The origin of sediment and particulate phosphorus inputs into water bodies in the Swiss Midlands - A twenty-year field study of soil erosion

Sediment (S) and particulate phosphorus (PP) inputs from soil erosion of arable land into surface waters contribute substantially to water pollution. We have mapped erosion and S input to water bodies after each erosive rainfall event on 203 arable fields in the Swiss Midlands over 20 years (=4060 field years) and quantified soil loss as well as S and PP input to water bodies. On average, 21% of the total soil loss reached water bodies. A total of 353 (9%) field years provided S and PP inputs. The mean rates of S and PP input were 0.10 t ha(-1) yr(-1) and 0.14 kg ha(-1) yr(-1), and maximum values for single events were 10.71 t ha(-1) and 12.96 kg ha(-1), respectively. Of all investigated fields, 61% were connected to water bodies, but 88% of the total S and PP input occurred indirectly via drainage pipes with inlet shafts from roads and farm tracks. The temporal and spatial variability of S and PP input to water bodies was high. Only 7 (3%) out of 203 fields contributed to more than 50% of the total S input, and the largest 10% of field year magnitudes contributed to 73% of the total observed S input. Linear structures, such as thalwegs, traffic lines, tramlines, furrows or compacted headlands, were important pathways. More than 90% of the S and PP input resulted from linear erosion features. A wider application of conservation tillage practices in the second 10-year phase of the study led to a 5-6 fold reduction in S and PP inputs into water bodies in comparison to the first 10-year phase. With the presented unique data set, a sound basis for modelling and model validation is available. Moreover, such long-term studies are suitable to evaluate the effectiveness of mitigation measures and programmes.

Automated summary

The study on arable land in the Swiss Midlands found that sediment and particulate phosphorus inputs from soil erosion significantly contribute to water pollution, with high temporal and spatial variability. Most of the sediment and phosphorus input into water bodies occurred indirectly through drainage pipes, indicating the importance of drainage infrastructure in water pollution control.