Fate Of Ammonium Research Articles

Transition of source/sink processes and fate of ammonium in groundwater along with redox gradients

Ammonium (NH4+) retention/removal processes in groundwater are of great interest because of the continuous increase in nitrogenous compound loading due to anthropogenic activities. However, the transition of multiple co-occurring transformation processes that determine the fate of NH4+ in groundwater along a redox gradient remains underexplored. We selected a high nitrogen (N) groundwater system in the western Hetao Basin, China, to identify and quantify NH4+ source and sink processes, including mineralization, dissimilatory nitrate reduction to ammonium (DNRA), nitrification, and anammox, to better understand the dynamics of NH4+. Based on redox-sensitive parameters, that is, the oxidation-reduction potential (ORP) and NH4+ and nitrate (NO3−) contents, etc., the groundwater system was classified into three zones from upstream to downstream: zone I (oxidizing), zone II (moderately reducing), and zone III (strongly reducing). Using the 15N tracing technique, we found that NH4+ was mainly produced by mineralization while < 2% was produced by DNRA throughout the study area. Mineralization increased downstream because the supply of biodegradable N-containing compounds was augmented, which created a strong redox gradient to host a serial reaction chain. In zone I, NH4+ was mainly transferred to NO3− via nitrification, whereas in zones II and III, NH4+ was mainly transferred to N2 via anammox. The average NH4+ production/consumption ratios (P/C) in zones I, II, and III were 0.7, 6.9, and 51.1, respectively. Obviously, the NH4+ purification ability can only exceed the supply under aerobic conditions, thus suggesting that NH4+ will accumulate without limitation and be retained in strongly reducing groundwater. The situation of NH4+ accumulation would deteriorate over space and time in groundwater as human activities increase without an additional artificial supply of oxidants. The results provide mechanistic insights for quantitatively comprehending the dynamics and fate of NH4+ in groundwater, shedding light on groundwater NH4+ mitigation techniques.

Sources of nitrous oxide and the fate of mineral nitrogen in subarctic permafrost peat soils

Abstract. Nitrous oxide (N2O) emissions from permafrost-affected terrestrial ecosystems have received little attention, largely because they have been thought to be negligible. Recent studies, however, have shown that there are habitats in the subarctic tundra emitting N2O at high rates, such as bare peat (BP) surfaces on permafrost peatlands. Nevertheless, the processes behind N2O production in these high-emission habitats are poorly understood. In this study, we established an in situ 15N-labeling experiment with two main objectives: (1) to partition the microbial sources of N2O emitted from BP surfaces on permafrost peatlands and (2) to study the fate of ammonium and nitrate in these soils and in adjacent vegetated peat (VP) surfaces showing low N2O emissions. Our results confirm the hypothesis that denitrification is mostly responsible for the high N2O emissions from BP. During the study period, denitrification contributed ∼ 79 % of the total N2O emissions from BP, whereas the contribution from ammonia oxidation was less (about 19 %). Both gross N mineralization and gross nitrification rates were higher in BP than in VP, with high C/N ratios and a low water content likely limiting N transformation processes and, consequently, N2O production in the latter soil type. Our results show that multiple factors contribute to high N2O production in BP surfaces on permafrost peatlands, with the most important factors being the absence of plants, an intermediate to high water content and a low C/N ratio, which all affect the mineral-N availability for soil microbes, including those producing N2O. The process understanding produced here is important for the development of process models that can be used to evaluate future permafrost–N feedbacks to the climate system.

Sources of ammonium enriched in groundwater in the central Yangtze River Basin: Anthropogenic or geogenic?

