共查询到20条相似文献,搜索用时 468 毫秒
1.
Indirect nitrous oxide (N 2O) emissions produced by nitrogen (N) leaching into surface water and groundwater bodies are poorly understood in comparison to direct N 2O emissions from soils. In this study, dissolved N 2O concentrations were measured weekly in both lowland headwater streams and subsurface agricultural field drain discharges over a 2‐year period (2013–2015) in an intensive arable catchment, Norfolk, UK. All field drain and stream water samples were found to have dissolved N 2O concentrations higher than the water–air equilibrium concentration, illustrating that all sites were acting as a net source of N 2O emissions to the atmosphere. Soil texture was found to significantly influence field drain N 2O dynamics, with mean concentrations from drains in clay loam soils (5.3 μg N L ?1) being greater than drains in sandy loam soils (4.0 μg N L ?1). Soil texture also impacted upon the relationships between field drain N 2O concentrations and other water quality parameters (pH, flow rate, and nitrate (NO 3) and nitrite (NO 2) concentrations), highlighting possible differences in N 2O production mechanisms in different soil types. Catchment antecedent moisture conditions influenced the storm event mobilisation of N 2O in both field drains and streams, with the greatest concentration increases recorded during precipitation events preceded by prolonged wet conditions. N 2O concentrations also varied seasonally, with the lowest mean concentrations typically occurring during the summer months (JJA). Nitrogen fertiliser application rates and different soil inversion regimes were found to have no effect on dissolved N 2O concentrations, whereas higher N 2O concentrations recorded in field drains under a winter cover crop compared to fallow fields revealed cover crops are an ineffective greenhouse gas emission mitigation strategy. Overall, this study highlights the complex interactions governing the dynamics of dissolved N 2O concentrations in field drains and headwater streams in a lowland intensive agricultural catchment. 相似文献
2.
The static closed chamber technique is used in the study on the CH 4 and N 2O fluxes from the soils of primeval Abies fabri forest, the succession Abies fabri forest and the clear-cut areas of mid-aged Abies fabri forest in the Gongga Mountain from May 1998 to September 1999. The results indicate the following: (i) The forest soil serves
as the source of atmospheric N 2O at the three measurement sites, while the fluxes of CH 4 are all negative, and soil is the sink of atmospheric CH 4. The comparative relations of N 2O emissions between the three sites are expressed as primeval Abies fabri forest < clear-cut areas < succession Abies fabri forest, and those of CH 4 consumption fluxes are primeval Abies fabri forest < succession Abies fabri forest < clear-cut areas, (ii) Significant seasonal variations of N 2O emission at various sites were observed, and two emission peaks of N 2O occurr during summer (July—August) and spring (February—March), whereas N 2O emission is relatively low in winter and spring (mid March—April). Seasonal variations of CH 4 consumption at each measurement site fluctuate drastically with unclear regularities. Generally, CH 4 consumption fluxes of succession Abies fabri forest and clear-cut areas are higher from mid May to late July but lower in the rest of sampling time, while the CH 4 flux keeps a relatively high value even up to September in primeval Abies fabri forest. In contrast to primeval Abies fabri forest, the CH 4 absorbabilities of succession Abies fabri forest and clear-cut areas of mid-aged Abies fabri forest are weaker. Particularly, the absorbability of the clear-cut areas is even weaker as compared with the other two sites,
for the deforestation reduces the soil absorbability of atmospheric CH 4. (iii) Evident diurnal variation regularity exists in the N 2O emissions of primeval Abies fabri forest, and there is a statistic positive correlation between the fluxes of N 2O and air temperature ( R=0.95, n=11, α· 0.01), and also the soil temperature of 5-cm layer ( R=0.81, n=11, α> 0.01), whereas the CH 4 diurnal variation regularities are unclear and have no significant correlation with the soil temperature of 5-cm layer and
air temperature. 相似文献
3.
