Main Sources Of Nitrate Research Articles

Eutrophication patterns in an eastern Mediterranean coastal lagoon: Vassova, Delta Nestos, Macedonia, Greece

The results of an intensive monitoring study of main eutrophication parameters in relation to fish farming management, climate and hydrography in the Vassova coastal lagoon (Nestos Delta) are presented. The overall aim is to produce basic knowledge in order to contribute to the management of eutrophication of coastal lagoons at local and national levels. Due to extensive spatiotemporal variability of the measured parameters correlation and regression polynomial analysis was used to identify patterns (p<0.05). Freshwater was the main source of nitrate and phosphate in the lagoon. This finding has justified the reduction of freshwater inflow in the past, which, however, has increased mean salinity to 30 PSU and reduced spatial salinity gradients. Maximum nitrate values in winter coincided with adverse climatic and hydrographic conditions (high precipitation, strong NE to E winds and low tide) and fish farming management that hinder water circulation. Dissolved phosphorus variability indicated the combination of the external (freshwaters) and internal (sediment) P-sources. N/P water values indicated nitrogen being the most important nutrient for primary producers throughout the year, except in winter, when phosphorus was the most important nutrient. Practical measures for improving fish farming practices to decrease “eutrophication risk” during winter are suggested. Existing nutrient data from the Vassova and from other Greek lagoons in comparison were also presented and discussed.

Modified Isotope Pairing Technique to Study N Transformations in Polluted Aquatic Systems: Theory

Denitrification of nitrate in sediments of polluted aquatic systems has the potential to release considerable nitrogen amounts into the atmosphere in the form of dinitrogen (N2) and/or nitrous oxide (N2O). Nitrate may diffuse into the anoxic sediment layer either from the oxic sediment layer (after being produced there by nitrifiers) or directly from the overlying water. Currently, the most common technique that explicitly distinguishes between the two main nitrate sources is the Isotope Pairing Technique (IPT). 15N-labeled nitrate is added to the water column, and formation of 15N labeled N2 molecules is subsequently monitored. The main shortcoming of the IPT is that the formation of N20 is ignored, thus resulting in an underestimation of sediment denitrification. Another limitation is the inability to account for a possible influx of nitrate through the hyporheic zone (e.g., nitrate-polluted groundwater) into the anoxic sediment layer. We have further developed and analyzed the theoretical basis of the original IPT. The two important factors that we took into account are the isotopic composition of N20 and the input of an external source of nitrate. We also examined the option of adding 15N-labeled ammonium to the water column to specifically adjustthe technique to field studies. The presented modified technique allows us to (i) improve the estimation of sediment denitrification capacity, (ii) gain an insight into the N20 formation mechanism(s) and fluxes, and (iii) assess inputs of nitrate-polluted water through the hyporheic zone.

Evaluating the source of streamwater nitrate using δ15N and δ18O in nitrate in two watersheds in New Hampshire, USA

AbstractThe natural abundance of nitrogen and oxygen isotopes in nitrate can be a powerful tool for identifying the source of nitrate in streamwater in forested watersheds, because the two main sources of nitrate, atmospheric deposition and microbial nitrification, have distinct δ18O values. Using a simple mixing model, we estimated the relative fractions in streamwater derived from these sources for two forested watersheds with markedly different streamwater nitrate outputs. In this study, we monitored δ15N and δ18O of nitrate biweekly in atmospheric deposition and in streamwater for 20 months at the Hubbard Brook Experimental Forest, New Hampshire, USA (moderate nitrogen export), and monthly in streamwater at the Bowl Research Natural Area, New Hampshire, USA (high nitrogen export). For rain, δ18O values ranged from +47 to +77‰ (mean: +58‰) and δ15N from −5 to +1‰ (mean: −3‰); for snow, δ18O values ranged from +52 to +75‰ (mean: +67‰) and δ15N from −3 to +2‰ (mean: −1‰). Streamwater nitrate, in contrast to deposition, had δ18O values between +12 and +33‰ (mean: +18‰) and δ15N between −3 and +6‰ (mean: 0‰). Since nitrate produced by nitrification typically has δ18O values ranging from −5 to +15‰, our field data suggest that most of the nitrate lost from the watersheds in streamflow was nitrified within the catchment. Our results confirm the importance of microbial nitrogen transformations in regulating nitrogen losses from forested ecosystems and suggest that hydrologic storage may be a factor in controlling catchment nitrate losses. Copyright © 2004 John Wiley & Sons, Ltd.

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.

