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Organic Soils (organic + soil)
Selected AbstractsAtmospheric impact of bioenergy based on perennial crop (reed canary grass, Phalaris arundinaceae, L.) cultivation on a drained boreal organic soilGCB BIOENERGY, Issue 3 2010NARASINHA J. SHURPALI Abstract Marginal organic soils, abundant in the boreal region, are being increasingly used for bioenergy crop cultivation. Using long-term field experimental data on greenhouse gas (GHG) balance from a perennial bioenergy crop [reed canary grass (RCG), Phalaris arundinaceae L.] cultivated on a drained organic soil as an example, we show here for the first time that, with a proper cultivation and land-use practice, environmentally sound bioenergy production is possible on these problematic soil types. We performed a life cycle assessment (LCA) for RCG on this organic soil. We found that, on an average, this system produces 40% less CO2 -equivalents per MWh of energy in comparison with a conventional energy source such as coal. Climatic conditions regulating the RCG carbon exchange processes have a high impact on the benefits from this bioenergy production system. Under appropriate hydrological conditions, this system can even be carbon-negative. An LCA sensitivity analysis revealed that net ecosystem CO2 exchange and crop yield are the major LCA components, while non-CO2 GHG emissions and costs associated with crop production are the minor ones. Net bioenergy GHG emissions resulting from restricted net CO2 uptake and low crop yields, due to climatic and moisture stress during dry years, were comparable with coal emissions. However, net bioenergy emissions during wet years with high net uptake and crop yield were only a third of the coal emissions. As long-term experimental data on GHG balance of bioenergy production are scarce, scientific data stemming from field experiments are needed in shaping renewable energy source policies. [source] Field and laboratory estimates of pore size properties and hydraulic characteristics for subarctic organic soilsHYDROLOGICAL PROCESSES, Issue 19 2007Sean K. Carey Abstract Characterizing active and water-conducting porosity in organic soils in both saturated and unsaturated zones is required for models of water and solute transport. There is a limitation, largely due to lack of data, on the hydraulic properties of unsaturated organic soils in permafrost regions, and in particular, the relationship between hydraulic conductivity and pressure head. Additionally, there is uncertainty as to what fraction of the matrix and what pores conduct water at different pressure heads, as closed and dead-end pores are common features in organic soil. The objectives of this study were to determine the water-conducting porosity of organic soils for different pore radii ranges using the method proposed by Bodhinayake et al. (2004) [Soil Sci. Soc. Am. J. 68:760,769] and compare these values to active pore size distributions from resin-impregnated laboratory thin sections and pressure plate analysis. Field experiments and soil samples were completed in the Wolf Creek Research Basin, Yukon. Water infiltration rates were measured 16 times using a tension infiltrometer (TI) at 5 different pressure heads from , 150 to 0 mm. This data was combined with Gardiner's (1958) exponential unsaturated hydraulic conductivity function to provide water-conducting porosity for different pore-size ranges. Total water-conducting porosity was 1·1 × 10,4, which accounted for only 0·01% of the total soil volume. Active pore areas obtained from 2-D image analysis ranged from 0·45 to 0·60, declining with depth. Macropores accounted for approximately 65% of the water flux at saturation, yet all methods suggest macropores account for only a small fraction of the total porosity. Results among the methods are highly equivocal, and more research is required to reconcile field and laboratory methods of pore and hydraulic characteristics. However, this information is of significant value as organic soils in permafrost regions are poorly characterized in the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source] Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1.HYDROLOGICAL PROCESSES, Issue 6 2001Field investigations Abstract To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995,96) had abnormally low snow precipitation, which gave a deep frost down to 40,80 cm, whereas the two following winters had frost depths of 5,20 cm. During winter 1995,96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5,7 vol.