Groundwater Tracer Research Articles

Trace Metal Dynamics in a Tropical Mangrove Tidal Creek: Influence of Porewater Seepage (Can Gio, Vietnam)

Mangrove soils are considered as sinks for trace metals, protecting coastal waters from pollutions. However, the cycling of trace metals in mangroves is complex due to various biogeochemical processes across the intertidal zone, notably the dissolution of bearing phases resulting in high trace metal concentrations in porewaters. Previous studies demonstrated a decrease of trace metal stocks in mangrove soils seaward, possibly due to the export of dissolved metals through tidal pumping. Can Gio mangrove is the largest one in Vietnam, developing downstream Ho Chi Minh City (Viet Nam’s biggest industrial city). The objectives of the present study were to characterize the dynamics of trace metals in a tidal creek of the Can Gio mangrove that does not receive any upstream inputs and to identify the role of porewater seepage on their dynamics. To reach our goals, surface water and suspended particulate matters were collected every 2 hours during two different tidal cycles (spring and neap tides) and at the two different seasons, dry and wet. Mangroves porewaters were also collected. In addition to particulate and dissolved trace metals, physico-chemical parameters and a groundwater tracer (Radon-222Rn) were measured. The results showed that trace metal concentrations at flood tides, both in the dissolved and the particulate phases, were in the same range that those measured in the Can Gio Estuary. Then during ebb tides, we evidenced high inputs of dissolved Fe, Mn, Co, and Ni from mangrove soils. However, the dynamics of these inputs differed depending on the element considered. Mn was exported from the tidal creek in its dissolved form. However concerning Fe, and to a lesser extent Co and Ni, we suggest that, when delivered to the creek from the soils under dissolved forms, these trace metals precipitated because of different physicochemical characteristics between mangrove soils and tidal creek, notably higher dissolved oxygen concentrations and higher pH. Consequently, these elements were exported to the estuary in particulate forms. We suggest that budget studies of trace metals in mangroves should be developed like the ones concerning carbon to efficiently determine their role as a barrier for pollutants between land and sea.

Carbon dioxide dynamics in a tropical estuary over seasonal and rain-event time scales

Tropical estuaries may release large amounts of carbon dioxide to the atmosphere, but remain understudied relative to temperate systems. Here, we investigate hydrological drivers of pCO2 along ~22 km of an aquatic continuum from the mountain river to the coastal ocean, including highly modified aquaculture and urban zones (Perancak Estuary, Ijo Gading River, Bali, Indonesia). We report seasonal spatial surveys (n = 8) and stationary time series observations (n = 4 days) during a rain event. Overall, pCO2 ranged from 330 μatm to 12,126 μatm, with the lowest values observed near the estuary mouth and in the river upstream of the urban zone, and the highest values in the upper estuary where radon (222Rn, a natural groundwater tracer) revealed elevated groundwater discharge. Average atmospheric CO2 fluxes in the upper estuary (107.3 mmol m−2 d−1) were ~5-fold greater than in the lower estuary (19.1 mmol m−2 d−1), while the river was a minor atmospheric CO2 sink (−0.2 mmol m−2 d−1). Overall, the estuary was a source of CO2 to the atmosphere with area-weighted emissions of ~67 mmol m−2 d−1. Seasonal spatial surveys revealed strong correlations between antecedent rainfall and pCO2 and 222Rn in the estuary, implying pCO2 responds to delayed groundwater discharge. A detailed 4-day time series covering an episodic flooding event revealed sharp transitions in CO2 drivers, including dilution by rainfall followed by inputs of CO2-enriched groundwater. Groundwater discharge, as traced by radon, explained most of pCO2 variability in dry and wet conditions. Overall, we highlight the importance of seasonal and episodic rainfall and how delayed groundwater seepage may drive CO2 distribution in a highly modified tropical estuary.

