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1.
Peatlands are an important store of soil carbon, and play a vital role in global carbon cycling, and when located in close proximity to urban and industrial areas, can also act as sinks of atmospherically deposited heavy metals. Large areas of the UK's blanket peat are significantly degraded and actively eroding which negatively impacts carbon and pollutant storage. The restoration of eroding UK peatlands is a major conservation concern, and over the last decade measures have been taken to try to control erosion and restore large areas of degraded peat. This study utilizes a sediment source fingerprinting approach to assess the effect of restoration practices on sediment production, and carbon and pollutant export in the Peak District National Park, southern Pennines (UK). Suspended sediment was collected using time integrated mass flux samplers (TIMS), deployed across three field areas which represent the surface conditions exhibited through an erosion–restoration cycle: (i) intact; (ii) actively eroding; and (iii) recently re‐vegetated. Anthropogenic pollutants stored near the peat's surface have allowed material mobilized by sheet erosion to be distinguished from sediment eroded from gully walls. Re‐vegetation of eroding gully systems is most effective at stabilizing interfluve surfaces, switching the locus of sediment production from contaminated surface peat to relatively ‘clean’ gully walls. The stabilization of eroding surfaces reduces particulate organic carbon (POC) and lead (Pb) fluxes by two orders of magnitude, to levels comparable with those of an intact peatland, thus maintaining this important carbon and pollutant store. The re‐vegetation of gully floors also plays a key role in decoupling eroding surfaces from the fluvial system, and further reducing the flux of material. These findings indicate that the restoration practices have been effective over a relatively short timescale, and will help target and refine future restoration initiatives. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
An understanding of the symbiotic water and gas exchange processes at the ecosystem scale is essential to the development of appropriate restoration plans of extracted peatlands. This paper presents ecosystem scale measurements of the atmospheric exchange of water and carbon dioxide (CO2) from a restored vacuum extracted peatland in eastern Québec, utilizing full‐scale micrometeorological measurements of both evaporation and CO2. The results indicate that the adopted restoration practices reduce the loss of water from the peat, but CO2 emissions are ～25% greater than an adjacent nonrestored comparison site. The blockage of drainage ditches and the existence of a mulch cover at the site keep the moisture conditions more or less constant. Consequently, the CO2 flux, which is predominantly soil respiration, is strongly controlled by peat temperature fluctuations. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

3.
The natural carbon storage function of peatland ecosystems can be severely affected by the abandonment of peat extraction, influencing peatland drainage, leading to large and persistent sources of atmospheric CO2. Moreover, these cutover peatlands have a low and variable water table position and high tension at the surface, creating harsh ecohydrological conditions for vegetation re‐establishment, particularly peat forming Sphagnum moss. Standard restoration techniques aim to restore the peatland to a carbon accumulating system through various water management techniques to improve hydrological conditions and by reintroducing Sphagnum at the surface. However, restoring the hydrology of peatlands can be expensive due to the cost of implementing the various restoration techniques. This study examines a peat extraction‐restoration technique where the acrotelm is preserved and replaced directly on the cutover peat surface. An experimental peatland adopting this acrotelm transplant technique had both a high water table and peat moisture conditions providing sufficient water at the surface for Sphagnum moss. Average water table conditions were higher at the experimental site (?8·4 ± 4·2 cm) compared to an adjacent natural site (?12·7 ± 6·0 cm) suggesting adequate moisture conditions at the restored surface. However, the experimental site experienced high variability in volumetric moisture content (VMC) in the capitula zone (upper 2 cm) where large diurnal changes in VMC (～30%) were observed, suggesting possible disturbance to the peat matrix structure during the extraction‐restoration process. However, soil–water retention analysis and physical peat properties (porosity and bulk density) suggest that no significant differences existed between the natural and experimental sites. Any structural changes within the peat matrix were therefore minimal. Moreover, low soil‐water tensions were maintained well above the laboratory measured critical Sphagnum threshold of 33% (?100 mb) VMC, further indicating favourable conditions for Sphagnum moss survival and growth. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

