Mean Nitrate Research Articles

Use of food waste-recycling wastewater as an alternative carbon source for denitrification process: A full-scale study

Using organic wastes as an alternative to commercial carbon sources could be beneficial by reducing costs and environmental impacts. In this study, food waste-recycling wastewater (FRW) was evaluated as an alternative carbon source for biological denitrification over a period of seven months in a full-scale sewage wastewater treatment plant. The denitrification performance was stable with a mean nitrate removal efficiency of 97.2%. Propionate was initially the most persistent volatile fatty acid, but was completely utilized after 19days. Eubacteriacea, Saprospiraceae, Rhodocyclaceae and Comamonadaceae were the major bacterial families during FRW treatment and were regarded as responsible for hydrolysis (former two) and nitrate removal (latter two) of FRW. These results demonstrate that FRW can be an effective external carbon source; process stabilization was linked to the acclimation and function of bacterial populations to the change of carbon source.

Annual nitrate drawdown observed by SOCCOM profiling floats and the relationship to annual net community production

AbstractAnnual nitrate cycles have been measured throughout the pelagic waters of the Southern Ocean, including regions with seasonal ice cover and southern hemisphere subtropical zones. Vertically resolved nitrate measurements were made using in situ ultraviolet spectrophotometer (ISUS) and submersible ultraviolet nitrate analyzer (SUNA) optical nitrate sensors deployed on profiling floats. Thirty‐one floats returned 40 complete annual cycles. The mean nitrate profile from the month with the highest winter nitrate minus the mean profile from the month with the lowest nitrate yields the annual nitrate drawdown. This quantity was integrated to 200 m depth and converted to carbon using the Redfield ratio to estimate annual net community production (ANCP) throughout the Southern Ocean south of 30°S. A well‐defined, zonal mean distribution is found with highest values (3–4 mol C m−2 yr−1) from 40 to 50°S. Lowest values are found in the subtropics and in the seasonal ice zone. The area weighted mean was 2.9 mol C m−2 yr−1 for all regions south of 40°S. Cumulative ANCP south of 50°S is 1.3 Pg C yr−1. This represents about 13% of global ANCP in about 14% of the global ocean area.

Chemical composition of ambient PM<sub>2. 5</sub> over China and relationship to precursor emissions during 2005–2012

Abstract. In this work, we presented the characteristics of PM2. 5 chemical composition over China for the period of 2005–2012 by synthesis of in situ measurement data collected from literatures and satellite-based estimates using aerosol optical depth (AOD) data and the GEOS-Chem chemical transport model. We revealed the spatiotemporal variations in PM2. 5 composition during 2005–2012 and investigated the driving forces behind the variations by examining the changes in precursor emissions using a bottom-up emission inventory. Both in situ observations and satellite-based estimates identified that secondary inorganic aerosols (i.e., sulfate, nitrate, and ammonium; SNA) ranked as the highest fraction of dust-free PM2. 5 concentrations, followed by organic matter (OM) and black carbon (BC). For instance, satellite-based estimates found that SNA, OM, and BC contributed to 59, 33, and 8 %, respectively, of national population-weighted mean dust-free PM2. 5 concentrations during 2005–2012. National population-weighted mean PM2. 5 concentration increased from 63.9 µg m−3 in 2005 to 75.2 µg m−3 in 2007 and subsequently decreased to 66.9 µg m−3 from 2007 to 2012. Variations in PM2. 5 concentrations are mainly driven by the decrease in sulfate and the increase in nitrate. Population-weighted mean sulfate concentration decreased by 2.4 % yr−1 during 2005–2012 (from 14.4 to 12.9 µg m−3), while population-weighted mean nitrate concentration increased by 3.4 % yr−1 during 2005–2012 (from 9.8 to 12.2 µg m−3), largely offsetting the decrease in sulfate concentrations. By examining the emission data from the Multi-resolution Emission Inventory for China (MEIC), we found that the changes in sulfate and nitrate concentrations were in line with the decrease in SO2 emissions and the increase in NOx emissions during the same period. The desulfurization regulation in power plants enforced around 2005 has been the primary contributor to the SO2 emission reduction since 2006. In contrast, growth of energy consumption and lack of control measures for NOx resulted in a persistent increase in NOx emissions until the installation of denitrification devices on power plants late in 2011, which began to take effect in 2012. The results of this work indicate that the synchronized abatement of emissions for multipollutants is necessary for reducing ambient PM2. 5 concentrations over China.

