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Lowland karst aquifers can generate unique wetland ecosystems which are caused by groundwater fluctuations that result in extensive groundwater–surface water interactions (i.e. flooding). However, the complex hydrogeological attributes of these systems, linked to extremely fast aquifer recharge processes and flow through well-connected conduit networks, often present difficulty in predicting how they will respond to changing climatological conditions. This study investigates the predicted impacts of climate change on a lowland karst catchment by using a semi-distributed pipe network model of the karst aquifer populated with output from the high spatial resolution (4 km) Consortium for Small-scale Modelling Climate Lokalmodell (COSMO-CLM) regional climate model simulations for Ireland. An ensemble of projections for the future Irish climate were generated by downscaling from five different global climate models (GCMs), each based on four Representative Concentration Pathways (RCPs; RCP2.6, RCP4.5, RCP6.0 and RCP8.5) to account for the uncertainty in the estimation of future global emissions of greenhouse gases. The one-dimensional hydraulic/hydrologic karst model incorporates urban drainage software to simulate open channel and pressurised flow within the conduits, with flooding on the land surface represented by storage nodes with the same stage volume properties of the physical turlough basins. The lowland karst limestone catchment is located on the west coast of Ireland and is characterised by a well-developed conduit-dominated karst aquifer which discharges to the sea via intertidal and submarine springs. Annual above ground flooding associated with this complex karst system has led to the development of unique wetland ecosystems in the form of ephemeral lakes known as turloughs; however, extreme flooding of these features causes widespread damage and disruption in the catchment. This analysis has shown that mean, 95th and 99th percentile flood levels are expected to increase by significant proportions for all future emission scenarios. The frequency of events currently considered to be extreme is predicted to increase, indicating that more significant groundwater flooding events seem likely to become far more common. The depth and duration of flooding is of extreme importance, both from an ecological perspective in terms of wetland species distribution and for extreme flooding in terms of the disruption to homes, transport links and agricultural land inundated by flood waters. The seasonality of annual flooding is also predicted to shift later in the flooding season, which could have consequences in terms of ecology and land use in the catchment. The investigation of increasing mean sea levels, however, showed that anticipated rises would have very little impact on groundwater flooding due to the marginal impact on ebb tide outflow volumes. Overall, this study highlights the relative vulnerability of lowland karst systems to future changing climate conditions, mainly due to the extremely fast recharge which can occur in such systems. The study presents a novel and highly effective methodology for studying the impact of climate change in lowland karst systems by coupling karst hydrogeological models with the output from high-resolution climate simulations.

Several different approaches have been developed to model the specific characteristics of karst aquifers, taking account of their inherent complex spatial and temporal heterogeneities. This paper sets out the development of a semidistributed modelling approach for applications in an Irish karst context using urban drainage software. The models have proven to be very useful for different studies, with examples given for the ecohydrology of ephemeral karst lakes, extreme groundwater-flood alleviation, karst network investigation, submarine groundwater discharge, and quantification of different recharge and flow components. The limitations of the approach are also highlighted, in particular not being able to simulate diffuse infiltration and flow paths explicitly across the groundwater catchment. Hence, a more distributed, finite-difference modelling approach using MODFLOW Unstructured Grid (USG) with the newly developed Connected Linear Network (CLN) process is then compared against the semidistributed approach on the same karst catchment. Whilst it has proven difficult to achieve the same levels of model performance in simulating the spring flows in the distributed model compared to the semidistributed model, the ability to interrogate the flow paths at any point on the three-dimensional aquifer is demonstrated, which can give new insights into flows (and potential contaminant transport) through such complex systems. The influence of the proximity of highly transmissive conduits on the flow dynamics through the much-lower transmissive matrix cells in which the network is embedded has been particularly investigated.Plusieurs approches différentes ont été développées pour modéliser les caractéristiques spécifiques des aquifères karstiques, prenant en compte leurs hétérogénéités spatiales et temporelles associées à leur complexité intrinsèque. Cet article présente le développement d’une approche de modélisation semi-distribuée appliquée à un contexte karstique irlandais en utilisant un logiciel de drainage urbain. Ces modèles se sont avérés très utiles pour différentes études, avec des exemples appliqués à l’écohydrologie de lacs karstiques éphémères, l’atténuation de crues extrêmes liées aux eaux souterraines, à l’étude du réseau karstique, à la décharge des sources sous-marines et à la quantification des différentes composantes aussi bien de la recharge que du débit. Les limites de cette approche sont aussi mises en évidence, avec en particulier l’incapacité de simuler l’infiltration diffuse et les voies d’écoulement de manière explicite au sein du bassin d’alimentation d’eaux souterraines. Par conséquent, une approche de modélisation plus distribuée aux différences finies utilisant le logiciel MODFLOW avec une grille non structurée (USG) intégrant le processus récemment développé de réseau linéaire connecté (CLN) est ensuite comparée à l’approche semi-distribuée appliquée au même bassin karstique. Alors qu’il s’est avéré difficile d’atteindre les mêmes niveaux de performance du modèle concernant la simulation du débit à la source à l’aide du modèle distribué en comparaison au modèle semi-distribué, la possibilité d’examiner les voies d’écoulement en tout point de l’aquifère en 3D est démontrée, ce qui peut donner de nouvelles connaissances sur les écoulements (et le transport potentiel de contaminants) au sein de tels systèmes complexes. L’influence de la proximité de conduits hautement transmissifs sur les écoulements dynamiques au travers des cellules de transmissivité plus faible de la matrice au sein de laquelle le réseau est intégré, a été particulièrement étudiée.Se han elaborado varios enfoques diferentes para modelar las características específicas de los acuíferos kársticos, teniendo en cuenta sus complejas y propias heterogeneidades espaciales y temporales. En el presente documento se expone la elaboración de un enfoque de modelización semidistribuido para aplicaciones en un contexto kárstico de Irlanda utilizando programas informáticos de drenaje urbano. Los modelos han demostrado ser muy útiles para diferentes estudios, y se dan ejemplos para la ecohidrología de los lagos kársticos efímeros, la mitigación de las inundaciones extremas de aguas subterráneas, la investigación de redes kársticas, la descarga submarina de aguas subterráneas y la cuantificación de diferentes componentes de la recarga y el flujo. También se ponen de relieve las limitaciones del enfoque, en particular el hecho de no poder simular explícitamente la infiltración difusa y las trayectorias de flujo a través de la cuenca de captación de aguas subterráneas. Por lo tanto, un enfoque de modelización de diferencias finitas distribuidas utilizando la red no estructurada (USG) de MODFLOW con el proceso de la Red Lineal Conectada (CLN) recientemente desarrollado se compara entonces con el enfoque semidistribuido en la misma cuenca kárstica. Si bien se ha demostrado que es difícil lograr los mismos niveles de rendimiento del modelo en la simulación de los flujos de manantiales en el modelo distribuido en comparación con el modelo semidistribuido, se demuestra la capacidad de interrogar las trayectorias de los flujos en cualquier punto del acuífero tridimensional, lo que puede dar nuevos conocimientos sobre los flujos (y el transporte de contaminantes potenciales) a través de sistemas tan complejos. Se ha investigado en particular la influencia de la proximidad de conductos altamente transmisivos en la dinámica de los flujos a través de las células de la matriz transmisiva, mucho más bajas, en las que está incorporada la red.鉴于岩溶含水层内在的复杂时空异质性, 已经开发出几种不同的方法来模拟岩溶含水层的特定性质。本文提出了基于城市排水软件的半分布式模型的开发方法, 并在爱尔兰喀斯特环境中应用。该模型已被证明对不同的研究非常有用, 并举例说明了季节性的喀斯特湖的生态水文学, 极端地下水洪涝减缓, 岩溶网络调查, 海底地下水排泄以及不同补给量和流动量的量化。还强调了该方法的局限性, 特别是不能明确模拟整个地下水盆地的扩散入渗和流动路径。因此, 然后将MODFLOW非结构化网格(USG)和新开发的连接线性网络(CLN)过程耦合的分布式有限差分方法与同一个喀斯特流域的半分布式方法进行了比较。尽管已证明分 布式模型模拟的泉流量难以达到与半分布式模型相比相同水平的模型性能, 但仍展示了在三维含水层上任意点处查询流路的能力, 这可以给出分析该类复杂系统流量(以及潜在的污染物传输)的新方法。特别研究了高传输管流的邻近度对通过嵌入网络的传导率低得多单元的流动动力学的影响。.Diversas abordagens diferentes foram desenvolvidas para modelar as características específicas dos aquíferos cársticos, levando em consideração suas complexas heterogeneidades espaciais e temporais inerentes. Este artigo apresenta o desenvolvimento de uma abordagem de modelagem semidistribuída para aplicações em um contexto cárstico irlandês usando software de drenagem urbana. Os modelos provaram ser muito úteis para diferentes estudos, com exemplos dados para a ecohidrologia de lagos cársticos efêmeros, alívio de inundações subterrâneas extremas, investigação de rede cárstica, descarga de água subterrânea submarina e quantificação de diferentes componentes de recarga e fluxo. As limitações da abordagem também são destacadas, em particular não ser capaz de simular infiltração difusa e caminhos de fluxo explicitamente através da captação de água subterrânea. Portanto, uma abordagem de modelagem de diferenças finitas, mais distribuída, usando MODFLOW Unstructured Grid (USG) com o processo de Rede Linear Conectada (RLC) recém-desenvolvido é então comparada com a abordagem semidistribuída na mesma bacia cárstica. Embora tenha se mostrado difícil alcançar os mesmos níveis de desempenho do modelo na simulação dos fluxos de nascente no modelo distribuído em comparação com o modelo semidistribuído, a capacidade de interrogar os caminhos de fluxo em qualquer ponto do aquífero tridimensional é demonstrada, o que pode dar novas percepções sobre os fluxos (e o transporte potencial de contaminantes) por meio de tais sistemas complexos. A influência da proximidade de condutos altamente transmissivos na dinâmica do fluxo através das células da matriz transmissiva muito inferior nas quais a rede está inserida foi investigada particularmente.