Nitrate dynamics in an Alpine forest site (Mühleggerköpfl). O and N stable isotope analysis in natural water samples.

Stable isotope analysis of 15N/14N and 18O/16O-nitrate was used to investigate the nitrate dynamics and potential groundwater pollution in an Alpine forest stand in Tyrol/Austria. The dynamics of delta15-N(nitrate) values were followed in a forest ecosystem. The stable isotopic values of the throughfall are comparable with other studies. The completely decoupled dynamics of the delta15-N(nitrate) of the precipitation and the surface water was observed. High variations in delta15N-nitrate values in rainfall indicate that nitrate of different sources is deposited at that site. A significant correlation between the delta15N(nitrate) values of the surface water and soil water was obtained, while no significant correlation between the delta15N(nitrate) values of any precipitation sample with the surface water could be found. This suggests that the main source of nitrate in soil water originates from microbiological activity such as nitrification reactions and less from nitrate input by deposition. The results of delta18O(nitrate) measurements strongly supported the microbiological origin of nitrate in the surface and soil water In an additional lysimeter experiment, 15N-labelled nitrate was applied to study nitrate transport in soil. After 130 days and the collection of 300 L leachate, a total of 52% of the applied nitrate was detected in seepage water.

Limitations of using delta 18O for the source identification of nitrate in agricultural soils.

The stable isotopic composition (delta 15N and delta 18O) of nitrate was analyzed in two lysimeter field experiments in order to identify the conditions under which the dual isotope approach can be applied to identify the main source of nitrate in agricultural soils. The first field experiment involved six lysimeters beneath fields that had been fertilized for 10 yr with the same type of fertilizer (NH4NO3; delta 15N = +1.2@1000, delta 18O = +18.6@1000). The isotope ratios of NO3- in the leachate (delta 15N approximately 0@1000; delta 18O approximately +2@1000) could not be interpreted in a conventional way with either fertilizer or soil organic nitrogen as main sources. These results provided clear evidence for the microbial immobilization and subsequent mineralization and nitrification to NO3- (mineralization-immobilization turnover concept). This process masked the original oxygen isotope ratio of the fertilizer source during the summer when microbial activity was high. A second experiment involving the application of Ca(NO3)2 to three lysimeters during the winter confirmed that the dual isotope approach remains valid for the source identification of nitrate under conditions of low microbial activity. The study reveals the limitation of the dual isotope approach to characterize nitrate sources under biologically active conditions and the ability to quantify microbial processes when the main sources can be controlled.

Seasonal characteristics of the major ions in the high-accumulation Dome Summit South ice core, Law Dome, Antarctica

Seasonal cycles of the chemical species Na+, Κ+ , Mg2+, Ca2+, CH3SO3 (MSA) Cl− NO3 − and NO3 − in the Dome Summit South (DSS) ice core from Law Dome were measured for a number of epochs (AD 1809-15, 1821-31 1980-92) span-nine a total of 28 years. These preliminary trace-chemical patterns show that the DSS site is mainly affected by marine air. The main features found in the seasonal pattern of sea-salt concentrations (e.g. Na+, Cl− and Mg2+) were a winter peak and a summer minimum. The variations in sea salts are believed to reflect aerosol production and transport due to the level of storminess, and are less affected by sea-ice extent. The seasonal cycles of marine biogenic compounds, non-sea-salt SO4 2- and MSA are in good agreement. They show a characteristic summer maximum arid a winter minimum, due to variations in biological activity. While the main sources of nitrate in polar snow remain unclear, the seasonal signal, including sub-seasonal structure, at DSS resembles that found m the atmosphere at coastal Antarctic sites. However, the timing of the nitrate maximum is different in the ice-core record compared with the aerosol records. Overall, the results indicate that the DSS core, with sub-seasonal resolution, contains a sensitive record for investigating climate variability.

Seasonal characteristics of the major ions in the high-accumulation Dome Summit South ice core, Law Dome, Antarctica

Seasonal cycles of the chemical species Na+, Κ+ , Mg2+, Ca2+, CH3SO3 (MSA) Cl− NO3 − and NO3 − in the Dome Summit South (DSS) ice core from Law Dome were measured for a number of epochs (AD 1809-15, 1821-31 1980-92) span-nine a total of 28 years. These preliminary trace-chemical patterns show that the DSS site is mainly affected by marine air. The main features found in the seasonal pattern of sea-salt concentrations (e.g. Na+, Cl− and Mg2+) were a winter peak and a summer minimum. The variations in sea salts are believed to reflect aerosol production and transport due to the level of storminess, and are less affected by sea-ice extent. The seasonal cycles of marine biogenic compounds, non-sea-salt SO4 2- and MSA are in good agreement. They show a characteristic summer maximum arid a winter minimum, due to variations in biological activity. While the main sources of nitrate in polar snow remain unclear, the seasonal signal, including sub-seasonal structure, at DSS resembles that found m the atmosphere at coastal Antarctic sites. However, the timing of the nitrate maximum is different in the ice-core record compared with the aerosol records. Overall, the results indicate that the DSS core, with sub-seasonal resolution, contains a sensitive record for investigating climate variability.

