) are longer than hydrologic time lags on this site (months to years). Future management should target farm surpluses that maintain a legacy store at or below a soil organic N mass of ∼20kgNha−1. Incorporation of biogeochemical and hydrologic time lag principles into future water quality regulations will provide regulators with realistic expectations when implementing policies.

Temporal variations of groundwater quality in the Western Jianghan Plain, China

The Western Jianghan Plain (WJHP) lies in the middle reaches of the Yangtze River. It has been impacted by anthropogenic activities during the past decades. The long-term variations of the WJHP's regional aquifer's hydrochemistry and groundwater quality have not been previously assessed. Sixteen physiochemical parameters at 29 monitoring wells within the Western Jianghan Plain were monitored during 1992–2010 and analyzed with multiple approaches. The confined groundwater is predominantly of the HCO3-Ca-Mg type with Cl−, SO42−, NH4-N, and NO3-N showing remarkable spatial variations. Correlation analysis was used to identify the origins and contamination sources of groundwater. The seasonal Mann-Kendall test revealed that pH, NO3-N, and Cl− concentrations at 27, 26 and 15 wells, respectively, exhibited significant increasing trends during 1992–2010. The increase of pH may be attributed to CO2 degassing caused by extensive groundwater extraction. Regional average NO3-N concentrations of groundwater increased coincidently with the increased use of fertilizer, which suggests that nitrate pollution is caused by agricultural activities. Abnormally high values of Cl− and SO42− at some wells were induced by industrial chemicals. In addition, the similarity of the temporal variations of the regional average of pH, NH4-N, and NO3-N concentrations in groundwater with those in the Yangtze River at the outlet of the Three Gorges Reservoir (TGR) suggests that the variations of these parameters in the WJHP is partly due to water storage by the TGR. This study presents an analysis of temporal variations of groundwater quality in the WJHP that reveals a relation between the creation of the TGR and downstream groundwater quality. This paper's findings provide clues for measures that could be taken to protect the groundwater quality of the WJHP's aquifer.

Distribution of nitrate and its implication for the contaminant source in groundwater of Huaibei Plain, Anhui Province

High concentration of NO3-N in groundwater can pose risk to human’s health, thus the study of NO3-N contamination in groundwater is a very important issue related to public health. Using a typical agriculture zone, Huaibei plain in Anhui Province of China as a field site, the temporal and spatial variation of groundwater NO3-N concentration was studied using a multivariate statistical factor analysis combined with Kaiser-Meyer-Olkin method based on a hydrogeological investigation from 2005 to 2009 year. The results show: (1) The contaminant in the groundwater of Huaibei Plain in Anhui Province are serious. 10% of the shallow groundwater samples in non-rainy season of 2005 exceeds the recommended value of NO3-N by Chinese drinking water standard (≥20 mg/L), while 17.5% exceeds the recommended value (11.3 mg/L) by EC. (2) About 15% of shallow groundwater in the whole study area was polluted in 2005 with the maximum of 97.67 mg/L; Groundwater NO3-N concentration is higher in non-rainy season than in rainy season. And the NO3-N content in groundwater shows the increasing trend at all three depths sampled from 2005 to 2009 year. (3) Groundwater nitrate pollution mainly derives from anthropogenic activities in Huaibei Plain, Anhui Province. Further quantitative analysis need to be studied in the future.

Excessive nitrogen application decreases grain yield and increases nitrogen loss in a wheat–soil system