Karstified carbonate aquifers may receive significant recharge contributions from losing streams, hence, the knowledge about surface water‐groundwater (SW‐GW) interactions is crucial with regard to water management (e.g., source protection zone delineation). The dynamics of SW‐GW interactions may depend on factors such as the relative water levels between streams and aquifers, resulting in a temporal variation of exchange, which imposes complexity to the understanding of such dynamics. This study highlights the use of high‐resolution time series and multiresolution analysis to help to gain insights into such complex dynamics. Wavelet coherence is applied on hourly time series of rainfall, stream, and spring discharges of a low‐lying karstified spring catchment to yield a correlation in the time‐frequency domain. This analysis provides comprehensive information on the overall impact of the river on the spring, which is supported by the cross‐correlation function, as well as by more detailed information, including time‐variant influences such as a threshold level of influence. Field observations of turbidity sampling at the spring appear to support this interpretation. This innovative approach relies on basic hydrological parameters, water level, or discharge, and is therefore applicable to many other systems with such existing time series., Article impact statement: Wavelet coherence yields high‐resolution information on surface water‐groundwater interaction.

Karstified carbonate aquifers are highly heterogeneous systems characterized by multiple recharge, flow, and discharge components. The quantification of the relative contribution of these components, as well as their numerical representation, remains a challenge. This paper identifies three recharge components in the time and frequency domain. While the analysis in the time domain follows traditional approaches, the analysis of the power spectrum allows frequencies associated with specific spectral coefficients and noise types to be distinguished more objectively. The analysis follows the presented hypothesis that the different frequency‐noise components are the result of aquifer heterogeneity transforming the random rainfall input into a sequence of non‐Gaussian signals. The distinct signals are then numerically represented in the context of a semidistributed pipe network model in order to simulate recharge, flow, and discharge of an Irish karst catchment more realistically. By linking the power spectra of the modeled recharge components with the spectra of the spring discharge, the information usually gained by classical performance indicators is significantly widened. The modeled spring discharge is well matched in the time and frequency domain, yet the different recharge dynamics explain the signal of the aquifer outlet in different noise domains across the spectrum. This study demonstrates the conjunctive use of frequency analysis in conceptualization of a hydrological system together with modeling and evaluation., Key Points Hydrograph analysis was coupled with frequency and noise analysis to identify recharge dynamics in a karst spring discharge time seriesRecharge, flow, and discharge were modeled in a semidistributed pipe network model considering aquifer heterogeneities and noise domainsA new model evaluation approach using noise analysis provided information on the individual contribution of the internal flows

Parametrising the spatially distributed dynamic catchment water balance is a critical factor in studying the hydrological system responses to climate and land use changes. This study presents the development of a geographic information system (GIS)-based set of algorithms (geographical spatially distributed water balance model (GEO-CWB)), which is developed from integrating physical, statistical, and machine learning models. The GEO-CWB tool has been developed to simulate and predict future spatially distributed dynamic water balance using GIS environment at the catchment scale in response to the future changes in climate variables and land use through a user-friendly interface. The tool helps in bridging the gap in quantifying the high-resolution dynamic water balance components for the large catchments by reducing the computational costs. Also, this paper presents the application and validation of GEO-CWB on the Shannon catchment in Ireland as an example of a large and complicated hydrological system. It can be concluded that climate and land use changes have significant effects on the spatial and temporal patterns of the different water balance components of the catchment.

Wetlands provide habitat for a wide variety of plant and animal species and contribute significantly to overall biodiversity in Ireland. Despite these known ecosystem services, the total wetland area in Ireland has reduced significantly over the past few decades leading to an ongoing need to protect such environments. The EU Habitats Directive (92/43/EEC) has recognised several wetlands types as “priority” habitats. This study concentrates on a subset of the priority habitats focussing on some groundwater dependent terrestrial ecosystems, (in particular calcareous fens and turloughs), as well as raised bogs. Monitoring these sites across the country by field visits is resource-intensive. Therefore, this study has evaluated remote sensing as a potentially cost-effective tool for monitoring the ecological health of the wetlands. Identification and presence of certain vegetation communities can indicate the condition of the wetland, which can be used for monitoring, for example, activities causing degradation or the progress of restoration attempts. The ecological composition of the wetlands has been analysed using open-source Sentinel-2 data. 10 bands of Sentinel-2 Level-2 data and 3 indices, Normalised Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and Normalised Difference Water Index (NDWI) were used to create vegetation maps of each wetland using Bagged Tree (BT) ensemble classifier and graph cut segmentation also known as MAP (maximum a posteriori) estimation. The proposed methodology has been validated on five raised bogs, five turloughs, and three fens at different times during 2017 and 2018 from which three case studies are presented. An overall classification accuracy up to 87% depending on the size of the vegetation community within each wetland has been achieved which suggests that the proposed method is appropriate for wetland health monitoring.