4.
The ecosystem services provided by forests modulate runoff generation processes, nutrient cycling and water and energy exchange between soils, vegetation and atmosphere. Increasing atmospheric CO2 affects many linked aspects of forest and catchment function in ways we do not adequately understand. Global levels of atmospheric CO2 will be around 40% higher in 2050 than current levels, yet estimates of how water and solute fluxes in forested catchments will respond to increased CO2 are highly uncertain. The Free Air CO2 Enrichment (FACE) facility of the University of Birmingham's Institute of Forest Research (BIFoR) is the only FACE in mature deciduous forest. The site specializes in fundamental studies of the response of whole ecosystem patches of mature, deciduous, temperate woodland to elevated CO2 (eCO2). Here, we describe a dataset of hydrological parameters – seven weather parameters at each of three heights and four locations, shallow soil moisture and temperature, stream hydrology and CO2 enrichment – retrieved at high frequency from the BIFoR FACE catchment.  相似文献   

5.
Peatlands are among the largest long‐term soil carbon stores, but their degradation can lead to significant carbon losses. This study considers the carbon budget of peat‐covered sites after restoration, following degradation by past wildfires. The study measured the carbon budget of eight sites: four restored‐revegetated sites, two unrestored bare soil control sites, and two intact vegetated controls over two years (2006–2008). The study considered the following flux pathways: dissolved organic carbon (DOC); particulate organic carbon (POC); dissolved carbon dioxide (CO2); primary productivity; net ecosystem respiration, and methane (CH4). The study shows that unrestored, bare peat sites can have significant carbon losses as high as 522 ± 3 tonnes C/km2/yr. Most sites showed improved carbon budgets (decreased source and/or increased sink of carbon) after restoration; this improvement was mainly in the form of a reduction in the size of the net carbon source, but for one restored site the measured carbon budget after four years of restoration was greater than observed for vegetated controls. The carbon sequestration benefit of peatland restoration would range between 122 and 833 tonnes C/km2/yr. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.

Knowledge of seasonal variation of net ecosystem CO2 exchange (NEE) and its biotic and abiotic controllers will further our understanding of carbon cycling process, mechanism and large-scale modelling. Eddy covariance technique was used to measure NEE, biotic and abiotic factors for nearly 3 years in the hinterland alpine steppe—Korbresia meadow grassland on the Tibetan Plateau, the present highest fluxnet station in the world. The main objectives are to investigate dynamics of NEE and its components and to determine the major controlling factors. Maximum carbon assimilation took place in August and maximum carbon loss occurred in November. In June, rainfall amount due to monsoon climate played a great role in grass greening and consequently influenced interannual variation of ecosystem carbon gain. From July through September, monthly NEE presented net carbon assimilation. In other months, ecosystem exhibited carbon loss. In growing season, daytime NEE was mainly controlled by photosynthetically active radiation (PAR). In addition, leaf area index (LAI) interacted with PAR and together modulated NEE rates. Ecosystem respiration was controlled mainly by soil temperature and simultaneously by soil moisture. Q 10 was negatively correlated with soil temperature but positively correlated with soil moisture. Large daily range of air temperature is not necessary to enhance carbon gain. Standard respiration rate at referenced 10°C (R 10) was positively correlated with soil moisture, soil temperature, LAI and aboveground biomass. Rainfall patterns in growing season markedly influenced soil moisture and therefore soil moisture controlled seasonal change of ecosystem respiration. Pulse rainfall in the beginning and at the end of growing season induced great ecosystem respiration and consequently a great amount of carbon was lost. Short growing season and relative low temperature restrained alpine grass vegetation development. The results suggested that LAI be usually in a low level and carbon uptake be relatively low. Rainfall patterns in the growing season and pulse rainfall in the beginning and at end of growing season control ecosystem respiration and consequently influence carbon balance of ecosystem.