Excessive use of nitrogen (N) fertilizers in wheat fields has led to elevated NO3-N concentrations in groundwater and reduced N use efficiency. Three-year field and 15N tracing experiments were conducted to investigate the effects of N application rates on N uptake from basal and topdressing 15N, N use efficiency, and grain yield in winter wheat plants; and determine the dynamics of N derived from both basal and topdressing 15N in soil in high-yielding fields. The results showed that 69.5–84.5% of N accumulated in wheat plants derived from soil, while 6.0–12.5%and 9.2–18.1% derived from basal 15N and top 15N fertilizer, respectively. The basal N fertilizer recovery averaged 33.9% in plants, residual averaged 59.2% in 0–200 cm depth soil; the topdressing N fertilizer recovery averaged 50.5% in plants, residual averaged 48.2% in 0–200 cm soil. More top 15N was accumulated in plants and more remained in 0–100 cm soil rather than in 100–200 cm soil at maturity, compared with the basal 15N. However, during the period from pre-sowing to pre-wintering, the soil nitrate moved down to deeper layers, and most accumulated in the layers below 140 cm. With an increase of N fertilizer rate, the proportion of the N derived from soil in plants decreased, but that derived from basal and topdressing fertilizer increased; the proportion of basal and top 15N recovery in plants decreased, and that of residual in soil increased. A moderate application rate of 96–168 kg N ha−1 led to increases in nitrate content in 0–60 cm soil layer, N uptake amount, grain yield and apparent recovery fraction of applied fertilizer N in wheat. Applying above 240 kg N ha−1 promoted the downward movement of basal and top 15N and soil nitrate, but had no significant effect on N uptake amount; the excessive N application also obviously decreased the grain yield, N uptake efficiency, apparent recovery fraction of applied fertilizer N, physiological efficiency and internal N use efficiency. It is suggested that the appropriate application rate of nitrogen on a high-yielding wheat field was 96–168 kg N ha−1.

Fate of Effluent‐Borne Contaminants beneath Septic Tank Drainfields Overlying a Karst Aquifer

Groundwater quality effects from septic tanks were investigated in the Woodville Karst Plain, an area that contains numerous sinkholes and a thin veneer of sands and clays overlying the Upper Floridan aquifer (UFA). Concerns have emerged about elevated nitrate concentrations in the UFA, which is the source of water supply in this area of northern Florida. At three sites during dry and wet periods in 2007-2008, water samples were collected from the septic tank, shallow and deep lysimeters, and drainfield and background wells in the UFA and analyzed for multiple chemical indicators including nutrients, nitrate isotopes, organic wastewater compounds (OWCs), pharmaceutical compounds, and microbiological indicators (bacteria and viruses). Median NO3-N concentration in groundwater beneath the septic tank drainfields was 20 mg L(-1) (8.0-26 mg L(-1)). After adjusting for dilution, about 25 to 40% N loss (from denitrification, ammonium sorption, and ammonia volatilization) occurs as septic tank effluent moves through the unsaturated zone to the water table. Nitrogen loading rates to groundwater were highly variable at each site (3.9-12 kg N yr(-1)), as were N and chloride depth profiles in the unsaturated zone. Most OWCs and pharmaceutical compounds were highly attenuated beneath the drainfields; however, five Cs (caffeine, 1,7-dimethylxanthine, phenol, galaxolide, and tris(dichloroisotopropyl)phosphate) and two pharmaceutical compounds (acetaminophen and sulfamethoxazole) were detected in groundwater samples. Indicator bacteria and human enteric viruses were detected in septic tank effluent samples but only intermittently in soil water and groundwater. Contaminant movement to groundwater beneath each septic tank system also was related to water use and differences in lithology at each site.

Nitrate Leaching in Two Irrigated Soils with Different Rates of Cattle Manure

Manure applied to irrigated land may potentially contaminate groundwater with NO3-N. An 8-yr field experiment was conducted in southern Alberta, Canada, to determine the effects of different rates of manure on NO3-N accumulation in two irrigated soil types and NO3-N leaching to shallow groundwater. An annual cereal silage was grown at each site and irrigation was based on soil moisture depletion. Treatments included a control, nitrogen fertilizer (NF) at 180 kg N ha(-1) yr(-1), and four rates of cattle (Bos taurus) manure (20, 40, 60, and 120 Mg ha(-1) yr(-1), wet-weight basis). Annual manure applications for 8 yr resulted in NO3-N accumulation in the soil profile at both sites. For every megagram of total N added from manure, NO3-N in the 0- to 1.5-m layer increased by about 50 kg ha(-1) at the coarse-textured (CT) site and by about 100 kg ha(-1) at the medium-textured (MT) site. Silage yield for all of the manure treatments was similar to yield for the NF treatment after the first 3 to 4 yr of annual manure applications. The greatest manure rate and NF treatments significantly increased NO3-N concentrations in groundwater at the CT site. Groundwater NO3-N concentrations were not adversely affected by manure or NF applications at the MT site. An annual cattle manure application rate of 20 Mg ha(-1) provided sufficient N for irrigated cereal silage production and minimized NO3-N leaching in a medium-textured soil.

