Numerically enhanced conceptual modelling (NECoM) applied to the Malta Mean Sea Level Aquifer

Conventional hydrogeological practice is to formulate a conceptual model, which is often the basis of a numerical model. The numerical model is then used to test groundwater management strategies. A workflow is proposed, employing the numerically enhanced conceptual model (NECoM) of the Mean Sea Level Aquifer (MSLA) on the island of Malta. The Malta MSLA is overexploited and under threat of salinization. Data (heads, chloride concentrations, electrical conductivity logs, tidal tests and qualitative analyses) were assimilated into a fast-running numerical model. Simultaneously, strategies for optimal acquisition of further data were examined through the modelling process. The model was delivered through the Energy and Water Agency, with suggestions for flexible model deployment. These workflows will, hopefully, spawn model improvements through further revision of the base concepts. The model allows the agency to make predictions, which have uncertainties that are quantified and reduced through data assimilation as new data become available. Contemplated management plans can therefore be properly assessed before implementation. The proposed NECoM approach can be generalized since it bases model usage on the premise that modelling should make maximum use of existing data by assimilating its information content, thereby highlighting the uncertainties of decision-critical predictions that remain because of data insufficiency. Thus, the presently disjointed process of modelling on the one hand, and data acquisition on the other, can be better aligned. Conceptual and numerical model development become parallel, rather than sequential, activities. Together, they enable predictions of future system behaviour for which bias is reduced and uncertainties quantified.

     

Geological and hydrogeological reconstruction of the main aquifers of the Maltese islands

Hydrogeology Journal - Geological and hydrogeological conceptualizations of the five main aquifers of Malta were performed by means of characterization of the groundwater bodies’ geometries...     

A qualitative risk assessment for the impacts of climate change on nationally and internationally important geoheritage sites in Scotland

Climate change is a significant concern for nature conservation in the 21?st century. One of the goals of the 2014 Scottish Climate Change Adaptation Programme is to identify the consequences of climate change for protected areas and to put in place adaptation or mitigation measures. As a contribution to the process, this paper develops a methodology to identify the relative level of risk to nationally and internationally important geological and geomorphological sites in Scotland from the impacts of climate change. The methodology is based on existing understanding of the likely responses of different types of geosite to specific aspects of climate change, such as changes in rainfall, rising sea levels or increased storminess, and is applied to assess the likelihood of damaging impacts on groups of similar geoheritage features in sites with similar characteristics. The results indicate that 80 (8.8%) of the ～900 nationally and internationally important geoheritage sites in Scotland are at ‘high’ risk from climate change. These include active soft-sediment coastal and fluvial features, finite Quaternary sediment exposures and landforms in coastal and river locations, active periglacial features, sites with palaeoenvironmental records, finite or restricted rock exposures and fossils. Using this risk-based assessment, development of indicative geoheritage climate-change actions have been prioritised for these sites. Depending on the characteristics of the sites, management options may range from ‘do nothing’ to rescue excavations and posterity recording. Monitoring is an essential part of the management process to trigger evidence-based interventions.     

Origin of quartz clusters in Vinalhaven granite and porphyry,coastal Maine

We use the crystallographic orientations of quartz crystals, as determined with EBSD, to provide new evidence for the formation of clustered quartz crystals during magma crystallization. Vinalhaven is dominated by granite, with minor porphyry that formed when granite remelted during input of coeval basalt. CL zoning suggests that most quartz clusters in granite and porphyry formed by synneusis, the “swimming together” of preformed crystals. In granite, most quartz pairs in clusters have random orientations—only about 10% have parallel or Esterel twin orientations. Porphyry has fewer quartz clusters, and all pairs have approximately parallel or Esterel twin orientations. CL zoning of quartz pairs in porphyry indicates that they attached prior to a major remelting event. Interpretation of the Vinalhaven quartz clusters leads us to propose that oriented synneusis occurs during crystal accumulation on a magma chamber floor. During hindered settling, some quartz crystals should have come into contact along their dipyramidal faces. Once in contact, continued settling and loss of interstitial melt may have rotated some quartz crystals such that lattices on their dipyramidal faces matched—producing parallel and Esterel twin orientations and creating strong bonds between pairs. Only a small proportion of pairs with matched dipyramidal faces formed in the granite and, during rejuvenation to produce porphyry, only these oriented pairs survived. Hence, the presence of oriented synneusis in a plutonic rock may demonstrate a history of crystal accumulation.     

