Simulating a century of soil erosion for agricultural catchment management

Abstract

Agricultural land management requires strategies to reduce impacts on soil and water resources while maintaining food production. Models that capture the effects of agricultural and conservation practices on soil erosion and sediment delivery can help to address this challenge. Historic records of climatic variability and agricultural change over the last century also offer valuable information for establishing extended baselines against which to evaluate management scenarios. Here, we present an approach that combines centennial-scale reconstructions of climate and agricultural land cover with modelling across four lake catchments in the UK where radiometric dating provides a record of lake sedimentation. We compare simulations using MMF-TWI, a catchment-scale model developed for humid agricultural landscapes that incorporates representation of seasonal variability in vegetation cover, soil water balance, runoff and sediment contributing areas. MMF-TWI produced mean annual sediment exports within 9-20% of sediment core-based records without calibration and using guide parameter values to represent vegetation cover. Simulations of land management scenarios compare upland afforestation and lowland field-scale conservation measures to reconstructed historic baselines. Oak woodland versus conifer afforestation showed similar reductions in mean annual surface runoff (8-16%) compared to current moorland vegetation but a larger reduction in sediment exports (26-46 versus 4-30%). Riparian woodland buffers reduced upland sediment yields by 15-41%, depending on understorey cover levels, but had only minor effect on surface runoff. Planting of winter cover crops in the lowland arable catchment halved historic sediment exports. Permanent grass margins applied to sets of arable fields across 15% or more of the catchment led to further significant reduction in exports. Our findings show the potential for reducing sediment delivery at the catchment scale with land management interventions. We also demonstrate how MMF-TWI can support hydrologically-informed decision making to better target conservation measures in humid agricultural environments.

On the evaluation of soil erosion models: Are we doing enough?

“…This interpretative description of a phenomenon is key to provide understanding and insight (Bailer-Jones, 2009), which is scientifically relevant on its own. Moreover, erosion models are used to make quantitative predictions and scenariobased simulations about how soil is redistributed in potentially complex landscapes, at multiple spatial and temporal scales (e.g., Eekhout et al, 2018;Panagos et al, 2015;Prasuhn et al, 2013;Shrestha and Jetten, 2018;Smith et al, 2018). Policymakers and stakeholders might find these predictions useful, as they may help substantiate environmentally sensitive decisions regarding soil, water, and food security.…”

Performance of the LandSoil expert‐based model to map erosion and sedimentation: application to a cultivated catchment in central Belgium

“…This concept takes heterogeneities into account, which constitutes a key to improving catchment behaviour modelling (López-Vicente et al, 2013). For instance, Smith et al (2018) demonstrated that models that capture the effects of spatial and temporal variations in agricultural and conservation practices on soil erosion and sediment delivery greatly improve the model outcome and facilitate decision making regarding catchment management practices. The difficulty lies in integrating connectivity into models without over-parameterization (Heckmann et al, 2014), because highly parameterized models have operational limitations (Blöschl and Sivapalan, 1995;Lane, Nichols and Paige, 1995;Seyfried and Wilcox, 1995).…”

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

“…Field amalgamation due to mechanisation over time, resulting in increased field size and reduced hedgerows, likely increased hillslope soil erosion risk and modified hydrological pathways (Thomas et al, ). However, the impact of cropped field positions on modelled mean suspended sediment yield versus the window of opportunity effect has been reported as 22% and 100%, respectively (Smith et al, ). This suggests the gradual amalgamation of fields is likely to have a minor impact on soil erosion and sediment delivery, particularly considering the low connectivity of the majority of catchment soils.…”