% in the mineral soil and 10,15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd. [source] Antioxidants in soil organic matter and in associated plant materialsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009D. L. Rimmer Summary The presence of antioxidants in soil could have a significant effect on the dynamics of soil organic matter. In this paper we report some preliminary experiments, which demonstrate that antioxidants can be extracted from soils and that the quantities vary from soil to soil. Extraction with 1.0 m NaOH was effective, and this was then used on a range of mineral and organic soils, and the antioxidant capacity of the resulting extracts was measured. The antioxidant capacities obtained were positively correlated with soil carbon contents and with the dissolved organic carbon contents of the extracts. Expressing the data per mass of soil carbon showed that the antioxidants generally decreased with depth in the soil profile, suggesting that they were subject to degradation during humification. In a follow-up study, soil, litter and fresh plant samples were collected from 15 sites with a wide variety of vegetation types and analysed for their antioxidant capacities. The aim was to show that the antioxidant capacities in the soils were related to the antioxidant capacities of the fresh plant material and/or litter above. The antioxidant capacities of the soil samples were less than those in either fresh material or litter. While there was a significant positive relationship between the antioxidant capacities of fresh material and litter, no relationship existed between the antioxidant capacities of the soils and those of either fresh material or litter. [source] Analysis of the variable charge of two organic soils by means of the NICA-Donnan modelEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007B. Vasiliadis Summary We have tested to see if the generic set of NICA-Donnan model parameters, used to describe isolated humic substances, can also describe soil humic substances in situ. A potentiometric back-titration technique was used to determine the variable surface charge of two organic peat soils at three different ionic strengths. The non-ideal, competitive-adsorption NICA-Donnan model was used to simulate the surface charge, by assuming a bimodal distribution of H+ affinity on the soil solid phase. The model provided an excellent fit to the experimental data. The Donnan volume, VD, varied slightly with ionic strength, although the variation was less than for humic substances in solution. The values obtained for the parameters that define the affinity distributions, the intrinsic proton binding constant (log Kiint) and the heterogeneity of the site (mi), were similar to those observed for isolated soil humic acids. The abundance of carboxylic groups in the whole soil represented 30% of the typical value for isolated soil humic acids. The composition of the organic matter of the whole soils, obtained by 13C CPMAS NMR, was comparable to the characteristic composition of soil humic acids. [source] Atmospheric impact of bioenergy based on perennial crop (reed canary grass, Phalaris arundinaceae, L.) cultivation on a drained boreal organic soilGCB BIOENERGY, Issue 3 2010NARASINHA J. SHURPALI Abstract Marginal organic soils, abundant in the boreal region, are being increasingly used for bioenergy crop cultivation. Using long-term field experimental data on greenhouse gas (GHG) balance from a perennial bioenergy crop [reed canary grass (RCG), Phalaris arundinaceae L.] cultivated on a drained organic soil as an example, we show here for the first time that, with a proper cultivation and land-use practice, environmentally sound bioenergy production is possible on these problematic soil types. We performed a life cycle assessment (LCA) for RCG on this organic soil. We found that, on an average, this system produces 40% less CO2 -equivalents per MWh of energy in comparison with a conventional energy source such as coal. Climatic conditions regulating the RCG carbon exchange processes have a high impact on the benefits from this bioenergy production system. Under appropriate hydrological conditions, this system can even be carbon-negative. An LCA sensitivity analysis revealed that net ecosystem CO2 exchange and crop yield are the major LCA components, while non-CO2 GHG emissions and costs associated with crop production are the minor ones. Net bioenergy GHG emissions resulting from restricted net CO2 uptake and low crop yields, due to climatic and moisture stress during dry years, were comparable with coal emissions. However, net bioenergy emissions during wet years with high net uptake and crop yield were only a third of the coal emissions. As long-term experimental data on GHG balance of bioenergy production are scarce, scientific data stemming from field experiments are needed in shaping renewable energy source policies. [source] Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soilsGLOBAL CHANGE BIOLOGY, Issue 7 2009MATTHEW D. WALLENSTEIN Abstract Arctic soils contain large amounts of organic matter due to very slow rates of detritus decomposition. The first step in decomposition results from the activity of extracellular enzymes produced by soil microbes. We hypothesized that potential enzyme activities are low relative to the large stocks of organic matter in Arctic tundra soils, and that enzyme activity is low at in situ temperatures. We measured the potential activity of six hydrolytic enzymes at 4 and 20 °C on four sampling dates in tussock, intertussock, shrub organic, and shrub mineral soils at Toolik Lake, Alaska. Potential activities