Mean Concentrations Of NO3 Research Articles

Assessment of the water quality of groundwater in Bohai Rim and the controlling factors—a case study of northern Shandong Peninsula, north China

This study collected 184 groundwater (GW) samples from 92 wells during the dry and wet seasons, respectively to understand the hydrochemical characteristics, water quality, and risk of GW nitrate (NO3−) to human health in northern Shandong Peninsula (NSP), China. The results showed that GW in the NSP is weakly alkaline and classified as hard fresh water. The mean concentration of NO3− in GW exceeded 100 mg·L−1, total hardness exceeded 450 mg·L−1, and total dissolved solids (TDS) was less than 1000 mg·L−1. A Piper diagram showed that the water chemistry of GW in the NSP was mainly of the SO4·Cl-Ca·Mg type. A Gibbs diagram and ion ratio analysis indicated that the weathering of silicate rocks and agricultural production were the dominant factors affecting the hydrochemical characteristics of GW in the NSP, with cation exchange, dissolution of salt rock, and weathering of carbonate rock also making contributions. Na+ and Cl− in GW are significantly affected by seawater aerosols in coastal areas. During the wet season, the hydrodynamic conditions of the aquifer are improved, agricultural activities are strengthened, and GW becomes generally homogenized. The water quality index classified the GW quality of the NSP as mainly of medium quality. There was a relatively consistent spatial distribution of water quality during different periods. Water samples of poor water quality were mainly distributed in the lower reaches of the Huangshui River. In addition, total hardness and NO3− concentrations were the main variables affecting the quality of GW in the NSP. The assessment of the risk NO3− in GW in the NSP to human health through the ingestion of drinking water demonstrated a significant risk (infants > children > adults). These results indicate the need for local management measures to reduce the potential health risks of GW quality in the NSP.

Coupling stable isotopes to evaluate sources and transformations of nitrate in groundwater and inflowing rivers around the Caohai karst wetland, Southwest China

Nitrate is one of the most common pollutants in aquatic ecosystems, particularly in highly vulnerable karst aquifers. In Caohai Lake, an important karst wetland in southwestern China, karst surface water and groundwater are important recharge water sources, and nitrates flow into the wetland along with the surface water and groundwater, degrading the wetland water quality. Therefore, identifying the sources of nitrate in the surface water and groundwater in the Caohai catchment is of great significance to the protection of the wetland water environment. In this study, the nitrate concentrations, hydrochemistry and multiple stable isotope ratios (δ18O-H2O, δD-H2O, δ15N-NO3- and δ18O-NO3-) were used to identify the sources and fate of the NO3- in the groundwater and inflowing rivers around the Caohai wetland. The results showed that the NO3- concentrations in the groundwater samples from the southern side exceeded the WHO limit during the wet season, while other samples did not exceed the limit. The mean concentrations of NO3- in groundwater were higher than those in the inflowing river water, and NO3- concentrations decreased in the order of wet season>dry season>normal season in the groundwater and inflowing rivers. The hydrochemistry and multiple isotope ratios suggest that the nitrate transformation was dominated by nitrification processes, while denitrification had an influence on the transformation of NO3- (as evidenced by isotopes) in groundwater during the dry season. According to the analyses based on a stable isotope analysis in R (SIAR), sewage and manure were the main sources of NO3- in the groundwater, while sewage, manure and chemical fertilizer were the major sources of NO3- in the inflowing river water; therefore, the scientific use of farmland fertilizers and the treatment of domestic sewage should be strengthened to safeguard groundwater quality and control the NO3- concentrations in rivers.

Dual-isotope-based source apportionment of nitrate in 30 rivers draining into the Bohai Sea, north China

