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1.
In late-successional steady state ecosystems, plants and microbes compete for nutrients and nutrient retention efficiency is expected to decline when inputs exceed biotic demand. In carbon (C)-poor environments typical of early primary succession, nitrogen (N) uptake by C-limited microbes may be limited by inputs of detritus and exudates derived from contemporaneous plant production. If plants are N-limited in these environments, then this differential limitation may lead to positive relationships between N inputs and N retention efficiency. Further, the mechanisms of N removal may vary as a function of inputs if plant-derived C promotes denitrification. These hypotheses were tested using field surveys and greenhouse microcosms simulating the colonization of desert stream channel sediments by herbaceous vegetation. In field surveys of wetland (ciénega) and gravelbed habitat, plant biomass was positively correlated with nitrate (NO3 ?) concentration. Manipulation of NO3 ? in flow-through microcosms produced positive relationships among NO3 ? supply, plant production, and tissue N content, and a negative relationship with root:shoot ratio. These results are consistent with N limitation of herbaceous vegetation in Sycamore Creek and suggest that N availability may influence transitions between and resilience of wetland and gravelbed stable states in desert streams. Increased biomass in high N treatments resulted in elevated rates of denitrification and shifts from co-limitation by C and NO3 ? to limitation by NO3 ? alone. Overall NO3 ? retention efficiency and the relative importance of denitrification increased with increasing N inputs. Thus the coupling of plant growth and microbial processes in low C environments alters the relationship between N inputs and exports due to increased N removal under high input regimes that exceed assimilative demand. 相似文献
2.
Mar��a Isabel Arce Rosa G��mez Mar��a Luisa Su��rez Mar��a Rosario Vidal-Abarca 《Hydrobiologia》2013,700(1):169-185
In this study, we tested the hypothesis that agriculture, through its influence on water NO3 ?-N availability, would control denitrification in agriculturally influenced temporary saline streams, and that water salinity would not affect this process. We also tested the effect of summer drought on the denitrification process. We approached these objectives by estimating sediment denitrification (using the acetylene inhibition technique) in two temporary Mediterranean streams following an increased natural water salinity and agricultural gradient under pre- and post-drought conditions. During the pre-drought conditions, the water NO3 ?-N concentration was the main predictor of denitrification rates. Together with the water NO3 ?-N concentration, sediment redox conditions and water salinity appeared to be significant predictors, the latter showing a negative effect. During the post-drought, denitrification rates dropped significantly in both streams and no abiotic factors seemed to significantly influence this process. Our results suggest that high water salinity and drought affected negatively the stream-denitrifying capacity. This study highlights that stressors such as water salinity and hydrological intermittency should be considered in future stream management plans in order to preserve the role of streams on controlling the NO3 ?-N export, especially in the context of a warmer and drier climate. 相似文献
3.
Influence of bioturbation on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in freshwater sediments 总被引:2,自引:0,他引:2
Intensive agriculture leads to increased nitrogen fluxes (mostly as nitrate, NO3 ?) to aquatic ecosystems, which in turn creates ecological problems, including eutrophication and associated harmful algal blooms. These problems have focused scientific attention on understanding the controls on nitrate reduction processes such as denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Our objective was to determine the effects of nutrient-tolerant bioturbating invertebrates (tubificid oligochaetes) on nitrogen cycling processes, specifically coupled nitrification–denitrification, net denitrification, DNRA, and biogeochemical fluxes (O2, NO3 ?, NH4 +, CO2, N2O, and CH4) in freshwater sediments. A mesocosm experiment determined how tubificid density and increasing NO3 ? concentrations (using N15 isotope tracing) interact to affect N cycling processes. At the lowest NO3 ? concentration and in the absence of bioturbation, the relative importance of denitrification to DNRA was similar (i.e., 49.6 and 50.4 ± 8.1 %, respectively). Increasing NO3 ? concentrations in the control cores (without fauna) stimulated denitrification, but did not enhance DNRA, which significantly altered the relative importance of denitrification compared to DNRA (94.6 vs. 5.4 ± 0.9 %, respectively). The presence of tubificid oligochaetes enhanced O2, NO3 ?, NH4 + fluxes, greenhouse gas production, and N cycling processes. The relative importance of denitrification to DNRA shifted towards favoring denitrification with both the increase in NO3 ? concentrations and the increase of bioturbation activity. Our study highlights that understanding the interactions between nutrient-tolerant bioturbating species and nitrate contamination is important for determining the nitrogen removal capacity of eutrophic freshwater ecosystems. 相似文献
4.
