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Plant roots can be very effective in stabilizing the soil against concentrated flow erosion. So far, most research on the erosion-reducing potential of plant roots was conducted on loamy soils. However susceptible to incisive erosion processes, at present, no research exists on the effectiveness of plant roots in reducing concentrated flow erosion rates in sandy soils. Therefore, the prime objective of this study was to assess the erosion-reducing potential of both fibrous and tap roots in sandy soils. Furthermore, we investigated potential effects of root diameter, soil texture and dry soil bulk density on the erosion-reducing potential of plant roots. Therefore, flume experiments conducted on sandy soils (this study) were compared with those on sandy loam and silt loam soils (using the same experimental set up). Results showed that plant roots were very efficient in reducing concentrated flow erosion rates in sandy soils compared to root-free bare soils. Furthermore, our results confirmed that fibrous roots were more effective compared to (thick) tap roots. Dry soil bulk density and soil texture also played a significant role. As they were both related to soil cohesion, the results of this study suggested that the effectiveness of plant roots in controlling concentrated flow erosion rates depended on the apparent soil cohesion. The nature of this soil type effect depended on the root-system type: fine root systems were most effective in non-cohesive soils while tap root systems were most effective in cohesive soils. For soils permeated with a given amount of fibrous roots, an increase of soil bulk density seemed to hamper the effectiveness of roots to further increase soil cohesion and reduce erosion rates. In soils reinforced by tap root systems, the erosion-reducing power of the roots depended on sand content: the higher the percentage of sand, the smaller the erosion-reducing effect for a given amount of roots. This was attributed to more pronounced vortex erosion around the thicker tap roots in non-cohesive soils, increasing soil erosion rates. The results presented in this study could support practitioners to assess the likely erosion-reducing effects of plant root systems based on both root and soil characteristics. [ABSTRACT FROM AUTHOR]

Rapid warming in Arctic ecosystems is resulting in increased frequency of disturbances such as fires, changes in the distribution and productivity of different plant communities, increasing thaw depths in permafrost soils and greater nutrient availability, especially nitrogen. Individually and collectively, these factors have the potential to strongly affect soil C decomposition rates, with implications for the globally significant stores of carbon in this region. However, considerable uncertainty remains regarding how C decomposition rates are controlled in Arctic soils. In this study we investigated how temperature, nitrogen availability and labile C addition affected rates of CO 2 production in short (10-day for labile C) and long-term (1.5 year for temperature and N) incubations of samples collected from burned and unburned sites in the Anaktuvuk river burn on the North Slope of Alaska from different depths (organic horizon, mineral horizon and upper permafrost). The fire in this region resulted in the loss of several cms of the organic horizon and also increased active layer depth allowing the impacts of four years of thaw on deeper soil layers to be investigated. Respiration rates did not decline substantially during the long-term incubation, although decomposition rates per unit organic matter were greater in the organic horizon. In the mineral and upper permafrost soil horizons, CO 2 production was more temperature sensitive, while N addition inhibited respiration in the mineral and upper permafrost layers, especially at low temperatures. In the short-term incubations, labile C additions promoted the decomposition of soil organic matter in the mineral and upper permafrost samples, but not in the organic samples, with this effect being lost following N addition in the deeper layers. These results highlight that (i) there are substantial amounts of labile organic matter in these soils (ii), the organic matter stored in mineral and upper permafrost in the tussock tundra is less readily decomposable than in the organic horizon, but that (iii) its decomposition is more sensitive to changes in temperature and that (iv) microbial activity in deeper soil layers is limited by labile C availability rather than N. Collectively, these results indicate that in addition to the loss of C by combustion of organic matter, increasing fire frequency also has the potential to indirectly promote the release of soil C to the atmosphere in the years following the disturbance. [ABSTRACT FROM AUTHOR]

Abstract: Recent research indicates that plant roots can reduce soil erosion rates during concentrated flow significantly. Earlier studies revealed the erosion-reducing effects of plant roots under controlled laboratory conditions and presented some equations applicable to the tested soil and flow conditions only. Although an attempt was made to unravel the impact of different environmental, plant and flow properties on the erosion-reducing potential of plant roots during concentrated runoff, significant effects were hard to demonstrate because of the small number of data. Therefore, the objective of this study is to pool different datasets (384 data collected under standardized experimental conditions in total) together for constructing empirically-based models predicting (1) soil detachment rates for both bare and root-permeated topsoils and (2) the erosion-reducing potential of plant roots during concentrated flow erosion. The model that best predicts absolute soil detachment rates from bare and root-permeated silt or sandy loam topsoils (ASD) requires information on root density, topsoil moisture content prior to concentrated flow erosion, bulk density and mean bottom flow shear stress. Although all these variables contribute significantly to the prediction of ASD, the validation results indicate that there is still a large scatter on the data. Especially for small detachment rates, the model tends to overestimate the observed values. Another model predicting the reduction in detachment rates of root-permeated topsoils compared to bare ones (RSD) does not show good validation results either. However, the model for fibrous root systems was found to be very promising. This model explains 79% of the variation using only root density and soil texture information and the validation results show that 69% of the variation in the validation dataset is accounted for by the model. For topsoils permeated with tap root systems, however, the model results were not satisfactory. Only 10% of the variation in the validation dataset could be explained by a model using root density and mean root diameter as input variables. We conclude that the erosion-reducing effect of topsoils permeated with fibrous roots can be predicted very well, whereas relative erosion rates for tap root-permeated topsoils still remain difficult to predict with the studied variables only. More process-based knowledge is needed to distinguish erosion-reducing effects from erosion-accelerating effects for tap root-permeated topsoils. [Copyright &y& Elsevier]

