Vegetated buffer strips (VBSs) are widely encouraged as a cost-effective strategy to address phosphorus (P) pollution associated with agricultural production. However, there is a lack of evidence in the effectiveness of these measures for tackling diffuse P pollution in cold-climate regions under concentrated runoff flow conditions. This research aimed to investigate the effects of VBSs on reducing P concentrations in surface runoff at three different watersheds in Manitoba, Canada. Surface runoff samples were collected in four sub-catchments from each watershed by installing paired weirs at 0.5-m and at 5-m into the VBSs along the expected runoff flow path. In addition, P concentrations were measured in soil samples collected within and outside of the runoff flow path to gain further insight into P dynamics within VBSs at each study site. The results indicate that VBSs had little or no significant effect on reducing the concentration of P forms in surface runoff in the majority of situations, resulting in reduced runoff losses of total, dissolved and particulate P concentrations in only 23, 12 and 12% of the situations, respectively. In addition, Olsen extractable P concentrations in VBS soils were not significantly different from field soils both within and outside of the flow path. The ineffective P retention by VBSs in this region is likely associated with the fact that the majority of the runoff flow is concentrated through small portions of VBSs and occurs during snowmelt when biogeochemical processes responsible for P retention in VBSs are limited. Further research is needed to develop alternative management practices that enhance P retention during concentrated snowmelt runoff events in such cold-climate regions.
The continued phosphorus (P) impairment of freshwaters and the associated risk of eutrophication raise questions regarding the efficiency of current beneficial management practices (BMPs) for improving water quality. Vegetated buffer strips (VBSs) are widely encouraged BMPs for reducing P export from agricultural land. However, there is a lack of evidence regarding the longterm efficiency of VBSs for reducing legacy P losses. This research used soil analyses to investigate the P removal efficiency of an unmanaged VBS for controlling P loss from agricultural land in Manitoba, Canada, between 1954 and 2011. The results showed statistically significant retention of total P, Olsen extractable P, and 0.01 M CaCl 2 extractable P by a 5-m wide VBS compared with field soils. We found that surface soils at 5-m into the VBS had a significantly greater P sorption capacity and a smaller degree of P saturation (DPS) than adjacent field soils. The elevated DPS in field soils is likely associated with gradual P enrichment as a result of manure or fertilizer application over time and the strong affinity of P compounds for soil. Although P stratification in the VBS over 57 yr resulted in a significant increase (?11%) in DPS of VBS topsoil compared with VBS subsoil, our findings do not support the saturation of VBS soils with P. However, cutting and removal of vegetation from VBS could be a useful strategy to remove P from VBS and minimize possible P remobilization associated with vegetation senescence, especially where the climate is cold and runoff is dominated by snowmelt.
Using industrial by-products (IBPs) in conjunction with buffer strips provides a potentially new strategy for enhancing soluble phosphorus (P) removal from agricultural runoff. Here, we investigate the feasibility of this approach by assessing the P sorption properties of IBPs at different solution-IBPs contact time (1-120 min) and solution pH (3, 5.5, 7.5), as well as possible adverse environmental effects including P desorption or heavy metal mobilisation from IBPs. Batch experiments were carried out on two widely available IBPs in the UK that demonstrated high P sorption capacity but different physicochemical characteristics, specifically ochre and Aluminium (Al) based water treatment residuals (Al-WTR). A series of kinetic sorption-desorption experiments alongside kinetic modelling were used to understand the rate and the mechanisms of P removal across a range of reaction times. The results of the kinetic experiments indicated that P was initially sorbed rapidly to both ochre and Al-WTR, followed by a second phase characterised by a slower sorption rate. The excellent fits of kinetic sorption data to a pseudo-second order model for both materials suggested surface chemisorption as the rate-controlling mechanism. Neither ochre nor Al-WTR released substantial quantities of either P or heavy metals into solution, suggesting that they could be applied to buffer strip soils at recommended rates (≤30 g kg(-1) soil) without adverse environmental impact. Although the rate of P sorption by freshly-generated Al-WTR applied to buffer strips reduced following air-drying, this would not limit its practical application to buffer strips in the field if adequate contact time with runoff was provided.
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