Denitrification Process In Soil Research Articles

Effects of Straw Amendment in Combination with Synthetic N Fertilizer Addition on N2O, N2, and Their Stoichiometric Ratios in Three Different Agro-Ecosystems

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control < KNO3 < rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Effect of Chemical Fertilizer and Manure Combined with Biochar on Denitrification Potential and Denitrifying Bacterial Community in Rhizosphere Soil

To clarify the effect of chemical fertilizer and manure combined with biochar on denitrifying microorganisms and denitrification potential of rhizosphere soil, a pot experiment growing lemon was conducted involving five treatments, namely no fertilization (CK), chemical fertilizer (CF), manure (M), chemical fertilizer combined with biochar (CFBC), and manure combined with biochar (MBC). We determined the characteristics of the rhizosphere soil nirS-, nirK-, and nosZ-type denitrifying bacteria populations; denitrification potential; and soil environmental factors to clarify the effects of chemical and manure combined with biochar on denitrification. Our results showed that compared with that in CK, the CF treatment reduced the rhizosphere soil denitrification potential by 47.7%, whereas the M and MBC treatments increased the denitrification potential by 2192.7% and 1989.9%, respectively. The M and MBC treatments increased the gene copy number of nirS and nosZ, the CF and CFBC treatments decreased the gene copy number of nirS and nosZ, and all four fertilization treatments increased the gene copy number of nirK. Stepwise regression analysis showed that pH was the main factor for the abundance of nirS-type denitrifying bacteria and SOM and NH+4-N were the main factors for the abundance of nirK-type denitrifying bacteria, whereas pH, NO-3-N, and N/P were main factors for the abundance of nosZ-type denitrifying bacteria. The results of partial least squares analysis indicated that the abundance of nirS-and nosZ-type denitrifying bacteria, pH, TN, and N/P were the main factors affecting rhizosphere denitrification potential. Therefore, in acidic purple soil, nirS- and nosZ-type denitrifying bacteria were the main drivers of the soil denitrification process in lemon rhizospheres under chemical fertilizer and pig manure combined with biochar, whereas fertilizer affected the rhizosphere soil denitrification process by regulating soil pH, TN, and N/P.

Detoxification pathways of multiple metals from intensive copper production by indigenous ureolytic microbes coupled with soil nitrogen transformation

The ubiquitous ureolytic microbes were potential to clean up toxic heavy metals from environment. Their responses and detoxification mechanisms are largely unknown for multiple metals in field soils. In this study, high-throughput sequencing of the urease-encoding genes and deep learning from bioinformatic analysis were conducted for identifying ureolytic prokaryote-related processes throughout China. The passive adsorption of heavy metals onto cell walls or cell surfaces was mainly performed by G+ ureolytic bacteria in soils located in the large-scale smelting areas with slightly high Hg and low Cu/Zn/Ni contents. For the large-scale smelting areas with the highest Cr and lowest Cu/As contents, the Cr(VI) was reduced to Cr(III) by G– ureolytic bacteria and then accumulated in their periplasmic spaces or cell surfaces. The G– ureolytic bacteria detoxified high contents of multiple metals by intracellular antioxidant defense mechanisms and extracellular urease-induced (co)precipitation in the medium-scale smelting areas, consistent with high urease activities and ureolytic microbial diversity. In addition, this large-scale field work verified that toxic metals stimulated the bacterial hydrolysis of urea as soil nitrogen fertilizers and depressed the bacterial fixation of nitrogen from air. Simultaneously, the heavy metals used nitrate-N and nitrite-N as alternative electron acceptors, driving the soil denitrification processes.

