Rewetting of milled peat: laboratory investigation of water movement and storage

Abstract. Air- dried milled peat (0.45 g g^-1 wet weight basis) is used as an electricity generating fuel in Ireland. It is stored on peat bogs in triangular section stockpiles. These stockpiles comprise of milled peat of varying types, classified by poured density, and are subject to rewetting during storage which incurs an economic penalty. A water applicator was constructed to study the nature of rewetting mechanisms in laboratory-scale milled peat stockpiles, and to assess some potential protection strategies. Results indicated that there were few consistent short-term mechanisms linked to milled peat type. Over a longer period, low density milled peat stored most water, high density milled peat generated most runoff from the stockpile surface, and under certain conditions, throughflow was very important in all milled peat types. The industrial implications of the findings conclude that protection strategies should focus on lower density stockpiles.     

Evaluation of phosphorus mobilization potential in rewetted fens by an improved sequential chemical extraction procedure

After rewetting of peatlands, phosphorus (P) pore‐water concentrations were up to three orders of magnitude greater than under pristine conditions. It was hypothesized that different mobilization processes such as ion‐exchange reactions, biotic/abiotic redox reactions, acidification and ongoing anaerobic decomposition of particulate organic matter by hydrolytic cleavage and fermentation might be responsible. To identify P pools in peat samples of varying degrees of decomposition, we modified and improved a sequential chemical extraction method that allowed conclusions on potential mobilization mechanisms in rewetted peatlands. The results indicated that the earlier drainage of rewetted fens strongly increased the P mobilization potential in the upper decomposed peat layers. Accordingly, the amount of P bound to redox‐sensitive (bicarbonate/dithionite soluble) compounds (BD‐P) was, on average, one order of magnitude greater in decomposed peat of rewetted fens (5.4–14.3 μmol P g^?1 dry matter or DM) than in underlying less‐decomposed peat layers (0.2–1.9 μmol P g^?1 DM) or slightly decomposed peat derived from pristine fens (0.4–2.0 μmol P g^?1 DM). The BD‐P fraction found in the upper very decomposed peat layers appears to be most important for P mobilization in rewetted fens and accounted for 85% of the variability of P mobilization rates. Despite uncertainties regarding P diagenetic processes in peat, as well as the development of microbial decomposition processes, in the long‐term, high pore‐water P concentrations can be expected in rewetted fens for decades to come.     

Acid Mine Drainage Treatment Assisted by Lignite-Derived Humic Substances

Rewetting of agriculturally used peatlands has been proposed as a measure to stop soil subsidence, conserve peat and rehabilitate ecosystem functioning. Unintended consequences might involve nutrient release and changes in the greenhouse gas (GHG) balance towards CH₄-dominated emission. To investigate the risks and benefits of rewetting, we subjected soil columns from drained peat- and clay-covered peatlands to different water level treatments: permanently low, permanently inundated and fluctuating (first inundated, then drained). Surface water and soil pore water chemistry, soil-extractable nutrients and greenhouse gas fluxes were measured throughout the experiment. Permanent inundation released large amounts of nutrients into pore water, especially phosphorus (up to 11.7 mg P-PO₄ l^?1) and ammonium (4.8 mg N-NH₄ l^?1). Phosphorus release was larger in peat than in clay soil, presumably due to the larger pool of iron-bound phosphorus in peat. Furthermore, substantial amounts of phosphorus and potassium were exported from the soil matrix to the surface water, risking the pollution of local species-rich (semi-)aquatic ecosystems. Rewetting of both clay and peat soil reduced CO₂ emissions. CH₄ emissions increased, but, in contrast to the expectations, the fluxes were relatively low. Calculations showed that rewetting reduced net cumulative GHG emissions expressed as CO₂ equivalents.     

