Abstract
Investigations at Hat Head in northern New South Wales, Australia, have shown that the depth and location of the saline interface changes significantly in response to storm-induced wave runup, rainfall recharge and regional groundwater discharge. The interplay between these three factors creates moving zones of fresh and salty water that displace each other over time, leading to the development of complex geochemical patterns. The results of an extensive hydrogeological investigation incorporating surface and borehole geophysics, drilling, monitoring and hydrochemical sampling on multiple occasions has demonstrated that the mixing zone between fresh groundwater and seawater occurs as zones of variable chemical composition which extend further inland and to greater depths than anticipated. The location and magnitude of these mixing zones varies over time scales of weeks. The chemical processes within these mixing zones are dominated by redox reactions that may never reach an equilibrium, with the system being episodically disturbed by new storm events. Diel changes from tides do not have an observable impact on the interface. An improved understanding of these processes will require regular monitoring and sampling from a range of vertical sampling points in the coastal zone, combined with routine monitoring using borehole induction logs.
Résumé
Des études réalisées à Hat Head, dans le nord de la Nouvelle Galles du Sud, Australie, ont montré que la profondeur et la position de l’interface eau douce-eau salée changent de manière significative en réponse aux ressacs des vagues induites par les tempêtes, à la recharge par la pluie et à l’émergence régionale des eaux souterraines. L’interaction entre ces trois facteurs constitue des zones de mouvement d’eau fraîche et d’eau salée qui se déplacent au fil du temps, conduisant au développement de signatures géochimiques complexes. Les résultats d’une étude hydrogéologique détaillée incluant de la géophysique de surface et en forage, des sondages, des suivis et des échantillonnages hydrochimiques fréquents ont démontré que la zone de mélange entre l’eau souterraine fraîche et l’eau de mer se manifeste sous forme de zones de composition chimique variable qui s’étendent plus loin à l’intérieur des terres et plus en profondeur que prévu. L’emplacement et l’ampleur de ces zones de mélange varient au fil des semaines. Les processus chimiques au sein de ces zones de mélange sont dominés par des réactions redox qui peuvent ne jamais atteindre l’équilibre, le système étant épisodiquement perturbé par de nouveaux évènements de tempêtes. Les cycles diurnes des marées ne montrent pas d’impact observable sur l’interface. Une amélioration de la compréhension de ces processus va nécessiter un suivi et un échantillonnage réguliers en zone côtière avec des points de prélèvements répartis verticalement, combinés à un suivi de routine avec des diagraphies de résistivité en forage.
Resumen
Las investigaciones realizadas en Hat Head, en el norte de New South Wales (Australia), han demostrado que la profundidad y la ubicación de la interfase salina cambian significativamente en respuesta a la sucesión de olas inducidas por las tormentas, la recarga de las precipitaciones y la descarga regional de aguas subterráneas. La interacción entre estos tres factores genera zonas móviles de agua dulce y salada que se desplazan entre sí con el tiempo, lo que da lugar al desarrollo de complejas configuraciones geoquímicas. Los resultados de una investigación hidrogeológica detallada que incorporó la geofísica de superficie y de pozo, la perforación, el monitoreo y el muestreo hidroquímico en múltiples ocasiones ha demostrado que la zona de mezcla entre las aguas dulces subterráneas y el agua de mar se produce en forma de zonas de composición química variable que se extienden más hacia el interior y a mayores profundidades de lo previsto. La ubicación y la magnitud de estas zonas de mezcla varían a lo largo de escalas de tiempo de semanas. Los procesos químicos dentro de estas zonas de mezcla están dominados por reacciones redox que tal vez nunca lleguen a un equilibrio, y el sistema se ve perturbado periódicamente por nuevas tormentas. Los cambios en el nivel de agua de las mareas no tienen un impacto observable en la interfase. Para comprender mejor estos procesos será necesario realizar un seguimiento y un muestreo periódico en una serie de puntos de muestreo verticales de la zona costera, combinados con un monitoreo sistemático mediante registros de inducción en perforaciones.