Excessive nitrate (NO3−) in rivers can lead to water quality deterioration, and can also be directly input into estuaries and oceans, thus posing a serious threat to the stability of their ecosystems. In this study, the concentration, isotopes and sources of NO3− in 30 rivers discharging into the Bohai Sea were comprehensively investigated. The mean concentration of NO3−-N was 2.24 ± 2.11 mg L−1, with obvious seasonal and spatial variations. In total, 104.24 kt of NO3−-N was discharged into the Bohai Sea annually, to which the Yellow River Basin and Liao River Basin made the largest contributions. The range of δ15N–NO3− was −1.1‰ to +33.2‰ (mean value, +11.4 ± 5.0‰), with no significant seasonal or spatial differences; the mean value of δ18O–NO3− was +9.4 ± 7.2‰, with much higher values seen in June. Based on the MixSIAR model, manure (24.3 ± 7.5%) and sewage (19.1 ± 14.5%) were the primary sources of NO3− in the 30 rivers, followed by NO3− fertilizers (16.3 ± 12.5%), soil N (15.5 ± 11.9%), atmospheric deposition of NO3− (13.5 ± 5.7%) and NH4+ fertilizers (11.4 ± 8.9%). This finding highlights the vital roles of sewage and manure management in riverine NO3−. Using a mathematical method, the contributions of various sources to each river were simulated. The results indicated that management of the Yellow River, Daliao River, Liao River, and Xiaoqing River is more urgently needed than that of other rivers to control Bohai NO3− pollution. We believe that this finding will provide guidance for scientific management of NO3− pollution in these 30 rivers and the Bohai Sea.

Land system transformations govern the trophic status of an urban wetland ecosystem: Perspectives from remote sensing and water quality analysis

AbstractGlobally, urban wetlands are facing immense pressure from land use land cover changes (LULCCs) and associated water quality degradation that is severely affecting the trophic status of these ecosystems. This study analyzed water quality degradation resulting from land system changes in the vicinity of Khushalsar, an urban Wetland, in Srinagar City from 1980 to 2017. The analysis of satellite data indicated that this Wetland lost ~18.1 ha from 1980 to 2017. During the same period, the urban area within the Wetland increased from 0.2% to 16.5%. The land cover changes assessed in the vicinity of Wetland indicated an increase of 119% and 62.8% in built‐up and roads respectively. The analysis of surface water quality of the Wetland showed widespread degradation. The Trophic state index ranged from 73.4 to 84.6 indicating hyper‐eutrophic waters. A snapshot of comparative water quality data from 2002 to 2018 revealed that the mean concentration of NO3−‐N increased from 219 to 433 μg L−1 and that of total phosphorus increased from 135.4 to 1,236 μg L−1 indicative of continuous nutrient enrichment. Hierarchical cluster analysis (HCA) grouped eight sampling sites into four clusters based on likeliness of water quality characteristics. Similarly, discriminant analysis showed the formation of similar patterns of clusters, corroborating the HCA. Principal component analysis suggested three principal components accounting for a cumulative variance of 90.61%. The unplanned land system changes vis‐a‐vis human‐induced water quality degradation together with the lack of a monitoring mechanism have brought the Khushalsar Wetland to its current hyper‐eutrophic state.

The influence of agriculture on the chemical composition of aerosols in the coastal zone of the Southern Baltic Sea (Gdynia)

In order to improve soil quality, size, and appearance of plants, various types of fertilizers are used in Poland. They are rich in nitrogen, phosphorus, calcium, and potassium. Plants are fertilized before sowing, during germination, and during crop growth. Such agricultural activity can have a negative effect on the chemical composition of atmospheric aerosols, which can be transported with air masses far away from the agricultural sources regions. The aim of the research was to estimate the influence of agriculture on the chemical composition of aerosols of various sizes (<0.45 to 10 µm) in the atmosphere of the coastal zone of the Baltic Sea. The samples were collected in Gdynia, from 11/05/2016 to 17/08/2016, only outside traffic hours (10:00 a.m. - 3:00 p.m.) and only when air masses were transported from over agricultural areas. Aerosols were collected using Tisch Environmental high-flow impactor. The ions (NO3?, PO43-, K+, Ca2+) were determined by Metrohm ion chromatography (881 Compact IC pro). The obtained results allowed us to conclude that the highest mean concentrations of NO3?, K+, Ca2+occurred in aerosols below 0.45 µm in diameter (0.26, 0.04 and 5.85 µg·m-3, respectively). Phosphates showed the highest average concentration (0.191 µg·m-3) in aerosols with a diameter from 1.5 to 3.0 µm. The concentration of calcium and nitrates was the highest in the days when advection from Western Kashubia was dominant. In turn, the highest concentrations of phosphates and potassium occurred on the days when air masses were transported from Vistula ?u?awy. All episodes occurred in the spring when agricultural activity related to fertilizing farmland was the highest and the average wind speed was lower than 5 m·s-1, which indicates local to the regional origin of the analyzed compounds in aerosols.

