11. Hydrogeology

11.1. Groundwater transport in cold, changing climates: theory, experiments, models

11.2. Groundwater – surface water interaction; chemical and quantitative impacts on rivers, lakes, wetlands, fjords and coastal areas.

11.3. Integrated Hydrological Modeling

11.4. Open session Hydrogeology

11.1. Groundwater transport in cold, changing climates: theory, experiments, models

                       ORAL PRESENTATIONS                    

Modelling snowmelt infiltration in a seasonally-frozen soil monitored by electrical resistivity measurements

Helen Kristine French¹, Andrew Binley² and Cliff Voss^3
1Norwegian University of Life Sciences, ²Lancaster Environment Centre, Lancaster University, UK, ³U.S. Geological Survey, Menlo Park, CA 94025 USA
Infiltration during snowmelt can be highly heterogeneous due to the formation of ice on the ground surface below the snow cover. In situations where snow is contaminated, such as along highways and airports due to de-icing agents, the area that takes part in the early infiltration will determine the retention time and potential for degradation in the unsaturated zone. In 2001, French and Binley (2004) observed a highly variable snowmelt infiltration over a small area at Gardermoen, Norway, monitored with time-lapse electrical resistivity measurements. In this study, we want to test the suitability of a newly developed numerical model for water and heat transport including phase change (modified version of SUTRA_ICE, described in McKenzie et al.,2007) in a variably saturated soil against field observations. Monitored weather and snow melt data defined the boundary conditions of a simulated unsaturated profile with seasonal freezing. The dependency of capillary pressure and permeability on water saturation is taken from the van Genuchten equation. Soil physical data and heterogeneity was based on local soil measurements. Different infiltration scenarios were tested. Soil temperatures, TDR measurements of soil moisture, a tracer experiment conducted at an adjacent site and changes in electrical resistivity were used to validate the model of infiltration and thawing. The model was successful in reproducing the thawing and soil moisture patterns observed in the soil, and hence looks like a promising tool for predicting snowmelt infiltration and melting of ground frost in a sandy unsaturated soil.

References
French, HK and Binley, A (2004) Snowmelt Infiltration: Monitoring Temporal and Spatial Variability using Time-Lapse Electrical resistivity. J. of Hyd., 297, 1-4, 174-186

McKenzie JM, Voss CI, Siegel DI (2007) Groundwater flow with energy transport and water-ice phase change: simulations, benchmarks, and application to freezing in peat bogs. Adv. Water Resources, 30:4 966-983 doi:10.1016

Numerical simulations of temperature-dependent transport in waste rock piles in permafrost-dominated environments

Daniele Pedretti¹ and Leslie Smith^2
1Geological Survey of Finland (GTK), ²University of British Columbia (UBC)
Waste rock piles (WRPs) contain unsaturated materials that can yield water with elevated solute concentrations as a consequence of sulphide mineral oxidation. Tracer tests can be used to provide insight to transport properties that affect the evolution of the effluent water quality over time. In cold environments, flow and transport are also affected by variably freezing conditions within the pile, a process that complicates the interpretation of tracer tests.

This contribution describes a numerical model simulating conservative solute transport in a homogeneous WRP with temperature-dependent boundary conditions and variably freezing cycles within the pile. The conceptual model is based on the experimental waste rock piles at the Diavik Diamond Mine in northern Canada, located in an area of continuous permafrost.

The results illustrate the key role of an explicit solution of temperature-dependent flow conditions to evaluate the seasonal and annual release of solute loads. The model illustrates the annual drainage cycles in the core of the pile, which were hypothesized to be characterized by distinct spring flushes and steady decline in flow prior to freeze-up. Solutes move within the unfrozen core of the pile even when the external portion of the pile starts to freeze. The temperature boundary conditions affect the (transient) flow geometry within the piles, and can complicate the interpretation of tracer tests. In particular, an apparent dual-porosity-like effect is produced on solute breakthrough curves even when the pile is physically simulated as a hydraulically and geochemically homogeneous single porosity domain.

Groundwater levels real time monitoring and visualization software demonstrated for Precambrian valley sediment aquifers in Ostrobothnia, W Finland

Niko Putkinen¹, Holger Kessler², Ben Wood², Elina Lindsberg¹, Harri Issakainen¹, Tero Rönkkö¹, Esa Kauniskangas¹ and Miikka Paalijärvi^1
1Geological Survey of Finland, ²Brittish Geological Survey
Old buried Precambrian valleys in Ostrobothnia, Kurikka, W Finland play a major role in the groundwater system and will ensure the future municipal drinking water supply for over 150000 people. Several year’s of intensive hydrogeological studies include 70 boreholes to the bedrock, ~200 km gravity measurements, numerous seismic profiles in the 100km2 study area. According to the reported results, it is possible to conclude the bedrock structures promote the most conductive hydrogeological units interlinks between faults, fractures and other structures, the topography of the glacially eroded bedrock surface and the overlying weathered bedrock surface and 50-100m thick highly variable glacial deposits include several confined – semi confined sand and gravel sediment aquifers and clayey till and marine silt aquitards.

In this project GTK and BGS are working together for water companies on developing free–to-use geological software for use in hydrogeological investigations and environmental monitoring. Data (e.g. gw-levels) will be collected in the field in real-time using an innovative sensor technique. The project will develop visualization capability for this data and interpolation routines will be added, allowing analysis of trends across monitoring sites. Connections to GTK corporate databases will be established, making data exploration simple and intuitive for GTK geoscientists and the supervising authority. Sharing real time groundwater data in Groundhog Desktop, and visualizing interactively in maps, logs and cross-sections, will significantly help environmental agencies to monitor and control the sustainable use of water.

                       POSTER PRESENTATIONS                    

Subpermafrost Groundwater and Pingos in Adventdalen

– Evaluating the Implication of Holocene Permafrost Formation in Near Coastal Areas –

Mikkel Toft Hornum¹, Peter Engesgaard², Søren Jessen³ and Andy Hodson Professor at UNIS
¹Master student at UCPH, guest master student at UNIS, ²Professor at UCPH, ³Associate professor at UCPH
In previously glaciated areas of the Arctic, substantial isostatic rebound and associated relative sea-level fall have lead to Holocene permafrost formation in former shallow marine areas. The study area for this work is Adventdalen in Svalbard, a glacial valley for which an extensive amount of research on geological and permafrost-related subjects exists. The implications of this landscape’s history for subpermafrost groundwater is investigated in three ways: 1) Electrical Resistivity Tomography (ERT) surveys around a pingo enable location of intrapermafrost groundwater flow paths. 2) A decoupled 1D/2D heat and groundwater flow model provides quantitative estimates of the potential discharge from the subpermafrost groundwater system as permafrost aggrades. 3) Artesian springs at three pingos facilitate hydrogeochemical interpretation of controlling processes along groundwater flow paths. Results from the flow and heat transport models suggest that the permafrost thickness has not yet reached equilibrium, and so frozen ground might still be developing in the lowest part of the permafrost. This implies that groundwater discharge from the subpermafrost aquifer could be driven by permafrost aggradation, leading to the artesian springs seen at the pingos. However, the spring water analyses show complex hydrogeochemistry probably due to freeze and thaw processes, although a common source is probable and a subpermafrost origin seems most likely. On the basis of the model results and the ERT, a new conceptual model of open-system pingo formation will therefore be presented.

