Decrease In Nitrate Concentration Research Articles

汉江上游金水河悬浮物及水体碳氮稳定同位素组成特征

Nitrogen and carbon are important elements regulating the structure and function of river ecosystems; therefore, determining their sources has important implications for integrated river basin management. Since physical processes and human activities can lead to different isotopic signatures in organic matter, the characteristics of the stable isotopes of carbon and nitrogen could be used to determine carbon and nitrogen sources in riverine systems. The upper Han River is the water source area for the Middle Route of the South-to-North Water Diversion Project (MR-SNWTP); hence, identifying pollutant origins in the riverine system is critically important for the interbasin water transfer project. In this study, we investigated the δ13C and δ15N values of particulate organic matter (POM) and δ15 N values of nitrogen including nitrate nitrogen (N-NO-3) and ammonium nitrogen (N-NH+4) to trace the sources of organic matter in the river ecosystem. The study site was the Jinshui River with a length of 87 km and drainage area of 730 km2 in the upper Han River during 2012— 2013. Furthermore, we measured chlorophyll content, turbidity, and the concentrations of N-NH+4 and N-NO-3 in the river system using YSI 6920. The results demonstrated spatial variability in POM, with higher content in the moderately disturbed zone and intensely disturbed zone than in the slightly disturbed zone. The concentration of ammonium showed seasonality with minimal concentrations (0.07 mg/ L) in the spring and maximum concentrations (0.45 mg/ L) in winter, whereas the maximum concentration of nitrate was 0.44 mg/ L in winter and the minimal value was 0.08 mg/ L in summer. The carbon isotope value of POM also showed an obvious seasonality, in decreasing order of spring, summer, winter, and fall. The turbidity reached its maximum in summer from the heavily rainfall in the same season due to the monsoon climate. The Chl/ turbidity ratio could be used to identify the contribution of algae to the total particulate organic materials in the river. Algae, which have a higher carbon isotope value (-21.18%--27.14%) than terrestrial organic matter (-27.34%--28.83%), were the main source of POM. POM with an N isotope range of -8.03%-14.5% primarily originated from soil organic matter and plankton. The dissolved nitrate with isotope ranges of -5.86%-17.20% for ammonium and -1.48%-15.86% for nitrogen in the riverine system primarily originated from precipitation, plankton, and fertilizer. Also, larger values for δ15 N-NH+4 and δ15N-NO-3 were observed in the growing season (i.e., spring/ summer), which was possibly due to the seasonally higher chlorophyll concentration (i.e., high algae density in the river). Additionally, the low nitrate stable isotope value and low concentration of ammonium and nitrate in summer were possibly due to nitrification and alga uptake in the riverine system. Moreover, microbial denitrification could increase the nitrate stable isotope value and decrease nitrate concentrations; our results showed that the maximum δ15 N value appeared in winter due to the low temperatures. The research implies that N-loading from the catchment reflects the upland land use pattern along the riverine system, and the isotopic technique could be an effective approach for quantifying pollutant sources in river systems.

Selenium fortification of hydroponically grown corn salad (Valerianella locusta)

There is increasing interest in the hydroponic technology to produce leafy vegetables for ready-to-eat salads. Optimisation of the growing system can lead to higher yield and/or improved nutritional value of the product. Selenium (Se) is an essential element for animal and humans, with quite a narrow range between deficiency and toxicity, whereas it is assumed beneficial for plants. In the present study, two cultivars (Gala and Baron) of corn salad (Valerianella locusta (L.) Laterr.) were used to test the possibility to increase Se content in the edible parts (leaves). Effects on yield, nitrate content, and accumulation of sulfur (S) and S-containing amino acids and Se and Se-containing amino acids were studied. Results showed that corn salad tolerates selenate (Na2SeO4) concentrations ranging from 10 to 40 µm in the nutrient solution, with plants accumulating Se at levels compatible with the need in human diets at 10 µm selenate. Se-treated plants showed some benefits with respect to a decrease of nitrate concentration and increase of pigment contents (chlorophylls and carotenoids). At 10 µm selenate, Se-cysteine and Se-methionine were produced, without affecting non-protein thiols or cysteine and methionine contents. At the higher Se supply, sulfate accumulated in the leaves with a parallel decrease in the amount of S-amino acids and a rise in the relative amount of Se-amino acids. Based on the chemical analyses, cv. Gala showed better tolerance than cv. Baron to moderate selenate supply (40 µm).

