Using a plant functional trait approach to increase buffer zone efficiency and reduce diffuse agricultural pollution

Brett, Aimee and Quinton, John and Stevens, Carly (2021) Using a plant functional trait approach to increase buffer zone efficiency and reduce diffuse agricultural pollution. PhD thesis, Lancaster University.

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Abstract

Buffer zones are vegetated strips made up of predominantly herbaceous species often containing a hedgerow or other woody layer. They are used as a barrier between agricultural fields and watercourses. Buffer zones are an important part of diffuse pollution prevention systems in agricultural environments. However, during extreme weather events, buffer zones can fail and pollution from sediment, phosphorus and nitrogen still occurs. A conceptual model was employed to identify plant functional traits that could be used to enhance the resistance and resilience of buffer zones to overland flow and sediment transfer. Five grassland plants species were phenotyped and then subjected to flume experiments, soil strength and hydrological measurements at two different growth stages. We then used a mixture of species and functional groups in a field plot experiment under simulated overland flow with sediment addition to assess the processes in the field. Finally, we examined the soil physical and hydrological processes in three different established buffer types. Significant relationships between root, leaf and morphological traits and saturated hydraulic conductivity, sediment capture, soil aggregate stability and overland flow resistance in the mesocosm experiment were found. However, these differences were not evident in the field plot experiment due to the heterogeneity of the landscape and environmental conditions. In addition, there were significant differences between the soil physical and hydrological properties between the established buffers and the crop area and between the different buffer types. This work demonstrates that functional traits can be used to influence surface runoff and soil physical and hydrological processes in a lab-based setting, however this may not necessarily translate to a field setting, especially over short growing periods. This work does show that broad-leaved trees can affect both the physics and hydrology of the soil even when they are relatively immature.