A pilot-scale, engineered poplar tree vadose zone system was utilized to determine effluent nitrate (NO3?) and ammonium concentrations resulting from intermittent dosing of a synthetic wastewater onto sandy soils at 4.5°C. The synthetic wastewater replicated that of an industrial food processor that irrigates onto sandy soils even during dormancy which can leave groundwater vulnerable to NO3? contamination. Data from a 21-day experiment was used to assess various Hydrus model parameterizations that simulated the impact of dormant roots. Bromide tracer data indicated that roots impacted the hydraulic properties of the packed sand by increasing effective dispersion, water content and residence time. The simulated effluent NO3? concentration on day 21 was 1.2 mg-N L?1 in the rooted treatments compared to a measured value of 1.0 ± 0.72 mg-N L?1. For the non-rooted treatment, the simulated NO3? concentration was 4.7 mg-N L?1 compared to 5.1 ± 3.5 mg-N L?1 measured on day 21. The model predicted a substantial “root benefit” toward protecting groundwater through increased denitrification in rooted treatments during a 21-day simulation with 8% of dosed nitrogen converted to N2 compared to 3.3% converted in the non-rooted test cells. Simulations at the 90-day timescale provided similar results, indicating increased denitrification in rooted treatments. 相似文献
5.
Hongyu Wang Yaping Ye Jinni Sai Dan Chen Kai Yang Jun Zhou 《Geomicrobiology journal》2016,33(6):505-512
Static experiments were conducted to investigate the effects of environmental factors on nitrate (NO3?-N)-removal efficiency, such as NO3?-N loading, pH value, C/N ratio and temperature in activated sludge using Fe (II) as electron donor. The results demonstrated that the average denitrification rate increased from 1.25 to 2.23 mg NO3?-N/(L·h) with NO3?-N loading increased from 30 to 60 mg/L. When pH increased from 7 to 8, the concentration of NO3?-N and nitrite (NO2?-N) in effluent were all maintained at quite low levels. C/N ratio had little impact on denitrification process, i.e., inorganic carbon (C) source could still be enough for denitrification process with C/N ratio as low as 5. Temperature had a significant effect on the denitrification efficiency, and NO3?-N removal efficiency of 92.03%, 96.77%, 97.67% and 98.23% could be obtained with temperature of 25°C, 30°C, 35°C and 40°C, respectively. SEM, XRD and XRF analysis was used to investigate microscopic surface morphology and chemical composition of the denitrifying activated sludge, and mechanism of the nitrate-dependent anaerobic ferrous oxidation (NAFO) bacterias could be explored with this research. 相似文献
6.