11.2. Groundwater – surface water interaction; chemical and quantitative impacts on rivers, lakes, wetlands, fjords and coastal areas.

                       ORAL PRESENTATIONS                    

Groundwater discharge and recharge patterns in complex aquifer system in a mine exploration area in Northern Finland

Susanne Charlotta Åberg¹, Kirsti Korkka-Niemi¹ and Veli-Pekka Salonen^1
1Department of Geosciences and Geography, University of Helsinki, P.O. Box 64, 00014 Helsinki
A prominent Cu-Ni showing named to as Sakatti has been discovered in Sodankylä (Brownscombe et al. 2015), close to Kitinen river and below the Natura 2000 protected Viiankiaapa mire. Understanding of the interaction of surface and groundwater is essential for sustainable ore exploration and development. However, the complexity of the sedimentation history of the surficial deposits makes the groundwater occurrences scattered and elusive. The mire hydrology and its relationship with groundwater recharge–discharge patterns is also crucial for mire vegetation, but has seldom been studied in Finland (Laitinen et al. 2005). Understanding groundwater-surface water interaction areas is also important when protecting habitats of groundwater dependent ecosystems (GDE).

MODFLOW-NWT model was utilized for defining the groundwater recharge and discharge patterns and to relate them with GDEs in the area. Hydrostratigraphic units of the model based on the previously created conceptual sedimentary model (Åberg et al. 2017). At the same time annual groundwater table fluctuation was studied from monitoring wells for definition to initial recharge rates. The recharge parameters were calibrated with parameter estimation. Hydraulic conductivities were manually calibrated with interpolation from previous k-value calculations. The model results indicated that major flow direction is towards the Kitinen river. The model underestimated the distribution of the discharge zone within mire area. It also slightly overestimated the recharge rates. The fluxes from the bedrock are needed in order to get more reliable results. Flow modelling was found to be effective tool for evaluating the conceptual sedimentary model.

References
Brownscombe W., Ihlenfeld C., Coppard J., Hartshorne C., Klatt S., Siikaluoma J.K. & Herrington R.J. 2015. Chapter 3.7 – The Sakatti Cu-Ni-PGE Sulfide Deposit in Northern Finland. In: O’Brien W.D.M.L. (ed.), Mineral Deposits of Finland, Elsevier, pp. 211-252.

Laitinen J., Rehell S. & Huttunen A. 2005. Vegetation-related hydrotopographic and hydrologic classification for aapa mires (Hirvisuo, Finland). In: Annales Botanici Fennici, JSTOR, pp. 107-121.

Åberg A.K., Salonen V.-P., Korkka-Niemi K., Rautio A., Koivisto E. & Åberg S.C. 2017. GIS-based 3D sedimentary model for visualizing complex glacial deposition in Kersilö, Finnish Lapland. Boreal Environment Research 22: 277–298.

Coastal groundwater in Western Sweden: Hydrogeological and societal challenges

Roland Barthel¹, Markus Giese¹, Ezra Haaf¹, Ingmar Geuze¹ and Michelle Nygren^1
1Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
Groundwater at the Swedish coast occurs in fractured bedrock or in isolated, shallow quaternary sedimentary formations. Those resources are of limited interest for public water supply. However, a large and growing number of poorly regulated private wells create an increasing pressure on groundwater in attractive coastal areas and on islands.

The “Koster” archipelago forms a microcosm of coastal groundwater problems in Sweden. Koster’s geology is dominated by fractured, crystalline bedrock, occasionally overlain by quaternary deposits. With around 300 permanent residents, and up to 6,000 summer guests in peak holiday season, the existing water supply based on 800 private wells reaches a limit. Water availability forms an obstacle to future development and the current situation is regarded as being unsustainable.

Groundwater on Koster was monitored over a period of 1.5 years. All observations were made in about 220 private, pumped wells. 350 samples were analysed for major ions and metals. Groundwater levels and in situ physicochemical parameters were measured at six occasions, and data loggers were installed in 10 wells.

Studies dealing with saltwater intrusion in fractured (bedrock) aquifers are rare. The hydrogeological assessment on Koster thus reveals interesting new insights into coastal groundwater in crystalline rock formations. However, the dominating management problem on Koster appears to be rather a combination of a lack of national regulations and an overly complex framework of responsibilities. This contribution attempts to combine hydrogeological and societal aspects and draws some wider-ranging conclusions on the relation between hydrogeological research and its application in decision making processes.

Spatial variability of water and nutrient fluxes in groundwater discharging to Ringkøbing Fjord

Carlos Duque¹, Joel Tirado-Conde², Sachin Karan³, Janja Svetina¹, Søren Jesen² and Peter Engesgaard^2
1Aarhus University, ²University of Copenhagen, ³Geological Survey of Denmark and Greenland (GEUS)
River and groundwater discharge to coastal waters bring nutrients that may cause eutrophication, algal blooms or hypoxic events. The quantification of nutrient discharge to coastal waters is essential for the management these areas and it is especially relevant in estuaries with a limited flushing by seawater. The quantification of the groundwater component is challenging since it takes places in the subsurface and under the water. Often it is estimated indirectly based on water budgets or regional numerical models on the scale of the estuary or study area. Likewise, the quantification of nutrient loading is usually carried out by assuming an average concentration. Nevertheless, it is well known that groundwater discharge, as well as nutrient concentrations are highly variable over short distances. This introduces uncertainties in the quantification of coastal nutrient exports. In this work, the spatial variability of the groundwater discharge and the groundwater nitrate and phosphorus concentration to Ringkøbing Fjord is measured directly at the horizontal and vertical meter scale to assess the range of variability that can be considered at these environments. The data are compared with the hydraulic conductivity measurements to investigate the potential correlations between fluxes, nutrient concentration level, and hydraulic conductivity at variable distances from shore and depths below the seafloor.

Use of Water Stable Isotopes and End Member Mixing Analysis to Map and Quantify Groundwater Exchange with Lakes

Peter Engesgaard¹, Ingeborg Solvang² and Emil Kristensen^3
1Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark, ²Multiconsult Norge AS, avd. Bergen, Norway, ³Freshwater Biological Laboratory, Department of Biology, University of Copenhagen, Denmark
Groundwater-lake exchanges are important in order to establish water budgets for lakes.

We used water stable isotopes (¹⁸O) to map discharge and recharge zones. In groundwater downstream of lake recharge zones (lake water seeping to groundwater) one expects to find a signal similar to that of the lake (typically enriched in ¹⁸O compared to groundwater) and in groundwater discharge zones, one expects to find a groundwater signal.

However, concentrations are ‘noisy’ due to rainfall-evaporation processes, groundwater flow, changes in residence time etc. An End Member Mixing Analysis accounting for end member uncertainty (rainwater, groundwater and lake water) was used to map seepage zones at Lake Tvorup Hul in National Park Thy, Denmark. A two-component analysis (Electrical Conductivity (EC) and 18O) was also used to better constrain the analysis under the assumption that EC behaved as a conservative tracer.

The 4 ha lake is located in sandy deposits. ¹⁸O and EC were measured in 30 wells (depth of 1.25 m) around and close to the lake. End member concentrations and uncertainty were determined by sampling groundwater in wells on the discharge side, as well as lake water and rainfall.

