Magnitude Of NO3 Research Articles

Sandy seepage faces as bioactive nitrate reactors: Biogeochemistry, microbial ecology and metagenomics

Subterranean estuaries are highly dynamic in processing dissolved inorganic nitrogen (DIN). Here we investigate DIN turnover in surface sediments (0–20 cm depth) at the higher, medium and lower intertidal of a seepage face, i.e., the outer “mouth” of the subterranean estuary, during four consecutive seasons in Sanggou Bay, China. Throughout the studied period, ammonium (NH4+) and nitrite (NO2−) concentrations in the sampled porewaters did not vary significantly with depth or season. In contrast, peaks in porewater nitrate (NO3−) concentration and decreases in δ15N-NO3− and δ18O-NO3− were observed in the 15–20 cm depth (bottom) sediment, particularly during summer and autumn. Coupled with NO3− production, the sediment total nitrogen was also markedly peaking in the bottom layer of the studied seepage face. Together with abundant heterotrophic microbes in the sediment, this NO3− accumulation was linked to a reaction chain including organic matter decomposition, ammonification and nitrification. During winter, porewater enrichment in total nitrogen occurred closer to the surface of the seepage face but triggered also active NO3− production. This pattern reinforced the importance of pelagic organic matter supply on NO3− production. In the shallower depths of the seepage face (<12 cm), active net NO3− removal occurred except in winter. The isotopic fractionation (δ15N-NO3− and δ18O-NO3−) and metagenomic results revealed denitrification as the main pathway for NO3− reduction. Biological assimilation from benthic primary producers may also consume a fraction of NO3− at the sediment water interface. Both NO3− production and removal significantly varied in magnitude with season (−13.6 to 6.2 nmol cm−3 h−1). Substrate supply was the key driver for nitrate cycling, as evidenced by the high NO3− production rate in spring by comparison to autumn. The highest NO3− turnover rates were found in summer, suggesting the combined influence of advection rates and sediment microbiota composition. In spite of active removal (peak NO3− removal capability: 61%), a significant amount of NO3− was still transported from the seepage face into the bay waters. The magnitude of NO3− fluxes ranged from 312 to 476 kg N d−1, accounting for approximately 15% of the total exogenous NO3− loading into the bay. NO3− isotopic fingerprint revealed chemical fertilizer as the main source of terrestrial NO3− in SGD, highlighting the importance of land use to coastal system nitrogen budgets.

Minimizing Soil Nitrogen Leaching by Changing Furrow Irrigation into Sprinkler Fertigation in Potato Fields in the Northwestern China Plain

Irrigation water is limiting for crop production in arid areas and application rates of fertilizers often exceed crop requirements, resulting in high accumulation of nitrate nitrogen (NO3−-N) in the soil. Management practices play a significant role in the leaching of NO3−-N. This experiment compares the effects of traditional furrow irrigation and sprinkler fertigation on the soil NO3−-N concentration trend throughout the cropping season in potato fields in China. Two irrigation systems that were fertilized, namely by furrow (NF-FI) and sprinkler fertigation (NF-SI), and two controlling without any fertilizer (C-FI and C-SI) were tested in the same experimental site for three consecutive years. Both the NF-FI soils and NF-SI soils with three replications and fertilizer applications of 273 kg N ha−1 exhibited a different trend of NO3−-N accumulation at different depths of soil profile. However, the magnitude of NO3−-N accumulation was low in the NF-SI soil profile. In NF-SI treatments, higher NO3−-N was observed at 20–40 cm soil layer. In the NF-FI, the concentration of the highest nitrate was observed at the 40–120 cm soil layer. The concentrations of NO3−-N in the fertilized soil were higher than those of the control soil for each irrigation system. Residual levels of NO3−-N in the soil depth of 40–120 cm from NF-FI were 1.54, 3.45 and 5.28 times higher than NF-SI after harvesting potatoes from 2015 to 2017. In NF-FI treatments, apparent nitrogen loss was 234.7, 237.5 and 276.7 kg ha−1 after harvesting potatoes in 2015, 2016 and 2017. Meanwhile, apparent nitrogen loss from NF-SI treatments was only 161.9, 132.1 and 148.9 kg ha−1, which was 31.0%, 44.4% and 46.2% lower than that of NF-FI in 2015, 2016 and 2017, respectively. The risk of NO3−-N leaching below the root zone from NF-FI was higher than that from NF-SI. It has been demonstrated that sprinkler fertigation can also be used as a tool for mitigating NO3−-N accumulation and apparent nitrogen loss.

