Differences In Nitrate Research Articles

Effects of food waste and green waste composts on yield and nitrogen‐use efficiency in irrigated tomato crops

AbstractComposts are increasingly used to enhance soil health and agricultural sustainability, but their impacts on nitrogen (N) availability are unclear. In a 3‐year field experiment with subsurface drip‐irrigated tomatoes (Solanum lycopersicum), we investigated the effects of food waste and green waste co‐compost (FW) and green waste compost (GW) on yield, nitrogen‐use efficiency (NUE), nitrate leaching potential, and fertilizer N retention. Various combinations of compost rates (0, 9, or 18 t ha−1) and fertilizer N levels (0%, 70%, 85%, and 100% of the recommended rate) were examined, and 15N‐labeled fertilizer was used. In Years 2 and 3, FW and GW either maintained or increased crop yield compared to no compost when 0% or 70% N was applied; however, lower NUE was observed in the compost treatments compared to no compost when 70% or 85% N was supplied. Postharvest, FW showed greater fertilizer N retention in topsoil than GW and controls, while no difference in nitrate leaching potential was found among treatments, except for Year 2 during which FW exhibited the lowest potential. These results suggest that compost can immobilize fertilizer N, reducing its uptake by crops but enhancing soil retention, potentially acting as an N source or a primer of soil N mineralization. Future research is needed to assess compost's impact on N gaseous emissions and distinguish its dual roles as an N source and a soil N mineralization primer. This is essential for developing nutrient management guidelines to minimize N losses.

Measuring Nitrate Leaching in the Vadose Zone of Loess Soils—Comparison of Batch Extraction and Centrifugation

The nitrate concentration in the subsoil moisture of the vadose zone is an important indicator for future groundwater quality, which is classically determined via centrifugation. Batch extraction is an inexpensive and easy alternative method, but whether these methods measure the same soil water, nitrogen species, and nitrate concentrations is unclear, in particular for loess soils. Two experiments were carried out to assess the differences in nitrate and other anion concentrations between centrifugated soil moisture (centrifugated at different speeds and times) and batch extractions (using double-distilled water and 0.01 M CaCl2). Batch extraction resulted in lower nitrate (−20%) and chloride (−15%) concentrations than centrifugation, mainly due to anion exclusion, where soil microporosity controls the contribution of diffusion, denitrification, and leaching processes. Vice versa, batch extraction overestimated the concentration of nutrients that occur as precipitates in or sorb the soil matrix, such as sulphate (+50%) and ammonium (+96%). Batch extractions can only be used as a proxy to determine actual nitrate concentrations of soil water. However, they are useful to monitor changes in nitrate leaching over time in response to (policy) measures taken. They can also be used as “early warning indicator” and to improve the reliability of spatial explicit monitoring networks.

Nitrate and Nitrite Metabolism in Aging Rats: A Comparative Study.

Nitric oxide (NO) (co)regulates many physiological processes in the body. Its short-lived free radicals force synthesis in situ and on-demand, without storage possibility. Local oxygen availability determines the origin of NO-either by synthesis by nitric oxide synthases (NOS) or by the reduction of nitrate to nitrite to NO by nitrate/nitrite reductases. The existence of nitrate reservoirs, mainly in skeletal muscle, assures the local and systemic availability of NO. Aging is accompanied by changes in metabolic pathways, leading to a decrease in NO availability. We explored age-related changes in various rat organs and tissues. We found differences in nitrate and nitrite contents in tissues of old and young rats at baseline levels, with nitrate levels being generally higher and nitrite levels being generally lower in old rats. However, there were no differences in the levels of nitrate-transporting proteins and nitrate reductase between old and young rats, with the exception of in the eye. Increased dietary nitrate led to significantly higher nitrate enrichment in the majority of old rat organs compared to young rats, suggesting that the nitrate reduction pathway is not affected by aging. We hypothesize that age-related NO accessibility changes originate either from the NOS pathway or from changes in NO downstream signaling (sGC/PDE5). Both possibilities need further investigation.