Prediction of agriculture derived groundwater nitrate distribution in North China Plain with GIS-based BPNN

In recent years, nitrate contamination of groundwater has become a growing concern for people in rural areas in North China Plain (NCP) where groundwater is used as drinking water. The objective of this study was to simulate agriculture derived groundwater nitrate pollution patterns with artificial neural network (ANN), which has been proved to be an effective tool for prediction in many branches of hydrology when data are not sufficient to understand the physical process of the systems but relative accurate predictions is needed. In our study, a back propagation neural network (BPNN) was developed to simulate spatial distribution of NO3-N concentrations in groundwater with land use information and site-specific hydrogeological properties in Huantai County, a typical agriculture dominated region of NCP. Geographic information system (GIS) tools were used in preparing and processing input–output vectors data for the BPNN. The circular buffer zones centered on the sampling wells were designated so as to consider the nitrate contamination of groundwater due to neighboring field. The result showed that the GIS-based BPNN simulated groundwater NO3-N concentration efficiently and captured the general trend of groundwater nitrate pollution patterns. The optimal result was obtained with a learning rate of 0.02, a 4-7-1 architecture and a buffer zone radius of 400 m. Nitrogen budget combined with GIS-based BPNN can serve as a cost-effective tool for prediction and management of groundwater nitrate pollution in an agriculture dominated regions in North China Plain.

Long-term effects of late-summer overseeding of winter rye on corn grain yield and nitrogen balance

Winter rye (Secale cereale) overseeded into standing corn (Zea mays L.) on sandy soil controlled NO3 leaching over the short-term (3 yr). Long-term effects were unknown, so yield and N balance were monitored for an additional 6 yr with and without a rye cover crop under conventional (CT) and no-till (NT) management at six fertilizer N rates. Corn yield was greater with rye cover cropping than without in 6 of the last 7 yr. Response exceeded 1600 kg grain ha-1 (average 100–200 kg fertilizer N ha-1) by year 8 (wet following a dry year) and was greater under NT than CT in dry years (years 7 and 9). The response is attributed to improved soil physical properties and N availability. Rye N uptake increased with fertilizer N rate particularly following dry growing seasons, with shoots containing up to 73 kg N ha-1. Post-harvest topsoil NO3 was reduced by the rye in all but the initial year, and groundwater NO3-N concentrations only exceeded 10 mg L-1 without rye. The overseeding system facilitates utilization of conserved N and reduces movement of NO3 to groundwater over the long term. Key words: Nitrogen management, Zea mays, Secale cereale, cover crop, soil nitrate, tillage

Nitrate Dynamics in Shallow Groundwater and the Potential for Transport to Off-Site Water Bodies

Large quantities of the nitrate leaching below the crop root-zone, particularly during the wet season, in the tropical Far North Queensland (FNQ) of Australia, may be entering off and on-site the water bodies. The objectives of this study were to (i) provide quantitative information on NO3-N in the shallow fluctuating groundwater (GW) that develops during the rainy season (January through May) in the Johnstone River Catchment (JRC) of FNQ and (ii) determine whether this NO3-N is potentially transportable to creeks/streams. The NO3-N concentration and GW table heights were monitored, at least at weekly intervals, in 6 piezometers, installed to 8.5–12.0 m depth in 6 different soil types under fertilized sugarcane (Saccharum Officinarum-S) in the JRC during the 1999 rainy season.Depending on the location of piezometers on the landscape and time of water sampling, the GW table fluctuated between from 1.5 to 11.5 m abovethe piezometer bottom. The NO3-N concentration in the fluctuating GW also showed spatio-temporal dynamics and it ranged from 0.60 to 3.70 mg L-1. The NO3-N adsorbed at anion exchanges sites, up to 10 m depth, ranged from 154 to 3956 kg ha-1, compared with 21 kgha-1 under rainforest. In the fluctuating GW, the NO3-N concentration increased with increasing GW table height and the NO3-N adsorbed at anion exchange sites (R2 = 0.96). The NO3-N load in the GW ranged from 40 to 110 kg ha-1 and it increased with increasing GW table and GW NO3-N concentration. The estimated N-load in the GW that was discharged into creeks/streams when the GW receded ranged from 21 to 81 kg ha-1. The results provide evidence that a(i) a major proportion of the NO3-N that was leaching below the sugarcane root-zone entered the shallow GW that developed during the rainy season, and (ii) a significant proportion of the NO3-N inthe GW was transported to creeks/streams when the GW table receded.