Enhanced heterotrophic denitrification in clay media: The role of mineral electron donors

Denitrification is expected to occur at and near the interface with clayey formations dedicated to radioactive waste disposal, due to the nitrate content in some waste canisters and the high probability of introducing denitrifiers during the operational phase. Nitrate reduction to nitrous-oxide gas by pure-strain Pseudomonas mandelii, in the presence or absence of sterilized Callovian–Oxfordian (COx) clay rock, was studied over a period of ~41.5months (1267days) by means of batch experiments. A culture medium with a similar porewater chemistry to that of COx rocks was used, supplemented with acetate and nitrate. Bacterial growth was monitored by genomic-DNA and narG-gene quantification. Nitrite accumulated in solution concomitantly with a decrease in nitrate content and the weak generation of nitrous oxide, but denitrification rates drastically decreased over the study period. Acetate was both oxidized to inorganic carbon and incorporated into biomass.The presence of solid COx particles significantly affected the geochemical reactions and particularly caused an enhanced nitrate reduction, a higher bacterial growth and the precipitation of calcium carbonate. Moreover, in the presence of COx a delay of several weeks was observed before the accumulation of nitrite in solution, leading to an imbalance between nitrate consumption and the production of nitrite, nitrous oxide and ammonium. Chemical oxidation of clay along with nitrite reduction to dinitrogen is expected to occur, explaining both the delay in nitrite accumulation and the apparent imbalance in nitrogen species. Although the electron donor of the COx oxidation was not identified, several hypotheses may be advanced, and we provide new insight into the biogeochemical and geochemical processes that may occur concomitantly at the excavation damaged interface of the clayey host rock after closure, resaturation and release of waste components in a nuclear waste repository. Because of denitrification, the oxidative impact of nitrate released from waste will diminish. However, nitrites produced through denitrification and diffusing into the rock will likely play in redox reaction via their abiotic reactivity which may occur within the compact clay formation despite a lack of space for bacterial activity.

Stimulating in situ denitrification in an aerobic, highly permeable municipal drinking water aquifer

A preliminary trial of a cross-injection system (CIS) was designed to stimulate in situ denitrification in an aquifer servicing an urban community in southern Ontario. It was hypothesized that this remedial strategy could be used to reduce groundwater nitrate in the aquifer such that it could remain in use as a municipal supply until the beneficial effects of local reduced nutrient loadings lead to long-term water quality improvement at the wellfield. The CIS application involved injecting a carbon source (acetate) into the subsurface using an injection-extraction well pair positioned perpendicular to the regional flow direction, up-gradient of the water supply wells, with the objective of stimulating native denitrifying bacteria. The pilot remedial strategy was targeted in a high nitrate flux zone within an aerobic and heterogeneous section of the glacial sand and gravel aquifer. Acetate injections were performed at intervals ranging from daily to bi-daily. The carbon additions led to general declines in dissolved oxygen concentrations; decreases in nitrate concentration were localized in aquifer layers where velocities were estimated to be less than 0.5m/day. NO3-15N and NO3-18O isotope data indicated the nitrate losses were due to denitrification. Relatively little nitrate was removed from groundwater in the more permeable strata, where velocities were estimated to be on the order of 18 m/day or greater. Overall, about 11 percent of the nitrate mass passing through the treatment zone was removed. This work demonstrates that stimulating in situ denitrification in an aerobic, highly conductive aquifer is challenging but achievable. Further work is needed to increase rates of denitrification in the most permeable units of the aquifer.

Nitrate exposure from drinking water in Denmark over the last 35 years

In Denmark, drinking water quality data covering the entire country for over 35 years are registered in a publicly-accessible database. These data were analysed to determine the fraction of population exposed to elevated nitrate concentrations. Data from 2,852 water supply areas from the 98 Danish municipalities were collected in one dataset. Public water supplies are extensively registered; private wells supplying only few households are neither monitored nor registered sufficiently. The study showed that 5.1% of the Danish population was exposed to nitrate concentrations 25 mg L−1 in 2012. Private well users were far more prone to exposure to elevated nitrate concentrations than consumers connected to public supplies. While the fraction exposed to elevated nitrate concentrations amongst public supply users has been decreasing since the 1970s, it has been increasing amongst private well users, leading to the hypothesis that the decrease in nitrate concentrations in drinking water is mainly due to structural changes and not improvement of the groundwater quality. A combination of this new drinking water quality map with extensive Danish health registers would permit an epidemiological study on health effects of nitrate, as long as the lack of data on private well users is addressed.