Seasonal sources of carbon to the Brazilian upwelling system

Environmental heterogeneity on coastal areas is an outcome of several hydrodynamic forces. Particularly, wind-driven upwelling is usually associated with alternating periods of water mixing and stratification. In addition, the effects of near shore oceanographic conditions may vary with coastline topography and anthropogenic impacts. Herein we evaluated the seasonal differences in the hydrodynamics of the Cabo Frio upwelling system (Brazil) in function of its local bay. Surface and deep water from 5 contrasting coastal areas were sampled 13 times during the spring/summer and in the fall/winter periods to use two-way Analysis of Variance comparing the measured variables in function of season and depth. Northeastern wind was predominant during both seasons but it was more intense during the spring/summer period when water temperature was colder and concentration of nutrients peaked. Southwestern wind was more common during the fall/winter period and was associated with cold fronts that decreased water salinity inner the bay. Consequently, the concentrations of nutrients, chlorophylls, prokaryotic secondary production (PSP) as well as fluorescent and non-fluorescent particles were significantly higher during the upwelling season while the concentration of particulate organic matter (POM) was highest during the non-upwelling season. Respectively, mean nitrate concentration varied from 2.2 to 0.9 μM, ammonium from 2.7 to 1.0 μM, chlorophyll a from 2.4 to 1.4 mg m−3, PSP from 1.8 to 1.0 μgC.L−1 h−1 and POM from 2.6 to 6.4 mg L−1. Contrasting surface and deep waters, mean nitrate concentration ranged from 0.9 to 2.2 μM, POM from 4.2 to 5.2 mg L−1 and PSP from 1.9 to 0.8 μgC.L−1 h−1. Three scenarios were identified: water stratification, upwelling and water homogenization. The first two scenarios were more common outside the bay during the upwelling season. When upwelling was intense, deep water temperature in the bay dropped to less than 20 °C resulting in the stratification of water column in shallow sites. Water homogenization was common in the whole system through the non-upwelling season and was more pronounced during cold fronts. Our results evidenced a strong seasonal variation of carbon origin which was mainly associated with phytoplankton during the upwelling season and to POM during the non-upwelling season. The seasonal effect of upwelling and cold fronts on the hydrodynamics of the Cabo Frio upwelling system varied at a small spatial scale in function of site depth.

Nitrate in drinking water and vegetables: intake and risk assessment in rural and urban areas of Nagpur and Bhandara districts of India.

The study focuses on the estimation of health risk from nitrate present in the drinking water and vegetables in Nagpur and Bhandara districts in the state of Maharashtra, India. Drinking water samples from 77 locations from the rural as well as urban areas and 22 varieties of vegetable were collected and analyzed for the presence of nitrate for a period of 1year (two seasons). The daily intake of nitrate from these water and vegetable samples was then computed and compared with standard acceptable intake levels to assess the associated health risk. The mean nitrate concentration of 59 drinking water samples exceeded the Bureau of Indian Standards limit of 45mg/L in drinking water. The rural and urban areas were found to have mean nitrate concentration in drinking water as 45.69±2.08 and 22.53±1.97mg/L, respectively. The estimated daily intake of drinking water samples from 55 study sites had nitrate concentration far below the safety margin indicating serious health risk. The sanitation survey conducted in 12households reported contaminated source with positive E. coli count in 20 samples as the major factor of health risk. The average nitrate concentration was maximum in beetroot (1349.38mg/kg) followed by spinach (1288.75mg/kg) and amaranthus (1007.64mg/kg). Among the samples, four varieties of the vegetables exceeded the acceptable daily intake (ADI) with an assumption of 0.5kg consumption of vegetables for an average of a 60-kg individual. Therefore, irrigation of these locally grown vegetables should be monitored periodically for nitrogen accumulation by the crop above the ADI limit. The application of nitrogenous fertilizers should also be minimized in the rural areas to help protect the nitrate contamination in groundwater sources.