Infant Methemoglobinemia in the Transylvania Region of Romania.

The incidence of infant methemoglobinemia reported in three counties of Transylvania, Romania, was evaluated from medical records, field visits, and interviews. Well water was the main source of nitrate for induction of acquired infant methemoglobinemia, which occurred post-breast-feeding when the infants consumed nitrate-contaminated water used in mixing formula. The average age of reported infants with methemoglobinemia was 39 days, supporting earlier observations that infants less than 4 months old are the most susceptible segment of the population. Vitamin C, rather than methylene blue, was the main medical intervention in the Transylvania region. The mean incidence rates of methemoglobinemia in the three counties (Saut-Mare, Mures, and Bistrita-Nasaud) ranged from 24 to 363 per 100,000 live births over a five-year period (1990-1994). These rates are below earlier reported incidence rates of up to 13% (13,000 per 100,000 live births). Three selected case reports are presented to describe hospital/clinic data, well-water data, and infant feeding practices. Recommendations for appropriate intervention programs are described. The significances of possible physical and neuropsychological effects on the development of children following methemoglobinemia are discussed and the need for further investigations is outlined.

Nitrate and nitrite in foods and the diet.

Concentrations of nitrate and nitrite have been determined in a range of foods and the dietary intake estimated from the MAFF Total Diet Study. The estimated dietary intake of nitrate ion for the UK population was 54 mg/day and the estimated dietary intake of nitrite ion was in the range 2.4-4.2 mg/day in 1985. The main source of nitrate in the diet is from the consumption of vegetables.

Diurnal variation of denitrification and nitrification in sediments colonized by benthic microphytes

Diurnal variation of denitrification in sediments with benthic microphytes was investigated by a 15N isotope-pairing technique in order to distinguish between coupled nitrification-denitrification and denitrification of nitrate supplied from the water column. Sediments were incubated in a continuous flowthrough system and exposed to diurnal light and dark cycles. Illumination of both limnetic and estuarine sediments doubled the rate of coupled nitrification-denitrification but reduced the rate of denitrification of nitrate supplied from the water column by -50%. Photosynthesis in the uppermost sediment layers during illumination led to deeper oxygen penetration and a resultant stimulation of nitrification. This stimulation may explain the increased rate of coupled nitrification-denitrification during illumination. The rate of denitrification of nitrate supplied from the water column was reduced during illumination due to a longer diffusion path between water and the anoxic denitrification zone. Denitrification, the bacterial reduction of nitrate to nitrogen gas via nitrite, is an important nitrogen sink in aquatic environments. There are two main sources of nitrate for sediment denitrification: nitrate diffusing into the sediment from the water column and nitrate produced by nitrification in the sediment (Jenkins and Kemp 1984; Seitzinger 1988). The processes of nitrification and denitrification are usually vertically separated within the sediment (Vanderborght and Billen 1975). Nitrification is strictly aerobic and therefore restricted to a thin oxic zone in the upper few millimeters of the sediment. Denitrification takes place in anoxic environments, and in many sediments, most activity is found just below the oxic-anoxic interface (Sweerts and de Beer 1989). The rates of nitrification and denitrification in the active microenvironments are controlled by the availability of substrates, which to a large extent are supplied by diffusion along

