Increase In Nitrate Concentration Research Articles

Responses of soil ammonia-oxidizing microorganisms to simulated nitrogen deposition in a natural Castanopsis carlesii forest

Subtropical region of China is one of the global hotspots receiving nitrogen deposition. Nitrogen deposition could affect the abundance and community structure of ammonia oxidizers including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and complete ammonia oxidizer (comammox Nitrospira), with consequences on soil nutrient cycling that are driven by microorganisms. There is limited understanding for the newly discovered comammox Nitrospira in the subtropical forest soils. Here, we investigated the effect of simulated N deposition on abundances of soil ammonia oxidizers in the Castanopsis fargesii Nature Reserve in Xinkou Town, Sanming City, Fujian Province, China. Soil samples were collected from the field plots which received long-term nitrogen deposition with different dosages, including: CK, no additional treatment; LN, low nitrogen deposition treatment, dosage of 40 kg N·hm-2·a-1; and HN, high nitrogen deposition treatment, dosage of 80 kg N·hm-2·a-1. After 8-year treatment, simulated N deposition decreased soil pH and organic matter content, and increased nitrate content. We failed to amplify the amoA gene of AOB in the tested soils. High nitrogen deposition increased the abundance of AOA, but did not affect the abundance of comammox Nitrospira clade A and clade B. The ratio of comammox Nitrospira to AOA decreased with N addition, indicating that N addition weakened the role of comammox Nitrospira in nitrification in the subtropical forest soils. However, there were strong non-specific amplifications for both comammox Nitrospira clades A and B, highlighting the demand for the development of high coverage and specificity primers for comammox Nitrospira investigations in the future. The abundance of comammox Nitrospira clade A was positively correlated with total nitrogen (TN) and NH4+ concentration, while that of clade B was positively associated with soil organic carbon (SOC), TN and NH4+ Concentration. Overall, our findings demonstrated that simulated N deposition increased the relative importance of AOA in nitrification in the natural Castanopsis carlesii forest soil. These findings could provide theoretical support in coping with global change and N deposition in these regions.

Femtosecond laser-induced photochemical synthesis of gold nanoparticles in nitrate solution

Femtosecond laser pulses are capable of ionizing water molecules through multiphoton absorption. The generated hydrated electron and hydrogen peroxide are responsible for the nucleation and growth of nanoparticles during a photochemical synthesis. The photochemical reduction kinetics follow an autocatalytic rate law, which is determined by nucleation rate k1 and growth rate k2. In this work, we investigated the effect of adding nitrate as electron scavenger on the laser-based photochemical synthesis of gold nanoparticle. The experiment results showed enhancements of both k1 and k2 with increasing nitrate concentration, indicating the formation of a large number of nuclei followed by fast growth process. TEM images and size distribution analysis confirmed the improved growth of gold nanoparticles. In the absence of scavenger, the gold nanoparticles produced were dominated by small particles with sizes <7 nm. Adding small amount of nitrate increased the mass fraction of larger particles (∼7–15 nm), thus tuning the average size of gold nanoparticles from 6.52 nm to 7.49 nm. Exceedingly high concentration of nitrate caused the formation of even larger particles, which connected to each other. While salt effects might interfere with both nucleation and growth process, generation of reducing species from electron scavenging reaction significantly contributed to the counterintuitive increase of nucleation rate. This study demonstrated the potential use of nitrate as a modifying agent for morphological control of gold nanoparticles.

A whole-ecosystem experiment reveals flow-induced shifts in a stream community.

The growing threat of abrupt and irreversible changes to the functioning of freshwater ecosystems compels robust measures of tipping point thresholds. To determine benthic cyanobacteria regime shifts in a potable water supply system in the tropical Andes, we conducted a whole ecosystem-scale experiment in which we systematically diverted 20 to 90% of streamflow and measured ecological responses. Benthic cyanobacteria greatly increased with a 60% flow reduction and this tipping point was related to water temperature and nitrate concentration increases, both known to boost algal productivity. We supplemented our experiment with a regional survey collecting > 1450 flow-benthic algal measurements at streams varying in water abstraction levels. We confirmed the tipping point flow value, albeit at a slightly lower threshold (40-50%). A global literature review broadly confirmed our results with a mean tipping point at 58% of flow reduction. Our study provides robust in situ demonstrations of regime shift thresholds in running waters with potentially strong implications for environmental flows management.