摘要
在澳大利亚New South Wales州北部的Hat Head开展的调查表明,咸水界面的深度和位置会因暴雨引起的波浪增加、降雨补给和区域地下水排泄而发生显著变化。这三个因素之间的相互作用产生了咸淡水的移动区域,这些区域随时间变化,从而导致复杂地球化学模式的形成。集成了地表和钻井地球物理,钻探,监测和多种场地的水化学采样,广泛的水文地质调查结果证明了咸淡水间的混合区化学成分是变动的,该混合区其向内陆延伸而且深度范围超过了预想的。这些混合区的位置和大小随几周的时间尺度而变化。这些混合区的化学过程主要由可能永远无法达到平衡的氧化还原反应所主导,新的暴雨事件偶尔干扰该系统。潮汐的昼夜变化不会对界面产生明显影响。更好地理解这些过程将需要对沿海地区大量垂直采样点进行定期监测和采样,并结合使用井孔感应测井的常规监测。
Resumo
Investigações em Hat Head, no norte de Nova Gales do Sul, na Austrália, mostraram que a profundidade e a localização da interface salina mudam significativamente em resposta ao acúmulo de ondas induzidas por tempestades, recarga de chuvas e descarga regional de águas subterrâneas. A interação entre esses três fatores cria zonas móveis de água doce e salgada que se deslocam ao longo do tempo, levando ao desenvolvimento de padrões geoquímicos complexos. Os resultados de uma extensa investigação hidrogeológica, incorporando perfuração e monitoramento geofísico superficial de poços e amostragem hidroquímica em várias ocasiões, demonstraram que a zona de mistura entre água doce e subterrânea e água do mar ocorre como zonas de composição química variável que se estendem mais para o interior e para profundidades maiores do que o previsto. A localização e magnitude dessas zonas de mistura variam ao longo de escala semanal. Os processos químicos nessas zonas de mistura são dominados por reações redox que podem nunca atingir um equilíbrio, com o sistema sendo episodicamente perturbado por novos eventos de tempestade. As variações diurnas das marés não têm um impacto observável na interface. Uma compreensão aprimorada desses processos exigirá monitoramento e amostragem regulares a partir de uma variedade de pontos de amostragem verticais na zona costeira, combinados a um monitoramento rotineiro usando registros de poços induzidos.
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References
Acworth RI (2007) Measurement of vertical environmental-head profiles in unconfined sand aquifers using a multi-channel manometer board. Hydrogeol J 15(7):1279–1289. https://doi.org/10.1007/s10040-007-0178-9
Acworth I (2019) Investigating groundwater. International Contributions to Hydrogeology 29, Taylor and Francis. https://doi.org/10.1201/9781351008525
Acworth R, Dasey G (2003) Mapping of the hyporheic zone around a tidal creek using a combination of borehole logging, borehole electrical tomography and cross-creek electrical imaging, New South Wales, Australia. Hydrogeol J 11(3):368–377. https://doi.org/10.1007/s10040-003-0258-4
Acworth R, Jorstad L (2006) Integration of multi-channel piezometry and electrical tomography to better define chemical heterogeneity in a landfill leachate plume within a sand aquifer. J Contam Hydrology 83(3–4):200–220. https://doi.org/10.1016/j.jconhyd.2005.11.007
Acworth R, Jankowski J, Soriano R, Turner I (1998) Interaction between coastal sand-dune aquifers, adjacent wetlands and sea water. In: Brahana JV (ed) Proceedings of XXIX IAH Congress: Gambling with Groundwater, Balkema, Rotterdam, The Netherlands, pp 461–468
Acworth R, Soriano R, Turner I (2000) The vertical head distribution in a coastal sand-dune aquifer. In: Sililo O (ed) Proc 30th IAH Congress on Groundwater: Past Achievements and Future Challenges, Cape Town, 26 Nov–1 Dec 2000, pp 67–72
Acworth RI, Hughes C, Turner I (2007) A radioisotope tracer investigation to determine the direction of groundwater movement adjacent to a tidal creek during spring and neap tides. Hydrogeol J 15(2):281–296. https://doi.org/10.1007/s10040-006-0085-5
Acworth RI, Rau GC, McCallum AM, Andersen MS, Cuthbert MO (2015) Understanding connected surface-water/groundwater systems using Fourier analysis of daily and sub-daily head fluctuations. Hydrogeol J 23:143–159. https://doi.org/10.1007/s10040-014-1182-5
Akumu CE, Pathirana S, Baban S, Bucher D (2011) Examining the potential impacts of sea level rise on coastal wetlands in north-eastern NSW, Australia. J Coast Conserv 15(1):15–22. https://doi.org/10.1007/s11852-010-0114-3
Andersen MS (2001) Geochemical processes at a seawater–freshwater interface. Environment and Resources DTU, Technical University of Denmark, Lyngby, Denmark
Andersen MS, Nyvang V, Jakobsen R, Postma D (2005) Geochemical processes and solute transport at the seawater/freshwater interface of a sandy aquifer. Geochim Cosmochim Acta 69(16):3979–3994. https://doi.org/10.1016/j.gca.2005.03.017
Andersen MS, Baron L, Gudbjerg J, Chapellier D, Jakobsen R, Gregersen J, Postma D (2007) Discharge of nitrate-containing groundwater into a coastal marine environment. J Hydrol 336:98–114. https://doi.org/10.1016/j.jhydrol.2006.12.023