John Karl Böhlke Ronald C. Antweiler Judson W. Harvey Andrew E. Laursen Lesley K. Smith Richard L. Smith Mary A. Voytek 《Biogeochemistry》2009,93(1-2):117-141
Denitrification is an important net sink for NO3 ? in streams, but direct measurements are limited and in situ controlling factors are not well known. We measured denitrification at multiple scales over a range of flow conditions and NO3 ? concentrations in streams draining agricultural land in the upper Mississippi River basin. Comparisons of reach-scale measurements (in-stream mass transport and tracer tests) with local-scale in situ measurements (pore-water profiles, benthic chambers) and laboratory data (sediment core microcosms) gave evidence for heterogeneity in factors affecting benthic denitrification both temporally (e.g., seasonal variation in NO3 ? concentrations and loads, flood-related disruption and re-growth of benthic communities and organic deposits) and spatially (e.g., local stream morphology and sediment characteristics). When expressed as vertical denitrification flux per unit area of streambed (U denit, in μmol N m?2 h?1), results of different methods for a given set of conditions commonly were in agreement within a factor of 2–3. At approximately constant temperature (~20 ± 4°C) and with minimal benthic disturbance, our aggregated data indicated an overall positive relation between U denit (~0–4,000 μmol N m?2 h?1) and stream NO3 ? concentration (~20–1,100 μmol L?1) representing seasonal variation from spring high flow (high NO3 ?) to late summer low flow (low NO3 ?). The temporal dependence of U denit on NO3 ? was less than first-order and could be described about equally well with power-law or saturation equations (e.g., for the unweighted dataset, U denit ≈26 * [NO3 ?]0.44 or U denit ≈640 * [NO3 ?]/[180 + NO3 ?]; for a partially weighted dataset, U denit ≈14 * [NO3 ?]0.54 or U denit ≈700 * [NO3 ?]/[320 + NO3 ?]). Similar parameters were derived from a recent spatial comparison of stream denitrification extending to lower NO3 ? concentrations (LINX2), and from the combined dataset from both studies over 3 orders of magnitude in NO3 ? concentration. Hypothetical models based on our results illustrate: (1) U denit was inversely related to denitrification rate constant (k1denit, in day?1) and vertical transfer velocity (v f,denit, in m day?1) at seasonal and possibly event time scales; (2) although k1denit was relatively large at low flow (low NO3 ?), its impact on annual loads was relatively small because higher concentrations and loads at high flow were not fully compensated by increases in U denit; and (3) although NO3 ? assimilation and denitrification were linked through production of organic reactants, rates of NO3 ? loss by these processes may have been partially decoupled by changes in flow and sediment transport. Whereas k1denit and v f,denit are linked implicitly with stream depth, NO3 ? concentration, and(or) NO3 ? load, estimates of U denit may be related more directly to field factors (including NO3 ? concentration) affecting denitrification rates in benthic sediments. Regional regressions and simulations of benthic denitrification in stream networks might be improved by including a non-linear relation between U denit and stream NO3 ? concentration and accounting for temporal variation. 相似文献
7.
Denitrification and nitrous oxide effluxes in boreal, eutrophic river sediments under increasing nitrate load: a laboratory microcosm study 总被引:1,自引:0,他引:1
Hanna Silvennoinen Anu Liikanen Jouni Torssonen C. Florian Stange Pertti J. Martikainen 《Biogeochemistry》2008,91(2-3):105-116
Intact sediment cores from rivers of the Bothnian Bay (Baltic Sea) were studied for denitrification based on benthic fluxes of molecular nitrogen (N2) and nitrous oxide (N2O) in a temperature controlled continuous water flow laboratory microcosm under 10, 30, 100, and 300 μM of 15N enriched nitrate (NO3 ?, ~98 at. %). Effluxes of both N2 and N2O from sediment to the overlying water increased with increasing NO3 ? load. Although the ratio of N2O to N2 increased with increasing NO3 ? load, it remained below 0.04, N2 always being the main product. At the NO3 ? concentrations most frequently found in the studied river water (10–100 μM), up to 8% of the NO3 ? was removed in denitrification, whereas with the highest concentration (300 μM), the removal by denitrification was less than 2%. However, overall up to 42% of the NO3 ? was removed by mechanisms other than denitrification. As the microbial activity was simultaneously enhanced by the NO3 ? load, shown as increased oxygen consumption and dissolved inorganic carbom efflux, it is likely that a majority of the NO3 ? was assimilated by microbes during their growth. The 15N content in ammonium (NH4 +) in the efflux was low, suggesting that reduction of NO3 ? to NH4 + was not the reason for the NO3 ? removal. This study provides the first published information on denitrification and N2O fluxes and their regulation by NO3 ? load in eutrophic high latitude rivers. 相似文献
8.