¹⁸O and EC were robust tracers able to identify discharge (South) and recharge (West, North) zones. On the Eastern shore the analysis showed a mixture of discharge/recharge explained by the proximity to a water divide and/or a more complex geology with near-surface clay and chalk. The identified seepage zones agree with an iso-potential map and spot measurements of seepage.

An integrated and coupled surface/subsurface water model to estimate lake hydrologic and biogeochemical budgets over Northern lake-rich regions

Zachary Hanson¹, Jacob Zwart¹, Alan Hamlet¹, Stuart Jones¹ and Diogo Bolster^1
1University of Notre Dame
Lakes are intense biogeochemical processors and play key roles in the global carbon cycle. However, to date large-scale models rely on multiplying a mean observed areal rates by regional or global lake surface area, treating all lakes as the same. This ignores the heterogeneous nature of these systems and their static nature renders them incapable of predicting how lake carbon cycling will change under future global change scenarios. To rectify this, we developed a process-based model incorporating surface and groundwater hydrology, physics, and ecology. The model can be applied over large geographic regions to hindcast and forecast lake hydrologic and carbon fluxes. We applied our model to simulate lake levels and daily carbon fluxes and pools for 3675 lakes in the Northern Highlands Lake District (NHLD), Wisconsin, USA from 1980-2010. The model produces patterns consistent with observations. We show that variability in lake carbon fluxes are related to some simple hydrologic metrics, such as the fraction of hydrologic export as evaporation. This can then predict important carbon processes and fluxes for the region. Hydrologic characteristics were evenly distributed across lake sizes; therefore, median areal lake carbon emissions and burial across the lake size gradient were similar, which meant that large lakes constitute an overwhelmingly large proportion of the total lake carbon flux for the region. Preliminary results forecasting behaviors over the next 50 years under climate change suggest dramatic changes in hydrologic and biogeochemical characteristics in the region.

Investigating groundwater contribution to lakes in clay dominated catchments

Jacob Kidmose¹, David Lajer Juul Kristensen², Catharina Simone Nisbeth² and Søren Jessen^2
1Geological Survey of Denmark and Greenland, ²University of Copenhagen
Groundwater discharge to lakes is normally investigated in geological environments dominated by permeable, high hydraulically conductive sediments, which can facilitate the groundwater-surface water interaction. This includes, for example, lakes set in glacial meltwater outwash planes comprising coarse-grained sandy aquifers. In other investigations, a sand, chalk, or other water baring hydrogeological units, are in contract with some parts of the lake, either in a bathymetrical deeper part, or in a horizontal zone of the lake. Few studies has been carried out in hydrogeological settings where the upper 10-20 meters near surface geology are dominated by low permeable materials as clays. Groundwater inputs, or exchanges with lakes in such hydro-geological settings are generally believed to be small and therefore often ignored in water balance calculations.

The presented study investigates the groundwater component in the water balance for a lake located on the island of Funen, Denmark. The lake rests upon 20 meter of low permeable till moraine clay which overlays an artesian aquifer, as indicated by piezometric heads and the occurrence of a spring located on a small island on the lake. Evaluation of the water balance combines results from continuous water quantitative and qualitative measurements at 11 surface inlets, 1 outlet and at the spring. Furthermore, in order to understand the physiography of the lake–aquifer system, geophysical surveys are conducted. The measured water fluxes shows an important discharge of groundwater to the lake, supported by isotopic analysis. Groundwater modelling is used to validate the measured water balance of the lake.

Geo-hydro-ecological factors affecting the distribution of endangered species of Viiankiaapa mire, in ore prospecting site

Kirsti Korkka-Niemi¹, Anne Rautio¹, Paula Bigler¹ and Susanne Åberg^1
1University of Helsinki, Department of geosciences and geography
Potential impacts of ore prospecting, as well as mining development activities, are often related to surface and groundwater resources and their interactions. A prominent Cu-Ni-PGE sulphide discovery named Sakatti has been discovered below the Natura 2000 protected Viiankiaapa mire, in Northern Finland. It is important to understand the possible association of the mire vegetation with groundwater–surface water interactions, as well as the geochemical features of the local bedrock.

This study aims to answer the question of how much the hydrological and hydrogeochemical factors control the patterns of endangered vegetation in Viiankiaapa mire. Especially in the areas rich in Hamatocaulis vernicosus, groundwater recharge-discharge patterns have been compiled on the basis of data collected by field studies, thermal infrared (TIR) remote sensing and laboratory analyses. Groundwater flow patterns have been determined by measuring water tables in observation wells and peat layers. Water samples (N=137) have been taken from groundwater and from peat layer, in order to determine the variations in water chemistry including stable isotopes, dissolved silica, main ions, pH, EC, DOC and trace elements. TIR survey using unmanned aerial vehicle has been used in order to observe groundwater discharge locations in the mire and to assess if endangered species prefer groundwater influenced habitats.

Temperature anomalies were detected, indicating cold groundwater discharging into the soil surface at some locations in the studied mire. Groundwater and surface water chemistry revealed significant vertical and horizontal variation. Geochemical stratification in peat layers could be observed in pH, EC, stable isotopes and some dissolved elements.

References
Korkka-Niemi, K., Rautio, A., Bigler, P., Åberg, S. 2017. Characterization of Geo-Hydro-Ecological Factors Affecting the Distribution of Endangered Species of Viiankiaapa Mire, in Ore Prospecting Site. – In: Wolkersdorfer, C.; Sartz, L.; Sillanpää, M. & Häkkinen, A.: Mine Water & Circular Economy (Vol II). – p. 1022 – 1029.

Lacustrine groundwater discharge and its relevance for eutrophication

Jörg Lewandowski¹, Karin Meinikmann¹, Gunnar Nützmann¹ and Donald O. Rosenberry^2
1Leibniz-Institute of Freshwater Ecology and Inland Fischeries and Humboldt University Berlin, ²US Geological Survey, Denver, Colorado, United States
Eutrophication is still a major threat to lakes. Typical anthropogenic nutrient sources include fertilizers, manure and sewage. As a first step towards an effective lake management all nutrient import pathways need to be precisely quantified. Nutrient loading via some pathways, for example streams, can be easily quantified quite accurately. The estimation of nutrient import to lakes by lacustrine groundwater discharge (LGD) is usually much more difficult. We discuss some reasons why LGD has often been underestimated and disregarded in lake nutrient budgets. We give a brief overview of measurement techniques, and present volumes, concentrations and loads reported in literature for LGD. Most measurement techniques are based on separate determinations of seepage volume and nutrient concentration of exfiltrating groundwater, and then multiplying both values. Concentrations of groundwater compounds vary along the flow path from the catchment to the lake. Especially the aquifer-lake interface is often considered a reactive zone. We describe the fate of nitrogen and phosphorus on their subsurface pathway from the catchment through the reactive interface into the surface water body. As a case study we present results from Lake Arendsee (Germany) where LGD is the major driver of intense eutrophication in the lake. More than 50 % of the total P load is of groundwater-borne origin in this case.

