Differences In Nitrate Concentrations Research Articles

Nitrate leaching from short-hydroperiod floodplain soils

Abstract. Numerous studies have shown the importance of riparian zones to reduce nitrate (NO3−) contamination coming from adjacent agricultural land. Much less is known about nitrogen (N) transformations and nitrate fluxes in riparian soils with short hydroperiods (1–3 days of inundation) and there is no study that could show whether these soils are a N sink or source. Within a restored section of the Thur River in NE Switzerland, we measured nitrate concentrations in soil solutions as an indicator of the net nitrate production. Samples were collected along a quasi-successional gradient from frequently inundated gravel bars to an alluvial forest, at three different depths (10, 50 and 100 cm) over a one-year period. Along this gradient we quantified N input (atmospheric deposition and sedimentation) and N output (leaching) to create a nitrogen balance and assess the risk of nitrate leaching from the unsaturated soil to the groundwater. Overall, the main factor explaining the differences in nitrate concentrations was the field capacity (FC). In subsoils with high FCs and VWC near FC, high nitrate concentrations were observed, often exceeding the Swiss and EU groundwater quality criterions of 400 and 800 μmol L−1, respectively. High sedimentation rates of river-derived nitrogen led to apparent N retention up to 200 kg N ha−1 yr−1 in the frequently inundated zones. By contrast, in the mature alluvial forest, nitrate leaching exceeded total N input most of the time. As a result of the large soil N pools, high amounts of nitrate were produced by nitrification and up to 94 kg N-NO3− ha−1 yr−1 were leached into the groundwater. Thus, during flooding when water fluxes are high, nitrate from soils can contribute up to 11% to the total nitrate load in groundwater.

Comparison of lysimeters and porous ceramic cups for measuring nitrate leaching in different soil types

Environmental concerns over nitrate levels in surface and ground water have led to increased efforts to measure nitrate leaching from farmland. This study compared two methods of measuring leaching (lysimeters versus ceramic suction cups) using 12 soil monolith lysimeters (70 cm deep) containing four replicates of three contrasting New Zealand soils: Gorge silt loam, Mataura sandy loam (both stone-free soils) and Lismore stony silt loam. The ceramic suction cups were installed at 35 cm and 60 cm depths. Urea solution was surface applied at 250 kg N ha−1, followed by regular weekly irrigation. Nitrate leaching loss was calculated by combining the volume of drainage water collected from each lysimeter with the nitrate concentration in either the lysimeter drainage solution or the solution from the suction cups. Cup samples were taken twice per irrigation/drainage sequence: during irrigation and then immediately after irrigation ceased. No evidence of any difference in nitrate concentration and in cumulative leaching was observed between the first and second cup sampling times. However, there was a large variation in individual values measured by the suction cup samples. There were differences between the cumulative leaching loss measured in the lysimeter drainage and values estimated from the cups in the Gorge and Lismore soils. The cumulative leaching loss, measured from the top cups, bottom cups and lysimeter drainage, was 64, 68 and 54 kg N ha−1 respectively in the Gorge soil, 57, 68 and 62 kg N ha−1 in the Mataura soil and 61, 103 and 99 kg N ha−1 in the Lismore soil. It was concluded that suction cups were inappropriate for the determination of cumulative leaching in the structured Gorge soil and the Lismore topsoil, but ceramic cups could provide useful data on cumulative leaching in the Mataura sandy loam soil. It was hypothesised that preferential flow was likely to be the cause of the differences between the results obtained from suction cups and the lysimeter drainage, especially in the Lismore and possibly the Gorge soils, where the small sampler size was not able to capture a representative sample of the pore network responsible for the soil drainage.