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7.
Knowledge of seasonal variation of net ecosystem CO2 exchange (NEE) and its biotic and abiotic controllers will further our understanding of carbon cycling process, mechanism and large-scale modelling. Eddy covariance technique was used to measure NEE, biotic and abiotic factors for nearly 3 years in the hinterland alpine steppe—Korbresia meadow grassland on the Tibetan Plateau, the present highest fluxnet station in the world. The main objectives are to investigate dynamics of NEE and its components and to determine the major controlling factors. Maximum carbon assimilation took place in August and maximum carbon loss occurred in November. In June, rainfall amount due to monsoon climate played a great role in grass greening and consequently influenced interannual variation of ecosystem carbon gain. From July through September, monthly NEE presented net carbon assimilation. In other months, ecosystem exhibited carbon loss. In growing season, daytime NEE was mainly controlled by photosynthetically active radiation (PAR). In addition, leaf area index (LAI) interacted with PAR and together modulated NEE rates. Ecosystem respiration was controlled mainly by soil temperature and simultaneously by soil moisture. Q 10 was negatively correlated with soil temperature but positively correlated with soil moisture. Large daily range of air temperature is not necessary to enhance carbon gain. Standard respiration rate at referenced 10°C (R 10) was positively correlated with soil moisture, soil temperature, LAI and aboveground biomass. Rainfall patterns in growing season markedly influenced soil moisture and therefore soil moisture controlled seasonal change of ecosystem respiration. Pulse rainfall in the beginning and at the end of growing season induced great ecosystem respiration and consequently a great amount of carbon was lost. Short growing season and relative low temperature restrained alpine grass vegetation development. The results suggested that LAI be usually in a low level and carbon uptake be relatively low. Rainfall patterns in the growing season and pulse rainfall in the beginning and at end of growing season control ecosystem respiration and consequently influence carbon balance of ecosystem.  相似文献   

8.
Jing Wang  Qiang Yu  Xuhui Lee 《水文研究》2007,21(18):2474-2492
Understanding the exchange processes of energy and carbon dioxide (CO2) in the soil–vegetation–atmosphere system is important for assessing the role of the terrestrial ecosystem in the global water and carbon cycle and in climate change. We present a soil–vegetation–atmosphere integrated model (ChinaAgrosys) for simulating energy, water and CO2 fluxes, crop growth and development, with ample supply of nutrients and in the absence of pests, diseases and weed damage. Furthermore, we test the hypotheses of whether there is any significant difference between simulations over different time steps. CO2, water and heat fluxes were estimated by the improving parameterization method of the coupled photosynthesis–stomatal conductance–transpiration model. Soil water evaporation and plant transpiration were calculated using a multilayer water and heat‐transfer model. Field experiments were conducted in the Yucheng Integrated Agricultural Experimental Station on the North China Plain. Daily weather and crop growth variables were observed during 1998–2001, and hourly weather variables and water and heat fluxes were measured using the eddy covariance method during 2002–2003. The results showed that the model could effectively simulate diurnal and seasonal changes of net radiation, sensible and latent heat flux, soil heat flux and CO2 fluxes. The processes of evapotranspiration, soil temperature and leaf area index agree well with the measured values. Midday depression of canopy photosynthesis could be simulated by assessing the diurnal change in canopy water potential. Moreover, the comparisons of simulated daily evapotranspiration and net ecosystem exchange (NEE) under different time steps indicated that time steps used by a model affect the simulated results. There is no significant difference between simulated evapotranspiration using the model under different time steps. However, simulated NEE produces large differences in the response to different time steps. Therefore, the accurate calculation of average absorbed photosynthetic active radiation is important for the scaling of the model from hourly steps to daily steps in simulating energy and CO2 flux exchanges between winter wheat and the atmosphere. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