15N-labelled NO3? was used in a surface-flow constructed wetland in spring to examine the relative importance of competing NO3? removal processes. In situ mesocosms (0.25 m2) were dosed with 2 l of 15NO3? (NaNO3, 300 mg N l?1, 99 atom% 15N) and bromide (Br?) solution (LiBr, 4.3 g l?1, as a conservative tracer). Concentrations of NO3?, Br?, dissolved oxygen and 15N2 were monitored periodically and replicate mesocosms were destructively sampled prior to and 6 days after 15N addition. Denitrification, immobilisation, plant uptake and dissimilatory NO3? reduction to NH4+ (DNRA) accounted for 77, 11, 9 and 2% of 15NO3? transformed during the experiment. Only 6% of denitrification gases were directly measured as atmospheric or dissolved 15N2; the remainder (71%) was determined via 15N mass balance. This indicated that a large proportion of the denitrification gases were entrapped within the soil matrix and/or plant aerenchyma. The floating plant Lemna minor exhibited a significantly higher NO3? uptake rate (221 mg kg?1 d?1) than Typha orientalis (10 mg kg?1 d?1), but periodic harvest of plants would remove <3% of annual NO3? inputs. Our results suggest that this 6-year-old constructed wetland functions effectively as a sink for NO3? during the growing season with less than one-quarter of the NO3? processed sequestered into wetland plant, algal and microbial N pools and the balance permanently removed by denitrification. 相似文献
9.
Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from
wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban
Greensboro, NC, USA, using two approaches: (1) natural abundance of 15N–NO3− in conjunction with background NO3−–N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ15N–NO3− and NO3−–N, combined with high concentrations of NO3−–N suggested that other factors were controlling NO3−–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed
that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas
upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into
the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant
sink for NO3−–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO3−–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO3−–N was lost downstream of the plant. This result suggests that controlling NO3−–N loading from the plant could result in considerable improvement of downstream water quality. 相似文献
10.
Jake J. Beaulieu Paul M. Mayer Sujay S. Kaushal Michael J. Pennino Clay P. Arango David A. Balz Timothy J. Canfield Colleen M. Elonen Ken M. Fritz Brian H. Hill Hodon Ryu Jorge W. Santo Domingo 《Biogeochemistry》2014,121(1):107-126
Nitrogen (N) retention in streams is an important ecosystem service that may be affected by the widespread burial of streams in stormwater pipes in urban watersheds. We predicted that stream burial suppresses the capacity of streams to retain nitrate (NO3 ?) by eliminating primary production, reducing respiration rates and organic matter availability, and increasing specific discharge. We tested these predictions by measuring whole-stream NO3 ? removal rates using 15NO3 ? isotope tracer releases in paired buried and open reaches in three streams in Cincinnati, Ohio (USA) during four seasons. Nitrate uptake lengths were 29 times greater in buried than open reaches, indicating that buried reaches were less effective at retaining NO3 ? than open reaches. Burial suppressed NO3 ? retention through a combination of hydrological and biological processes. The channel shape of two of the buried reaches increased specific discharge which enhanced NO3 ? transport from the channel, highlighting the relationship between urban infrastructure and ecosystem function. Uptake lengths in the buried reaches were further lengthened by low stream biological NO3 ? demand, as indicated by NO3 ? uptake velocities 17-fold lower than that of the open reaches. We also observed differences in the periphyton enzyme activity between reaches, indicating that the effects of burial cascade from the microbial to the ecosystem scale. Our results suggest that stream restoration practices involving “daylighting” buried streams have the potential to increase N retention. Further work is needed to elucidate the impacts of stream burial on ecosystem functions at the larger stream network scale. 相似文献
11.