Detection of groundwater flux changes in response to two large earthquakes using long-term bedrock temperature time series

Heat as a groundwater tracer has potential application in identifying earthquake-induced changes in fluid flow. Since convective heat transport modifies the phase and amplitude of periodic oscillations under pure heat conduction condition, temporal variation of groundwater flux can thus be derived from multi-depth periodic temperature signals. Here we present groundwater flux changes after two large earthquakes nearby, determined from in situ bedrock temperature measurements in the Xianshuihe fault zone, at the eastern margin of the Tibetan Plateau. Five-year temperature time series at six different locations are recorded by high sensitivity temperature sensors (10−4 K) installed at various depths ranging from 0 to 20 m. Groundwater fluxes are estimated through time-varying amplitudes and phases of the annual oscillations, extracted from the Dynamic Harmonic Regression technique. Results show different hydrological responses to these two earthquakes. After the 2013 Ms 7.0 Lushan earthquake, sustained rise in upward flux was revealed at all locations in the intermediate-field, contradicting to the modeled coseismic static dilatational strains. However, groundwater flux patterns after the 2014 Ms 6.3 Kangding earthquake are consistent with the coseismic volumetric strain distribution of a quadrantal pattern of this event. We propose that enhanced hydraulic permeability by dynamic stress might cause the increased upward fluid flux after the Lushan earthquake in the intermediate-field, while coseismic static volumetric strain may account for the hydrological changes after the Kangding earthquake in the near-field. This is the first time that temperature–time series are used to quantify continuous earthquake-related changes in groundwater fluxes. In situ temperature monitoring can provide insights into earthquake-driven hydrologic responses, and also offer additional information to identify temporal changes in crustal strain or hydraulic properties.

The hydrological function of a large chain-of-ponds: a wetland system with intermittent surface flows

Like many wetlands globally, the Mulwaree River chain-of-ponds system exists in two dichotomous states characterised by the presence or absence of surface flow connecting large, deep, permanently inundated ponds. We develop a conceptual model of hydrological function of this chain-of-ponds system combining surface and subsurface water levels, 2H and 18O stable isotopes and 222Rn as a groundwater tracer over a period of time that incorporated extended dry periods and large rainfall events. During high-flow or flood events, ponds are connected by flow along connecting channels and preferential flow paths. The water column is fully mixed to depths of up to 7 m. During high-flow, water level in the ponds can be greater than the water level in the surrounding floodplain aquifer, producing a hydraulic gradient away from the ponds, reflecting a losing wetland system. During no-flow periods, connecting channels and preferential flow paths are dry. A thermocline develops within the ponds and surface waters become enriched in 2H and 18O with evaporation losses. During periods of no-flow, increases in water level beyond atmospheric flux often occur during winter. Only small groundwater inflows enter the ponds from the floodplain aquifer. The hydrological function of this chain-of-ponds system is delicately balanced making it potentially sensitive to changes in climate that alter rainfall and evaporation rates, and any local-scale groundwater interference activities. Efforts to conserve and protect this system, and the aquatic ecosystems it supports, will be critical into the future.

Groundwater Constituents and Trace Elements in the Basement Aquifers of Africa and Sedimentary Aquifers of Asia: Medical Hydrogeology of Drinking Water Minerals and Toxicants