The typology of Irish hard-rock aquifers based on an integrated hydrogeological and geophysical approach

Groundwater flow in hard-rock aquifers is strongly controlled by the characteristics and distribution of structural heterogeneity. A methodology for catchment-scale characterisation is presented, based on the integration of complementary, multi-scale hydrogeological, geophysical and geological approaches. This was applied to three contrasting catchments underlain by metamorphic rocks in the northern parts of Ireland (Republic of Ireland and Northern Ireland, UK). Cross-validated surface and borehole geophysical investigations confirm the discontinuous overburden, lithological compartmentalisation of the bedrock and important spatial variations of the weathered bedrock profiles at macro-scale. Fracture analysis suggests that the recent (Alpine) tectonic fabric exerts strong control on the internal aquifer structure at meso-scale, which is likely to impact on the anisotropy of aquifer properties. The combination of the interpretation of depth-specific hydraulic-test data with the structural information provided by geophysical tests allows characterisation of the hydrodynamic properties of the identified aquifer units. Regionally, the distribution of hydraulic conductivities can be described by inverse power laws specific to the aquifer litho-type. Observed groundwater flow directions reflect this multi-scale structure. The proposed integrated approach applies widely available investigative tools to identify key dominant structures controlling groundwater flow, characterising the aquifer type for each catchment and resolving the spatial distribution of relevant aquifer units and associated hydrodynamic parameters.     

Scaling up point-in-space heat tracing of seepage flux using bed temperatures as a quantitative proxy

It is challenging to quantify reach-scale surface-water–groundwater interactions, while maintaining the fine-scale spatial resolution required in hyporheic studies. One-dimensional heat-transport modeling was used to simulate streambed fluxes at discrete points using time-series temperature records. A predictive relationship was then developed between point-in-time streambed temperature and modeled flux rates. Flux was mapped at high spatial resolution by applying the predictive relationship to mapped streambed temperatures, which allowed for high-resolution quantification of flux by proxy. Inferred patterns of flux are consistent with morphology and yielded a net flux to a 30-m stream reach of 1.0?L s^–1. Discharge of saline groundwater (5.7?g L^–1 Cl^–) allowed for comparison between the temperature proxy method and geochemical variability. Maximum upwelling locations (>35 cm day^–1) were spatially coincident with areas of high conductance at the bed interface (5–25?mS cm^–1). Differences between gross flux estimates from heat and geochemical methods are attributed to differences in the spatial extent over which estimates were derived and limited sensitivity of the temperature-as-proxy method. When bed temperatures are near their inherent limits (groundwater and stream-water temperatures) the flux magnitude can be underestimated. Caution must be used when determining gross, reach-scale fluxes from temperature-as-proxy methods when flux rates are outside the sensitivity limits.     

Imaginative geographies of gender and HIV/AIDS: moving beyond neoliberalism

This paper examines how neoliberal development discourse contributes to the production and maintenance of problematic gendered hierarchies and spaces. By interrogating the basic assumptions undergirding this discourse, this paper explores how neoliberalism produces spaces which normalise certain identities—especially those associated with individualism and economic rationality, and makes errant values such as communalism and altruism. Drawing on perspectives from feminist geographies, we argue that by normalising and privileging certain masculine identities, neoliberalism reinscribes and legitimizes gendered power relations that are counterproductive to addressing HIV/AIDS. The ‘ideal’ person fighting HIV/AIDS in the neoliberal framework is rational, competitive and self-interested, but these characteristics are complicit in worsening HIV prevalence and mobilize problematic gender roles and identities. Given the pervasiveness of this ideology in Malawi, we propose ways in which families, communities and institutions can challenge and reshape gender identities and potential solutions to HIV within this context.     

Chemical evolution of shallow playa groundwater in response to post-pluvial isostatic rebound, Honey Lake Basin, California–Nevada, USA

The 1,750-km² endorheic Honey Lake basin (California–Nevada, USA) was part of the 22,000-km² Pleistocene Lake Lahontan pluvial lake system which existed between 5,000 and 40,000 years BP. The basin consists of two subbasins separated by a low elevation divide. Groundwater in the western subbasin has a maximum total dissolved solids (TDS) content of only ～1,300 mg/L; however eastern subbasin groundwater has a maximum TDS of ～46,000 mg/L. This TDS distribution is unexpected because 94% of surface water TDS loading is to the western subbasin. In situ reactions and upwelling thermal groundwater contributing to groundwater chemistry were modeled using NETPATH. The TDS difference between the subbasins is attributed to post-Lake Lahontan isostatic rebound about 13,000 years ago. Prior to rebound the subbasins did not exist and the low point of the basin was in the eastern area where hydraulic isolation from the larger Lake Lahontan and frequent desiccation of the basin surface water resulted in evaporite mineral deposition in accumulating sediments. After rebound, the terminal sink for most surface water shifted to the western subbasin. Although most closed basins have not been impacted by isostatic rebound, results of this investigation demonstrate how tectonic evolution can impact the distribution of soluble minerals accumulating in shallow basins.