Land use interacts with changes in catchment hydrology to generate chronic nitrate pollution in karst waters and strong seasonality in excess nitrate export

Agricultural land in karst systems can pollute water courses, with polluted waters travelling quickly to and through the sub-surface. Understanding how rapidly nitrate moves within the highly-transmissive karst critical zone (from soils to aquifers) is limited by low resolution data. To understand nitrate behavior and its controls, we deployed sensor technology at five sites to generate autonomously high-resolution time series of discharge and NO3−–N, which is the major nitrogenous component, in a farmed karst catchment in Southwestern China. The [NO3−–N] time series exhibited rapid response to rainfall-induced increases in discharge and a large magnitude in [NO3−–N], from 0.72 to 16.3 mg/L across five sites. However, the magnitude of NO3−–N response at each site was varied during rainfall events (wet season) and dry season. The highest mean [NO3−–N] and normalized annual fluvial export occurred in a headwater catchment with a developed karst aquifer system. Seasonal variation in NO3−–N export occurred in response to source availability, most notable in catchments with valley agriculture: in the wet season up to 94% of nitrate was exported from the headwater catchments within two months, but at the larger catchment scale, over the 6 month wet season, only 61% of total export occurred. At the larger catchment scale, [NO3−–N] were lower due to buffering by the karstic aquifer network. From the time series we observe little decrease in [NO3−–N] as discharge decreases in the dry season, indicating the karst aquifers are chronically-polluted with nitrate through slow flow pathways.

Impact of drainage type on simultaneous nitrogen losses in Atlantic Canada

Nitrogen (N) losses from agricultural tile drainage systems are environmental and economic losses for producers. This field study quantified N losses from three reps of shallow (SD), deep/conventional (DD), and controlled drainage (CD) on farmland in Nova Scotia. Drainage systems were under corn and alfalfa–oats–clover production. Outflow water and gas samples were obtained and analyzed for nitrate and nitrous oxide. Nitrate-N loads were 5.0, 11.1, and 6.4 kg ha−1 in 2015; 1.8, 6.7, and 2.8 kg ha−1 in 2016; and 0.74, 1.8, and 1.6 kg ha−1 in 2017 for SD, DD, and CD, respectively. Controlled drainage reduced NO3−-N loading by 42.3%–58.2% when compared with the conventional/DD in 2 of 3 yr of study, whereas SD was found to reduce NO3−-N loading by 54.9%–73.1% compared with DD in all years studied. Total NO3−-N losses in this study were measured during the growing season (1 Apr. to 31 Oct.); the magnitude of NO3−-N losses and treatment effects may vary if studied year-round. Nitrous oxide fluxes were variable and low in magnitude throughout the study. Cumulated N2O losses were &lt;1% of the applied N for all drainage types. Controlled drainage increased yields compared with SD and DD. The use of CD in the region could aid in reducing climate stresses, as well as overall NO3−-N loads exiting drainage systems and may enhance crop yields compared with conventional systems. Future studies on dissolved N2O losses from drainage water may provide important insight into whether dissolved N2O losses exceed surface emissions.

Accumulation of nitrate N in the soil profile and its implications for the environment under dryland agriculture in northern China: A review

Nitrate (NO3-) leaching and water contamination have become a worldwide concern. In this review, some examples are presented to show the extent and magnitude of NO3- accumulation in the soil profiles and its potential effects on contamination of ground water and surface water under dryland farming in northern China. Climatic and management factors affecting NO3- leaching are also discussed. In northern China, rainfall is relatively sparse, but the high intensity of precipitation and porous soils play an important role in the accumulation of NO3N in soil and its subsequent leaching in the soil profile. There is a risk of nitrate accumulation and leaching when high rates of fertilizer N are applied to improve crop yields, and it becomes even worse when conventional land use is changed from cereal crops to vegetable crops and fruit orchards. Under such conditions, shallow ground water might be polluted by NO3-. This suggests that more attention should be paid to prevent this problem by using best management practices, especially by controlling the amount of N fertilizer input, balanced fertilization, split N application, inclusion of crops with deep taproots in the rotation and minimizing summer fallow (especially tilled) frequency. Key words: Accumulation, contamination, dryland farming, ground water, leaching, nitrate, northern China

Leaching versus input of nitrogen, potassium and magnesium in different fertilizer regimens in Christmas tree stands of Abies nordmanniana in Denmark

The effects of nitrogen (N), potassium (K) and magnesium (Mg) fertilization and deposition on nutrient leaching were assessed in four Danish Nordmann fir Christmas tree stands on former arable land. NPK 23-3-7 fertilizer type was applied in doses between 0 and 1200 kg ha−1 year−1. Deposition of N, K and Mg varied between 16 and 21 kg N ha−1 year−1, 2 and 10 kg K ha−1 year−1, and 2 and 3 kg Mg ha−1 year−1. The concentration of NO3–N in the soil water on the sandy sites was characterized by notable pulses contrasting the mitigated peaks on the clayey site. In general, the soil water concentrations and leaching reflected the fertilization, except for K at one clayey site. Mean annual leaching of NO3–N ranged from approximately 6 kg ha−1 year−1 in the control treatment to 235 kg ha−1 year−1 in the 1200 kg ha−1 year−1 fertilizer treatment. In the treatment with the commonly used 300 kg NPK 23-3-7 fertilizer NO3–N leaching was estimated to be approximately 46 kg ha−1 year−1. Annual leaching of N was described in a general model based on the fertilizer input. K and Mg leaching were distinctly more site specific than was N leaching. The magnitude of NO3–N leaching caused by application of 300 kg NPK 23-3-7 fertilizer was between the leaching amounts observed in traditional Danish forestry and Danish agriculture.

