Preprints
https://doi.org/10.5194/hess-2020-248
https://doi.org/10.5194/hess-2020-248

  21 Jul 2020

21 Jul 2020

Review status: this preprint was under review for the journal HESS but the revision was not accepted.

Contrasting physical controls on phosphorus transport to shallow groundwater at the hillslope scale

Maelle Fresne1,2,3, Phil Jordan2, Per-Erik Mellander1,3, Karen Daly3, and Owen Fenton3 Maelle Fresne et al.
  • 1Agricultural Catchments Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Co. Wexford, Ireland
  • 2School of Geography and Environmental Sciences, Ulster University, Coleraine, UK
  • 3Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Co. Wexford, Ireland

Abstract. In well-drained agricultural catchments transport of phosphorus (P) to groundwater (GW) can be controlled by static and dynamic factors and where surface water is GW fed this can lead to elevated P concentrations at the catchment outlet. In order to better control P transport along hillslopes a spatial and temporal conceptual view of P loss to GW must be developed. Initially in the present study, hillslope GW quality and rainfall data were examined for 2017 utilising a transect of piezometers at upslope (US), midslope (MS) and downslope (DS) locations. Two dominant scenarios emerged where GW P concentrations at DS and MS were simultaneously low or at other times DS became elevated and MS remained low. To examine the potential reasons for such scenarios, a one-dimensional hydrological transport model was developed for the unsaturated zone at DS and MS using rainfall and depth specific soil physical and hydraulic data. Results indicated that the DS zone facilitated transport (higher sand content, soil saturated hydraulic conductivity (Ks) and lower soil compaction) with higher modelled concentration peaks towards higher GW P concentrations whereas the MS zone had more potential to attenuate transport (lower soil Ks and higher soil compaction). Moreover, inter-annual variations of GW P concentrations at DS were related to rainfall and GW level. Hence, mitigation strategies should particularly (but not exclusively) focus on reducing P sources in the DS zone. This also indicates a need to identify hotspots of facilitated transport to shallow GW using finer scale soil properties surveys. Here, this is defined by low soil compaction, high sand content and soil Ks. However, challenges arise as soil properties can vary in time with soil management and with the difficulty of assessing the transport potential of deeper soil.

Maelle Fresne et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Maelle Fresne et al.

Maelle Fresne et al.

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Short summary
We identifies the role of physical controls (soil properties, rainfall and groundwater level) on phosphorus transport to shallow groundwater at the hillslope scale. Spatial variations in phosphorus transport to groundwater were related to soil properties whereas temporal variations were related to rainfall and groundwater level. The findings provide a support for the localisation of critical zones of phosphorus loss to groundwater and where reduction of phosphorus sources should be prioritized.