9.
Increases in atmospheric CO2 concentration not only affects climate variables such as precipitation and air temperature, but also affects intrinsic ecosystem physiological properties such as bulk stomatal conductance and intercellular CO2 concentration. De-convolving these two effects remains uncertain in biosphere–atmosphere water and carbon cycling. Using a simplified analytical net ecosystem CO2 exchange (NEE) model, tested with recently collected flux measurements in a humid grassland ecosystem in Ireland, we assess how much projected climate shifts affect net canopy photosynthesis (A) without physiological adjustments and contrast those findings with published field data on physiological adjustments for several grassland ecosystems. Our analysis suggests that the intrinsic grassland ecosystem physiological adjustment of A is about 45 times more important than the resulting climatic forcing shifts from the IS92a scenario (and a doubling of atmospheric CO2 concentration). Also, our analysis shows that increase in precipitation results in concomitant decrease in the two climate variables—net radiation and vapor pressure deficit, and these decreases have opposite (and almost canceling) effects on A. Implications to afforestation policy and future experimental efforts to quantify the carbon sink from humid grassland ecosystems are also discussed.  相似文献   

10.
Soil organic carbon (SOC) is an important component of the global carbon cycle yet is rarely quantified adequately in terms of its spatial variability resulting from losses of SOC due to erosion by water. Furthermore, in drylands, little is known about the effect of widespread vegetation change on changes in SOC stores and the potential for water erosion to redistribute SOC around the landscape especially during high‐magnitude run‐off events (flash floods). This study assesses the change in SOC stores across a shrub‐encroachment gradient in the Chihuahuan Desert of the south‐west USA. A robust estimate of SOC storage in surface soils is presented, indicating that more SOC is stored beneath vegetation than in bare soil areas. In addition, the change in SOC storage over a shrub‐encroachment gradient is shown to be nonlinear and highly variable within each vegetation type. Over the gradient of vegetation change, the heterogeneity of SOC increases, and newer carbon from C3 plants becomes dominant. This increase in the heterogeneity of SOC is related to an increase in water erosion and SOC loss from inter‐shrub areas, which is self‐reinforcing. Shrub‐dominated drylands lose more than three times as much SOC as their grass counterparts. The implications of this study are twofold: (1) quantifying the effects of vegetation change on carbon loss via water erosion and the highly variable effects of land degradation on soil carbon stocks is critical. (2) If landscape‐scale understanding of carbon loss by water erosion in drylands is required, studies must characterize the heterogeneity of ecosystem structure and its effects on ecosystem function across ecotones subject to vegetation change. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
The projected changes in carbon exchange between China terrestrial ecosystem and the atmosphere and vegetation and soil carbon storage during the 21st century were investigated using an atmos-phere-vegetation interaction model (AVIM2). The results show that in the coming 100 a, for SRES B2 scenario and constant atmospheric CO2 concentration, the net primary productivity (NPP) of terrestrial ecosystem in China will be decreased slowly, and vegetation and soil carbon storage as well as net ecosystem productivity (NEP) will also be decreased. The carbon sink for China terrestrial ecosystem in the beginning of the 20th century will become totally a carbon source by the year of 2020, while for B2 scenario and changing atmospheric CO2 concentration, NPP for China will increase continuously from 2.94 GtC·a?1 by the end of the 20th century to 3.99 GtC·a?1 by the end of the 21st century, and vegetation and soil carbon storage will increase to 110.3 GtC. NEP in China will keep rising during the first and middle periods of the 21st century, and reach the peak around 2050s, then will decrease gradually and approach to zero by the end of the 21st century.  相似文献   

12.
As a result of serious soil erosion on the Loess Pla-teau of China, about 1.6 billion tons of silt discharge into the downstream and 0.4 billion tons deposit on the riverbed every year, causing serious threat to the life and property of the local people on both banks of the lower Yellow River[1]. Since the 1950s, the Chinese government has initiated the work on soil and water conservation and environmental management on the Loess Plateau and formulated the guiding principle of hillslope and …  相似文献   