Seasonal variation of potential denitrification rates of surface sediment from Meiliang Bay, Taihu Lake, China

The regulatory effects of environmental factors on denitrification were studied in the sediments of Meiliang Bay, Taihu Lake, in a monthly sampling campaign over a one-year period. Denitrification rates were measured in slurries of field samples and enrichment experiments using the acetylene inhibition technique. Sediment denitrification rates in inner bay and outer bay ranged from 2.8 to 51.5 nmol N 2/(g dw (dry weight)·hr) and from 1.5 to 81.1 nmol N 2/(g dw·hr), respectively. Sediment denitrification rates were greatest in the spring and lowest in the summer and early autumn, due primarily to seasonal differences in nitrate concentration and water temperature. For each site, positive and linear relationships were regularly observed between denitrification rate and water column nitrate concentration. Of various environmental factors on denitrification that we assessed, nitrate was determined to be the key factor limiting denitrification rates in the sediments of Meiliang Bay. In addition, at the two sites denitrification rates were also regulated by temperature. The addition of organic substrates had no significant effect on denitrification rate, indicating that sediment denitrification was not limited by organic carbon availability in the sediments. Nitrate in the water column was depleted during summer and early autumn, and this suppressed effective removal of nitrogen from Taihu Lake by denitrification.

Influence of hydrological connectivity of riverine wetlands on nitrogen removal via denitrification

Wetland ecosystems in agricultural areas often become progressively more isolated from main water bodies. Stagnation favors the accumulation of organic matter as the supply of electron acceptors with water renewal is limited. In this context it is expected that nitrogen recycling prevails over nitrogen dissipation. To test this hypothesis, denitrification rates, fluxes of dissolved oxygen (SOD), inorganic carbon (DIC) and nitrogen and sediment features were measured in winter and summer 2007 on 22 shallow riverine wetlands in the Po River Plain (Northern Italy). Fluxes were determined from incubations of intact cores by measurement of concentration changes or isotope pairing in the case of denitrification. Sampled sites were eutrophic to hypertrophic; 10 were connected and 12 were isolated from the adjacent rivers, resulting in large differences in nitrate concentrations in the water column (from <5 to 1,133 μM). Benthic metabolism and denitrification rates were investigated by two overarching factors: season and hydrological connectivity. SOD and DIC fluxes resulted in respiratory quotients greater than one at most sampling sites. Sediment respiration was coupled to both ammonium efflux, which increased from winter to summer, and nitrate consumption, with higher rates in river-connected wetlands. Denitrification rates measured in river-connected wetlands (35–1,888 μmol N m−2 h−1) were up to two orders of magnitude higher than rates measured in isolated wetlands (2–231 μmol N m−2 h−1), suggesting a strong regulation of the process by nitrate availability. These rates were also significantly higher in summer (9–1,888 μmol N m−2 h−1) than in winter (2–365 μmol N m−2 h−1). Denitrification supported by water column nitrate (DW) accounted for 60–100% of total denitrification (Dtot); denitrification coupled to nitrification (DN) was probably controlled by limited oxygen availability within sediments. Denitrification efficiency, calculated as the ratio between N removal via denitrification and N regeneration, and the relative role of denitrification for organic matter oxidation, were high in connected wetlands but not in isolated sites. This study confirms the importance of restoring hydraulic connectivity of riverine wetlands for the maintenance of important biogeochemical functions such as nitrogen removal via denitrification.

Nitrate in leafy vegetables, culinary herbs, and cucumber grown under cover in Estonia: content and intake

The content of nitrate in leafy vegetables, culinary herbs, and cucumber was determined during the years 2006–2008. All samples of Estonian origin, except white cabbage, were grown under cover. Seasonal differences in nitrate concentrations were observed in lettuce and spinach. Nitrate concentrations in lettuce were 22% and those in spinach were 24% higher in winter crops compared with samples collected in summer. The mean nitrate level was 3023 mg kg–1 for fresh lettuce and 2337 mg kg–1 for spinach. On average, 11.6% of fresh lettuce and spinach samples nitrate concentration exceeded the maximum level specified in European Commission Regulation No. 1881/2006. The mean levels were 999 mg kg–1 for imported iceberg lettuce and 1287 mg kg–1 for frozen spinach, which are below the maximum European Commission limits. Parsley, dill, basil, thyme, and rucola contained high concentrations of nitrate from mean levels of 2134 mg kg–1 for parsley up to 8150 mg kg–1 for rucola. Mean nitrate concentrations ranged from 382 to 1115 mg kg–1 for white cabbage and Chinese cabbage, respectively. The per capita mean daily intake of nitrates related to the consumption of leafy vegetables, culinary herbs, and cucumber for the whole Estonian population was 31.3 mg day–1, which comprised 14.2% of the acceptable daily intake (ADI).