Nitrogen concentrations in a small Mediterranean stream: 1. Nitrate 2. Ammonium

Abstract. The importance of storm frequency as well as the groundwater and hyporheic inputs on nitrate (NO3-N) and ammonium (NH4-N) levels in stream water were studied in a small perennial Mediterranean catchment, Riera Major, in northeast Spain. NO3-N concentrations ranged from 0.15 to 1.9 mg l-1. Discharge explained 47% of the annual NO3-N concentration variance, but this percentage increased to 97% when single floods were analysed. The rate of change in nitrate concentration with respect to flow, ΔNO3-N/ΔQ, ranged widely from 0 to 20 μg NO3-N s l-2. The ΔNO3-N/ΔQ values fitted to a non linear model with respect to the storm flow magnitude (ΔQ) (r2=0.48, d.f.=22, P&lt;0.01). High values of ΔNO3-N/ΔQ occurred at intermediate ΔQ values, whereas low ΔNO3-N/ΔQ values occurred during severe storms (ΔQ &gt; 400 l s-1). N3-N concentrations exhibit anticlockwise hysteresis patterns with changing flow and the patterns observed for autumnal and winter storms indicated that groundwater was the main N3-N source for stream and hyporheic water. At baseflow, NO3-N concentration in groundwater was higher (t=4.75, d.f.=29, P&gt;0.001) and co-varied with concentrations in the stream (r=0.91, d.f.=28, P&lt;0.001). In contrast, NO3-N concentration in hyporheic water was identical to that in stream water. The role of the hyporheic zone as source or sink for ammonium was studied hyporheic was studied comparing its concentrations in stream and hyporheic zone before and after a major storm occurred in October 1994 that removed particulate organic matter stored in sediments. Results showed high ammonium concentrations (75±28 s.d. μg NH4-N l-1) before the storm flow in the hyporheic zone. After the storm, the ammonium concentration in the hyporheic dropped by 80% (13.6±8 μg N4-N l-1) and approached to the level found in stream water (11±8 μg NH4-N l-1) indicating that indisturbed hyporheic sediments act as a source for ammonium. After the storm, the ammonium concentrations in the stream, hyporheic and groundwater zones were very similar suggesting that stream ammonium concentrations are sustained mainly by input from groundwater. The present study provides evidence that storm flow magnitude is an important source of variability of nitrate concentration and fluxes in Mediterranean streams subjected to an irregular precipitation regime with prolonged dry periods.

Nitrogen circulation in a Mediterranean holm oak forest, La Castanya, Montseny, northeastern Spain

Abstract. The importance of storm frequency as well as the groundwater and hyporheic inputs on nitrate (NO3-N) and ammonium (NH4-N) levels in stream water were studied in a small perennial Mediterranean catchment, Riera Major, in northeast Spain. NO3-N concentrations ranged from 0.15 to 1.9 mg l-1. Discharge explained 47% of the annual NO3-N concentration variance, but this percentage increased to 97% when single floods were analysed. The rate of change in nitrate concentration with respect to flow, ΔNO3-N/ΔQ, ranged widely from 0 to 20 μg NO3-N s l-2. The ΔNO3-N/ΔQ values fitted to a non linear model with respect to the storm flow magnitude (ΔQ) (r2=0.48, d.f.=22, P&lt;0.01). High values of ΔNO3-N/ΔQ occurred at intermediate ΔQ values, whereas low ΔNO3-N/ΔQ values occurred during severe storms (ΔQ &gt; 400 l s-1). N3-N concentrations exhibit anticlockwise hysteresis patterns with changing flow and the patterns observed for autumnal and winter storms indicated that groundwater was the main N3-N source for stream and hyporheic water. At baseflow, NO3-N concentration in groundwater was higher (t=4.75, d.f.=29, P&gt;0.001) and co-varied with concentrations in the stream (r=0.91, d.f.=28, P&lt;0.001). In contrast, NO3-N concentration in hyporheic water was identical to that in stream water. The role of the hyporheic zone as source or sink for ammonium was studied hyporheic was studied comparing its concentrations in stream and hyporheic zone before and after a major storm occurred in October 1994 that removed particulate organic matter stored in sediments. Results showed high ammonium concentrations (75±28 s.d. μg NH4-N l-1) before the storm flow in the hyporheic zone. After the storm, the ammonium concentration in the hyporheic dropped by 80% (13.6±8 μg N4-N l-1) and approached to the level found in stream water (11±8 μg NH4-N l-1) indicating that indisturbed hyporheic sediments act as a source for ammonium. After the storm, the ammonium concentrations in the stream, hyporheic and groundwater zones were very similar suggesting that stream ammonium concentrations are sustained mainly by input from groundwater. The present study provides evidence that storm flow magnitude is an important source of variability of nitrate concentration and fluxes in Mediterranean streams subjected to an irregular precipitation regime with prolonged dry periods. Keywords: nitrate, discharge regime, hyporheic zone, groundwater, Mediterranean, stream, Riera Major