Fire effects on riparian vegetation recovery and nutrient fluxes in Brazilian Cerrado

AbstractFire can change gallery forest vegetation structure, thereby altering nutrient fluxes between terrestrial and aquatic ecosystems. In Brazilian savannas, which are fire‐prone ecosystems, the fire regime is changing due to human activities such as converting native vegetation to farmland and urban areas. Uncontrolled wildfires in these savannas can reach gallery forests, which are more sensitive to fire impacts, leading to concerns about the effects of fire on gallery forest vegetation structure and freshwater ecosystems. We analysed the relationships between fire severity (the degree to which the fire has changed an area), percentage of burned area, variation in precipitation with gallery forest and savanna vegetation structure recovery and input of nutrients (NH4, , and ) to streams for 16 months after a fire event in five watersheds associated with small streams. One year after the fire, vegetation recovery (NDVI) was lower in gallery forest areas than in savanna woodlands, despite the more severe fires in savannas. The short‐term effects of fire on gallery forest vegetation included increased nitrate concentrations in streams, which were also influenced by increased precipitation and the extent of the burned area. The nutrient inputs into the stream stabilized within 1 year. However, gallery forest vegetation did not fully recover at that time and may continue to alter the functioning of the aquatic ecosystem. Together, these results demonstrate the need for an integrated fire management plan that considers both gallery forests and the surrounding savannas in the landscape to address consequences to aquatic ecosystems.

Quantifying the relative contributions of aqueous phase and photochemical processes to water-soluble organic carbon formation in winter in a megacity of South China

To identify potential formation mechanisms of water-soluble organic carbon (WSOC) and quantify their contributions to WSOC in urban Guangzhou of south China, a comprehensive campaign was carried out in winter of 2019–2020. During the campaign, WSOC, total carbon (TC), black carbon (BC), water-soluble inorganic ions (WSIIs) and fourteen elements in PM2.5 were collected using inline instruments. Bulk PM2.5 and size-segregated particle samples were also synchronously collected using offline instruments for analyzing the dominant chemical components including WSOC, organic carbon (OC), elemental carbon (EC) and WSIIs. In addition, gaseous pollutants (e.g., NH3, SO2, HNO3, NO2, O3) and meteorological parameters were also measured during the same period. PM2.5 pollution episodes during the campaign period were mainly driven by increased nitrate concentrations. The mass concentration of WSOC increased from 3.9 ± 1.1 μg m−3 on non-episode days to 6.8 ± 0.6 μg m−3 on episode days, although the mass ratio of WSOC to OC in PM2.5 changed little (<4%). Photochemical processes dominated WSOC formation in the afternoon and aqueous phase chemical processes played the dominant role in the night, from which newly formed WSOC distributed in the condensation mode and the droplet mode, respectively. Source apportionment analysis using positive matrix factorization (PMF) model suggested that on average 35% and 65% of WSOC mass in PM2.5 were related with the photochemical processes and aqueous phase chemical processes, respectively. Aqueous phase chemical processes were highly affected by nitrate pollution, which was closely related with O3 pollution.

Evaluation of Compost and Soil Mix Ratios for Perennial Ryegrass Establishment on Topsoil and Subsoil