The accumulation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in the sediment and plants growing in a constructed wetland used to treat highway runoff in Ireland has been quantified after 6 and 9year periods of operation. The spatial distribution of the metals' deposition showed strong evidence of flow channelling through the wetland with a strong correlation between the spatial accumulation, particularly for Cr, Cu, Pb and Zn with most of these metals deposited towards the front of the wetland in the sediment. Highest accumulation in the wetland was for Zn, followed by Cu, Pb, Cr, Ni and Cd. The study also quantified that an almost negligible mass of metals had accumulated in the vegetation compared to the sediment. However, an apparent increase in metal accumulation with time may be linked to the cumulative annual production and deposition of organic matter, indicating the importance of the vegetation as an integral part of the treatment process. Based on the measured accumulation and projected runoff loads over the 9year period, the apparent removal efficiencies were 5% (Cd), 60% (Cu), 31% (Pb) and 86% (Zn). This equates to accumulation rates of 0.1 (Cd), 15.6 (Cu), 11.6 (Pb) and 88.3 (Zn) g per m2 highway drained per year.

The presence of a first flush (FF) of suspended solids (SS) in stormwater runoff has important implications for the design of treatment facilities, as does the particle size of solids. Whilst numerous studies have examined the FF behaviour of SS, few have disaggregated FF trends by particle size. In this study, the FF behaviour of SS was investigated in five size ranges, sampled from an urban stormwater drainage system located in Dublin, Ireland. A weak FF was exhibited in the gross fraction of SS, with just two events from 14 transporting more than 50% of the SS mass in the first 25% of runoff, implying that treatment structures should be capable of removing SS throughout the storm event. In the majority of rain events, the FF strength increased with decreasing particle size, probably related to the lower intensities required to dislodge solids at the onset of rainfall. Although FF strength was correlated with rain event characteristics, prediction intervals were too broad to confirm FF presence based on rainfall data alone. Therefore, the design of smaller treatment volumes based on an assumption of FF must be justified by local monitoring data.

Conventional methods of monitoring wetlands and detecting changes over time can be time-consuming and costly. Inaccessibility and remoteness of many wetlands is also a limiting factor. Hence, there is a growing recognition of remote sensing techniques as a viable and cost-effective alternative to field-based ecosystem monitoring. Wetlands encompass a diverse array of habitats, for example, fens, bogs, marshes, and swamps. In this study, we concentrate on a natural wetland – Clara Bog, Co. Offaly, a raised bog situated in the Irish midlands. The aim of the study is to identify and monitor the environmental conditions of the bog using remote sensing techniques. Environmental conditions in this study refer to the vegetation composition of the bog and whether it is in an intact (peat-forming) or degraded state. It can be described using vegetation, the presence of water (soil moisture) and topography. Vegetation indices (VIs) derived from satellite data have been widely used to assess variations in properties of vegetation. This study uses mid-resolution data from Sentinel-2 MSI, Landsat 8 OLI for VI analysis. An initial study to delineate the boundary of the bog using the combination of edge detection and segmentation techniques namely, entropy filtering, canny edge detection, and graph-cut segmentation is performed. Once the bog boundary is defined, spectra of the delineated area are studied. VIs like NDVI, ARVI, SAVI, NDWI, derived using Sentinel-2 MSI and Landsat 8 OLI are analysed. A digital elevation model (DEM) was also used for better classification. All of these characteristics (features) serve as a basis for classifying the bog into broad vegetation communities (termed ecotopes) that indicate the quality of raised bog habitat. This analysis is validated using field derived ecotopes. The results show that, by using spectral information and vegetation index clustering, an additional linkage can be established between spectral RS signatures and wetland ecotopes. Hence, the benefit of the study is in understanding ecosystem (bog) environmental conditions and in defining appropriate metrics by which changes in the conditions can be monitored.

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.

This paper presents results on the characterisation of sediment build-up on roads and footpaths of a residential catchment in Dublin, Ireland. Compared to power and exponential functions, the linear function provided the best fit of the road sediment build-up in terms of total and size-fractionated loads. Significant road sediment build-up rates were recorded for the majority of size fractions on the three street zones sampled, however it was not possible to separate build-up rates between size fractions due to random variation in sediment loads. There was a significant difference in total road sediment build-up between two of the sampling zones, which was likely due to the proximity to a highly trafficked road. Build-up rates on footpaths could not be separated from random variation. Footpath sediment loads were between 6% and 22% of road sediment loads, with texture depth identified as an important difference between these surfaces.

Aerosol observations above the Southern Ocean and Antarctic sea ice are scarce. Measurements of aerosols and atmospheric composition were made in East Antarctic pack ice on board the Australian icebreaker Aurora Australis during the spring of 2012. One particle formation event was observed during the 32 days of observations. This event occurred on the only day to exhibit extended periods of global irradiance in excess of 600 W m−2. Within the single air mass influencing the measurements, number concentrations of particles larger than 3 nm (CN3) reached almost 7700 cm−3 within a few hours of clouds clearing, and grew at rates of 5.6 nm h−1. Formation rates of 3 nm particles were in the range of those measured at other Antarctic locations at 0.2–1.1 ± 0.1 cm−3 s−1. Our investigations into the nucleation chemistry found that there were insufficient precursor concentrations for known halogen or organic chemistry to explain the nucleation event. Modelling studies utilising known sulfuric acid nucleation schemes could not simultaneously reproduce both particle formation or growth rates. Surprising correlations with total gaseous mercury (TGM) were found that, together with other data, suggest a mercury-driven photochemical nucleation mechanism may be responsible for aerosol nucleation. Given the very low vapour pressures of the mercury species involved, this nucleation chemistry is likely only possible where pre-existing aerosol concentrations are low and both TGM concentrations and solar radiation levels are relatively high (∼ 1.5 ng m−3 and ≥ 600 W m−2, respectively), such as those observed in the Antarctic sea ice boundary layer in this study or in the global free troposphere, particularly in the Northern Hemisphere.

Groundwater flooding is a phenomenon which has become recognised as a significant natural hazard in recent years. The Gort lowland karst catchment situated in south Co. Galway on the western coast of Ireland has experienced two extreme groundwater flood events in the past decade leading to considerable damage and disruption. Groundwater flooding in the catchment typically occurs following periods of sustained heavy rainfall when sufficient capacity is not available in the bedrock to store and convey water to the sea. The underground karst conduit system therefore surcharges to the ground surface through a system of estavelles and floods low-lying areas of ground known as turloughs (ephemeral lakes). A 1D/2D pipe network model of the karst conduit system of the Gort lowland karst was developed in order to simulate the flooding mechanisms across the catchment as well as to assess flood alleviation options. The nature of the underground karstic connections in the system has been determined from a combination of available field data (dye tracing, water chemistry data etc.) and cross-frequency analysis on the turlough fluctuation time series data over several years. The availability of high accuracy LiDAR data of the catchment then allowed the flooding regime to be accurately simulated on the ground surface. The model was calibrated using historic continuous water level data for a number of turloughs in the catchment and then validated using historic peak spot flood levels. The model was then used to identify appropriate potential groundwater flood alleviation measures for the catchment. The impacts of such measures on both the salinity of Kinvara bay, through increased freshwater discharges, and eco-hydrology of the protected wetland habitats within the turloughs was also investigated. The study demonstrated that the measures proposed can be developed without inducing undesirable impacts to either salinity in Kinvara Bay (and thus mariculture) or to the protected turlough habitats. The study has also demonstrated the suitability and functionality of such karst models for examining groundwater flood management options and eco-hydrology in karst catchments.

peer-reviewed The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO3−) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH4+) due to limited ability to nitrify NH4+. Vertical flow CWs have good NH4+ removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N2O) emissions but increase methane (CH4) emissions; subsurface flow CWs increase N2O and carbon dioxide (CO2) emissions, but decrease CH4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs. The research was funded by Irish Research Council and Department of Agriculture, Food and Marine in Association with The University of Dublin, Trinity College.