Characterizing nitrogen distribution, source and transformation in groundwater of ecotone of agriculture–animal husbandry: an example from North China

The ecological environment of the ecotone of agriculture–animal husbandry in North China is fragile and the groundwater resources are in short supply, in particular, nitrogen contamination is serious. So, the nitrogen source, distribution and transformation in groundwater need to be investigated. A case study was conducted in Tuoketuo County, Inner Mongolia. Hydro-geological, hydro-geochemical, and quality monitoring of groundwater were investigated in the study area. Altogether, 66 groundwater samples were taken with an equal number from both the unconfined and confined aquifers in the study area. The results show that the ammonium compound (NH4+) was the most prevalent species of nitrogen contamination. Both the irrigations of farmland with contaminated surface water and the excessive usage of chemical fertilizers were probably two major non-point sources of nitrogen contamination. The large-scale dairy farm effluents also play an important role in nitrogen contamination in local areas of an unconfined aquifer. The nitrogen contamination in the confined aquifer was mainly due to the leakage recharge of the contaminated unconfined water. The mean concentrations of NO3−, NO2− and NH4+ in confined aquifer were significantly lower and the areas exceeding the water quality standard were similar but smaller than those in an unconfined aquifer. The spatial distributions, migration and transformation of ammonium (NH4+), nitrate (NO3−) and nitrite (NO2−) in the investigation area were closely related to the characteristics of the groundwater flow system and the hydro-geochemical environment. In the groundwater recharge area, nitrification plays a leading role, with NO3− as the major contaminant. Along the groundwater discharge zone, the denitrification, anammox and dissimilatory nitrate reduction to ammonium (NDRA) processes may occur, causing NH4+ to become the main contaminant. The Cl– contamination was also severe both in unconfined and confined aquifers. High concentrations of NO3− and NH4+ were mainly observed in the groundwater of Ca·Mg–Cl and Na–Cl types. The background type of water for unconfined and confined aquifers was mainly Ca–HCO3. This study will provide helpful information to identify the most contaminated locations in the study area for environmental management in future and provides a reference for preserving the environment of ecologically fragile areas.

Nitrate Content in Drinking Water in Gilan and Mazandaran Provinces, Iran

Water pollution issue has become one of the most important public awareness issues. The excessive use of the fertilizers and pesticides in agriculture with the threat of the chemicals in water and crops especially in the two north provinces of Iran is a major concern of Iranian environmental scientists. This project is a trial to find out the status of nitrate content in drinking water of two great provinces in the north of Iran. The objectives of the present research: Determination the level of nitrate (mg/L) in drinking water of some agricultural and industrial cities and comparing of the probable effects of different industrial factories on the level of nitrate in drinking water of them. The tap water samples of 60 different sites from Rasht , Bandar Anzali and Talesh in Gilan province and Sari, Behshar and Amol in Mazandaran province in three consequent months in summer season (July, August and September) in 2013, were collected and by spectroscopy method were determined. There are no wastewater collection, treatment and disposal system in these cities. Sampling was replicated twice within each month at intervals of two weeks and the mean value considered as a result of one sample. To evaluate variability of nitrate content within sub-samples, five sub-samples (900 sub-samples) on the whole were analyzed separately. The mean concentrations of NO3- (mg/L) in most examined water samples were lower than acceptable ranges (NO3- ≤ 50 (mg/L) and only 11% of all samples were higher than it. A highly significant, positive correlation was found between nitrate contents of the August and September drinking water samples , compared to July ones. Results shows a significant difference between locations (p<0.03) and in the different sites as nitrate content in drinking water in industrial locations were obviously higher than other locations in the cities.