Close coupling of N‐cycling processes expressed in stable isotope data at the redoxcline of the Baltic Sea

AbstractOver the past decades, the hypoxic state of the central Baltic Sea has deteriorated because of eutrophication, but little is known about the extent to which related factors such as nitrogen removal have been altered. The Baltic Sea is a stratified semi‐enclosed basin with a large, anoxic bottom water mass in its central Gotland Basin and highly active microbial nitrogen transformation processes at the redoxcline, the interface between oxic and anoxic waters. In this study, we identified and quantified the dominant transformation processes of reactive nitrogen by exploiting fine resolution profiles of δ15NNO3, δ18ONO3, and δ15NNH4 through the pelagic redoxcline between 60 and 140 m. Our results showed increasing δ15NNO3 and δ18ONO3 values with decreasing nitrate concentrations, but the associated low apparent isotope effect (ε = ~5‰), as inferred from a closed system Rayleigh model, was not consistent with the high ε (~25‰) characteristic of denitrification in the water column. These findings could be explained by substrate limitation. The observed δ18ONO3:δ15NNO3 ratio of 1.38:1 rather than the usual 1:1 ratio typical for denitrification‐dominated systems could be explained by the occurrence of both nitrification and denitrification. We then developed a numeric reaction‐diffusion model, according to which a realistic denitrification rate of 14 nmol N L−1 d−1 was estimated, and a nitrification rate of 6.6 nmol N L−1 d−1 confirmed. Our study not only demonstrates the value of stable isotope data for investigating nitrogen transformation processes but also highlights that care is needed in interpreting systems with closely coupled processes such as those at ocean redoxclines.

포화층 토양미생물에 의한 하천수의 nitrate 제거: 실험실규모 컬럼 실험

대수층 함양 및 회수(Aquifer recharge and recovery)기술은 안정적으로 안전한 상수원수를 확보하기 위해 이용되는 기술의 하나이다. 이 기술을 통해 대수층에 하천수를 인위적으로 주입하여 저장하고 필요할 때 퍼 올려 상수 원수로 사용할 수 있다. 이 기술에서 주입된 물이 저장되는 동안 대수층의 토착미생물에 의해 수질이 개선되는 것을 이해하는 것은 중요하다. 그래서 본 연구에서는 실험실규모의 컬럼 반응기를 이용하여 대수층을 모사한 포화층 토양에 존재하는 미생물에 의한 <TEX>$NO_3{^-}$</TEX> 제거를 조사하였다. <TEX>$NO_3{^-}$</TEX>는 낙동강의 대표적인 무기 오염물 중의 하나이다. 낙동강 하류에서 최근 2년간 측정된 <TEX>$NO_3{^-}$</TEX> 농도 범위를 고려해서 <TEX>$NO_3{^-}$</TEX> 농도를 달리한 하천수를 반응기에 주입하였다: 5.07, 6.81, 8.27, 그리고 11.07 mg <TEX>$NO_3{^-}/l$</TEX>. 본 연구에서 사용한 다양한 <TEX>$NO_3{^-}$</TEX>농도에 상관없이 유입수가 반응기에 체류하는 동안 <TEX>$NO_3{^-}$</TEX>는 농도가 감소되어 유출수는 1.49 mg <TEX>$NO_3{^-}/l$</TEX>이하로 측정되었으며 본 실험기간 동안 평균 pH 7.98을 유지하였다. 한편 abiotic control 반응기에서는 유입수에 포함된 <TEX>$NO_3{^-}$</TEX> 농도와 유출수의 <TEX>$NO_3{^-}$</TEX> 농도는 거의 차이가 없었다. 그래서 본 실험조건하에서 반응기로 도입된 하천수의 <TEX>$NO_3{^-}$</TEX>이 포화층의 미생물에 의해 제거됨을 알 수 있었다. 본 연구에서 도출된 결과는 대수층 함양 및 회수기술에서 대수층의 미생물에 의해 수질이 개선되는 것을 이해하는 데 도움을 줄 것이다. Aquifer recharge and recovery is a technology used to ensure a stable supply of clean water. During the process, river water is injected into a soil aquifer and stored. The stored water is then recovered and used to produce drinking water. It is important to understand quality improvement of the injected water while it is stored in the aquifer. In the present study, a lab-scale column reactor containing saturated-zone soil was employed to mimic an aquifer. The reactor was used to investigate microbial removal of nitrate that is a major inorganic contaminant detected in the Nakdong River. The reactor was introduced with river water that contained nitrate at concentrations (5.07, 6.81, 8.27, and 11.07 mg <TEX>$NO_3{^-}/l$</TEX>) detected downstream of the Nakdong River in the past 2 years. The nitrate concentrations decreased during the introduced water is retained in the reactor. Effluent from the reactor contained 1.49 mg <TEX>$NO_3{^-}/l$</TEX> or less and had an average pH of 7.98 regardless of the nitrate concentrations of the influent. However abiotic control reactor showed similar nitrate-concentrations in its influent and effluent. Considering the result of abiotic control, the decreased nitrate concentration observed in the test column suggested that microorganisms in saturated-zone soil removed nitrate in the river water introduced into the reactor. Results of this study will be used to better understand microbial improvement of water quality in aquifer recharge and recovery technology.

