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1.
Perennial pools are common natural features of peatlands, and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology, and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools, respectively, but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water‐table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool‐level fluctuations were not the same as those of local water tables in the adjacent peat. Pool‐level time series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20–30 cm higher or lower than water levels in pools only 1–4 m away. However, as peat hydraulic conductivity was very low (median of 1.5 × 10?5 and 1.4 × 10?6 cm s?1 at 30 and 50 cm depths at the natural pool site), there was little deep subsurface flow interaction. We conclude that (a) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and (b) surface and near‐surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies.  相似文献   

2.
The relationship between stream water DOC concentrations and soil organic C pools was investigated at a range of spatial scales in subcatchments of the River Dee system in north‐east Scotland. Catchment percentage peat cover and soil C pools, calculated using local, national and international soils databases, were related to mean DOC concentrations in streams draining small‐ (<5 km2), medium‐ (12–38 km2) and large‐scale (56–150 km2) catchments. The results show that, whilst soil C pool is a good predictor of stream water DOC concentration at all three scales, the strongest relationships were found in the small‐scale catchments. In addition, in both the small‐ and large‐scale catchments, percentage peat cover was as a good predictor of stream water DOC concentration as catchment soil C pool. The data also showed that, for a given soil C pool, streams draining lowland (<700 m) catchments had higher DOC concentrations than those draining upland (>700 m) catchments, suggesting that disturbance and land use may have a small effect on DOC concentration. Our results therefore suggest that the relationship between stream water DOC concentration and catchment soil C pools exists at a range of spatial scales and this relationship appears to be sufficiently robust to be used to predict the effects of changes in catchment soil C storage on stream water DOC concentration. Copyright © 1999 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.
Global peatlands store an unparalleled proportion of total global organic carbon but it is vulnerable to erosion into fluvial systems. Fluvial networks are being recognized as areas of carbon transformation, with eroded particulate organic carbon processed to dissolved organic carbon and CO2. Existing studies indicate biodegradation and photodegradation as key processes controlling the transformation of organic carbon in fluvial systems, with initial concentrations of dissolved organic carbon (DOC) identified as a control on the rate of carbon mineralization. This study manipulates temperature and incident light intensity to investigate carbon mineralization rates in laboratory simulations of peatland sediment transport into fluvial systems. By directly measuring gaseous CO2 emissions from sampled stream water, the relationship of temperature and light intensity with carbon efflux is identified. In simulations where sediment (as particulate organic matter, POM) is absent, temperature is consistently the dominant factor influencing carbon efflux rates. This influence is independent of the initial DOC concentration of the water sample. In simulations where POM was added, representing a peatland river receiving eroded terrestrial sediment, initial DOC concentration predicts 79% of the variation in total gaseous carbon efflux whereas temperature and light intensity predict 12% and 3%, respectively. When sampled stream water's mineralization rates in the presence of added POM are analysed independently, removing DOC as a model variable, the dominant variable affecting CO2 efflux is opposite for each sample. This study presents novel data suggesting peatland erosion introduces further complexity to dynamic stream systems where rates of carbon transformation processes and the influence of specific environmental variables are interdependent. Anthropogenic climate change is identified as a leading risk factor perpetuating peatland erosion; therefore, understanding the fate of terrestrial sediment in rivers and further quantifying the benefits of protecting peatland soils will be of increasing importance to carbon budgeting and ecosystem function studies.  相似文献   

5.
Fluvial organic carbon (OC) transformations are an important component of carbon cycling and greenhouse gas production in inland waters resulting in considerable recent interest in the fate of fluvial OC exported from carbon rich soils such as peatlands. Additionally, peatland catchments are important drinking water collection areas, where high OC concentrations in runoff have water treatment implications. This analysis presents the results from a year‐round intensive study within a water treatment catchment draining an area of peatland, considering carbon transformations along a continuum from headwater river, through a storage reservoir and pipe, to a water treatment works. The study uses a unique combination of methods (colourmetric, ultrafiltration, and 14C radiocarbon dating) to assess catchment wide changes in fluvial carbon composition (colour, size, and age) alongside concentration measures. The results indicate clear patterns of carbon transformations in the river and reservoir and dissolved low molecular weight coloured carbon to be most subject to change, with both loss and replacement within the catchment residence time. Although the evidence suggests dissolved OC (DOC) gains are from particulate OC breakdown, the mechanisms of DOC loss are less certain and may represent greenhouse gas losses or conversions to particulate OC. The transformations presented here appear to have minimal impact on the amount of harder to treat (<10 kDa) dissolved carbon, although they do have implications for total DOC loading to water treatment works. This paper shows that peatland fluvial systems are not passive receptors of particulate and dissolved organic carbon but locations where carbon is actively cycled, with implications for the understanding of carbon cycling and water treatment in peatland catchments.  相似文献   

