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1.
Sandra Petrakis Angelia Seyfferth Jinjun Kan Shreeram Inamdar Rodrigo Vargas 《Biogeochemistry》2017,133(2):147-164
Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0–10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO2, CH4, and N2O fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO3 ?), and polymerase chain reaction–denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO2 (Wetland), >23,000% for CH4 (Creek), and >110,000% for N2O (Forest Soils) following pulse events. The Creek soil produced the highest soil CO2 emissions, the Wetland soil produced the highest CH4 emissions, and the Forest soils produced the highest N2O emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large N2O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes. 相似文献
2.
Carolyn A. Pugh David E. Reed Ankur R. Desai Benjamin N. Sulman 《Biogeochemistry》2018,137(1-2):15-25
Wetlands play a disproportionately large role in global terrestrial carbon stocks, and from 1 year to the next individual wetlands can fluctuate between carbon sinks and sources depending on factors such as hydrology, temperature, and land use. Although much research has been done on short-term seasonal to annual wetland biogeochemical cycles, there is a lack of experimental evidence concerning how the reversibility of wetland hydrological changes will influence these cycles over longer time periods. Five years of drought-induced declining water table at Lost Creek, a shrub fen wetland in northern Wisconsin, coincided with increased ecosystem respiration (Reco) and gross primary production (GPP) as derived from long-term eddy covariance observations. Since then, however, the average water table level at this site has increased, providing a unique opportunity to explore how wetland carbon fluxes are affected by interannual air temperature differences as well as changing water table levels. Water table level, as measured by water discharge, was correlated with Reco and GPP at interannual time scales. However, air temperature had a strong correlation with Reco, GPP, and net ecosystem productivity (NEP) at monthly time scales and correlated with NEP at inter-annual time scales. Methane flux was strongly temperature-controlled at seasonal time scales, increasing an order of magnitude from April to July. Annual methane emissions were 51 g C m?2. Our results demonstrate that over multi-year timescales, water table fluctuations can have limited effects on wetland net carbon fluxes and instead at Lost Creek annual temperature is the best predictor of interannual variation. 相似文献
3.
Analyzing the ecosystem carbon and hydrologic characteristics of forested wetland using a biogeochemical process model 总被引:5,自引:0,他引:5
A comprehensive biogeochemical model, Wetland‐DNDC, was applied to analyze the carbon and hydrologic characteristics of forested wetland ecosystem at Minnesota (MN) and Florida (FL) sites. The model simulates the flows of carbon, energy, and water in forested wetlands. Modeled carbon dynamics depends on physiological plant factors, the size of plant pools, environmental factors, and the total amount and turnover rates of soil organic matter. The model realistically simulated water level fluctuation, forest production, carbon pools change, and CO2 and CH4 emission under natural variations in different environmental factors at two sites. Analyses were focused on parameters and inputs potentially cause the greatest uncertainty in calculated change in plant and soil C and water levels fluctuation and shows that it was important to obtain accurate input data for initial C content, climatic conditions, and allocation of net primary production to various forested wetland components. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on site‐specific conditions such as climate and soil. This paper explores the ability of using the biogeochemical process model Wetland‐DNDC to estimate the carbon and hydrologic dynamics of forested wetlands and shifts in these dynamics in response to changing environmental conditions. 相似文献
4.
Drew M. Ballantyne John A. Hribljan Thomas G. Pypker Rodney A. Chimner 《Wetlands Ecology and Management》2014,22(1):35-47
Northern peatland water table position is tightly coupled to carbon (C) cycling dynamics and is predicted to change from shifts in temperature and precipitation patterns associated with global climate change. However, it is uncertain how long-term water table alterations will alter C dynamics in northern peatlands because most studies have focused on short-term water table manipulations. The goal of our study was to quantify the effect of long-term water table changes (~80 years) on gaseous C fluxes in a peatland in the Upper Peninsula of Michigan. Chamber methods were utilized to measure ecosystem respiration (ER), gross primary production (GPP), net ecosystem exchange (NEE), and methane (CH4) fluxes in a peatland experiencing levee induced long-term water table drawdown and impoundment in relation to an unaltered site. Inundation raised water table levels by approximately ~10 cm and resulted in a decrease in ER and GPP, but an increase of CH4 emissions. Conversely, the drained sites, with water table levels ~15 cm lower, resulted in a significant increase in ER and GPP, but a decrease in CH4 emissions. However, NEE was not significantly different between the water table treatments. In summary, our data indicates that long-term water table drawdown and inundation was still altering peatland gaseous C fluxes, even after 80 years. In addition, many of the patterns we found were of similar magnitude to those measured in short-term studies, which indicates that short-term studies might be useful for predicting the direction and magnitude of future C changes in peatlands. 相似文献
5.