The occurrence of excessive ammonium in groundwater threatens human and aquatic ecosystem health across many places worldwide. As the fate of ammonium in groundwater systems is often affected by a complex mixture of transport and biogeochemical transformation processes, identifying the sources of groundwater ammonium is an important prerequisite for planning effective mitigation strategies. Elevated ammonium was found in both a shallow and an underlying deep groundwater system in an alluvial aquifer system beneath an agricultural area in the central Yangtze River Basin, China. In this study we develop and apply a novel, indirect approach, which couples the random forest classification (RFC) of machine learning method and fluorescence excitation-emission matrices with parallel factor analysis (EEM-PARAFAC), to distinguish multiple sources of ammonium in a multi-layer aquifer. EEM-PARAFAC was applied to provide insights into potential ammonium sources as well as the carbon and nitrogen cycling processes affecting ammonium fate. Specifically, RFC was used to unravel the different key factors controlling the high levels of ammonium prevailing in the shallow and deep aquifer sections, respectively. Our results reveal that high concentrations of ammonium in the shallow groundwater system primarily originate from anthropogenic sources, before being modulated by intensive microbially mediated nitrogen transformation processes such as nitrification, denitrification and dissimilatory nitrate reduction to ammonium (DNRA). By contrast, the linkage between high concentrations of ammonium and decomposition of soil organic matter, which ubiquitously contained nitrogen, suggested that mineralization of soil organic nitrogen compounds is the primary mechanism for the enrichment of ammonium in deeper groundwaters.

The fate of ammonium in phengite at high temperature

Nitrogen (N) is the main component of the atmosphere and is largely considered as a volatile element. However, most researchers now agree that a significant amount of N, in the form of ammonium (NH4+) substituting for K+ in some K-bearing minerals such as clays, micas, and feldspars, can be transferred to the deep Earth through subduction. The fate of ammonium in those minerals during subduction is still poorly known but is likely controlled by temperature and pressure pathways. In an attempt to contribute to understanding the fate of N during high-temperature processes, we carried out in situ high-temperature IR and Raman spectra measurements to investigate the rate and mechanism of NH4+ loss in phengite. We observed that a new OH band at 3425 cm−1 became prominent above 400 °C, and did not change with times during isothermal annealing at 500 and 700 °C. The N-H stretching band shifted to higher wavenumbers in the temperature interval from −150 to 20 °C, while linearly shifted to lower wavenumbers in the temperature interval from 20 to 500 °C and remained stable above 500 °C. The N-H bending band linearly shifted to lower wavenumbers in the temperature interval from −150 to 400 °C and remained stable. The K-O stretching frequency decreased with increasing temperature to 600 °C, and then remained stable. These processes were reversible until dehydration and ammonium loss from phengite starting at 800 °C. The results suggest that (1) at low temperatures, ammonium is ordered and hydrogen bonding between ammonium and the framework evolves during cooling; (2) at high temperatures, the N-H interatomic distance of NH4+ lengthens with increasing temperature until 500 °C. N-H bond subsequently no longer lengthens, accompanied by H transferring from N to neighboring O and forming a new OH band at 3425 cm−1. At 800 °C, H+ starts breaking from N and leaving others to form NH3 and OH−. This study has implications for evaluating the extent to which these minerals can preserve information regarding nitrogen behavior during high-temperature processes.

Effect of Elodea nuttallii-Immobilized Nitrogen Cycling Bacteria on the Mechanism of Nitrogen Removal in Polluted River Water

Surface water, Elodea nuttallii and undisturbed sediment cores from the Qinshui River in Gonghu Bay were collected to carry out a simulation experiment in a laboratory to study the effect of Elodea nuttallii-immobilized nitrogen-cycling bacteria on nitrogen removal mechanisms from the river water. In this study, the transformation and fate of ammonium among four different treatment groups were investigated by using a stable 15 N isotope pairing technique combined with high-throughput sequencing technology[Treatment A:bare sediment, Treatment B:sediment+immobilized nitrogen cycling bacteria (INCB), Treatment C:sediment+E. nuttallii, Treatment D:sediment+INCB+E. nuttallii]. The results of the 15 N mass-balance model showed that there were three pathways to the ultimate fate of nitrogen:precipitated with the sediments, absorbed by E. nuttallii, and consumed by microbial processes[denitrification and anaerobic ammonium oxidation (ANAMMOX)]. The percentages of E. nuttallii assimilated in the 15 NH4+ were 25.44% and 19.79% for treatments C and D. The sediment storage ratio of 15 NH4+ accounted for 7.94%, 5.52%, 6.47% and 4.86% in treatments A, B, C, and D, respectively. The proportion of 15 NH4+ lost as 15 N-labelled gas were 16.06%, 28.86%, 16.93% and 33.09% in the four different treatment groups, respectively. Denitrification and anammox were the bacterial primary processes in N2 and N2O production. The abundance and diversity of microorganisms was relatively higher in the treatment with E. nuttallii-immobilized nitrogen cycling bacteria (E-INCB) assemblage technology applied. Furthermore, the removal rates of 15 NH4+ were 24%, 34.38%, 48.84% and 57.74% in treatments A, B, C and D, respectively. These results show that the E-INCB assemblage technology may improve the capacity for nitrogen removal from the river water.