6.
The Malloryville Wetland Complex, a small kettle-hole peatland, contains a diversity of peatland types. The wetland has a ‘rich’ side that contains wetland vegetation associated with solute-rich, near-neutral pH (minerotrophic) water, and a ‘poor’ side containing vegetation that grows in solute-poor and acidic (ombrotrophic) water. Vertical head gradients at piezometer clusters located in the rich side clearly show that groundwater is moving upwards towards the land surface, consistent with the vegetation types and surface water quality. In contrast, vertical head gradients also show that groundwater is moving upward in the poor side even though the vegetation and surface water chemistry are not minerotrophic. An incipient raised bog in the center of the poor side is the only site where groundwater moves consistently downward.

A peat core collected at the bog center shows that the bog site was initially covered by minerotrophic vegetation, typically found in groundwater discharge zones, which was later replaced by ombrotrophic bog vegetation. Theoretical computer simulation experiments of the bog hydrogeologic setting through time suggest that the direction of vertical groundwater flow at the bog site permanently changed from up to down when a water table mound developed under a convex-shaped fen peat mound that probably formed because of differential peat accumulation. Ombrotrophic conditions and bog vegetation probably began when the fen water table mound grew sufficiently large enough to divert the upward movement of regional groundwater. The transition from rich to poor environments probably occurred when the wetland water table was substantially below the elevation of the surrounding regional water table.  相似文献   


7.
On patterned peatlands, open water pools develop within a matrix of terrestrial vegetation (‘ridges’). Regional patterns in the distribution of ridge–pool complexes suggest that the relative cover of these two surface types is controlled in part by climate wetness, but landscape topography must also be an important controlling factor. In this paper, a functional model that relates relative cover of ridges and pools to climate and surface gradient was developed and tested. The model was formulated in terms of a water budget, based on the differential effects of ridges and pools on losses by evapotranspiration and subsurface flow. It predicts a positive relationship between surface gradient and ridge proportion, with a linear effect related to water supply and ridge hydraulic conductivity, modified at high ridge proportion by differences in evapotranspiration between ridges and pools. The limit to patterned peatland distribution occurs where the surface is completely covered by ridges. The model may be sensitive or insensitive to climate differences between localities, depending on whether hydraulic characteristics of ridge peat co‐vary with water supply. To distinguish between these alternative hypotheses, surface gradient and ridge proportion were surveyed along 20 transects in each of three localities in Scotland that differ threefold in net precipitation to pools. The results of the field survey served to reject the climate‐sensitive hypothesis, but were consistent with the climate‐insensitive hypothesis. Analysis of the residuals suggested that variation within localities was related more to topographic control of water supply than to ridge hydraulic conductivity or developmental stage. Hence, within this maritime climate region, the distribution of ridge–pool complexes and the relative abundance of pools are controlled mainly by topographic variables. Field surveys across both maritime and continental regions are required to confirm a subtle climatic effect that allows pools to occur on higher gradients in drier climates than in wetter climates. Further development and testing of the functional model will provide a stronger basis for assessing potential feedback between climate change, peatland surface structure and methane emission from pools. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