Monitoring of in vivo manipulation of nitric oxide synthases at the rat retina using the push–pull perfusion sampling and capillary electrophoresis

Proteins play a variety of functional roles in tissues that underlie tissue health. The measurement of protein function is important to both understand normal and dysfunctional tissue states. Low-flow push-pull perfusion sampling (LFPS) has been used to collect submicroliter volumes of extracellular fluid which are well suited to capillary electrophoresis for compositional quantitative analysis. In this study, LFPS is used to deliver pharmacological agents to the in vivo retinal tissues at the probe sampling tip during sampling to measure protein function. Two native nitric oxide synthase enzymes were pharmacologically inhibited and the enzyme product NO metabolite, nitrate, was determined with capillary electrophoresis from the perfusates. LFPS delivered inhibitors including the non-selective N(G)-nitro-Larginine methyl ester (L-NAME), the nNOS selective 7-nitroindazole (7-NI), and eNOS N5-(1-imioethyl)-L-ornithine, dihydrochloride (L-NIO) were perfused to the sampling region either directly over a rat retina optic nerve head or 1-mm peripheral to the ONH. At the PONH, 65, 55 and 60% of baseline nitrate levels, respectively, were observed with inhibitor infusion. These are statistically significant (P<0.05) compared to saline drug infusion. However, infusion of the inhibitors to the ONH did lead to significant nitrate concentration decreases. This data suggests that the endogenous enzymes, nNOS and eNOS, are both spatially and functionally localized to the PONH at the in vivo rat retina.

Chloride ion as nitrification inhibitor and its biocidal potential in soils

The accumulation of chlorine ion in soils and plants due to the continued use of potassium chloride triggers a series of physiological disorders in plants and microorganisms deserving special attention. This study aimed to evaluate the inhibition potential of chloride ions added to soils as ammonium chloride (AC) and/or KCl in the reaction of soil nitrification. The experiment was conducted under laboratory conditions. The soil was incubated for 21 days at 70% of maximum water retention capacity at 25 °C. The addition of AC, combined with KCl, decreased nitrate concentration in the soil. The increase of Cl content in the soil with the use of AC resulted in an inhibition of soil nitrification. The agricultural potential of using AC as N source was shown in many crops, although, caution regarding excess is recommended, which results in a build-up of salt in the soil and causes injury to the root system and microorganisms.

Modelling green macroalgal blooms on the coasts of Brittany, France to enhance water quality management

First recorded in the 1970s, massive green macroalgal blooms have since become an annual recurrence in Brittany, France. Eutrophication (in particular to anthropogenic nitrogen input) has been identified as the main factor controlling Ulva ‘green tide’ events. In this study, we modelled Ulva proliferation using a two-dimensional model by coupling hydrodynamic and biological models (coined ‘MARS-Ulves’) for five sites along the Brittany coastline (La Fresnaye Bay, Saint-Brieuc Bay, Lannion Bay, Guissény Bay and Douarnenez Bay). Calibration of the biological model was mainly based on the seasonal variation of the maximum nitrogen uptake rate (VmaxN) and the half-saturation constant for nitrogen (KN) to reproduce the internal nutrient quotas measured in situ for each site. In each bay, model predictions were in agreement with observed algal coverage converted into biomass. A numerical tracking method was implemented to identify the contribution of the rivers that empty into the study bays, and scenarios of decreases in nitrate concentration in rivers were simulated. Results from numerical nitrogen tracking highlighted the main nitrogen sources of green tides and also showed that each river contributes locally to green tides. In addition, dynamic modelling showed that the nitrate concentrations in rivers must be limited to between 5 and 15mgl−1, depending on the bay, to reduce Ulva biomass by half on the coasts. The three-step methodology developed in this study (analysing total dissolved inorganic nitrogen flux from rivers, tracking nitrogen sources in Ulva and developing scenarios for reducing nitrogen) provides qualitative and quantitative guidelines for stakeholders to define specific nitrogen reduction targets for better environmental management of water quality.

