Hydrology and water quality of the headwaters of the River Severn: Stream acidity recovery and interactions with plantation forestry under an improving pollution climate

This paper presents new information on the hydrology and water quality of the eroding peatland headwaters of the River Severn in mid-Wales and links it to the impact of plantation conifer forestry further down the catchment.The Upper Hafren is dominated by low-growing peatland vegetation, with an average annual precipitation of around 2650 mm with around 250 mm evaporation. With low catchment permeability, stream response to rainfall is “flashy” with the rising limb to peak stormflow typically under an hour. The water quality is characteristically “dilute”; stormflow is acidic and enriched in aluminium and iron from the acid organic soil inputs. Baseflow is circum-neutral and calcium and bicarbonate bearing due to the inputs of groundwater enriched from weathering of the underlying rocks. Annual cycling is observed for the nutrients reflecting uptake and decomposition processes linked to the vegetation and for arsenic implying seasonal water-logging within the peat soils and underlying glacial drift. Over the decadal scale, sulphate and nitrate concentrations have declined while Gran alkalinity, dissolved organic carbon and iron have increased, indicating a reduction in stream acidification.Within the forested areas the water quality is slightly more concentrated and acidic, transgressing the boundary for acid neutralisation capacity as a threshold for biological damage. Annual sulphate and aluminium concentrations are double those observed in the Upper Hafren, reflecting the influence of forestry and the greater ability of trees to scavenge pollutant inputs from gaseous and mist/cloud-water sources compared to short vegetation. Acidification is decreasing more rapidly in the forest compared to the eroding peatland possibly due to the progressive harvesting of the mature forest reducing the scavenging of acidifying inputs. For the Lower Hafren, long-term average annual precipitation is slightly lower, with lower average altitude, at around 2520 mm and evaporation is around double that of the Upper Hafren.     

Reconsideration of the settlement behavior of peat from view point of hydraulic conductivity

This paper deals with the settlement of peat from the view point of hydraulic conductivity (k). The validity of using the oedometer tests, including the calculation method, for measuring k is carefully examined by numerical analysis as well as a test combined with an oedometer and a hydraulic conductivity test. It is found from these studies that the conventional oedometer test (JIS A 1217, 2009) can be evaluated to measure k for peat with the same accuracy as that for usual clays, provided that the incremental load ratio is unity. The significant difference in the characteristics of k for peat and usual clayey soils is their relation between the compression index (C_c) and the hydraulic conductivity change index (C_k). As a result, rather than remaining constant during consolidation, the coefficient of consolidation (c_v) of peat decreases considerably with increasing consolidation pressure (p), while the c_v coefficient for usual clayey soil is almost constant at the normally consolidated stage. The influence of c_v dependent on p is studied by a numerical analysis for the one dimensional consolidation problem as well as for the ground improved by vertical drain. It is found that if the incremental consolidation pressure (Δp/p) is large, careful judgment is required when adopting conventional consolidation analyses, especially in case of the vertical drain.     

泥炭对砂基运动场坪床基质理化性质及草坪草的影响

研究不同泥炭施用量对砂基运动场坪床根层基质孔隙度、渗透性、pH值等理化性状的影响,以及对草坪草再生速度、成坪时间、生物量等的影响,探讨泥炭的改良效果及合理的施用量。结果表明:(1)泥炭施入能够使坪床基质的渗透性降低,总孔隙度和毛管孔隙度增大,毛管孔隙和非毛管孔隙的比例趋于平衡,有利于提高坪床保水能力和通气性。(2)泥炭有机质含量高,能改善坪床的养分供应状况,增强草坪草再生能力,缩短成坪时间,提高草坪质量。(3)由于泥炭的pH值偏低,过多施用会使坪床基质偏酸,不利于草坪草生长,因此应控制其用量,适宜的用量为10%~15%。     

汞在泥炭上的吸附特征研究

采用批次法研究了汞在三江平原泥炭、吉林双阳泥炭上等温吸附特征及介质pH值、背景离子浓度的影响。实验结果表明:两种泥炭吸附等温线均同时符合Langmuir和Freundlich等温吸附方程,而与Langmuir方程的拟合效果更好; 在溶液汞浓度相同时,温度升高,泥炭对汞的吸附量降低;在相同的条件下,三江平原泥炭对汞的吸附量大于吉林双阳泥炭对汞的吸附量;两种泥炭对汞的吸附量受pH值的影响明显且都在pH 6.0左右具有最大的吸附量;在酸性条件下,吸附介质的pH值升高利于泥炭对汞的吸附;介质的离子浓度升高,可以使两种泥炭对汞的吸附量迅速降低。     

Impact of Temperature and Loading on the Mitigation of AMD in Peat Biofilter Columns

The mitigation of AMD at Canadian mine sites using passive treatment technologies requires a combined strategy that minimizes the effect of climatic variability on the treatment performance of the system. A vertical-flow combined passive treatment system was developed consisting of an oxidation/precipitation basin for excess iron removal; an unsaturated flow peat biofilter for heavy metal sorption and the reduction of oxygen concentrations; a sulfate reducing bacteria bioreactor for alkalinity generation and sulfate reduction; and, an anoxic limestone drain for alkalinity addition. Laboratory investigations were undertaken to characterize AMD mitigation through the peat biofilter under unsaturated flow conditions and to assess its performance in the combined passive system. Peat column sorption studies were conducted at 20 and 0°C to assess the effect of temperature on metal retention. At 0°C, a metal removal efficiency of Cd < Mn < Zn < Al < Ni < Cu < Fe was noted. At 20°C, however, sulfate-reducing conditions developed in the column as a result of the flow regime, which facilitated the establishment of anaerobic zones within the peat column, leading to a significant increase in effluent pH and metal removal. Sequential extraction indicated that Fe, Cu, and Al were typically bound to the organic matter fraction, while Mn, Zn, Ni, and Cd were primarily associated with the exchangeable fraction.     