Soil denitrification rates are more sensitive to hydrological changes than restoration approaches in a unique riparian zone

Abstract Riparian zones, an aquatic‐terrestrial interface, can intercept more than half of nitrogen (N) exported from terrestrial ecosystems to adjacent rivers, primarily by denitrification processes. However, damming has disrupted natural patterns and processes of flooding and vegetation community assemblages, and yet little is known about how hydrological changes and ecosystem restoration affect the biogeochemical functioning in the riparian ecosystems. We conducted an in situ experiment to evaluate the effects of hydrological change (e.g. altering flooding intensity and frequency) and restoration approaches (e.g. natural regeneration and active revegetation) on denitrification rates and the abundance of denitrifier genes in the riparian zone of the Three Gorges Reservoir, China. Our results showed that active revegetation did not significantly increase denitrification rates compared to the natural regeneration, but their underlying mechanism was different. At the natural regeneration area, the denitrification rate was primarily regulated by soil properties and abundance of nosZ gene, while at the active revegetation area, it was controlled merely by the abundance of nosZ gene. In addition, vegetation types showed little effect on the soil denitrification process, and the denitrification rate decreased with flooding intensity by reducing denitrifier gene abundance. The periodic flooding treatment doubled the denitrification rate compared with the no flooding treatment, which might be attributed to the enhancement of soil carbon availability. Our results suggest that in terms of N removal via denitrification processes, natural regeneration is a priority approach to restoring degraded riparian ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

No significant change noted in annual nitrous oxide flux under precipitation changes in a temperate desert steppe

AbstractAs the third most important greenhouse gas, nitrous oxide (N2O) poses a significant threat to global warming and the ozone layer. However, the effects of precipitation changes on N2O emissions in arid areas remain unclear, particularly in desert steppe environments. Therefore, an in situ control experiment was conducted from July 2018 to July 2020 to examine the N2O emissions with changes in precipitation in the Urat Desert Steppe, northwestern China. The results showed that the N2O emission rate was relatively low in this desert steppe, at −0.04 to +15.0 μg N m−2 hr−1 with an annual flux of 0.20 ± 0.03 kg N ha−1. An increasing trend of N2O emission was observed in the early growing season (February to June 2019) when the precipitation was increased by 40% and 60% of its natural level. In contrast, no significant change in N2O emissions was observed when the precipitation was decreased during the same period. During the middle and late growing season and in the nongrowing season, precipitation changes did not significantly affect N2O emissions. In particular, no significant change in the annual N2O flux was observed during the entire observation period whether the precipitation was increased or decreased. Furthermore, the results of a structural equation model showed that the most important controlling factor for N2O emission is an abundance of key functional ammonia monooxygenase genes of ammonia‐oxidizing archaea, which are restricted by the soil NH4+‐N content, followed by abundances of key functional NO2− reductase (nirK) and N2O reductase (nosZ) genes. In contrast, the indirect effect of soil moisture on the abundance of nosZ compensated for the direct effect of soil moisture on N2O emissions. These results show that the primary and secondary origins of N2O emissions are soil ammonia oxidation and soil denitrification processes, respectively. In these two processes, N2O emissions are influenced more by the abundance of key functional microorganisms than by soil moisture, which might be limited mainly by the available soil nitrogen. Overall, the N2O emissions in the desert steppe environment were not sensitive to precipitation changes and were regulated mainly by nitrogen‐related key functional microorganisms.

Regulation of the product stoichiometry of denitrification in intensively managed soils