Rising demand for minerals and metals, including for use in the technology sector, has led to a resurgence of interest in exploration of mineral resources located on the seabed. Such resources, whether seafloor massive (polymetallic) sulfides around hydrothermal vents, cobalt-rich crusts (CRCs) on the flanks of seamounts or fields of manganese (polymetallic) nodules on the abyssal plains, cannot be considered in isolation of the distinctive, in some cases unique, assemblages of marine species associated with the same habitats and structures. In addition to mineral deposits, there is interest in extracting methane from gas hydrates on continental slopes and rises. Many of the regions identified for future seabed mining are already recognized as vulnerable marine ecosystems (VMEs). Since its inception in 1982, the International Seabed Authority (ISA), charged with regulating human activities on the deep-sea floor beyond the continental shelf, has issued 27 contracts for mineral exploration, encompassing a combined area of more than 1.4 million km2, and continues to develop rules for commercial mining. At the same time, some seabed mining operations are already taking place within continental shelf areas of nation states, generally at relatively shallow depths, and with others at advanced stages of planning. The first commercial enterprise, expected to target mineral-rich sulfides in deeper waters, at depths between 1,500 and 2,000 m on the continental shelf of Papua New Guinea, is scheduled to begin early in 2019. In this review, we explore three broad aspects relating to the exploration and exploitation of seabed mineral resources: (1) the current state of development of such activities in areas both within and beyond national jurisdictions, (2) possible environmental impacts both close to and more distant from mining activities and (3) the uncertainties and gaps in scientific knowledge and understanding which render baseline and impact assessments particularly difficult for the deep sea. We also consider whether there are alternative approaches to the management of existing mineral reserves and resources, which may reduce incentives for seabed mining.

The complexity of groundwater flooding poses unique challenges to policy makers and flood risk management agencies. An understanding of the interactions among recharge, storage and transport mechanisms during flood conditions is a precursor to effective groundwater flood risk assessment, but is often absent due to a lack of adequate data. The example of the Gort Lowlands, a major lowland karst catchment in the Republic of Ireland, is used to elucidate key flood mechanisms which must be considered when characterising groundwater flood risk in a lowland karst setting. The combination of large quantities of allogenic recharge, a high-capacity conduit system and deep surface depressions renders the catchment susceptible to groundwater flooding. Observed flood mechanisms include backwater flooding of sinks, overland flow caused by the overtopping of sink depressions, high water levels in turlough basins and surface ponding in local epikarst watersheds. Flood hazard maps are developed for the region using data collected during a major flood event in the winter of 2009, representing a significant contribution in the assessment and management of groundwater flood risk in Ireland. Major challenges to groundwater flood management and forecasting remain, however, and are discussed in the context of the prevailing hydrogeological and ecohydrological setting.

Summary 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 16 m3/s with a mean value of 8.7 m3/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 2 m3/s, thus the total mean discharge from both Kinvara Springs was determined to be 11.9–12.3 m3/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 1230 kg/day N and 24.3 kg/day P. This research illustrates the benefits of a numerical modelling approach to the quantification of SGD when used in the appropriate hydrological scenario.

The long-term performance of a constructed wetland treating highway runoff has been studied with respect to heavy metal removal in a temperate, maritime Irish climate. The accumulation of heavy metals in both the sediment and the plants growing in the wetland have been quantified over a 6 year period of operation as well as the spatial distribution of the metals’ deposition. Based on the measured accumulation and projected runoff loads over a 6 year period, the removal efficiencies were 7% (Cd), 60% (Cu), 20% (Pb) and 73% (Zn), values which are much less than the apparent removal efficiencies for the system determined from monitoring the inlet and outlet of discrete storm events which were 95% (Cd), 88% (Cu), 86% (Pb) and 95% (Zn). The study also quantified that an almost negligible mass metals had accumulated in the vegetation compared to the sediment. There was a strong correlation between the spatial accumulation of Cu, Pb and Zn with most of these metals deposited at front of the wetland in the sediment. Finally, although the wetland was initially planted with Typha latifolia over one half and Phragmites australis the other half, after 6 years of operation the Phragmites had spread to colonise almost all of the wetland.

Quantifying the proportion of the river hydrograph derived from the different hydrological pathways is essential for understanding the behaviour of a catchment. This paper describes a new approach using the output from master recession curve analysis to inform a new algorithm based on the Lyne and Hollick ‘one-parameter’ signal analysis filtering algorithm. This approach was applied to six catchments (including two subcatchments of these) in Ireland. The conceptual model for each catchment consists of four main flow pathways: overland flow, interflow, shallow groundwater and deep groundwater. The results were compared with those of the master recession curve analysis, a recharge coefficient approach developed in Ireland and the semi-distributed, lumped and deterministic hydrological model Nedbor-Afstromings-Model. The new algorithm removes the ‘free variable’ aspect that is typically associated with filtering algorithms and provides a means of estimating the contribution of each pathway that is consistent with the results of hydrograph separation in catchments that are dominated by quick response pathways. These types of catchments are underlain by poorly productive aquifers that are not capable of providing large baseflows in the river. Such aquifers underlie over 73% of Ireland, ensuring that this new algorithm is applicable in the majority of catchments in Ireland and potentially in those catchments internationally that are strongly influenced by the quick-responding hydrological pathways. Copyright © 2013 John Wiley & Sons, Ltd.

Summary This research has used continuous water level measurements five groundwater-fed lakes (or turloughs) in a linked lowland karst network of south Galway in Ireland over a 3 year period in order to elucidate the hydrogeological controls and conduit configurations forming the flooded karstic hydraulic system beneath the ground. The main spring outflow from this network discharges below mean sea level making it difficult to determine the hydraulic nature of the network using traditional rainfall–spring flow cross analysis, as has been done in many other studies on karst systems. However, the localised groundwater–surface water interactions (the turloughs) in this flooded lowland karst system can yield information about the nature of the hydraulic connections beneath the ground. Various different analytical techniques have been applied to the fluctuating turlough water level time series data in order to determine the nature of the linkage between them as well as hydraulic pipe configurations at key points in order to improve the conceptual model of the overall karst network. Initially, simple cross correlations between the different turlough water levels were carried out applying different time lags. Frequency analysis of the signals was then carried out using Fast Fourier transform analysis and then both discrete and continuous wavelet analyses have been applied to the data sets to characterise these inherently non-stationary time-series of fluctuating water levels. The analysis has indicated which turloughs are on the main line conduit system and which are somewhat off-line, the relative size of the main conduit in the network including evidence of localised constrictions, as well as clearly showing the tidal influence on the water levels in the three lower turloughs at shallow depths ∼8 km from the main spring outfall at the sea. It has also indicated that the timing of high rainfall events coincident with maximum spring tide levels may promote more consistent, long duration flooding of the turloughs throughout the winter.

