Exploring the relationship between groundwater geochemical factors and denitrification potentials on a dairy farm in southeast Ireland

NOTICE: this is the author’s version of a work that was accepted for publication in the journal Ecological Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Ecological Engineering, volume 37, issue 9, September 2011, 1304-1313. DOI: 10.1016/j.ecoleng.2011.03.025peer-reviewedNitrate (NO3−) loss from agriculture to shallow groundwater and transferral to sensitive aquatic ecosystems is of global concern. Denitrifying bioreactor technology, where a solid carbon (C) reactive media intercepts contaminated groundwater, has been successfully used to convert NO3− to di-nitrogen (N2) gas. One of the challenges of groundwater remediation research is how to track denitrification potential spatially and temporally within reactive media and subsoil. First, using δ15N/δ18O isotopes, eight wells were divided into indicative transformational processes of ‘nitrification’ or ‘denitrification’ wells. Then, using N2/argon (Ar) ratios these wells were divided into ‘low denitrification potential’ or high denitrification potential’ categories. Secondly, using falling head tests, the saturated hydraulic conductivity (Ksat) in each well was estimated, creating two groups of ‘slow’ (0.06 m day−1) and ‘fast’ (0.13 m day−1) wells, respectively. Thirdly, two ‘low denitrification potential’ wells (one fast and one slow) with high NO3− concentration were amended with woodchip to enhance denitrification. Water samples were retrieved from all wells using a low flow syringe to avoid de-gassing and analysed for N2/Ar ratio using membrane inlet mass spectrometry. Results showed that there was good agreement between isotope and chemical (N2/Ar ratio and dissolved organic C (DOC)) and physio-chemical (dissolved oxygen, temperature, conductivity and pH) parameters. To explain the spatial and temporal distribution of NO3− and other parameters on site, the development of predictive models using the available datasets for this field site was examined for NO3−, Cl−, N2/Ar and DOC. Initial statistical analysis was directed towards the testing of the effect of woodchip amendment. The analysis was formulated as a repeated measures analysis of the factorial structure for treatment and time. Nitrate concentrations were related to Ksat and water level (p < 0.0001 and p = 0.02, respectively), but did not respond to woodchip addition (p = 0.09). This non-destructive technique allows elucidation of denitrification potential over time and could be used in denitrifying bioreactor technology to assess denitrification hotspots in reactive media, while developing a NO3− spatial and temporal predictive model for bioreactor site specific conditions

A methodological framework to determine optimum durations for the construction of soil water characteristic curves using centrifugation

peer-reviewedDuring laboratory assessment of the soil water characteristic curve (SWCC), determining equilibrium at various pressures is challenging. This study establishes a methodological framework to identify appropriate experimental duration at each pressure step for the construction of SWCCs via centrifugation. Three common temporal approaches to equilibrium – 24-, 48- and 72-h – are examined, for a grassland and arable soil. The framework highlights the differences in equilibrium duration between the two soils. For both soils, the 24-h treatment significantly overestimated saturation. For the arable site, no significant difference was observed between the 48- and 72-h treatments. Hence, a 48-h treatment was sufficient to determine ‘effective equilibrium’. For the grassland site, the 48- and 72-h treatments differed significantly. This highlights that a more prolonged duration is necessary for some soils to conclusively determine that effective equilibrium has been reached. This framework can be applied to other soils to determine the optimum centrifuge durations for SWCC construction.Teagasc Walsh Fellowship Programm

An Integrated Approach to Characterising the Hydrogeology of the Tynagh Mine Catchment, County Galway, Ireland

The first major Pb-Zn mine in Ireland, located near the village of Tynagh, in east County Galway operated from the early 1960s until the early 1980s producing almost eight million tonnes of ore from surface and underground workings. Prompted by pressure from members of the local community, the EPA completed the first environmental monitoring of the site and its environs in 2003, finding that surface waters were being negatively impacted by uncontrolled runoff from mine tailings and mine wastes. This study was undertaken to characterise the hydrogeology of the area, and to assess the status of the groundwater. Data sets were compiled from various state agencies and field data collection included well surveying and mapping, hydraulic head measurement, in situ well testing and recovery of samples for analysis. Thirty-nine wells were surveyed and 20 of those were sampled between 2008 and 2013. Samples were analysed for major anion and cations and a suite of metals (incl. Fe, Mn, Ba, As, Ni, Zn, Pb, Cu and Cd). The results are presented and discussed in the context of the geology, hydrogeology, mineralisation and regulations. A limited number of wells hydraulically downgradient of the mine site show consistent and persistent concentrations of elements that are above threshold levels or regulatory standards. Further, these wells are associated with the North Tynagh Fault, a deep seated, high angle normal fault that trends west-east for approximately 10 kilometres. This fault is shown to have been a critical factor in the deposition of mineral deposits in the Carboniferous period, and to have facilitated movement of acidic water that decalcified and weathered several million tonnes of rock during the Tertiary. This fault is now a key element of the local hydrogeology: significantly more groundwater moves through this discrete feature than through the mass of regional rock. Statistical analyses of the data sets using PCA, Q-Mode and Hierarchical Factor Analysis, and Trend Analysis confirm the importance of this structural feature and highlight specific relationships between various elements found in the groundwater samples. The importance of taking a multi-disciplinary approach to characterising complex groundwater settings is stressed and there is a discussion of the importance of good governance of water resources and groundwater in the context of the Water Framework Directive, and stressing the concepts of Integrated Catchment Management