《Journal of Fermentation and Bioengineering》1993,75(4):304-308
Propionate and NH4+ were accumulated in the effluent during anaerobic treatment of five-fold diluted distillery wastewater from shochu making. Propionate could be removed efficiently during biological denitrification by the addition of NO3− (4.2 g/l) to the anaerobically treated wastewater. At a hydraulic retention time of more than 2 h, a TOC removal efficiency of 90% could be achieved. The wastewater was then treated aerobically by biological nitrification. With a hydraulic retention time of more than 14 h the efficiency of reduction of NH4+ could be maintained above 97%. In order to reduce the amount of NO3− addition necessary for the removal of propionate, simultaneous removal of propionate and NH4+ was studied by recirculating the effluent from a nitrification process to a denitrification process using denitrification and nitrification reactors connected in series. At a recirculation ratio of 2, the amount of NO3− that had to be added was reduced to 0.3 g/l of anaerobically treated wastewater, which corresponds to 6.9% of the theoretical value. Under the same conditions except for the addition of NO3− at 1.0 g/l, TOC and BOD in the effluent from the nitrification were 23 and 5 mg/l respectively, which are sufficiently low to allow discharge into river water. Moreover, the NO3− concentration in the effluent decreased with increases in the recirculation ratio. 相似文献
12.
Jonathan M. O’Brien Walter K. Dodds Kymberly C. Wilson Justin N. Murdock Jessica Eichmiller 《Biogeochemistry》2007,84(1):31-49
We conducted 15NO3− stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed
to measure nitrate (NO3−) cycling dynamics. Mean ambient NO3− concentrations of the streams ranged from 0.9 to 21,000 μg l−1 NO3−–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two
to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which
stream biota utilized available NO3−-decreased along the gradient of increasing NO3−. Observed functional relationships of biological N transformations (uptake and nitrification) with NO3− concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical
relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase
with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient
of NO3− concentrations, but only accounted for ∼1% of total NO3− uptake. On average, 20% of stream water NO3− was lost to denitrification per km, but the percentage removed in most streams was <5% km−1. Although the rate of cycling was greater in streams with larger NO3− concentrations, the relative proportion of NO3− retained per unit length of stream decreased as NO3− concentration increased. Due to the rapid rate of NO3− turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove
N through denitrification is highly variable. 相似文献
13.
The influence of hydrology and soil properties on disproportionately high (“hot”) rates of nitrate (NO3 ?) removal via denitrification has been relatively well established. It is poorly understood, however, how the unique soil characteristics of brownfield wetlands contribute to or hinder denitrification. In this study, we examined drivers of “hot” denitrification rates over time (“hot moments”) and space (“hotspots”) in a watershed located on an unrestored brownfield in New Jersey, USA. We carried out measurements of denitrification over 9-day sequences during three seasons in sites with the same vegetation (Phragmites australis) but different soils (fill material, remnant marsh soils, flooded organic-rich soils). Denitrification rates above the 3rd quartile value of the data distribution were defined as “hot” and the most important drivers of these rates were determined using mixed models. Porosity and NO3 ? availability were the strongest spatial and temporal predictors, respectively, of high denitrification rates, with coarse-textured, unflooded fill materials unexpectedly supporting the highest rates. These results suggest that pore-scale hydrology is a more complex controller of wetland denitrification than previously thought. Course-textured, unflooded soils have high fractions of air-filled pores relative to flooded soils, leading to more endogenous NO3 ? production, and less diffusion constraints than fine-textured soils, leading to higher NO3 ? availability to denitrifiers in suboxic pores. Laboratory studies confirmed denitrifiers were limited by NO3 ? availability. However, denitrification rates in all soils matched or exceeded atmospheric NO3 ? deposition and stormwater NO3 ? loading at the site, suggesting that brownfields may play an important role in NO3 ? removal from urban stormwater. 相似文献
14.