A novel spectrophotometric method for indirect determination of nitric oxide (NO) in serum

BackgroundIt is essential in clinical medicine to develop a simple and accurate analytical method for detecting nitric oxide (NO) in blood or other body fluid. In order to overcome the shortcomings of previous methods, this experiment developed a novel indirect analytical method of NO in serum. MethodsAfter nitrate was reduced by copper-coated cadmium granules, the nitrite produced was determined by diazotization of fuchsin acid and coupling to resorcinol. The maximum absorption appeared at 436nm, with which the concentration of NO can be determined indirectly. ResultsNO concentration and absorbance were linearly correlated over the concentration ranging from 0 to 198μmol/l, r=0.999. The CVs were 7.16% for within-run and 9.07% for between-run assays, respectively. The average recovery rate ranged from 90.6% to 105.2%. The mean concentration of NO3−/NO2− was 59.2±17.0μmol/l in serum of 30 normal volunteers. The serum concentration of NO3−/NO2− decreased significantly in patients with congestive heart failure (CHF) compared to the normal volunteers, P<0.05. ConclusionsThis method offers a reliable, simple, reagent safe and inexpensive analytical platform for the determination of NO in serum. Using this approach, we determined that the synthesis of endogenous NO decreased in patients with CHF.

Enhancements of major aerosol components due to additional HONO sources in the North China Plain and implications for visibility and haze

The Weather Research and Forecasting/Chemistry model (WRF-Chem) was updated by including photoexcited nitrogen dioxide (NO2) molecules, heterogeneous reactions on aerosol surfaces, and direct emissions of nitrous acid (HONO) in the Carbon-Bond Mechanism Z (CBM-Z). Five simulations were conducted to assess the effects of each new component and the three additional HONO sources on concentrations of major chemical components. We calculated percentage changes of major aerosol components and concentration ratios of gas NOy (NOyg) to NOy and particulate nitrates (NO3−) to NOy due to the three additional HONO sources in the North China Plain in August of 2007. Our results indicate that when the three additional HONO sources are included, WRF-Chem can reasonably reproduce the HONO observations. Heterogeneous reactions on aerosol surfaces are a key contributor to concentrations of HONO, nitrates (NO3−), ammonium (NH4+), and PM2.5 (concentration of particulate matter of ⩽2.5 μm in the ambient air) across the North China Plain. The three additional HONO sources produced a ∼5%–20% increase in monthly mean daytime concentration ratios of NO3− /NOy, a ∼15%–52% increase in maximum hourly mean concentration ratios of NO3−/NOy, and a ∼10%–50% increase in monthly mean concentrations of NO3− and NH4t+ across large areas of the North China Plain. For the Bohai Bay, the largest hourly increases of NO3− exceeded 90%, of NH4t+ exceeded 80%, and of PM2.5 exceeded 40%, due to the three additional HONO sources. This implies that the three additional HONO sources can aggravate regional air pollution, further impair visibility, and enhance the incidence of haze in some industrialized regions with high emissions of NOx and particulate matter under favorable meteorological conditions.

Relationship between catchment characteristics and nitrogen forms in Cao-E River Basin, Eastern China

The distribution of different nitrogen forms and their spatial and temporal variations in different pollution types of tributaries or reaches were investigated. Based on the catchments characteristics the tributaries or reaches can be classified into 4 types, including headwater in mountainous areas (type I), agricultural non-point source (NPS) pollution in rural areas (type II), municipal and industrial pollution in urban areas (type III), and combined pollution in main stream (type IV). Water samples were collected monthly from July 2003 to June 2006 in the Cao-E River Basin in Zhejiang, eastern China. The concentrations of NO3(-)-N, NH4(+)-N, and total nitrogen (TN) were measured. The mean concentrations of NO3(-)-N were decreased in the sequence type IV > type II > type I > type I, whereas, NH4(+)-N, total organic nitrogen (TON), and TN were in the sequence: type III > type IV > type II > type I. In headwater and rural reaches, CNO3(-)-N was much higher than CNH4(+)-N. In urban reaches, TON and NH4(+)-N were the main forms, accounting for 54.7% and 32.1% of TN, respectively. In the whole river system, CNH4(+)-N decreased with increasing distance from cities, and CNO3(-)-N increased with the increasing area of farmland in the catchments. With increased river flow, CNO3(-)-N increased and CNH4(+)-N decreased in all types of reaches, while the variations of CTON and CTN were different. For TN, the concentration may be decreased with the increase of river flow, but the export load always increased.