Poorly drained depressions can be hotspots of nutrient leaching from agricultural soils.

Much of the US Corn Belt has been drained with subsurface tile to improve crop production, yet poorly drained depressions often still flood intermittently, suppressing crop growth. Impacts of depressions on field-scale nutrient leaching are unclear. Poor drainage might promote denitrification and physicochemical retention of phosphorus (P), but ample availability of water and nutrients might exacerbate nutrient leaching from cropped depressions. We monitored nitrate, ammonium, and reactive P leaching across multiple depression-to-upland transects in north-central Iowa, using resin lysimeters buried and retrieved on an annual basis. Crops included conventional corn/soybean (Zea mays/Glycine max) rotations measured at fields with and without a winter rye (Secale cereale) cover crop, as well as juvenile miscanthus (Miscanthus × giganteus), a perennial grass. Leaching of nitrogen (N) and P was greater in depressions than in uplands for most transects and years. The median difference in nutrient leaching between paired depressions and uplands was 56kg N ha-1 year-1 for nitrate (p=0.0008), 0.6kg N ha-1 year-1 for ammonium (p=0.03), and 2.4kg P ha-1 year-1 for reactive P (p=0.006). Transects managed with a cover crop or miscanthus tended to have a smaller median difference in nitrate (but not ammonium or P) leaching between depressions and uplands. Cropped depressions may be disproportionate sources of N and P to downstream waters despite their generally poor drainage characteristics, and targeted management with cover crops or perennials might partially mitigate these impacts for N, but not necessarily for P.

New insights on simultaneous nitrate and phosphorus removal in pyrite-involved mixotrophic denitrification biofilter for a long-term operation: Performance change and its underlying mechanism

Simultaneous nitrate and phosphorus removal can be completed by pyrite- and influent organics-involved mixotrophic denitrification and chemical phosphorus removal via iron precipitation. However, so far, how their removal performances change with iron precipitation accumulation remains unclear. In this study, the differences in nitrate and phosphorus removal from municipal tailwater between volcanic and pyrite supported biofilters (V-BF, P-BF) for a long-term operation were investigated, as well as the underlying mechanism for these differences. The nitrate removal efficiencies (NREs) in P-BF were greater than those in V-BF due to the synergistic effect of influent organic and pyrite, as evidenced by comparable TOC consumption and Fe2+/SO42− production. The NREs in P-BF were gradually lower than in V-BF as a result of bacterial cell-iron encrustation observed in TEM images, which would deteriorate microbial activity. However, the phosphorus removal efficiencies (PREs) in P-BF remained consistently higher than in V-BF, resulting from chemical phosphorus removal which was confirmed that P, Fe and O elements dominated on the pyrite surface after use by SEM-EDS. The dominant denitrifying bacteria differed significantly, autotrophic and heterotrophic denitrifying microorganisms coexisted in P-BF. The relative abundances of the narG coding gene in P-BF were higher than that in V-BF, which was consistent with the total relative abundances of identified denitrifying bacteria. Besides, the mechanism of simultaneous nitrogen and phosphorus removal in the pyrite-involved mixotrophic denitrification process has been deduced. This work has significant implications for the practical application of a pyrite-involved mixotrophic denitrification process for low C/N wastewater treatment.

Linking Dominant Rainfall‐Runoff Event Hydrologic Response Dynamics With Nitrate and Chloride Load Estimates of Three Boreal Shield Catchments