Effects of nitrate concentration on the denitrification potential of a calcic cambisol and its fractions of N2, N2O and NO 总被引:1,自引:0,他引:1
Rui Wang Qi Feng Tingting Liao Xunhua Zheng Klaus Butterbach-Bahl Wei Zhang Chunyi Jin 《Plant and Soil》2013,363(1-2):175-189
Background and aims
The direct measurement of denitrification dynamics and its product fractions is important for parameterizing process-oriented model(s) for nitrogen cycling in various soils. The aims of this study are to a) directly measure the denitrification potential and the fractions of nitrogenous gases as products of the process in laboratory, b) investigate the effects of the nitrate (NO 3 ? ) concentration on emissions of denitrification gases, and c) test the hypothesis that denitrification can be a major pathway of nitrous oxide (N2O) and nitric oxide (NO) production in calcic cambisols under conditions of simultaneously sufficient supplies of carbon and nitrogen substrates and anaerobiosis as to be found to occur commonly in agricultural lands.Methods
Using the helium atmosphere (with or without oxygen) gas-flow-soil-core technique in laboratory, we directly measured the denitrification potential of a silt clay calcic cambisol and the production of nitrogen gas (N2), N2O and NO during denitrification under the conditions of seven levels of NO 3 ? concentrations (ranging from 10 to 250 mg N kg?1 dry soil) and an almost constant initial dissolved organic carbon concentration (300 mg C kg?1 dry soil).Results
Almost all the soil NO 3 ? was consumed during anaerobic incubation, with 80–88 % of the consumed NO 3 ? recovered by measuring nitrogenous gases. The results showed that the increases in initial NO 3 ? concentrations significantly enhanced the denitrification potential and the emissions of N2 and N2O as products of this process. Despite the wide range of initial NO 3 ? concentrations, the ratios of N2, N2O and NO products to denitrification potential showed much narrower ranges of 51–78 % for N2, 14–36 % for N2O and 5–22 % for NO.Conclusions
These results well support the above hypothesis and provide some parameters for simulating effects of variable soil NO 3 ? concentrations on denitrification process as needed for biogeochemical models. 相似文献15.
Heterotrophic nitrification and aerobic denitrification by a novel Halomonas campisalis 总被引:1,自引:0,他引:1
Yan Guo Xuemei Zhou Yuguang Li Ke Li Caixia Wang Jianfei Liu Daojiang Yan Yilan Liu Dehui Yang Jianmin Xing 《Biotechnology letters》2013,35(12):2045-2049
A novel halophilic strain that could carry out heterotrophic nitrification and aerobic denitrification was isolated and named as Halomonas campisalis ha3. It removed inorganic nitrogen compounds (e.g. NO3 ?, NO2 ? and NH4 +) simultaneously, and grew well in the medium containing up to 20 % (w/v) NaCl. PCR revealed four genes in the genome of ha3 related to aerobic denitrification: napA, nirS, norB and nosZ. The optimal conditions for aerobic denitrification were pH 9.0, at 37 °C, with 4 % (w/v) NaCl and sodium succinate as carbon source. The nitrogen removal rate was 87.5 mg NO3 ?–N l?1 h?1. Therefore, this strain is a potential aerobic denitrifier for the treatment of saline wastewater. 相似文献
16.
