Sediment rating curve dynamicity at field scale: Insights into the resilience of agricultural land to sediment loss?

Agricultural soils are suffering from intensive management and environmental pressures threatening both production and regulating functions. Robust land in terms of sediment loss regulation is vital for reducing sediment pressures on aquatic environments. However, explicit evaluations of agricultural land robustness for sediment loss regulation are scant, limiting the broader understanding of soil resistance against erosion in the context of changing rainfall patterns. This study therefore investigated changes in soil drainage season turbidity (T n ) and flow (Q) relationships through time using dynamic linear models which provide insights into the overall degree of T n -Q dynamicity. Dynamicity (δ) scores can provide time-integrated rapid initial assessment of sediment loss regulation of the system over a given period through rating curve relationships. We find that δ scores remained highly variable and inconsistent through time, signifying they are not a sufficiently sensitive parameter to detect changes in T n -Q over soil drainage seasons at the field scale, irrespective of land use. Therefore, dynamicity should be used as a diagnostic indicator rather than a standalone metric for the dynamic robustness of sediment loss regulation. We further compared the variations of the intercept (β 0 ) and slope (β 1 ) coefficients in the linear models to understand dynamic robustness. Permanent grassland exhibited higher dynamic robustness compared to neighbouring tilled arable land and highly responsive surface flow pathways, whereas the erosion process on arable land is mainly characterised by saturation-excess surface runoff and rill erosion. After grassland was converted to arable use, our results indicate reduced dynamic robustness for sediment loss regulation, most likely associated with tillage practices and limited surface cover as both factors drive a temporal shift in sediment availability and the transport capacity of runoff.