Nitrogen Dynamics in Ice Storm-Damaged Forest Ecosystems: Implications for Nitrogen Limitation Theory

Despite the widely recognized importance of disturbance in accelerating the loss of elements from land, there have been few empirical studies of the effects of natural disturbances on nitrogen (N) dynamics in forest ecosystems. We were provided the unusual opportunity for such study, partly because the intensively monitored watersheds at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, experienced severe canopy damage following an ice storm. Here we report the effects of this disturbance on internal N cycling and loss for watershed 1 (W1) and watershed 6 (W6) at the HBEF and patterns of N loss from nine other severely damaged watersheds across the southern White Mountains. This approach allowed us to test one component of N limitation theory, which suggests that N losses accompanying natural disturbances can lead to the maintenance of N limitation in temperate zone forest ecosystems. Prior to the ice storm, fluxes of nitrate (NO3−) at the base of W1 and W6 were similar and were much lower than N inputs in atmospheric deposition. Following the ice storm, drainage water NO3− concentrations increased to levels that were seven to ten times greater than predisturbance values. We observed no significant differences in N mineralization, nitrification, or denitrification between damaged and undamaged areas in the HBEF watersheds, however. This result suggests that elevated NO3- concentrations were not necessarily due to accelerated rates of N cycling by soil microbes but likely resulted from decreased plant uptake of NO3-. At the regional scale, we observed high variability in the magnitude of NO3- losses: while six of the surveyed watersheds showed accelerated rates of NO3− loss, three did not. Moreover, in contrast to the strong linear relationship between NO3− loss and crown damage within HBEF watersheds [r2: (W1 = 0.91, W6 = 0.85)], stream water NO3− concentrations were weakly related to crown damage (r2 = 0.17) across our regional sites. The efflux of NO3− associated with the ice storm was slightly higher than values reported for soil freezing and insect defoliation episodes, but was approximately two to ten times lower than NO3− fluxes associated with forest harvesting. Because over one half of the entire year’s worth of N deposition was lost following the ice storm, we conclude that catastrophic disturbances contribute synergistically to the maintenance of N limitation and widely observed delays of N saturation in northern, temperate zone forest ecosystems.

Soil Solution Chemistry at Different Positions on Slope in a Conifer Plantation Forest

It is known that soil property varies along the slope. It suggests that soil solution chemistry also differs topographically. To determine the variation in soil solution chemistry within one watershed, soil solution chemistry at the different positions of the slope was investigated. Soil N transformation changed along the slope. NH4+ ratio to inorganic N (NH4+ + NO3−) increased upslope. The tendency was verified by laboratory incubation. After incubation most of the mineralized N was nitrified at the lower part of the slope, while little nitrification occurred at the upper part of the slope. At the ridge and the backslope inorganic N form in soil solution was concomitant with inorganic N form by incubation. At the ridge NH4+ was predominant form in soil solution, at that time major anion was sea salt originated Cl−. From this, soil solution chemistry seems to be regulated by the external nutrient source at the ridge. In the second year of lysimeter installation NO3− concentration increased in both sites and the ratio of NH4+ to inorganic N decreased. It was considered due to the effect of lysimeter installation. The lag time and the magnitude of NO3− increase were different between the ridge and the backslope. It would be related with soil N transformation in pre-disturbance. The influence of disturbance were shown in other solute concentrations of soil solution.

A study of the reactions of NO3 radicals with organic sulfides: Reactivity trend at 298 K

AbstractA laser flash photolysis‐long path laser absorption technique has been employed to investigate the kinetics of NO3 reactions with CH3SCH3(𝓀1), CD3SCD3(𝓀2), and C2H5SC2H5(𝓀3) in 500 torr air at 298 K. The dependence of 𝓀1 on total pressure (20–500 torr) and oxygen partial pressure (0—100 torr) has also been investigated, with no dependence observed. Measured rate coefficients in units of 10−13 cm3 molecule−1 s−1 are 𝓀1 = 13 ± 3, 𝓀2 = 3.4 ± 0.8, and 𝓀3 = 48 ± 12, where the quoted uncertainties are 2σ estimates of absolute accuracy. The magnitude of NO3 + sulfide rate coefficients and negative activation energies for 𝓀1 (reported by other investigators) suggest that reaction does not proceed via a direct hydrogen abstraction mechanism. However, the reactivity trend observed in this study provides evidence that the reaction mechanism does involve breaking a carbon‐hydrogen bond.