Calibration of the DRASTIC ground water vulnerability mapping method.

Ground water vulnerability maps developed using the DRASTIC method have been produced in many parts of the world. Comparisons of those maps with actual ground water quality data have shown that the DRASTIC method is typically a poor predictor of ground water contamination. This study significantly improved the effectiveness of a modified DRASTIC ground water vulnerability map by calibrating the point rating schemes to actual ground water quality data by using nonparametric statistical techniques and a geographic information system. Calibration was performed by comparing data on nitrite plus nitrate as nitrogen (NO2 + NO3-N) concentrations in ground water to land-use, soils, and depth to first-encountered ground water data. These comparisons showed clear statistical differences between NO2 + NO3-N concentrations and the various categories. Ground water probability point ratings for NO2 + NO3-N contamination were developed from the results of these comparisons, and a probability map was produced. This ground water probability map was then correlated with an independent set of NO2 + NO3-N data to demonstrate its effectiveness in predicting elevated NO2 + NO3-N concentrations in ground water. This correlation demonstrated that the probability map was effective, but a vulnerability map produced with the uncalibrated DRASTIC method in the same area and using the same data layers was not effective. Considerable time and expense have been out-laid to develop ground water vulnerability maps with the DRASTIC method. This study demonstrates a cost-effective method to improve and verify the effectiveness of ground water vulnerability maps.

Monitoring nitrate leaching from submerged drains.

Monitoring nitrate N (NO3-N) leaching is important in order to judge the effect that agricultural practices have on the quality of ground water and surface water. Measuring drain discharge rates and NO3-N concentrations circumvents the problem of spatial variability encountered by other methods used to quantify NO3-N leaching in the field. A new flow-proportional drainage water sampling method for submerged drains has been developed to monitor NO3-N leaching. Both low and high discharge rates can be measured accurately, and are automatically compensated for fluctuations in ditch-water levels. The total amount of NO3-N leached was 10.6 kg N ha(-1) for a tile-drained silt-loam soil during the 114-d monitoring period. The NO3-N concentrations fluctuated between 5 mg L(-1) at deep ground water levels and 15 mg L(-1) at shallow levels, due to variations in water flow. A flow-proportional drainage water sampling method is required to measure NO3-N leaching accurately under these conditions. Errors of up to 43% may occur when NO3-N concentrations in the drainage water are only measured at intervals of 30 d and when the precipitation excess is used to estimate cumulative NO3-N leaching. Measurements of NO3-N concentrations in ground water cannot be used to accurately estimate NO3-N leaching in drained soils.

Management and utilization of poultry wastes.