of N -acetyl glucosaminidase, ,-glucosidase, and peptidase tended to be greatest at the end of winter, suggesting that microbes produced enzymes while soils were frozen. In general, enzyme activities did not increase during the Arctic summer, suggesting that enzyme production is N-limited during the period when temperatures would otherwise drive higher enzyme activity in situ. We also detected seasonal variations in the temperature sensitivity (Q10) of soil enzymes. In general, soil enzyme pools were more sensitive to temperature at the end of the winter than during the summer. We modeled potential in situ,-glucosidase activities for tussock and shrub organic soils based on measured enzyme activities, temperature sensitivities, and daily soil temperature data. Modeled in situ enzyme activity in tussock soils increased briefly during the spring, then declined through the summer. In shrub soils, modeled enzyme activities increased through the spring thaw into early August, and then declined through the late summer and into winter. Overall, temperature is the strongest factor driving low in situ enzyme activities in the Arctic. However, enzyme activity was low during the summer, possibly due to N-limitation of enzyme production, which would constrain enzyme activity during the brief period when temperatures would otherwise drive higher rates of decomposition. [source] Contrasting effects of repeated summer drought on soil carbon efflux in hydric and mesic heathland soilsGLOBAL CHANGE BIOLOGY, Issue 10 2008ALWYN SOWERBY Abstract Current predictions of climate change include altered rainfall patterns throughout Europe, continental USA and areas such as the Amazon. The effect of this on soil carbon efflux remains unclear although several modelling studies have highlighted the potential importance of drought for carbon storage. To test the importance of drought, and more importantly repeated drought year-on-year, we used automated retractable curtains to exclude rain and produce repeated summer drought in three heathlands at varying moisture conditions. This included a hydric system limited by water-excess (in the UK) and two mesic systems with seasonal water limitation in Denmark (DK) and the Netherlands (NL). The experimental rainfall reductions were set to reflect single year droughts observed in the last decade with exclusion of rain for 2,3 months of the year resulting in a 20,26% reduction in annual rainfall and 23,38% reduction in mean soil moisture during the drought period. Unexpectedly, sustained reduction in soil moisture over winter (between drought periods) was also observed at all three sites, along with a reduction in the maximum water-holding capacity attained. Three hypotheses are discussed which may have contributed to this lack of recovery in soil moisture: hydrophobicity of soil organic matter, increased water use by plants and increased cracking of the soil. The responses of soil respiration to this change in soil moisture varied among the sites: decreased rates were observed at the water-limited NL and DK sites whilst they increased at the UK site. Reduced sensitivity of soil respiration to soil temperature was observed at soil moisture contents above 55% at the UK site and below 20% and 13% at the NL and DK sites, respectively. Soil respiration rates recovered to predrought levels in the NL and DK sites during the winter re-wetting period that indicates any change in soil C storage due to changes in soil C efflux may be short lived in these mesic systems. In contrast, in the hydric UK site after 2 years of drought treatment, the persistent reduction in soil moisture throughout the year resulted in a year-round increase in soil respiration flux, a response that accelerated over time to 40% above control levels. These findings suggest that carbon-rich soils with high organic matter content may act as a significant source of CO2 to the atmosphere following repeated summer drought. Nonrecovery of soil moisture and a persistent increase in soil respiration may be the primary mechanism underlying the reported substantial losses of soil carbon from UK organic soils over the last 20 years. These findings indicate that the water status of an ecosystem will be a critical factor to consider in determining the impact of drought on the soil carbon fluxes and storage. [source] Storage and mobility of black carbon in permafrost soils of the forest tundra ecotone in Northern SiberiaGLOBAL CHANGE BIOLOGY, Issue 6 2008GEORG GUGGENBERGER Abstract Boreal permafrost soils store large amounts of organic carbon (OC). Parts of this carbon (C) might be black carbon (BC) generated during vegetation fires. Rising temperature and permafrost degradation is expected to have different consequences for OC and BC, because BC is considered to be a refractory subfraction of soil organic matter. To get some insight into stocks, variability, and characteristics of BC in permafrost soils, we estimated the benzene polycarboxylic acid (BPCA) method-specific composition and storage of BC, i.e. BPCA-BC, in a 0.44 km2 -sized catchment at the forest tundra ecotone