Molecular weight spectra of dissolved organic carbon in a rewetted Welsh peatland and possible implications for water quality

Abstract. Demand for water from catchments dominated by upland peat as a source of drinking water supplies in the UK is likely to increase in the future as demand per capita continues to rise (Thomsen 1990) and/or summer droughts increase in frequency (Arnell 1992). Concern has been expressed in recent years over rising colour levels (related to dissolved organic carbon (DOC) and iron (Fe)) from such catchments (e.g. Kay et al. 1989) causing reduced drinking water quality. One of the major causes of increased DOC concentrations is rewetting following periods of relative drought (Mitchell & McDonald 1992). Experimental rewetting of a naturally drained wetland in Mid‐Wales over four years was found to substantially increase the concentrations of DOC, and Fe in the pore‐water, with peak values of >60 mg dm^–3 (Fe) and >300 mg dm^–3 (DOC) after rewetting, compared with typical values of <1 mgdm^–3 (Fe) and <15 mg dm^–3 (DOC) under the drained conditions. Seasonal peak concentrations of Fe and DOC have since remained at these higher levels. Rewetting produced a selective enrichment of the >5000 to <90 000 apparent molecular weight (AMW) material and this fraction was found to yield peak Fe concentrations. Two additional peaks of DOC were also found in the experimental wetland (not present in the control wetland), of >90 000 to <200 000 AMW and >200 000 AMW material. The AMW spectrum of DOC in the experimental wetland changed with season, and the >90 000 to <200 000 AMW fraction could only be seen in spring, representing a transient pool of carbon that is rapidly transformed in or transported from the wetland. These findings suggest that rewetting of peatland following drought (e.g. due to climate change) has the potential to reduce water quality. Moreover, recent interest in restoration (rewetting) of drained peatlands (Wheeler & Shaw 1995) could create an additional source of DOC rich water.     

2种典型耕作方式影响下的蔗田土壤孔隙结构及其水分运动特性

为了明确农业生产过程中耕作方式对田间土壤孔隙结构及土壤水分运动特性的影响,以广西农地蔗田为研究对象,基于土壤切片技术分析研究免耕和垄耕2种典型耕作方式蔗田的田间土壤孔隙结构特征,并结合土柱模拟入渗试验,探究土壤孔隙结构对土壤水分运动的影响,进一步揭示孔隙结构与土壤水分运动特性之间的相互作用关系。结果表明：随着土层深度的增加,免耕蔗田孔隙形态以聚集的团块状分布为主,垄耕蔗田孔隙形态以条状分布为主。与免耕蔗田相比,垄耕蔗田的土壤总孔隙度和>2.5 mm孔径的孔隙度分别增加32.5%和21.9%。垄耕蔗田在局部土层深度范围内显著增加上下土层孔隙的变异度(p<0.05),显著降低土壤孔隙的连通性(平均邻近指数为0.448)(p<0.05),土壤孔隙形态相对规则(平均成圆率为0.335)。对于土壤水分运动特性,免耕蔗田总体的土壤饱和导水率和质量流率显著高于垄耕蔗田(p<0.05),初始含水率显著低于垄耕蔗田(p<0.05),质量流率随时间变化强度相对较大,提高水流入渗能力。垄耕降低土壤孔隙结构连通性,使水分蓄存在表层土壤中,一定程度上可降低土壤水分的入渗现象,改变蔗...     

Temporal trends in bromide release following rewetting of a naturally drained gully mire

Abstract. Recently, there has been interest in the occurrence of bromide (Br^-) in natural waters since it has been demonstrated that Br^-, in association with humic substances in raw waters, is readily incorporated into haloacetic acids in the form of organically bound bromine (Br) during water chlorination. We report results of the effects of experimentally rewetting a naturally drained gully mire on the hydrochemistry of Br^-, iron (Fe) and dissolved organic carbon (DOC) in the peat water. Results obtained over a three year period showed that rewetting substantially increased the concentrations of these solutes in the pore water, with peak values of 1 mg dm^-3 (Br^-), > 60 mg dm^-3 (Fe) and > 300 mg dm^-3 (DOC) detected in some samples after rewetting, compared with typical values < 0.05 mg dm^-3 (Br^-), < 1 mg dm^-3 (Fe) and < 15 mg dm^-3 (DOC) under the drained conditions. Bromide, Fe and DOC release were highly seasonal, with the largest concentrations observed in late-summer to autumn. However, whereas seasonal peak concentrations of Fe and DOC have since remained at these higher levels, seasonal peak concentrations of Br^- were progressively attenuated over time, suggesting the latter phenomenon is a flush effect, with no longer-term consequences for water quality.     

