Estimation of greenhouse gas emission reductions based on vegetation changes after rewetting in Drentsche Aa brook valley

From the historical hourly water level data during 29 years, from 1988 to 2016, annual mean water level, annual highest high water level, annual lowest low water level, annual maximum range of tide and some others levels at coastal hydrological stations of the Mekong delta are computed. Results show that at these stations, the annual mean water level and the volume of sea water entering in the delta with tide are increasing; the volume of inland water evacuated to the sea with tide tends to decrease. Evolution of the annual lowest low water level shows an increasing trend, faster in the last 14 years at most of the coastal stations. During 1988–2016 the annual maximum range of tide increases in the eastern coast stations, decreases at Nam Can, and in the western coast stations except Xẽo Ro, but decreases at most of stations during 2003–2016 except Binh Đại, Xẽo Ro and Rạch Gia. The changes of the water levels at the estuarine areas reported in this chapter are informative for the planning of water regulation works in the Mekong Delta, especially relating to the construction of the sluicegates Cai Lớn and Cai Be currently under study and the planned ones on the Tiền River branches such as Ham Luong and Cổ Chien. Whether and how the changes of water levels highlighted at Nam Can station are relevant to the confluence and interaction between the tides of the East Sea (South China Sea) and the West Sea (Gulf of Thailand) in the context of global climate change, sea level rise, is an open issue.

An important share of the greenhouse gas (GHG) emissions of many European and South-East Asian countries is originating from degraded peatlands. However, only the GHG balances of a few sites can be measured directly, as these measurements are both cost- and labour-intensive. Therefore, reliable methods for upscaling peatland GHG balances to a larger scale are necessary. Ideally, such upscaling methods use readily available data and also allow for the assessment of scenarios and implemented restoration measures.In this study, we focused on unused and extensively used bogs in Germany and collected a dataset of published annual balances of carbon dioxide (CO2) and methane (CH4) from bogs within Germany and the surrounding temperate Europe. Each site was assigned to one of eight vegetation types, which are based on a clustering of the German federal biotope type classification to enable later upscaling based on this data. The relationships of the annual CO2 and CH4-balances to vegetation type, mean annual water level and temperature were then analysed with mixed effects modelling.As expected, wet extensive grassland had relatively high CO2 and low methane emissions, while semi-natural bogs showed a small CO2-uptake but higher methane emissions. Most degeneration stages showed an intermediate behaviour. Noteworthy are the comparatively low CH4 emissions of recently rewetted sites with sparse vegetation and of wet unused forested areas. Due to very little available data, the uncertainties of GHG emissions from some vegetation types are large. For very wet vegetation types such as semi-natural Sphagnum-dominated sites, water levels did not improve the GHG emission estimates compared to solely using vegetation data. For dryer sites such as wet extensive grassland, incorporating water levels significantly improved the estimation of both CO2 and CH4 fluxes.The results are broadly in line with previous findings and provide a basis for future upscaling to a German-wide estimation. In some cases, knowledge on water levels after having taking restoration measures will still improve the estimation of GHG exchange. The most severe data shortage occurred for recently rewetted sites with sparse vegetation and wet unused forested bogs as well as subalpine and alpine peatlands.