Potassium Fertilization - An Effective Mitigator of Unused Nitrogen in Forage Sorghum

Forages tend to accumulate elevated levels of nitrate when fields are heavily fertilized with nitrogenous fertilizers or are environmentally stressed due to drought, cold, frost, hail, etc. Elevated levels of nitrate have detrimental effects on animal health and are regarded as a causative factor for several mass cattle-death incidents. It was observed that nitrate concentration in Sorghum bicolor L. obtained from local fields of Uttar Pradesh (Ghaziabad and Meerut) and Haryana (Gurgaon and Faridabad) exceeded the safe limit (2500 mg of nitrate kg-1 of fresh wt.) in a significant number of samples (31.7%) studied. Given this, the investigation was conducted in earthen pots to determine nitrate contents in 16 genotypes of S. bicolor L. A significant difference in nitrate content was observed among genotypes, many of which accumulated nitrate to toxic levels. POP-52 (V9), a high nitrate reductase (HNR) genotype and EB-15 (V7), a low nitrate reductase (LNR) genotype of sorghum were selected to study the effect of potassium (K) application on nitrate accumulation in specially designed PVC-drums. The minimum nitrate concentration (V9= 816.6 mg/kg fresh wt. and V7= 2691.8 mg/kg fresh wt.), coupled with maximum NR activity (V9= 9.916 μmol NO2 –1 h–1 g–1 fresh wt. and V7= 5.018 μmol NO2 –1 h–1 g–1 fresh wt.) were observed in 60 day old K60 treated plants. K application reduced the nitrate concentration by 35.24% in V9 and by 25.54% in V7 genotypes by increasing nitrate reductase (NR) activity by 86.23 % in V9 and lesser increase of 32.07% in V7 genotype of sorghum at 30 days. A two- fold (approx.) decrease in nitrate concentration was observed at K60 in both genotypes from 30 to 60-days-after-sowing. K application also reduced considerably the nitrate in the leachate indicating that K is effective in mitigating nitrate pollution in plants and soil. The data emphasizes the importance of K in increasing the nitrogen use efficiency and of balanced fertilization in combating the nitrate-related implications on human beings, animals and environment.

Dynamics of a cyanobacterial bloom in a hypereutrophic reservoir, Lake Chivero, Zimbabwe

Blooming and non-blooming periods between 2004 and 2006 in a hypereutrophic reservoir, where cyanobacterial blooms have previously been reported to be permanent, presented an opportunity to characterise factors that may favour cyanobacterial dominance. As a bloom developed in May 2004, a shift to dominance by Microcystis aeruginosa, similar to competitive exclusion, was observed. The period of M. aeruginosa dominance was characterised by the lowest Secchi depth and euphotic zone depth readings, and a decline of non-buoyant species because of competitive exclusion by M. aeruginosa, which reduced light availability in the water column. After the bloom collapsed, the euphotic zone depth increased, followed by the establishment of a Cryptomonas–Cyclotella phytoplankton assemblage. Cyanobacterial dominance within the phytoplankton assemblage was favoured by an extended stratification and was limited by nitrogen (mainly ammonium) availability. Other taxa were limited by light availability, as shown by their decline when M. aeruginosa dominated. The period of extended stratification, an increase in ammonium concentration and a decrease in nitrate concentration promoted dominance by M. aeruginosa.