“Translating” a density-independent groundwater model into a SEAWAT model

Thomas Ljungberg^1
1Department of Geoscience, Aarhus University.
In coastal regions, the higher density of the saline groundwater influences the flow pattern of the lighter fresh/brackish groundwater as it makes its way to the sea. In order to get the best possible understanding of the flow patterns when modelling such coastal aquifers it is necessary to take the density difference into account, e.g. by setting up a SEAWAT model. However, SEAWAT can easily become unstable if the cell volumes across the model are not uniform, and it does best if several model layers represent each geological unit [Guo & Langevin, 2002]. These requirements make it difficult to assign values of hydraulic parameters to the model, as the geological units rarely are uniformly distributed across the modelled area. Besides this, when considering density differences and solute transport, the complexity of the calculations means that the runtime of such a model is much longer than for a density-independent model of the same system. In my Master’s thesis I set up a 5-layer density-independent MODFLOW model with non-uniform cell volumes, and calibrated it from measurements of hydraulic head. Subsequently, this model was “translated” into a 10-layer density-independent model with uniform cell volumes, and then further developed into a SEAWAT model, and it was shown that these three models produced very similar results, as far as hydraulic heads go. In this talk I will present the technique that was used for translating the model, and show that the models do indeed produce similar results.

References
Guo, W. & Langevin, C. D. 2002: User’s guide to SEAWAT: A Computer Program for Simulation of Three-Dimensional Variable-Density Groud-Water Flow. U.S. Geological Survey. Techniques of Water-Resources Investigations 6-A7.

Developing methods to assess quantitative and chemical contact between groundwater and the various surface water bodies in relation to update of river basin management plans in Denmark

Bertel Nilsson¹, Lars Troldborg² and Lærke Thorling^3
1Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen, Denmark., ²Geological Survey of Denmark and Greenland (GEUS), C.F. Møllers Allé 8, Bygning 1110, , Denmark., ³Geological Survey of Denmark and Greenland (GEUS),C.F. Møllers Allé 8, Bygning 1110, 8000, Denmark.
The European Water Frame Directive (WFD) sets out objectives for the water environment. These include the protection of, enhancement and restoration of surface water, groundwater and groundwater dependent terrestrial ecosystems (GWDTE).

The Geological Survey of Denmark and Greenland has in collaboration with Aarhus University recently started developing methods to assess the chemical and quantitative interaction between groundwater bodies, rivers, lakes, coastal water and GWDTE. The task is to review national monitoring programs in terms of how well the data collection on hydrological and chemical data capture the potential interaction between the around 400 Danish groundwater bodies and surface water bodies. The hydraulic contact between the groundwater, rivers, lakes and coastal water will be quantified using a national hydrological model for Denmark. Results and experiences obtained on the various parts of the hydrological cycle will be presented. The work is funded by the Danish EPA.

Using the stable oxygen isotope of phosphate as a tracer for various phosphorus sources to Lake Nørresø, Denmark.

Catharina S. Nisbeth¹, David W O’Connell² and Søren Jessen^1
1University of Copenhagen, Dept. of Geosciences and Natural Resource Management, Copenhagen, Denmark, ²Department of Civil and Environmental Engineering, Trinity College Dublin, College Green, Museum Bui
Eutrophication of freshwater ecosystems is in particular sensitive to phosphorus input. Thus, identifying the different phosphorus sources and their relative fraction of the total phosphorus load is essential for restoration and improvement of eutrophic aquatic ecosystems. Analyzing the oxygen isotopes of phosphate (δ¹⁸Op) of phosphate in the various PO₄ fractions could provide the necessary knowledge for tracing the origin of the different phosphorus sources. Furthermore, δ¹⁸Op could also be used to identify which sources are most significant in the degradation of the associated freshwater ecosystems at a local scale. The method utilizes that the P-O bond in the orthophosphate, is resistant to inorganic hydrolysis at temperatures and pH levels found in natural abiotic aquatic ecosystems. Subsequently, the δ¹⁸Op will reflect the isotopic signature of the sources ¹. However, biological activity alters the source δ¹⁸Op signatures, which leads to an isotopic equilibrium between the ambient water and the phosphate ².

This method is contingent upon an extended knowledge of the δ¹⁸Op signatures from different phosphate sources. Nonetheless, the various source signatures have not yet been entirely evolved and more research has to be conducted in order to constrain these signatures further.

This study focuses on identification of the δ¹⁸Op signatures for the main phosphate sources to the eutrophic lake, Nørresø, in Denmark. The aim was to i) identify which of the phosphate sources constituted the largest fraction of the total phosphate input to the lake, and ii) investigate if some of the sources in fact came from the same place of origin.

References
1.       Tamburini, F., Bernasconi, S. M., Angert, A., Weiner, T. & Frossard, E. A method for the analysis of the δ¹⁸O of inorganic phosphate extracted from soils with HCl. Eur. J. Soil Sci. 61, 1025–1032 (2010).

2. Blake, R. E., O’Neil, J. R. & Surkov, A. V. Biogeochemical cycling of phosphorus: Insights from oxygen isotope effects of phosphoenzymes. Am. J. Sci. 305, 596–620 (2005).

Trophic state control of groundwater-fed ecosystems by groundwater-borne phosphorus

Catharina Simone Nisbeth¹, Jacob Kidmose², Kaarina Weckström³, Kasper Reitzel⁴, Bent Vad Odgaard⁵, Aia Aistrup Eriksen⁵, Ole Bennike⁶, Bertel Nilsson², Lærke Thorling⁷, Suzanne McGowan⁸, Anders Schomacker⁹, Marie-Louise Siggaard-Andersen⁹, David Lajer Juul Kristensen¹ and Søren Jessen^1
1Department of Geosciences and Natural Resource Management, University of Copenhagen, ²Department of Hydrology, Geological Survey of Denmark and Greenland, ³Department of Environmental Sciences, University of Helsinki, ⁴Department of Biology, University of Southern Denmark, ⁵Department of Geoscience, Aarhus University, ⁶Department of Marine Geology, Geological Survey of Denmark and Greenland, ⁷Groundwater and Quaternary Geology Mapping, Geological Survey of Denmark and Greenland, ⁸School of Geography, University of Nottingham, ⁹Natural History Museum of Denmark, University of Copenhagen
Understanding P cycling in the terrestrial hydrosphere is important to manage ecosystems. We conduct a cross-disciplinary study of groundwater P cycling by comparing the current water and P balance of a 70 ha lake (Nørresø, Fyn, Denmark) in a clayey till dominated landscape to the lake’s Holocene trophic history, as retrieved from sediment cores. The diatom and pigment records of core samples with ¹⁴C ages predating human influence (>6000 yr BP) indicate that the lake was never P-poor but rather meso- to eutrophic. The current lake water balance indicates a ~35% groundwater contribution, while ~65% comes from about ten ditch streams and direct precipitation. A groundwater-fed spring at 1 m elevation above lake level exists on a small island and shows that there is an artesian aquifer beneath the confining till. Furthermore, metre-scale circular ice holes during the winter supports groundwater discharge to the lake from an artesian aquifer via discrete discharge zones in the lake bed. The spring water is anoxic, ferrous, and contains 130 µg P/L. Similar water quality and total-P contents of 150-390 µg/L are observed in artesian glaciofluvial sand probed by water supply wells distanced 0.5 to 2.7 km from the lake. If the P concentration of the spring is representative for the artesian aquifer, the aquifer’s groundwater discharge constitutes ~90% of the external source of P to the lake. The combined data suggest that geogenic P may be mobilized within and transported through aquifers and may ultimately control the trophic state of groundwater dependent ecosystems.