Andersen MS, Jakobsen R, Nyvang V, Christensen F, Engesgaard P, Postma D (2008) Density driven seawater plumes in a shallow aquifer caused by a flooding event: field observations, consequences for geochemical reactions and potentials for remediation schemes. In: GQ07: Securing Groundwater Quality in Urban and Industrial Environments, Proc. 6th International Groundwater Quality Conference, Fremantle, Western Australia, 27 December 2007, IAHS Publ. 324, IAHS, Wallingford, UK, pp 483–490
Appelo CAJ, Postma D (2005) Geochemistry, groundwater and pollution, 2nd edn. Balkema, Leiden, The Netherlands
Archie G (1942) The electrical resistivity log as an aid in determining some reservoir characteristics. Trans ASCE 146:54–62. https://doi.org/10.2118/942054-G
Barlow P (2003) Ground water in freshwater–saltwater environments of the Atlantic Coast. US Geol Surv Circ 1262
Beekman HE, Anthony C, Appelo CAJ (1990) Ion chromatography of fresh- and salt-water displacement: laboratory experiments and multicomponent transport modelling. J Contam Hydrol 7:21–37. https://doi.org/10.1016/0169-7722(91)90036-Z
Berner RA (1981) A new geochemical classification of sedimentary environments. J Sedimeny Petrol 51:359–365. https://doi.org/10.1306/212F7C7F-2B24-11D7-8648000102C1865D
Brooke B, Preda M, Lee R, Cox M, Olley J, Pietsc T, Price D (2008) Development, composition and age of indurated sand layers in the Late Quaternary coastal deposits of northern Moreton Bay, Queensland. Aust J Earth Sci 55:141–157. https://doi.org/10.1080/08120090701689316
Chapelle FH (2001) Ground-water microbiology and geochemistry. Wiley, New York
Dasey GR (2010) Geophysical and hydrogeological assessment of the interaction of saline and fresh groundwater near a tidal creek. PhD Thesis, School of Civil and Environmental Engineering, UNSW, Sydney, Australia
Fairbanks RG (1989) A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature 342:637–642. https://doi.org/10.1038/342637a0
Jakobsen R, Postma D (1994) In-situ rates of sulphate reduction in an aquifer (Rømø, Denmark) and implications for the reactivity of organic matter. Geology 22:1103–1106. https://doi.org/10.1130/0091-7613(1994)022<1103:ISROSR>2.3.CO;2
Jankowski J, Beck P (2000) Aquifer heterogeneity: hydrogeological and hydrochemical properties of the Botany Sands aquifer and their impact on contaminant transport. Aust J Earth Sci 47(1):45–64. https://doi.org/10.1046/j.1440-0952.2000.00768.x
Jiao J, Post V (2019) Coastal hydrogeology. Cambridge University Press, Cambridge, UK
Kiss E (1984) Investigation of some asymmetric triazines as reagents for the spectrophotometric microdetermination of the iron oxidation state in silicates. Anal Chim Acta 161:231–244
Loke M (2001) RES2DINV Ver 3.4 manual: rapid 2D and 3D resistivity and IP inversion using the least squares method, https://www.geoelectrical.com. Accessed 30 September 2018
Loke M (2016) Tutorial: 2-D and 3-D electrical imaging surveys. https://www.geotomosoft.com. Accessed 26 June 2016
Lusczynski N (1961) Head and flow of groundwater of variable density. J Geophys Res 66:4247–4255. https://doi.org/10.1029/jz066i012p04247
Malott S, O’Carroll DM, Robinson CE (2016) Dynamic groundwater flows and geochemistry in a sandy nearshore aquifer over a wave event. Water Resour Res 52:5248–5264. https://doi.org/10.1002/2015WR017537
Manson F, Loneragan N, Skilleter G, Phinn S (2005) An evaluation of the evidence for linkages between mangroves and fisheries: a synthesis of the literature and identification of research directions. Oceanogr Mar Biol 43:485–515
McAllister SM, Barnett JM, Heiss JW, Findlay AL, MacDonald DJ, Dow CL, Luther III GW, Michael HA, Chan CS (2015) Dynamic hydrologic and biogeochemical processes drive microbiologically enhanced iron and sulfur cycling within the intertidal mixing zone of a beach aquifer. Limnol Oceanogr 60:329-345
Postma D, Jakobsen R (1996) Redox zonation: equilibrium constraints on the Fe(III)/SO4– reduction interface. Geochim Cosmochim Acta 60:3169–3175. https://doi.org/10.1016/0016-7037(96)00156-1
Rau GC, Post VEA, Shanafield MA, Krekeler T, Banks EW, Blum P (2019) Error in hydraulic head and gradient time-series measurements: a quantitative appraisal. Hydrol Earth System Sci. https://doi.org/10.5194/hess-23-3603-2019
Reid N, Nunn P, Sharpe M (2014) Indigenous Australian stories and sea-level change. In: 18th Conference of the Foundation for Endangered Languages (FEL): Indigenous Languages: Value to the Community, Okinawa, Japan, 17–20 September 2014
Robinson C, Gibbes B, Carey H, Li L (2007) Salt–freshwater dynamics in a sub-terranean estuary over a spring-neap tidal cycle. J Geophys Res C: Oceans 112(C9). https://doi.org/10.1029/2006JC003888.