AbstractUnderstanding hydrological dynamics in boreal Shield catchments is critical for projecting changes in stream runoff and chemistry in a region that is, sensitive to climate change. Previous work has mostly focused on a limited number of events over one or a few seasons because of the relative scarcity of high‐frequency datasets and automated tools for rainfall‐runoff event delineation. For the boreal region, a greater understanding of seasonality in hydrologic response and solute export related to rainfall‐initiated events is needed, as significant shifts in hydrologic regimes from climate change are expected. This study aimed to help resolve these knowledge gaps by assessing event‐scale hydrologic response dynamics and stream loads of nitrate and chloride using long‐term data from three boreal Shield catchments. Hydrometric and stream chemistry data from 2001 to 2018 were analyzed to delineate rainfall‐runoff events and estimate event nitrate and chloride loads. Event hydrologic response and loads were highly variable, especially with respect to catchment runoff initiation. Only subtle differences in hydrologic response dynamics were observed between summer and fall events, while seasonal differences in event nitrate and chloride loads were most statistically significant. Interestingly, a wide range of rainfall‐runoff events classified by response magnitude and timing was associated with differences in nitrate and chloride export. This study further confirms the utility of long‐term high‐frequency datasets and illustrates the need for additional work to further assess long‐term changes in event‐based hydrologic response and stream solute concentrations in the boreal region.

Natural allelic variation in a modulator of auxin homeostasis improves grain yield and nitrogen use efficiency in rice.

The external application of nitrogen (N) fertilizers is an important practice for increasing crop production. However, the excessive use of fertilizers significantly increases production costs and causes environmental problems, making the improvement of crop N-use efficiency (NUE) crucial for sustainable agriculture in the future. Here we show that the rice (Oryza sativa) NUE quantitative trait locus DULL NITROGEN RESPONSE1 (qDNR1), which is involved in auxin homeostasis, reflects the differences in nitrate (NO3-) uptake, N assimilation, and yield enhancement between indica and japonica rice varieties. Rice plants carrying the DNR1indica allele exhibit reduced N-responsive transcription and protein abundance of DNR1. This, in turn, promotes auxin biosynthesis, thereby inducing AUXIN RESPONSE FACTOR-mediated activation of NO3- transporter and N-metabolism genes, resulting in improved NUE and grain yield. We also show that a loss-of-function mutation at the DNR1 locus is associated with increased N uptake and assimilation, resulting in improved rice yield under moderate levels of N fertilizer input. Therefore, modulating the DNR1-mediated auxin response represents a promising strategy for achieving environmentally sustainable improvements in rice yield.

Assessment of the combined nitrate and nitrite exposure from food and drinking water: application of uncertainty around the nitrate to nitrite conversion factor

ABSTRACTDietary exposure to nitrate and nitrite occurs via three main sources; occurrence in (vegetable) foods, food additives in certain processed foods and contaminants in drinking water. While nitrate can be converted to nitrite in the human body, their risk assessment is usually based on single substance exposure in different regulatory frameworks. Here, we assessed the long-term combined exposure to nitrate and nitrite from food and drinking water. Dutch monitoring data (2012–2018) and EFSA data from 2017 were used for concentration data. These were combined with data from the Dutch food consumption survey (2012–2016) to assess exposure. A conversion factor (median 0.023; range 0.008–0.07) was used to express the nitrate exposure in nitrite equivalents which was added to the nitrite exposure. The uncertainty around the conversion factor was taken into account by using conversion factors randomly sampled from the abovementioned range. The combined dietary exposure was calculated for the Dutch population (1–79 years) with different exposure scenarios to address regional differences in nitrate and nitrite concentrations in drinking water. All scenarios resulted in a combined exposure above the acceptable daily intake for nitrite ion (70 µg/kg bw), with the mean exposure varying between 95–114 µg nitrite/kg bw/day in the different scenarios. Of all ages, the combined exposure was highest in children aged 1 year with an average of 250 µg nitrite/kg bw/day. Vegetables contributed most to the combined exposure in food in all scenarios, varying from 34%–41%. Food additive use contributed 8%–9% to the exposure and drinking water contributed 3%–19%. Our study is the first to perform a combined dietary exposure assessment of nitrate and nitrite while accounting for the uncertain conversion factor. Such a combined exposure assessment overarching different regulatory frameworks and using different scenarios for drinking water is a better instrument for protecting human health than single substance exposure.