The influence of episodic flooding on a pelagic ecosystem in the East China Sea

Abstract. This study was designed to determine the effects of flooding on a pelagic ecosystem in the East China Sea (ECS) with a focus on plankton activity and plankton community respiration (CR). In July 2010, a flood occurred in the Changjiang River. As a comparison, a variety of abiotic and biotic parameters were monitored during this flooding event and during a non-flooding period (July 2009). During the flood, the Changjiang diluted water (CDW) zone covered almost two-thirds of the ECS, which was approximately 6 times the area covered during the non-flooding period. The mean nitrate concentration was 3-fold higher during the 2010 flood (6.2 vs. 2.0 µM in 2009). CR was also higher in the 2010 flood: 105.6 mg C m−3 d−1 vs. only 73.2 mg C m−3 d−1 in 2009. The higher CR in 2010 could be attributed to phytoplankton respiration, especially at stations in the CDW zone that were not previously characterized by low sea surface salinity in 2009. In addition, zooplankton (> 330 µm) were another important component contributing to the high CR rate observed during the 2010 flood; this was a period also associated with a significant degree of fCO2 drawdown. These results collectively suggest that the 2010 flood had a significant effect on the carbon balance in the ECS. This effect might become more pronounced in the future, as extreme rainfall and flooding events are predicted to increase in both frequency and magnitude due to climate change.

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

Groundwater resources are important sources of drinking water in Africa, and they are hugely important in sustaining urban livelihoods and supporting a diverse range of commercial and agricultural activities. Groundwater has an important role in improving health in sub-Saharan Africa (SSA). An estimated 250 million people (40% of the total) live in urban centres across SSA. SSA has experienced a rapid expansion in urban populations since the 1950s, with increased population densities as well as expanding geographical coverage. Estimates suggest that the urban population in SSA will double between 2000 and 2030. The quality status of shallow urban groundwater resources is often very poor due to inadequate waste management and source protection, and poses a significant health risk to users, while deeper borehole sources often provide an important source of good quality drinking water. Given the growth in future demand from this finite resource, as well as potential changes in future climate in this region, a detailed understanding of both water quantity and quality is required to use this resource sustainably. This paper provides a comprehensive assessment of the water quality status, both microbial and chemical, of urban groundwater in SSA across a range of hydrogeological terrains and different groundwater point types. Lower storage basement terrains, which underlie a significant proportion of urban centres in SSA, are particularly vulnerable to contamination. The relationship between mean nitrate concentration and intrinsic aquifer pollution risk is assessed for urban centres across SSA. Current knowledge gaps are identified and future research needs highlighted.

Enhanced Nitrate Reduction within a Constructed Wetland System: Nitrate Removal within Groundwater Flow

Within the Midwest United States, agricultural fields are drained by tile drainage systems. These systems are emplaced to enhance crop production, but they serve as a direct flowpath to surface streams, delivering excess nutrients to the streams. Identifying and establishing methods to reduce excess nutrient delivery to surface streams has become a priority. Surface processes within wetlands, both natural and constructed, have been shown to abate excess nutrients. This work explores the benefit associated with the subsurface flow of seepage from a wetland. Water level monitoring and geochemical analyses were used to ascertain the reduction of nitrate occurring in the subsurface following leakage from a wetland. Receiving only tile-drainage water, the wetland waters had a mean nitrate as nitrogen (NO3-N) concentration of 19.80 mg/L, which is a magnitude larger than the measured NO3-N concentration in the upgradient groundwater of 1.53 mg/L. As water travels in subsurface away from the wetland, the NO3-N concentrations decrease to 10.99 mg/L, a 44.5% reduction. The reduction occurs over a distance of 47 m, representing a 0.16 mg/L decrease in NO3-N per meter of travel distance.

