Exploring the Link between Soil Surface Features and Erosion Sensitivity in an Elementary Agricultural Watershed in Northern France

In agricultural areas such as developed on the European loess belt, soil erosion causes off-site damages and the decrease of crop grows. The elevated rate of soil erosion raises also the question of sustainability of agriculture in these areas. During runoff events, erosion causes the loss of soil fertility and degradation of river water quality through the export of particles, nutrients, and chemicals such as pesticides. This study shows novel results of high-resolution monitoring of soil erosion processes in an elementary agricultural watershed in northern France (the Pommeroye). Several parameters, such as pluviometry, runoff volume, sediment yield, and soil surface characteristics were recorded between April 2021 and March 2022 and subsequently compared to previous results obtained between 2016 and 2018. The recent results demonstrate an increase of the total/annual sediment yield of 117% despite no noticeable modification of the liquid runoff volume. This highlights the evidence of an ongoing soil degradation with time. Despite recorded spring and summer storm events, their total sediment yield stays low compared to autumn and winter sediment yield (5%). The detailed monitoring of soil surface parameters, such as vegetation cover, roughness, and surface crusting allow the characterization of vegetation cover changes which appears to be the main parameter governing soil erosion sensitivity. This sensitivity is obviously linked to the seasonal and intra-seasonal variability of rainfall events which induce winter soil saturation. The use of the WaterSed numerical model regarding three different runoff events highlights the spatial variability of erosion events depending on the soil surface characteristics of each crop type. The modeling results clearly underline the importance of winter vegetation cover with a six-fold reduction of sediment yield during winter runoff event, and the need of the raising awareness among farmers and public policy to change urgently winter coverage habits that threaten the sustainability of food supply by reducing the fertile soil content