8.
Peatlands cover a very small area of the Earth, but store globally significant quantities of carbon and export disproportionate quantities of fluvial organic carbon, especially when the peatlands are degraded or disturbed. Peatland headwater catchments with high concentrations of dissolved and particulate organic carbon (DOC and POC) provide an opportunity to investigate the possibility of competing effects that could lead to enhanced or diminished turnover of DOC in the presence of POC. Both POC and DOC can be degraded by light and microbes, producing smaller molecules and releasing CO2 and CH4 to the atmosphere, and POC can inhibit light penetration, stabilize DOC by providing adsorption sites and providing surfaces for microbes to interact with DOC. However, the majority of peatland fluvial carbon studies are conducted using filtered water samples, and measure only the DOC concentration, so the impact of the particulate organic matter (POM) on in-stream processing of organic carbon is relatively unknown. It is therefore possible that studies have underestimated carbon transformations in rivers as they have not considered the interaction of the particulate material on the dissolved concentrations; there could be higher losses than previously estimated, increasing the contribution of peatland headwaters to GHG emissions. In this study, we assessed if the current approach of DOC degradation studies accurately represent the impact of POM on DOC degradation, by quantifying DOC production from POM, and therefore POC, over time in water with manipulated POM concentrations. Both filtered and unfiltered water lost 60% of the DOC over 70 hours, whereas the treatment with additional POM lost only 35%. The results showed that filtering does not significantly impact the DOC degradation rates; however, when the POC concentration was doubled, there was a significant reduction in DOC degradation, suggesting that filtering would still be necessary to get accurate rates of DOC transformations in waters with high POC concentrations.  相似文献   

9.
Dissolved organic carbon export from a cutover and restored peatland   总被引：1，自引：0，他引：1  
High demand for horticultural peat has increased peatland drainage and peat extraction in Canada. The hydrology and carbon cycling of these cutover peatlands is greatly altered, necessitating active restoration efforts to permit the regeneration of Sphagnum mosses and the re‐establishment of natural peatland function. The effect of peatland extraction and restoration on the export of dissolved organic carbon (DOC) was examined for three successive seasons (May to October, 1999 to 2001) at two different sites (cutover and restored) in eastern Québec. A shift towards higher DOC concentrations was observed following peatland extraction (maximum: 182·6 mg L?1) and concentrations remained high post‐restoration (maximum: 191·0 mg L?1). The cutover site exported more DOC than the restored site in all three study seasons. The highest exports occurred during the wettest year (1999), with cutover and restored site export of 10·3 and 4·8 g m?2, respectively. In 2000, 8·5 g C m?2 was released from the cutover site, while the restored site released less than half that amount (3·4 g C m?2). In 2001, the restored site released about the same amount of DOC as in the previous year (3·5 g C m?2), while the cutover site load dropped to 6·2 g C m?2. Both sites were net exporters of DOC in all years. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

10.
Fred Worrall  Simon Dixon 《水文研究》2013,27(26):3994-4003
Given the continuing concern about rising concentrations of dissolved organic carbon (DOC) in stream water leaving peat‐covered catchments, this study has considered the impact of managed burning or cutting of Calluna vulgaris, a dominant vegetation cover in many UK peatlands. Pristine mature Calluna stands were compared with those that had been subject to cutting and or managed burning up to 5 years after intervention. The study measured the DOC concentration of both soil and surface runoff water over a period of 12 months in comparison with water table depth, conductivity, and pH. The results show the following:
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11.
Waterborne carbon (C) export from terrestrial ecosystems is a potentially important flux for the net catchment C balance and links the biogeochemical C cycling of terrestrial ecosystems to their downstream aquatic ecosystems. We have monitored hydrology and stream chemistry over 3 years in ten nested catchments (0.6–15.1 km2) with variable peatland cover (0%–22%) and groundwater influence in subarctic Sweden. Total waterborne C export, including dissolved and particulate organic carbon (DOC and POC) and dissolved inorganic carbon (DIC), ranged between 2.8 and 7.3 g m–2 year–1, representing ~10%–30% of catchment net ecosystem exchange of CO2. Several characteristics of catchment waterborne C export were affected by interacting effects of peatland cover and groundwater influence, including magnitude and timing, partitioning into DOC, POC, and DIC and chemical composition of the exported DOC. Waterborne C export was greater during the wetter years, equivalent to an average change in export of ~2 g m–2 year–1 per 100 mm of precipitation. Wetter years led to a greater relative increase in DIC export than DOC export due to an inferred relative shift in dominance from shallow organic flow pathways to groundwater sources. Indices of DOC composition (SUVA254 and a250/a365) indicated that DOC aromaticity and average molecular weight increased with catchment peatland cover and decreased with increased groundwater influence. Our results provide examples on how waterborne C export and DOC composition might be affected by climate change. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
We investigated the effects of ditch blocking on fluvial carbon concentrations and fluxes at a 5‐year, replicated, control‐intervention field experiment on a blanket peatland in North Wales, UK. The site was hydrologically instrumented, and run‐off via open and blocked ditches was analysed for dissolved organic carbon (DOC), particulate organic carbon, dissolved carbon dioxide, and dissolved methane. DOC was also analysed in peat porewater and overland flow. The hillslope experiment was embedded within a paired control‐intervention catchment study, with 3 years of preblocking and 6 years of postblocking data. Results from the hillslope showed large reductions in discharge via blocked ditches, with water partly redirected into hillslope surface and subsurface flows, and partly into remaining open ditches. We observed no impacts of ditch blocking on DOC, particulate organic carbon, dissolved carbon dioxide or methane in ditch waters, DOC in porewaters or overland flow, or stream water DOC at the paired catchment scale. Similar DOC concentrations in ditch water, overland flow, and porewater suggest that diverting flow from the ditch network to surface or subsurface flow had a limited impact on concentrations or fluxes of DOC entering the stream network. The subdued response of fluvial carbon to ditch blocking in our study may be attributable to the relatively low susceptibility of blanket peatlands to drainage, or to physical alterations of the peat since drainage. We conclude that ditch blocking cannot be always be expected to deliver reductions in fluvial carbon loss, or improvements in the quality of drinking water supplies.  相似文献   