Mitigation of Diffuse Phosphorus Pollution during Rewetting of Fen Peat Soils: A Trans-European Case Study

Intensive cultivation of fen peat soils (Eutric Histosols) for agricultural purposes, started in Europe about 250 years ago, resulting in decreased soil fertility, increased oxidation of peat and corresponding CO₂-emissions to the atmosphere, nutrient transfer to aquatic ecosystems and losses in the total area of the former native wetlands. To prevent these negative environmental effects set-aside programs and rewetting measures were promoted in recent years. Literature results and practical experiences showed that large scale rewetting of intensively used agricultural Histosols may result in the mobilisation of phosphorus (P), its transport to adjacent surface waters and an accelerated eutrophication risk. The paper summarises results from an international European Community sponsored research project and demonstrates how results obtained at different scales and from different scientific disciplines were compiled to derive a strategy to carry out rewetting measures. A decision support system (DSS) for a hydrologically sensitive area in the Droemling catchment in north-eastern Germany was developed and is presented as a tool to regulate rewetting in order to control P release. It is demonstrated that additional laboratory experiments to identify essential processes of P release during rewetting and the site-specific management of the water table, the involvement of specific knowledge and experience of the stakeholders are necessary to develop an applicable DSS. The presented DSS is practically used to prevent freshwater resources from diffuse P pollution.     

Simple and Rapid Laboratory Method for Rewetting Dry Soil for Incubations

Soil microbial activity is greatly affected by soil water content. Determining the appropriate moisture content to rewet soils that have been dried in preparation for laboratory incubations to determine microbial activity can be laborious and time-consuming. The most common methods used achieve sufficient moisture content for peak microbial respiration are gravimetric water content, soil matric potential, or percentage of water-filled pore space (WFPS). Alternatively, a fast, simple, and accurate way to ensure that a given soil receives the appropriate amount of water for peak soil microbial respiration is to rely on natural capillary action for rewetting the dry soil. The capillary method is related to the gravimetric method for water uptake and has a strong correlation with WFPS. A microbial respiration test was conducted to compare rewetting methods. The 24-h carbon dioxide (CO₂) / carbon (C) results were very similar and strongly correlated using the gravimetric method and the capillary method for rewetting dried soil.     

Effects of experimental drying intensity and duration on respiration and methane production recovery in fen peat incubations

Drying and rewetting to a variable extent influence the C gas exchange between peat soils and the atmosphere. We incubated a decomposed and compacted fen peat and investigated in two experiments 1) the vertical distribution of CO₂ and CH₄ production rates and their response to drying and 2) the effects of temperature, drying intensity and duration on CO₂ production rates and on CH₄ production recovery after rewetting. Surface peat down to 5 cm contributed up to 67% (CO₂) and above 80% (CH₄) of the depth-aggregated (50 cm) production. As CO₂ production sharply decreased with depth water table fluctuations in deeper peat layers are thus not expected to cause a substantial increase in soil respiration in this site. Compared to anaerobic water saturated conditions drying increased peat CO₂ production by a factor between 1.4 and 2.1. Regarding the effects of the studied factors, warmer conditions increased and prolonged drying duration decreased CO₂ production whereas the soil moisture level had little influence. No significant interactions among factors were found. Short dry events under warmer conditions are likely to result in greatest peaks of CO₂ production rates. Upon rewetting, CH₄ production was monitored over time and the recovery was standardized to pre-drying levels to compare the treatment effects. Methane production increased non-linearly over time and all factors (temperature, drying intensity and duration) influenced the pattern of post-drying CH₄ production. Peat undergoing more intense and longer drying events required a longer lag time before substantial CH₄ production occurred and warmer conditions appeared to speed up the process.     