淡水水生生态系统温室气体排放的主要途径及影响因素研究进展 总被引:12,自引:0,他引:12
淡水水生生态系统是全球陆域生态系统的重要组成部分,近年来,关于淡水水生生态系统温室气体排放的研究日益增多。基于国内外目前对湖泊、河流、水库及浅水池塘等淡水生态系统开展的最新研究成果,总结分析了淡水水生生态系统温室气体排放的3个主要途径及相应观测方法。气泡排放的观测方法有倒置漏斗法、开放式动态箱法和超声探测技术;植物传输的观测方法有密闭箱法和植株切割法;扩散途径的观测方法有静态浮箱法、模型估算法/梯度法、微气象学法、TDLAS吸收光谱法等。从物理因素、化学因素、生物因素、水动力因素和人类活动等角度,深入探讨了淡水水生生态系统温室气体排放通量的影响因素。最后根据当前研究中存在的不足,对今后的研究方向提出了建议,以期为我国进一步深入开展相关研究提供借鉴。 相似文献
6.
Forest bioenergy opportunities may be hindered by a long greenhouse gas (GHG) payback time. Estimating this payback time requires the quantification of forest‐atmosphere carbon exchanges, usually through process‐based simulation models. Such models are prone to large uncertainties, especially over long‐term carbon fluxes from dead organic matter pools. We propose the use of whole ecosystem field‐measured CO2 exchanges obtained from eddy covariance flux towers to assess the GHG mitigation potential of forest biomass projects as a way to implicitly integrate all field‐level CO2 fluxes and the inter‐annual variability in these fluxes. As an example, we perform the evaluation of a theoretical bioenergy project that uses tree stems as bioenergy feedstock and include multi‐year measurements of net ecosystem exchange (NEE) from forest harvest chronosequences in the boreal forest of Canada to estimate the time dynamics of ecosystem CO2 exchanges following harvesting. Results from this approach are consistent with previous results using process‐based models and suggest a multi‐decadal payback time for our project. The time for atmospheric carbon debt repayment of bioenergy projects is highly dependent on ecosystem‐level CO2 exchanges. The use of empirical NEE measurements may provide a direct evaluation of, or at least constraints on, the GHG mitigation potential of forest bioenergy projects. 相似文献
7.
Carbon fluxes from a tropical peat swamp forest floor 总被引:3,自引:0,他引:3
Jyrki Jauhiainen Hidenori Takahashi† Juha E. P. Heikkinen‡ Pertti J. Martikainen‡ Harri Vasander§ 《Global Change Biology》2005,11(10):1788-1797
A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO2) and methane (CH4) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO2 emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO2 m?2 and less than 1.36±0.57 g CH4 m?2. On the basis of the carbon emitted, CO2 is clearly a more important greenhouse gas than CH4. CO2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering. 相似文献
8.
Coastal forested wetlands provide important ecosystem services such as carbon sequestration, nutrient retention, and flood protection, but they are also important sources of greenhouse gas emissions. Human appropriation of surface water and extensive ditching and draining of coastal plain landscapes are interacting with rising sea levels to increase the frequency and magnitude of saltwater incursion into formerly freshwater coastal wetlands. Both hydrologic change and saltwater incursion are expected to alter carbon and nutrient cycling in coastal forested wetlands. We performed a full factorial experiment in which we exposed intact soil cores from a coastal forested wetland to experimental marine salt treatments and two hydrologic treatments. We measured the resulting treatment effects on the emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) over 112 days. Salinity effects were compared across four treatments to isolate the effects of increases in ionic strength from the impact of adding a terminal electron acceptor (SO42?). We compared control treatments (DI addition), to artificial saltwater (ASW, target salinity of 5 parts per thousand) and to two treatments that added sulfate alone (SO42?, at the concentration found in 5 ppt saltwater) and saltwater with the sulfate removed (ASW-SO42?, with the 5 ppt target salinity maintained by adding additional NaCl). We found that all salt treatments suppressed CO2 production, in both drought and flooded treatments. Contrary to our expectations, CH4 fluxes from our flooded cores increased between 300 and 1200% relative to controls in the ASW and ASW-SO42? treatments respectively. In the drought treatments, we saw virtually no CH4 release from any core, while artificial seawater with sulfate increased N2O fluxes by 160% above DI control. In contrast, salt and sulfate decreased N2O fluxes by 72% in our flooded treatments. Our results indicate that salinization of forested wetlands of the coastal plain may have important climate feedbacks resulting from enhanced greenhouse gas emissions and that the magnitude and direction of these emissions are contingent upon wetland hydrology. 相似文献
9.