Seasonal and inter-annual variability in nutrient supply in relation to mixing in the Bay of Biscay

A key challenge in oceanography is to capture and quantify processes that happen on short time scales, seasonal changes and inter-annual variations. To address this problem the P&O European Ferries Ltd. Ship MV Pride of Bilbao was fitted with a FerryBox from 2002 to 2010 and data returned to NOC in real time providing near continuous measurements between UK (Portsmouth) and Spain (Bilbao) of temperature, salinity, chlorophyll-fluorescence and oxygen. Additional monthly samples were collected on manned crossings. Over 6000 samples were analysed for nitrate (nitrate and nitrite) concentrations. The timing of nitrate concentration increases (with winter mixing) and decreases (with the spring bloom) are different on and off shelf and in autumn nitrate concentrations remain high on the shelf. Off shelf in the Bay of Biscay, the mixed layer depth assessed using Argo floats, was found to vary from 212m in relatively mild winters (such as 2007/2008) to 476m in cold winters (2009/2010). Years with deeper mixing were associated with an increase in nitrate concentrations in the surface waters (~3μmoll−1) and the increased vertical nutrient supply resulted in higher productivity the following spring. Bloom progression could be seen through the increase in oxygen anomaly and decrease in nitrate concentrations off shelf prior to changes further north on the shelf and phytoplankton growth was initiated as shoaling begins. The full dataset demonstrates that ships of opportunity, particularly ferries with consistently repeated routes, can deliver high quality in situ measurements over large time and space scales that currently cannot be delivered in any other way.

Model study on present and future eutrophication and nitrogen fixation in the Gulf of Finland, Baltic Sea

The response of nutrient and chlorophyll fields to climate change by the end of the twenty-first century was evaluated in the Gulf of Finland (Baltic Sea) using comparison of a hindcast simulation for 1997–2006 and future climate forcing, assuming an A1B greenhouse gas emission scenario and business-as-usual riverine nutrient load for 2090–2099. The comparison of simulated oxygen, phosphate and nitrate levels from the hindcast model with the measurements indicated a good performance of the 3D ecosystem model, except for overestimated near-bottom layer nitrates. The mean chlorophyll level was slightly overestimated by the model, whereas the variability in the surface layer chlorophyll level was well reproduced. Future projection simulations indicate no considerable changes in the upper layer oxygen concentrations compared with the hindcast simulation and observations, but deeper near-bottom layers were projected to become anoxic, causing an increase in phosphate and a decrease in nitrate concentrations in these layers. The increase in surface layer phosphate and the decrease in nitrate concentrations lead to an increase in summer cyanobacteria blooms and an increase in nitrogen fixation, which therefore led to an increase in the annual mean chlorophyll content in the upper layer.

Simulating the long term impact of nitrate mitigation scenarios in a pilot study basin

The agro-hydrological model TNT2 was used to explore for a period of 14 years (1987–2001) the likely consequences of mitigation scenarios on nitrate contamination of the stream water in a small agricultural catchment. The Best Management Practices (BMPs) historically designed and implemented in 1992 and two devised agricultural scenarios (catch crop (CC) implementation and a global reduction of N fertilizer) are evaluated in term of nitrate contamination in the environment. Two of the BMPs consist in implementing natural strips of Poplar and rye-grass strips (5 meters large) along stream and ditches and the third is a delay in the burial of wheat straws (from August to October). Simulations indicated that natural strips implementation would lead to a slight decrease of Nitrate Fluxes (NF) in river by respectively 3.3% and 6.6% for rye-grass and poplar strips: a benefit associated to the non fertilization of strips area. Denitrification has not been particularly disrupted in such areas. The delay in the burial of wheat straw in autumn decreases annual mineralization rate and annual plant uptake (by respectively 9 and 13kgNha−1y−1) but increases denitrification fluxes by 6kgNha−1y−1. This would lead to a slight decrease by 6% of NF in stream (equivalent to 3.3mgNO3−l−1) and an average decrease of the following sunflower yield by 27%. The global reduction of fertilization by 10% would decreased NF in stream by 13.8% (equivalent to 8mgNO3−l−1), with a global decrease by 8kgNha−1y−1 of plant uptake. The cumulative effect of BMPs and CC would have together lead to a decrease of nitrate concentration from 57.5 to 46.6mgNO3−l−1 reaching the UE environmental quality objectives (below 50mgNO3−l−1). Spring crops yield following CC would have been penalized and the decrease of NF is balanced by an increase of denitrification fluxes in the environment contributing to release of N2O, a greenhouse gas, into the atmosphere.