13.
In peatlands, fluvial erosion can lead to a dramatic decline in hydrological function, major changes in the net carbon balance and loss of biodiversity. Climate and land management change are thought to be important influences on rates of peat erosion. However, sediment production in peatlands is different to that of other soils and no models of erosion specifically for peatlands currently exist. Hence, forecasting the influence of future climate or spatially‐distributed management interventions on peat erosion is difficult. The PESERA‐GRID model was substantially modified in this study to include dominant blanket peat erosion processes. In the resulting fluvial erosion model, PESERA‐PEAT, freeze–thaw and desiccation processes were accounted for by a novel sediment supply index as key features of erosion. Land management practices were parameterized for their influence on vegetation cover, biomass and soil moisture condition. PESERA‐PEAT was numerically evaluated using available field data from four blanket peat‐covered catchments with different erosion conditions and management intensity. PESERA‐PEAT was found to be robust in modelling fluvial erosion in blanket peat. A sensitivity analysis of PESERA‐PEAT showed that modelled sediment yield was more sensitive to vegetation cover than other tested factors such as precipitation, temperature, drainage density and ditch/gully depth. Two versions of PESERA‐PEAT, equilibrium and time‐series, produced similar results under the same environmental conditions, facilitating the use of the model at different scales. The equilibrium model is suitable for assessing the high‐resolution spatial variability of average monthly peat erosion over the study period across large areas (national or global assessments), while the time‐series model is appropriate for investigating continuous monthly peat erosion throughout study periods across smaller areas or large regions using a coarser‐spatial resolution. PESERA‐PEAT will therefore support future investigations into the impact of climate change and management options on blanket peat erosion at various spatial and temporal scales. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

14.
The hydrological recovery of watersheds from disturbances such as fire and harvest can change the magnitude and distribution of flow paths as the canopy regenerates. The spatial distribution of net water input to the soil–topography system is mediated by vegetation patterns through the processes of interception, evapotranspiration and snowmelt. We have previously described RHESSys, a distributed model of water and carbon flux with a prescribed canopy cover. Although the canopy structure varied spatially it did not change through time. We present an expanded model in which carbon and nitrogen are dynamically coupled with distributed hydrology. The model fixes and allocates canopy carbon annually to reflect changes in climate forcing. We test the interactions of the forest ecosystem to distributed hydrology through controlled experiments. In the first experiment, we prescribe canopy cover and examine the sensitivity of the hydrological outputs to the distribution of vegetation. The canopy distribution is found to have significant effects on simulated hydrological outputs where evaporative demand exceeds available water. In a second experiment we simulate the canopy leaf area index (LAI) across the topography and through time. The model is executed over 100 years using repeated 10-year meteorological records to investigate spatial and temporal patterns of LAI. Annual precipitation and temperature differences result in temporally fluctuating LAI about a reasonably stable long-term mean. The topographical position has a strong effect on local forest canopy characteristics. As expected, simulated ecosystem processes are found to be sensitive to rooting depth in more water limited environments. © 1997 John Wiley & Sons, Ltd.  相似文献   

15.
We measured soil, stem and branch respiration of trees and shrubs, foliage photosynthesis and respiration in ecosystem of the needle and broad-leaved Korean pine forest in Changbai Mountain by LI-6400 CO2 analysis system. Measurement of forest microclimate was conducted simultaneously and a model was found for the relationship of soil, stem, leaf and climate factors. CO2 flux of different components in ecosystem of the broad-leaved Korean pine forest was estimated based on vegetation characteristics. The net ecosystem exchange was measured by eddy covariance technique. And we studied the effect of temperature and photosynthetic active radiation on ecosystem CO2 flux. Through analysis we found that the net ecosystem exchange was affected mainly by soil respiration and leaf photosynthesis. Annual net ecosystem exchange ranged from a minimum of about ?4.671 μmol·m?2·s?1 to a maximum of 13.80 μmol·m?2·s?1, mean net ecosystem exchange of CO2 flux was ?2.0 μmol·m?2·s?1 and 3.9 μmol·m?2·s?1 in winter and summer respectively (mean value during 24 h). Primary productivity of tree, shrub and herbage contributed about 89.7%, 3.5% and 6.8% to the gross primary productivity of the broad-leaved Korean pine forest respectively. Soil respiration contributed about 69.7% CO2 to the broad-leaved Korean pine forest ecosystem, comprising about 15.2% from tree leaves and 15.1% from branches. The net ecosystem exchange in growing season and non-growing season contributed 56.8% and 43.2% to the annual CO2 efflux respectively. The ratio of autotrophic respiration to gross primary productivity (R a:GPP) was 0.52 (NPP:GPP=0.48). Annual carbon accumulation underground accounted for 52% of the gross primary productivity, and soil respiration contributed 60% to gross primary productivity. The NPP of the needle and broad-leaved Korean pine forest was 769.3 gC·m?2·a?1. The net ecosystem exchange of this forest ecosystem (NEE) was 229.51 gC·m?2·a?1. The NEE of this forest ecosystem acquired by eddy covariance technique was lower than chamber estimates by 19.8%.  相似文献   

