No description available.

Seedbanks provide many ecosystem services that support wildlife and regulate soil function. The fate of arable seeds is vital in shaping the aboveground composition of plant communities in agroecosystems. Understanding seed fate informs seedbank dynamics with multi-species interactions, as well as safeguarding arable biodiversity and food security. While many seed fate pathways are well known, the role of myxospermy in temperate agricultural soils is rarely addressed. Mucilage released by myxospermous seeds can modify the soil physical, hydraulic and microbial environment surrounding the seed. The principle biophysical mechanisms underlying the redistribution of weed seeds in eroded soils are unknown. It is possible that myxospermy delivers crucial services at the field scale, such as soil stability and water retention. However, modifications of the soil physical environment have been investigated using only a single-species approach and are often tested with extracted mucilage rather than seeds in-situ. As multiple taxa produce myxospermous seeds, the effects of a single species cannot be generalised. As seeds co-exist in the soil as multi-species communities, a multi-species approach is needed to further understand the functionality of seed mucilage and their implications for soil, relative to the wider seedbank. This thesis focussed on examining the mechanisms responsible for the adhesive interactions between soil and myxospermous seeds and discusses the ecological function and behaviour at the soil particle scale.

Excessive delivery of fine sediment from agricultural river catchments to aquatic ecosystems can degrade chemical water quality and ecological habitats. Management of accelerated soil losses and the transmission of sediment-associated agricultural pollutants, such as phosphorus, is required to mitigate the drive towards sustainable intensification to increase global food security. Quantifying soil erosion and the pathways and fate of fine-grained sediment is presently under-researched worldwide, and particularly in Ireland. This thesis established a sediment monitoring network upon an existing catchment study programme (Agricultural Catchments Programme) in five instrumented catchments (~10 km2) across Ireland. The research used novel, high quality measurement and analysis techniques to quantify sediment export, determine controls on soil erosion and sediment transport, and identify sediment contributions from multiple sources in different agricultural systems over time to evaluate approaches to fine sediment management. Results showed suspended sediment measurement using a novel ex situ methodology was valid in two of the study catchments against in situ and direct depth-integrated cross-section methodologies. Suspended sediment yields in the five intensive agricultural catchments were relatively low compared to European catchments in the same climatic zone, attributed to regionally-specific land use patterns and land management practices expressed in terms of ‘landscape complexity’ (irregular, small field sizes partitioned by abundant hedgerows and high drainage ditch densities) resulting in low field-to-channel connectivity. Variations in suspended sediment yield between catchments were explained primarily by soil permeability and ground cover, whereby arable land use on poorly-drained soils were associated with the largest sediment yields. Storm-event sediment export and sediment fingerprinting data demonstrated that sediment connectivity fluctuations resulted from rainfall seasonality, which in turn regulated the contrasting spatial and temporal extent of surface hydrological pathways. Increased transport occurred when and where sediment sources were available as a result of hillslope land use (low groundcover) or channel characteristics. Field topsoils were most vulnerable when low groundcover coincided with surface hydrological pathways; frequently on poorly-drained soils and following extreme rainfall events on well-drained soils as storage decreased. Although well-drained soils currently demonstrate low water erosion risk, past sugar beet crops exposed freshly drilled soils during periods of greater rainfall risk and soil removal during crop harvesting. Sediment loss from grassland catchments dominated by poorly-drained soils and extensive land drainage (sub-surface and surface) primarily derived from channel banks due to the delivery of high velocity flows from up-catchment drained hillslopes. Catchment specific soil erosion and sediment loss mitigation measures are imperative to cost-effectively preserve or improve soil and freshwater ecosystem quality worldwide.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references.