Evaluation of Beetroot Juice Blends with Carrot and Apple Juice as Healthy Beverage

The consumption of beetroot juice may lower blood pressure (BP) and therefore reduce the risk of cardiovascular events. The aim of this study was to produce of beetroot juice blends with carrot and apple juice as healthy beverage and new product as a reduction in BP. Juices from beetroot (Beta vulgaris), carrot (Drocus carota), and apple (Mallus Pumilla Fam.) were optimized to a blended beverage which was pasteurized (90°C for 25 sec) and stored for 21 days in glass bottles at refrigerated temperature. Physic-chemical and sensory analysis was evaluated. Marginal changes in pH, total soluble solids, acidity, vitamin C and total carotenoids were observed. The highest content of total carotenoids in the beetroot, carrot, and apple juice blends of 50:20:30 (V/V/V) (T4) was found (55.03mgL-1) to be increased with increasing the proportion of carrot juice. Estimation of vitamin C content of the same sample at 21 day (30.40mg/100ml) showed high improvement in nutritional value of beetroot juice incorporated with carrot and apple juice. The mean nitrate and nitrite levels in the juices ranged from 0.005 to 0.002mg/L and 0.092 to 0.005 mg/L. during storage period; respectively. The mean overall acceptability scores of more than 8 for juice samples up to 30% apple juice incorporation indicated the commercial scope for manufacturing good and nutritious beetroot juice blended with carrot and apple juice, which will also be helpful in providing dietary requirement of beta carotene to the consumer. Heat pasteurization was effective for inactivating the microbial flora. However, the shelf life of juice was established within 21 days. The product is recommended for children, youth and elderly persons to be used within 21 days.

Quantifying an aquifer nitrate budget and future nitrate discharge using field data from streambeds and well nests

AbstractNovel groundwater sampling (age, flux, and nitrate) carried out beneath a streambed and in wells was used to estimate (1) the current rate of change of nitrate storage, /dt, in a contaminated unconfined aquifer, and (2) future [ ]FWM (the flow‐weighted mean nitrate concentration in groundwater discharge) and (the nitrate flux from aquifer to stream). Estimates of /dt suggested that at the time of sampling (2013) the nitrate storage in the aquifer was decreasing at an annual rate (mean = −9 mmol/m2yr) equal to about one‐tenth the rate of nitrate input by recharge. This is consistent with data showing a slow decrease in the [ ] of groundwater recharge in recent years. Regarding future [ ]FWM and , predictions based on well data show an immediate decrease that becomes more rapid after ∼5 years before leveling out in the early 2040s. Predictions based on streambed data generally show an increase in future [ ]FWM and until the late 2020s, followed by a decrease before leveling out in the 2040s. Differences show the potential value of using information directly from the groundwater—surface water interface to quantify the future impact of groundwater nitrate on surface water quality. The choice of denitrification kinetics was similarly important; compared to zero‐order kinetics, a first‐order rate law levels out estimates of future [ ]FWM and (lower peak, higher minimum) as legacy nitrate is flushed from the aquifer. Major fundamental questions about nonpoint‐source aquifer contamination can be answered without a complex numerical model or long‐term monitoring program.