Differential contributions of NO3\u2212/NH4+ to nitrogen use in response to a variable inorganic nitrogen supply in plantlets of two Brassicaceae species in vitro

BackgroundThe primary sources of nitrogen for plants have been suggested to be nitrate (NO3−) and ammonium (NH4+). However, when both nitrate and ammonium are simultaneously available to plants, it is very difficult to differentially quantify NO3−/NH4+ utilization in culture media or soil. Consequently, the contribution of NO3−/NH4+ to total inorganic nitrogen assimilation cannot be determined.ResultsWe developed a method called the bidirectional stable nitrogen isotope tracer to differentially quantify the nitrate and ammonium utilization by Orychophragmus violaceus (Ov) and Brassica napus (Bn) plantlets in vitro. The utilization efficiency of nitrate was markedly lower than the utilization efficiency of ammonium for plantlets of both Ov and Bn. In both Ov and Bn, the proportion of NO3−/NH4+ utilization did not show a linear relationship with inorganic nitrogen supply. The Ov plantlets assimilated more nitrate than the Bn plantlets at the lowest inorganic nitrogen concentration.ConclusionsQuantifying the utilization of nitrate and ammonium can reveal the differences in nitrate and ammonium assimilation among plants at different inorganic nitrogen supply levels and provide an alternate way to conveniently optimize the supply of inorganic nitrogen in culture media.

How grazing affects soil quality of soils formed in the glaciated northeastern United States.

Historically, much of the New England landscape was converted to pasture for grazing animals and harvesting hay. Both consumer demand for local sustainably produced food, and the number of small farms is increasing in RI, highlighting the importance of characterizing the effects livestock have on the quality of pasture soils. To assess how livestock affect pasture on Charlton and Canton soils series in RI, we examined soil quality in farms raising beef cattle (Bos taurus), sheep (Ovis aries), and horses (Equus ferus caballus), using hayed pastures as a control. We sampled three pastures per livestock type and three control hayed pastures in May, August, and October 2012. Hay fields and pastures grazed by sheep had statistically significant (P < 0.001) better soil quality than pastures grazed by beef cattle or horses. This was driven by parameters including penetration resistance, bulk density, aggregate stability, and infiltration rate. Hayfields also showed higher soil quality measures than grazed pastures for organic matter content and active C. In addition, significant differences in nitrate and phosphate concentrations were observed among livestock types. Respiration and infiltration rates, pH, and ammonium concentrations, on the other hand, did not differ significantly among pasture types. When all soil quality indicators in this study were weighed equally, soil quality scores followed the order: hay > sheep > beef cattle > horses. The results of our study provide baseline data on the effect different types of livestock have on pasture soil quality in RI, which may be useful in making sound land use and agricultural management decisions.

Differences in nitrate and phosphorus export between wooded and grassed riparian zones from farmland to receiving waterways under varying rainfall conditions

Agricultural activities in catchments can cause excessive nutrient loads in waterways. Catchment nitrogen (N) and phosphorus (P) flows may be intercepted and assimilated by riparian vegetation. While prior studies suggest that woody vegetation is preferable for reducing P loads, the question remains: is woody vegetation or grass cover more effective at reducing catchment N and P exports to waterways. To address this we investigated the relative importance of vegetation type, hydrologic and soil microbial processes on N and P losses from soil to a stream. The study involved the analysis of data from two soil microcosm experiments, and a field case study. We found P leaching loss from riparian zones depended significantly on vegetation type (woody vs. grass cover), with lower P exported from wooded riparian zones, irrespective of the scale of rainfall. For N leaching losses, the scale of rainfall had an effect. During high rainfall, vegetation type had a major effect on N leaching loss, with lower N exported from grassed verses wooded riparian zones. However, under low rainfall conditions, soil type and soil C and N stores, potential indicators of soil microbial activity, rather than vegetation cover, affected N leaching. It is hypothesized that soil microbes were reducing N removal under these conditions. We reason that nitrifiers may have played an important role in soil N cycling, as increased soil ammonium had a strong positive effect on nitrate leaching loads, mediated through soil nitrate stores. Whereas, N immobilization, via incorporation into microbial biomass, and denitrification processes appeared to be limited by C availability, with increased C associated with reduced N leaching. Overall, this study identified that N leaching losses from riparian zones appeared to be affected by two different processes, vegetative uptake and soil microbial processes, the relative importance of which was driven by hydrological conditions.