13.
Large peatland complexes dominate the landscape of the James Bay Lowland in subarctic Ontario, Canada. However, there is not a thorough understanding of the hydrological processes occurring in these important systems, particularly how ladder fens connect large domed bogs to the aquatic ecosystems that drain the peatland complex. Ladder fens consist of a pool‐rib topography where flow downgradient is controlled by the peat ribs. Within the ribs, low‐lying preferential flow paths typically enhance the transmission of water, whereas the elevated ridge microforms impede water flow to downgradient aquatic ecosystems. To assess the hydrological connectivity, we study the role of the water table, peat transmissivity, and microtopography of a small ladder fen for 3 summers (2013–2015) in the James Bay Lowland. The system was manipulated with a sustained hydrological forcing (water addition) to the upslope boundary of the fen during 2014 (38 m3/day) and 2015 (30 m3/day). There was an exponential increase in transmissivity towards the peat surface due to extremely high‐hydraulic conductivities within the upper few centimeters of the peat deposit. At the maximum water table, the saturated hydraulic conductivity of the 0.1 m layer of peat below the water table varied depending on peat microtopography (preferential flow paths = 42–598 m/day and ridges = 16–52 m/day), resulting in high‐hydrological connectivity periods. Furthermore, during 2015, there was an abnormally large amount of precipitation (300 mm vs. long‐term average ~ 100 mm) that resulted in complete surface water connectivity of the site. This caused rapid movement of water from the head of system to the outlet (~15 hr) and runoff ratios >1, compared to low‐water table periods (runoff ratio ~ 0.05). This study highlights the profound importance of the transmissivity–water table feedback mechanism in ladder fens, on controlling the water retention and drainage of large peatland complexes.  相似文献   

14.
To establish the influence of phytoplankton blooms on the dynamics and sources of dissolved organic carbon (DOC) in Lake Taihu, the concentrations and stable carbon isotope values (δ13C) of DOC and particulate organic carbon (POC) were analyzed, along with environmental factors, including water temperature, chlorophyll a (Chl a) concentration, phytoplankton community and total bacterial abundance, from March to August 2013 at five sites in Lake Taihu. Significant differences were observed in the DOC concentrations and δ13CDOC values at the sampling sites. On average, the proportion of DOC in the total organic carbon (TOC) pool ranged from 30% ± 10% to 81% ± 7%. POC was positively associated with both Chl a concentration and cyanobacteria biomass, suggesting that cyanobacteria blooms contribute to the POC pool in Lake Taihu. Depleted 13C in DOC relative to POC was observed in August, indicating that DOC was partially derived from POC in August. However, Chl a explained only 40% of the variation in DOC in the entirety of Lake Taihu, and at two sites far from the estuary, the contribution of allochthonous carbon was less than 50% in August. These results suggested a greater influence of allochthonous sources on the DOC pool. Moreover, the biodegradability of DOC was further determined by the total dissolved carbohydrates to DOC ratio (TCHO/DOC), specific UV absorbance (SUVA254), and the concentrations of bioavailable DOC (BDOC). On average, 17% of the variation in DOC was attributable to the BDOC pool, and the BDOC concentration correlated positively with Chl a, cyanobacteria biomass, and total bacterial abundance, suggesting that cyanobacteria–derived DOC is biodegradable and is preferentially utilized by bacteria.  相似文献   