Soil physical characteristics of peat soils

Drainage and intensive use of fens lead to alterations in the physical characteristics of peat soils. This was demonstrated using parameters of water balance (available water capacity) and the evaluated unsaturated hydraulic conductivity. Deriving the distribution of the pore size from the water retention curve was flawed because of shrinkage due to drainage, especially at high soil water potentials. These errors became greater as the peat was less influenced by soil‐genetic processes. The water retention curves (desorption) evaluated in the field and the laboratory satisfactorily corresponded. However, the wetting‐ and drainage‐curves obtained in the field differed up to 30 vol.‐% water content at same soil water potentials. These differences were largely due to a wetting inhibition.     

Kinetics and mechanism of free fatty acid formation on the surface of milled rice

The presence of free fatty acid (FFA) is an important factor in determining rice quality for brewing. FFA formation in milled rice during storage was monitored, and a two-parameter semiempirical kinetic model giving product concentration as a function of time is proposed to describe FFA formation on milled rice during storage. The model was tested using sets of data obtained from partially milled rice samples stored at 24, 37, and 50 degrees C and fully milled rice stored at 37 degrees C and 70% relative humidity. The predicted values provide very good fits (R(2) >or= 97%) of the experimental data at all storage temperatures. A two-substrate reaction mechanism representing a two-phase process is also presented. Milled rice FFA at a given storage time varied with storage temperatures. The kinetic model and mechanisms proposed could be useful in describing and predicting FFA contents of milled rice during storage and transportation.     

Experimental drought alters rates of soil respiration and methanogenesis but not carbon exchange in soil of a temperate fen

The impact of intensified drought and rewetting on C cycling in peatlands is debated. We conducted drying/rewetting (DW) experiments with intact monoliths of a temperate fen over a period of 10 months. One treatment with original vegetation (DW-V) and one defoliated treatment (DW-D) were rewetted after an experimental drought of 50 days; another treatment was kept permanently wet (W-V). Soil water content was determined by the TDR technique, C fluxes from chamber measurements and gas profiles in the soils, and respiration from mass balancing CO₂ and CH₄ fluxes in the peat using hourly to weekly data. Zones of high root associated respiration were determined from a ¹³C labeling experiment. Autotrophic respiration contributed from 55 to 65% to an average ecosystem respiration (ER) of 92 (DW-D), 211 (DW-V), and 267 mmol m^?2 d^?1 (W-V). Photosynthesis ranged from 0 (DW-D) to 450 mmol m^?2 d^?1 (W-V), and strongly declined for about 30 days after rewetting (DW-V), while ER remained constant during the drying and rewetting event. Drying raised air-filled porosity in the soil to 2–13%, temporarily increased respiration to estimated anaerobic and aerobic rates of up to 550 and 1000 nmol cm^?3 d^?1, and delayed methane production and emission by weeks to months. Root associated respiration was concentrated in the uppermost peat layer. In spite of clear relative changes in respiration during and after drought, the impact on carbon exchange with the atmosphere was small. We attribute this finding to the importance of respiration in the uppermost and soil layer, which remained moist and aerated, and the insensitivity of autotrophic respiration to drought. We expect a similar dynamics to occur in other temperate wetland soils in which soil respiration is concentrated near the peatland surface, such as rich minerotrophic fens.     

Bodenphysikalische Bewertung der Kompostwirkung durch Laboruntersuchungen

<?show $38#Bo;>Soil physical evaluation of the efficiency of addition of composts to soils by laboratory experiments Additionally to long‐term field experiments a laboratory method was tested for evaluation the physical efficiency of addition of composts to soil. The parameters maximal water holding capacity (MWK), bulk density (TRD), and total pore volume (PV) were determined under reproducible conditions for compost‐soil‐mixtures in comparison to equivalent mixtures of soil with standard‐peat‐litter. The ratio of the coefficients of regression for compost‐soil‐mixtures to those for standard‐peat‐litter‐soil‐mixtures is the so‐called equivalent of standard‐peat‐litter (TMÄ). The efficiency of changes of soil physical properties due to the addition of compost to soil is characterized by TMÄ.<?show $6#>     