The Interaction between Arbuscular Mycorrhizal Fungi and Endophytic Bacteria Enhances Plant Growth of Acacia gerrardii under Salt Stress.

Microbes living symbiotically in plant tissues mutually cooperate with each other by providing nutrients for proliferation of the partner organism and have a beneficial effect on plant growth. However, few studies thus far have examined the interactive effect of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) in hostile conditions and their potential to improve plant stress tolerance. In this study, we investigated how the synergistic interactions of endophytic bacteria and AMF affect plant growth, nodulation, nutrient acquisition and stress tolerance of Acacia gerrardii under salt stress. Plant growth varied between the treatments with both single inoculants and was higher in plants inoculated with the endophytic B. subtilis strain than with AMF. Co-inoculated A. gerrardii had a significantly greater shoot and root dry weight, nodule number, and leghemoglobin content than those inoculated with AMF or B. subtilis alone under salt stress. The endophytic B. subtilis could alleviate the adverse effect of salt on AMF colonization. The differences in nitrate and nitrite reductase and nitrogenase activities between uninoculated plants and those inoculated with AMF and B. subtilis together under stress were significant. Both inoculation treatments, either B. subtilis alone or combined with AMF, enhanced the N, P, K, Mg, and Ca contents and phosphatase activities in salt-stressed A. gerrardii tissues and reduced Na and Cl concentration, thereby protecting salt-stressed plants from ionic and osmotic stress-induced changes. In conclusion, our results indicate that endophytic bacteria and AMF contribute to a tripartite mutualistic symbiosis in A. gerrardii and are coordinately involved in the plant adaptation to salt stress tolerance.

Long-term trends of chemical characteristics and sources of fine particle in Foshan City, Pearl River Delta: 2008–2014

Foshan is a major international ceramic center and the most polluted city in the Pearl River Delta (PRD). Here we present the results of the first long-term PM2.5 (particles <2.5μm) sampling and chemical characterization study of the city. A total of 2774 samples were collected at six sites from 2008 to 2014, and analyzed for water soluble species, elements and carbonaceous species. The major constituents of PM2.5 were sulfate, OC (Organic Carbon), nitrate, ammonium and EC (Elemental Carbon), which accounted for 50%–88% of PM2.5. PM2.5 and the most abundant chemical species decreased from 2008 to 2011, but rebounded in 2012–2013. After 2008, the chemical composition of PM2.5 changed dramatically due to the implementation of pollution control measures. From 2008 to 2011, SO42− and NO3− were the two largest components; subsequently, however, OC was the largest component. The respective contributions of SO42−, NO3− and OC to the sum of water soluble species and carbonaceous species were 30.5%, 22.9% and 19.9% in 2008; and 20.2%, 16.5% and 30.2% in 2014. Distinct differences in nitrate and sulfate, and in mass ratio [NO3−]/[SO42−] imply that mobile sources tended to more important in Foshan during 2012–2014. The results indicate that pollution control measures implemented during 2008–2014 had a large effect on anthropogenic elements (Pb, As, Cd, Zn and Cu) and water soluble species, but little influence on crustal elements (V, Mn, Ti, Ba and Fe) and carbonaceous species. The PMF method was used for source apportionment of PM2.5. Industry (including the ceramic industry and coal combustion), vehicles and dust were the three most important sources and comprised 39.2%, 20.0% and 18.4% of PM2.5 in 2008, respectively. However, secondary aerosols, vehicles and industry were the three most important sources and comprised 29.5%, 22.4% and 20.4% of PM2.5 in 2014, respectively. During the seven year study interval, the contributions of primary sources (industry and dust) decreased significantly, but secondary sources increased dramatically. Industry, dust and vehicles contributed 36.6μgm−3, 13.9μgm−3, and 9.2μgm−3 to the reduction of PM2.5, respectively.