Robinson C, Xin P, Li L, Barry D (2014) Groundwater flow and salt transport in a subterranean estuary driven by intensified wave conditions. Water Resour Res 50(1):165–181. https://doi.org/10.1002/2013WR013813
Roy P, Zhuang W-Y, Birch G, Cowell P, Congxian L (1997) Quaternary geology of the Forster - Tuncurry coast and shelf, southeast Australia. Technical report, Geological Survey of New South Wales, NSW Department of Mineral Resources, Sydney
Saenger P, Gartside D, Funge-Smith S (2013) A review of mangrove and seagrass ecosystems and their linkage to fisheries and fisheries management. RAP Publ. 2013/09, Food and Agriculture Organization of the United Nations, FAO Regional Office for Asia and the Pacific, Bangkok Thailand
Sheaves M, Baker R, Nagelkerken I, Connolly RM (2015) True value of estuarine and coastal nurseries for fish: incorporating complexity and dynamics. Estuar Coasts 38(2):401–414. https://doi.org/10.1007/s12237-014-9846-x
Shen C, Zhang C, Kong J, Xim P, Chunhui L, Zhao Z, Li L (2019) Solute transport influenced by unstable flow in beach aquifers. Adv Water Resour 125:68–81. https://doi.org/10.1016/j.advwatres.2019.01.009
Simmons CT, Fenstemaker TR, Sharp JM Jr (2001) Variable-density groundwater flow and solute transport in heterogeneous porous media: approaches, resolutions and future challenges. J Contam Hydrol 52(1-4):245–275. https://doi.org/10.1016/S0169-7722(01)00160-7
Soriano RS (2004) Groundwater dynamics in coastal sand-dune aquifers: the impacts of transient boundary conditions. PhD Thesis, School of Civil and Environmental Engineering, University of New South Wales, Sydney
Turner IL, Coates B, Acworth RI (1997) Tides, waves and the super-elevation of groundwater at the coast. J Coastal Res 13(1):45–60. https://doi.org/10.1021/BI00235A008
Turner IL, Acworth RI (2004) Field measurements of beach face salinity structure using cross-borehole resistivity imaging. J Coastal Res 20(1):194–201. https://doi.org/10.2112/1551-5036(2004)20[753:FMOBSS]2.0.CO;2
Turner IL, Rau G, Andersen MS, Austin M, Puleo J, Masselink G (2013) Coastal sand barrier hydrology: observations from the BARDEX II prototype-scale laboratory experiment. J Coastal Res 65:1886–1891. https://doi.org/10.2112/SI65-319.1
Turner IL, Rau GA, Austin MJ, Andersen MS (2016) Groundwater fluxes and flow paths within coastal barriers: observations from a large-scale laboratory experiment (BARDEX II). Coast Eng 113:104–116. https://doi.org/10.1016/j.coastaleng.2015.08.004
Van Camp M, Vauterin P (2005) TSoft: graphical and interactive software for the analysis of time series and Earth tides. Comput Geosci 31(5):631–640. https://doi.org/10.1016/j.cageo.2004.11.015
Acknowledgements
A debt of gratitude is owed to Mark Groskops for working out how to achieve the many preliminary designs and installations at Hat Head. Roy Soriano compiled much of the hydraulic head data and helped established the manometer systems as a part of his PhD studies. Rolf Beck was responsible for carrying out most of the extensive hydrochemical analysis and developed new methods for ferrous iron and sulphide field determinations. Peter Blanch carried out the sedimentary analysis of the HH14 core data presented here while completing a B. Eng. (Civil) at the University of New South Wales. We acknowledge the helpful comments of Pradeep K. Naik and two other anonymous reviewers during the preparation of this report.
Funding
This work was achieved without any grant payments; however, the Water Research Laboratory facilitated a significant contribution through support to the senior author.
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Acworth, R.I., Andersen, M.S. & Dasey, G.R. An investigation of the spatial and temporal variability of the saline interface in a sandy aquifer subject to storm wave runup and rainfall recharge. Hydrogeol J 28, 1695–1719 (2020). https://doi.org/10.1007/s10040-020-02155-5
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DOI: https://doi.org/10.1007/s10040-020-02155-5