水库近岸湿地(消落带)土壤N2O释放和反硝化作用是消落带氮的生物地球化学过程的重要组成部分.以三峡水库支流澎溪河高阳平湖库湾消落带为研究对象,于2013年落干初期,采用C2H2抑制-原状土柱培养法研究该处自然植被恢复区、农耕区和对照组等不同土地类型土壤的N2O释放速率和反硝化速率,并测定了土壤p H值、氧化还原电位、温度、有机质、总氮、铵态氮、硝态氮和土壤孔隙含水量等环境指标.结果表明,自然植被恢复区土壤N2O释放速率为9.88±6.49 g N/(hm2·d),反硝化速率为58.94±52.84 g N/(hm2·d);农耕区土壤N2O释放速率和反硝化速率分别为7.71±4.44和30.70±25.68 g N/(hm2·d).不同土地类型间N2O释放速率差异显著,落干初期土壤氧含量、含水量及氮含量对不同土地类型N2O释放和反硝化作用影响明显.土壤氧含量的升高促进了自然植被恢复区的N2O释放,并在一定程度上抑制了该区域反硝化作用.农耕区土壤含水量高于自然植被恢复区,可能致使N2O释放速率低于自然植被恢复区,而反硝化速率高于自然植被恢复区.消落带土壤氮含量降低同反硝化速率降低有一定联系. 相似文献
4.
The increasing concentration of greenhouse gas in the atmosphere and their resultant climatic and environmental changes have been drawing much attention of the governments of various countries in recent years. The sphere of global influence and the comp… 相似文献
5.
Soil erosion has been identified as a potential global carbon sink since eroded organic matter is replaced at source and eroded material is readily buried. However, this argument has relied on poor estimates of the total fate of in‐transit particulates and could erroneously imply soil erosion could be encouraged to generate carbon stores. These previous estimates have not considered that organic matter can also be released to the atmosphere as a range of greenhouse gases, not only carbon dioxide (CO 2), but also the more powerful greenhouse gases methane (CH 4) and nitrous oxide (N 2O). As soil carbon lost by erosion is only replaced by uptake of CO 2, this could represent a considerable imbalance in greenhouse gas warming potential, even if it is not significant in terms of overall carbon flux. This work therefore considers the flux of particulate organic matter through UK rivers with respect to both carbon fluxes and greenhouse gas emissions. The results show that, although emissions to the atmosphere are dominated by CO 2, there are also considerable fluxes of CH 4 and N 2O. The results suggest that soil erosion is a net source of greenhouse gases with median emission factors of 5.5, 4.4 and 0.3 tonnes CO 2eq/yr for one tonne of fluvial carbon, gross carbon erosion and gross soil erosion, respectively. This study concludes that gross soil erosion would therefore only be a net sink of both carbon and greenhouse gases if all the following criteria are met: the gross soil erosion rate were very low (<91 tonnes/km 2/yr); the eroded carbon were completely replaced by new soil organic matter; and if less than half of the gross erosion made it into the stream network. By establishing the emission factor for soil erosion, it becomes possible to properly account for the benefits of good soil management in minimizing losses of greenhouse gases to the atmosphere as a by‐product of soil erosion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
Among the potential effects of climate change on subalpine forest ecosystems during the winter season, the shift in snowline towards higher altitudes and the increase in frequency of rain events on the snowpack are of particular interest. Here, we present the results of a 2‐year field experiment conducted in a forest stand ( Larix decidua) in NW Italy at 2020 m a.s.l. From 2009 to 2011, we monitored soil physical characteristics (temperature and moisture), and soil and soil solution chemistry, in particular carbon (C) and nitrogen (N) forms and their change in time, as affected by simulated late snowpack accumulation and rain on snow events. Late snowpack accumulation determined a stronger effect on soil thermal and moisture regimes than rain on snow events. Also soil chemistry was significantly affected by late snowfall simulation. Although microbial biomass C and N were not reduced by soil freezing, soil contents of the more labile dissolved organic carbon and inorganic N increased when the soil was affected by mild/hard freezing. Variations in the soil solution were shifted with respect to those observed in soil, with an increase in N‐NO 3? concentrations occurring during spring and summer. This study highlights the potential N loss in subalpine soils under changing environmental conditions driven by a changing climate. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