Land‐use effects on resource net flux rates and oxygen demand in stream sediments

Summary Human land use in stream catchments modifies biogeochemical cycles. Here, 19 streams across a land use and cover gradient were investigated to determine how the landscape and associated conditions influenced sediment oxygen demand (SOD) and resource (carbon, nitrogen and phosphorus) net flux rates across the sediment–water interface of each stream. Resource net flux rates and SOD were determined from intact sediment cores collected in each stream and incubated in the dark. Stream water was then passed over the top of sealed cores, and net flux rates were determined by measuring the difference in nitrate (), soluble reactive phosphorus (SRP), quality and quantity of dissolved organic carbon (DOC) and dissolved oxygen between inflowing and outflowing water. Streams with more agricultural land in their catchments had higher ambient , SRP and protein‐like dissolved organic matter (DOM) and a larger fraction of DOM in a reduced oxidative state (as inferred using an optical DOM redox index). Sediment oxygen demand was best predicted by sediment organic content and was negatively related to wetland area and positively with row crop (arable) agriculture. These patterns indicate that streams affected by agriculture have relatively more nutrients and labile DOM than streams with greater wetland cover. Most (75%) of the variation in net flux into the stream sediments could be explained by ambient and protein‐like DOM. All but one stream had a net release of dissolved organic carbon (DOC) into the water column; however, streams with higher uptake rates lost carbon to the water column more slowly. Among streams, SRP net flux was low, varied between uptake and release and did not relate to landscape and ambient conditions. Phosphorus cycling was not affected by processes captured in this study. Net flux rates suggest that benthic net uptake increased with increased concentration and that more DOC was retained when the labile carbon pool increased with agricultural land use in the catchment. These links suggest that strategies put forward to increase the efficiency of removal should consider the composition of the carbon pool in addition to hydrological alterations.

The influence of genetic variation and nitrogen source on nitrate accumulation and iso-osmotic regulation by lettuce

Characterisation of genetic variation in nitrate accumulation by lettuce will inform strategies for selecting low-nitrate varieties more capable of meeting EU legislation on harvested produce. This study uses a population of recombinant inbred lines (RILs) of lettuce to determine how genotypic differences influence N uptake, N assimilation and iso-osmotic regulation, and to identify key related traits prior to future genetic analysis. Measurements were made on plants grown to maturity in soil fertilised with ammonium nitrate, and in a complete nutrient solution containing only nitrate-N. A simple osmotic balance model was developed to estimate variations in shoot osmotic concentration between RILs. There were significant genotypic variations in nitrate accumulation when plants were grown either with nitrate alone or in combination with ammonium. Ammonium-N significantly reduced nitrate in the shoot but had no effect on its relative variability, or on the ranking of genotypes. Shoot nitrate-N was correlated positively with total-N and tissue water, and negatively with assimilated-C in both experiments. Corresponding relationships with assimilated-N and shoot weight were weaker. Estimated concentrations of total osmotica in shoot sap were statistically identical in all RILs, despite variations in nitrate concentration across the population. Approximately 73% of the genotypic variability in nitrate accumulation within the population of RILs arose from differences in nitrate uptake and only 27% from differences in nitrate assimilated, irrespective of whether or not part of the N was recovered as ammonium, or whether the plants were grown in soil or solution culture. Genotypic variability in nitrate accumulation was associated with changes in concentrations of other endogenous solutes (especially carboxylates and soluble carbohydrates) and of tissue water, which minimised differences in osmotic potential of shoot sap between RILs. This offers the opportunity of using the regulation of these solutes as additional traits to manipulate nitrate accumulation.