[1] In lowland karst areas of Ireland topographic depressions which get intermittently flooded on an annual cycle via groundwater sources are termed turloughs. These are sites of high ecological interest as they have communities and substrate characteristic of wetlands. The flooding in many turlough basins is due to insufficient capacity of the underground karst system to take increased flows following excessive precipitation events, causing the conduit-type network to surcharge. Continuous water level measurements have been taken in five linked turloughs in the lowland karst area of south Galway over a 3 year period. These water level fluctuations, in conjunction with river inputs and precipitation, were then used to elucidate the hydrogeological controls forming the hydraulic system beneath the ground. A model of the karst network has been developed using a pipe network model with the turloughs represented as ponds. The contribution to the karst network from diffuse flow through the epikarst via the matrix and fracture flow has also been modeled using a combination of an infiltration module and network of permeable pipes. The final model was calibrated against two separate hydrological years and in general provided a good simulation for all of the turloughs water levels particularly for the year with one main filling event. The model also accurately picked up the tidal response observed in these turloughs at shallow depths. The model has been used to predict the groundwater discharge to the coast via the main spring which had not heretofore been possible to measure, being below the sea level.

Upward-looking sonar (ULS) instruments have become the primary source of data for high resolution and long duration measurements of sea ice drafts to support engineering requirements for oil and gas exploration projects, along with long-term scientific studies of the underside of the sea-ice canopy in the Arctic and other ice-infested areas. ASL's Ice Profiler Sonar (IPS) has been widely used to provide continuous accurate measurements for ice draft at a horizontal resolution of 1 m, which enables the measurement of ice thickness values over periods from 1–2 seconds up to several years, as well as detailed characterization of many hundreds to thousands of keel shapes and other ice features. In 2014, an important redesign of the IPS instrument was initiated to provide improved performance of the original instrument developed in the 1990s and last upgraded by ASL Environmental Sciences Inc. in 2007–2008.

Summary Ephemeral karst lakes (turloughs) are wetlands at the interface between groundwater and surface water, and are a characteristic feature of the Irish karst landscape. They are transient lakes resulting from a combination of high rainfall and, accordingly, high groundwater levels in topographic depressions in karstified limestone terrain. Turloughs are a valuable example of a Groundwater Dependent Terrestrial Ecosystem (GWDTE), providing a habitat for many floral and faunal species of both national and international importance. The extensive, recurring groundwater floods that originate at turloughs also represent the primary form of groundwater flooding found in Ireland. This study addresses the need for a comprehensive study of turlough hydrology based on quantitative hydrological and topographic parameters. In doing so it takes the first step towards the goals of ensuring the conservation status of these protected ecosystems, as well as providing a basis for determining the hazards associated with groundwater flooding in Ireland. The hydrodynamics of turloughs have been elucidated through the measurement of relevant hydrological parameters, the mapping of topography within turlough basins, and the analysis and interpretation of extensive hydrological datasets over a 3 year period. From this analysis a conceptual understanding of the hydrological operation of turloughs has been developed and the characteristic hydrological diversity of these habitats has been quantified.

peer-reviewed Estimating losses of dissolved carbon (C) and nitrogen (N) via groundwater in an agricultural system provides insights into reducing uncertainties in the terrestrial C and N balances. In addition, quantification of dissolved nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) in groundwaters beneath agricultural systems is important for global greenhouse gas (GHG) budgets. Dissolved C (DC: dissolved organic carbon (DOC) + CO2-C + CH4-C) and dissolved nitrogen (DN: NO3−-N + NH4+ + NO2−-N + N2O-N + N2) in groundwater were measured in two low permeability (0.05 m d−1) aquifers in Ireland. Groundwater in multilevel piezometers was sampled monthly over two years. Mean groundwater discharge to surface water was higher in 2009 (587–836 mm) than in 2010 (326–385 mm). Dissolved C and N delivery to surface water via groundwater caused substantial losses of terrestrial C and N. The extent of delivery was site specific and depended on N input, recharge and aquifer permeability. Mean dissolved N losses ranged from 8–12% of N input in low permeability to 27–38% in high permeability aquifers. The dominant fraction of DN was NO3−-N (84–90% of DN) in high permeability aquifers and N2 (46–77% of DN) in low permeability aquifers. Indirect N2O emissions via groundwater denitrification accounted for 0.03–0.12% of N input, which was equivalent to 3–11% of total N2O emissions. Dissolved C loss to surface waters via groundwater was not significant compared to total carbon (TC) content of the topsoil (0.06–0.18% of TC). Site characteristics contributed greatly to the distribution of N between NO3−-N and dissolved N gases, N2O and N2. Indirect GHG emissions from groundwater were an important part of farm nutrient budgets, which clearly has implications for national GHG inventories. Department of Agriculture, Food and the Marine, Ireland - Research Stimulus Fund Programme (Grant RSF 06383); Department of Civil, Structural and Environmental Engineering, Trinity College Dublin

Irish turloughs are hydrologically dynamic karst wetlands that are frequently used as marginal grazing land. We hypothesised that flood duration (FD) is a key driver of the spatial distribution of selected soil properties, and consequently turlough grazing practices. Six soil samples were collected during dry periods from eighteen turloughs between 2006 and 2008. Samples (n = 104) were analysed for pH, organic matter (OM) content, calcium carbonate content (CaCO3), sand/silt/clay content (INORG), total nitrogen (TN) and total phosphorus (TP). Data on flooding duration, flood frequency, grazing regime and vegetation type were collated for each soil sampling point. Multivariate and univariate statistical analyses were used to examine the relationships between soil properties, grazing regime and flooding variables. There was a positive association between CaCO3, FD and sedge-dominated communities, whereas INORG had a positive association with grazing and grassland. There was a strong positive association between TN, TP, OM and soil depth rather than FD, and OM was found to be an efficient predictor of TN. Extended FDs in ephemeral karst wetlands are likely to increase the extent and degree of calcium carbonate accumulation in soils, thus, reducing the grazing potential of land.

HELDERCUNHA PEREIRA 1*, NORMAN ALLOTT 2, CATHERINE COXON 3, OWEN NAUGHTON 4, PAUL JOHNSTON 4 AND LAURENCE GILL 4 1 CENTRE FOR THE ENVIRONMENT, TRINITY COLLEGE DUBLIN, DUBLIN 2, IRELAND, DEPARTMENT OF ZOOLOGY, TRINITY COLLEGE DUBLIN, DUBLIN 2, IRELAND, 3 DEPARTMENT OF GEOLOGY, TRINITY COLLEGE DUBLIN, DUBLIN 2, IRELAND AND DEPARTMENT OF CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING, TRINITY COLLEGE DUBLIN, DUBLIN 2, IRELAND

Groundwater recharge was investigated in the most extensive sand and gravel aquifer (area of approximately 200 km2) in the Republic of Ireland as part of a wider study seeking to derive recharge estimates using aquifer vulnerability mapping. The proportion of effective rainfall (total rainfall minus actual evapotranspiration) that leads to recharge is known as the recharge coefficient. The recharge investigation involved a variety of approaches, including soil moisture budgeting, well hydrograph analysis, numerical modelling and a catchment water balance. The adoption of multiple techniques provided insights on recharge and also on aquifer properties. Comparison of two soil moisture budgeting approaches (FAO Penman-Monteith with Penman-Grindley) showed how variations in the effective rainfall values from these methods influence groundwater levels simulated in a numerical groundwater model. The catchment water balance estimated the recharge coefficient to be between 81 and 85%, which is considered a reasonable range for this aquifer, where overland flow is rarely observed. The well hydrograph analysis, using a previous estimate of specific yield (0.13), gave recharge coefficients in the range of 40–80%, considered low for this aquifer: a revised specific yield of 0.19 resulted in a more reasonable range of recharge coefficients of between 70 and 100%.

