nuig biogeoscience research group

Groundwater study – progress

• Caherglassaun Geophysical Survey (2011)
• Groundwater Chemistry Project Update (2010)
• Nutrient Loading to Galway Bay Project Update (2010)
• Geophysical survey (2009)
• Groundwater well survey (2008)
• Radon sampling campaign (2008)

Groundwater Well Survey (2008) 

Over the past eight months, a field sampling campaign has begun along the coastal regions of Counties Galway and Clare.  Preliminary water quality and water level data has been collected from a number of groundwater wells and springs in the areas. 

Michael G. Kelly and Barbara Petrunic (NUIG) at the recently drilled Ardrahan Town water supply well. (2008)	Florian Einsiedl (NUIG) collecting water samples from John Finnegan's groundwater well. (2008)

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Radon Sampling Campaign (2008)

A tracer study using naturally occurring Radon was conducted in the Kinvarra region.  Seawater and groundwater samples were collected in order to identify submarine groundwater discharge points.  This work was in collaboration with the Department of Analytical Chemistry, Helmholz Centre for Environmental Research-UFZ, Germany.

Florian Einsiedl (NUIG) working with equipment used during the radon sampling campaign in Kinvarra Bay.(2008)		Rachel Cave (NUIG) and Shane Rooney (NUIG) onboard the vessel used to collect radon measurements in Kinvarra Bay. (2008)

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Geophysical Surveys (2009)

• July 2009: Bell harbour. A Marine Electrical Resistivity Survey was carried out to find zones of freshwater intrusion. This was the first sea trial of the new Marine Resistivity kit.  A series of water samples were collected for future analysis along with temperature salinity data.

NUIG Biogeoscience Group Members (left to right): Catherine Elder, Aisling Smith (PhD Candidate), Shane Rooney & Eve Daly.

• June 2009: Peterswell turlough near Gort. A Geophysical survey using Electrical Resistivity and Ground Penetrating radar was conducted. The aim of this work was to delineate the groundwater conduit feeding the turlough.

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Groundwater Chemistry Project Update (2010) 

Objectives

Overall objective of study was to investigate the groundwater chemistry in the coastal karstic regions that are located in Co. Galway and Co. Clare.  The data were used to assess the spatial variation in major ion chemistry, the nutrient levels of the groundwater sources in the region, and the extent of inland salt-water intrusion within the groundwater environment.  The results will provide an overall understanding of the geochemistry of the groundwater that is discharging into the coastal zones and the extent of seawater influence on the groundwater resource.

Brief summary of methods

Geochemical study

• 24 wells that were in use by owners at time of study
• Existing taps used for sample collection
• Continuously pumped wells may not represent “natural” conditions

Hydrogeological study

• 6 unused wells
• Water levels and field parameters (temp, conductivity) monitored
• Monitoring was carried out manually (short-term) or using dataloggers (long-term)

 

Figure 1. Map showing sampling locations rounded to nearest 1000 m. 

A few preliminary results

General Groundwater Chemistry

• Based on the Piper diagram shown below, the groundwater has a carbonate signature suggesting that the wells are installed in the limestone bedrock.
• The background water (open circles) varies primarily in the cation content.   The anion content in the background groundwater is fairly consistent.
• The higher Mg content in some of the background water samples likely reflects variations in limestone composition.
• Several near-coastal wells show evidence of salt-water intrusion.  Three samples (open triangles) show signs of salt-water influence as Na & Cl content is greater in these samples compared to background samples (open circles), which tend to be clustered in the bottom left corner of the diagram.  Seawater is represented by the open star symbol.

Salt-water influence in some wells may be the result of pumping as these wells were in use by the owner at the time of sampling.

 

Figure 2. Piper diagram showing general water chemistry signature for samples collected in May 2009.

Hydrogeological Study

• Dataloggers were used in three wells to investigate tidal response.
• An example dataset is provided here from one such well.
• In this well, water levels clearly respond to tides in Galway Bay.

 

Figure 3. Select data from a datalogger installed at a well located near the coastal zone.

For more information on these datasets please contact Dr. Barbara Petrunic ( barbara.petrunicnuigalway.ie )

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Nutrient Loading to Galway Bay Project Update (2010)

Seasonal monitoring at two tidal stations at Parkmore Quay (mouth of Kinvarra Bay) and Linnane's Quay (mouth of Augninish Bay) was carried out in 2009/2010 (Figure 1).

Figure 1. Tidal station locations.

Tidal station monitoring consists of taking half-hourly water samples over a 13-hour period at spring and again at neap tides at each station, in each season. Kinvarra Bay has significant known sources of submarine groundwater discharge (SGD), while neighbouring Aughinish Bay is believed to have much less input from SGD.

Both bays support shellfish aquaculture which has the potential to be affected both positively and negatively by SGD. The positive effects include enhanced input of organic carbon, and of nutrients, with the latter leading to increased phytoplankton growth in the bay, and increasing the food available for filter feeders such as mussels. Negative inputs include the potential for hyper-nutrification leading to eutrophication, and for the input of pathogens.

Long-term monitoring of instruments to measure temperature and salinity were placed in both bays, recording at 10-minute intervals. These data are used to examine the variability of the freshwater regime in the bays, to calculate the volume of SGD input to each bay on a daily basis, to compare it to rainfall data, and to calculate the loads of nutrient and carbon being delivered to each bay by SGD. (A Smith, in prep) (Figure 2).

Figure 2. Example SGD calculation for Kinvarra Bay.

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Geophysical Survey of Caherglassaun

Yvonne O'Connell (PhD Candidate) and Shane Rooney (Technical Staff) conducting a geophysical survey using towed electrical resistivity tomography (ERT) across Caherglassaun Lough, Co. Galway. Some results of the survey can be found in the poster on the groundwater publications webpage.

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