The use of groundwater, a major source of potable water, in developing countries has proven to be an invaluable resource for local populations. The ability to safely use this water for drinking, however, depends on its chemical quality, a factor primarily controlled by various aquifer attributes such as geology and geochemistry. On a global scale, groundwater is primarily sourced from either sedimentary or basement aquifers. In this study, we compared the groundwater constituents and trace elements found in these two types of aquifer system in the context of medical hydrogeology, i.e. the status of groundwater mineral nutrients and pollutants, and their complex interaction in relation to human health. The evaluation work used a collated geochemical dataset developed for Bangladesh sedimentary aquifer data (n = 474), basement aquifer data from Northern Ghana (n = 184) and Central Tanzania (n = 73). An assessment of the mineral concentration in regards to dietary needs showed that the sedimentary aquifers found in Bangladesh have almost double the concentration of salubrious minerals such as calcium, magnesium and iron relative to the basement aquifers (Ghana and Tanzania). It should be noted, however, that the groundwater was also found to contain excessive levels of arsenic in the sedimentary aquifers and high levels of fluoride in those countries sourcing water from within basement rock; levels at which both elements pose a serious public health threat. Excessive sodium in drinking water is also an issue as this, combined with the normal dietary sodium level intake, may lead to hypertension and cardio-metabolic diseases. Unfortunately, health-based guideline values for drinking water containing sodium are non-existent or poorly defined, a fact which warrants further consideration at both a national and international level. The use of groundwater for drinking may assist in increasing the level of mineral nutrient uptake in the local population, however, it must also be augmented by a nutritious food supply in order to satisfy normal human dietary requirements.

Capabilities of an optical direct push probe for 2D-subsurface imaging

Characterization of hydrological conditions at polluted sites is critical for understanding of contaminant distribution and transport. Standard techniques for site characterization, such as soil coring together with well installation for piezometric measurements and water sampling, allow only some insights into subsurface properties and processes. To obtain additional data, direct-push techniques are often used in soils and unconsolidated formations. The various available techniques provide high resolution information on cm to mm scale. Recently, the Optical Imaging Profiler (OIP) was developed for detection of fluorescent contaminants. Here, we have investigated the applicability of the OIP for groundwater tracing using fluorophores. Our laboratory experiments show that it is possible to qualitatively trace various fluorophores meaning that light emitted by the fluorophores can be detected by a standard digital camera sensor. The measured fluorescence depends on the number of fluorophore molecules present in the pore space adjacent to the OIP and decreases with smaller pore size as well as fluorophore concentration. In a field trial, an injected eosin Y solution could be very clearly detected after the injection within a radius of 0.5 m around the injection point. When the OIP is equipped with a second light source emitting visible light, images of the soil texture and color can be captured. Sediment color can act as a proxy for various soil properties. Tests at a second field site, indicate that detected variation in soil color depend on water saturation and redox processes. Hence, the OIP is a flexible, cost effective and multifunctional tool for characterization of contaminated sites.

Sulfur Hexafluoride and Potassium Bromide as Groundwater Tracers for Managed Aquifer Recharge.

Sulfur hexafluoride (SF6 ) is an established tracer for use in managed aquifer recharge projects. SF6 exsolves from groundwater when it encounters trapped air according to Henry's law. This results in its retardation relative to groundwater flow, which can help determine porous media saturation and flow dynamics. SF6 and the conservative, nonpartitioning tracer, bromide (Br- added as KBr), were introduced to recharge water infiltrated into stacked glacial aquifers in Thurston County, Washington, providing the opportunity to observe SF6 partitioning. Br- , which is assumed to travel at the same velocity as the groundwater, precedes SF6 at most monitoring wells (MWs). Average groundwater velocity in the unconfined aquifer in the study area ranges from 3.9 to 40 m/d, except in the southwestern corner where it is slower. SF6 in the shallow aquifer exhibits an average retardation factor of 2.5 ± 3.8, suggesting an air-to-water ratio on the order of 10-3 to 10-2 in the pore space. Notable differences in tracer arrival times at adjacent wells indicate very heterogeneous conductivity. One MW exhibits double peaks in concentrations of both tracers with different degrees of retardation for the first and second peaks. This suggests multiple flowpaths to the well with variable saturation. The confining layer between the upper two aquifers appears to allow intermittent connection between aquifers but serves as an aquitard in most areas. This study demonstrates the utility of SF6 partitioning for evaluating hydrologic conditions at prospective recharge sites.