Nutrient contamination of surface and groundwaters is an issue of growing importance as the risks associated with agricultural runoff escalate due to increasing demands on global food production. In this study, the nutrient flux occurring within the surface and groundwaters of a lowland karst catchment in western Ireland was investigated with the aid of alkalinity sampling and a hydrological model. Water samples were tested from a variety of rivers, lakes (or turloughs), boreholes and springs at monthly intervals over three 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 allogenic and autogenic 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, nutrient concentrations were found to reduce over the flooded period, even though the turloughs hydrological functioning (and the hydrological model) suggested this should not occur. 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.

Models of glacio-hydro-isostatic rebound and the concomitant sea-level change have been progressively improved over the past three decades. Recently, the procedures used by the group at the Australian National University (ANU) for the hydro-isostatic component of the theory have been questioned (Quat. Sci. Rev. 21 (2002) 409) although the details of the ANU group's procedures have not been published because they are mainly computational in nature rather than representing significant conceptual advances. Because of this criticism, we set out here in detail the procedures that have been used for the treatment of the migration of shorelines as sea levels rise and fall, the effect of retreat and advancing grounded ice on shelves and shallow seas, and the transitions from grounded to floating ice (and vice versa). We conclude that there is no basis for the criticism, that these formulations and their implementation provide a high resolution and complete description of both sea-level change and of the estimates of volumes of ice exchanged with the oceans. The results from this formulation are confirmed by the entirely independent analyses of Milne et al. (Quat. Sci. Rev. 21 (2002) 361) and Mitrovica and Milne (Geophys. J. Int. (2002), submitted for publication) who conclude that our formulation is significantly more accurate than the procedure advocated by Peltier (Science 265 (1994) 195; Rev. Geophys. 36 (1998a) 603, Geophys. Res. Lett. 25 (1998b) 3955).

Summary It has been proposed that the deglaciation of the Northern Hemisphere triggered large earthquakes within intraplate environments and in this paper we examine this hypothesis by evaluating quantitatively the stress state in the lithosphere produced by time-dependent surface loads. A series of models demonstrate the dependence of horizontal incremental stress in an elastic plate overlying an inviscid or viscoelastic mantle on the lateral extent of a load applied at the surface. The horizontal stress is largest when the dominant wavelength (that is twice the diameter) of the load is close to eight times the elastic thickness of the plate when the mantle is inviscid and, for the particular viscosity model employed in this paper, close to 12 times the elastic thickness for a viscoelastic mantle. At wavelengths close to the critical wavelength, the horizontal incremental stress may be up to six times as large as the vertical incremental stress. For appropriate earth-model parameters amplification of horizontal stress is close to maximum for ice loads with a radius of 280 km, comparable to the dimensions of the former ice sheet over Great Britain. This amplification may be sufficiently large that loading by small ice sheets can lead to failure on marginally stable faults, in contrast to the behaviour for large ice sheets. The models also predict greater fault instability for Fennoscandia than for the larger Laurentide ice sheet, consistent with the observation of large postglacial faults in northern Sweden. The model is used to predict the stability of faults and style of faulting due to rebound stresses in the absence of a background tectonic stress field since the last glacial maximum (∼ 18 000 years ago) in Northern Europe. Within the formerly glaciated region thrust faulting is predicted to occur at the end of deglaciation and normal faulting is predicted to occur in peripheral regions for the entire period since the last glacial maximum.

The nitrogen (N) removal efficiency of constructed wetlands (CWs) is very inconsistent and does not alone explain if the removed species are reduced by physical attenuation or if they are transformed to other reactive forms (pollution swapping). There are many pathways for the removed N to remain in the system: accumulation in the sediments, leaching to groundwater (nitrate-NO3- and ammonium-NH4+), emission to atmosphere via nitrous oxide- N2O and ammonia and/or conversion to N2 gas and adsorption to sediments. The kinetics of these pathways/processes varies with CWs management and therefore needs to be studied quantitatively for the sustainable use of CWs. For example, the quality of groundwater underlying CWs with regards to the reactive N (Nr) species is largely unknown. Equally, there is a dearth of information on the extent of Nr accumulation in soils and discharge to surface waters and air. Moreover, CWs are rich in dissolved organic carbon (DOC) and produce substantial amounts of CO2 and CH4. These dissolved carbon (C) species drain out to ground and surface waters and emit to the atmosphere. The dynamics of dissolved N2O, CO2 and CH4 in CWs is a key "missing piece" in our understanding of global greenhouse gas budgets. In this review we provide an overview of the current knowledge and discussion about the dynamics of C and N in CWs and their likely impacts on aquatic and atmospheric environments. We suggest that the fate of various N species in CWs and their surface emissions and subsurface drainage fluxes need to be evaluated in a holistic way to better understand their potential for pollution swapping. Research on the process based N removal and balancing the end products into reactive and benign forms are critical to assess environmental impacts of CWs. Thus we strongly suggest that in situ N transformation and fate of the transformation products with regards to pollution swapping requires further detailed examination.

The study was funded by Department of Agriculture and Food through the Research Stimulus Fund Programme (Grant RSF 06383) in collaboration with the Department of Civil, Structural & Environmental Engineering, Trinity College Dublin, Ireland. peer-reviewed Over-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N + N2-N) mole fractions were measured in situ with a push–pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002 μg kg−1 d−1, respectively. Estimated N2O-N/(N2O-N + N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53 mg L−1) than no cover crop (0.90 mg L−1) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances.

Observations of sea levels during the Last Glacial Maximum (LGM) at localities far from the former ice margins constrain the global change in ice volume from the LGM to the present at about 52U10 6 km 3 . Regional studies of sealevel change from observations near and within the margins of the former ice sheets constrain ice volumes of the individual ice sheets and have led to an imbalance between the global estimate of ice volume and the sum of the individual ice-sheet volumes. The latter estimates are reliable only when the observational record from localities close to the ice mass extends well into Lateglacial times, which is generally not the case for the major ice sheets. Ice volumes during the LGM and earliest part of the Lateglacial period can therefore be substantially increased without affecting the predictions of Lateglacial and Postglacial sea level in a significant manner, provided that a rapid reduction in ice volume occurred in early Lateglacial time. New far-field data for LGM and Lateglacial sea-level change indicates that a rapid rise in sea level of about 15 m occurred at about 16 500^16 000 14 C (or 19 200^18 700 calibrated) years ago. This leads to the inference that during the LGM the ice sheet volumes of the major ice sheets were greater than inferred from regional rebound analyses and that rapid reductions in volume occurred at the termination of the LGM. The timing of this occurrence does not coincide with any recognised Heinrich event, although pulses of ice-rafted debris originating from both northern ice sheets do occur in some high latitude cores. An Antarctic contribution to the post-LGM melting event also cannot be ruled out, the timing coinciding with evidence for the onset of warming in southern latitudes and the addition of meltwater into the Southern Ocean. fl 2000 Elsevier Science B.V. All rights reserved.

During the Last Glacial Maximum, ice sheets covered large areas in northern latitudes, and global temperatures were significantly lower than today. But few direct estimates exist of the volume of the ice sheets, or the timing and rates of change during their advance and retreat. Here we analyze four distinct sediment facies in the shallow, tectonically stable Bonaparte Gulf, Australia - each of which is characteristic of a distinct range in sea level - to estimate the maximum volume of land-based ice during the last glaciation and the timing of the initial melting phase. We use faunal assemblages and preservation status of the sediments to distinguish open marine, shallow marine, marginal marine and brackish conditions, and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio-hydroisostatic modelling. Our results indicate that from at least 22,000 to 19,000 (calendar) years before present, land-based ice volume was at its maximum, exceeding today's grounded ice sheets by 52.5 x 10 exp 6 cu km. A rapid decrease in ice volume by about 10 percent within a few hundred years terminated the Last Glacial Maximum at 19,000 +/- 250 years.