REDUCING NITRATE CONTENT IN LETTUCE BY PRE-HARVEST CONTINUOUS LIGHT DELIVERED BY RED AND BLUE LIGHT-EMITTING DIODES

Effect of pre-harvest continuous light with different red/blue ratio on photon flux density (R/B ratio) on reducing nitrate accumulation was studied by growing lettuce (Lactuca sativa L.) under continuous illumination delivered by light-emitting diodes (LEDs). Results show that nitrate concentration decreased by 1648.0–2061.1 mg kg−1 in leaf blade and 962.9–2090.3 mg kg−1 in petiole, accompanied by a dramatic increase in soluble sugar content. Compared with monochromatic red light treatment, the decrease in nitrate concentration and increase in soluble sugar content in lettuce under mixed red and blue light were more pronounced. The lowest nitrate concentration was observed in the treatment with R/B ratio of 4. It's concluded that pre-harvest exposure to 48 h continuous LED light could effectively reduce nitrate accumulation in lettuce and this process is strongly affected by R/B ratio of light. This study may provide new perspective for pre-harvest quality management of vegetable, especially in commercial leaf vegetable production under artificial lighting.

Bottle gourd rootstock-grafting affects nitrogen metabolism in NaCl-stressed watermelon leaves and enhances short-term salt tolerance

The plant growth, nitrogen absorption, and assimilation in watermelon (Citrullus lanatus [Thunb.] Mansf.) were investigated in self-grafted and grafted seedlings using the salt-tolerant bottle gourd rootstock Chaofeng Kangshengwang (Lagenaria siceraria Standl.) exposed to 100mM NaCl for 3d. The biomass and NO3− uptake rate were significantly increased by rootstock while these values were remarkably decreased by salt stress. However, compared with self-grafted plants, rootstock-grafted plants showed higher salt tolerance with higher biomass and NO3− uptake rate under salt stress. Salinity induced strong accumulation of nitrate, ammonium and protein contents and a significant decrease of nitrogen content and the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) in leaves of self-grafted seedlings. In contrast, salt stress caused a remarkable decrease in nitrate content and the activities of GS and GOGAT, and a significant increase of ammonium, protein, and nitrogen contents and NR activity, in leaves of rootstock-grafted seedlings. Compared with that of self-grafted seedlings, the ammonium content in leaves of rootstock-grafted seedlings was much lower under salt stress. Glutamate dehydrogenase (GDH) activity was notably enhanced in leaves of rootstock-grafted seedlings, whereas it was significantly inhibited in leaves of self-grafted seedlings, under salinity stress. Three GDH isozymes were isolated by native gel electrophoresis and their expressions were greatly enhanced in leaves of rootstock-grafted seedlings than those of self-grafted seedlings under both normal and salt-stress conditions. These results indicated that the salt tolerance of rootstock-grafted seedlings might (be enhanced) owing to the higher nitrogen absorption and the higher activities of enzymes for nitrogen assimilation induced by the rootstock. Furthermore, the detoxification of ammonium by GDH when the GS/GOGAT pathway was inhibited under salt stress might play an important role in the release of salt stress in rootstock-grafted seedlings.

Nitrate and nitrite in leek and spinach from Urmia district and their changes as affected by boiling

Aims: This study was carried out to determine nitrite and nitrate levels in fresh leek and spinach from different greengrocers' shops of Urmia (Iran) and then the effect of boiling and the effect of aqueous boiling pH were studied. Materials and Methods: Nitrite and nitrate content of 15 market samples of leek and spinach from Urmia region were determined by spectrophotometric method. Effect of boiling and their pH levels at home processing condition were studied. Results: Results showed that the fresh vegetables had only traces of nitrite and the level of nitrate was 36-328 ppm KNO 3 . In the most of samples, nitrite and nitrate contents in spinach were greater than in leek, but lower than standard International Organization for Standardization levels in Iran. Boiling process was carried out, according to home conditions and it caused a decrease in nitrate levels between 23% and 61% in leak and spinach samples, respectively. T-test analysis of the boiled vegetables showed a significant reduction about 75% in nitrate content (in dry weight vegetable content), in the samples, but an increase in nitrate content in the boiled water of the sample was observed. The effect pH of boiling (4-8) shows that with an increase in pH, there was a decrease in nitrate contents of boiled water. Conclusion: The experiment showed that the leek and spinach marketed in Urmia region were safe for consumption and boiling of vegetables caused the release of nitrates from vegetables to water after the cooking process. It is of particular importance not to use the vegetable cooking water for use in pureeing homemade baby foods.