淡水湿地水文过程控制着湿地植被景观的形成与演变. 基于Landsat TM/ETM⁺遥感影像数据，利用决策树分类法提取鄱阳湖湿地1992、1999、2006、2012年4期景观信息，通过景观格局指数、转移矩阵和质心迁移法对苔草景观的空间变化及其与水文过程关系进行分析. 结果表明：研究期间，鄱阳湖湿地秋、冬季苔草景观分布面积受到水位和退水过程的影响，低水位年的中滩位缓慢退水与低滩位快速出露更有利于苔草景观的扩张；苔草景观的空间格局与水位关系密切，在低水位年份，低位洲滩提前出露，苔草景观分布高程较低，部分低位光滩被苔草所侵占，原苔草分布的部分洲滩转变为芦荻景观，景观的破碎化程度较重，在高水位年份，低位洲滩长期被水体淹没，苔草景观分布高程相对较高，部分芦荻分布区被苔草所侵占，而原苔草景观的部分区域转变为水体和光滩，由于该期间苔草主要集中分布在湖周和入湖河口地带的高位洲滩上，其景观破碎化程度较轻；水位年际间的升降变化会影响苔草景观质心位置，年均水位上升引起景观质心发生向湖岸方向推进，而年均水位下降则会导致苔草景观质心向湖心方向转移.;The formation and evolution of vegetation landscape are controlled by the hydrological processes in freshwater wetlands. Based on the Landsat TM/ETM⁺ remote sensing images, the landscape information on Lake Poyang Wetland in 1992, 1999, 2006 and 2012 was extracted by using decision tree classification. The spatial variation of Carex landscape was analyzed by means of landscape pattern index, transfer matrix and centriod shifting methods. Meanwhile, the relationship between Carex landscape and hydrological processes was also preliminarily discussed. Results showed that the distribution and area of Carex landscape in autumn were influenced by the water level and recession process of Lake Poyang Wetland during the study period, the slow recession of intermediate-elevation(14-16 m) areas and fast emersion of low-elevation(12-14 m) areas play a more important role in the formation and expansion of Carex landscape than the water level. The spatial pattern Carex landscape in Lake Poyang Wetland was closely related to the annual mean water level. In the year of low annual mean water level, the distribution elevation of Carex landscape is relatively low, some exposed mudflats were occupied by Carex landscape, and the original distribution areas of Carex landscape were partly replaced by Phragmites and Triarrhena landscape, the fragmentation degree of Carex landscape was relatively heavy. While in the year with high annual mean water level, many low bottomlands were submerged, the elevation of Carex distributed was relatively high. Many regions of Phragmites and Triarrhena landscape were occupied by Carex, while the original distribution areas of Carex landscape became partly mudflat or water landscape types. Affected by the rising water level, Carex landscape mainly shifted and centered on the high zones of estuary of input rivers and lakeshore, thus the fragmentation degree of Carex landscape was relatively light. In addition, water level inter-annual fluctuation will affect the centroid position of Carex landscape, with centriod shifting to the lakeshore during the rising water level; vice verse to the lake center during the falling water level falling.

Effects of changes in throughfall on soil GHG fluxes under a mature temperate forest, northeastern China

Lakeshores are ecotones encompassing diverse habitats that support high biodiversity, interact with pelagic ecosystems, and provide desirable ecosystem services. Hydrological regimes altered by climate change significantly impact lakeshore ecosystems. In this opinion paper, we highlight ecological consequences of distinct multiannual hydrological regimes (superimposed on natural seasonal ones) that affect the lakeshore environment of stratified lakes. Under natural hydrological conditions (Regime A), lakes maintain a stable annual mean water level, supporting diverse biota adapted to the seasonal fluctuations of water level. By contrast, under multiannual drought, the annual mean water level continuously declines (Regime B), and the resulting exposed shores become covered with dense vegetation, dominated by a few species. As the waterline recedes, structural complexity in the shallow water is reduced, limiting populations of native invertebrates and fish and facilitating establishment of invasive species. Storm-induced rapid rises in annual mean water levels during extremely rainy years (Regime C) are the least studied. While lake refilling is intuitively beneficial, undesirable short-term effects are common, including organic matter accumulation and decomposition, temporary hypoxia, pungent odors, loss of fish habitat, and formation of mosquito-infested shore pools. Littoral zone recovery and alleviation of nuisances occur only after the extreme conditions subside. Under climate change, the frequency and intensity of Regimes B and C are likely to increase. From a management perspective, maintaining water levels close to natural amplitudes can minimize the adverse conditions and damage caused by Regimes B and C.