in northern Siberia. Furthermore, we assessed the BPCA-BC export with the stream draining the catchment. The catchment is composed of various landscape units with south-southwest (SSW) exposed mineral soils characterized by thick active layer or lacking permafrost, north-northeast (NNE) faced mineral soils with thin active layer, and permafrost-affected raised bogs in plateau positions showing in part thermokarst formation. There were indications of vegetation fires at all landscape units. BC was ubiquitous in the catchment soils and BPCA-BC amounted to 0.6,3.0% of OC. This corresponded to a BC storage of 22,3440 g m,2. The relative contribution of BPCA-BC to OC, as well as the absolute stocks of BPCA-BC were largest in the intact bogs with a shallow active layer followed by mineral soils of the NNE aspects. In both landscape units, a large proportion of BPCA-BC was stored within the permafrost. In contrast, mineral soils with thick active layer or lacking permafrost and organic soils subjected to thermokarst formation stored less BPCA-BC. Permafrost is, hence, not only a crucial factor in the storage of OC but also of BC. In the stream water BPCA-BC amounted on an average to 3.9% of OC, and a yearly export of 0.10 g BPCA-BC m,2 was calculated, most of it occurring during the period of snow melt with dominance of surface flow. This suggests that BC mobility in dissolved and colloidal phase is an important pathway of BC export from the catchment. Such a transport mechanism may explain the high BC concentrations found in sediments of the Arctic Ocean. [source] Climate change cannot be entirely responsible for soil carbon loss observed in England and Wales, 1978,2003GLOBAL CHANGE BIOLOGY, Issue 12 2007PETE SMITH Abstract We present results from modelling studies, which suggest that, at most, only about 10,20% of recently observed soil carbon losses in England and Wales could possibly be attributable to climate warming. Further, we present reasons why the actual losses of SOC from organic soils in England and Wales might be lower than those reported. [source] Predicting potential impacts of climate change on the geographical distribution of enchytraeids: a meta-analysis approachGLOBAL CHANGE BIOLOGY, Issue 11 2007MARÍA JESÚS I. BRIONES Abstract The expectation that atmospheric warming will be most pronounced at higher latitudes means that Arctic and montane systems, with predominantly organic soils, will be particularly influenced by climate change. One group of soil fauna, the enchytraeids, is commonly the major soil faunal component in specific biomes, frequently exceeding above-ground fauna in biomass terms. These organisms have a crucial role in carbon turnover in organic rich soils and seem particularly sensitive to temperature changes. In order to predict the impacts of climate change on this important group of soil organisms we reviewed data from 44 published papers using a combination of conventional statistical techniques and meta-analysis. We focused on the effects of abiotic factors on total numbers of enchytraeids (a total of 611 observations) and, more specifically, concentrated on total numbers, vertical distribution and age groupings of the well-studied species Cognettia sphagnetorum (228 observations). The results highlight the importance of climatic factors, together with vegetation and soil type in determining global enchytraeid distribution; in particular, cold and wet environments with mild summers are consistently linked to greater densities of enchytraeids. Based on the upper temperature distribution limits reported in the literature, and identified from our meta-analyses, we also examined the probable future geographical limits of enchytraeid distribution in response to predicted global temperature changes using the HadCM3 model climate output for the period between 2010 and 2100. Based on the existing data we identify that a maximum mean annual temperature threshold of 16 °C could be a critical limit for present distribution of field populations, above which their presence would decline markedly, with certain key species, such as C. sphagnetorum, being totally lost from specific regions. We discuss the potential implications for carbon turnover in these organic soils where these organisms currently dominate and, consequently, their future role as C sink/source in response to climate change. [source] Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysisHYDROLOGICAL PROCESSES, Issue 21 2010F. Rezanezhad Abstract In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 µm) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air-filled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd. [source] Storage dynamics and streamflow in a catchment with a variable contributing areaHYDROLOGICAL PROCESSES, Issue 16 2010C. Spence Abstract Storage heterogeneity effects on runoff generation have been well documented at the hillslope or plot scale. However, diversity across catchments can increase the range of storage conditions. Upscaling the influence of small-scale storage on streamflow across the usually more heterogeneous