Quantification of submarine/intertidal groundwater discharge and nutrient loading from a lowland karst catchment

• Published in: Journal of hydrology (Amsterdam) Vol. 519; pp. 2318 - 2330
• Main Authors: McCormack, T., Gill, L.W., Naughton, O., Johnston, P.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.11.2014; Elsevier
• Subjects: Discharge; Earth sciences; Earth, ocean, space; Exact sciences and technology; Flow rate; Freshwater; Hydrogeology; Hydrology; Hydrology. Hydrogeology; Ireland; Karst; Modelling; Networks; Nutrient loading; Nutrients; Outlets; Salinity; Springs; Submarine groundwater discharge; Europe; Ireland; Western Europe; ANE, Eire; Modelling; Karst; Nutrient loading; Submarine groundwater discharge; Ireland; Salinity; models; salinity; attenuation; submarine springs; ground water; concentration; karst; networks; nutrients; drainage basins; aquifers; bays; discharge; flow
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2014.09.086

•Hydraulic model used to estimate submarine groundwater discharge from intertidal karst springs.•Modelled estimate of submarine groundwater discharge validated by salinity survey.•Nutrient loading from karst springs estimated via combination of sampling and hydraulic modelling.•Hydrological model has shown submarine groundwater discharge and nutrient loading to be lower than previous estimates. Submarine groundwater discharge (SGD) is now recognised to be a process of significant importance to coastal systems and is of increasing interest within oceanographic and hydrologic research communities. However, due to the inherent difficulty of measuring SGD accurately, its quantification at any particular location is a relatively slow process often involving multiple labour intensive methods. In this paper, the SGD occurring at Kinvara Bay, the outlet of a lowland karst catchment in Western Ireland, is estimated using a hydrological model of the karst aquifer and then further verified by means of a relatively simple salinity survey. Discharge at Kinvara predominantly occurs via two springs, Kinvara West (KW) which serves as the outlet of a major, primarily allogenically fed, karst conduit network and Kinvara East (KE) which discharges water from more diffuse/autogenic sources. Discharge from these springs occurs intertidally and as such, their flow rates cannot be measured using traditional methods. Using the hydrological model, flow rates from KW were seen to vary between 5 and 16m3/s with a mean value of 8.7m3/s. Through hydrochemical analysis, this estimated discharge was found to be supplemented by an additional 14–18% via sources not accounted for by the model. Mean discharge at KE was also estimated as approximately 2m3/s, thus the total mean discharge from both Kinvara Springs was determined to be 11.9–12.3m3/s. Overall, the range of discharge was found to be lower than previous studies have estimated (as these studies had no means of quantifying attenuation within the conduit network). Combining this discharge with nutrient concentrations from the springs, the nutrient loading from the springs into the bay was estimated as 1230kg/dayN and 24.3kg/day P. This research illustrates the benefits of a numerical modelling approach to the quantification of SGD when used in the appropriate hydrological scenario.