Waste by-products such as excreta or bedding material that are generated by the worldwide annual production of more than 40 million metric tons (t) of poultry meat and 600 billion eggs are generally land applied as the final step of a producer's waste management strategy. Under proper land application conditions, the nutrients and organisms in poultry wastes pose little environmental threat. Environmental contamination occurs when land application of poultry wastes is in excess of crop utilization potential, or is done under poor management conditions causing nutrient loss from environmental factors such as soil erosion or surface runoff during rainfall. Environmental parameters of concern are N, P, and certain metals (Cu and Zn in particular), as well as pathogenic microorganisms that may be contained in poultry waste. The biochemical cycle of N is very dynamic, and N contained in poultry waste may either be removed by crop harvest, leave the animal production facility, waste treatment lagoon, or application field as a gas (NH3, NO, NO2, N2O, or N2), or, due to its mobility in soil, be transported in organic or inorganic N forms in the liquid state via surface runoff or leaching into groundwater. Elevated concentrations of NO3-N in groundwater used for human consumption is a health risk to infants that are susceptible to methemoglobinemia. An environmental impact resulting from elevated NO3-N is eutrophication of surface waters. Ammonia loss from poultry waste is an environmental concern because of volatilized wet and dry deposits of NH3 into nitrogen-sensitive ecosystems. Phosphorus in poultry wastes may contribute to environmental degradation by accelerating the process of eutrophication. Unlike N, P is very immobile in soil and must first be transported to a surface water environment to have an environmental impact. It is generally accepted, however, that this nutrient affects receiving waters via transport in eroding soil as sediment-bound P or in surface runoff as soluble inorganic or organic P. Numerous studies have reported that excess P contained in land-applied manures may contribute to eutrophication. Soils containing P concentrations that greatly exceed the agronomic potential of crops may require years or even decades to return to levels that are crop limiting for this nutrient. Environmental concerns include the capacity of such soils to adsorb new P and the amount of P loss from these soils from erosion, runoff, drainage, or leaching to groundwater. Although much information is available regarding the loss of P from agricultural fields from erosion and runoff, less information is available regarding P losses from fields receiving poultry wastes. However, studies have shown that there are many challenges to controlling P losses from fields receiving manures. In addition, subsurface transport of P resulting from repeated application of poultry manure onto soils that are artificially drained is an environmental concern where drainage waters enter or interact with water bodies sensitive to eutrophication. Trace elements such as As, Co, Cu, Fe, Mn, Se, and Zn are often added in excess to poultry feed to increase the animal's rate of weight gain, feed efficiency, and egg production and to prevent diseases. Because most of the excess trace elements are not absorbed by the bird, the concentration of elements excreted in the manure will reflect dietary overformulation. Because trace elements are generally required in very small quantities for crop growth and, like P, are immobile in most soil types, their concentrations will increase with repeated land application of poultry wastes. Of particular concern are accumulations of Cu and Zn in certain soil types utilized for certain crops. Copper and Zn toxicity for some crops have been documented in some areas receiving repeated land-applied poultry wastes. A potential environmental concern relative to poultry litter and trace elements in receiving soils involves the transpor

Nutrient Discharge Beneath Urban Lawns To A Sandy Coastal Aquifer, Perth, Western Australia

Excess nitrogen and phosphorus leaching beneath urban lawns on sandy soils in metropolitan Perth, Western Australia, may pose a serious threat not only to the quality of the underlying groundwater but also to many surface-water bodies. In this study, suction-driven lysimeters were developed and used to quantify water and nutrient fluxes below the root zone at four urban lawn sites in Perth. The four sites received similar fertiliser treatment but differed in irrigation regimes. Over a period of 12 months, up to 51 percent of incident water passed below the root zone. Annual flow-weighted concentrations of NO3-N in the leachate ranged from 0.8–5.4 mg/L, whereas PO4-P concentrations ranged from 0.003–0.034 mg/L. At most sites, NO3-N concentrations periodically equalled or exceeded the World Health Organization (WHO) drinking-water limit of 10 mg/L; high concentration were maintained for longer periods at two sites with coarser sands and high irrigation regimes. Evidence exists that concentrations of N and P in urban groundwater are reduced through dilution and possibly through chemical transformation and adsorption. It is unlikely that NO3-N concentrations in groundwater will exceed the WHO drinking limit except for relatively short periods of time. However, nutrients (especially N) from fertilised lawns are a threat to wetlands and waterways into which nutrient-rich groundwater is discharged. Modified management practices for urban lawns, or alternative-style home gardens may need to be developed in order to minimise nutrient enrichment of groundwater and water bodies. Some suggestions for these are presented.