Soil degradation during construction often results in soil loss through erosion and reduced vegetation establishment. Composted organic materials are used to restore soil health of compromised urban soils when planting trees and shrubs; however, less is known about compost amendments for turfgrass establishment. The objective of this trial was to determine the effects of differing compost incorporation rates in two soil types on perennial ryegrass [PR (Lolium perenne)] establishment. The hypothesis was that as compost incorporation rates increase, turfgrass germination would increase until the compost rate becomes detrimental to turfgrass germination because of increased nitrate content and electrical conductivity (EC) levels. A salt-sensitive PR cultivar and a salt-tolerant PR cultivar were seeded into a loam topsoil and a clay subsoil at soil:compost volume ratios of 100:0, 80:20, 70:30, 60:40, 50:50, 40:60, and 0:100 using a mixed-source mature compost. Percent green cover (PGC) and leachate pH, EC, and nitrate content were measured during the 5-week establishment period. This trial showed that with a suitable topsoil, compost incorporation may be unnecessary to obtain acceptable PGC, but that compost additions (30% to 40%) to a clay subsoil achieve faster establishment while limiting the potential for reduced establishment because of increased nitrate content or EC associated with greater levels of compost incorporation. The EC or pH of soil:compost leachate was not found to predict turfgrass establishment. This trial suggests that soil type should be considered when making compost use rate recommendations; however, further research is needed to link compost physiochemical properties to compost use rates.

Nitrate adsorption onto surface-modified red mud in batch and fixed-bed column systems: equilibrium, kinetic, and thermodynamic studies.

This research aimed to develop a novel composite as a low-cost adsorbent for the removal of nitrate ion from aqueous solutions. The characterization of this composite (composition of red mud with dimethyldioctadecylammonium bromide (DDAB)) was performed by XRF, XRD, FTIR, and BET analyses. The most influential variables on nitrate adsorption, including contact time, solution acidity, adsorbent amount, and temperature were studied. The maximum amount of nitrate adsorbed onto the prepared adsorbent was obtained at pH 5.5 and contact time 30min. The heterogeneous adsorption occurred during the uptake of nitrate. The results of kinetic study revealed that intra-particle diffusion was the major limitation for nitrate adsorption rate. The values of thermodynamic parameters illustrate the non-spontaneous, associative, and exothermic adsorption process. Increasing the temperature enhances the tendency of the process to non-spontaneously. Research on fixed-bed column has been done under different initial nitrate concentrations. The adsorption capacity of nitrate was increased with an increase in the initial concentration of nitrate. The results of column data were successfully explained using the Thomas and Yoon-Nelson models.

Optimal Nitrate Supplementation in Phaeodactylum tricornutum Culture Medium Increases Biomass and Fucoxanthin Production.

Phaeodactylum tricornutum is a model diatom with numerous potential applications in the industry, including the production of high-value carotenoid pigments such as fucoxanthin. This compound is a potent antioxidant currently extracted mainly from brown macroalgae. Fucoxanthin exhibits several biological properties with well-known beneficial effects in the treatment and prevention of lifestyle-related diseases. P. tricornutum offers a valuable alternative to macroalgae for fucoxanthin production as it has a specific productivity that is 10-fold higher as compared with macroalgae. However, production processes still need to be optimised to become a cost-effective alternative. In this work, we investigated the optimal supplementation of nitrate in a cultivation medium that is currently used for P. tricornutum and how this nitrate concentration affects cell growth and fucoxanthin production. It has previously been shown that the addition of sodium nitrate increases productivity, but optimal conditions were not accurately determined. In this report, we observed that the continuous increase in nitrate concentration did not lead to an increase in biomass and fucoxanthin content, but there was rather a window of optimal values of nitrate that led to maximum growth and pigment production. These results are discussed considering both the scale up for industrial production and the profitability of the process, as well as the implications in the cell’s metabolism and effects in fucoxanthin production.

Diatoms from the Spring Ecosystems Selected for the Long-Term Monitoring of Climate-Change Effects in the Berchtesgaden National Park (Germany)

We studied diatoms from the fifteen springs selected in the Berchtesgaden National Park on behalf of the Bavarian State Ministry for the Environment to be sentinel environments of climate-change effects. For three of these springs, diatom data based on samples taken in 1997 were also available. A total of 162 species belonging to 49 genera were found sampling three microhabitat types (lithic materials, bryophytes, surface sediments). The cumulative percentage of all species included in a threat category including endangered species was 43%, confirming previous findings for comparable environments of the Alps. We could find a statistically significant positive association between the Meinzer variability index for discharge and the cumulative relative abundance of aerial diatom species. This study thus highlighted once again the relevance of discharge (and associated water-level) variability as an environmental determinant of diatom assemblages in spring ecosystems. Increased nitrate concentrations in some springs, likely due to diffuse airborne pollution and, locally, to impacts such as forest management, game, and cattle, led to a relevant occurrence of eutraphentic diatom species. Our results show a segregation of the older data in non-parametric diatom-based ordinations, suggesting a strong potential for the use of spring diatoms in studies aiming at tracking the effects of climate and environmental change.