AbstractCrop residue amendment in conjunction with synthetic nitrogen (N) fertilization is a common agricultural practice that increases soil fertility and crop yield. However, such a practice may also change soil denitrification process. Here, we conducted an incubation experiment with a robotized continuous flow N2 free incubation system [using helium (He) and oxygen (O2)] and measured fluxes of N2O and N2 at a high resolution in an intensively managed soil to examine the interaction effect of straw amendment and N fertilization on soil denitrification. Four treatments were set consisting of (a) a nonamended treatment (Control); (b) a Straw treatment (2 g straw kg−1 dry soil); (c) a KNO3 treatment (KNO3, 15 mM KNO3); and (d) a Straw + KNO3 treatment (2 g straw kg−1 dry soil and 15 mM KNO3). During the oxic phase (80% He plus 20% O2) of the experiment (initial 2 days), flux rates of N2O were 0.54 and 0.38 kg N/ha day−1 in the Control and KNO3 treatments, respectively. Meanwhile, straw amendment triggered N2O fluxes immediately after the onset of treatments, which was more evident in the Straw + KNO3 treatment. During the anoxic phase (100% He), both N2O and N2 emissions increased in all treatments, with the effect being more pronounced in the Straw and Straw + KNO3 treatments. In line with the observed differences in gas fluxes, the abundances of nirK, nirS, and nosZ genes increased clearly in these treatments. Overall, the mean N2O/(N2O + N2) ratio (0.69 ± 0.03) in the Control treatment was significantly lower compared to the KNO3 treatment (18.8%) and higher than the straw‐amended soils (31.9% and 17.4% compared to the Straw and Straw + KNO3 treatments, respectively). Taken together, our results suggest straw amendment significantly altered N2O and N2 fluxes by decreasing the N2O/(N2O + N2) ratio; however, the effects of straw amendment depended on soil nitrate content.

Trichloroethylene inhibits nitrogen transformation and microbial community structure in Mollisol.

Trichloroethylene (TCE) is the most ubiquitous halogenated organic pollutant in the environment, it is one of the 129 priority control pollutants. In order to clarify the influence of TCE on microorganisms and nitrogen transformation in Mollisol is the core purpose of this study. Results showed that 10 mg kg-1 TCE is the concentration limit of ammonification in Mollisol. When the concentration of TCE reached 10 mg kg-1 and the effect lasted for over 7 days, the process of ammonia oxidation to nitric acid in Mollisol will be affected. TCE affected the process of nitrate (NO3-) transformation into nitrite (NO2-) by affecting the activity of nitrate reductase, thereby affected the denitrification process in soil. When the concentration of TCE is more than 10 mg kg-1 it reduced the ability of soil microorganisms to obtain nitrogen, thereby affecting soil nitrogen transformation. RDA (Redundancy analysis) showed that the activity of nitrate reductase and the number of nitrifying bacteria and denitrifying bacteria in soil was negatively correlated with the incubation of TCE. In addition, soil nitrate reductase, nitrite reductase, peroxidase activity, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria were negatively correlated with TCE concentration. Beyond that PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) of functional gene structure depend on KEGG (Kyoto Encyclopedia of Genes and Genomes) showed that 20 mg kg-1 TCE significantly inhibited the metabolism of energy and other substances in Mollisol. Based on the above, it is found that TCE significantly affected nitrification and denitrification in Mollisol, thus the nitrogen transformation in Mollisol was affected by TCE contamination.

Responses of soil nosZ-type denitrifying microbial communities to the various land-use types of the Loess Plateau, China

Microbial denitrification is an important part of the soil nitrogen cycling process and is the main way that naturally-fixed nitrogen returns to the atmosphere. Research to date has mainly focused on the effects of temperature, pH and carbon sources on denitrification, with the effects of different vegetation types thought to be relatively small. This study investigated the soil denitrification process in the Loess hilly region of China. Four typical land-use types were selected: farmland (FL), abandoned land (AL), Caragana korshinskii (CK), and Robinia pseudoacacia (RP). The functional gene nosZ, which regulates nitrous oxide reductase (N2OR), was selected as the target primer. High-throughput sequencing was carried out and the composition of soil properties was determined. The physicochemical properties of soil, including nitrate nitrogen and organic carbon levels, were studied to explore soil microbial compositions and species diversities and their main influences. Compared with FL, the content of ammonium nitrogen (AN) in AL, CK, and RP soils was 28.5%, 29.7% and 28.8% higher, respectively, while nitrate nitrogen was 1.39-, 1.96-, and 1.55-fold higher, respectively. The Shannon index showed that the microbial diversity of the nosZ gene in RP was greater than that in FL. Nonmetric multidimensional scaling analysis showed that the FL distribution was much different from those of AL, CK, and RP; meanwhile, the AL, CK, and RP distributions tended to overlap, which indicates that there were only small differences in species compositions. Redundancy analysis showed that AN is a key environmental factor affecting the nosZ type microorganisms composition in different taxonomic levels, and the contribution rates can reach 74.3% (p = 0.006), 73.2% (p = 0.004), and 62.6% (p = 0.008), respectively (from phylum to order). This study revealed the α- and β -diversities of nosZ type microorganisms and the key environmental influences on the composition of microorganisms with the land-use change. It provides a reference for further study on the heterogeneity of nitrogen output processes in different land use types.