Seasonality and controls of phytoplankton productivity in the middle Cape Fear River, USA

Our 1 year study was aimed at assessing seasonal patterns and controls on phytoplankton primary production (PPR) and biomass (chlorophyll a) in a fourth order section of the middle Cape Fear River in North Carolina, USA, and to determine the impact of three low-head lock and dam (LD) structures on these variables within the 70 km study reach of this coastal river. Mean concentrations of NO3 −–N, NH4 +–N and soluble reactive phosphorus (SRP) averaged 52.9, 6.0, and 3.6 μmol l−1 in monthly sampling, while the average light attenuation coefficient was 2.4 m−1. The average euphotic depth was 2.1 m. Nutrient concentrations and attenuation coefficients were not significantly different above versus below each LD, or along the entire study reach. Significantly higher concentrations of dissolved O2 below versus above each LD were attributed to re-aeration during spillway transit. No seasonal pattern in physicochemical properties was apparent. Phytoplankton chlorophyll a concentrations ranged from <1 to 36 μg l−1, while rates of primary production ranged from 18 to 2,580 mg C m−2 day−1, with values for both variables peaking in the spring and early summer. Chlorophyll a and primary productivity values were consistently higher above versus below each LD in May and June suggesting a seasonal effect, but values were otherwise similar such that overall means were not significantly different. Several factors point to light as the primary control on phytoplankton in the middle Cape Fear River: high nutrient concentrations; a low ratio of euphotic : mixing depth (0.46); progressive increases in chlorophyll a and radiocarbon uptake in all treatments in quarterly nutrient enrichment bioassays conducted at levels of irradiance elevated relative to in situ river values; and consistently low quarterly values of $$ P^{{\text{B}}}_{{\text{m}}} $$ (maximum rate of chlorophyll-normalized C uptake; ≤3.7 mg C mg chl a−1 h−1) and I k (light saturation parameter; ≤104 μmol photons m−2 s−1) for photosynthetic light–response (P–I) curves.

ATMOSPHERIC NITROGEN DEPOSITION TO THE NEW JERSEY COASTAL WATERS AND ITS IMPLICATIONS

In situ measurements of atmospheric NO3− and NH4+ at Sandy Hook on the northern New Jersey (USA) coast and at Tuckerton on the southern New Jersey coast reveal significant temporal and spatial variations of these inorganic N constituents. The mean concentration of NO3− in precipitation was higher at Sandy Hook (44.6 μmol/L) than at Tuckerton (29.1 μmol/L). The mean concentration of NH4+ in precipitation exhibited a similar pattern, being higher at Sandy Hook (26.3 μmol/L) than at Tuckerton (18.3 μmol/L). Aerosol NO3− and NH4+ concentrations at Sandy Hook were also higher than those at Tuckerton. On an annual basis, the total atmospheric deposition of NO3− was estimated to be 51.1 mmol·m−2·yr−1 at Sandy Hook and 32.9 mmol·m−2·yr−1 at Tuckerton. For NH4+, the total atmospheric deposition was 32.8 mmol·m−2·yr−1 at Sandy Hook and 20.3 mmol·m−2·yr−1 at Tuckerton. Wet deposition accounted for up to 89% of the total NO3− deposition and 76–91% of the total NH4+ deposition on the New Jersey coast.By comparison, NO3− and NH4+ concentrations are relatively low in estuarine waters of New Jersey. The annual mean NO3− concentrations recorded in surface waters of the Mullica River–Great Bay Estuary near the Tuckerton atmospheric site during the 2002–2004 period were as follows: 12.1 μmol/L for the upper estuary, 4.5 μmol/L for the mid‐estuary, 2.5 μmol/L for the lower estuary, and 1.2 μmol/L for the bay inlet area. The annual mean NH4+ concentrations in these waters were as follows: 1.5 μmol/L for the upper estuary, 3.8 μmol/L for the mid‐estuary, 3.8 μmol/L for the lower estuary, and 2.4 μmol/L for the bay inlet area. In the Barnegat Bay–Little Egg Harbor Estuary, the mean concentrations of NO3− plus NO2− were &lt;4 μmol/L. In this system, atmospheric deposition accounts for ∼39% of the total N load. These results suggest that atmospheric deposition appears to be an important pathway of new N inputs to New Jersey coastal waters and a potentially significant N enrichment source for biotic production.

