Influence of land management on soil erosion, connectivity, and sediment delivery in agricultural catchments: Closing the sediment budget

Abstract

Agricultural land, and arable farming in particular, is commonly associated with increased soil erosion risk. Such systems are most vulnerable during low groundcover periods, but downstream delivery is ultimately controlled by connectivity. This study provides a catchment-scale sediment budget integrating three discrete but complementary investigations spanning different temporal and spatial scales. The first gives details on suspended sediment fluxes at the catchment outlet (2009–2012). The second provenances sources of fluxes using quantitative sediment fingerprinting. The third sets recent data in a multidecadal (60-year) context using radiometric (137Cs) field-scale soil loss estimates. The catchment observatory (11 km2) is low relief with predominantly well-drained soils and dominated by spring-sown cereal cropping through the study period. Modelling 137Cs inventory losses across 30 fields provided a catchment-wide mean soil loss of 2.0 Mg ha−1 yr−1. Although such rates are not atypical of intensively managed agriculture across Europe, they are considerably higher than contemporary sediment export yields of 0.12 Mg ha−1 yr−1 of which fingerprinting revealed that contemporary slope erosion contributed less than 25% (0.03 Mg ha−1 yr−1). No evidence of floodplain or in-channel sediment storage was consistent with disconnectivity. Instead, it is hypothesised that soil loss is associated with coextraction from root crop harvesting of previously widespread sugar beet crops. Considering that the highest mass-specific 137Cs concentration occurred during the 1960s, there appears to have been significant depletion of the cumulative 137Cs inventory where root crop harvesting occurred as compared with atmospheric fallout ‘reference sites.' The study highlights the value of multiple methodologies when seeking to understand legacy issues within agricultural catchment settings.