A groundwater tracing investigation to determine Kalisirah Karst Springs catchment area, Kebumen Regency, Central Java

Water tracing was conducted at Karangbolong Karst as a rapid assessment of the Kalisirah spring hydrological characteristics. This study was conducted to determine the movement of underground flow and the estimation of the Catchment Area using the Todd Nomogram and field observations. The results of flow tracing tests conducted in Pocung Cave indicate that there is underground river network connectivity between Pocung Cave, Jeblosan Sinkhole and Kalisirah Springs. Based on topographic survey and flow tracing test, the calculation of the estimated area of the Kalisirah catchment area is 180 Ha. The results were also validate using other parameters, namely flowrate and rainfall in the research location using Todd Nomogram. The estimated area of the Kalisirah catchment area with the Todd Nomogram is 189.2 Ha. The calculation of the estimated area of Kalisirah catchment area based on topographic survey and water tracing is relevant with the estimated area with Todd Nomogram. Groundwater tracing investigation can be used to determine karst spring catchment area, as a preliminary study to understanding the karst hydrology.

Major and trace (including arsenic) groundwater chemistry in central and southern Myanmar

Myanmar, in Southeast Asia, is categorized as a Least Developed Country, facing substantial challenges towards meeting 2030 Sustainable Development Goal targets, including ensuring access to safe water and sanitation. The occurrence of geogenic contaminants, notably arsenic, in Myanmar groundwaters is relatively poorly understood, particularly as compared to other countries in South/Southeast Asia. Improving the understanding of groundwater quality in Myanmar is hence a major concern and relevant to the health of millions of local inhabitants who extensively use groundwater. A groundwater survey was undertaken at 85 sites across five distinctly contrasting zones within three of Myanmar's main river basins (Chindwin-Ayeyarwady, Sittaung, and Salween) to assess the occurrence of arsenic and other potentially harmful elements, and to study the dominant geochemical controls in each zone/basin. A significant number of samples were affected by water quality issues, based on World Health Organization (WHO) guidelines, including elevated arsenic (>10 μg.L−1) in 14% of all samples within the basins studied. Fluoride, nitrate, salinity, iron, manganese, and aluminum also exceeded WHO drinking water guidelines in some locations. Arsenic typically occurred as inorganic AsIII and largely arose from the reductive dissolution of Fe(Mn)-(hydro)xides and was broadly associated with relatively high HCO3 and NH4. Variable dominant geochemical controls on groundwater composition were identified, notably (i) calcite and dolomite dissolution in the Salween basin; (ii) cation exchange, carbonate dissolution and saline intrusion in the Ayeyarwady delta; and (iii) gypsum dissolution, silicate weathering, and cation exchange in Chindwin-Middle Ayeyarwady. This reconnaissance study provides new information on groundwater composition and corresponding geochemical controls across contrasting, and previously underrepresented, areas of Myanmar and may help to inform further hazard assessment, monitoring and/or mitigation strategies.

Using radon to quantify groundwater discharge and methane fluxes to a shallow, tundra lake on the Yukon-Kuskokwim Delta, Alaska

Northern lakes are a source of greenhouse gases to the atmosphere and contribute substantially to the global carbon budget. However, the sources of methane (CH4) to northern lakes are poorly constrained limiting our ability to the assess impacts of future Arctic change. Here we present measurements of the natural groundwater tracer, radon, and CH4 in a shallow lake on the Yukon-Kuskokwim Delta, AK and quantify groundwater discharge rates and fluxes of groundwater-derived CH4. We found that groundwater was significantly enriched (2000%) in radon and CH4 relative to lake water. Using a mass balance approach, we calculated average groundwater fluxes of 1.2 ± 0.6 and 4.3 ± 2.0 cm day−1, respectively as conservative and upper limit estimates. Groundwater CH4 fluxes were 7—24 mmol m−2 day−1 and significantly exceeded diffusive air–water CH4 fluxes (1.3–2.3 mmol m−2 day−1) from the lake to the atmosphere, suggesting that groundwater is an important source of CH4 to Arctic lakes and may drive observed CH4 emissions. Isotopic signatures of CH4 were depleted in groundwaters, consistent with microbial production. Higher methane concentrations in groundwater compared to other high latitude lakes were likely the source of the comparatively higher CH4 diffusive fluxes, as compared to those reported previously in high latitude lakes. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for CH4 release across Arctic landscapes.