Global inland water greenhouse gas (GHG) geographical patterns and escape mechanisms under different water level

In order to understand high-resolution environmental changes, historical water level changes on decadal and centennial scales have been conventionally analyzed employing documentary records and lake sediments. However, annual records are still limited. Here we report the discovery of water level observations (up to monthly) in the historical literature of the Qing Dynasty (1644–1912 AD). We reconstruct the chronologies of annual mean, maximum and minimum water level changes of Lake Weishan from 1758–1902 AD. The chronologies are compared with the precipitation data (dryness/wetness index data) of four stations in the vicinity of Lake Weishan (i.e., Heze, Jinan, Linyi and Xuzhou). We suggest that the annual water level changes are related to the amount of precipitation at the four stations. In addition, the flooding of the Yellow River significantly affects Lake Weishan, always resulting in extremely high annual mean, maximum and minimum water levels in the lake. The flooding in 1871 and 1873 AD even destroyed the banks between Lake Weishan-Zhaoyang-Nanyang and Lake Dushan, thus forming a united lake. In particular, we identify a high water level interval from 1851–1855 AD, just prior to the Yellow River channel change event in 1855 AD.

The Welsh Government is committed to reduce greenhouse gas (GHG) emissions from agricultural systems and combat the effects of future climate change. In this study, the ECOSSE model was applied spatially to estimate GHG and soil organic carbon (SOC) fluxes from three major land uses (grass, arable and forest) in Wales. The aims of the simulations were: (1) to estimate the annual net GHG balance for Wales; (2) to investigate the efficiency of the reduced nitrogen (N) fertilizer goal of the sustainable land management scheme (Glastir), through which the Welsh Government offers financial support to farmers and land managers on GHG flux reduction; and (3) to investigate the effects of future climate change on the emissions of GHG and plant net primary production (NPP). Three climate scenarios were studied: baseline (1961–1990) and low and high emission climate scenarios (2015–2050). Results reveal that grassland and cropland are the major nitrous oxide (N2O) emitters and consequently emit more GHG to the atmosphere than forests. The overall average simulated annual net GHG balance for Wales under baseline climate (1961–1990) is equivalent to 0.2 t CO2e ha−1 y−1 which gives an estimate of total annual net flux for Wales of 0.34 Mt CO2e y−1. Reducing N fertilizer by 20 and 40 % could reduce annual net GHG fluxes by 7 and 25 %, respectively. If the current N fertilizer application rate continues, predicted climate change by the year 2050 would not significantly affect GHG emissions or NPP from soils in Wales.

Three years of CO2, CH4 and N2O fluxes from different sheepfolds in a semiarid steppe region, China

Mitigating Curtailment and Carbon Emissions through Load Migration between Data Centers

Abstract. Fluxes of the three main greenhouse gases (GHG) CO2, CH4 and N2O from peat and other soils with high organic carbon contents are strongly controlled by water table depth. Information about the spatial distribution of water level is thus a crucial input parameter when upscaling GHG emissions to large scales. Here, we investigate the potential of statistical modeling for the regionalization of water levels in organic soils when data covers only a small fraction of the peatlands of the final map. Our study area is Germany. Phreatic water level data from 53 peatlands in Germany were compiled in a new data set comprising 1094 dip wells and 7155 years of data. For each dip well, numerous possible predictor variables were determined using nationally available data sources, which included information about land cover, ditch network, protected areas, topography, peatland characteristics and climatic boundary conditions. We applied boosted regression trees to identify dependencies between predictor variables and dip-well-specific long-term annual mean water level (WL) as well as a transformed form (WLt). The latter was obtained by assuming a hypothetical GHG transfer function and is linearly related to GHG emissions. Our results demonstrate that model calibration on WLt is superior. It increases the explained variance of the water level in the sensitive range for GHG emissions and avoids model bias in subsequent GHG upscaling. The final model explained 45% of WLt variance and was built on nine predictor variables that are based on information about land cover, peatland characteristics, drainage network, topography and climatic boundary conditions. Their individual effects on WLt and the observed parameter interactions provide insight into natural and anthropogenic boundary conditions that control water levels in organic soils. Our study also demonstrates that a large fraction of the observed WLt variance cannot be explained by nationally available predictor variables and that predictors with stronger WLt indication, relying, for example, on detailed water management maps and remote sensing products, are needed to substantially improve model predictive performance.