16.
Estimates of greenhouse gas evasion from rivers have been refined over the past decades to constrain their role in global carbon cycle processes. However, despite 55% of the human population living in urban areas, urban rivers have had limited attention. We monitored carbon dynamics in an urbanized river (River Kelvin, 331 km2, UK) to explore the drivers of dissolved carbon lateral and vertical export. Over a 2-year sampling period, riverine methane (CH4) and carbon dioxide (CO2) concentrations were consistently oversaturated with respect to atmospheric equilibria, leading to continual degassing to the atmosphere. Carbon stable isotopic compositions (δ13C) indicated that terrestrially derived carbon comprised most of the riverine CH4 and dissolved CO2 (CO2*) load while dissolved inorganic carbon (DIC) from groundwater was the main form of riverine DIC. The dynamics of CH4, CO2*, and DIC in the river were primarily hydrology-controlled, that is, [CH4] and [CO2*] both increased with elevated discharge, total [DIC] decreased with elevated discharge while the proportion of biologically derived DIC increased with increasing discharge. The concentration of dissolved organic carbon (DOC) showed a weak relationship with river hydrology in summer and autumn and was likely influenced by the combined sewer overflows. Carbon emission to the atmosphere is estimated to be 3.10 ± 0.61 kg C·m−2·yr−1 normalized to water surface area, with more than 99% emitted as CO2. Annual carbon loss to the coastal estuary is approximately 4.69 ± 0.70 Gg C yr−1, with annual DIC export approximately double that of DOC. Per unit area, the River Kelvin was a smaller carbon source to the atmosphere than natural rivers/streams but shows elevated fluxes of DIC and DOC under comparable conditions. This research illustrates the role urban systems may have on riverine carbon dynamics and demonstrates the potential tight link between urbanization and riverine carbon export.  相似文献   

17.
Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short‐term (1–15 years) sediment deposition and gully stabilization. In well‐vegetated gully systems ( ≥ 30% of ground vegetation cover), 0.035 m3 m–1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short‐term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
Coastal peatlands represent an interface between marine and terrestrial ecosystems; their hydrology is affected by salt and fresh water inflow alike. Previous studies on bog peat have shown that pore water salinity can have an impact on the saturated hydraulic conductivity (Ks) of peat because of chemical pore dilation effects. In this study, we aimed at quantifying the impact of higher salinities (up to 3.5% NaCl) on Ks of fen peat. Two experiments employing a constant‐head upward‐flow permeameter and differing in measurement and salinity change duration were conducted. Additionally, a third experiment to determine the impact of water salinity on the release of dissolved organic carbon (DOC) of the studied peat type was carried out. The results show a decrease of Ks with time, which does not depend on the water salinity but is differently shaped for different peat types. We assume pore clogging due to a conglomerate of physical, chemical, and biological processes, which rather depend on water movement rate and time than on water salinity. However, an increased water salinity did increase the DOC release. We conclude that salinity‐dependent behaviour of Ks is a function of peat chemistry and that for some peat types, salinity may only affect the DOC release without having a pronounced impact on water flow.  相似文献   