Impacts of changing climate and atmospheric deposition on N and S drainage losses from a forested watershed of the Adirondack Mountains, New York State

AbstractBiogeochemical responses to changing climate and atmospheric deposition were investigated using nitrogen (N) and sulfur (S) mass balances, including dry deposition and organic solutes in the Arbutus Lake watershed in the Adirondack Mountains, New York State. Long‐term monitoring of wet‐only precipitation (NADP/NTN, 1983–2001) and dry deposition (AIRMoN, 1990–2001) at sites adjacent to the watershed showed that concentrations of SO42− in precipitation, SO42− in particles,and SO2 vapor all declined substantially (P&lt;0.005) in contrast to no marked temporal changes observed for most N constituents (NH4+ in precipitation, HNO3 vapor, and particulate NO3−), except for NO3− in precipitation, which showed a small decrease in the late 1990s. From 1983 to 2001, concentrations of SO42− in the lake outlet significantly decreased (−2.1 μeq L−1 yr−1, P&lt;0.0001), whereas NO3− and dissolved organic N (DON) concentrations showed no consistent temporal trends. With the inclusion of dry deposition and DON fluxes into the mass balance, the retained portion of atmospheric N inputs within the main subcatchment increased from 37% to 60%. Sulfur outputs greatly exceeded inputs even with the inclusion of dry S deposition, while organic S flux represented another source of S output, implying substantial internal S sources. A significant relationship between the annual mean concentrations of SO42− in lake discharge and wet deposition over the last two decades (r=0.64, P&lt;0.01) suggested a considerable influence of declining S deposition on surface water SO42− concentrations, despite substantial internal S sources. By contrast, interannual variations in both NO3− concentrations and fluxes in lake discharge were significantly related to year‐to‐year changes in air temperature and runoff. Snowmelt responses to winter temperature fluctuations were crucial in explaining large portions of interannual variations in watershed NO3− export during the months preceding spring snowmelt (especially, January–March). Distinctive response patterns of monthly mean concentrations of NO3− and DON in the major lake inlet to seasonal changes in air temperature also suggested climatic regulation of seasonal patterns in watershed release of both N forms. The sensitive response of N drainage losses to climatic variability might explain the synchronous patterns of decadal variations in watershed NO3− export across the northeastern USA.

Detection of nitrate leaching through bypass flow using pan lysimeter, suction cup, and resin capsule

We compared the use of mixed-bed ion exchange resin capsules (RC), suction cups (SC), pan lysimeters (PL), and subsurface drainage (DR) for the detection of nitrate movement through a clayey soil where onion (Allium cepa L.) had been cultivated over a period of seven months. At the topsoil level, solutions collected with SC showed higher concentrations of NO3 − than the PL-collected samples. At 80-cm depth, however, the concentrations of NO3 − were higher for the DR and PL samples than for the SC samples, suggesting that bypass or macropore flow was the primary mechanism of NO3 − transport to subsurface drainage or groundwater, while solutions collected by SC mostly represented solutions inside soil aggregates. The use of the resin capsule method resulted in higher values of NO3 − at 15- than at 50-cm depth initially but the trend was reversed after sufficient leaching and plant uptake. High and significant correlations were obtained between the amount of NO3 − adsorbed on RC at 15-cm depth and the mean concentration of NO3 − in the DR samples during the RC installation period and between the NO3 − adsorbed on RC at 50-cm depth and the mean NO3 − concentration of PL samples at 80-cm depth. Such results indicate that the RC method which enables the detection of nitrate transport via macropore flow is a promising technique for nitrate leaching measurements.