Groundwater vulnerability and trace element dispersion in the Quaternary aquifers along middle Upper Egypt.

Association of trace metal concentrations in water is problematic; however, its information is scarce and sometimes contradicted. This work presents variations in dissolved major constituents and trace element concentrations along the quaternary aquifers located in middle Upper Egypt (Minia and Assiut governorates). A total of 205 groundwater samples from these aquifers were collected. Auxiliary parameters (pH, alkalinity, and conductivity), major cations (Ca2+, Mg2+, Na+, and K+), dominant anions (HCO3-, SO42-, Cl-, and NO3-), and trace element (B, Fe, Cu, Mn, Ni, Pb, Cd, and Cr) concentrations were measured in all samples. Univariate (correlation coefficient and scatter matrix) analysis was employed combined with multivariate (principal coordinates analysis) analysis to identify the chemical characteristics of groundwater that are responsible for generating most of the variability within the dataset. Also, hierarchical cluster analysis was applied to classify the geochemical origin of the groundwater constituents. The results indicate that the groundwater pollution is mainly due to water-rock interactions, including aquifer matrix dissolution, redox reaction of trace metals, input from wastewater, and agricultural fertilizers.

Global Research Trends and Hotspots on Submarine Groundwater Discharge (SGD): A Bibliometric Analysis.

Submarine groundwater discharge (SGD), a major component of the hydrological cycle, has significant impacts on the sustainable development of the marine environment. This study aimed to examine the literature characteristics and research hotspots of SGD based on Web of Science’s citation database from 1998–2019. With systematic bibliometric analysis, insights were made into multiple aspects including research output, subject categories, journals, countries/territories, institutions, authors, and hotspots and research trends. Results showed that the current amount of publications on SGD has increased exponentially. The characteristics of multi-subject, active international and inter-institutional collaborations were identified. There were 11 core journals publishing the research on SGD, and the number of covered journals increased linearly from 1998. USA had distinct advantages in publication outputs and took the core position in international collaborations. At present, the research hotspots of SGD mainly include the following: dynamics process and estimation of SGD with hydrogeological methods, tracer techniques, geochemical process in subterranean estuary, and dissolved material inputs to coastal waters via SGD. Citation analysis implied much development space in carbon flux transported by SGD and the implement of head as groundwater tracer. These results provided an instructive perspective of the present situation and future research direction on SGD.

Submarine Groundwater and Vent Discharge in a Volcanic Area Associated With Coastal Acidification

AbstractWe investigated submarine groundwater discharge (SGD) in a volcanic coastal area that hosts the world's most biodiverse reefs. Measurements of 222Rn activity in coastal seawater, a tracer for groundwater, indicated prevalent SGD. In areas where seawater 222Rn activity was generally higher, we discovered hydrothermal springs emitting acidic waters (pH ~5.4–6.0) and venting magmatic CO2 that brought local pCO2 levels up to 95,000 ppm. The collection of vents raised CO2 and lowered pH over 1–2 km of coastline. The hydrogen and oxygen isotope compositions of water and chloride concentration revealed that the springs discharge recirculated seawater mixed variably with terrestrial groundwater. Shallower springs and pore water have a higher proportion of terrestrial groundwater than deeper springs, which emit mostly recirculated seawater. This suggests that different SGD mechanisms are present. The SGD could be contributing to the evolution and function of the biodiverse ecosystem, but it also represents myriad pathways for contamination.