Abstract. Peat extraction leaves a land surface with a strong relief of deep cutover areas and higher ridges. Rewetting inundates the deep parts, while less deeply extracted zones remain at or above the water level. In temperate fens the flooded areas are colonized by helophytes such as Eriophorum angustifolium, Carex spp., Typha latifolia or Phragmites australis dependent on water depth. Reeds of Typha and Phragmites are reported as large sources of methane, but data on net CO2 uptake are contradictory for Typha and rare for Phragmites. Here, we analyze the effect of vegetation, water level and nutrient conditions on greenhouse gas (GHG) emissions for representative vegetation types along water level gradients at two rewetted cutover fens (mesotrophic and eutrophic) in Belarus. Greenhouse gas emissions were measured campaign-wise with manual chambers every 2 to 4 weeks for 2 years and interpolated by modelling. All sites had negligible nitrous oxide exchange rates. Most sites were carbon sinks and small GHG sources. Methane emissions generally increased with net ecosystem CO2 uptake. Mesotrophic small sedge reeds with water table around the land surface were small GHG sources in the range of 2.3 to 4.2 t CO2 eq. ha−1 yr−1. Eutrophic tall sedge – Typha latifolia reeds on newly formed floating mats were substantial net GHG emitters in the range of 25.1 to 39.1 t CO2 eq. ha−1 yr. They represent transient vegetation stages. Phragmites reeds ranged between −1.7 to 4.2 t CO2 eq. ha−1 yr−1 with an overall mean GHG emission of 1.3 t CO2 eq. ha−1 yr−1. The annual CO2 balance was best explained by vegetation biomass, which includes the role of vegetation composition and species. Methane emissions were obviously driven by biological activity of vegetation and soil organisms. Shallow flooding of cutover temperate fens is a suitable measure to arrive at low GHG emissions. Phragmites australis establishment should be promoted in deeper flooded areas and will lead to moderate, but variable GHG emissions or even occasional sinks. The risk of large GHG emissions is higher for eutrophic than mesotrophic peatlands. Nevertheless, flooding of eutrophic temperate fens still represents a safe GHG mitigation option because even the hotspot of our study, the floating tall sedge – Typha latifolia reeds, did not exceed the typical range of GHG emissions from drained fen grasslands and the spatially dominant Phragmites australis reed emitted by far less GHG than drained fens.