environment of the catchment has been difficult. The objective of this study was to observe the distribution of storage in a heterogeneous catchment and evaluate its significance and potential influence on streamflow. The study was conducted in the subarctic Canadian Shield: a region with extensive bedrock outcrops, shallow predominantly organic soils, discontinuous permafrost and numerous water bodies. Even when summer runoff was generated from bedrock hillslopes with small storage capacities, intermediary locations with large storage capacities, particularly headwater lakes, prevented water from transmitting to higher order streams. The topographic bounds of the basin thus constituted the maximum potential contributing area to streamflow and rarely the actual area. Topographic basin storage had little relation to basin streamflow, but hydrologically connected storage exhibited a strong hysteretic relationship with streamflow. This relationship defines the form of catchment function such that the basin can be defined by a series of storing and contributing curves comparable with the wetting and drying curves used in relating tension and hydraulic conductivity to water content in unsaturated soils. These curves may prove useful for catchment classification and elucidating predominant hydrological processes. Copyright © 2009 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. [source] Towards an energy-based runoff generation theory for tundra landscapesHYDROLOGICAL PROCESSES, Issue 23 2008William L. Quinton Abstract Runoff hydrology has a large historical context concerned with the mechanisms and pathways of how water is transferred to the stream network. Despite this, there has been relatively little application of runoff generation theory to cold regions, particularly the expansive treeless environments where tundra vegetation, permafrost, and organic soils predominate. Here, the hydrological cycle is heavily influenced by 1) snow storage and release, 2) permafrost and frozen ground that restricts drainage, and 3) the water holding capacity of organic soils. While previous research has adapted temperate runoff generation concepts such as variable source area, transmissivity feedback, and fill-and-spill, there has been no runoff generation concept developed explicitly for tundra environments. Here, we propose an energy-based framework for delineating runoff contributing areas for tundra environments. Aerodynamic energy and roughness height control the end-of-winter snow water equivalent, which varies orders of magnitude across the landscape. Radiant energy in turn controls snowmelt and ground thaw rates. The combined spatial pattern of aerodynamic and radiant energy control flow pathways and the runoff contributing areas of the catchment, which are persistent on a year-to-year basis. While ground surface topography obviously plays an important role in the assessment of contributing areas, the close coupling of energy to the hydrological cycles in arctic and alpine tundra environments dictates a new paradigm. Copyright © 2008 John Wiley & Sons, Ltd. [source] Field and laboratory estimates of pore size properties and hydraulic characteristics for subarctic organic soilsHYDROLOGICAL PROCESSES, Issue 19 2007Sean K. Carey Abstract Characterizing active and water-conducting porosity in organic soils in both saturated and unsaturated zones is required for models of water and solute transport. There is a limitation, largely due to lack of data, on the hydraulic properties of unsaturated organic soils in permafrost regions, and in particular, the relationship between hydraulic conductivity and pressure head. Additionally, there is uncertainty as to what fraction of the matrix and what pores conduct water at different pressure heads, as closed and dead-end pores are common features in organic soil. The objectives of this study were to determine the water-conducting porosity of organic soils for different pore radii ranges using the method proposed by Bodhinayake et al. (2004) [Soil Sci. Soc. Am. J. 68:760,769] and compare these values to active pore size distributions from resin-impregnated laboratory thin sections and pressure plate analysis. Field experiments and soil samples were completed in the Wolf Creek Research Basin, Yukon. Water infiltration rates were measured 16 times using a tension infiltrometer (TI) at 5 different pressure heads from , 150 to 0 mm. This data was combined with Gardiner's (1958) exponential unsaturated hydraulic conductivity function to provide water-conducting porosity for different pore-size ranges. Total water-conducting porosity was 1·1 × 10,4, which accounted for only 0·01% of the total soil volume. Active pore areas obtained from 2-D image analysis ranged from 0·45 to 0·60, declining with depth. Macropores accounted for approximately 65% of the water flux at saturation, yet all methods suggest macropores account for only a small fraction of the total porosity. Results among the methods are highly equivocal, and more research is required to reconcile field and laboratory methods of pore and hydraulic