Effects of Aeration Rates and Patterns on Shortcut Nitrification and Denitrification

The effects of aeration rates and aeration patterns on the oxidation of ammonia-nitrogen into nitrite were investigated. The influent high ammonia-nitrogen synthetic wastewater resembled to those of the catalytic process of the petrochemical refinery. The method involved the biological shortcut nitrification and denitrification lab-scale’s sequencing batch reactor (SBR) process based on intermittent aerations and aeration patterns. All the operations were carried out in a 20 L working volume SBR bioreactor, and the influent synthetic wastewater’s concentration was always 1000 mg/L ammonia-nitrogen NH4-N concentration at a C/N (carbon/nitrogen) ratio of 2.5:1. Effective shortcut nitrification to nitrite was registered at 1.1 mg-O2/L (i.e. 9 L-air/min) with 99.1% nitrification efficiency, 99.0% nitritation rate and 2.6 mg-NO3--N/L nitrate concentration. The best results with 99.3% nitrification efficiency were recorded when operating at 1.4 mg-O2/L (i.e. 12 L-air/min). According to these experiments, it results that the nitrite accumulation rate was related to aeration rate and cycle’s duration. However, at 1.7 mg-O2/L (i.e. 15 L-air/min), the system was limited by an increase in nitrate concentration with more than 5 mg/L which could be a point of reverse to conventional nitrification. The best total nitrogen (TN) removal was about 71.5%.

Understanding upper water mass dynamics in the Gulf of Mexico by linking physical and biogeochemical features

In the Gulf of Mexico (GoM), the upper 300 m of the water column contains a mixture of water types derived from water masses from the North Atlantic and the Caribbean Sea, namely Caribbean Surface Water (CSW), Subtropical Underwater (SUW), Gulf Common Water (GCW), and Tropical Atlantic Central Water (TACW). These are mainly altered by mesoscale processes and local evaporation, which modulate biogeochemical cycles. In this study, we improve our understanding of water mass dynamics by including biogeochemical data when evaluating the T-S relationship to define water-mass boundaries, particularly when the observed thermohaline characteristics overlap. The variables considered were apparent oxygen utilization (AOU), nitrate, and dissolved inorganic carbon (DIC). The data were obtained from eight cruises carried out in the central and southern regions of the GoM and an additional cruise that covered the entire coastal-ocean region. The new proposed boundaries were instrumental in clarifying the dynamics of surface waters. Of note, GCW on the western side of the GoM is not formed from the mixing of CSW and SUW but by the mixing of remnant CSW with TACW. In winter, a remnant of CSW mixed with GCW, and the biogeochemical composition of surface waters was affected, as observed from an increase in nitrate and DIC concentrations and positive AOU values. CSW was mainly detected at the surface during summer with negative AOU values, low DIC values, and almost undetectable nitrate concentrations. The presence or absence of CSW modulated the depth of the nitracline and likely influenced primary productivity.

Формирование нано- и микроструктурированных слоев серебра при термическом разложении пленки поливинилового спирта с азотнокислым серебром

The results of experimental study of morphology of silver nanostructures, which appear during thermal destruction of polyvinyl alcohol film with silver nitrate are presented. It is shown that during the increase of silver nitrate concentration the maximum size of the formed particles increases from tens of nanometers up to 2 μm, and their shape transforms from spherical to irregular. The growth of silver nanoparticles occurs at the expense of small silver nanoparticles migration on a substrate surface, their gathering near the large nanoparticles and confluence of small nanoparticles with larger ones.