Effects of Groundwater‐Flow Paths On Nitrate Concentrations Across Two Riparian Forest Corridors1

Speiran, Gary K., 2010. Effects of Groundwater‐Flow Paths on Nitrate Concentrations Across Two Riparian Forest Corridors. Journal of the American Water Resources Association (JAWRA) 46(2):246‐260. DOI: 10.1111/j.1752‐1688.2010.00427.xAbstract: Groundwater levels, apparent age, and chemistry from field sites and groundwater‐flow modeling of hypothetical aquifers collectively indicate that groundwater‐flow paths contribute to differences in nitrate concentrations across riparian corridors. At sites in Virginia (one coastal and one Piedmont), lowland forested wetlands separate upland fields from nearby surface waters (an estuary and a stream). At the coastal site, nitrate concentrations near the water table decreased from more than 10 mg/l beneath fields to 2 mg/l beneath a riparian forest buffer because recharge through the buffer forced water with concentrations greater than 5 mg/l to flow deeper beneath the buffer. Diurnal changes in groundwater levels up to 0.25 meters at the coastal site reflect flow from the water table into unsaturated soil where roots remove water and nitrate dissolved in it. Decreases in aquifer thickness caused by declines in the water table and decreases in horizontal hydraulic gradients from the uplands to the wetlands indicate that more than 95% of the groundwater discharged to the wetlands. Such discharge through organic soil can reduce nitrate concentrations by denitrification. Model simulations are consistent with field results, showing downward flow approaching toe slopes and surface waters to which groundwater discharges. These effects show the importance of buffer placement over use of fixed‐width, streamside buffers to control nitrate concentrations.

Sediment pool and plant content as indicators of nitrogen regimes in Portuguese estuaries

Excess nutrient loading is a major environmental problem that greatly affects the community structure and ecosystem function of rivers and estuaries. Human activities have greatly intensified the delivery of nutrients to aquatic environments causing eutrophication in many European waters. To evaluate whether different nitrogen regimes affect the N contents of sediments and macrophytes, two Portuguese estuaries with different intensities of land use in their watersheds — Mondego and Mira — were studied. We measured N concentrations in water, plant aboveground biomass and leaf N and C concentrations in Spartina maritima, Halimione portulacoides, and Zostera noltii; N and C concentrations were also measured both in the bare sediment and in sediment directly beneath plant canopies. The different intensity of land use practices did not consistently result in differences among nitrogen-related variables in Mondego and Mira estuaries. Concentrations of DIN in water were rather high compared to most other estuaries elsewhere. There was no difference in nitrate concentrations in the water column, but ammonium and dissolved organic N concentrations were higher in Mondego than in Mira. Aboveground biomass of H. portulacoides and Z. noltii was greater in Mondego, but not that of S. maritima. %N in the sediments beneath S. maritima and H. portulacoides and in the leaves of H. portulacoides was larger in Mondego than in Mira, but these effects were not observed for other variables and were of small magnitude. The links between N in plants and in ambient water and sediment were also hard to interpret. % N in leaves was positively related to N content of sediments and to nitrate concentration in the water column, but was inversely related to ammonium concentration in water. We conclude that Mondego and Mira estuaries are quite well-enriched in nitrogen, and that it is not evident that they differ in the level of nitrogen enrichment. Because marsh plants in Mondego and Mira are likely N-saturated, it is unlikely to think that nitrogen concentrations or contents in water, plants, or sediment can well serve as sentinels for nitrogen enrichment, as internal pools and processes are either full or N-replete.

Indirect radiative forcing and climatic effect of the anthropogenic nitrate aerosol on regional climate of China

The regional climate model (RegCM3) and a tropospheric atmosphere chemistry model (TACM) were coupled, thus a regional climate chemistry modeling system (RegCCMS) was constructed, which was applied to investigate the spatial distribution of anthropogenic nitrate aerosols, indirect radiative forcing, as well as its climatic effect over China. TACM includes the thermodynamic equilibrium model ISORROPIA and a condensed gas-phase chemistry model. Investigations show that the concentration of nitrate aerosols is relatively high over North and East China with a maximum of 29 µg m−3 in January and 8 µg m−3 in July. Due to the influence of air temperature on thermodynamic equilibrium, wet scavenging of precipitation and the monsoon climate, there are obvious seasonal differences in nitrate concentrations. The average indirect radiative forcing at the tropopause due to nitrate aerosols is −1.63 W m−2 in January and −2.65 W m−2 in July, respectively. In some areas, indirect radiative forcing reaches −10 W m−2. Sensitivity tests show that nitrate aerosols make the surface air temperature drop and the precipitation reduce on the national level. The mean changes in surface air temperature and precipitation are −0.13 K and −0.01 mm d−1 in January and −0.09 K and −0.11 mm d−1 in July, respectively, showing significant differences in different regions.

