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Volume 20, issue 5 | Copyright
Hydrol. Earth Syst. Sci., 20, 2119-2133, 2016
https://doi.org/10.5194/hess-20-2119-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Jun 2016

Research article | 01 Jun 2016

Quantifying the influence of surface water–groundwater interaction on nutrient flux in a lowland karst catchment

T. McCormack1, O. Naughton2, P. M. Johnston1, and L. W. Gill1 T. McCormack et al.
  • 1Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Dublin 2, Ireland
  • 2Civil Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland

Abstract. Nutrient contamination of surface waters and groundwaters is an issue of growing importance as the risks associated with agricultural run-off escalate due to increasing demands on global food production. In this study, the influence of surface water–groundwater interaction on the nutrient flux in a lowland karst catchment was investigated with the aid of alkalinity sampling and a hydrological model. The objective of the study was to determine the impact of ephemeral karst lakes (turloughs) on the surface water–groundwater nutrient flux, and whether these lakes act as sources or sinks of nutrients within the groundwater flow system. Water samples were tested from a variety of rivers, turloughs, boreholes and springs at monthly intervals over 3 years. Alkalinity sampling was used to elucidate the contrasting hydrological functioning between different turloughs. Such disparate hydrological functioning was further investigated with the aid of a hydrological model which allowed for an estimate of allogenically and autogenically derived nutrient loading into the karst system. The model also allowed for an investigation of mixing within the turloughs, comparing observed behaviours with the hypothetical conservative behaviour allowed for by the model. Within the turloughs, recorded nutrient concentrations were found to reduce over the flooded period, even though the turloughs hydrological functioning (and the hydrological model) suggested this would not occur under conservative conditions. As such, it was determined that nutrient loss processes were occurring within the system. Denitrification during stable flooded periods (typically 3–4 months per year) was deemed to be the main process reducing nitrogen concentrations within the turloughs, whereas phosphorus loss is thought to occur mostly via sedimentation and subsequent soil deposition. The results from this study suggest that, in stable conditions, ephemeral lakes can impart considerable nutrient losses on a karst groundwater system.

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In this study, the influence of surface water–groundwater interaction on the nutrient flux in a lowland karst catchment in western Ireland was investigated with the aid of alkalinity sampling and a hydrological model. Results indicated that denitrification within a number of ephemeral lakes is the main process reducing nitrogen concentrations within the turloughs, whereas phosphorus loss is thought to occur mostly via sedimentation and subsequent soil deposition.
In this study, the influence of surface water–groundwater interaction on the nutrient flux in a...
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