Transport and transformation of nitrate in a riparian wetland

Rasmus Jes Petersen¹, Christian Prinds¹, Bo Vangsø Iversen¹, Charlotte Kjærgaard², Søren Jessen³ and Peter Engesgaard^3
1Department of Agroecology, Aarhus University, ²SEGES, ³Department of Geosciences, Copenhagen University
Even though riparian wetlands have been intensively studied during the past 30 years these areas still function as a “black box” with regards to removal of nitrogen input from surrounding areas. To comply with regulations of the European Water Framework Directive, Danish agriculture is to reduce the load of nitrogen from agricultural fields to fresh water bodies. One initiative is moving from a uniform regulation of nitrogen application to a spatially differentiated regulation where less fertilizer should be applied to vulnerable areas. This leads to the identification of vulnerable and robust areas, in which riparian wetlands plays an important role.

The present case study investigates the transport and transformation of nitrate entering a riparian wetland via drain water from surrounding agricultural areas. The drain pipes are cut off at the hillslope and drain water irrigates the wetland. Depending on the saturation state of the wetland soils and the amount of water entering during precipitation events, a part of the water infiltrates into the wetland sediments and travels towards the stream. Some of the infiltrated water may be caught by drains within the wetland soils and transported directly to the stream. The remaining water can be either evapotranspired or transported directly to the stream via overland flow. Preliminary results show an efficient denitrification of nitrate infiltrating into the studied wetland soils. The nitrogen removal efficiency at different drain outlets seems then to be largely controlled by the amount of drain water input relative to the infiltration capacity of the wetland soil.

Mapping surface flow in low-gradient areas with thermal remote sensing

Christian Prinds¹, Rasmus Jes Petersen¹, Rene Larsen¹, Mogens Greve¹ and Bo Vangsø Iversen^1
1Aarhus University, Dept. of Agroecology
Thermal infrared (TIR) imagery has long been used for mapping groundwater-surface water interactions and mainly for locating areas of groundwater seepage in lakes and shorelines (Rundquist et al. 1985, Banks et al. 1996). In this study, we used the method for locating discharge from tile drains into lowlands and water bodies (lakes, streams, ditches etc.). Tile drains are one of the main end points for nutrients applied to the agricultural fields and a fast conduit. When studying the function of riparian lowlands and wetlands as nutrient buffer zones, it is essential to know 1) the location of drainage input into the buffer system and 2) the flow path of the water. The TIR imagery was collected by a UAV (eBee from SenseFly) with a thermal camera (ThermoMap from SenseFly) at early spring in 2016 and 2017. The surveys are conducted in cold periods where discharging drainage water (and groundwater) are warm anomalies compared to the cold soil. We hereby obtain maps of the area’s thermal signature at the time of flight. The drainage outlets are easily observed as sharp point sources of warm water and surface flows are also remarkably clear making TIR a usable approach for mapping of flow direction in low-gradient areas such as riparian lowlands and wetlands. The flow systems can be compared to topographically modelled surface flow using high-resolution DEMs and flow direction algorithms.

References
Banks, W.S.L et al. (1996) Using thermal-infrared imagery to delineate ground-water discharge, Ground Water, 34, 3, 434-443

Rundquist, D. et al. (1985) Airborne Thermal Mapping of a Flow-through Lake in the Nebraska Sandhills, Water Resources Bulletin, 21, 6, 989-994

Using land-based and waterborne hydrogeophysical methods to infer geological controls on groundwater discharge to a lake

Eva Sebok¹, Sachin Karan² and Peter Engesgaard^3
1Department of Geosciences and Natural Resource Management, University of Copenhagen; COWI A/S, ²Geological Survey of Denmark and Greenland (GEUS), Department of Geochemistry, ³Department of Geosciences and Natural Resource Management, University of Copenhagen
The geological heterogeneity of stream and lake sediments can lead to spatially heterogeneous groundwater discharge to surface waters, which can be detected by Distributed Temperature Sensing (DTS). The heterogeneity of underwater sediments can also be mapped by waterborne geophysical surveys such as floating electrode Electrical Resistivity Tomography (ERT). However, ERT and DTS measurements are rarely combined to detect the spatial variability in groundwater discharge to surface waters. The aim of this study was therefore to: (1) test the use of DTS in a deeper lake environment up to 4 m of water depth and (2) assess if sediment heterogeneity indicated by waterborne geophysical surveys can result in potential discharge patterns detected by DTS.

Lake Tissø is the fourth largest lake in Denmark with a surface area of 12.3 km², maximal depth of 13 m and a present surface water extraction of 5 million m³/year. At the Eastern lakeshore potential locations of groundwater discharge in the near-shore region were mapped by DTS. Sediment properties were surveyed with both on-land and waterborne ERT and the resulting resistivity data were used as input to a 2D flow model aimed to test the potential discharge locations interpreted from the DTS survey. Our results show that potential patterns of groundwater discharge agree well with the location of a higher resistivity/coarser material zone detected 60-140 m offshore. The numerical flow model also confirmed that the surveyed sediment distribution can result in discharge patterns detected by DTS measurements.

                       POSTER PRESENTATIONS                    

Potential for Lake Bank Filtration at Lake Tissoe, Denmark

Franciska Amalie Køhn¹, Eva Sebok² and Peter Engesgaard^1
1Department of Geosciences and Natural Resource Management, University of Copenhagen, ²Department of Geosciences and Natural Resource Management, University of Copenhagen; COWI A/S
In collaboration with Kalundborg Forsyning (KALFOR), COWI is currently investigating the potential of Lake Bank Filtration (LBF) at Lake Tissø, Denmark. Challenges associated with pumping up groundwater in close vicinity to the lake are the temporal variability in the groundwater-lake seepage, where clogging of the lakebed, as well as the drastic changes of the lake stage throughout the year (160 cm), may influence LBF efficiency. Several field methods were applied to understand the temporal behavior of the transient seepage patterns and to investigate the (in)filtration potential of the near-lake area. Based on data (hydraulic conductivity values, borehole information, resistivity profiles, sediment samples) about the geological setting of the area, a conceptual 2D/3D geological model was developed in GeoScene3D. In addition to hydraulic field and tracer data the geological model was used to develop a 2D/3D hydrogeological conceptual model to examine the groundwater-lake interaction. Finally, a 3D flow- and multiple tracer transport model was developed in MODFLOW and MT3D to explore the impacts of a pumping test carried out at the field site for assessing the potential for LBF.

An evaluation of tools to standardise groundwater resource assessment for coastal areas in Sweden

Ingmar Geuze¹ and Roland Barthel^1
1Department of Earth Sciences, University of Gothenburg, Sweden
Groundwater problems in coastal regions are usually not associated with the sparsely populated shores of water-rich Scandinavia. However, the combination of local geology and the specific conditions of water usage create challenges even there. Along the Swedish coast, much of the groundwater occurs in fractured bedrock or in relatively small, shallow, and isolated Quaternary sedimentary formations. Those aquifers are usually not considered relevant as water resources and have thus previously not received much attention from water authorities or researchers. Nevertheless, a possible long-term solution to the increasing pressure on water resources could be found within the utilisation of these groundwater systems.