Nitrate loss from a tile-drained reclaimed marsh soil from SW Spain amended with different products

Tile drainage and soil amendments have been found to affect losses of nitrate N from agricultural soils. This work was aimed at measuring nitrate N losses in a tile-drained marsh soil from SW Spain under traditional fertilization and irrigation practices, and how these losses were influenced by the application of soil amendments. To this end, a randomised block experiment with three replications was performed during two consecutive growing seasons—2003 to 2004 with cotton and sugar beet, respectively—involving four different amendment treatments: (1) control without amendment, (2) phosphogypsum (PG), (3) manure, and (4) sugar factory refuse lime (SFRL). Flow-weighted (FW) nitrate–N concentrations in drainage water, estimated as the slope of the regression of the instantaneous nitrate–N flow as a function of drain flow rate, was decreased by PG in some drainage events in the 2003 season and in the four last events of the 2004 season when compared with control without amendment. The increased FW nitrate–N concentrations in drainage from SFRL in comparison to control in a drainage event of 2003 season, and in the four last events of 2004, can be explained by the contribution of N present in the amendment. These effects did not account for significant differences in nitrate–N loss among treatments over the whole season in 2003, when they ranged from 19.3 to 24.9 kg N ha−1, accounting for 6–8% of applied N, nor in 2004, when they ranged from 4 to 6 kg N ha−1, accounting for 3–4% of applied N. The decrease in mean FW nitrate–N concentration after the third drainage event in 2003 was not the consequence of the depletion of total soil nitrate–N because soil mineral N was increased on average by 205 kg N ha−1 during the season. The high N extractions by sugar beet and the subsequent decrease in total soil nitrate–N can contribute to explain the decrease of mean FW nitrate–N concentrations along the 2004 season. Greater absolute nitrate–N loss in 2003 than in 2004 was explained by the lower efficiency of the furrow irrigation when compared with sprinkler irrigation. Results also revealed that traditional management of N fertilizer was inadequate: rates applied to cotton were excessive, increasing the risk of N losses not only during the cotton season, but also at the beginning of the following season.

GIS and ordination techniques for studying influence of watershed characteristics on river water quality

Landscape characteristics of twenty-eight sub-catchments within the Miyun reservoir watershed in Miyun County, northeast Beijing of China were examined to identify relationships with stream water chemistry. The influences of the entire catchment and 300 m buffer zone on water quality were compared using multiple regression analysis and redundancy analysis during three seasons. Results showed that strong seasonal differences in nitrate, nitrite and ammonium are observed whereas no difference in total phosphorus and conductivity. Landscape factors were significantly correlated to stream water quality. Residential area and stream density contributed markedly to river condition variability. Water quality was better explained by interactions with the landscape during and after rainy season. There was also a seasonal shift in the landscape factors that were the dominant explanatory variables. The relationships between landscape attributes and water quality on watershed scale were slightly different from those on riparian scale; however, landscape attributes may have stronger influences on water chemistry.

Characteristics of PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; speciation in representative megacities and across China