Temporal Trends in Nitrate and Selected Pesticides in Mid‐Atlantic Ground Water

Evaluating long-term temporal trends in regional ground-water quality is complicated by variable hydrogeologic conditions and typically slow flow, and such trends have rarely been directly measured. Ground-water samples were collected over near-decadal and annual intervals from unconfined aquifers in agricultural areas of the Mid-Atlantic region, including fractured carbonate rocks in the Great Valley, Potomac River Basin, and unconsolidated sediments on the Delmarva Peninsula. Concentrations of nitrate and selected pesticides and degradates were compared among sampling events and to apparent recharge dates. Observed temporal trends are related to changes in land use and chemical applications, and to hydrogeology and climate. Insignificant differences in nitrate concentrations in the Great Valley between 1993 and 2002 are consistent with relatively steady fertilizer application during respective recharge periods and are likely related to drought conditions in the later sampling period. Detecting trends in Great Valley ground water is complicated by long open boreholes characteristic of wells sampled in this setting which facilitate significant ground-water mixing. Decreasing atrazine and prometon concentrations, however, reflect reported changes in usage. On the Delmarva Peninsula between 1988 and 2001, median nitrate concentrations increased 2 mg per liter in aerobic ground water, reflecting increasing fertilizer applications. Correlations between selected pesticide compounds and apparent recharge date are similarly related to changing land use and chemical application. Observed trends in the two settings demonstrate the importance of considering hydrogeology and recharge date along with changing land and chemical uses when interpreting trends in regional ground-water quality.

Eutrophication in Portuguese estuaries evidenced by δ15N of macrophytes

Terrestrial inputs of nitrogen in estuaries are increasing and altering salt marsh primary production, plant communities and associated biota. We used N isotope ratios and %N in Spartina maritima, Halimione portulacoides, Zostera noltii and below-canopy sediments to study eutrophica- tion caused by anthropogenic land-derived nitrogen in the Mondego and Mira estuaries, Portugal. In spite of different land use practice intensities between estuaries, there were no marked differences in nitrate concentrations in the water column, but ammonium, total dissolved nitrogen and dissolved organic nitrogen concentrations were greater in the Mondego estuary. Sediment and shoot N con- tents suggest a general pattern of high nitrogen regimes in Mondego and Mira, and point to a some- what higher delivery of nitrogen into the Mondego. However, these parameters were not sensitive indicators of level of eutrophication. In contrast, δ 15 N ratios in plant shoots differed significantly and were higher in Mondego for all 3 plant species. Plant δ 15 N signatures were therefore more sensitive sentinels of land-derived nitrogen load. The parallel increase of δ 15 N in shoots and sediments indi- cated that both shoots and sediments followed and reflected the level of eutrophication and some larger whole estuary difference in N loads. Thus, nitrogen isotopic signatures in macrophytes and sediments were useful indicators of land-derived nitrogen in estuaries.

Effects of Lumbricus terrestris L. on nitrogen dynamics beyond the burrow

The degree to which earthworms can affect the availability of plant nutrients depends on their distribution following formation in burrow soil. We conducted a mesocosm-scale laboratory experiment to test the hypothesis that anecic earthworms (those that build semi-permanent vertical burrows) can affect C and N dynamics beyond the confines of the soil immediately surrounding their burrows. Nitrate and ammonium concentrations and the rate of C mineralization were determined in burrow (defined as soil within 5 mm from the macropore wall, regardless of its origin) and bulk soil of treatments amended with Lumbricus terrestris (WORM) and in treatments containing artificial burrows (ARTF) and artificial burrows containing corn leaves (LEAF) periodically over the course of 16 weeks. Comparisons were made to soil in unamended treatments (CTRL) under two different moisture regimes, WET and DRY, during the course of the experiment. Nitrate concentration was significantly higher in WORM and LEAF bulk soil than in CTRL soil, but only under WET conditions. Differences in nitrate concentrations appeared after incubation for 5 weeks and persisted for 11 weeks. Ammonium concentration and C mineralization in bulk soil were not significantly different from CTRL soil for any of the treatments regardless of moisture regime, although values for both variables were significantly higher in burrow than in bulk soil in WORM and LEAF treatments. Anecic earthworms can enhance nitrate concentrations in soil beyond the confines of the burrow, a process that appears to be facilitated with increased soil moisture.