No attempt has been made to review and evaluate the results of individual investigations carried out by different municipalities in coastal areas. Thus the status of coastal groundwater systems in Sweden remains unclear and a standard methodology that could be applied for groundwater resource assessment in Swedish coastal areas does not exist. Hydrogeological investigations involve high costs, meaning that performed investigations should yield reliable results that fill multiple uses. With the project presented here, an attempt is made to develop a standard methodology for the specific hydrogeological conditions on the Swedish coastline.

We present firstly the results of an online survey carried out among Swedish coastal municipalities, illustrating the various types of problems, methods of investigation used and measures taken. We secondly review various methods commonly applied, in conjunction with a proposal for a standard methodology that may be applicable on a national level.

Keywords: Coastal aquifers, groundwater assessment

Formation of saltwater intrusions in the low-lying coastal areas during the Holocene in Southern Jutland

Rena Meyer¹, Peter Engesgaard¹ and Torben O. Sonnenborg^2
1Department of Geosciences and Natural Resource Management University of Copenhagen, Denmark, ²Geological survey of Denmark and Greenland (GEUS), Copenhagen, Denmark
Aquifers in low-lying coastal areas are threatened by saltwater intrusions, as a result of low head gradients, high abstraction rates and land management, and climate change. Understanding the evolution and driving mechanisms of saltwater intrusions can help to adapt water management strategies to mitigate the impact. The 1700 km²-large study area in the border region between Denmark and Germany, adjacent to the Wadden Sea, has undergone a complex (hydro-)geological evolution; lying in the glacial foreland likely under permafrost conditions during LGM and experiencing a relative rise in sea level during the Holocene. Airborne electromagnetic surveys indicate saltwater up to 20 km inland. Reclaimed from the Wadden Sea, these low-lying areas have been protected from flooding by dikes for the last 200 years and have been heavily drained. In order to identify the origin and dynamics of the saltwater and the role of heterogeneous geology, a 3D regional-scale density-driven flow-and-transport model was used. The formation of saltwater intrusions was simulated during the Holocene taking into account changing conditions caused by flooding and dike construction. The results reveal that the saltwater originate from a combination of remnant (pre-Holocene) seawater, Holocene transgression and recent drainage. Main features controlling the progression of the modern seawater into the coastal aquifers are buried valleys providing preferential flow path for saltwater in combination with an extensive Miocene clay layer hindering saltwater intrusion and land management with dike construction transforming the shallow aquifer from being salt saturated during flooding to being refreshed after the dike was built.

Temperature profiles to measure groundwater discharge to Ringkøbing Fjord.

Joel Tirado-Conde¹, Carlos Duque², Sachin Karan³ and Peter Engesgaard^1
1Department of Geosciences and Natural Resource Management. University of Copenhagen, ²Department of Geoscience. Aarhus University, ³Department of Geochemistry. Geological Survey of Denmark and Greenland (GEUS)
Groundwater discharge or upwelling plays an important role in the ecological and hydrological dynamics in coastal areas, bringing fresh water inputs to saline water systems. However, locating it both in space and time as well as quantifying how much groundwater flows upward to coastal areas requires a big effort since these are very heterogeneous systems. Seasonal changes in rainfall, temperature and water level lead to temporal variability, while variations in the hydraulic properties and hydrological processes can generate spatial heterogeneity, making the process of measuring those fluxes complicated and requiring multiple measurements to obtain accurate results. Furthermore, the non-steady position of the fresh water-salt water interface increases the uncertainty surrounding these processes. Using temperature as a tracer, the groundwater inputs to a surface water body can be calculated by means of solving analytically the conduction-convection equation, shortening considerably the amount of field work needed to obtain groundwater upwelling fluxes. In this work groundwater upwelling in the Ringkøbing Fjord coastal area was obtained using two methods: direct upward flow measurements and indirect flow calculations with shallow fjord bed temperature profiles. These two different sets of data are compared in order to assess their feasibility to map and quantify upwelling. Addressing the strengths and weaknesses of each method, we aim to better constrain the reliability of them in order to improve the quality of the data collection process.

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11.3. Integrated Hydrological Modeling

                       ORAL PRESENTATIONS                    

Assessing the impact of model structure on uncertainty in integrated hydrological modelling

Michael Butts¹, Sílvia Leirião¹, Douglas Graham¹ and Jeremy Kobor^2
1DHI, Agern Alle 5, DK 2970 Denmark, ²Now at O’Connor Environmental, Inc., PO Box 794, Healdsburg, CA 95448,USA
Understanding and quantifying model uncertainty is essential for decision-making in water resources management. Model uncertainty comes from the forcing data (rainfall, evapotranspiration), the boundary conditions and the parameters. It also arises from the model structure, including the process descriptions, numerical approximations, and geological models. In practice, we trade-off the complexity of the model required to capture the relevant catchment processes against the accuracy needed to make reliable decisions.

In this paper, we examine the impact of model structure on model calibration and prediction uncertainty in three case studies. The first study assesses the impact of land use change in the Napa Valley, USA. We present a model framework that allows for a range of model structures, which we used to calibrate in separate steps the surface water and then the groundwater. In the second case, we systematically explored different models and model structures for rainfall-runoff processes in the Blue River, USA. In this case, the uncertainties in the predicted flows due to model structure were larger than uncertainties from both the rainfall and the model parameters. Finally, we are currently using the same modelling framework to investigate the impact on model structure and calibration on an integrated hydrological model of the Hinds catchment, New Zealand where changes in water allocation and land use may result in unacceptable flow reductions in an extensive coastal spring system. The aim is to explore different facets of risk calculation based on Bayes equation to determine whether the proposed changes lead to unacceptable flow reductions

Can new drain concepts improve local drain flow performance in catchment scale modelling (MIKE SHE)?

Ida Bjørnholt Karlsson¹, Anker Lajer Højberg¹ and Bo Vangsø Iversen^2
1Geological Survey of Denmark and Greenland (GEUS), ²Institut for Agroøkologi, Aarhus Universitet
Nitrate leaching to groundwater, surface water and oceans are an increasing issue for areas with intensive agriculture. The drainage flow system is important for the transportation of water but also works as a potential fast track with limited reduction for nitrate pollutants. As the need for catchment models that can simulate and predict nitrate transport and degradation grows, so does the necessity for models able to adequately represent drainage flow on local scale.

In this study (TReNDS, Højberg et al. 2016-2018) the aim is to test whether or not knowledge about the mechanisms controlling drain flow creation can be used to develop new drain concepts; that can improve local scale performance. The concepts must be founded in data obtainable on catchment scale; as they potentially should be incorporated into national modelling schemes.

A fully distributed hydrological MIKE SHE model for the 101 km² Norsminde catchment, Denmark is used (Hansen et al., 2014; He et al., 2015). The catchment is dominated by agriculture and an extensive drainage network. The concepts are built on theses of differentiated occurrence and parameterization for different drain types (tile, natural and urban drain); and important variables (such as TWI and clay content in the soil, (Iversen, 2016)) controlling the generation of drain flow that can be accounted for within the limitations in the MIKE SHE model concept. Measured drainage from eight drain flow stations (Kjærgaard et al., 2011-2015) are used for evaluating any gain of the implementation of the drain concepts on dynamics and quantity.