Nitrogen assessment points: development and application to high‐elevation lakes in the Sierra Nevada, California

AbstractIncreased nitrogen (N) inputs to oligotrophic high‐elevation lakes are contributing to long‐term eutrophication, changes in nutrient cycles, and shifts in phytoplankton communities. State of California water quality standards do not adequately protect mountain lake ecosystems from atmospheric deposition, including lakes in national parks and other protected areas. The development of quantitative nutrient assessment points based on measurable ecological effects specific to high‐elevation lakes is an important step in long‐term protection of these ecosystems. We conducted in situ bioassay experiments during the phytoplankton growing season and modeled the response of phytoplankton to nutrient additions using algal growth models. Phytoplankton responded to nutrient additions (N and N + phosphorus) in five of seven experiments conducted in N‐limited lakes. Results were modeled using Michaelis‐Menten, Monod, and dose–response curves and used to calculate effective doses (ED) for excess phytoplankton growth. The 10%, 50%, and 90% ED estimates were determined for early and late hydrologic seasons. Results for the 10% ED were 0.33 (early hydrologic season) and 0.89 (late hydrologic season), the 50% ED were 1.0 μmol/L (early hydrologic season) and 4.0 μmol/L (late hydrologic season), and the 90% ED were 3.1 μmol/L (early hydrologic season) and 18 μmol/L (late hydrologic season). We then applied these assessment points to lake chemistry data from the National Park Service's Inventory and Monitoring Program to assess the status of lakes across Yosemite, Sequoia, and Kings Canyon national parks. Mean nitrate concentration during the growing season was 4.58 μmol/L and ranged from <0.04 to 11.8 μmol/L (n = 75). The 10% ED were exceeded by 28% (late hydrologic season) and 37% (early hydrologic season) of lakes, the 50% ED were exceeded by 18% (late hydrologic season) and 29% (early hydrologic season) of lakes, and the 90% ED were exceeded by 0.0% (late hydrologic season) and 21% (early hydrologic season) of lakes. Our results suggest that phytoplankton populations in many Sierra Nevada lakes are affected by N deposition based on exceedance of growth assessment points. The most sensitive lakes are typically found at higher elevations in watersheds with steep, north‐facing slopes and minimal vegetation.

Estuarine circulation-driven entrainment of oceanic nutrients fuels coastal phytoplankton in an open coastal system in Japan

We investigated interactions among seasonal fluctuations in phytoplankton biomass, riverine nutrient flux, and the fluxes of nutrients entrained by estuarine circulation in Tango Bay, Japan, to determine the influence of freshwater inflows to an open bay on coastal phytoplankton productivity. The riverine nutrient flux was strongly regulated by river discharge. Estuarine circulation was driven by river discharge, with high fluxes of nutrients (mean nitrate + nitrite flux: 5.3 ± 3.5 Mg [mega grams]-N day−1) between winter and early spring, enhanced by nutrient supply to the surface water via vertical mixing. In contrast, low-nutrient seawater was delivered to the bay between late spring and summer (1.0 ± 0.8 Mg-N day−1). Seasonal fluctuations in phytoplankton biomass were affected by the entrained fluxes of oceanic nutrients and variation in the euphotic zone depth, and to a lesser degree by the riverine nutrient flux. Bioassays and stoichiometric analyses indicated that phytoplankton growth was limited by nitrogen and/or phosphorus. Both the entrainment of oceanic nutrients and the euphotic zone depth affected the duration and magnitude of blooms. Our findings show that, unlike semi-enclosed bays, seasonal variations in coastal phytoplankton in an open coastal system are primarily fueled by the entrainment of oceanic nutrients and are influenced by both freshwater inflow and coastal conditions (e.g. vertical mixing and wind events).

Trends in soil solution dissolved organic carbon (DOC) concentrations across European forests