characteristics. However, this information is of significant value as organic soils in permafrost regions are poorly characterized in the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source] Snow, frozen soils and permafrost hydrology in Canada, 1999,2002HYDROLOGICAL PROCESSES, Issue 1 2005Ming-Ko Woo Abstract An overview is provided of Canadian research on snow, frozen soils and permafrost hydrology for 1999,2002, the period between the 1999 IUGG meeting in Birmingham and the 2003 IUGG in Sapporo. Snow research during this period emphasized the blowing snow and sublimation processes, the role of trees in snow distribution, and melt and the effect of heat advection on snowmelt, from patch to regional scales. Regional-scale studies, largely in connection with the Mackenzie GEWEX study, examined the snow conditions of the lower Mackenzie basin and developed a coupled land surface scheme,hydrological model that incorporates snow processes. In frost hydrology, the effects of organic soils on runoff generation and flow delivery were given much attention. Field investigations ranged from plot to hillslope scales, and the results indicate that organic layers of high porosity permit the production of quick flow, even when frozen. Highly fractured bedrock in the Canadian Shield has likewise the effect of permitting snowmelt infiltration at below-freezing temperatures. Finally, changes in snow-covered areas and in snow equivalent over periods from a decade to a century were examined. The responses of snow and ground ice to the warm year of 1998 were also studied as an indication of hydrological responses to climatic warming. Copyright © 2005 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. [source] Mechanics of land subsidence due to groundwater pumpingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2010Muniram Budhu Abstract This paper presents the formulation of the basic mechanics governing the changes in stress states from groundwater pumping and comparisons among predicted land subsidence from this mechanics with existing analyses and field data. Land subsidence is a growing, global problem caused by petroleum and groundwater withdrawal, mining operations, natural settlement, hydro-compaction, settlement of collapsible soils, settlement of organic soils and sinkholes. This paper is concerned with the land subsidence due to groundwater level decline by groundwater pumping. It is shown that the stress state consists of asymmetric stresses that are best simulated by a Cosserat rather than a Cauchy continuum. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement and macro-rotation. The latter occurs when conditions are favorable (e.g. at a vertical interface) for the micro-rotation imposed by asymmetric stresses to become macro-rotation. When the length of the cone of depression is beyond ,2 times the thickness of the aquifer, simple shear on vertical planes with rotation is the predominant deformation mode. Otherwise, simple shear on horizontal planes is present. The predicted subsidence using the mechanics developed in this paper compares well with data from satellite-borne interferometric synthetic aperture radar. Copyright © 2009 John Wiley & Sons, Ltd. [source] Vegetation transition following drainage in a high-latitude hyper-oceanic ecosystemAPPLIED VEGETATION SCIENCE, Issue 2 2010Anna Maria Fosaa Abstract Questions: How does draining affect the composition of vegetation? Are certain functional groups favoured? Can soil parameters explain these differences? Location: Central Faroe Islands, treeless islands in the northern boreal vegetation zone. Since 1987, an area of 21 km2 at 100,200 m a.s.l. was drained in order to provide water for hydro-electric production. Method: Vegetation and soil of a drained area and a control, undrained neighbouring area of approximately the same size were sampled in 2007. Six sites were sampled in each area. The vegetation was classified with cluster analysis. Results: Four plant communities were defined in the area: Calluna vulgaris,Empetrum nigrum,Vaccinium myrtillus heath, Scirpus cespitosus,Eriophorum angustifolium blanket mire, Carex bigelowii,Racomitrium lanuginosum moss-heath, Narthecium ossifragum,Carex panacea mire. Heath was more extensively distributed within, and was the dominant community of the drained area, whereas moss-heath was more extensive in the undrained area. Blanket mire and mire had approximately the same distribution in both areas. For the blanket mire, species composition indicated drier conditions in the drained than in the undrained area. The drained area had higher frequencies of woody species and lichens, grasses had finer roots and available soil phosphate was considerably higher, whereas the undrained area had higher frequencies of grasses and sedges. Conclusion: The dominant plant communities were different in the two areas, which indicated that the blanket mire was drying in the drained area. Higher concentration of soil phosphate in the drained area also indicated increased decomposition of organic soils owing to desiccation. [source] | ||||||||||||||||