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Spatial variability is all that stands between hydrology and science, forcing us to deal in probabilities and averages. Because of scale, we can not consider forces on individual soil particles, water molecules and solute ions when addressing human size problems. We must therefore look at aggregate properties and mean values for parameters and inputs in computer modeling of hydrologic phenomena. This research explores the impact of spatially variable inputs on the Water Erosion Prediction Project soil erosion computer program. Distributions of input variables are generated and assigned randomly to a grid of homogeneous rangeland hillslope elements. Values for runoff volume and sediment loss from each flow path are recorded and averaged to provide a distribution of outputs in the form of a sensitivity analysis. Variabilities of slope, slope length, soil textures, soil characteristics, terrain, convex and concave slopes, soil saturation, rainfall amount and vegetation were examined. Results show that use of mean inputs values in the WEPP representative hillslope model yields very similar outputs to the spatially variable research model using a distribution of inputs in all simulations in the case of totally random bare rangeland soils. When a decreasing trend in soil clay content is introduced in the variable model, the hillslope model using average values as inputs no longer provides a good estimate of the sediment loss. When random vegetation is generated and added to the simulation, runoff volume continues to be similar between the two models, but the sediment loss is much higher in the spatially variable model. In addition, the results of the standard hillslope model are much less responsive to changes in slope than those of the spatially variable model. It is concluded that spatial variability of soils must be considered when there is a linear change in input values with slope position. Likewise spatial variability of vegetation needs to be addressed in order to accurately estimate erosion on the rangeland watersheds considered in this dissertation. It is also found that this type of simulation provides a model for sensitivity analysis of a complex computer programs. Physically related inputs can be generated in such a way as to preserve the desired interrationships and distributions of inputs can be directly compared to generated distributions of outputs.

In 1985 the USDA - Agricultural Research Service initiated a national project called Water Erosion Prediction Project (WEPP) to develop a new generation water erosion prediction technology which will replace the USLE by 1992, the most widely used technology for estimating soil erosion by water. For simplicity, the WEPP model was developed assuming quasi-steady state conditions. An evaluation of the effects of formulating the unsteady state sediment continuity equation by assuming quasi-steady state conditions is presented. A methodology was developed to study soil erosion process in rainfall simulator plots treated as a microwatersheds. This was achieved by explicitly separating interrill and rill areas in the rainfall simulator plots using areal photographs and microtopographic data. A detailed analysis was conducted using response surface plots on the model structure of both formulations of the sediment continuity equation. The shape of the response surface plots indicated for each formulation whether the soil erosion parameter estimates were successfully identified. As an additional information, the sediment concentration graphs and the total sediment yield were used to determine major differences between the two formulations of the sediment continuity equation. Rainfall simulator plot data collected in five locations of the US were used for the calibration and validation of the model WESP. The unsteady state approach yielded lower values of the objective function than the quasi-steady state formulation. Using the unsteady state approach, physical interpretation may be associated with the soil erosion parameter values Kᵣ, T(cr), and Vₑ. The quasi-steady state soil erosion estimates showed a weak and unclear physical association. The shape of the sediment concentration graphs were similar for both formulations of the sediment continuity equation. The benefit obtained by using the more complicated unsteady state approach was a more accurate estimation of the peak, or maximum, sediment concentration. Total sediment yield estimates from both formulations were similar. Thus, insignificant benefit was obtained from using the unsteady state approach. In this study hydrographs reached equilibrium due to the long duration of simulated rainfall. The two model formulations might perform far differently under experimental conditions where steady state runoff is not reached.

No description available.

This thesis summarizes the efforts of two years of field investigation and water quality data analysis. With a focus on construction sites, background monitoring was carried out at two sites and data from a third, active site was also included for analysis. The water quality data was used to estimate event-based sediment yield from each location, and continuously-collected rainfall, water level and turbidity data was used to calibrate an event-based hydrologic model (SEDCAD). Based on the results of this research and the outputs of the calibrated model, an event-based sediment yield equation calibrated for Southern Ontario conditions is presented in conjunction with an IDF design tool. The IDF design tool can be used to effectively size and site construction-phase erosion and sediment controls before shovels break ground. The regulatory framework by which such controls are assessed is also discussed, and improvements to existing stormwater management guidelines are proposed.

No description available.