Statistical Analysis of Nitrate Movement through the Soil in Central Kansas

An earlier investigation by the Kansas Geological Survey in central Kansas studied the movement of nitrate from fertilizer through soil into the groundwater. Nitrate concentrations in soil water were measured on samples collected at three locations during a three-year span, from sets of lysimeters buried at different depths. Although patterns seemed apparent in the resulting measurements, no statistical analyses were performed to test their significance; this re-study of the data uses analyses of variance to test for differences in nitrate concentration attributable to time and to depth in the soil. The mean nitrate concentration of samples collected in the first year of the experiment was significantly higher than the means of second and third year samples at all three locations, perhaps reflecting the confounding influence of a previous flooding experiment. ANOVAs of depth across years determined few significant differences in nitrate concentration with depth. The wintertime gap in measurements and unequal sampling through time precludes formal time-series analyses, but graphs of concentration versus time show that peak concentration occurs at later times with increasing depth, and that maximum concentration decreases with depth. These statistical analyses support the conclusions from the original investigation.

The effect of different factors on the content of nitrate in some potato varieties

The ability for nitrate accumulation in potato tubers as affected by mineral fertilisation (N, K2O and MgO), genotype and the site of cultivation was studied in a three-year-long field experiment. Fertilisation with potassium chloride and potassium sulphate increased nitrate concentration in the tubers while additional magnesium fertilisation reduced nitrate concentration. Significant differences in nitrate concentrations were observed in potato tubers depending on genetic conditions as well as on the cultivation location (with the same soil and climatic conditions, varieties and tillage). The nitrate content decreased as the result of storage at 4 °C. Concentration of these ions in tubers of table and industrial potatoes did not exceed Acceptable Daily Intake level determined by WHO.

Seasonal variations and mechanisms of groundwater nitrate pollution in the Gaza Strip

Nitrate represents one of the major pollutants of groundwater in the Gaza Strip. Several cases of blue babies disease were reported in the last couple of years. The present study is an investigation of the seasonal variations in nitrate concentration to better understand the mechanisms and parameters controlling this perilous pollutant. Nitrate was analysed in 100 wells (47 agricultural and 53 domestic) in five governorates. The results showed that 90% of the tested wells have nitrate far beyond the allowed values set by the World Health Organization (WHO). The average concentration of nitrate in domestic wells is 128 mg/L in June-July and 118 mg/L in Jan-Feb, and for the agricultural wells, the average is 100 mg/L in June-July, and 96 mg/L for Jan-Feb. The results suggest that the seasonal differences in nitrate concentrations of the domestic wells are slightly more observable than those of the agricultural wells. The environmental factors that control nitrate in groundwater are: a partially-confined aquifer, lack of a sewage system, population density, the presence of refugee camps, the presence of fertilizers and the annual rain. The variations in nitrate concentration of the domestic wells are not of considerable values. It is suggested that concrete policies in pollution control and/or prevention measures could be formulated upon better understanding of the environmental factors.

Study of sugarbeet genotype response to nitrogen nutrition using leaf analysis

Nitrogen rates and NPK ratios applied in the study had different effects on total nitrogen and nitrate contents in the laminas and petioles of the studied sugarbeet genotypes. Amount of nitrates, especially in the petioles can be considered the most reliable indicator for determining sugarbeet plant supply with nitrogen. Differences in nitrate content found among the genotypes indicate the necessity of knowing the genetic specificity in nitrogen nutrition for individual genotypes.