氯化钠用于喀斯特地区地下水示踪试验的应用研究

氯化钠用于喀斯特地区地下水示踪试验的应用研究

A Review of Tracing Groundwater Contamination with Multiple Isotopes

A Review of Tracing Groundwater Contamination with Multiple Isotopes

Using water level and temperature time series to improve hydrogeological parameterization in a complex alluvial system

A new pumping station was designed in the northern high plain of the province of Padua (Veneto region, north-eastern Italy), aiming to reach an overall abstraction rate of about 2 m3/s, in order to relevantly contribute to the regional drinking water supply. Local unconfined aquifer is a highly permeable alluvial system, hydraulically connected to the Brenta river, one of the most important groundwater recharging sources of the entire hydrogeological basin, and the Camazzole lake, a former open-pit mine. This lake deepens below the water table and is directly connected to the surrounding phreatic aquifer and indirectly to the river, forming a 3-element hydraulic equilibrium. In order to evaluate the sustainability of the groundwater exploitation, this case study required an in-depth analysis of the hydrogeological resource, focusing on the estimation of hydraulic conductivity values and distribution. A numerical simulation was needed since the first step of the study, to plan the following field activities and provide a rough representation of the expectable drawdown in the pumped aquifer, even if the initial model had a very high level of uncertainty. Before the pumping tests no experimental data were available, so a homogeneous distribution of hydraulic conductivity was preliminarily assigned to the entire mesh, referring to a single bibliographic value available for the aquifer. After the analytical interpretation of pumping tests, different punctual values of hydraulic conductivity were estimated, but the parameter field was still very difficult to define, due to the complexity of the hydrogeological context and the non-uniqueness of the possible spatial interpolations. The availability of groundwater level observations at a larger scale allowed to calculate a set of hydraulic conductivity fields through the pilot points method, integrating the pumping tests results and extending aquifer characterization to a wider domain. The numerical model was finally calibrated with groundwater temperature monitored trends, reproducing the interaction between the lake and the phreatic aquifer through a heat transport simulation. The resulting hydraulic conductivity distribution has been considerably refined, especially at the interface between the lake and the aquifer, and the parameterization has been further validated using heat as a groundwater tracer.

Elevated dissolved heavy metal discharge following rainfall downstream of intensive horticulture

Heavy metals may be released from soils during rain events. Observations during the first flush (rain event preceded by dry period) are difficult, but may account for a large fraction of annual loads. Here, we report detailed time series measurements of dissolved heavy metals and the groundwater tracer radon (222Rn) over multiple rain events from a creek draining a catchment dominated by intensive horticulture on the subtropical east coast of Australia. The creek drains to an intermittently closed and open lake or lagoon (ICOLL), a typical estuary type along the east coast of Australia. A sandbank prevents the estuary mouth from connecting with the ocean during dry conditions. Following a 109 mm rain event, the ICOLL began to drain to the coastal ocean. Mean export of Hg, Cu, and Zn was 0.23 ± 0.05, 1.06 ± 0.25, and 15.70 ± 2.69 g m−2 day−1 for the entire time series and 0.72 ± 0.17, 1.27 ± 0.12, 24.14 ± 3.82 g m−2 day−1 averaged from high resolution sampling over 72 h of the first flush event. Trends of Hg export differed from the other heavy metals. Over 79% of the estimated Hg export occurred within 72 h of the ICOLL opening, compared to 30 and 38% of Cu and Zn. The first flush and subsequent major rain events (> 50 mm day-1) drove concentrations of Hg, Cu and Zn to exceed the Australia and New Zealand Environment and Conservation Council (ANZECC) water quality guidelines (WQG) for both fresh and marine water. Comparisons of heavy metal export to downstream estuary sediment burial rates revealed that the estuary is likely a source of dissolved Hg and Cd to the coastal ocean when the ICOLL is open.

