EGU2020-7081
https://doi.org/10.5194/egusphere-egu2020-7081
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Assessing the role of colloidal phosphorus delivery processes in groundwater-fed agricultural catchments

Maelle Fresne1,2,3, Phil Jordan2, Karen Daly3, Owen Fenton3, and Per-Erik Mellander1,3
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

Soil colloids with high sorbing capacities can enhance transport of phosphorus (P) from soils to groundwater and the delivery of P to surface water via groundwater pathways. However, only particulate and dissolved P fractions are generally monitored at the catchment scale.

To add important insights into the particulate to dissolved P concentration spectrum in the soil-water environment, the role of colloidal P delivery processes to surface water was studied in two agricultural catchments. The catchments were dominated by belowground pathways but had contrasting land use (arable and grassland). Particulate, coarse colloidal (0.20 – 0.45 μm) and finer colloidal (< 0.20 μm) P fractions were monitored along hillslopes in the free soil solution, shallow groundwater and stream water on a weekly basis for background characterisation and at higher frequency during rainfall events. An automated sampler was deployed in the stream and an automated, low-flow and low-disturbance sampler was developed to sample groundwater. Multi-parameter probes were also deployed to monitor stream water and shallow groundwater physico-chemical parameters. Stream discharge was measured at high frequency using a flow velocimeter in order to quantify P loads, apportion hydrological pathways and study concentration-discharge hysteresis.

Preliminary findings showed higher background P and unreactive P concentrations in the stream and groundwater in the grassland catchment. In the arable catchment (rainfall event in June 2019) P was mainly lost through deeper baseflow (92% of the total event flow) as reactive P in the finer colloidal fraction (0.070 mg P/ha) and only a small fraction lost as particulate unreactive P (0.008 mg P/ha). In the grassland catchment (rainfall event in October 2019), P was mainly lost through quickflow (37% of the total flow) even tough deeper baseflow was also important (33%). Losses were mainly reactive P in the finer colloidal fraction (13.6 mg P/ha) but also as unreactive P (4.5 mg P/ha). Concentration-discharge hysteresis suggested a smaller and easily mobilised P source in the arable catchment and a larger P source, followed by the mobilisation of a second but smaller source via a second hydrological surface pathway in the grassland catchment.

Further monitoring campaigns during more rainfall events in the grassland catchment are required to better understand colloidal P delivery and the spatial/temporal dynamics between rainfall events in relation to soil conditions and rainfall patterns. This will help to better target mitigations measures according to P species and fractions, hydrological flowpaths, and rainfall patterns – important in the context of a changing climate.

How to cite: Fresne, M., Jordan, P., Daly, K., Fenton, O., and Mellander, P.-E.: Assessing the role of colloidal phosphorus delivery processes in groundwater-fed agricultural catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7081, https://doi.org/10.5194/egusphere-egu2020-7081, 2020

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