Seasonal metrics and environmental responses to forestry soil surface CO2 emission effluxes among three types of lower subtropical forests were consistently monitored over two years with static chamber-gas chromatograph techniques among three types of lower subtropical forests. Results showed that annual CO2 effluxes (S+L) reached 3942.20, 3422.36 and 2163.02 CO2 g·m−2·a−1, respectively in the monsoon evergreen broadleaf forest, mixed broadleaf-coniferous forest and coniferous forest. All the three types of forests revealed the same characteristics of seasonal changes with the CO2 effluxes peaking throughout June to August. During this peaking period, the effluxes were 35.9%, 38.1% and 40.2% of the total annual effluxes, respectively. The CO2 emission process responding to the environmental factors displayed significantly different patterns in forestry soils of the three types of forests. The coniferous forest (CF) was more sensitive to temperature than the other two types. The Q
10 values were higher, along with greater seasonal variations of the CO2 efflux, indicating that the structurally unique forestry ecosystem has disadvantage against interferences. All the three types of forestry CO2 effluxes showed significant correlation with the soil temperature (T
s), soil water content (M
s) and air pressure (P
a). However, stepwise regression analysis indicated no significant correlation between air pressure and the soil CO2 efflux. With an empirical model to measure soil temperature and water content in 5 cm beneath the soil surface, the CO2 effluxes accounting for 75.7%, 77.8% and 86.5% of the efflux variability respectively in soils of BF, MF and PF were calculated. This model can be better used to evaluate the CO2 emission of soils under water stress and arid or semi-arid conditions. 相似文献
8.
Seasonal metrics and environmental responses to forestry soil surface CO 2 emission effluxes among three types of lower subtropical forests were consistently monitored over two years with static chamber-gas chromatograph techniques among three types of lower subtropical forests. Results showed that annual CO 2 effluxes (S+L) reached 3942.20, 3422.36 and 2163.02 CO 2 g·m ?2·a ?1, respectively in the monsoon evergreen broadleaf forest, mixed broadleaf-coniferous forest and coniferous forest. All the three types of forests revealed the same characteristics of seasonal changes with the CO 2 effluxes peaking throughout June to August. During this peaking period, the effluxes were 35.9%, 38.1% and 40.2% of the total annual effluxes, respectively. The CO 2 emission process responding to the environmental factors displayed significantly different patterns in forestry soils of the three types of forests. The coniferous forest (CF) was more sensitive to temperature than the other two types. The Q 10 values were higher, along with greater seasonal variations of the CO 2 efflux, indicating that the structurally unique forestry ecosystem has disadvantage against interferences. All the three types of forestry CO 2 effluxes showed significant correlation with the soil temperature ( T s), soil water content ( M s) and air pressure ( P a). However, stepwise regression analysis indicated no significant correlation between air pressure and the soil CO 2 efflux. With an empirical model to measure soil temperature and water content in 5 cm beneath the soil surface, the CO 2 effluxes accounting for 75.7%, 77.8% and 86.5% of the efflux variability respectively in soils of BF, MF and PF were calculated. This model can be better used to evaluate the CO 2 emission of soils under water stress and arid or semi-arid conditions. 相似文献
9.
Soils release more carbon, primarily as carbon dioxide (CO 2), per annum than current global anthropogenic emissions. Soils emit CO 2 through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO 2 emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO 2 emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO 2 release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm –3, 1·3 g cm –3, 1·5 g cm –3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO 2 release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO 2 is positive: CO 2 emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO 2 emission: soil compacted to a bulk density of 1·1 g cm –3 emitted 32% more CO 2 than soil compacted to 1·5 g cm –3. Furthermore we found that the magnitude of CO 2 effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO 2 emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
10.