Abstract. Dissolved organic carbon (DOC) in surface waters is connected to DOC in soil solution through hydrological pathways. Therefore, it is expected that long-term dynamics of DOC in surface waters reflect DOC trends in soil solution. However, a multitude of site studies have failed so far to establish consistent trends in soil solution DOC, whereas increasing concentrations in European surface waters over the past decades appear to be the norm, possibly as a result of recovery from acidification. The objectives of this study were therefore to understand the long-term trends of soil solution DOC from a large number of European forests (ICP Forests Level II plots) and determine their main physico-chemical and biological controls. We applied trend analysis at two levels: (1) to the entire European dataset and (2) to the individual time series and related trends with plot characteristics, i.e., soil and vegetation properties, soil solution chemistry and atmospheric deposition loads. Analyses of the entire dataset showed an overall increasing trend in DOC concentrations in the organic layers, but, at individual plots and depths, there was no clear overall trend in soil solution DOC. The rate change in soil solution DOC ranged between −16.8 and +23 % yr−1 (median = +0.4 % yr−1) across Europe. The non-significant trends (40 %) outnumbered the increasing (35 %) and decreasing trends (25 %) across the 97 ICP Forests Level II sites. By means of multivariate statistics, we found increasing trends in DOC concentrations with increasing mean nitrate (NO3−) deposition and increasing trends in DOC concentrations with decreasing mean sulfate (SO42−) deposition, with the magnitude of these relationships depending on plot deposition history. While the attribution of increasing trends in DOC to the reduction of SO42− deposition could be confirmed in low to medium N deposition areas, in agreement with observations in surface waters, this was not the case in high N deposition areas. In conclusion, long-term trends of soil solution DOC reflected the interactions between controls acting at local (soil and vegetation properties) and regional (atmospheric deposition of SO42− and inorganic N) scales.

CONCENTRATION OF NITRATE/ NITRITE IN GROUNDWATER WELLS IN BAGHDAD CITY, IRAQ

Both Nitrate and Nitrite are naturally occurring in the environment, products by oxidation of nitrogen by microorganism in plants, soil and water. The objective of this study was to investigate and determine the nitrate/ nitrite compounds in groundwater wells of Baghdad city/ Iraq. During a period of three months (January, April and August 2014), 26 samples of water were examined. The results showed that mean Nitrate concentration in water samples were 52.66 ppm, 15.03 ppm, 8.53 ppm, 12.30 ppm, 13.36 ppm, 50.56 ppm for three Months (January, April and August) and Nitrite concentration were 4.05 ppm, 072 ppm, 0.85 ppm, 0.88 ppm, 1.05 ppm, 3.11 ppm at Dyala Ridge, Salikh, Doura, Al-Jadria, Ghazalyia – Ammiria, and Abu-Ghreeb locations, respectively. Both Nitrate, Nitrite in Two area (Abu-Ghreeb, Dyala) had been more than the others locations due to increasing use of artificial fertilizers, the disposal of wastes and changes in land use are the main factors responsible for the progressive increase in nitrate/ Nitrite levels in both locations. One of the important issue that protection these area by apply many actions to reduce or remove nitrate concentration from groundwater.

Nitrate and nitrite content of vegetables, fruits, grains, legumes, dairy products, meats and processed meats

Background and aimThe aim of this study was to investigate the contents of nitrate/nitrite in frequently consumed food items among Iranians. MethodsStratified random sampling was conducted seasonally from November 2014 through January 2016 for samples collected from the main municipal markets of Tehran. To determine the nitrate/nitrite contents of foods, spectrophotometric methods, developed by International Organization for Standardization (ISO), were used. ResultsMethod limit of detection (LOD) was 0.61mg100g−1 and 0.10mg100g−1, for nitrate and nitrite, respectively, and method limit of quantification (LOQ) was 1.86mg100g−1 and 0.16mg 100g−1 for nitrate and nitrite, respectively. A relatively high nitrate concentration was observed in breads (∼50.0mg 100g−1). Mean ranges of nitrate and nitrite in fruits were 7.50–46.8mg 100g−1 and 0.15–0.71mg 100g−1, respectively. Vegetables with the highest nitrate concentrations included radish (625mg 100g−1), beetroot (495mg 100g−1), tarragon (424mg 100g−1), lettuce (365mg 100g−1), mint (279mg 100g−1), and celery (261mg 100g−1). Nitrite content of vegetables ranged 0.21–0.74mg 100g−1. In dairy products, mean nitrite and nitrate content ranged 0.14–0.45mg 100g−1 and 1.26–5.75mg 100g−1. Mean nitrate and nitrite concentrations in meats and processed meats were 5.56–19.4mg 100g−1 and 2.93–13.9mg 100g−1, respectively. ConclusionThis database could provide opportunities to quantify nitrate and nitrite exposure of Iranians and to evaluate risk-benefit of nitrate-nitrite exposure.