Formation of nano- and microstructured layers of silver during thermal destruction of polyvinyl alcohol with silver nitrate

The results of experimental study of morphology of silver nanostructures, which appear during thermal destruction of polyvinyl alcohol film with silver nitrate are presented. It is shown that during the increase of silver nitrate concentration the maximum size of the formed particles increases from tens of nanometers up to 2 μm, and their shape transforms from spherical to irregular. The growth of silver nanoparticles occurs at the expense of small silver nanoparticles migration on a substrate surface, their gathering near the large nanoparticles and confluence of small nanoparticles with larger ones. Keywords: nanoparticle, silver, polyvinyl alcohol, morphology, absorption, luminescence .

Explaining the Variability in High‐Frequency Nitrate Export Patterns Using Long‐Term Hydrological Event Classification

AbstractRunoff events play an important role in nitrate export from catchments, but the variability of export patterns between events and catchments is high and the dominant drivers remain difficult to disentangle. Here, we rigorously asses if detailed knowledge on runoff event characteristics can help to explain this variability. To this end, we conducted a long‐term (1955–2018) event classification using hydro‐meteorological data, including rainfall characteristics, soil moisture and snowmelt, in six neighboring mesoscale catchments with contrasting land use. We related these event characteristics to nitrate export patterns from high‐frequency nitrate concentration monitoring (2013–2017) using concentration‐discharge (CQ) relationships. Our results show that low‐magnitude rainfall‐induced events with dry antecedent conditions exported lowest nitrate concentrations and loads but exhibited highly variable CQ relationships. We explain this by a low fraction of active flow paths, revealing the spatial heterogeneity of nitrate sources within the catchments and by an increased impact of biogeochemical retention processes. In contrast, high‐magnitude rainfall or snowmelt‐induced events exported highest nitrate concentrations and loads and converged to similar chemostatic export patterns across all catchments, without exhibiting source limitation. We explain these homogeneous export patterns by high catchment wetness that activated a high number of flow paths and by higher nitrate availability during high‐flow seasons. Long‐term hydro‐meteorological data indicated an increased number of events with dry antecedent conditions in summer and a decreased number of snow‐influenced events. These trends will likely continue and cause increased nitrate concentration variability during low‐flow seasons and changes in the timing of nitrate export peaks during high‐flow seasons.

IMPACT OF FOLIAR SPRAY WITH SACCHAROMYCES CEREVISIAE EXTRACT IN DIFFERENT FORMS AND CONCENTRATIONS ON GROWTH, PRODUCTIVITY AND QUALITY OF LETTUCE PLANTS

This investigation was adopted during the two consecutive winter seasons of 2019/2020 and 2020/2021, to examine the impact of foliar spray with bread yeast in different forms and concentrations on the development, production yield and quality of lettuce cv. Dark Green (Lactuca sativa L.). This experiment was consisted of twelve treatments which were the combinations between four yeast forms (untreated yeast cells, yeast extract, yeast cells treated with nitric acid 50% and yeast cells treated with urea at three concentrations (1, 2 and 3, w/v).The results showed that, foliar spraying with yeast cells treated with urea at the highest concentration 3% recorded the largest values of the height of plant, leaf area per plant, total fresh and dry weights/plant, total chlorophyll, yield and its components, N, K and dry matter percentages in lettuce leaves in both seasons, with no significant differences between foliar spray with yeast cells treated with urea or with nitric acid treatments regarding number of leaves/plant, P (%) and nitrate content. In general, foliar spraying with yeast cells treated with urea at 3% increased yield and its component but at the same time increased nitrate content in leaves and decreased the quality of lettuce plants. Accordingly, it may be prudent to avoid using a high concentration of yeast cells treated with urea, in order to preserve the quality of lettuce plants, and instead of that it can be used a medium concentration to get the best quality and reasonable yield.