Kazuto Ishikawa Takashi Ohmori Hirokuni Miyamoto Toshiyuki Ito Yoshifumi Kumagai Masatoshi Sonoda Jirou Matsumoto Hisashi Miyamoto Hiroaki Kodama 《Applied microbiology and biotechnology》2013,97(3):1349-1359
NO 3 ? is a major nitrogen source for plant nutrition, and plant cells store NO 3 ? in their vacuoles. Here, we report that a unique compost made from marine animal resources by thermophiles represses NO 3 ? accumulation in plants. A decrease in the leaf NO 3 ? content occurred in parallel with a decrease in the soil NO 3 ? level, and the degree of the soil NO 3 ? decrease was proportional to the compost concentration in the soil. The compost-induced reduction of the soil NO 3 ? level was blocked by incubation with chloramphenicol, indicating that the soil NO 3 ? was reduced by chloramphenicol-sensitive microbes. The compost-induced denitrification activity was assessed by the acetylene block method. To eliminate denitrification by the soil bacterial habitants, soil was sterilized with γ irradiation and then compost was amended. After the 24-h incubation, the N2O level in the compost soil with presence of acetylene was approximately fourfold higher than that in the compost soil with absence of acetylene. These results indicate that the low NO 3 ? levels that are often found in the leaves of organic vegetables can be explained by compost-mediated denitrification in the soil. 相似文献
17.
Birgit Koehler Marife D. Corre Kristin Steger Reinhard Well Erwin Zehe Juvia P. Sueta Edzo Veldkamp 《Biogeochemistry》2012,111(1-3):695-713
Atmospheric nitrogen (N) deposition is rapidly increasing in tropical regions. We investigated how a decade of experimental N addition (125 kg N ha?1 year?1) to a seasonal lowland forest affected depth distribution and contents of soil nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4), as well as natural abundance isotopic signatures of N2O, nitrate (NO3 ?) and ammonium (NH4 +). In the control plots during dry season, we deduced limited N2O production by denitrification in the topsoil (0.05–0.40 m) as indicated by: ambient N2O concentrations and ambient 15N-N2O signatures, low water-filled pore space (35–60%), and similar 15N signatures of N2O and NO3 ?. In the subsoil (0.40–2.00 m), we detected evidence of N2O reduction to N2 during upward diffusion, indicating denitrification activity. During wet season, we found that N2O at 0.05–2.00 m was mainly produced by denitrification with substantial further reduction to N2, as indicated by: lighter 15N-N2O than 15N-NO3 ? throughout the profile, and increasing N2O concentrations with simultaneously decreasing 15N-N2O enrichment with depth. These interpretations were supported by an isotopomer map and by a positive correlation between 18O-N2O and 15N-N2O site preferences. Long-term N addition did not affect dry-season soil N2O-N contents, doubled wet-season soil N2O-N contents, did not affect 15N signatures of NO3 ?, and reduced wet-season 15N signatures of N2O compared to the control plots. These suggest that the increased NO3 ? concentrations have stimulated N2O production and decreased N2O-to-N2 reduction. Soil CO2-C contents did not differ between treatments, implying that N addition essentially did not influence soil C cycling. The pronounced seasonality in soil respiration was largely attributable to enhanced topsoil respiration as indicated by a wet-season increase in the topsoil CO2-C contents. The N-addition plots showed reduced dry-season soil CH4-C contents and threshold CH4 concentrations were reached at a shallower depth compared to the control plots, revealing an N-induced stimulation of methanotrophic activity. However, the net soil CH4 uptake rates remained similar between treatments possibly because diffusive CH4 supply from the atmosphere largely limited CH4 oxidation. 相似文献
18.
Long-term elevated atmogenic deposition (~5 g m?2 year?1) of reactive nitrogen (N) causes N saturation in forests of subtropical China which may lead to high nitrous oxide (N2O) emissions. Recently, we found high N2O emission rates (up to 1,730 μg N2O–N m?2 h?1) during summer on well-drained acidic acrisols (pH = 4.0) along a hill slope in the forested Tieshanping catchment, Chongqing, southwest China. Here, we present results from an in situ 15N–NO3 ? labeling experiment to assess the contribution of nitrification and denitrification to N2O emissions in these soils. Two loads of 99 at.% K15NO3 (equivalent to 0.2 and 1.0 g N m?2) were applied as a single dose to replicated plots at two positions along the hill slope (at top and bottom, respectively) during monsoonal summer. During a 6-day period after label application, we found that 71–100 % of the emitted N2O was derived from the labeled NO3 ? pool irrespective of slope position. Based on this, we assume that denitrification is the dominant process of N2O formation in these forest soils. Within 6 days after label addition, the fraction of the added 15N–NO3 ? emitted as 15N–N2O was highest at the low-N addition plots (0.2 g N m?2), amounting to 1.3 % at the top position of the hill slope and to 3.2 % at the bottom position, respectively. Our data illustrate the large potential of acid forest soils in subtropical China to form N2O from excess NO3 ? most likely through denitrification. 相似文献
19.