Rainwater chemical composition at the end of the mid-summer drought in the Caribbean shore of the Yucatan Peninsula

Rainwater was sampled at Puerto Morelos in the Caribbean coast of the Yucatan Peninsula during two sampling periods: from 27 August to 6 September 2000 (at the end of the summer drought), and from 7 to 27 September 2000 (just after the summer drought). Rainwater chemical composition (except nitrate concentration) was similar to that observed in other regions in the Caribbean Sea. Sodium and magnesium presented the highest average concentrations, sea-salt aerosols being almost the unique source, of 91% and 95%, respectively. Excess potassium, calcium and sulfate originated from non-sea-salt sources. Excess sulfate concentration was 0.65 mg l −1, which agrees with the background concentration of 0.48 mg l −1, as it was expected. However, rainwater nitrate concentration was much higher than that observed in the rest of the Caribbean Sea region. Nitrate concentration was as high as nearly 20 times the background value of 0.155 mg l −1. According to wind data analysis, only nitrate concentration depended on wind direction. Nitrate concentration peaked when wind blew from the Yucatan Peninsula, and it was higher when forest fires were spotted, therefore forest fires must have been the main nitrate source during the dry period. Forest fires emit nitrogen oxides that are rapidly converted to HNO 3. This was strongly supported by the fact that the lowest pH value (3.48) was measured in the rainwater sample with the highest nitrate concentration (4.51 mg l −1), and that 80% of the rain samples presented pH values below 5.6. Also, there was a significant difference in nitrate concentrations between the dry and humid periods, whereas the rest of the ionic species did not present significant differences. However, nitrate concentration was still higher than in other Caribbean regions during the humid period, suggesting that other sources are important too. These sources could not be identified.

Long‐term disadvantages of selective root placement: root proliferation and shoot biomass of two perennial grass species in a 2‐year experiment

Summary The long‐term benefits of root foraging in heterogeneous environments are unclear. The short duration of many previous studies may have overlooked the effects of patch depletion and root turnover, which may limit the long‐term rewards of root foraging for perennial plants. The benefits of root foraging were investigated for Holcus lanatus and Nardus stricta over two growing seasons. Shoot biomass of each species was measured in homogeneous nutrient‐rich and nutrient‐poor treatments and in a heterogeneous treatment consisting of a nutrient‐rich and a nutrient‐poor side, at a high and a low overall level of nutrient availability at the same patch contrast. Large initial differences in nitrate concentrations in the soil solution between the soil types disappeared so that, after several months, nitrate levels were low in all soil types. In heterogeneous treatments, Holcus was able to proliferate roots in the nutrient‐rich side compared with the nutrient‐poor side, but only at the high overall level of nutrient availability. Nardus did not selectively place roots in the nutrient‐rich side of the heterogeneous treatment at either nutrient level. Root longevity, as determined by minirhizotron observations, revealed that roots of Holcus tended to be shorter lived than those of Nardus, and to live longer in nutrient‐poor soils. Initially, Holcus produced more shoot biomass in the heterogeneous treatments, at both overall levels of nutrient availability, than expected from values in the homogeneous treatments, but this advantage disappeared by the end of the first growing season and, after 2 years, shoot biomass in the heterogeneous treatments was much less than expected. At the high overall level of nutrient availability, Holcus shoot biomass was not significantly greater than that produced in the homogeneous nutrient‐poor treatment. In contrast, shoot biomass of Nardus in the heterogeneous treatment was similar to the expected value, both after the first and second growing seasons. For Holcus, fast root proliferation and presumably a high nutrient uptake resulted in increased shoot biomass in the short term, but this was then curtailed by rapid patch depletion and high losses due to a limited root life span. We discuss the implications for the long‐term rewards of root proliferation in perennial species of heterogeneous environments.

Application of Diatom Indices in a Planted Ditch Constructed for Tertiary Sewage Treatment in Schwaan, Germany

The present study quantified the decrease of organic and trophic pollution in a constructed wetland used for tertiary sewage treatment. Different diatom indices [the saprobic zoning system of LANGE-BERTALOT (1978, 1979), the saprobic index (SI) of ROTT et al. (1997), as well as the trophic indices of SCHIEFELE and KOHMANN (1993); KELLY and WHITTON (1995) and ROTT et al. (1999)] were tested for their effectiveness in detecting changes in water quality of highly organic and trophic waters. The saprobic zoning system detected nearly the same pollution levels as the chemical data, but the measured saprobic characteristics (e.g. TOC: Total Organic Carbon) did not correspond to significant changes in the diatom assemblages. The data suggested that the results of the saprobic zoning system were influenced by differences in nitrate concentrations. The trophic diatom indices correlated relatively well with the inorganic compound chemical data.