Physical and mechanical properties of washed sediment mixed with organic matter

Soil from cleaning and washing of sugar beet during processing is collected and decanted in tanks each year over a period of several months. Instead of spreading it on agricultural land, another option is to reuse the sediment for crop growth. The physical and mechanical properties of the non-structured washed soil (WS) and the efficiency of added organic matter (peat and green waste compost) were evaluated by comparison with an arable silt loam soil (AS). Water retention data were expressed in a double-exponential function which characterized soil structural and matrix pore space. The effects on saturated hydraulic conductivity and pore space morphology from applying loads of 60 and 200 kPa on two initial volumetric water contents (12 and 25%) were investigated using image analysis. WS was a silt loam with no plasticity, and its void ratio and water retention were higher than the AS before compression. However, WS had a very small amount of structural pore space and despite its higher void ratio, its hydraulic conductivity was always lower than AS after compression. Organic matter improved all the WS properties by increasing structural porosity and vertical stress resistance. Organic matter created elongated and tortuous pores and increased K _s values by changing pore size distribution. During compression large pores with a radius >1500 μm disappeared in WS mixtures but were still observed in AS and were maintained by aggregate stability.     

Effect of Aging on the Quality of Glutinous Rice Crackers

The experiment was conducted to study the effects of aging on the physicochemical properties of two Thai cultivars of milled glutinous rice (RD6 and RD8). The amylose and protein content of rice samples did not change when stored from 0 to 4 months. Amylograph curves from samples of milled rice stored from 0 to 8 months were analyzed. Both cultivars gave constant gelatinization temperature during aging. The values for peak viscosity, final viscosity on cooking at 94°C, viscosity on cooling to 50°C and breakdown decreased significantly for RD6 cultivar, whereas the setback value and consistency were not changed significantly. For RD8 cultivar, no significant difference was observed for viscosity on cooling to 50°C and consistency during aging up to 8 months. Peak viscosity and breakdown value were reduced during storage, whereas the final viscosity on cooking at 94°C and setback value increased with time. Raw milled rice of both RD6 and RD8 cultivars have similar water uptake rates. Stored rice tended to have a lower water uptake rate which increased proportionately with soaking time. Samples from both rice cultivars were used to make rice crackers to study the effects of aging on quality. Volume expansion of rice crackers made from RD6 and RD8 cultivars tended to decrease during storage which resulted in an increase in the hardness of the crackers.     

Responses of carbon,nitrogen and phosphorus to two consecutive drying–rewetting cycles in soils

Drying and rewetting cycles are known to be important for the dynamics of carbon (C), phosphorus (P), and nitrogen (N) in soils. This study reports the short‐term responses of these nutrients to consecutive drying and rewetting cycles and how varying soil moisture content affects microbial biomass C and P (MBC and MBP), as well as associated carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions. The soil was incubated for 14 d during which two successive drying–rewetting episodes were imposed on the soils. Soils subjected to drying (DRW) were rewetted on the seventh day of each drying period to return them to 60% water holding capacity, whilst continually moist samples (M), with soil maintained at 60% water holding capacity, were used as control samples. During the first seven days, the DRW samples showed significant increases in extractable ammonium, total oxidized nitrogen, and bicarbonate extractable P concentrations. Rewetting after the first drying event produced significant increases only in CO₂ flux (55.4 µg C g^?1 d^?1). The MBC and MBP concentrations fluctuated throughout the incubation in both treatments and only the second drying–rewetting event resulted in a significantly MBC decrease (416.2 and 366.8 mg kg^?1 in M and DRW soils, respectively). The two drying–rewetting events impacted the microbial biomass, but distinguishing the different impacts of microbial versus physical impacts of the perturbation is difficult. However, this study, having a combined approach (C, N, and P), indicates the importance of understanding how soils will react to changing patterns of drying–rewetting under future climate change.     