Hydrologic gradient and vegetation controls on CH4 and CO2 fluxes in a spring-fed forested wetland 总被引:2,自引:0,他引:2
Four different habitats in a spring-fed forested wetland (Clear Springs Wetland, Panola County, Mississippi, USA) varying
in hydrologic regime were examined for methane and carbon dioxide fluxes from soils over 15 and 9 months, respectively. There
was an increasing gradient of CH4 flux rates from an unflooded upper-elevation forest site to an occasionally flooded bottomland forest site to a shallow permanently
flooded site, and then to a deeper-water permanently flooded site. Depending on the time of year, all sites were sources of
methane but only at the upper-elevation forest site, when gravimetric soil moisture content fell below 54%, was atmospheric
methane consumed. On average, summer CH4 emission rates were higher than those in other seasons. A multiple regression model with soil temperature and soil redox
potential as independent variables could explain 65% of the variation in CH4 flux rates. In the flooded zone, variation in CH4 flux rates was correlated with aboveground plant biomass and stem density of emergent vascular plants, and plant-mediated
CH4 transport depended on plant type. The efflux of CH4 to plant biomass (Eff:B) ratio was generally lower in Hydrocotyle umbellata compared to Festuca
obtusa. Compared to several other freshwater forested wetlands in the southeastern USA, this spring-fed forested wetland ecosystem
was a strong source of atmospheric CH4, likely due to a long hydroperiod and high soil organic matter content. Carbon dioxide fluxes show a reverse spatial pattern
than CH4 fluxes with highest CO2 emissions in the non-flooded zone at all times of the year, indicating the dominance of aerobic soil respiration. A multiple
regression model also revealed a strong dependency of CO2 fluxes (r
2 = 0.73) on soil temperature and soil redox potential.
Handling editor: J. M. Melack 相似文献
10.
Effects of aggregated classifications of forest composition on estimates of evapotranspiration in a northern Wisconsin forest 总被引:1,自引:0,他引:1
D. S. MACKAY† D. E. AHL† B. E. EWERS S. T. GOWER S. N. BURROWS S. SAMANTA K. J. DAVIS‡ 《Global Change Biology》2002,8(12):1253-1265
Forest management presents challenges to accurate prediction of water and carbon exchange between the land surface and atmosphere, due to its alteration of forest structure and composition. We examined how forest species types in northern Wisconsin affect landscape scale water fluxes predicted from models driven by remotely sensed forest classification. A site‐specific classification was developed for the study site. Using this information and a digital soils database produced for the site we identified four key forest stand types: red pine, northern hardwoods, aspen, and forested wetland. Within these stand types, 64 trees representing 7 species were continuously monitored with sap flux sensors. Scaled stand‐level transpiration from sap flux was combined with a two‐source soil evaporation model and then applied over a 2.5 km × 3.0 km area around the WLEF AmeriFlux tower (Park Falls, Wisconsin) to estimate evapotranspiration. Water flux data at the tower was used as a check against these estimates. Then, experiments were conducted to determine the effects of aggregating vegetation types to International Geosphere– Biosphere Program (IGBP) level on water flux predictions. Taxonomic aggregation resulting in loss of species level information significantly altered landscape water flux predictions. However, daily water fluxes were not significantly affected by spatial aggregation when forested wetland evaporation was included. The results demonstrate the importance of aspen, which has a higher transpiration rate per unit leaf area than other forest species. However, more significant uncertainty results from not including forested wetland with its high rates of evaporation during wet summers. 相似文献