NITRATE IN RIVER AND SUBSURFACE DRAINAGE FLOWS FROM AN EAST CENTRAL ILLINOIS WATERSHED

The objective of this study was to quantify the effects of crop management systems on the movement of nitrate to a drinking water reservoir in a watershed with intensive row-crop agriculture and sub-surface drainage in eastern Illinois (USA). Nitrate concentrations and sub-surface tile flow were monitored for six years at fields with various tillage and cropping management practices; the eight tile systems drained areas varying from 3 to 21 ha. Nitrate concentrations were also determined at various locations along the main stream of the watershed at locations that defined watershed sizes from 6910 to 48 900 ha. Concentrations of nitrate-N in the river followed a pronounced seasonal cycle, with maximum concentrations between 10 and 15 mg/L occurring in the spring and minimum concentrations of 0 to 5 mg/L occurring in the autumn. There were no significant differences in nitrate concentrations among specific sampling locations along the river, suggesting that the entire watershed is contributing more or less equally to the nitrate load. Nitrate-N concentrations from the tile drains varied from 0 to 39 mg/L and differed among field and cropping management systems used. Seasonal variations of nitrate concentrations in tile drain effluent were not as well defined as observed in the river. Nitrate-N concentrations in tile drain effluent were higher from fields where greater amounts of nitrogen fertilizer were applied, particularly when the fertilizer was applied prior to planting. Pre-plant application systems with average nitrogen application of 107 kg-N/ha/yr yielded a mean concentration of nitrate-N of 16.8 mg/L in the tile drain outflow which was significantly greater than the mean concentration of nitrate-N of 10.2 mg/L from the side dress and manure application systems that had received an average nitrogen application of 93 kg-N/ha/yr. The mean concentration of nitrate-N in tile drain discharge from continuous grass was 1.0 mg/L. Nitrate-N losses from cropped fields ranged from 14 to 35 kg/ha/yr depending upon the management system, which were 14 to 36% of the nitrogen applied. Losses from the grassed system were 3.8 kg/ha/yr and at the most upstream river station were 11 kg/ha/yr of nitrate-N.

The Relative Merits of Monitoring and Domestic Wells for Ground Water Quality Investigations

AbstractThe results of two studios of the effect of agricultural hind use on shallow ground water quality indicate that monitoring wells may be a better choice than domestic wells for studies of pesticide occurrence or transport, or for use as early‐warning indicators of potential drinking water contamination. Because domestic wells represent the used resource, and because domestic well water may be affected by historical rather than current pesticide and land‐use practices, domestic wells would be the best choice for an investigation of drinking water quality. The key difference between the domestic and monitoring wells appears to be that the monitoring wells in this study were installed exclusively to sample the shallowest possible ground water. For these studies. 48 shallow domestic wells and 41 monitoring wells were located randomly within two land‐use settings (row crops and orchards) in an irrigated agricultural region of eastern Washington and sampled for 145 pesticides (including nine pesticide degradates) and common water quality indicators. Constructing and sampling monitoring wells required approximately four times the resources (including manpower and materials) as locating and sampling domestic wells. Sample collection and quality assurance procedures and analytical techniques were identical except that a portable submersible pump was required for monitoring wells. In both land‐use sellings, no significant difference in nitrate concentration was found between well types; however, the average number of pesticides detected per well was significantly higher (p&lt;0.05) in the monitoring wells. A greater variety of pesticides was detected in monitoring wells: many were detected only in monitoring wells. More than 60% of detections of pesticides that were found only in domestic wells were of compounds that are no longer in use. These differences in ground water quality found in this studs relate lo the depth of the well and are apparently related lo the age of ground water in the two types of wells and the greater effects of sorption, degradation, dilution, and dispersion that accompany longer ground water residence times. The decision to invest resources in monitoring wells should be made in light of the study objective and should consider these differences in results from the two types of wells as well as the relative costs.