Denitrification kinetics and denitrifier abundances in sediments of lakes receiving atmospheric nitrogen deposition (Colorado, USA) 总被引:2,自引:0,他引:2
The transport and deposition of anthropogenic nitrogen (N) to downwind ecosystems is significant and can be a dominant source of new N to many watersheds. Bacterially mediated denitrification in lake sediments may ameliorate the effects of N loading by permanently removing such inputs. We measured denitrification in sediments collected from lakes in the Colorado Rocky Mountains (USA) receiving elevated (5–8?kg?N?ha?1?y?1) or low (<2?kg?N?ha?1?y?1) inputs of atmospheric N deposition. The nitrate (NO3 ?) concentration was significantly greater in high-deposition lakes (11.3?μmol?l?1) compared to low-deposition lakes (3.3?μmol?l?1). Background denitrification was positively related to NO3 ? concentrations and we estimate that the sampled lakes are capable of removing a significant portion of N inputs via sediment denitrification. We also conducted a dose–response experiment to determine whether chronic N loading has altered sediment denitrification capacity. Under Michaelis–Menten kinetics, the maximum denitrification rate and half-saturation NO3 ? concentration did not differ between deposition regions and were 765?μmol?N?m?2?h?1 and 293?μmol?l?1?NO3 ?, respectively, for all lakes. We enumerated the abundances of nitrate- and nitrite-reducing bacteria and found no difference between high- and low-deposition lakes. The abundance of these bacteria was related to available light and bulk sediment resources. Our findings support a growing body of evidence that lakes play an important role in N removal and, furthermore, suggest that current levels of N deposition have not altered the abundance of denitrifying bacteria or saturated the capacity for sediment denitrification. 相似文献
20.
Factors Controlling Sediment Denitrification in Midwestern Streams of Varying Land Use 总被引:1,自引:0,他引:1
We investigated controls on stream sediment denitrification in nine headwater streams in the Kalamazoo River Watershed, Michigan,
USA. Factors influencing denitrification were determined by using experimental assays based on the chloramphenicol-amended
acetylene inhibition technique. Using a coring technique, we found that sediment denitrification was highest in the top 5 cm
of the benthos and was positively related to sediment organic content. To determine the effect of overlying water quality
on sediment denitrification, first-order stream sediments were assayed with water from second- and third-order downstream
reaches, and often showed higher denitrification rates relative to assays using site-specific water from the first-order stream
reach. Denitrification was positively related to nitrate (NO3
−) concentration, suggesting that sediments may have been nutrient-limited. Using stream-incubated inorganic substrata of varying
size classes, we found that finer-grained sand showed higher rates of denitrification compared to large pebbles, likely due
to increased surface area per volume of substratum. Denitrification was measurable on both inorganic substrata and fine particulate
organic matter loosely associated with inorganic particles, and denitrification rates were related to organic content. Using
nutrient-amended denitrification assays, we found that sediment denitrification was limited by NO3
− or dissolved organic carbon (DOC, as dextrose) variably throughout the year. The frequency and type of limitation differed
with land use in the watershed: forested streams were NO3
−-limited or co-limited by both NO3
− and DOC 92% of the time, urban streams were more often NO3
−-limited than DOC-limited, whereas agricultural stream sediments were DOC-limited or co-limited but not frequently limited
by NO3
− alone. 相似文献