Effect of a cold-climate buffer zone on minimising diffuse pollution from agriculture

Abstract

Vegetative buffer zones adjacent to streams can filter diffuse pollution from agriculture. Under Nordic climatic conditions, major runoff from agriculture occurs during winter and especially during snowmelt. Field experiments documenting runoff and retention processes in buffer zones during winter conditions are essential. Agricultural runoff and buffer zone retention of nutrients and particles during winter and summer are compared. The study is based upon 8 years of data collected from 5 to 10 m wide buffer zones compared to plots without buffer zones. Volume proportional samples were collected after each runoff episode. Results show that the difference between precipitation and runoff is much higher during summer than winter, due to higher evapotranspiration and infiltration during the summer. Over 90% of total particle and phosphorus runoff occurred during winter. There was no significant difference in retention of particles and particle-bound nutrients during winter compared to summer. Sedimentation is one of the most important retention processes in surface runoff buffer zones. High retention during winter is probably caused by higher surface runoff and erosion. High surface runoff and flow velocity could cause erosion of coarser particles, which were more easily trapped in the buffer zone. High particle concentration in the runoff water may also enhance the aggregation of fine particles.