19.
Dissolved organic carbon (DOC) originating in peatlands can be mineralized to carbon dioxide (CO2) and methane (CH4), two potent greenhouse gases. Knowledge of the dynamics of DOC export via run‐off is needed for a more robust quantification of C cycling in peatland ecosystems, a prerequisite for realistic predictions of future climate change. We studied dispersion pathways of DOC in a mountain‐top peat bog in the Czech Republic (Central Europe), using a dual isotope approach. Although δ13CDOC values made it possible to link exported DOC with its within‐bog source, δ18OH2O values of precipitation and run‐off helped to understand run‐off generation. Our 2‐year DOC–H2O isotope monitoring was complemented by a laboratory peat incubation study generating an experimental time series of δ13CDOC values. DOC concentrations in run‐off during high‐flow periods were 20–30 mg L?1. The top 2 cm of the peat profile, composed of decaying green moss, contained isotopically lighter C than deeper peat, and this isotopically light C was present in run‐off in high‐flow periods. In contrast, baseflow contained only 2–10 mg DOC L?1, and its more variable C isotope composition intermittently fingerprinted deeper peat. DOC in run‐off occasionally contained isotopically extremely light C whose source in solid peat substrate was not identified. Pre‐event water made up on average 60% of the water run‐off flux, whereas direct precipitation contributed 40%. Run‐off response to precipitation was relatively fast. A highly leached horizon was identified in shallow catotelm. This peat layer was likely affected by a lateral influx of precipitation. Within 36 days of laboratory incubation, isotopically heavy DOC that had been initially released from the peat was replaced by isotopically lighter DOC, whose δ13C values converged to the solid substrate and natural run‐off. We suggest that δ13C systematics can be useful in identification of vertically stratified within‐bog DOC sources for peatland run‐off.  相似文献   

20.
Spatio-temporal patterns and driving mechanisms of forest carbon dioxide (CO2) exchange are the key issues on terrestrial ecosystem carbon cycles, which are the basis for developing and validating ecosystem carbon cycle models, assessing and predicting the role of forests in global carbon balance. Eddy covariance (EC) technique, an important method for measuring energy and material exchanges between terrestrial ecosystems and the atmosphere, has made a great contribution to understanding CO2 exchanges in the biosphere during the past decade. Here, we synthesized published EC flux measurements at various forest sites in the global network of eddy flux tower sites (FLUXNET) and regional flux networks. Our objective was to explore spatio-temporal patterns and driving factors on forest carbon fluxes, i.e. net ecosystem productivity (NEP), gross primary productivity (GPP) and total ecosystem respiration (TER). Globally, forest NEP exhibited a significant latitudinal pattern jointly controlled by GPP and TER. The NEP decreased in an order of warm temperate forest > cold temperate and tropical rain forests > boreal and subalpine forests. Mean annual temperature (MAT) made a greater contribution to forest carbon fluxes than sum of annual precipitation (SAP). As MAT increased, the GPP increased linearly, whereas the TER increased exponentially, resulting in the NEP decreasing beyond an MAT threshold of 20°C. The GPP, TER and NEP varied substantially when the SAP was less than 1500 mm, but tended to increase with increasing SAP. Temporal dynamics in forest carbon fluxes and determinants depended upon time scales. NEP showed a significant interannual variability mainly driven by climate fluctuations and different responses of the GPP and TER to environmental forcing. In a longer term, forest carbon fluxes had a significant age effect. The ecosystem was a net carbon source right after clearcutting, gradually switched to a net carbon sink when the relative stand age (i.e. ratio of actual stand age to the stand rotation age) approached 0.3, and maximized carbon sequestration capacity at premature or mature stand stages. This temporal pattern of NEP was correlated with stand leaf area index and associated GPP. This study highlights the significance of spatio-temporal dynamics in the CO2 exchange in forest carbon cycling studies. It is also suggested that in addition to forest biomes, interannual variations and stand age effects of forest carbon fluxes should be considered in the global carbon balance.  相似文献   

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