The Fate of Ammonium in Integrated Vertical-flow Constructed Wetlands Using Stable Isotope Technique

The fate of ammonium (NH4+) was investigated using the N-15 tracer stable isotope technique in integrated vertical-flow constructed wetlands (IVCWs). Two types of IVCW systems were built: unplanted IVCWs (control) and planted IVCWs. The results showed that a high NH4+ removal efficiency (95.4%) in the planted IVCWs. Plants not only removed NH4+ by direct uptake (13.6 +/- 0.7%) but also improved the NH4+ removal capacity of IVCWs, compared with the control. Besides plant uptake, microbial conversion was the dominant mechanism of NH4+ removal in IVCWs, and a large proportion (75.2-85.6%) of added NH4+ may be permanently removed via anammox and nitrification-denitrification processes in IVCWs.

Drainage-Process Analyses for Agricultural Non-Point-Source Pollution from Irrigated Paddy Systems

The aim of this study was to investigate the effects of drainage processes on non-point-source pollution in a complex irrigation and drainage system. Field experiments were conducted to measure quality and quantity of leakage and irrigation-return water in field drains, lateral drains, and the main drain during paddy-growing periods for 2 years. Water-flow and chemical-transport processes from paddy fields to field drains were simulated numerically. A modified Muskingum method was proposed to calculate the processes of water flow and chemical transport in lateral and main drains. Results showed that the Muskingum method was applied successfully to calculate the drainage and chemical-transport processes, as well as to quantify the effect of drain storage on the processes. Results from the field experiments and simulations indicated that the fate of ammonium (NH4+), nitrate (NO3−), and chemical oxygen demand (COD) in the system was primarily controlled by the drainage processes. Mass of NH4+ discharged from paddy fields to drains was mainly through subsurface flow (i.e., the leakage from paddy fields to field drains) and mass of NO3− mainly through deep leakage (i.e., the leakage from paddy fields to groundwater and finally to drains). The COD transportation was through irrigation-return water, subsurface flow, and deep leakage. Eighty-one percent of the discharged NH4+ mass by leakage and 64% of the discharged NO3− mass were through subsurface flow and deep leakage, respectively. Approximately 15% of the applied nitrogen in the paddy field was lost through the drainage processes. Within the total discharged nitrogen in the main drain, 38% and 62% were from subsurface flow and deep leakage, respectively. The methods and results from this study should be useful to characterize non-point-source pollution in paddy-irrigation district.

Transport and fate of ammonium and its impact on uranium and other trace elements at a former uranium mill tailing site

The remediation of ammonium-containing groundwater discharged from uranium mill tailing sites is a difficult problem facing the mining industry. The Monument Valley site is a former uranium mining site in the southwest US with both ammonium and nitrate contamination of groundwater. In this study, samples collected from 14 selected wells were analyzed for major cations and anions, trace elements, and isotopic composition of ammonium and nitrate. In addition, geochemical data from the U.S. Department of Energy (DOE) database were analyzed. Results showing oxic redox conditions and correspondence of isotopic compositions of ammonium and nitrate confirmed the natural attenuation of ammonium via nitrification. Moreover, it was observed that ammonium concentration within the plume area is closely related to concentrations of uranium and a series of other trace elements including chromium, selenium, vanadium, iron, and manganese. It is hypothesized that ammonium–nitrate transformation processes influence the disposition of the trace elements through mediation of redox potential, pH, and possibly aqueous complexation and solid-phase sorption. Despite the generally relatively low concentrations of trace elements present in groundwater, their transport and fate may be influenced by remediation of ammonium or nitrate at the site.