Abstract: Traditional vegetative techniques to control gully development rely mainly on the effects of above ground biomass, whereas little attention has been given to the role of below ground biomass. Yet, in a context where above ground biomass may temporarily or spatially disappear (e.g. due to fire or grazing), roots can play an important role in protecting soil against erosion. Few studies have investigated the impacts of roots of natural vegetation (such as grass) on the resistance of topsoils in concentrated flow erosion zones, although grasses grow in many environments. Therefore, the objective of this study is to investigate the impact of root density and root length density of grass on the erodibility of root-permeated saturated topsoils. Three plots were established on a sandy loam. Their treatments were (1) bare, (2) low density drilled grass and (3) high density drilled grass, simulating different root densities. After one month, topsoil samples were taken and subjected to concentrated flow using a hydraulic flume in the laboratory. Slope, flow discharge, mean velocity, water temperature and sediment concentration were measured. Root density and root length density values were assessed. Relative soil detachment rates and mean flow shear stresses were calculated. The results indicate a negative exponential relation between the relative soil detachment rate and root density as well as root length density, independent of the applied flow shear stresses. However, the best relationship fitting the data is the Hill curve, indicating that relative soil detachment rates decrease to very low values (0.05) with an increase in root density from 0 to 4 kg m−3 or root length density from 0 to 400 km m−3. A comparison between the effects of vegetation cover on sheet and rill erosion rates and those of the root area ratio of grass roots on relative soil detachment rates reveals that grass roots are very effective in reducing soil detachment rates. The equations obtained can be used to predict the effect of grass roots on soil erosion rates during concentrated runoff and to evaluate the ability of roots to increase topsoil resistance against erosion by concentrated flow. Calculations of relative erosion rates using the equations from the RUSLE and WEPP models indicate that the observed trend is better predicted with the RUSLE model and the WEPP model for croplands than with the WEPP model for rangelands. [Copyright &y& Elsevier]

Abstract: Soil erodibilty during concentrated flow (K c) and critical flow shear stress (τ cr), both reflecting the soil''s resistance to erosion by concentrated runoff, are important input parameters in many physically-based soil erosion models. Field data on the spatial and temporal variability of these parameters is limited but crucial for accurate prediction of soil loss by rill or gully erosion. In this study, the temporal variations in K c and τ cr for a winter wheat field on a silt loam soil under three different tillage practices (conventional ploughing, CP; shallow non-inversion tillage, ST; deep non-inversion tillage, DT) in the Belgian Loess Belt were monitored during one growing season. Undisturbed topsoil samples (0.003m3) were taken every three weeks and subjected to five different flow shear stresses (τ =4–45Pa) in a laboratory flume to simulate soil detachment by concentrated flow. To explain the observed variation, relevant soil and environmental parameters were measured at the time of sampling. Results indicated that after two years of conservation tillage, K c(CP)> K c(DT)> K c(ST). K c values can be up to 10 times smaller for ST compared to CP but differences strongly vary over time, with an increasing difference with decreasing soil moisture content. The beneficial effects of no-tillage are not reflected in τ cr. K c values vary from 0.006 to 0.05sm−1 for CP and from 0.0008 to 0.01sm−1 for ST over time. Temporal variations in K c can be mainly explained by variations in soil moisture content but consolidation effects, root growth, residue decomposition and the presence of microbiotic soil crusts as well play a role. τ cr values increase with increasing soil shear strength but K c seems more appropriate to represent the temporal variability in soil erosion resistance during concentrated flow. The large intra-seasonal variations in K c, which are shown to be at least equally important as differences between different soil types reported in literature, demonstrate the importance of incorporating temporal variability in soil erosion resistance when modelling soil erosion by concentrated flow. [Copyright &y& Elsevier]

Introduction/Background Rehabilitation services are increasingly targeting involvement in daily life. Within the ICF this is referred to as participation. Questions regarding its conceptualization have been raised and a consensus is lacking. Material and method In a first phase a critical review of the literature was performed to detect recurring conceptual problems in applying participation and to detect how researchers deal with these. This leaded in the second phase to a systematic review to identify how participation measures are operationalized. Results Phase 1 resulted in possible solutions to overcome 4 recurring key-limitations: (1) how to deal with ambiguity and vagueness about the term itself, (2) how to differentiate between activity and participation (3) what is the current empirical knowledge about the subjective aspects of participation (4) what are the different ways to measure participation. Phase 2 resulted in 18 instruments operationalising participation in different ways: (a) unidimensional; the frequency of performing activities (b) unidimensional; the limitations in experiencing participation when performing activities (c) multidimensional; multiple subjective dimensions when performing activities and (d) multidimensional: objective and subjective dimensions. Conclusion Notwithstanding an increasing body-of-knowledge some issues still remain blurred and specifically how participation is measured is subject to debate. This leads to difficulties to use participation in clinical practice. However: insight in current body-of-knowledge and awareness of shortcomings might inspire professionals aiming it's application. [ABSTRACT FROM AUTHOR]