Spatiotemporal variations of surface water quality in a medium-sized river catchment (Northwestern Germany) with agricultural and urban land use over a five-year period with extremely dry summers

Medium-sized rivers, which are used for intensive agriculture and urban infrastructure, are subject to manifold hydrochemical stressors. Identifying and monitoring these stressors is important for river basin management and a functioning ecosystem. To understand the spatiotemporal variation of surface water quality in a highly modified lowland river, the Münstersche Aa River (Northwestern Germany) with 62% of land used for agriculture and 26% urban/residential area, was exemplarily studied. A total of 519 samples were collected using two automated high-frequency samplers and five catchment-wide sampling campaigns. They covered the five-year period 2015–2020 and included two extremely dry summers. The Münstersche Aa catchment is dominated by low permeable strata resulting in surface water runoff (Baseflow Index: 0.41) which leads to a high amplitude of discharge variation (mean discharge: 0.7 m3/s) with high flow conditions in winter/spring, and low discharge during summer/fall. In wintertime, maximum nitrate concentrations (up to 73 mg NO3/L) and loads (up to 1300 t NO3/a; up to 98% in winter) correlate with high-flow conditions. δ18O and δ15N isotopic analysis indicated manure from farmland as the major source of nitrate whereas the impact of municipal wastewater treatment plants was neglectable. Increased nitrate concentrations are linked to the higher proportion of farmland in the upper catchment (77%) compared with the lower catchment (47%). In summertime, at extremely low flow conditions, surface water consisted of up to 100% of treated wastewater, resulting in the highest measured chloride, sodium and potassium concentrations. The river is impacted by strongly seasonal and different stressors, which can be expected to intensify with ongoing climate change. Results from this study may help to adapt monitoring schemes for the Münstersche Aa but also for other lowland streams with comparable land-use targeting the goals of the Water Framework Directive.

Environmental Assessment of Surface Water Body Quality (on the Example of the Psel River)

Purpose. To analyze the qualitative malt of the surface water body to determine changes in its ecological status. Methods. Statistical and systematic analysis of ecological status changes was performed according to the interactive map "Monitoring and ecological assessment of water resources of Ukraine" of the river Psel for 2012 - 2020 on the following indicators: nitrates, nitrites, phosphates, ammonium ions, sulfates, chlorides. Results. It was found that in the Psel River in 2019 there was a decrease in the total phosphate content from point Nr 1 to point Nr 6. At the same time, there is a significant increase near Bishkin village. The reason may be the placement of a fence post in a settlement where there are no treatment facilities. There is an increase in nitrate concentration, while in the Kaminne village and Velyka Bagachka urban-type settlement there is a decrease in nitrate concentrations, which may be associated with their consumption of phytoplankton, which should lead to increased turbidity and biological oxygen demand. The increased concentration of nitrites indicates the intensity of decomposition of organic matter, and the delay of oxidation of NO2– to NO3–, which clearly indicates the pollution of the reservoir. Nitrates and nitrites enter the water from the effluents of industrial and agricultural enterprises. The decrease in the ammonium ions concentration (the Chervone village) is most likely due to their oxidation, dissolved in water by oxygen, with the formation of nitrate ions. There is an increase in chloride content. The increase in chloride concentration near the Byshkin village and the Kaminne village is due to the pollution of surface water bodies with domestic wastewater. There is an increase in the sulfates content. For the manufacture of fertilizers or chemicals in the technological process at the enterprise sulfuric acid is used. Therefore, it can be assumed that the discharges of untreated water by the enterprise can be the reason for the increase in the content of sulfates in the river water. Conclusions. An analysis of changes in the ecological status of the Psel River on the basis of data «Monitoring and environmental assessment of water resources of Ukraine» for 2012 – 2020 was performed. It is revealed that the river Psel is under rgular technogenic impact, has a tendency to steady deterioration of its ecological condition.