References

Hansen, A. L., Gunderman, D., He, X., and Refsgaard, J. C.: Uncertainty assessment of spatially distributed nitrate reduction potential in groundwater using multiple geological realizations, Journal of Hydrology, 519, Part A, 225-237, http://dx.doi.org/10.1016/j.jhydrol.2014.07.013, 2014.

He, X., Højberg, A. L., Jørgensen, F., and Refsgaard, J. C.: Assessing hydrological model predictive uncertainty using stochastically generated geological models, Hydrological Processes, 29, 4293-4311, 10.1002/hyp.10488, 2015.

Højberg, A. L., et al. TReNDS. http://trends.nitrat.dk/, 2016-2018.

Iversen, B. V., Kjærgaard, C., Petersen, R. J., Møller, A. B., Christensen, S., Rasmussen, K. R., Ringgaard, J., SEGES, and Bioscience, A. I. f.: Dræn: Kortlægning og afstrømningsdynamik, Hydrologidag, 27. oktober 2016, 2016.

Kjærgaard, C. et al.: IDræn projektet. www.idraen.dk, 2011-2015.

Integrated hydrology in the COHERENT project

Morten Andreas Dahl Larsen¹, Kirsten Halsnæs¹ and Martin Drews^1
1Technical University of Denmark
The COHERENT project, funded by Innovation Fund Denmark, was instigated on Nov. 1 and addresses risks in the coastal zone of both natural and anthropogenic origin and the interplay between them. The presentation will present work led by the presenting author which specifically addresses the impact of inland/watershed hydrology on natural hazards in the coastal zone, most often flooding events on coastal cities, and the interactions with adaptation practices, urban development and management. The topic is highly relevant due to projected increases in frequencies and magnitudes of natural hazards in the coastal zone under current climate change potentially resulting in high social and economic costs.

The physical impact of coastal flooding is made up of mainly the impact of the storm surge itself as well as waves, tides and a general increase in sea level and the assessment of potential adaptation measures can be complex. The vulnerability can however increase for the fluvial part with higher stream flow and groundwater level, with temporal scales in the order of days to seasons. Another influence comes from the pluvial side when rainfall events occur simultaneously, with temporal scales in the order of minutes to days. A key objective of the work is therefore to assess the influence of inland-watershed hydrology on the risk hazards for current and future conditions within the three cases of the project; Skive, Ringkøbing and Aabenraa municipalities. A key objective is close interaction with municipalities and stakeholders to reflect applied conditions and assess true projected urban development goals.

A watershed scale approach to model iron concentration in river

Markus Saari¹, Hannu Marttila¹, Pekka Rossi¹ and Heini Postila^2
1Water resources and environmental engineering research unit, University of Oulu, ²Water resources and environmental engineering research unit, University of OuluUniversity of Oulu
Numerous studies have reported increases in iron concentrations in freshwaters especially in boreal regions. The significant role of iron in biochemical processes and element cycles makes this matter of concern among research community. With infrequent sampling (weekly interval) in main rivers we have limited process understanding to evaluate main drivers behind the iron transport in watershed scale. To enhance this, we used watershed scale SWAT model for typical clayey soiled and agriculture dominated river basin in Southern Finland. In this type of watershed, the mobility of iron is dominated by the erosion and transportation of suspended solids, especially clay particles. The strong linear correlation between TSS, turbidity and iron concentration was utilized to model iron transportation in watershed scale. Successful model calibration and validation allowed us to study main sources for iron transport and seasonal dynamics. Based on the modelling results the most crucial times for iron transport are late autumn rainfalls which cause significant erosion on agricultural lands. We further used the model to predict future land use and climate change scenarios and possibilities to mitigate their joint effects to iron transport.

                       POSTER PRESENTATIONS                    

 Estimated variation in pesticide leaching through greens and fairways based on detailed fate-descriptions in 12-cm soil profiles

Sachin Karan¹, Nora Badawi¹, Anne M. D. Jensen² and Annette E. Rosenbom^1
1Geological Survey of Denmark and Greenland (GEUS), Department of Geochemistry, ²University of Copenhagen, Department of Geosciences and Natural Resource Management
Leaching resulting from treating golf courses with pesticides is presently not well known. Although studies have shown that 90-100% of applied pesticides can be microbially removed in turfs with a surface near thatch layer, this is not ubiquitous. The retardation of pesticides in soils is compound specific, but also controlled by the hydrogeological setting that for fairways can include the presence of wormholes. Thus, potential rapid preferential flow and transport may make fairways more vulnerable in regards to leaching.

Based on both detailed fate (degradation and sorption) and hydrogeological descriptions of the upper 12-cm soil profile of golf courses, the leaching potential of tebuconazole (TBZ) through six greens (three USGA and three push-up greens) and of MCPA through three fairways (low, medium and highly fertilized) were estimated numerically using COMSOL Multiphysics. All the golf courses were located in areas characterized as macro porous clay till settings. The impact of fate processes on the leaching potential of:

• TBZ as:

– an analytical grade compound,

–  a commercial formulation,

–  a commercial formulation in combination with a surfactant product

• MCPA as:

–  an analytical grade compound

–  a commercial formulation

was evaluated numerically for greens and preferential transport for fairways given the presence of a wormhole. The preliminary simulation results indicate that

–  TBZ has a high potential for leaching through the greens in high concentration

–  MCPA has a low potential for leaching through the fairways given a high degree of degradation in the upper 12 cm.

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11.4. Open session Hydrogeology

                       ORAL PRESENTATIONS                    

Skåningshave – a new major well-field on the island of Lolland (S.Denmark). Development and hydrogeology.

Kristian Bitsch¹, Karl Jørgensen² and Mikael Jørgensen^3
1Rambøll, Hannemanns Allé 53, DK-2350 Copenhagen S, ²Municipality of Lolland, Jernbanegade 7, DK-4930 Maribo, ³NIRAS, Sortemosevej 19, DK-3450 Allerød
The Island of Lolland lies in the southern part of Denmark and comprises 1242 km². The Island is very flat having an average of 7 m in altitude and a maximum of 30 m above sea level. The surface of the Island is dominated by glacigene sediments of late Weichselian age, clayey tills and glaciofluviatile outwash sediments forming discontinuous basins. The prequaternary are Maasthrictian-Campanian chalks in the north and Paleocene clays to the south. Non-saline groundwater forms a shallow lens with a maximum depth of 50 m in the northern 2/3 of the island. The water supply structure is based on 4 municipal and 25 community waterworks, delivering a total of 2 + 1 million m³ per year. A new infrastructure project demands up to 450 000 m³/year. 100 000 m³/year can be delivered by the existing waterworks. In the central part of the island a widespread layer of outwash sands was recognized. The area had just been subjected to an intensive geological and geophysical mapping using all existing well data, seismic profiling and extensive SkyTem mapping, which had been used to make a new regional geological and hydrological model of the area. This model was used as the basis for producing a detailed well field model later improved with additional data from MRS soundings and 6 new wells including a major testpumping. This led to a new model and an abstraction strategy minimizing the impact on the surrounding wetlands including the large NATURA 2000 area, the Maribo Lakes.