湖泊等内陆水体是大气N 2O潜在的重要排放源,也是全球N 2O收支估算的重要组成部分。目前全球湖泊普遍面临富营养化和蓝藻暴发等问题,明晰藻型湖泊N 2O排放强度及其环境影响因子对准确估算湖泊N 2O排放和预测其未来变化至关重要。本研究选择太湖藻型湖区为研究对象,同时选取人为活动影响较小的湖心区作为对比区域,基于2011年8月至2013年8月为期2年的逐月连续观测,探讨藻型湖区N 2O排放特征及其影响因素。结果表明,藻型湖区呈现极强的N 2O排放,其排放通量为(4.88±3.05) mmol/(m 2·d),是参考区域(湖心:(2.10±4.31) mmol/(m 2·d))的2倍多。此外,在藻型湖区中不同点位N 2O排放差异显著,受河流外源输入影响,近岸区是N 2O的热点排放区,其年均排放通量高达10.93 mmol/(m 2·d)。连续观测表明N 2 相似文献
11.
Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO 2 emission of 11?±?2?t day ?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H 2S/SO 2, CO 2/SO 2, and H 2O/SO 2 molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H 2O, CO 2, and H 2S emission rates were 562, 394, and 3?t day ?1, respectively. The total output of diffuse CO 2 emissions from the summit of Sierra Negra volcano was 990?±?85?t day ?1, with 605?t day ?1 being released by a deep source. The diffuse-to-plume CO 2 emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H 2O; the main noncondensable components amounted to 97.4?mol% CO 2, 1.5?mol% SO 2, 0.6?mol% H 2S, and 0.35?mol%?N 2. The higher H 2S/SO 2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. 3He/ 4He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25? R A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively. 相似文献
12.
In this research, an integrated simulation–optimization modeling approach (ISOMA) was developed for supporting agricultural N 2O emission mitigation at the watershed scale. This approach can successfully combine soil N 2O emission simulation and the consequential mitigation management within a general modeling framework. Also, uncertainties associated with the key soil parameter can be effectively reflected and addressed through adoption of Monte Carlo analysis for the simulation results. The Monte Carlo simulated results were then used to generate fuzzy membership functions that can be consequentially used for emission mitigation management, reflecting the combined uncertainties for N 2O emission simulation and mitigation management. The developed ISOMA was then applied to a reservoir watershed in Miyun county of Beijing municipality. In the studying watershed, the simulation model was calibrated and verified. Then, N 2O emission from multiple agricultural land-use patterns were predicted. The amounts of N 2O emission of four land use patterns (i.e., cash tree, orchard, cropland, and natural forest) were (536.9, 590.8, 653.1), (237.7, 254.4, 275.9), (79.5, 100.7, 105.1), (33.0, 47.3, 61.1) kg CO 2 eq ha ?1 year ?1, respectively. Two scenarios (i.e., G 1 and G 2) were set up according to development priorities of local economy and society. Meanwhile, multiple credibility levels were considered according to the risk of N 2O emission. The land use patterns could be adjusted according to solutions of ISOMA. The developed methods could help regional manager choose various production patterns with cost-effective agriculture N 2O emission management schemes in the Miyun reservoir watershed. The manager also can obtain deeply insights into the tradeoffs between agricultural benefits and system reliabilities. 相似文献
13.
We investigated greenhouse gas emissions (CO 2, CH 4, and N 2O) from reservoirs located across an altitude gradient in Switzerland. These are the first results of greenhouse gas emissions from reservoirs at high elevations in the Alps. Depth profiles were taken in 11 reservoirs located at different altitudes between the years 2003 and 2006. Diffusive trace gas emissions were calculated using surface gas concentrations, wind speeds and transfer velocities. Additionally, methane entering with the inflowing water and methane loss at the turbine was assessed for a subset of the reservoirs. All reservoirs were emitters of carbon dioxide and methane with an average of 970?±?340?mg?m ?2?day ?1 (results only from four lowland and one subalpine reservoir) and 0.20?±?0.15?mg?m ?2?day ?1, respectively. One reservoir (Lake Wohlen) emitted methane at a much higher rate (1.8?±?0.9?mg?m ?2?day ?1) than the other investigated reservoirs. There was no significant difference in methane emissions across the altitude gradient, but average dissolved methane concentrations decreased with increasing elevation. Only lowland reservoirs were sources for N 2O (72?±?22???g?m ?2?day ?1), while the subalpine and alpine reservoirs were in equilibrium with atmospheric concentrations. These results indicate reservoirs from subalpine/alpine regions to be only minor contributors of greenhouse gases to the atmosphere compared to other reservoirs. 相似文献
14.