Effect of silicon on barley growth and N2O emission under flooding

The global climate change is related with greenhouse gas emission from cultivated soils – carbon dioxide, methane and nitrous oxide. The emissions of N2O also have negative influence on ozone layer of our planet. The major source of the nitrous oxide is denitrification process in soil, which controlled by specific soil microbe society. The pot experiment with flooding to accelerate the denitrification process and the application of the monosilicic acid as a source of soluble form of Si was carried out with barley. Several forms of nitrous oxide emission (unlimited carbon denitrification and potential denitrification with or without ethylene application) were measured. The obtained data showed that the application of monosilicic acid to brown soil when growing barley under conditions of soil flooding has a significant effect on nitrogen emission and can change the N2O:N2 ratio. The application of the monosilicic acid reduced the uC-D N2O emission, while increased the PD N emission. Generally the application of the water soluble Si decreased the N2O:N2 ratio. We suggested that the presence of monosilicic acid in the system provides a more complete denitrification process with the formation of N2 in the NO3− → NO2− → NO→N2O → N2 reaction sequence, while the deficiency of bioactive Si mainly provides the formation and emission of N2O. Considering that N2 is not a greenhouse gas, we can conclude that application of monosilicic acid to the soil can reduce greenhouse gas emissions and reduce the impact of global climate change on agricultural activity.

Disturbances of electron production, transport and utilization caused by chlorothalonil are responsible for the deterioration of soil denitrification

Extensive use of pesticides poses significant threats to soil denitrification process and might affect the emission of the greenhouse gas nitrous oxide (N2O) from soils. Previous studies on soil denitrification have frequently focused on natural factors or nitrogen fertilization, but have ignored the role of pesticides. In this study, the effects of chlorothalonil (CHT, a common pesticide) and its major metabolite 4-hydroxychlorothalonil (4OH-CHT) on soil denitrification were explored. Results showed that soil denitrification rates (15N pairing method) were declined by 27.4%–72.2%, whereas N2O emissions were unexpectedly increased by 83.9%–299.5%. These disturbances were caused by CHT, rather than by its metabolite 4OH-CHT, and noncompetitive inhibition was observed with an inhibition constant of 9.74 mg kg−1. Mechanistic studies further revealed that CHT inhibited soil denitrification process by deteriorating organic matter metabolism (electron production), electron respiration chain (electron transport), and denitrifying enzymes activities (electron utilization), more than by influencing denitrifier communities and denitrifying gene abundances. Furthermore, structural equation modeling suggested that electron respiration chain and N2O reductase activities were the most important drivers in explaining denitrification in CHT-polluted soils. Our results imply that the wide use of pesticides in agricultural production may disturb soil nitrogen cycle and increase the production of potent greenhouse gas N2O.

Assessment of the Spatial and Temporal Variations of Water Quality for Agricultural Lands with Crop Rotation in China by Using a HYPE Model.