Mineralisation of nitrogen in a chronosequence of rehabilitated bauxite mines

Mine site rehabilitation should aim to establish quickly and maintain the processes of nutrient cycling at rates comparable with, or approaching, those of native forests. Current management strategies for rehabilitating bauxite mines and other mine sites in Australia usually include planting fast-growing understorey species at high densities and applying fertiliser. We provide the first detailed study of nitrogen (N) availability and N transformations (mineralisation/immobilisation) in such rehabilitated mine sites. Mean concentrations of NO3– (0–5 cm) in a chronosequence (7, 13, 22, and 27 years old) of rehabilitated mine sites ranged from 0.5 to 1.3 kg/ha, and NH4+ from 4.0 to 9.5 kg/ha. In burnt and unburnt native jarrah (E. marginata Donn ex. Smith) forests adjacent to the mine site, mean NO3– concentrations in surface soil (0–5 cm) were 0.8 kg/ha (burnt) and 1.1 kg/ha (unburnt), and mean NH4+ concentrations were 6.8 kg/ha (burnt) and 7.8 kg/ha (unburnt). Concentration of NH4+ at 0–5 cm was strongly related to soil water content (R2 = 0.69, P &lt; 0.05) in rehabilitation sites, but not at 5–10 cm depth. Rates of N mineralisation (0–5 cm) in rehabilitation sites ranged from 34 to 52 kg/ha.year, of the same order as rates in native forest soil. In all rehabilitation and native forest sites, rates of N mineralisation were significantly related to rates of N-uptake at both 0–5 and 5–10 cm depth (R2 &gt; 0.63, P &lt; 0.05). Soil C/N ratios (0–5 cm) in rehabilitation sites ranged from 22.4 to 38.8, and in native forests from 35.6 (burnt) to 40.3 (unburnt). Soil C/N ratios increased with depth in both rehabilitation and native forest sites (ranged from 31.2 to 51.6). Availability of water was the major determinant of nitrogen availability in this strongly Mediterranean climate.

Chemical and isotopic profiles from snow pits and shallow firn cores on Campbell Glacier, northern Victoria Land, Antarctica

The chemical (Na+, K+, Mg2+, Ca2+, CH3SO3 − (MSA), Cl− , NO3 − , SO4 2-) and isotopic (δl8O) composition of snow and firn samples from Campbell Glacier, northern Victoria Land, Antarctica, was studied to evaluate the accumulation rate of snow and to investigate the chemical contribution from some emission sources (marine biogenic activity, sea and crust). During the 1994-95 Italian Antarctic Expedition, snow and firn were collected from snow pits and from cores obtained from drilling at three sites (A: 74°41'S, 164°30' E; B: 74°15' S, 164° '04' E; C: 73°45' S, 163°20' E), located ai 50 m (on the floating glacier tongue), 800 m and 1580 m a.s.l., respectively. The mean concentration of sea salt decreased with increasing distance from the coast and with altitude. Generally, the Na+/K+ and Na+/Ca2+ ratios were much lower than the bulk sea-water ratios at sites B and C. The MSA showed mean concentrations (0.27 and 0.17 ¿teq 1 at sites B and C, respectively) consistent with data obtained from other Antarctic sites. The mean concentrations of NO3 ranged from 2.1 μeq 1−1 (site A) to 0.97 μeq1 1 (site C).The mean nss (non-sea-salt) SO4 2-/SO4 2- ratio was -0.055,0.54 and 0.42 at sites A, B and C, respectively. Moreover, the relationship between a2+, nssCa2+, SO4 2- and nssSO4 was quite different at sites B and C. in order to expla in the relationships between the elements and compounds studied at these sites, chemical fractionation and/or reactions inside air masses and différent origin of the air masses at the two sites should be considered. A comparison of the isotopic and chemical profiles was carried out in order to provide a more reliable chronological scale. The chemical and δ18O seasonal variations recorded along the firn cores from the upper site of Campbell Glacier seem to be fairly homogeneous. This made it possible to identify many annual cycles (14-18 years for the 7 m firn core). Using the measured density values, the accumulation rale was also calculated for lower and upper Campbell Glacier. It did not appear to differ between the two sites (150-170 kg m −2a−1 at site B and 140-180 kg m−2a−1at site C) and is in keeping with rates calculated previously for the same area.

The extent of snowpack influence on water chemistry in a North Cascades Lake

Integrated snowpack samples and lakewater samples were collected from a low‐alkalinity watershed in the North Cascades in 1984 and 1985 and analyzed for inorganic chemical parameters. Mean concentrations of NO3− and SO4−2 from North Cascades snowpack were near 4.5 and 5.5 μeq L−1, respectively. Mean pH was 5.2–5.3. During melting, anion levels in the snowpack decreased and pH increased. By July, mean NO3− and SO4−2 concentrations were 0.32 and 1.73 μeq L−1, respectively, and mean pH was 5.48. Acid neutralizing capacity at the lake outlet during snowmelt was diluted to 50% of April premelt values. During snowmelt runoff there was no apparent neutralization of bicarbonate by strong acids. By comparing lakewater NO3− concentrations to snowpack concentrations, over 75% of the NO3− in the lake could be attributed to a snowpack source. An estimated 30% of the SO4−2 in the lake was derived from the snowpack.