Infiltration Mechanism Controls Nitrification and Denitrification Processes under Dairy Waste Lagoon

Earthen waste lagoons are commonly used to store liquid wastes from concentrated animal feeding operations. The fate of ammonium (NH) and nitrate (NO) was studied in the vadose zone below earthen-clay dairy farm waste lagoons using three independent vadose zone monitoring systems. The vadose zone was monitored from 0.5 to 30 m below land surface through direct sampling of the sediment porewater and continuous measurement of the sediment profile's water content variations. Four years of monitoring revealed that wastewater infiltration from the lagoon is controlled by two mechanisms: slow (mm d), constant infiltration from the lagoon bed; and rapid (m h) infiltration of wastewater and rainwater via preferential flow in desiccation cracks formed in the unsaturated clay sediment surrounding the lagoon banks. The preferential flow mechanism is active mainly during wastewater-level fluctuations and intensive rain events. The vadose zone below the waste sources remained unsaturated throughout the monitoring period, and all infiltrating NH was oxidized in the upper 0.5 m. The NH oxidation (nitrification) was coupled with NO reduction (denitrification) and depended on the sediment water content, which was controlled by the infiltration mechanism. Coupled nitrification-denitrification (CND) resulted in 90 to 100% reduction in the total nitrogen mass in the vadose zone, with higher removal under high water content (∼0.55 m m). Mass balance of nitrogen and isotopic composition of NO indicated that CND, rather than cation exchange capacity, is the key factor regulating nitrogen's fate in the vadose zone underlying earthen waste lagoons.

Isotopic Approach to Determining the Fate of Ammonium Regenerated from Sediments in a Eutrophic Sub-estuary of Waquoit Bay, MA

We measured fluxes of NH 4 + and NO 3 − and δ15N of NH 4 + , sediment, and porewater NH 4 + from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH 4 + flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not differ along the estuary. The δ15N of regenerated NH 4 + ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰. Based on differences between the δ15N of regenerated NH 4 + and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after remineralization of NH 4 + . Differences between the δ15N of regenerated NH 4 + and the δ15N of porewater NH 4 + provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH 4 + underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification, NH 4 + flux released 1.4 mol N m−2 year−1 to the water column and could provide 42% of phytoplankton nitrogen requirements.

Geochemistry of Inorganic Nitrogen in Waters Released from Coal-Bed Natural Gas Production Wells in the Powder River Basin, Wyoming

Water originating from coal-bed natural gas (CBNG) production wells typically contains ammonium and is often disposed via discharge to ephemeral channels. A study conducted in the Powder River Basin, Wyoming, documented downstream changes in CBNG water composition, emphasizing nitrogen-cycling processes and the fate of ammonium. Dissolved ammonium concentrations from 19 CBNG discharge points ranged from 95 to 527 microM. Within specific channels, ammonium concentrations decreased with transport distance, with subsequent increases in nitrite and nitrate concentrations. Removal efficiency, or uptake, oftotal dissolved inorganic nitrogen (DIN) varied between channel types. DIN uptake was greater in the gentle-sloped, vegetated channel as compared to the incised, steep, and sparsely vegetated channel and was highly correlated with diel patterns of incident light and dissolved oxygen concentration. In a larger main channel with multiple discharge inputs (n=13), DIN concentrations were >300 microM, with pH > 8.5, after 5 km of transport. Ammonium represented 25-30% of the large-channel DIN, and ammonium concentrations remained relatively constant with time, with only a weak diel pattern evident. In July 2003, the average daily large-channel DIN load was 23 kg N day(-1) entering the Powder River, an amount which substantially increased the total Powder River DIN load after the channel confluence. These results suggest that CBNG discharge may be an important source of DIN to western watersheds, at least at certain times of the year, and that net oxidation and/or removal is dependent upon the extent of contact with sediment and biomass, type of drainage channel, and time of day.

Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries

Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.