Many water quality models have been successfully used worldwide to predict nutrient losses from anthropogenically impacted catchments, but hydrological and nutrient simulations with limited data are difficult considering the transfer of model parameters and complication of model calibration and validation. This study aims: (i) to assess the performance capabilities of a new and relatively more advantageous model, namely, Hydrological Predictions for the Environment (HYPE), that simulates stream flow and nutrient load in agricultural areas by using a multi-site and multi-objective parameter calibration method and (ii) to investigate the temporal and spatial variations of total nitrogen (TN) and total phosphorous (TP) concentrations and loads with crop rotation by using the model for the first time. A parameter estimation tool (PEST) was used to calibrate parameters. Results show that the parameters related to the effective soil porosity were highly sensitive to hydrological modeling. N balance was largely controlled by soil denitrification processes. P balance was influenced by the sedimentation rate and production/decay of P in rivers and lakes. The model reproduced the temporal and spatial variations of discharge and TN/TP relatively well in both calibration (2006–2008) and validation (2009–2010) periods. Among the obtained data, the lowest Nash-Suttclife efficiency of discharge, daily TN load, and daily TP load were 0.74, 0.51, and 0.54, respectively. The seasonal variations of daily TN concentrations in the entire simulation period were insufficient, indicated that crop rotation changed the timing and amount of N output. Monthly TN and TP simulation yields revealed that nutrient outputs were abundant in summer in terms of the corresponding discharge. The area-weighted TN and TP load annual yields in five years showed that nutrient loads were extremely high along Hong and Ru rivers, especially in agricultural lands.

Macroscopic assessment of nanosilver toxicity to soil denitrification kinetics.

A large increase in commercial and home use of silver nanoparticle (AgNP) products and technologies has raised concerns about their impact on environmental health. While several sources cite soils and sediments as the predominant sink for AgNPs in natural environments, few studies contribute to risk assessment of AgNPs in terrestrial environments. In this study, the effect of AgNPs ([Ag]: 1-100 mg/kg, 15-50 nm with 0-90% polyvinylpyrrolidone [PVP] capping agent) on soil denitrification processes was investigated with batch kinetic experiments using well-characterized AgNPs. Although the effects on denitrification kinetics and equilibrium end-points were variable among the AgNPs, denitrification kinetics were limited under certain conditions (e.g., PVP-coated AgNPs ≥ 10 mg/kg). In assessing the impact of AgNPs on ecosystem processes, it is important to consider the interactions of AgNPs with soils and sediments in addition to the physicochemical properties (size, coating agents, sedimentation rate, solubility, surface charge properties, dispersibility) of AgNPs.

Effects of Ce(III) and CeO₂ nanoparticles on soil-denitrification kinetics.

Cerium (Ce)-based compounds, such as CeO₂ nanoparticles (NPs), have received much attention in the last several years due to their popular applications in industrial and commercial uses. Understanding the impact of CeO₂ NPs on nutrient cycles, a subchronic toxicity study of CeO₂ NPs on soil-denitrification process was performed as a function of particle size (33 and 78 nm), total Ce concentration (50-500 mg L(-1)), and speciation [Ce(IV) vs. Ce(III)]. The antimicrobial effect on the soil-denitrification process was evaluated in both steady-state and zero-order kinetic models to assess particle- and chemical-species specific toxicity. It was found that soluble Ce(III) was far more toxic than Ce(IV)O₂ NPs when an equal total concentration of Ce was evaluated. Particle size-dependent toxicity, species-dependent toxicity, and concentration-dependent toxicity were all observed in this study for both the steady-state and the kinetic evaluations. Changes in physicochemical properties of Ce(IV)O₂ NPs might be important in assessing the environmental fate and toxicity of NPs in aquatic and terrestrial environments.

Dominant process and mechanism of nitrous oxide flux in an alpine meadow on the Tibetan plateau

Nitrous oxide emission (N2O) and its main process in a Kobresia humillis meadow were measured by acetylene inhibition during the growing season in 2009, and the DNDC model was validated by the N2O fluxes of 2004 and 2005. The average fluxes were 2.91±0.46 and 1.97±0.58 μg/m2/h from nitrification-denitrification and soil denitrification process, thus indicating that the potential nitrification might be the dominant process in the alpine meadow. DNDC model also revealed that nitrification contributed 52.85% to N2O flux, while denitrification contributed about 47.15%. The N2O flux could be well captured considering the main affecting factors by a linear regression model (r2=0.663), which demonstrated that soil temperature and biomass played a large part in N2O emission, while biomass, soil organic matter and mineral nitrogen concentration could also simulate the emission. Nevertheless, warming and increasing precipitation would mitigate the emission.