A mesocosm study on biogeochemical role of rice paddy soils in controlling water chemistry and nitrate attenuation during infiltration

Rice paddies typically lie near surface water and play an important role in controlling surface water quality. To evaluate the role of rice paddy soils in determining the fate of nitrate, three different mesocosms were used in this study. Two mesocosms (M1 and M2) were covered with a rice paddy soil and the other mesocosm (M3) with a dry field soil. Rice was harvested in two mesocosms (M2 and M3) during the growing season. An amended groundwater containing high concentrations of NaNO3 and KBr was repeatedly applied to the mesocosms to infiltrate under saturated conditions. Under these experimental conditions, we monitored time-series variations of pH, Eh, DO, DOC, alkalinity and the concentrations of nitrate, bromide (as a conservative tracer) and dissolved Fe and Mn in the inflow water (flooding water just below the water/soil interface) and outflow water (drained water after infiltration through mesocosm materials) for about two months to examine the fate of nitrate. The Eh and DO data in all mesocosms showed that strong reducing conditions were rapidly and efficiently established in infiltrating waters. In the mesocosms (M1 and M2) with a rice paddy soil, dramatic decreases of nitrate concentrations were observed both in the inflow and outflow waters. Nitrate removal from the inflow waters occurs due to immobilization, while nitrate is removed during infiltration through mesocosm materials by denitrification coupled with organic carbon oxidation, as is indicated by the increases in alkalinity and dissolved Fe and Mn. Interestingly, there was no significant difference in the nitrate removal capacity between M1 (no cultivation) and M2 (rice cropping). In contrast to M1 and M2, there was no large decrease of nitrate concentrations in the inflow waters of M3 (rice cropping with a dry field soil). In addition, nitrate concentrations in the outflow waters of M3 rose steeply again after 30 days, in concert with increasing Eh and decreasing alkalinity. These observations in M3 are attributed to both the low organic carbon content and the generation of large pores by root growth, resulting in the rapid loss of denitrification capacity. This study implies that rice paddy fields play an important role in controlling (attenuate) agricultural nitrate in groundwater discharging to streams; thus, the extent of rice paddies should be carefully considered when evaluating the nitrate loads to streams via groundwater flow.

Management, regulation and environmental impacts of nitrogen fertilization in northwestern Europe under the Nitrates Directive; a benchmark study

Abstract. Implementation of the Nitrates Directive (NiD) and its environmental impacts were compared for member states in the northwest of the European Union (Ireland, United Kingdom, Denmark, the Netherlands, Belgium, Northern France and Germany). The main sources of data were national reports for the third reporting period for the NiD (2004–2007) and results of the MITERRA-EUROPE model. Implementation of the NiD in the considered member states is fairly comparable regarding restrictions for where and when to apply fertilizer and manure, but very different regarding application limits for N fertilization. Issues of concern and improvement of the implementation of the NiD are accounting for the fertilizer value of nitrogen in manure, and relating application limits for total nitrogen (N) to potential crop yield and N removal. The most significant environmental effect of the implementation of the NiD since 1995 is a major contribution to the decrease of the soil N balance (N surplus), particularly in Belgium, Denmark, Ireland, the Netherlands and the United Kingdom. This decrease is accompanied by a modest decrease of nitrate concentrations since 2000 in fresh surface waters in most countries. This decrease is less prominent for groundwater in view of delayed response of nitrate in deep aquifers. In spite of improved fertilization practices, the southeast of the Netherlands, the Flemish Region and Brittany remain to be regions of major concern in view of a combination of a high nitrogen surplus, high leaching fractions to groundwater and tenacious exceedance of the water quality standards. On average the gross N balance in 2008 for the seven member states in EUROSTAT and in national reports was about 20 kg N ha−1 yr−1 lower than by MITERRA. The major cause is higher estimates of N removal in national reports which can amount to more than 50 kg N ha−1 yr−1. Differences between procedures in member states to assess nitrogen balances and water quality and a lack of cross-boundary policy evaluations are handicaps when benchmarking the effectiveness of the NiD. This provides a challenge for the European Commission and its member states, as the NiD remains an important piece of legislation for protecting drinking water quality in regions with many private or small public production facilities and controlling aquatic eutrophication from agricultural sources.