15.
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   

16.
Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

17.
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18.
We observed polymictic behaviour in stream pools in Long Meadow, Sequoia National Park, California—part of the Southern Sierra Critical Zone Observatory. Stream pools stratified thermally during the day time and were isothermal at night—this pattern persists from the middle of summer into the fall. We found that four characteristics typical of a mountain meadow environment—low stream flow, open sky, cold groundwater discharge, and elevated organic carbon concentrations—are particularly conducive to pool stratification. Incoming shortwave radiation was the dominant energy input to heat pool water while nighttime emitted longwave radiation was the major cooling mechanism. Relatively cold groundwater discharge into the pool bottom increased density stratification within the pool. Elevated DOC concentrations increased the capacity of the pool to absorb photosynthetically active radiation and also promoted stratification. Stream velocities in the meadow were generally insufficient to meet threshold Richardson numbers and mix the pools during the daytime; smaller stream cross sectional areas would have potential for destabilizing pools in the daytime. We propose a conceptual model for describing polymictic stream pools and assessing the potential for polymictic pools to occur. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
A peatland complex disturbed by berm construction in the 1950s was used to examine the long‐term impact of water table (WT) manipulation on peatland hydraulic properties and moisture retention at three adjacent sites with increasing depth to WT (WET, INTermediate reference and DRY). Saturated hydraulic conductivity (Ks) was found to decrease with depth by several orders of magnitude over a depth of 1–1.5 m at all sites. The depth dependence of WT response to rainfall was similar across sites: WT response increased from 1 : 1 at the surface, to 5 : 1 at 50 cm depth. While surface specific yield (Sy) values were similar across all sites, it decreased with depth at a rate of 0.014 cm?1 in hollows and 0.007 cm?1 in hummocks. Bulk density (ρb) exhibited similar depth‐dependent trends as Sy and explains a high amount of variance (r2 > 0.69) in moisture retention across a range of pore water pressures (?15 to ?500 cm H2O). Because of higher ρb, hollow peat had greater moisture retention, where site effects were minimal. However, the estimated residual water content for surface Sphagnum samples, while on average lower in hummocks (0.082 m3 m?3) versus hollows (0.087 m3 m?3), increased from WET (0.058 m3 m?3) to INT (0.088 m3 m?3) to DRY (0.108 m3 m?3) which has important implications for moisture stress under conditions of persistent WT drawdown. Given the potential importance of microtopographic succession for altering peatland hydraulic structure, our findings point to the need for a better understanding of what controls the relative height and proportional coverage of hummocks in relation to long‐term disturbance‐response dynamics. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

20.
A significant proportion of tropical peatlands has been drained for agricultural purposes, resulting in severe degradation. Hydrological restoration, which usually involves blocking ditches, is therefore a priority. Nevertheless, the influence of ditch blocking on tropical peatland hydrological functioning is still poorly understood. We studied water-level dynamics using a combination of automated and manual dipwells, and also meteorological data during dry and wet seasons over 6 months at three locations in Sebangau National Park, Kalimantan, Indonesia. The locations were a forested peatland (Forested), a drained peatland with ditch dams (Blocked), and a drained peatland without ditch dams (Drained). In the dry season, water tables at all sites were deeper than the Indonesian regulatory requirement of 40 cm from the peat surface. In the dry season, the ditches were dry and water did not flow to them. The dry season water-table drawdown rates — solely due to evapotranspiration — were 9.3 mm day−1 at Forested, 9.6 mm day−1 at Blocked, but 12.7 mm day−1 at Drained. In the wet season, the proportion of time during which water tables in the wells were deeper than the 40 cm limit ranged between 16% and 87% at Forested, 0% at Blocked, and between 0% and 38% at Drained. In the wet season, water flowed from the peatland to ditches at Blocked and Drained. The interquartile range of hydraulic gradients between the lowest ditch outlet and the farthest well from ditches at Blocked was 3.7 × 10−4 to 7.8 × 10−4 m m−1, but 1.9 × 10−3 to 2.6 × 10−3 m m−1 at Drained. Given the results from Forested, a water-table depth limit policy based on field data may be required, to reflect natural seasonal dynamics in tropical peatlands. Revised spatial designs of dams or bunds are also required, to ensure effective water-table management as part of tropical peatland restoration.  相似文献   

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