Late Pleistocene and Holocene sea level change is caused mostly by melting of ice sheets since the Last Glacial Maximum and the Earth's delayed uplift in response to changes in the surface load. Records of sea level change therefore contain information on Earth rheology and ice sheet history and have been used to constrain ice and Earth models. A method is presented which finds an ice model that simultaneously fits the sea level record and the constraints on ice elevation. It infers the ice model which maximizes the smoothness of the surface and thus produces realistic ice models with the minimum detail required to fit the observations. This is a significant improvement on previous work in which the ice model was iteratively improved by ad hoc adjustments resulting in a model that is dependent on the initial model. The method is applied to the British Isles and a model with a spatial resolution of 50 km and temporal resolution of 1000 years is obtained for the late glacial period. Glaciological data determining the maximum elevation of the ice provide an important constraint on the model as does information on the timing of formation of such trimline data. It is possible to infer ice volumes up to a few thousand years before the earliest sea level data, and therefore the availability of early sea level data is most important to constraining ice models for the time of maximum glaciation.

A spherical, self-gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in North America. The predicted onset time of a pulse of earthquake activities, the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin. It is found that glacial unloading is able to trigger paleo-earthquakes within the ice margin near Charlevoix (47.5°N, 70.1°W) and in Wabash Valley (38.5°N, 87°W) outside the ice margin. However, rebound stress decays away from the former ice margin, thus glacial unloading is unlikely to have triggered the large M8 earthquakes in New Madrid (36.6°N, 89.5°W).

SUMMARY The best available rebound model is used to investigate the role that postglacial rebound plays in triggering seismicity in Fennoscandia. The salient features of the model include tectonic stress due to spreading at the North Atlantic Ridge, overburden pressure, gravitationally self-consistent ocean loading, and the realistic deglaciation history and compressible earth model which best fits the sea-level and ice data in Fennoscandia. The model predicts the spatio-temporal evolution of the state of stress, the magnitude of fault instability, the timing of the onset of this instability, and the mode of failure of lateglacial and postglacial seismicity. The consistency of the predictions with the observations suggests that postglacial rebound is probably the cause of the large postglacial thrust faults observed in Fennoscandia. The model also predicts a uniform stress field and instability in central Fennoscandia for the present, with thrust faulting as the predicted mode of failure. However, the lack of spatial correlation of the present seismicity with the region of uplift, and the existence of strike-slip and normal modes of current seismicity are inconsistent with this model. Further unmodelled factors such as the presence of high-angle faults in the central region of uplift along the Baltic coast would be required in order to explain the pattern of seismicity today in terms of postglacial rebound stress. The sensitivity of the model predictions to the eVects of compressibility, tectonic stress, viscosity and ice model is also investigated. For sites outside the ice margin, it is found that the mode of failure is sensitive to the presence of tectonic stress and that the onset timing is also dependent on compressibility. For sites within the ice margin, the eVect of Earth rheology is shown to be small. However, ice load history is shown to have larger eVects on the onset time of earthquakes and the magnitude of fault instability.

Changes in the ice load since the time of the Last Glacial Maximum (LGM) contribute to the present- day vertical motion of the Antarctic continent. The obser- vation of these motions will reveal information on the ice load history. Predictions of uplift rates along a transect across the Lambert Glacier region, East Antarctica, from the coast to the southernmost rock outcrops of the Prince Charles Mountains have been computed for three deglacia- tion scenarios. The relative vertical velocities between sites on the transect are -7 to +7 mm/yr and are large enough to be detected from continuous GPS observations taken at permanent sites over several years. When available, such in- formation will discriminate between the currently available models for deglaciation of East Antarctica.

SUMMARY The rate of change of the spherical harmonic degree 2 component of the Earth’s gravitational potential (CoA 20) and polar wander velocity are two signals which are sensitive to Late Pleistocene deglaciation, current changes in sea level and deep mantle viscosity. Diierent load and earth models have been used in earlier papers to predict the component of these geophysical signals caused by the collapse of the last great ice sheets and recent melting of polar ice caps. In this paper, we present a systematic analysis of the dependence of the predictions on parameters of the ice and earth model. We show that the key parameters of the ice model which govern the predictions are the mass, the location of the centre of mass and the midpoint of the deglaciation phase. Of secondary importance is the length of the deglaciation phase and the mean ice load prior to the Last Glacial Maximum.These conclusions enable us to make a more robust inference of mantle viscosity than has been made before, allowing for the uncertainties in the model of Late Pleistocene and present deglaciation. As previous authors have shown, the lower-mantle viscosity is the most important rheological parameter and therefore theCoA 20 observation complements sea level observations, which are primarily sensitive to lithospheric thickness and the viscosity of the upper part of the mantle. Using realistic constraints on the sizes, locations and timing of deglaciation of the Late Pleistocene ice sheets and current changes in polar ice caps, the observation of CoA 20 is used to infer lower-mantle viscosity as a function of the present rate of sea level change. If the present rate of non-steric sea level change is 1 mm yr {1 and that change has been occurring for less than 1000 years, then the lower-mantle viscosity satis¢es log10 glm~21:82+0:15, which is consistent with inferences drawn from recent sea level analyses and con¢rms other analyses of theCoA 20 observation. If the polar wander signal is produced entirely by postglacial rebound and current sea level change, no more than 20 per cent of the present contribution to global sea level change comes from Greenland. The above conclusions also hold if the density discontinuities at 420 and 670 km are modelled as phase boundaries rather than material (chemical) boundaries.

For several years NO2 and OClO, two species important to understanding ozone destruction in the Antarctic stratosphere, have been measured at Arrival Heights, Antarctica by two groups: New Zealand's National Institute of Water and Atmospheric Research (NIWA) and the NOAA Aeronomy Laboratory in Boulder, Colorado. Using data independently collected by these two groups during the Austral spring of 1996, it is shown that the two data sets are in extremely close agreement. Besides offering validation of the instrumentation and analysis techniques of both groups, this result provides confidence in the more complete history of these species gained by combining the two data sets.

The eustatic component of relative sea-level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles. This has been quantified for the period since the Last Glacial Maximum by correcting observed sea-level change for the glacio-hydro-isostatic contributions using realistic ice distribution and earth models. During the Last Glacial Maximum (LGM) the eustatic sea level was 125±5 m lower than the present day, equivalent to a land-based ice volume of (4.6–4.9)×107 km3. Evidence for a non-uniform rise in eustatic sea level from the LGM to the end of the deglaciation is examined. The initial rate of rise from ca. 21 to 17 ka was relatively slow with an average rate of ca. 6 m ka−1, followed by an average rate of ca. 10 m ka−1 for the next 10 ka. Significant departures from these average rates may have occurred at the time of the Younger Dryas and possibly also around 14 ka. Most of the decay of the large ice sheets was completed by 7 ka, but 3–5 m of water has been added to the oceans since that time.