Groundwater trace elements change induced by M5.0 earthquake in Yunnan

Geochemical compositions changes in groundwater in response to earthquakes have been documented for decades, and most such studies have documented the changes in major ions or geochemical gases (e.g., Radon). Changes in trace elements, however, have received less attention. In this paper, we collected groundwater samples from a wellbore in Yunnan Province weekly and analyzed both the major and trace chemical compositions from February 2018 to September 2018. Combined with well water level records, we found that the August 2018 Tonghai M5.0 earthquake caused changes in both water levels and trace elements but caused no significant changes in the stable isotope and major ions. Such a response indicates that trace elements are more sensitive to crustal strain than are the major elements and isotopes. And We considered that earthquake-induced shaking caused a breach in the hydraulic barrier of the isolated reservoir that led to the mixing of water with low concentrations of trace elements as the mechanism to explain the coseismic response. This study demonstrate that some trace elements are more sensitive to earthquake strain than the commonly used chemical constitutents and that trace element monitoring should considered to be a priority in the future to provide a complete assessment of the sensitivity of different chemical constitutents to earthquake stresses.

Depth‐Resolved Groundwater Chemistry by Longitudinal Sampling of Ambient and Pumped Flows Within Long‐Screened and Open Borehole Wells

AbstractDepth‐resolved chemistry samples are critical to a wide range of groundwater investigations. If a well intersects zones of variable concentrations, a pumped sample is a composite of the inflows, which mix in the well. Where discrete concentrations are required, excessive mixing makes samples less useful and potentially misleading. However, installations for depth‐discrete sampling are expensive, particularly for regional studies, so sometimes there is incentive to use existing infrastructure designed for other purposes (e.g., supply wells). This paper shows how the resolution of groundwater chemistry derived from long‐screened and open borehole wells can be improved by measuring and sampling the in‐well vertical flow regimes in ambient (unpumped) and/or pumped conditions. The ambient flow regime, driven by a natural vertical head gradient, is shown to be particularly useful to sample groundwater native to defined inflow zones (head in the zone > head in the well) and avoid zones impacted by the invasion of intraborehole flow (head in the zone < head in the well). Depth‐specific samples are interpreted either as native groundwater from a discrete source, subject only to analytical error, or a mixture from multiple sources that can be deconvolved, incorporating error in both flow and concentration measurements. Depth‐resolved age tracers (chlorofluorocarbons, 14C, and He) in groundwater from three supply wells are verified with samples from a multidepth nest of piezometers. Results show old groundwater at all depths and the simultaneous occurrence of young water at shallower depths in undisturbed dual‐porosity fractured aquifers in the Pilbara region of Western Australia.

Parallels between stream and coastal water quality associated with groundwater discharge.

Groundwater-surface water interactions drive water quality in both streams and the coastal ocean, where groundwater discharge occurs in streams as baseflow and along the coastline as submarine groundwater discharge (SGD). Groundwater contributions to streams and to the coastal ocean were quantified in three urban streams in Kāneʻohe Watershed, Hawaiʻi. We used radon as a groundwater tracer to show that baseflow contributions to streams ranged from 22 to 68% along their reaches leading to the coast of Kāneʻohe Bay. Total SGD was 4,500, 18,000, and 23,000 m3/day for the northwest, central, and southern sectors of the bay, respectively. Total groundwater (stream baseflow + SGD) dissolved nutrient fluxes were significantly greater than those sourced from stream surface runoff. The studied streams exhibited increasing nutrient levels downstream from groundwater inputs with high nutrient concentrations, negatively impacting coastal water quality. SGD dynamics were also assessed during the anomalously high perigean spring tides in 2017, where SGD was four times greater during the perigean spring tide compared to a spring tide and resulted in strong shifts in N:P ratios, suggesting that rising sea level stands may disrupt primary productivity with greater frequency. This study demonstrates the importance of considering baseflow inputs to streams to coastal groundwater budgets and suggests that coastal water quality may be improved through management and reduction of groundwater contaminants.