Policies to reduce nitrogen loss to water from agriculture in the United Kingdom

Water supply companies in England face increasing difficulty and costs in meeting the 50 mg l −1 nitrate limit in drinking water from groundwater sources. Some surface water abstractions also exceed the limit, but usually only in late autumn. Nitrogen-limited eutrophication is not a significant problem of estuary or coastal waters in the UK. Local problems are under investigation but the cause is rarely clear. Agricultural land is recognized as the main source of nitrate reaching ground and surface waters in the UK. Considerable research has been carried out on nitrate and farming systems. There is a substantial, ongoing government funded research programme. A significant remaining problem is the ability to relate losses from agriculture to nitrate in abstracted water or entering tidal waters. Much work remains to be done to improve our predictive ability. In 1989, the UK government set up a Pilot Nitrate Scheme. This involved ten Nitrate Sensitive Areas. These were groundwater catchments in which farmers were invited on a voluntary basis to enter into 5 year contracts with the Ministry of Agriculture, Fisheries and Food (MAFF). The basis of the agreements are that the farmer will carry out a range of modifications to current farming practice, thus reducing nitrate loss. There are also options for converting current arable to extensive grass. These areas will initially run for 5 years. In addition nine Nitrate Advisory Areas were targeted for intensive advice. In 1991, MAFF published its Code of Good Agricultural Practice for the Protection of Water. This provides guidance to farmers on the agreed balance between agricultural production and environmental protection of water which all farmers should follow. It includes a section on nitrate. In 1989, the UK government set up a Pilot Nitrate Scheme. This involved ten Nitrate Sensitive Areas. These were groundwater catchments in which farmers were invited on a voluntary basis to enter into 5 year contracts with the Ministry of Agriculture, Fisheries and Food (MAFF). The basis of the agreement is that the farmer will carry out a range of modifications to current farming practice, thus reducing nitrate loss. There are also options for converting current arable to extensive grass. These areas will initially run for 5 years. In addition nine Nitrate Advisory Areas were targeted for intensive advice.

Sources and sinks of nutrients in a New Zealand hill pasture catchment III. Nitrogen

AbstractA study was made of the nitrogen (N) inputs to, and exports from, a stream draining a pasture catchment near Hamilton, New Zealand, in order to plan measures for minimizing N losses to natural waters.An estimated 7 kg N ha−1 was exported from the catchment during 1981 of which 86 per cent was in reduced forms (Kjeldahl‐N, TKN) and the remainder as nitrate‐N (NO3‐N). Virtually all of the reduced N inputs came from saturated overland flow whereas NO3‐N inputs were dominantly subsurface derived. The TKN exported by individual storm events could be predicted (R2 = 0.97) from peak flow and from the peak flow rate in the seven days preceding the storm. A TKN balance for eight events showed that except for large floods (return period approximately a year) the stream system was a net sink for TKN. During large floods, scouring of the organic rich seepage areas resulted in the stream system itself being a net source of TKN.Microbial assays for nitrification and denitrification activity indicated that the main nitrate source was the well‐aerated greywacke and ash soils and that the permanently saturated seepage zones were a significant nitrate sink. An in‐stream nitrate addition experiment showed that up to 20mg N m−2 h−1 was removed from the stream. Simultaneous measurements of in situ denitrification activity demonstrated that only about 1 per cent of this removal could be accounted for by denitrification. It was inferred that plant uptake was responsible for the remainder.Retention of near‐stream seepage areas is suggested as a measure for minimizing NO3‐N export, whilst removal of stock from seasonally saturated areas during periods of saturatior should reduce soil loss and hence TKN inputs to the stream.

Pollution of drinking water with nitrate

The main sources of nitrate in man are food and drinking water. The legislature in West Germany intends to lower the permitted level of nitrate in drinking water from the present 90 mg/l to 50 mg/l in 1982. The European Community has issued a directive that recommends a level of only 25 mg/l, and for babies 10 mg/l nitrate should not be exceeded. At present, nitrate cannot be removed from raw water at an acceptable cost. The problem of high nitrate content is mainly one of drinking water generation from ground water. Several analyses indicate rising concentrations of nitrate in ground water in different regions of West Germany, especially in the last few years. The following sources of nitrate-contamination of ground water aquifers in West are discussed: natural sources; over-manuring of agricultural areas with natural organic fertilizers; over-manuring of agricultural areas with synthetic fertilizers.

Night-time [formula omitted] chemistry and nitrate in dew water

Night-time gas-phase chemistry and deposition of HNO 3, NO 3 and N 2O 5 to dew water have been evaluated by using a one-layer model and dew nitrate data obtained at a site on Allegheny Mountain in southwest Pennsylvania. The major source of dew nitrate is generally HNO 3 vapor generated by photochemical reactions during daylight hours. However, if N 2O 5 is deposited to dew as efficiently as HNO 3 vapor, the night-time deposition of N 2O 5 is shown to contribute significantly to dew nitrate. For a few events where the highest NO 2 concentrations (13–16 ppb) were measured, it is shown that the deposition of N 2O 5 could have been the main source of nitrate in dew water.