An experimental and modeling study of ash deposition behaviour for co-firing peat with lignite
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Eighteen peat samples, collected from vertical profiles in the interior of four domed ombrogenous peat deposits in Indonesia, were radiocarbon dated to determine onset and rate of peat accumulation. Onset of peat accumulation appears to be due to the following: a change to a wetter climate, a rise in the water table, availability of a platform for peat, and a decrease in sediment influx. A decrease in the rate of peat accumulation indicates a decrease in biomass production, possibly due to a decrease in nutrient availability, or an increase in biomass degradation, possibly due to increased aerobic degradation as a result of a drop in the water table. The earliest onset of peat, ca 10 ka, was observed 120 km inland at ca 18 m elevation. Peat started to accumulate at the rate of 0.9 mm/yr and slowed down to 0.2 mm/yr 4.3 ka when the peat was 5.7 m thick. Three of the peat deposits lie closer to the coast (0--43 km) and closer to present sea level ([minus]3 to +7 m). Peat in these deposits started to accumulate 6--4 ka. The youngest deposit has accumulated peat at an average rate of 1.6 mm/yr for the full 6.5 mmore » peat thickness. The other two peat deposits started accumulating at a rapid rate of 5 and 6 mm/yr and then slowed to 1.2 and 1.7 mm/yr at 4.2 and 3.4 ka, when the peat was 3.5 and 7.5 m thick, respectively. None of the deposits show compaction of the lower part of the peat profile (autocompaction). The data indicates (1) a change to a wetter climate ca 10 ka when sea-level rise drowned about half the area of the Sunda and Sahul Shelfs and (2) a subsequent slight drop in sea level starting at ca 6 ka resulted in subaerial exposure of extensive coastal lowlands.« less
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Abstract. Substantial deposits of peat have accumulated since the last glacial. Since peat accumulation rates are rather low, this process was previously neglected in carbon cycle models. For assessments of the global carbon cycle on millennial or even longer timescales, though, the carbon storage in peat cannot be neglected any more. We have therefore developed a dynamic model of wetland extent and peat accumulation in order to assess the influence of peat accumulation on the global carbon cycle. The model is based on the dynamic global vegetation model LPJ and consists of a wetland module and routines describing the accumulation and decay of peat. The wetland module, based on the TOPMODEL approach, dynamically determines inundated area and water table, which change depending on climate. Not all temporarily inundated areas accumulate peat, though, but peat accumulates in permanently inundated areas with rather stable water table position. Peatland area therefore is highly uncertain, and we perform sensitivity experiments to cover the uncertainty range for peatland extent. The peat module describes oxic and anoxic decomposition of organic matter in the acrotelm, i.e., the part of the peat column above the permanent water table, as well as anoxic decomposition in the catotelm, the peat below the summer minimum water table. We apply the model to the period of the last 8000 years, during which the model accumulates 330 PgC as catotelm peat in the peatland areas north of 40° N, with an uncertainty range from 240 PgC to 490 PgC. This falls well within the range of published estimates for the total peat storage in high northern latitudes, considering the fact that these usually cover the total carbon accumulated, not just the last 8000 years we considered in our model experiments. In the model, peat primarily accumulates in Scandinavia and eastern Canada, though eastern Europe and north-western Russia also show substantial accumulation. Modelled wetland distribution is biased towards Eurasia, where inundated area is overestimated, while it is underestimated in North America. Latitudinal sums compare favourably to measurements, though, implying that total areas, as well as climatic conditions in these areas, are captured reasonably, though the exact positions of peatlands are not modelled well. Since modelling the initiation of peatland growth requires a knowledge of topography below peat deposits, the temporal development of peatlands is not modelled explicitly, therefore overestimating peatland extent during the earlier part of our experiments. Overall our results highlight the substantial amounts of carbon taken up by peatlands during the last 8000 years. This uptake would have substantial impacts on the global carbon cycle and therefore cannot be neglected.
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Indonesia has been known as a home of the tropical peatlands. The peatlands are mainly in Sumatera, Kalimantan and Papua Islands. Spatial information on peatland depth is needed for the planning of agricultural land extensification. The research objective was to develop a preliminary estimation model of peat thickness classes based on land cover approach and analyse its applicability using Landsat 8 image. Ground data, including land cover, location and thickness of peat, were obtained from various surveys and peatlands potential map (Geology Map and Wetlands Peat Map). The land cover types were derived from Landsat 8 image. All data were used to build an initial model for estimating peat thickness classes in Merauke Regency. A table of relationships among land cover types, peat potential areas and peat thickness classes were made using ground survey data and peatlands potential maps of that were best suited to ground survey data. Furthermore, the table was used to determine peat thickness classes using land cover information produced from Landsat 8 image. The results showed that the estimated peat thickness classes in Merauke Regency consist of two classes, i.e., very shallow peatlands and shallow peatlands. Shallow peatlands were distributed at the upper part of Merauke Regency with mainly covered by forest. In comparison with Indonesia Peatlands Map, the number of classes was the two classes. The spatial distribution of shallow peatlands was relatively similar for its precision and accuracy, but the estimated area of shallow peatlands was greater than the area of shallow peatlands from Indonesia Peatlands Map. This research answered the question that peat thickness classes could be estimated by the land cover approach qualitatively. The precise estimation of peat thickness could not be done due to the limitation of insitu data.
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