Three techniques for obtaining soil water solutions (gravitational and matrical waters extracted using both in situ tension lysimeters and in vitro pressure chambers) and their later chemical analysis were performed in order to know the evolution of the soil‐solution composition when water moves down through the soil, from the Ah soil horizon to the BwC‐ or C‐horizons of forest soils located in western Spain. Additionally, ion concentrations and water volumes of input waters to soil (canopy washout) and exported waters (drainage solutions from C‐horizons) were determined to establish the net balance of solutes in order to determine the rates of leaching or retention of ions. A generalized process of sorption or retention of most components (even Cl ?) was observed, from the soil surface to the C‐horizon, in both gravitational and matrical waters, with H 4SiO 4, Mn 2+, Na +, and SO 42? being the net exported components from the soil through the groundwater. These results enhance the role of the recycling effect in these forest soils. The net percentages of elements retained in these forest soils, considering the inputs and the outputs balance, were 68% K +, 85% Ca 2+, 58% Mg 2+, 7% Al 3+, 5% Fe 3+, 34% Zn 2+, 57% Cl ?, and 20% NO 3?, and about 75% of dissolved organic carbon was mineralized. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
15.
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO 2 fluxes and quantify CO 2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO 2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m −2 day −1. Comparative maps of soil CO 2 flux were simulated and CO 2 emission rates estimated from three accumulation chamber (AC) CO 2 flux surveys. Least-squares inversion of measured eddy covariance CO 2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO 2 emission rates estimated based on simulated AC soil CO 2 fluxes. Spatial distributions of modeled surface CO 2 fluxes based on EC and AC observations showed moderate to good correspondence ( R
2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO 2 emissions over relatively large areas. 相似文献
16.
湖、库水体是重要的N 2O排放源,在全球氮素循环及全球气候变化中具有重要作用.本文综述了目前有关湖、库水体N 2O排放研究进展,重点介绍湖、库水体N 2O产生和排放的过程、不同时空尺度的排放特征、N 2O排放的影响因子框架及监测方法.湖、库水体N 2O不仅源于内部微生物硝化作用、反硝化作用、硝化-反硝化耦合作用、脱氮作用以及极少数底栖无脊椎动物代谢过程,同时流域上游河流汇入、地表径流输入、污水排放以及地下水排泄等构成湖、库水体N 2O的重要外源,但目前对内源/外源的相对贡献的定量化研究不足;湖、库水体N 2O排放方式包括扩散、植物传输及少量气泡排放,对水库而言,大坝下游水电涡轮机形成的脱气作用可能是N 2O排放的潜在途径.对文献综合分析表明,湖、库水体N 2O排放通常呈现明显的季节变化(夏季>冬季)和日变化,同时在全球(一般低纬度>高纬度)、区域及水体内部等不同尺度上表现出显著的空间变异性;这种时空变异特征主要受到湖、库自身理化因子(温度、营养盐、溶解氧、C/N、水文)、生物因子(水生植物、藻华)以及陆域人类活动(污水排放、农业活动以及城市化等)的影响;湖、库N 2O排放不同监测方法的差异也是潜在的影响因素,传统的漂浮箱法和薄边界层法均可能低估水体N 2O排放通量,未来需将传统的监测方法与新型的涡度相关法相结合,减小监测方法的不确定性.结合当前湖、库水体N 2O排放的研究不足,建议未来可以从湖、库N 2O产生的微生物机制,区域尺度上人类活动与湖、库群N 2O排放的耦合关系,水陆交错带的产、排过程,变化环境下的湖、库N 2O排放以及监测方法等方面深入研究. 相似文献
17.