Temporal evolution of nitrogen compounds in Swedish precipitation since 1955

Nitrate (NO3−) and ammonium (NH4+) ions are important determinants of the ionic strength and pH of precipitation1. The deposition of these ions on vegetation and on the ground also constitutes a significant source of nutrients for plants. This is particularly the case in polluted regions, for example, Europe, where the deposition of nitrogen compounds is enhanced2. There are indications (for example, increased run-off of nitrogen3) that forests in some parts of Europe have reached saturation levels with respect to nitrogen deposition; and excessive wet and dry deposition of nitrogen compounds has been suggested as a possible cause of the extensive damage to forests in Europe4. Data from Rothamsted, UK, indicate that the mean concentration of NO3− in precipitation doubled between the 1850s and I960 (ref. 5); similarly, the NH4+ concentration probably increased between the 1880s and 1960. A review of precipitation chemistry data from Europe indicates an approximately threefold increase in NO3− deposition between the 1890s and the late 1970s6. The present analysis of data from the European Air Chemistry Network reveals that the NO3− concentration at most stations approximately doubled between the late 1950s and early 1970s, with a less pronounced increase in NH4+. Detailed analysis of data from 12 Swedish stations showed no further increase of NO3− or NH4+ between 1972 and 1984. In contrast, the sulphate concentration decreased by ∼30% for the same locations and time period.

Transport of ammonium- and nitrate-nitrogen in surface runoff from pasture as influenced by urea application

The effect of a surface application of urea on the transport of N in surface runoff from permanent pasture in New Zealand was investigated under natural rainfall conditions. Maximum concentrations of NH4− N(3.6 mg l−1) and NO3−N(4.5 mg l−1) in surface runoff were attained 3 and 1 week, respectively, following urea application (60 kg N ha−1). Amounts of NH4−N, NO3−N, and total N transported in surface runoff from unfertilized (1.58, 0.52, and 4.73 kg ha−1 yr−1, respectively) and fertilized pasture (1.74, 1.09, and 8.96 kg ha−1 yr−1)were less than inputs in precipitation (2.09, 3.63, and 10.9 kg ha−1 yr−1), respectively. Amounts of NH4−N, NO3−N, and total N transported in surface runoff were only 0.3, 1.0, and 7.1 % of that applied. The mean annual concentration of NH4−N (0.9 mg l−1) in surface runoff from unfertilized pasture was above the recommended levels for drinking water (0.5 mg l−1) and the mean concentration of NO3−N (0.5 mg l−1) was greater than levels associated with accelerated cutrophication (0.3 mg l−1 ). The practicality of attaining or maintaining N concentrations in surface runoff from fertilized agricultural land below recommended levels is questioned.

Losses of Nitrogen in Surface Runoff in the Blackland Prairie of Texas

AbstractOur objective in this study was to determine NO3−‐N and total N losses in surface runoff from Houston Black clay, a swelling clay soil with a relatively low infiltration rate. The study was carried out on duplicate 4‐ha watersheds cropped to a rotation of grain sorghum (Sorghum bicolor [L.]), cotton (Gossypium hirsutum [L.]), and oats (Avena sativa [L.]), all fertilized at recommended rates of N application. The loss of NO3−‐N varied considerably during the study, depending on events before each runoff‐producing storm. Concentrations of NO3−‐N were usually highest just after fertilizer application when the soil was near field capacity and lowest when large amounts of water infiltrated into dry soil immediately before runoff. During runoff‐producing storms just after fertilizer application, the concentrations were lowest in the initial runoff and highest near the end of the runoff event. To compute NO3−‐N losses with reasonable accuracy on these soils, the shape of the entire NO3−‐N concentration curve needed to be well defined.In general, the results of this study indicate that a small and probably insignificant amount of N is lost to surface waters when crops are fertilized at recommended N rates in the Texas Blackland Prairie. For the entire 5‐year study, the mean concentration of NO3−‐N in runoff was 2.9 and 2.3 ppm NO3−‐N for the duplicate watersheds. The mean total loss of NO3−‐N was 3.2 kg ha−1 year−1. Losses of sediment associated N were about 5 kg N ha−1 year−1.