Kinvara is a small rural town in Co. Galway, South-west of Ireland. The bay is a smaller inlet of the larger Galway Bay. At low tide, water can be seen discharging from the land into the coastal ocean. Where does this come from? And what impact does it have? Another interesting feature of this town is the disappearing and reappearing rivers, swallow holes and turloughs, which dominate the landscape. Are these two connected?
Image 1: Dunguaire Castle with the SGD site
To answer these questions, we must look at both, the geology of the area and the groundwater, which flows underneath the area, eventually discharging into Kinvara Bay, known as submarine groundwater discharge (SGD), and how these interact.
SGD is described as any and all flow of water on continental margins from the seabed to the coastal ocean. Kinvara Bay is the main focal point for waters discharging from the Gort-Kinvara aquifer. Groundwater can be clearly seen discharging as a constant gentle swirling of water from the earth into the bay at low tide. (See above image) Dye tracer studies have also shown this to be the main discharge point. There is a lesser discharge point situated at the arch site about 50 metres to the left of the castle site. It has been shown that these two sites discharge waters from different sources, using isotope analysis. SGD has been shown to contain higher concentrations of nutrients, metals and carbon than surface waters. This is due to the constant temperature, low oxygen concentration and the dark conditions of waters underground. Hence, degradation reactions are minimised. Therefore, SGD discharges contain higher fluxes of these materials than surface waters, making them more important parameters for the budgets of these materials in the coastal ocean. Kinvara bay has no surface waters discharging into it, therefore, the major portion of the terrestrial inputs of nutrients, metals, carbon and bacteria are from the groundwater source. This makes the studies of SGD very important in this region.
Image 2: SGD discharge point with Arch site in the background
A question arises, why does SGD flow under Kinvara and why is there such a large discharge considering there are no surface discharges?
This aquifer is composed of carboniferous shelf limestones, which gives rise to karst systems. Karst aquifers are characterised by large fissures, cracks and tunnels which can create underground rivers, hence increasing transport of groundwater and any contaminants present. Rainfall is rapidly incorporated into the groundwater by infiltration and mixing of surface and groundwater happens quickly. Therefore, any contaminants, such as fertilisers, present in the soil or surface waters can infiltrate the underground system and be transported to the bay.
Image 3: A small turlough
The area is characterised by disappearing rivers and turloughs, which expose groundwaters to the environment before returning underground again. A turlough is a topographic depression in karst, which is intermittently flooded on an annual cycle from the seasonal rise in groundwater. In the Kinvara region the main cause of flooding is the limits of underground karst system as a conduit for the large volumes of water following excessive rainfall. Turloughs can encompass very large areas. There are many species of flora and fauna, which live in turloughs and are dependent on this type of system. The groundwater provides the necessary water and nutrients.
Image 4: A larger turlough
SGD is a very important area of study for this region as there are many groundwater dependent ecosystems, both in turloughs and at the subterranean estuary. Groundwater has the capacity to become enriched in contaminants such as nutrients, carbon and metals. The nutrients can then be utilised by these communities. Groundwater in this region is used as drinking water and for agricultural purposes, often untreated; hence, it is vital as a health standard to ensure that contaminants such as bacteria and nitrates are maintained below the safe threshold.
Image 5: The bay on a sunny day