Effectiveness and comparison of physical barriers on seawater intrusion and nitrate accumulation in upstream aquifers

Physical barrier is a coastal engineering widely used to prevent seawater intrusion. However, previous studies have not evaluated the combined influence of type and structure of the physical barrier on nitrate accumulation in upstream aquifers. Furthermore, the mechanisms of nitrate accumulation caused by the physical barriers are still unclear. In this study, numerical simulations were conducted to investigate the mechanisms and influence of the physical barrier on seawater intrusion and NO3− accumulation. The results show that constructing physical barrier can result in the reduction of nitrate discharge to the sea and accumulation of nitrate in upstream aquifers. The accumulation degree is significant if the barrier height is large; the barrier location is near the sea; the nitrate infiltration rate is large; the infiltration nitrate concentration is large; the inflow is weak, and the inflow DOC concentration is low. A cut-off wall is more likely to cause nitrate accumulation than a subsurface dam. It can result in mean nitrate concentration in groundwater upstream increasing by more than 30 %. Because a nitrate accumulation zone is formed behind the cut-off wall where the flow is slow and dissolved oxygen carbon is difficult to be replenished so that the denitrification is weak. Despite the subsurface dam may not result in a significant increase in nitrate concentration, it cannot be applied to the areas where SI has occurred due to the residual seawater problem. The nitrate accumulation in the upstream aquifer is a long-term process that lasts for more than three years to reach a pseudo-steady state. Seasonal variations of inflow and infiltration lead to fluctuation of mean nitrate concentration, thereby the nitrate accumulation rate increased after April and weakened between July and December.

Health risk assessment of nitrate in drinking water in Shiraz using probabilistic and deterministic approaches and impact of water supply

Increased nitrate concentration in water resources due to human activities and lack of wastewater management can affect consumers' health adversely. The objective of this study is health risk assessment of nitrate in distribution drinking water in Shiraz using probabilistic and deterministic approaches. Nitrate concentration was determined in 31 sampling sites of distribution system. N-carcinogenic human health risk as a consequence of the drinking contaminated water to nitrate was assessed in four age groups (less than 2, 2 to 6, 6 to 16, and more than 16 years). Also, health Hazard Quotient (HQ) and sensitivity analysis were investigated using the Monte Carlo simulation technique with a probabilistic approach. The lowest and highest two-year mean concentration were 2.1, 58.35 and the total two-year mean of nitrate concentration was 22.6 mg/l. Nitrate concentration was higher than standard level in grab sampling at some points. While the total mean of HQ was less than the adopted threshold in all age groups, the results showed that HQ at some sites is higher than adopted threshold level. The minimum and maximum of the HQ belonged to adults (0.22) and infants (0.8). The mean and the 90th percentile estimated HQ using probabilistic approach for infants, children, teenagers, and adults were (0.78, 1.66), (0.45, 0.0.95), (0.41, 0.86), and (0.23, 0.48), respectively. Sensitivity analysis indicated that concentration is the most effective parameter in HQ. Considering that the highest estimated HQ was related to infants and also increased nitrate concentration can have adverse health effects for this age group, it is suggested to apply management and control measures to reduce the nitrate concentration in groundwater resources with a high concentration of nitrate.

Increased nitrate concentration differentially affects cell growth and expression of nitrate transporter and other nitrogen-related genes in the harmful dinoflagellate Prorocentrum minimum

The molecular mechanisms through which dinoflagellates adapt to nitrate fluctuations in aquatic environments remain poorly understood. Here, we sequenced the full-length cDNA of a nitrate transporter (NRT) gene from the harmful marine dinoflagellate Prorocentrum minimum Schiller. The cDNA length was 2431 bp. It encoded a 529-amino acid protein, which was phylogenetically clustered with proteins from other dinoflagellates. Nitrate supply promoted cell growth up to a certain concentration (∼1.76 mM) but inhibited it at higher concentrations. Interestingly, at the inhibitory concentrations, nitrite levels in the medium were considerably increased. Nitrate concentration affected the expression of PmNRT, nitrite transporter (PmNiRT), nitrate reductase (PmNR), and nitrite reductase (PmNiR). Specifically, PmNRT was upregulated after 24 h, with ∼6-fold change compared with the control level, in both nitrate-depleted and nitrate-repleted cultures. In addition, PmNR transcript levels increased to the maximum of 4-fold at 48 h but decreased thereafter. In contrast, PmNiR levels remained unchanged in both nitrate-repleted and nitrate-depleted cultures. Therefore, P. minimum likely copes with nitrate fluctuations in its environment by regulating a set of genes responsible for nitrate uptake.