Search

There are a variety of buffering features within the landscape that can be used to trap sediment and associated contaminants such as phosphorus (P), thereby helping to reduce sediment and P delivery to watercourses. Astroturf mats (n = 136) were placed within contrasting buffer features at nine sites [mid-field hedges (two sites), edge-of-field grass strips (six sites) and channel wetlands (one site)] within the River Parrett basin in England. Sediment was recorded on the mats at seven of the sites during the 18-month sampling period. At the other two sites either there was insufficient erosion or sediment by-passed the mats. At the seven sites where mats collected sediment, there was a considerable range in sediment deposition over the 18-month sampling period with site-average values (based on all mats at a site) ranging from 0.02 ± 0.06 to 1.15 ± 1.88 g cm )2 ; the average for all 136 mats was 0.41 ± 1.08 g cm )2 , or approximately 0.27 g cm )2 year )1 . Most of the sediment collected on the mats (n = 60) was sand-sized (>63 lm) material. The site-average total-P content of the

Modifications are made to the revised Morgan–Morgan–Finney erosion prediction model to enable the effects of vegetation cover to be expressed through measurable plant parameters. Given the potential role of vegetation in controlling water pollution by trapping clay particles in the landscape, changes are also made to the way the model deals with sediment deposition and to allow the model to incorporate particle-size selectivity in the processes of erosion, transport and deposition. Vegetation effects are described in relation to percentage canopy cover, percentage ground cover, plant height, effective hydrological depth, density of plant stems and stem diameter. Deposition is modelled through a particle fall number, which takes account of particle settling velocity, flow velocity, flow depth and slope length. The detachment, transport and deposition of soil particles are simulated separately for clay, silt and sand. Average linear sensitivity analysis shows that the revised model behaves rationally. For bare soil conditions soil loss predictions are most sensitive to changes in rainfall and soil parameters, but with a vegetation cover plant parameters become more important than soil parameters. Tests with the model using field measurements under a range of slope, soil and crop covers from Bedfordshire and Cambridgeshire, UK, give good predictions of mean annual soil loss. Regression analysis of predicted against observed values yields an intercept value close to zero and a line slope close to 1·0, with a coefficient of efficiency of 0·81 over a range of values from zero to 38·6 t ha−1. Copyright © 2007 John Wiley & Sons, Ltd.

A prototype Decision Support System (DSS), Buffers DSS, is presented to aid effective design (e.g., width) and placement of vegetated buffer features within field systems. A modified version of the Morgan–Morgan–Finney erosion model was used to simulate the effects of vegetation and particle-size selectivity in the detachment, transport, and deposition of sediment within agricultural fields. Evaluation of the model concluded that stem diameter and density of plants in a buffer were key parameters affecting the trapping efficiency, while soil texture affected transmission distance and therefore required buffer width. The model output in combination with other evidence was used to produce a quick and easy look-up table to determine the required buffer width to prevent > 2 t ha −1 yr −1 of eroded soil from leaving a field, which ranges from 130 m width depending on soil type and % ground cover. This look-up table forms an integral part of the Buffers DSS. The Buffers DSS has been designed with end users in mind, specifically farmers and farm advisors. Thus, the Buffers DSS utilizes information already generated from agri-environment schemes and combines this information with quick and easy look-up tables that take into account site-specific soil texture, slope, and vegetation characteristics. The purpose of the Buffers DSS is to aid decision making. It provides guidance on the best locations in which to place vegetated buffer features, in order to optimize sediment and sediment-associated pollutant trapping, while also minimizing the area of land that is removed from agricultural production.