Greenhouse gas fluxes during rewetting of peatlands by use of effluents – a lysimeter study

Abstract

The present study aims at assessing the effect of using the effluent of a wastewater treatment plant as an alternative measure for rewetting nutrient-rich fen soils over the growing season on the emission of greenhouse gas (GHG) and at discussing possible changes in the greenhouse potential as a result of this practice. In order to allow a discussion on GHG based on integrated CH₄, N₂O, and CO₂ flux rates, fluxes were measured in our lysimeter study using the chamber methodology from May to December in 2003 and 2004. The study compares the gaseous fluxes of fen soils in lysimeters treated with the effluent and/or freshwater for rewetting. Only freshwater was applied to the control lysimeter. The source of water hardly had any statistically significant effect on trace gas fluxes. However, there was a trend towards higher CH₄ emissions at the effluent lysimeters compared to the control lysimeter. Effluent usage did not decrease the greenhouse effect at the same rate, which could be observed at the control. Nevertheless, regarding gaseous emissions the use of effluents could prove to be a solution to the current problem of today's major peat oxidation and fen soil loss by drainage.     

Hysterese der Wasserspannungskurve in organogenen Böden

Soil water hysteresis in organic soils In 20 undisturbed samples of peat, muck, peaty soil and humic sand, the hysteresis of the moisture characteristic by soil suction from 0 to –9,8 kPa and from 0 to –29,4 kPa was measured. The greatest hysteresis was found in peat. Suction values from –1 to –3 kPa caused differences of 0,076 cm³/cm³ in water content during drying and wetting. In muck with low ash content and in humic sand the hysteresis was smaller. In peaty soil and muck with high ash content (> 40 %) it diminished to twice or three times lower values in comparison with those in peat. In organic soils the hysteresis decreases clearly by soil suction higher than –6 kPa. Repetition of drying and wetting gave a diminution (ca. 30 %) of the hysteresis loop in peat and displaces it towards the field of lower water content. The hysteresis of muck did not change considerably. The change of the porosity structure (pore ϕ > 30 μm) during the repetition of drying and wetting indicate that some soil shrinkage has occured.     

基于CT图像的土壤孔隙结构三维重建及水力学性质预测

为了更好地了解土壤孔隙结构对水分运动过程的影响机制,该文利用黄淮海平原原状潮土CT扫描图像,通过数字图像分析和计算机重建技术对孔隙结构进行三维重建,根据图像分析获得的孔隙大小分布和连通性等形态学参数建立了用于描述孔隙尺度结构特征对水分运动影响机制的网络模型,据此预测了样本尺度(样本体积为385.84cm3)的土壤水力学性质。结果表明,模型预测的水力学性质和实测值基本吻合,变化趋势基本一致,二者的决定系数达0.94以上。结果表明相关网络模型可以较好地模拟孔隙尺度的水分运动过程,可用于预测土壤的非饱和水力学性质。     

Growth of Hedera helix L. Container Plants in Compost Substrates Made with Miscanthus ogiformis Honda Straw and Various N-Sources

Ammonium sulfate or urea were added as N-source to shredded straw of Miscanthus ogiformis ‘Giganteus’ and water was included as control. The combined materials were composted for seven months, and the resulting composts were tested as growth substrates for nursery container plants and compared with fertilized and unfertilized peat substrates. The pH was below recommended level for the compost substrate made with ammonium sulfate and for the unfertilized peat substrate throughout the experiment. Electrical conductivity and concentrations of most nutrients were low and decreased throughout the experiment for all growth substrates. Shrinking of the growth substrates after 4, 12 or 17 months was larger for compost substrates than for peat substrates. Bulk density increased in compost substrates and decreased in peat substrates, while the total loss of C was greater in compost substrates than in peat. Water retention was lower and air volume greater for compost substrate made with ammonium sulfate than for fertilized peat. Algae and mosses did not occur on Miscanthus compost growth substrates in contrast to peat substrates. The shoot length and dry matter of Hedera helix, produced after four and 12 months of growth, and five months following cut back, showed that plants can grow well in compost substrates made of Miscanthus straw and ammonium sulfate or urea. However, the compost substrates could not fully substitute for fertilized or unfertilized peat substrate with respect to dry matter production.