Abstract. It is generally known that managed, drained peatlands act as carbon (C) sources. In this study we examined how mitigation through the reduction of the intensity of land management and through rewetting may affect the greenhouse gas (GHG) emission and the C balance of intensively managed, drained, agricultural peatlands. Carbon and GHG balances were determined for three peatlands in the western part of the Netherlands from 2005 to 2008 by considering spatial and temporal variability of emissions (CO2, CH4 and N2O). One area (Oukoop) is an intensively managed grass-on-peatland area, including a dairy farm, with the ground water level at an average annual depth of 0.55 (±0.37) m below the soil surface. The second area (Stein) is an extensively managed grass-on-peatland area, formerly intensively managed, with a dynamic ground water level at an average annual depth of 0.45 (±0.35) m below the soil surface. The third area is a (since 1998) rewetted former agricultural peatland (Horstermeer), close to Oukoop and Stein, with the average annual ground water level at a depth of 0.2 (±0.20) m below the soil surface. During the measurement campaigns we found that both agriculturally managed sites acted as C and GHG sources and the rewetted former agricultural peatland acted as a C and GHG sink. The ecosystem (fields and ditches) total GHG balance, including CO2, CH4 and N2O, amounted to 3.9 (±0.4), 1.3 (±0.5) and −1.7 (±1.8) g CO2-eq m−2 d−1 for Oukoop, Stein and Horstermeer, respectively. Adding the farm-based emissions to Oukoop and Stein resulted in a total GHG emission of 8.3 (±1.0) and 6.6 (±1.3) g CO2-eq m−2 d−1, respectively. For Horstermeer the GHG balance remained the same since no farm-based emissions exist. Considering the C balance (uncertainty range 40–60%), the total C release in Oukoop and Stein is 5270 and 6258 kg C ha−1 yr−1, respectively (including ecosystem and management fluxes), and the total C uptake in Horstermeer is 3538 kg C ha−1 yr−1. Water bodies contributed significantly to the terrestrial GHG balance because of a high release of CH4. Overall, this study suggests that managed peatlands are large sources of GHGs and C, but, if appropriate measures are taken, they can be turned back into GHG and C sinks within 15 years of abandonment and rewetting. The shift from an intensively managed grass-on-peat area (Oukoop) to an extensively managed one (Stein) reduced the GHG emissions mainly because N2O emission and farm-based CH4 emissions decreased.

<p>The vast majority of peatlands in the North German Plain are cultivated as grassland. Intensive drainage measures are a prerequisite for conventional agricultural use of peatlands, but this practice causes high emissions of greenhouse gases (GHG), mainly carbon dioxide (CO<sub>2</sub>). Thus, raising the water levels is necessary to reduce or stop CO<sub>2</sub> emissions. Water management options such as submerged drains (SD) and ditch blocking (DB) are discussed as a potential compromise between maintaining the trafficability for intensive grassland use and reducing the GHG emissions. Furthermore, grassland renewal is regularly practiced to improve the fodder quality for dairy farming; however, this might cause additional release of GHGs, especially nitrous oxide (N<sub>2</sub>O). Here, we present results of a four-year study on the GHG emissions from an intensively used grassland on fen peat equipped with SD and DB. Additionally, the effect of grassland renewal by shallow ploughing and direct sowing was evaluated.</p><p>The target groundwater levels were set to -0.30 m below ground. In the first year, the water management system was optimized. In the following years, mean annual water levels at the parcels with SD were -0.23 m and at the parcels with DB -0.37 m. The groundwater level at the SD parcels was around 0.18 m higher than at the conventionally drained control parcels. Thus, water management by SD enabled us to even surpass the target water levels. However, year two and three of the study were dryer than usual, the differences between the SD parcels and the control parcels are expected to be lower in wet years. DB, in contrast, raised the water levels only marginally.</p><p>During the first three years, control parcels with ditch drainage emitted 27-49 t CO<sub>2</sub>-eq. ha<sup>-1</sup> a<sup>-1</sup>. This is within the typical range of emissions from grasslands on fen peat in Germany. On average, the parcels with SD showed slightly lower emissions than the drained control parcels, but these were highly variable (16-60 t CO<sub>2</sub>-eq. ha<sup>-1</sup> a<sup>-1</sup>). Due to similar groundwater levels the emissions from the parcel with DB (23-43 t CO<sub>2</sub>-eq. ha<sup>-1</sup> a<sup>-1</sup>) were comparable to the drained control parcels. Reasons for the high CO<sub>2</sub> emissions despite increased groundwater levels by SD remain so far unclear. Both types of grassland renewal lead to higher N<sub>2</sub>O emissions during the first year after renewal. Afterwards, effects became ambiguous.  </p><p>Results from the fourth measurement year (2020) will be presented as well. So far, the data seems to support the results of the previous years.</p>

Estimates of GHG emissions by hydroelectric reservoirs: The Brazilian case