The effect of hedgerow wild-margins on topsoil hydraulic properties, and overland-flow incidence, magnitude and water-quality
Overland and shallow-subsurface flows from agricultural catchments are believed to contribute towards flood-risk and water-quality degradation across the globe. Hedgerows are commonplace agricultural features that may disrupt these rapid hydrological pathways. Research into the hydrological functioning of hedgerows is very limited however, with no field-based quantitative comparison of overland-flows within hedgerows versus other land-uses. This research is the first globally to observe changes in overland-flow incidence, volume and water-quality, alongside topsoil hydraulic and physico-chemical properties, induced by a hedgerow and adjoining wild-margin within a grassland landscape. bservations were conducted within two replicated paired-plots between a hedgerow wild-margin and a bordering pasture, within Cumbria, UK. Compared to adjacent pasture, hedge-margins significantly reduced topsoil dry bulk-density and increased porosity, and significantly increased the topsoil median permeability by a factor of 22–27. Overland-flow models, based on direct observations, highlight that hedge-margins are slower to produce overlandflows than pastures, requiring an equal or greater amount of saturation before the onset of overland-flow generation. Hedge-margins resultantly produced less overland-flow volume, likely due to increased infiltration, percolation and/or evapotranspiration. Soil saturation models, also based on direct observations, confirm pastures saturate faster than hedge-margins, with hedge-margins having extremely variable dynamics in relation to precipitation, whereas pastures have more moderate and consistent dynamics. Overland-flow water-quality from ‘wash-off’ experiments highlight that hedge-margins may store substantially more nitrate (70–260%), nitrate-nitrite (640–650%), and loose sediment (540–3970%) on the ground surface compared to pastures; although further experimentation is needed to determine contaminant mobilization potential.
Author(s): Wallace, EE; McShane, G; Tych, W; Kretzschmar, A; McCann, T; Chappel, NA
Journal: Hydrological Processes