A meta-analysis and statistical modelling of nitrates in groundwater at the African scale

Abstract. Contamination of groundwater with nitrate poses a major health risk to millions of people around Africa. Assessing the space–time distribution of this contamination, as well as understanding the factors that explain this contamination, is important for managing sustainable drinking water at the regional scale. This study aims to assess the variables that contribute to nitrate pollution in groundwater at the African scale by statistical modelling. We compiled a literature database of nitrate concentration in groundwater (around 250 studies) and combined it with digital maps of physical attributes such as soil, geology, climate, hydrogeology, and anthropogenic data for statistical model development. The maximum, medium, and minimum observed nitrate concentrations were analysed. In total, 13 explanatory variables were screened to explain observed nitrate pollution in groundwater. For the mean nitrate concentration, four variables are retained in the statistical explanatory model: (1) depth to groundwater (shallow groundwater, typically < 50 m); (2) recharge rate; (3) aquifer type; and (4) population density. The first three variables represent intrinsic vulnerability of groundwater systems to pollution, while the latter variable is a proxy for anthropogenic pollution pressure. The model explains 65 % of the variation of mean nitrate contamination in groundwater at the African scale. Using the same proxy information, we could develop a statistical model for the maximum nitrate concentrations that explains 42 % of the nitrate variation. For the maximum concentrations, other environmental attributes such as soil type, slope, rainfall, climate class, and region type improve the prediction of maximum nitrate concentrations at the African scale. As to minimal nitrate concentrations, in the absence of normal distribution assumptions of the data set, we do not develop a statistical model for these data. The data-based statistical model presented here represents an important step towards developing tools that will allow us to accurately predict nitrate distribution at the African scale and thus may support groundwater monitoring and water management that aims to protect groundwater systems. Yet they should be further refined and validated when more detailed and harmonized data become available and/or combined with more conceptual descriptions of the fate of nutrients in the hydrosystem.

Optimizing Sampling Strategies for Riverine Nitrate Using High-Frequency Data in Agricultural Watersheds.

Understanding linked hydrologic and biogeochemical processes such as nitrate loading to agricultural streams requires that the sampling bias and precision of monitoring strategies be known. An existing spatially distributed, high-frequency nitrate monitoring network covering ∼40% of Iowa provided direct observations of in situ nitrate concentrations at a temporal resolution of 15 min. Systematic subsampling of nitrate records allowed for quantification of uncertainties (bias and precision) associated with estimates of various nitrate parameters, including: mean nitrate concentration, proportion of samples exceeding the nitrate drinking water standard (DWS), peak (>90th quantile) nitrate concentration, and nitrate flux. We subsampled continuous records for 47 site-year combinations mimicking common, but labor-intensive, water-sampling regimes (e.g., time-interval, stage-triggered, and dynamic-discharge storm sampling). Our results suggest that time-interval sampling most efficiently characterized all nitrate parameters, except at coarse frequencies for nitrate flux. Stage-triggered storm sampling most precisely captured nitrate flux when less than 0.19% of possible 15 min observations for a site-year were used. The time-interval strategy had the greatest return on sampling investment by most precisely and accurately quantifying nitrate parameters per sampling effort. These uncertainty estimates can aid in designing sampling strategies focused on nitrate monitoring in the tile-drained Midwest or similar agricultural regions.