Abstract. Based on PM2.5 chemical data sets from literature and from our surface observations, chemical species and reconstructed speciation of PM2.5 in representative Chinese megacities and across China were compared to draw insights into the characteristics of PM2.5 speciation. PM2.5 mass concentrations and speciation compositions varied substantially over geographical regions in China. Near six-fold variations in average PM2.5 concentrations (34.0–193.4 μg m−3) across China were found with high PM2.5 levels (&gt;100 μg m−3) appearing in the cities in the northern and western regions and low levels (&lt;40 μg m−3) in the remote forest area (Changbai Mountain) and in Hong Kong. The percentages of the sum of sulfate, nitrate and ammonium, organic matter, crustal material, and elemental carbon in PM2.5 mass ranged 7.1–57 %, 17.7–53 %, 7.1–43 %, and 1.3–12.8 %, respectively. At both urban and rural sites in the eastern region, the sum of sulfate, nitrate and ammonia typically constituted much higher fractions (40–57 %) of PM2.5 mass, indicative of more local formation/production and regional transport of the secondary aerosols, thus more intensive characteristic of "complex atmospheric pollution" compared to the western region. Organic matter had significant contribution to PM2.5 over all the sites. Organic matter plus sulfate, nitrate, and ammonia accounted for 53–90 % of PM2.5 mass across China. PM2.5 speciation across China was also characterized by high content of crustal material, which was usually at more than ~10 μg m−3 level or shared ~10 % of PM2.5 mass in urban areas, due to transported desert dust and locally induced dust. In four representative megacities (i.e. Beijing, Chongqing, Shanghai, and Guangzhou), PM2.5 mass and major components (except sulfate) were at higher levels than those in US continental east by one order of magnitude. Distinct differences in nitrate and sulfate levels and their mass ratio [NO3−]/[SO42−] imply that mobile sources are likely more important in Guangzhou, whereas in Chongqing it is stationary (coal combustion) sources. The observed intra-city variations in PM2.5 mass and speciation indicate that both local emissions and regional transportation contributed significantly to high fine particle loadings in Beijing, while local contribution likely played a predominant role in Chongqing. During the ten-year period from 1999 through 2008 in urban Beijing, both the sum of sulfate, nitrate, and ammonia and [NO3−]/[SO42−] ratio exhibited steadily increasing trends, implying that the characteristic of "complex atmospheric pollution" and the contribution from mobile sources were being enhanced.

Uptake and Assimilation of Nitrate and Iron in Cultivated and Wild Vaccinium Species

Growth of cultivated Vaccinium species on soils with a pH above 6.0 is inhibited and production can be extended to these types of soils only after extensive soil modifications. V. arboreum is a wild species that grows on soils with higher pH values. The aim of the present study was to characterize differences in nitrate and iron assimilation in cultivated vs. wild Vaccinium. Genotypes from V. corymbosum and V. arboreum were grown hydroponically with different nitrate and iron concentrations. Nitrate and iron uptake were significantly greater in V. arboreum compared with V. corymbosum. This was correlated with increased nitrate reductase and ferric chelate reductase activities and increased tissue concentrations of reduced nitrogen and iron in V. arboreum. The wild species, V. arboreum, clearly exhibits an increased ability to assimilate nitrate and iron compared with V. corymbosum. This greater capacity for assimilation may play a significant role in this species' broader soil adaptation.

Diel Variation Related to Thermal Mixing in a Subtropical and in a North-Temperate Shallow Floodplain Lake

ABSTRACT Shallow floodplain habitats connected to large rivers undergo seasonal flooding making them integral parts of large river ecosystems. In tropical and subtropical regions, water mixing in these habitats is described as polymictic, yet little description exists for other large river floodplain lakes. In this study, the effect of thermal input on die1 mixing was compared between subtropical Garças Lake (GL)(1.2 m depth) connected to the Paraná River, Brazil and temperate Crane Lake (CL)(0.5 m depth) connected to the Illinois River, USA. Physical, chemical, and microbial variables were measured at 3 h intervals on clear, nearly windless (avg. < 1.2 m s−1) days in summer (GL, 8–9 Jan 02; CL, 8–9 Aug 02). Nocturnal, convective mixing was evident for temperature (range: GL, 28–33 °C; CL, 23–32 °C) and oxygen (range GL: 23–196%; CL: 24–200%) in each system by nightfall (1930h) and correlated with differences in nitrate and ammonia. Although total bacterial density differed between surface and bottom water samples by afternoon, it was similar at both depths by evening (CL, 2230h) or early morning (GL, 430h)Diel mixing occurred in both systems and has important implications in nutrient cycling, coupling of oxic-anoxic processes, and distribution of microbiota.