How does it feel? The affective domain and undergraduate student perception of fieldwork set in a broad pedagogical perspective

Fieldwork in the earth sciences is much valued by students, teachers and prospective employers alike, yet it has been reduced as a component of many undergraduate programmes in recent times. This study presents the results of an investigation of the undergraduate student perception of fieldwork, specifically in the context of the affective domain, and considers the effectiveness of field-based training as a pedagogical tool. Fieldwork provides the learner with a deep and immersive learning environment, where they are required to apply knowledge and theory acquired in class to the natural world, and to then analyse its validity. Strong spatial and temporal reasoning skills are routinely employed, and construction of maps is central to the learning experience, as it requires students to carefully observe their surroundings and make informed and reasoned decisions as to what is important and truly necessary to document. As part of this study students from a single higher education institution in Ireland were provided with anonymous questionnaires and polled for their opinions prior to and following a phase of residential fieldwork. The results clearly show an appreciation of not just the cognitive benefits, but also the transferable, technical and social skills developed and improved through their varied first-hand real world fieldwork experiences. These findings are much in keeping with those of previous studies. Overall, the student study group demonstrated enhanced affective domain responses to residential fieldwork: a recurring theme in the responses was recognition of the importance and value of sound observation and scientific rigor. These skills could subsequently be applied to many other areas of student learning, thus helping them to consolidate and integrate their knowledge base. The capacity of field training to transform the way students think was very evident – they became knowledge generators rather than just knowledge recipients.Received: 21 March 2018 Accepted: 08 May 2018 Published online: 31 May 2018</p

Terrestrial and marine electrical resistivity to identify groundwater pathways in coastal karst aquifers

Groundwater movement in karst aquifers is characterised by high‐velocity fissure and conduit flow paths, and in coastal karst aquifers, these act as pathways for saline intrusion and freshwater discharge to the sea. This paper examines groundwater movement in two neighbouring catchments in the west of Ireland that represent canonical coastal karst aquifers dominated by discharges in the intertidal zone and at offshore submarine springs. Terrestrial and surface‐towed marine electrical resistivity tomography, coupled with ancillary hydrogeological data, identifies the influence of faulting and conduits on groundwater egress/saltwater ingress. The on‐shore and off‐shore subsurface geometry of major fault zones is identified, and the tidal influence of seawater and ground‐water flow is demonstrated in these zones and karst springs. Imaging of these sub‐surface structures is a pre‐requisite for numerical modelling of current and future climate‐driven freshwater–seawater interactions in karst coastal aquifers

Saltwater wedge variation in a non-anthropogenic coastal karst aquifer influenced by a strong tidal range (Burren, Ireland)

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A Pleistocene deposit preserved in deep karst at Coolough, County Galway, western Ireland

Buried karst features result from a complex interplay between carbonate bedrock and structural geology. The enhancement of carbonate aquifers through this interplay creates hydrogeologically complex subsurface drainage networks and highly variable surface topographies. This article reports on the sediment fill and fossil pollen record from a large enclosed negative karst landform at Coolough, near Galway City in the west of Ireland. The landform was discovered during the preliminary site investigation for the proposed N6 Galway City Ring Road. Major joint sets developed in the Carboniferous (Mississippian) Limestone bedrock govern the local hydrogeology and structural evidence suggests that a local fault has controlled the east-west propagation of the deep enclosed depression. Fluvial and lacustrine palaeoenvironments are interpreted from the sediments infilling the enclosed depression, within which three discrete diamicts are identified, potentially representing distinct phases of glaciation. Pollen assemblages, which reflect palaeoenvironments of open woods and grasslands, have been correlated with other deposits in Ireland and Europe and suggest a minimum date of the Early Pleistocene for the oldest of the diamicts, and thus an upper age limit on the development of the karst depression. Fluvial disturbance to the deposit is evident and is likely to be responsible for the chronological discrepancy between the Early Pleistocene and Middle Pleistocene sediments both recorded from the deposit infill. The findings of this multidisciplinary study contribute to an understanding of Quaternary landscape evolution in western Ireland.The authors would like to extend gratitude to Geological Survey Ireland and Science Foundation Ireland for funding this research (Grant Number 16/SP/4319), conducted within the Irish Centre for Research in Applied Geosciences (iCRAG). A special thanks to both Marie Fleming and Les Brown of Arup for initiating this research project, for providing the preliminary field data, and for all their valuable ideas and contributions. Very special thanks to Professor Peter Coxon (Trinity College Dublin) for helping to analyse the sediment core and for sharing valuable information and data from his research at the Pollnahallia site.peer-reviewed2021-11-0