Optimization of citric acid production by <Emphasis Type="Italic">Aspergillus niger</Emphasis> NRRL 567 grown in a column bioreactor

Citric acid production using Aspergillus niger NRRL 567 grown on peat moss has been optimized in a column bioreactor using a statistically based method. A 23 full factorial design with eight fermentation conditions was applied to evaluate significance on citric acid production and their interactions between variables, where the three independent variables evaluated were aeration rate, bed depth and temperature. Aeration rate and fermentation temperature were identified to be significant variables. Citric acid production markedly increases with aeration rate and fermentation temperature; however, the bed depth of solid substrate showed an insignificant effect on citric acid production. The optimum fermentation condition for citric acid production in a column bioreactor consisted of aeration rate of 0.84 vvm, bed depth of 22 cm and fermentation temperature of 32 °C. Under a given condition, a maximum citric acid production of 120.6 g/l was predicted and matched well with the experimental value of 123.9 g/kg.     

An experimental and modeling study of ash deposition behaviour for co-firing peat with lignite

Co-firing peat with lignite for power generation was studied at pilot-scale, focusing on the issue of ash deposition, the major concern for this application. A specially designed probe was used to measure the rate of ash deposition under similar conditions of power plant boiler operation. Fraction of peat in the feed was varied up to 100%. It was observed that whereas the ash deposition decreased in general with increasing fraction of low-ash peat, the decrease was significantly less than expected from ash content of the feed, suggesting higher deposition tendency of ash from the peat. Chlorine content in the deposited ash showed a maximum at a certain blend ratio of the feed, which could not be explained by fuel chlorine content alone. The ash and chlorine deposition behaviour has been analyzed and simulated by mathematical models where interactions between fuel chlorine, alkali and ash particles are parameterized. The models ought to be useful for control and optimization purposes, and also be useful for co-firing other fuel blends.     

煤系有机质生成烃类中甾烷系列化合物地球化学特征——以高温封闭体系下热模拟实验为例

选择泥炭和褐煤进行热模拟试验并开展对比研究,目的是全面获得煤系有机质生烃特征。通过对草本泥炭和褐煤的热模拟实验液态产物饱和烃进行色谱—质谱分析得到,在泥炭和褐煤热模拟样品中均检测出丰富的甾族系列化合物,且以C29甾烷占优势。研究发现,随热模拟温度增高,C29甾烷相对含量减少,温度在350℃之后趋于稳定;而C27甾烷和C28甾烷相对含量具有增加的趋势,暗示了C29甾烷的去甲基效应。C2920S/（20S＋20R）值和C29ββ/（ββ＋αα）值可以判识样品是否成熟或未熟,是良好的成熟度指标。∑重排甾烷/∑规则甾烷值可以区分成样品成熟度。研究发现,在低演化阶段,泥炭和褐煤模拟曲线存在显著差异,而在高演化阶段,二者吻合较好。所以,对比研究泥炭和褐煤的地球化学特征,对认识煤系有机质生烃特征具有重要意义。     

Effect of fertilization on the biomass production of coppiced mixed birch and willow stands on a cut-away peatland

This investigation deals with the biomass production of coppiced mixed birch and willow stands growing on a peat cut-away area at Aitoneva, Kihniö (62°12′N, 23°18′E), Finland. The 16-year-old stands were harvested and left to coppice for 14 years, fertilization experiment (control, PK and wood ash fertilization) with three replications was established after the clear cutting. The mother stands before clear cutting (11,000 stems per hectare on average) were dominated by silver birch (69% of the stem number). After clear cutting the number of stems rose 7-fold to 75 500 stems ha⁻¹. Now the stands were dominated by Betula pubescens with 46% out of the total stem number, the share of B. pendula being only 25% and with Salix spp 29%. At the age of 14 years self-thinning had decreased the stem number to 12,800 stems ha⁻¹. The leafless biomass production of the coppiced stands on the control plots was lower than that of the seed originated mother stands had been during the previous rotation. However, with fertilization the 14-year-old coppiced stands reached the same total production as the 16-year-old mother stands had reached. The foliar phosphorus concentrations showed a severe phosphorus deficiency on the controls. Fertilization increased biomass of the stands considerably. After 14 growing seasons the above-ground leafless dry-mass of the fertilized stands was 61.8 (PK-fertilization) and 61.4 t ha⁻¹ (Ash) and that of the control stands 37.6 t ha⁻¹. A single PK fertilizer application had increased the standing biomass by 24 t ha⁻¹ (64%). Even though fertilization increased biomass production it did not increase nutrient concentrations of wood and bark, but rather decreased them. Fertilization decreased the nitrogen concentrations of leafless above-ground biomass.     

In Situ Pore Pressure Responses of Native Peat and Soil under Train Load: A Case Study

Settlement and formation of piping holes on surfaces were observed along a rail embankment subject to normal traffic load. Piezometers were installed in the native peat and soil underneath the embankment inside and outside problematic area to measure the pore pressure responses during train traffic. Peculiar pore pressure responses were observed. Cyclic pore pressures were only measured during the first 60–80?s of the 6-min train passage, and thereafter the pressures decayed rapidly to the initial values. The pore pressure changes in the shallow peat layer were lower than those in the deep soil layer. Possible mechanisms causing such peculiar pore pressure responses, surface settlement, and piping holes were explored and identified. It was found that the stiffness contrast between the stiff, upper granular fill and the soft, native peat material could lead to a redistribution of tensile stress in the granular fill layer to the peat layer due to the moving train load. This stress redistribution promotes the propensity of vertical piping in the peat layer.