There is a general agreement that forest ecosystems in the Northern Hemisphere function as signifi-cant sinks for atmospheric CO2; however, their magnitude and distribution remain large uncertainties. In this paper, we report the carbon (C) stock and its change of vegetation, forest floor detritus, and mineral soil, annual net biomass increment and litterfall production, and respiration of vegetation and soils between 1992 to 1994, for three temperate forest ecosystems, birch (Betula platyphylla) forest, oak (Quercus liaotungensis) forest and pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the C budgets of these forest ecosystems. Our results indicated that total C density (organic C per hectare) of these forests ranged from 250 to 300 t C ha-1, of which 35―54 t C ha-1 from vegetation biomass C and 209―244 t C ha-1 from soil organic C (1 m depth, including forest floor detritus). Biomass C of all three forests showed a net increase, with 1.33―3.55 t C ha-1 a-1 during the study period. Litterfall production, vegetation autotrophic respiration, and soil heterotrophic respira-tion were estimated at 1.63―2.34, 2.19―6.93, and 1.81―3.49 t C ha-1 a-1, respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t C ha-1 a-1, about half of which (46%―59%, 3.20―5.89 t C ha-1 a-1) was converted to net primary production. Our results suggested that pine forest fixed C of 4.08 t ha-1 a-1, whereas secondary forests (birch and oak forest) were nearly in balance in CO2 exchange between the atmosphere and ecosystems. 相似文献
18.
Although riparian zones are well known to reduce nitrogen (N) and phosphorus (P) runoff to streams, they also have the potential to affect greenhouse gas (CO 2, N 2O, and CH 4) fluxes to the atmosphere. Following large storms, soil biogeochemical conditions often become more reduced, especially in oxbow depressions and side channels, which can lead to hot moments of greenhouse gas production. Here, we investigate the impact of the remnants of Hurricane Irene and Tropical Storm Lee on riparian zone hydrology (water table: WT), and biogeochemistry (oxidation‐reduction potential [ORP], dissolved oxygen [DO], NO 3?, PO 43?, CO 2, N 2O, CH 4). Results indicate that large storms have the potential to reset WT levels for weeks to months. Overbank flooding at our site following Irene and Lee led to the infiltration of well‐oxygenated water at depth (higher DO and ORP) while promoting the development of anoxic conditions within soil aggregates near the soil surface (increased N 2O and CH 4 fluxes). A short‐term increase in CO 2 emission was observed following Irene at our site where aerobic respiration was water‐limited. Over a 2‐year period, an oxbow depression exhibited higher WT, higher N 2O and CH 4 fluxes (hot moment), higher CO 2 fluxes (seasonal), and lower NO 3? concentrations (seasonal) than the rest of the riparian zone. However, neither Irene, nor Lee, nor the oxbow depression significantly impacted PO 43?. Dissolved organic carbon, ORP, and DO data illustrate the time‐lag (>20 years) between the creation of an oxbow depression and the development of reducing conditions despite clear differences in riparian zone and oxbow WT dynamics. 相似文献
19.
The oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water. The carbon isotopic cycle for CO 2 in soils can be described in terms of the proportion of biomass using the C 4 photosynthetic pathway and the CO 2 respiration rate of the soil; at low soil respiration rates significant atmospheric CO 2 mixing can occur. In general, the carbon isotopic composition of soil carbonate is related to the proportion of C 4 biomass present in soil, but soils that freeze to the depth of carbonate formation often have a significant atmospheric component. This suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation. Because of these relationships, the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred. 相似文献
20.
Considering only net free energy change for the dissimilatory reduction of nitrate ion, the most efficient reaction with limited organic substrate is that resulting in the production of N 2. Under conditions of abundant organic substrate and limited electron acceptor the reduction of nitrate to the level of ammonium would be more efficient.
Thus the appearance of N 2O in denitrification must reflect a metabolic accident or some reaction barrier (e.g., the activation energy of some intermediate) which prevents the full utilization of this energy.Laboratory studies with microaerophylic systems indicate that under these reducing conditions both nitrate ion and N 2O can be reduced to the level of ammonium. The quantitative significance of these processes under natural conditions has not been evaluated but they may provide a significant sink for atmospheric N 2O. 相似文献
|