Le protoxyde d’azote (N2O), puissant gaz à effet de serre émis par les sols agricoles : méthodes d’inventaire et leviers de réduction

Nitrous oxide (N2 O) is a greenhouse gas that mainly originates from soils and agricultural activities. International initiatives require that countries calculate national inventories of their N2 O emissions from agricultural soils. Several methodologies can be applied: (i) Tier I Intergovernmental Panel on Climate Change (IPCC) default approach that only takes into account nitrogen (N) input, (ii) Country-specific methodologies (Tier II and Tier III) that account for regional climatic and land use impacts on N2 O emission factors, and include several sources. Strategies to mitigate N2 O emissions from agricultural soils are based on a rational use of N resource and the stimulation of soil aerobic conditions and biological activity. Management practices to reduce the N2 O emissions should be focused on: (i) Avoiding the soil denitrification process by maximizing soil aeration and reducing their acidity, (ii) Improving N fertilization by reducing free N in soil and optimizing N use efficiency in cropping systems, (iii) Direct actions on the microbial processes by limiting the nitrification process and stimulating the last step of the denitrification process (N2 O reduction to N2 ).

Effect of Silver Nanoparticles on Soil Denitrification Kinetics

Abstract The toxicity of silver nanoparticles to bacteria, while frequently demonstrated in laboratory settings, has not been well established within environmental media. This study investigates the effect of three different silver nanoparticles (35–60 nm, uncoated and coated with 0.3% polyvinylpyrrolidone) at various concentrations (1, 10, or 100 mg/L) on the microbial-facilitated soil denitrification process using native bacteria in a soil (Toccoa sandy loam) environment. The sorption of silver nanoparticles onto soil was observed through an isotherm study. It was found that silver nanoparticles exhibited much less toxicity to the denitrifying bacterial community than was expected. The toxicity was not correlated with either coatings or particle size; instead, only one type of larger silver nanoparticle (uncoated 50-nm silver particles) exhibited any toxicity, and only at a very high (100 mg/L) concentration. Toxicity was linked, however, to the silver nanoparticle affinity for soil surfaces (Kd), as de...

Denitrifier Community Dynamics in Soil Aggregates under Permanent Grassland and Arable Cropping Systems

A better understanding of the spatial distribution of denitrifiers and their activity may lead to an improved understanding of the denitrification process in soil. This study determined the spatial distribution of the total bacterial community (16S rRNA), components of the denitrifier community (cnorBP; Pseudomonas mandelii and related species; nosZ), and denitrification activity across a range of soil aggregate size fractions (4–8, 1–2, and 0.25–0.5 mm) under permanent grassland (PG) and arable cropping (AC) systems. Aggregate size fraction had no significant effect on the abundance of the nosZ or cnorBP gene‐bearing bacteria in soil from the AC system. The highest abundance of denitrifier bacteria was measured in the smallest size fraction in the PG system. Respiration did not differ among aggregate size fractions within the PG system; however, respiration was higher for the PG system than the AC system for all aggregate size fractions. For the AC system, higher respiration was measured in the 0.25‐ to 0.5‐mm aggregate fraction than the 4‐ to 8‐mm aggregate fraction. Denitrifying enzyme activity (DEA) was higher in the largest size fraction of the PG system than the AC system; however, DEA did not differ among aggregate size fractions within each management system. Cumulative denitrification during a 72‐h incubation was significantly higher in the largest aggregate size fractions under both management systems. The results indicate that the differences among the aggregate size fractions were small in magnitude and that the spatial location of the denitrification activity and the abundance of the denitrifier bacteria were uncoupled across aggregate size fractions in the contrasting management systems.