Investigating controls on groundwater drought hazard in Scandinavia

Ezra Haaf¹, Pekka M. Rossi², Bjørn Kløve² and Roland Barthel^1
1Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden, ²Water Resources and Environmental Engineering Research Unit, University of Oulu, Finland
Drought has historically been a minor issue in Sweden and Finland, countries of high water abundancy. However, since late 2015 into 2017 large parts of Sweden and Finland have been classified with medium to high risk for drought impact according to the drought monitor of the JRC of the European Commission. In Sweden, the Swedish Geological Survey (SGU) has reported falling groundwater levels through their monitoring program, particularly during the summer in Southeastern Sweden. By spring of 2017, this problem had intensified and groundwater drought had been registered in large parts of the country. Impacts on society have been rules on water use, irrigation ban and private drinking water wells running dry in certain regions. In Finland, groundwater levels have been periodically reported to be low during the 2000s based on the monitoring network by Finnish Environmental Institute, which has caused worries in water usage. Although some of the Swedish aquifers are recovering as of autumn 2017, the drought is still persisting in many systems. The current understanding of severity and persistence as well as propagation of drought into groundwater for Swedish and Finnish groundwater systems is very limited. Here, we investigate patterns of groundwater droughts historically and geographically. Furthermore, we explain the sensitivity and persistence based on geologic and environmental controls for different types of groundwater systems with decision tree learning.

                       POSTER PRESENTATIONS                    

Sustainable Water Resources in Iranian Qanats

Fataneh Hajatpour Birgani¹ and Rodney Stevens^1
1Department of Earth Sciences, University of Gothenburg
Qanats are water-transport tunnels with a lower slope than the groundwater surface they intersect, typically in arid regions with alluvial-fan geomorphology. Since the traditional qanat technique (Persian origin in 1st millennium) relies solely on gravitational drainage to assess deep groundwater resources, they are suitable in rural areas, and the over 50,000 active qanats in the Middle East are a crucial supply for drinking and agricultural water for numerous population centers. Qanat sustainability is related to changes in climate, population and land-use. Importantly, groundwater lowering by excessive pumping decreases or stops qanat discharge. We have considered the qanat sensitivity to these influences by characterizing the geomorphologic, geologic, climatic and resource-management associations in selected case studies. Debris-flow alluvial fans can be expected to have steeper groundwater gradients than do stream-flood fans. This is due to the greater surface slope and the lower hydraulic conductivity associated with fine-grained, debris-flow deposits. The internal stratigraphy can further reflect the fan evolution over time and further influence reservoir character. This poster presents a problem analysis of qanat resources, their future potential and vulnerability. The study is a part of the KERMIT project (Knowledge Exchange for Resource Management and International Trust, see separate abstract by Stevens et al., this volume), which uses the endemic knowledge of refugees in Sweden to develop case studies and cooperation networks both within Sweden and abroad.

Fracture minerals investigations at Kyläniemi, Southern Finland: Paleohydrogeological implications

Minja Seitsamo-Ryynänen^1
1Department of Geosciences and Geography, University of Helsinki, Finland
In crystalline bedrock environments, a bulk of groundwater flow occurs in channels provided by fracture networks. Isotopic compositions of precipitated fracture minerals can be utilized to gain information about the origin, age and compositional evolution of the deep groundwaters in crystalline bedrock.

The aim of this study is to investigate the hydrogeochemical evolution of groundwaters in the crystalline bedrock at Kyläniemi, located in Southern Finland near Salpausselkä end-moraines. Fracture mineral samples containing calcite and/or pyrite were collected from water-conducting fractures at the upper ∼500 m of the bedrock. These fracture filling calcites occur as thin ∼200–350 μm crusts on open fracture surfaces, and the pyrites as small euhedral crystals.

In addition to optical microscopy and chemical composition analyses, the calcite fillings are analyzed for the isotopic composition on carbon and oxygen, and the pyrites for the isotopic composition on sulfur. The δ¹⁸O values of the latest calcite generations are expected to show values indicating the influence of glacial melt waters. The δ¹³C values of calcite and δ³⁴S values of pyrite should demonstrate the evolution of redox environment fronts.

The results of this study are compared to those of previous studies conducted at Olkiluoto (Sahlstedt et al. 2010, 2013, 2016) which is the chosen geological repository site for spent nuclear fuel. Unlike Olkiluoto, the Kyläniemi site rose above the sea-level in early Holocene. Thus, late-stage groundwater evolution is unaffected by brackish water intrusions related to Yoldia Sea and Littorina Sea stages.

References
Sahlstedt, E., Karhu, J.A. & Pitkänen, P. 2010: Indications for the past redox environments in deep groundwaters from the isotopic composition of carbon and oxygen in fracture calcite, Olkiluoto, SW Finland. Isotopes in Environmental and Health Studies, 46:3, 370-391

Sahlstedt, E., Karhu, J.A., Pitkänen, P. & Whitehouse, M. 2013: Implications of sulfur isotope fractionation in fracture-filling sulfides in crystalline bedrock, Olkiluoto, Finland. Applied Geochemistry 32, 52–69.

Sahlstedt, E., Karhu, J.A., Pitkänen, P. & Whitehouse, M. 2016: Biogenic processes in crystalline bedrock fractures indicated by carbon isotope signatures of secondary calcite. Applied Geochemistry 67, 30–41

Stable water isotopes in snow: Changes throughout the season in Finse, Norway

Evelien van Dijk^1
1University of Oslo
Here we present changes of stable water isotopes within the snow pack throughout one season from the Finse area in southern Norway.

Stable water isotopes have become a key element in hydrological and atmospheric research topics. They can be used to get an understanding about the changes in the snow pack throughout the snow season. For this study, 215 samples from several snow pits were analyzed for stable water isotopes throughout the snow season 2016-2017. Sites were selected by looking at the snow drift patterns and snow accumulation to get an undisturbed stratigraphy. The Lagrangian particle model Flexpart will be used to model the moisture sources for this snow pack to get a fuller understanding of the snow processes and the atmospheric part of the hydrological cycle. As snow is a water storage it is important to understand which processes play a role within the snow pack during accumulation and melt and how these processes influence the deformation and melting. By understanding how the snow melt phases change, better predictions about the spring floods can be estimated. Modeling the moisture sources is important to give a better understanding of the atmospheric part of the hydrological cycle. The atmospheric part of the cycle is not yet fully understood, and by using the isotopic composition of snow to track air parcels back in time a better understanding can be accomplished.

References
Dietermann, N. and Weiler, M. (2013). Spatial distribution of stable water isotopes in alpine snow cover. Hydrology and Earth System Sciences, 17(7):2657

Landais, A., Steen-Larsen, H. C., Guillevic, M., Masson-Delmotte, V., Vinther, B., and Winkler, R. (2012). Triple isotopic composition of oxygen in surface snow and water vapor at neem (greenland). Geochimica et Cosmochimica Acta, 77:304–316.

Sodemann, H., Schwierz, C., and Wernli, H. (2008). Interannual variability of greenland winter precipitation sources: Lagrangian moisture diagnostic and north atlantic oscillation influence. Journal of Geophysical Research: Atmospheres, 113(D3)