Effect of support medium, hydraulic loading rate and plant density on water quality and growth of halophytes in marine aquaponic systems

The development of marine intensive land-based aquaculture systems has been limited due to the absence of methods to manage saline wastewater. Aquaponic systems, although commonly applied to freshwater aquaculture, can potentially manage nutrient wastes while providing a secondary product. The aim of this study was to evaluate both the capacity for water treatment and the production requirements of two saltwater-tolerant plant species (Sesuvium portulacastrum and Batis maritima) when grown hydroponically in a marine aquaponic system. The presence of plants was found to significantly contribute to nitrate removal, such that mean nitrate concentrations were 10.1 ± 5.4 and 12.1 ± 6.1 mg/L NO3−-N in planted and unplanted treatments respectively. The use of coconut fibre as a planting medium also significantly contributed to nitrate removal, such that mean nitrate concentrations were 9.78 ± 5.4 and 12.4 ± 6.0 mg/L NO3−-N in coconut fibre and expanded clay treatments respectively. Daily nitrogen removal was greatest in the coconut fibre/plants treatment, ranging from −18% to 67%. Hydraulic loading rate, plant species and plant density did not significantly affect water quality or plant growth. The low flow/saltwort/low density treatment had the greatest mean daily nitrogen removal, ranging from 25% to 172%. The results indicate that the main nitrogen removal mechanisms were simultaneous nitrification–denitrification in the hydroponic plant beds and nitrogen removal through plant growth. This study demonstrates that marine aquaponics could be an effective way to manage nutrient removal in marine land-based aquaculture systems.

A critical re-evaluation of controls on spatial and seasonal variations in nitrate concentrations in river waters throughout the River Derwent catchment in North Yorkshire, UK.

Since mean nitrate concentration along single river channels increases significantly with percent arable land use upstream of sampling points and autumn/early winter flushes in nitrate concentration are widespread, it is generally concluded that farmers contribute most of the nitrate. For the River Derwent in North Yorkshire, the correlation between nitrate concentration and percent arable land use is much poorer when tributary data are included in the equation, because of greater variations in dilution by water draining upland areas and in other N input sources. For the whole river system therefore, percent upland moorland/rough grazing land cover is an appreciably better predictor than percent arable land use for nitrate concentration. Upland land use encompasses the higher precipitation and runoff in such areas, and the subsequent greater dilution downstream of both arable land runoff and effluent from treatment works, as well as an inverse correlation to percent arable land use. This is strongly supported by the observation that, for the Derwent, Meteorological Office rainfall data alone proved even better than percent moorland rough grazing for predicting nitrate concentration. The dilution effect is therefore substantial but highly seasonal; lower runoff and dilution in summer offset the lower leaching losses from arable land, and higher dilution and runoff in winter offset greater nitrate leaching losses from arable soils. Because of this, coupled to improved efficiency of nitrogen fertilizer use, seasonality trends in nitrate concentrations that were pronounced a decade ago now have all but disappeared in the catchment.

Concentrações de nitrito e nitrato em salsichas

Objective: To determine nitrite and nitrate levels, hydrogen potential (pH), and water activity (aw) in sausages marketed in Southern Brazil, and compare the levels among different brands. Methods: Quantitative experimental cross-sectional study conducted with 72 sausage samples collected in two municipalities in the Regiao do Vale do Taquari, Rio Grande do Sul,,between June and August 2015. Three samples from different batches of each eight distinct sausage brands which were supervised by the Federal Inspection Service were analyzed in triplicate according to their nitrite and nitrate levels, pH and water activity. Data underwent ANOVA and Chi-squared tests with p<0.05. Results: Samples met the recommended standards for pH and water activity (6.33 ± 0.32 and 0.91 ± 0.01, respectively), while 40.3% (29) and 50.0% (36) of the samples presented nitrite and nitrate levels, respectively, significantly above what is recommended by the legislation (p<0.05). The mean nitrite levels of the remaining samples were significantly lower (p=0.001), and mean nitrate levels were significantly higher (p=0.009) than the value established by legislation. Conclusion: The samples met the recommended levels of pH and water activity. Of eight brands assessed, three presented satisfactory levels of nitrate and nitrite. The mean levels of nitrite and water activity were significantly lower and the mean levels of nitrate and pH were significantly higher than the recommendations. Additionally, mean nitrate and nitrite levels of five brands were significantly higher than what is recommended by the legislation.