Spatially explicit estimation of soil denitrification rates and land use effects in the riparian buffer zone of the large Guanting reservoir

An important function of riparian ecosystems, usually characterized as nitrate-loaded wetland environments, is nitrogen removal by denitrification. Riparian buffer zones around large dams and water reservoirs are also recognized as hotspots for emission of nitrogen (N 2) and nitrous oxide (N 2O), the latter being a strong greenhouse gas. Research has proven that land use has an important effect on soil denitrification. A spatial landscape-scale approach for analyzing denitrification processes and land use effects can therefore be considered important for an adequate assessment and management of NO 3 − losses and N 2O emissions in riparian ecosystems. In this study, we couple a soil denitrification process model with remote sensing data and techniques to analyze the spatial and temporal dynamics of soil denitrification in the riparian area of the Guanting reservoir, an important water supply of Beijing, China. SPOT-5 and Landsat TM5 satellite data were used to interpret the spatial land surface information and derive model parameters. A laboratory-scale anaerobic incubation experiment was used to estimate the soil denitrification model parameters for the different soil types. Modeling results were compared and validated with data from a nearby experimental N 2O emission research site. The overall average soil denitrification rate (SDR) of the Guanting riparian basin was 32.45 mg N m − 2 d − 1 during the simulation period from March to September 2007, with a maximum of 370.49 mg N m − 2 d − 1 appeared in August and the minimum of 0.02 mg N m − 2 d − 1 in March. Bottomland and wetlands had large SDR's, with an average daily rate of 80.20 and 136 mg N m − 2 d − 1 respectively. Forest, grassland and shrub showed lower values, with average daily rates of 25.21, 18.77 and 16.59 mg N m − 2 d − 1 respectively. The modeling results also indicated that farmland and orchards had a relative high SDR (34.09 and 33.25 mg N m − 2 d − 1 respectively), with large fluctuations observed between June and August due to agricultural practices. As soil denitrification rates and N 2 and N 2O emissions showed to be strongly correlated to the different land use practices, this could be taken into consideration when planning best management strategies for non-point source pollution control and greenhouse gas mitigation.

Influence of soil type on N2O and CH4soil fluxes in Hungarian grasslands

Soil fluxes of methane and nitrous oxide were determined for grasslands on sandy, loess and clay soils in Hungary. As the direction of methane flux (emission or uptake) depends on the soil characteristics bi-directional fluxes were observed. For sandy and loess grasslands the sink and source processes are practically balanced showing a negligible low mean methane flux for 2006–2007 (−0.04–0.05 kg CH 4 ha −1 yr −1 ). In this period the clay grassland functioned as a weak sink for methane (−0.34 kg CH 4 ha −1 yr −1 ). Average soil nitrous oxide emission fluxes for the period of 2002–2006 was 0.5 kg N ha −1 yr −1 for sandy and loess while 0.2 kg N ha −1 yr −1 for clay grassland, respectively, with substantial inter-annual variations. Taking into account the total atmospheric N-input 0 to 8 per cent of deposited nitrogen is emitted from the soils in the form of N 2 O as the intermediate product of soil denitrification processes.

KINETIC FORMULATION OF THE DENITRIFICATION PROCESS IN SOIL

Kinetic formulation of denitrification process in soil was developed based on a model of competitive Michaelis-Menten type enzyme kinetics. Several values of parameters were chosen to plot the concentrations of NO−3, NO−2, N2O-N and N2-N at various times of incubation under different initial concentrations of NO−3. According to the model the disappearance rate of NO−3 was found to be independent of initial concentration of NO−3 and was nearly constant, similar to zero order rate of disappearance. The initial rate of NO−2 formation was independent of the NO−3 concentration. However, the maximum concentration of NO−2 and the time at which the maximum was found were found to be dependent upon the NO−3 concentration. When there was very little accumulation of NO−2 in the system, the initial rate of N2O formation was found to be independent of NO−3 concentration. However, if there was high accumulation of NO−2, the initial rate of N2O formation became inversely related to NO−3 concentration. The initiation of N2 formation was generally slower as the concentration of NO−3 increased. The composition of gas mixture, N2O and N2, was found to vary depending upon the initial NO−3 concentration and with the time of incubation. The formulation presented herein describes the features of denitrification experimentally observed fairly well.