Potential acidifying capacity of deposition: Experiences from regions with high NH4+ and dry deposition in China

Acid rain may cause soil acidification possibly leading to indirect forest damage. Assessment of acidification potential of atmospheric deposition is problematic where dry and occult deposition is significant. Furthermore, uncertainty is enhanced where a substantial part of the potential acidity is represented by deposition of ammonium (NH4+) since the degree of assimilation and nitrification is not readily available.Estimates of dry deposition based on deposition velocity are highly uncertain and the models need to be verified or calibrated by field measurements of total deposition. Total deposition may be monitored under the forest canopy. The main problem with this approach is the unknown influence of internal bio-cycling. Moreover, bio-cycling may neutralize much of the acidity by leaching of mainly K+. When the water percolates down into the rooting zone this K+ is assimilated again and acidity is regenerated. Most monitoring stations only measure deposition. Lacking measurements of output flux of both NH4+ and NO3− from the soil one cannot assess current net N transformation rates. Assumptions regarding the fate of ammonium in the soil have strong influence on the estimated acid load. Assuming that all the NH4+ is nitrified may lead to an overestimation of the acidifying potential.In parts of the world where dry deposition and ammonium are important special consideration of these factors must be made when assessing the acidification potential of total atmospheric loading. In China dry and occult deposition is considerable and often greater than wet deposition. Furthermore, the main part of the deposited N is in its reduced state (NH4+). The IMPACTS project has monitored the water chemistry as it moves through watersheds at 5 sites in China. This paper dwells at two important findings in this study. 1) Potassium leached from the canopy by acid rain is assimilated again upon entering the mineral soil. 2) Nitrification apparently mainly takes place in forest floor (H- and O-) horizon as NH4+ that escapes this horizon is efficiently assimilated in the A-horizon. This suggests that the potential acidification capacity of the deposition may be found in the throughfall and forest floor solution by treating K+ and NH4+, respectively, as acid cations in a base neutralization capacity (BNC) calculation.

Inorganic and organic nitrogen cycling in the Southern California Bight

On the basis of mass balance calculations performed for nitrogen (N) uptake experiments in the Southern California Bight (SCB), it has been suggested that a significant portion of dissolved inorganic N (DIN) uptake results in the production of dissolved organic N (DON). To investigate this process, the fate of ammonium (NH 4 +) and nitrate (NO 3 −) uptake was quantified within the euphotic zone at three coastal stations in the SCB using 15N tracer techniques. Several trends in the fate of DIN and the production of DON were observed. First, production of particulate N (PN), from both NH 4 + and NO 3 −, was quantitatively more important in near surface waters, while DON release dominated within the nitracline. Second, the percentage of gross N uptake released as DON was generally higher when NO 3 −, rather than NH 4 +, was the substrate. Third, the percentage of N released as DON was higher at night, relative to the day. Fourth, rates of DON release were significantly correlated to NH 4 + regeneration, suggesting that similar mechanisms are responsible for both processes—presumably grazing. The results of this study indicate that the DON pool is a sink for DIN uptake on the time scale of hours. One implication of this finding is that new production estimates based on 15NO 3 − uptake rates will likely underestimate particle flux out of the surface layer because the rate of NO 3 − uptake is underestimated due to loss of DO 15N during the incubation. On time scales of months to years, however, the N that is taken up as NO 3 − and released as DON will likely contribute to export flux via incorporation of the dissolved phase during seasonal mixing into sinking particles or transport. The export of DON on these time scales argues for the use of gross uptake rates to calculate f-ratios.

Nitrapyrin effect on corn N‐15 uptake efficiency, denitrification and nitrate leaching

Abstract The effect of nitrapyrin on the fate of fertilizer nitrogen (N) applied to soil needs further investigation. Our objective was to determine the effect of nitrapyrin under two different leaching regimes on the fate of ammonium sulfate‐nitrogen [(NH4)2SO4‐N] added to the soil, namely corn N uptake, denitrification, nitrate leaching and soil residual N. A Nunn sandy clay loam soil (fine, montmorillonitic, mesic, aridic, argiustoll), low in residual inorganic N was used. Nitrogen‐15 enriched (NH4)2SO4 (5 atom% N‐15) was applied at five rates (0, 50, 100, 200, and 400 mg/kg), nitrapyrin at three rates 0, 1.3, and 2.6 μL/kg (0, 2.36, and 4.72 L/ha) and leaching at two rates (0 and 1000 mL over field capacity in two 500‐mL increments at 3 and 6 weeks after planting) in a complete factorial arrangement with three replications. Corn (Zea mays L.) seeds were planted in pots (2 kg soil/pot) and allowed to grow for 80 days in a greenhouse. The atom% N‐15 values were determined in plant tops, leachates and so...