Northwestern Europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the Last Glacial Maximum. Models for this rebound and associated sea- level change require a detailed knowledge of the ice-sheet geometry, including the ice thickness through time. Existing ice-sheet reconstructions are strongly model-dependent, and inversions of sea-level data for the mantle response may be a function of the model assumptions. Thus inverse solutions for the sea-level data are sought that include both ice- and earth-model parameters as unknowns. Sea-level data from Fennoscandia, the North Sea, the British Isles and the Atlantic and English Channel coasts have been evaluated and incorporated into the solutions. The starting ice sheet for Fennoscandia is based on a reconstruction of a model by Denton & Hughes (1981) that is characterized by quasi-parabolic cross-sections and symmetry about the load centre. Both global (northwestern Europe as a whole) and regional (subsets of the data) solutions have been made for earth-model parameters and ice-height scaling parameters. The key results are as follows. (1) The response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across Scandinavia, the North Sea and the British Isles. (2) This response can be adequately modelled by an effective elastic lithosphere of thickness 65–85 km and by an effective upper-mantle viscosity (from the base of the lithosphere to the 670 km depth seismic discontinuity) of about 3–4×10^20 Pa s. The effective lower-mantle viscosity is at least an order of magnitude greater. (3) The ice thickness over Scandinavia at the time of maximum glaciation was only about 2000 m, much less than the 3400 m assumed in the Denton & Hughes model. (4) The ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi-parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin.

Understanding denitrification rates in groundwater ecosystems can help predict where agricultural reactive nitrogen (N) contributes to environmental degradation. In situ groundwater denitrification rates were determined in subsoil, at the bedrock interface and in bedrock at two sites, grassland and arable, using an in situ ‘push–pull’ method with 15N-labelled nitrate (NO3 −–N). Measured groundwater denitrification rates ranged from 1.3 to 469.5 μg N kg−1 day−1. Exceptionally high denitrification rates observed at the bedrock interface at grassland site (470 ± 152 μg N kg−1 day−1; SE, standard error) suggest that deep groundwater can serve as substantial hotspots for NO3 −–N removal. However, denitrification rates at the other locations were low and may not substantially reduce NO3 −–N delivery to surface waters. Denitrification rates were negatively correlated with ambient dissolved oxygen, redox potential, k s and NO3 − (all p values, p

Ground-based measurements of stratospheric OClO and HCl total columns are reported. The data were obtained during the spring season of 1993 at Arrival Heights (77.8°S/166.7°E), Antarctica, using zenith sky and direct sun absorption spectroscopy in the visible and infrared spectral regions. Together these data sets represent complementary measurements of chlorine species in Antarctica over an extended period in spring. To illustrate aspects of Antarctic stratospheric chemistry and dynamics that are significant in current studies of ozone depletion, the OClO and HCl data are supplemented by simultaneously measured NO2 data as well as ancillary data from other sources. Observations of OClO, HCl and NO2 provide an indication of the degree of the perturbed chemistry that is operating in the spring stratosphere. The measurements illustrate the repartitioning of active chlorine into the less reactive HCl reservoir as spring progresses. Comparison of the data with total ozone and stratospheric temperature records shows that the springtime chlorine variations are in agreement with currently accepted models of Antarctic ozone depletion chemistry.

SUMMARY Observations of sea-level change since the time of the last glacial maximum provide important constraints on the response of the Earth to changes in surface loading on time-scales of 103-104 years. This response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers. Considerable trade-off between the parameters describing these layers can occur, and different combinations can give rise to comparable predictions of sea-level change. In particular, the trade-off between lithospheric thickness and upper-mantle viscosity can be important, and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations. In particular, thin-lithosphere models will lead to low estimates for the upper-mantle viscosity, while thick-lithosphere models lead to high viscosity values. However, either solution may represent only a local minimum in the model parameter space, and may not correspond to the optimum solution. It becomes important, therefore, that in the inversion of observational data, a comprehensive search is conducted throughout the entire model-parameter space, to ensure that the solution identified does indeed correspond to the optimum solution. The sea-level data for the British Isles lend themselves well to such an inversion because of the relatively high quality of the data, the good geographic distribution of the data relative to the former ice sheet, and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat. Furthermore, because of the contribution to the sea-level signal from the distant ice sheets, as well as from the melt-water load, the observational data base for the region also has some resolving power for the viscosity of the deeper mantle. The parameter space explored is defined by up to five mantle layers, the lithosphere of effective elastic thickness D,, and a series of upper-mantle layers, i = 2-4, extending down to depths of 200, 400 and 670 km, respectively, each of viscosity qi, and a lower-mantle layer of viscosity qlm extending down to the coremantle boundary. The range of parameters explored is 30 < D, I 120 km, 3 x lOI9 Iqi

A practical technology based on moored subsea instrumentation has been developed to measure the draft of polar pack ice. The technology exploits the complementary capabilities of an ice-profiling sonar designed and built for the application and of a commercially available acoustic Doppler sonar. The former instrument observes the zenithal range of sea ice passing through its single narrow sonar beam, while the latter observes the radial motion of the ice along its four inclined beams. The sequence of ranges obtained by the ice-profiling sonar is combined with supplementary observations of hydrostatic pressure to yield a sequence of ice draft versus time; the sequence of Doppler speeds provides ice velocity that can be integrated to obtain displacement; by combining the draft and displacement sequences the profile of draft versus position is obtained. The foremost practical problem in calibration is establishing the temporal variation in the zero-draft reference. The technology is well suited to u...

Ground based infrared observations of HNO3 column amount at Lauder, New Zealand (45°S, 170°E), show significant increases in HNO3 following the arrival of Pinatubo volcanic aerosols. The increase first became apparent in September 1991 when the HNO3 amount was higher than that expected from the regular seasonal variation by 2.3 × 1015 cm−2, which corresponds to 16% of the unperturbed value. Between September 1991 and May 1993, the observed HNO3 amounts were systematically higher, typically by 1.5 to 3.5 × 1015 cm−2 or 10 to 30%. After June 1993, the observed HNO3 amounts were close to the unperturbed values. The decrease in stratospheric NO2 due to the volcanic aerosols was observed at Lauder after August 1991 [Johnston et al., 1992, 1993]. The start of the HNO3 increase and the general trend are in agreement with those expected from the NO2 decrease when heterogeneous reactions on the sulfate aerosols are considered. Model calculations, in which observed aerosol fields have been used, qualitatively agree with these observed trends, although the magnitude of the changes have been underestimated. These results provide further understanding of the impact of heterogeneous chemistry on the partitioning between NO2 and HNO3.

The results from an Irish EPA-funded project on the effectiveness of using constructed wetlands for treating wastewater from single households is presented, which has contributed to the design guidelines included in the new EPA Code of Practice. Three subsurface flow gravel-filled wetlands were constructed on separate sites--one to provide secondary treatment and the other two to provide tertiary treatment stages for the domestic effluent. A comprehensive analysis over three years was then conducted to provide a robust characterization of the internal dynamics of the systems, particularly with respect to N and P removal as well as evaluating the temporal water balance across the different seasons. The removal of Total N was only 29% and 30% in the secondary and tertiary treatment wetlands, respectively; particularly disappointing for the tertiary treatment process, which was receiving nitrified effluent. Studies on the (15)N stable isotope confirmed that 35% of the ammonium from the septic tank was passing straight through the process without taking part in any biogeochemical processes. However, influent N in the wetlands was shown to be biologically assimilated into organic nitrogen and then released again as soluble ammonium--so-called nitrogen "spiraling." Removal of Total P in the wetlands averaged from 28% to 45% with higher P removals measured during summer periods, although the effluent concentrations were still found to be high (5 mg/l on average). The phosphorus in the plant material was also analysed revealing that the annual above-ground stem matter only accounted for 1.3% to 8.4% of the annual total P-load in the wetlands. Finally, the water balance analyses showed that the mean flow discharging from both the secondary and tertiary treatment wetlands was slightly greater than the mean flow to the reed bed over the trial period, with rainfall acting to increase flows by 13% and 5%, respectively, on average in winter while just about balancing evapotranspiration in the summer.