Tamborski Joseph

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  • Article
    DSi as a tracer for submarine groundwater discharge
    (Frontiers Media, 2019-09-13) Oehler, Till ; Tamborski, Joseph ; Rahman, Shaily ; Moosdorf, Nils ; Ahrens, Janis ; Mori, Corinna ; Neuholz, René ; Schnetger, Bernhard ; Beck, Melanie
    Submarine groundwater discharge (SGD) is an important source of nutrients and metals to the coastal ocean, affects coastal ecosystems, and is gaining recognition as a relevant water resource. SGD is usually quantified using geochemical tracers such as radon or radium. However, a few studies have also used dissolved silicon (DSi) as a tracer for SGD, as DSi is usually enriched in groundwater when compared to surface waters. In this study, we discuss the potential of DSi as a tracer in SGD studies based on a literature review and two case studies from contrasting environments. In the first case study, DSi is used to calculate SGD fluxes in a tropical volcanic-carbonate karstic region (southern Java, Indonesia), where SGD is dominated by terrestrial groundwater discharge. The second case study discusses DSi as a tracer for marine SGD (i.e., recirculated seawater) in the tidal flat area of Spiekeroog (southern North Sea), where SGD is dominantly driven by tidal pumping through beach sands. Our results indicate that DSi is a useful tracer for SGD in various lithologies (e.g., karstic, volcanic, complex) to quantify terrestrial and marine SGD fluxes. DSi can also be used to trace groundwater transport processes in the sediment and the coastal aquifer. Care has to be taken that all sources and sinks of DSi are known and can be quantified or neglected. One major limitation is that DSi is used by siliceous phytoplankton and therefore limits its applicability to times of the year when primary production of siliceous phytoplankton is low. In general, DSi is a powerful tracer for SGD in many environments. We recommend that DSi should be used to complement other conventionally used tracers, such as radon or radium, to help account for their own shortcomings.
  • Article
    Investigating boron isotopes for identifying nitrogen sources supplied by submarine groundwater discharge to coastal waters
    (Frontiers Media, 2020-08-11) Tamborski, Joseph ; Brown, Caitlin ; Bokuniewicz, Henry J. ; Cochran, J. Kirk ; Rasbury, E. Troy
    Stable isotopes of oxygen, nitrogen, and boron were used to identify the sources of nitrate (NO3–) in submarine groundwater discharge (SGD) into a large tidal estuary (Long Island Sound, NY, United States). Potential contaminants such as manure, septic waste and fertilizer overlap in δ15N and δ18O but have been shown to have distinctive δ11B in non-coastal settings. Two distinct subterranean estuaries were studied with different land-use up gradient, representative of (1) mixed medium-density residential housing and (2) agriculture. These sites have overlapping δ15N and δ18O measurements in NO3– and are unable to discriminate between different N sources. Boron isotopes and concentrations are measurably different between the two sites, with little overlap. The subterranean estuary impacted by mixed medium-density residential housing shows little correlation between δ11B and [B] or between δ11B and salinity, demonstrating that direct mixing relationships between fresh groundwater and seawater were unlikely to account for the variability. No two sources could adequately characterize the δ11B of this subterranean estuary. Groundwater N at this location should be derived from individual homeowner cesspools, although measured septic waste has much lower δ11B compared to the coastal groundwaters. This observation, with no trend in δ11B with [B] indicates multiple sources supply B to the coastal groundwaters. The agricultural subterranean estuary displayed a positive correlation between δ11B and [B] without any relationship with salinity. Binary mixing between sea spray and fertilizer can reasonably explain the distribution of B in the agricultural subterranean estuary. Results from this study demonstrate that δ11B can be used in combination with δ15N to trace sources of NO3– to the subterranean estuary if source endmember isotopic signatures are well-constrained, and if the influence of seawater on δ11B signatures can be minimized or easily quantified.
  • Article
    Radium mass balance sensitivity analysis for submarine groundwater discharge estimation in semi-enclosed basins: the case study of Long Island Sound
    (Frontiers Media, 2020-07-17) Tamborski, Joseph ; Cochran, J. Kirk ; Bokuniewicz, Henry J. ; Heilbrun, Christina ; Garcia-Orellana, Jordi ; Rodellas, Valenti ; Wilson, Robert
    Estimation of submarine groundwater discharge (SGD) to semi-enclosed basins by Ra isotope mass balance is herein assessed. We evaluate 224Ra, 226Ra, and 228Ra distributions in surface and bottom waters of Long Island Sound (CT-NY, United States) collected during spring 2009 and summer 2010. Surface water and bottom water Ra activities display an apparent seasonality, with greater activities during the summer. Long-lived Ra isotope mass balances are highly sensitive to boundary fluxes (water flux and Ra activity). Variation (50%) in the 224Ra, 226Ra, and 228Ra offshore seawater activity results in a 63–74% change in the basin-wide 226Ra SGD flux and a 58–60% change in the 228Ra SGD flux, but only a 4–9% change in the 224Ra SGD flux. This highlights the need to accurately constrain long-lived Ra activities in the inflowing and outflowing water, as well as water fluxes across boundaries. Short-lived Ra isotope mass balances are sensitive to internal Ra fluxes, including desorption from resuspended particles and inputs from sediment diffusion and bioturbation. A 50% increase in the sediment diffusive flux of 224Ra, 226Ra, and 228Ra results in a ∼30% decrease in the 224Ra SGD flux, but only a ∼6–10% decrease in the 226Ra and 228Ra SGD flux. When boundary mixing is uncertain, 224Ra is the preferred tracer of SGD if sediment contributions are adequately constrained. When boundary mixing is well-constrained, 226Ra and 228Ra are the preferred tracers of SGD, as sediment contributions become less important. A three-dimensional numerical model is used to constrain boundary mixing in Long Island Sound (LIS), with mean SGD fluxes of 1.2 ± 0.9 × 1013 L y–1 during spring 2009 and 3.3 ± 0.7 × 1013 L y–1 during summer 2010. The SGD flux to LIS during summer 2010 was one order of magnitude greater than the freshwater inflow from the Connecticut River. The maximum marine SGD-driven N flux is 14 ± 11 × 108 mol N y–1 and rivals the N load of the Connecticut River.
  • Article
    Nutrient fluxes associated with submarine groundwater discharge from karstic coastal aquifers (Côte Bleue, French Mediterranean coastline)
    (Frontiers Media, 2020-02-18) Bejannin, Simon ; Tamborski, Joseph ; van Beek, Pieter ; Souhaut, Marc ; Stieglitz, Thomas ; Radakovitch, Olivier ; Claude, Christelle ; Conan, Pascal ; Pujo-Pay, Mireille ; Crispi, Olivier ; Le Roy, Emilie ; Estournel, Claude
    Determination of submarine groundwater discharge (SGD) from karstic coastal aquifers is important to constrain hydrological and biogeochemical cycles. However, SGD quantification using commonly employed geochemical methods can be difficult to constrain under the presence of large riverine inputs, and is further complicated by the determination of the karstic groundwater endmember. Here, we investigated a coastal region where groundwater discharges from a karstic aquifer system using airborne thermal infrared mapping and geochemical sampling conducted along offshore transects. We report radium data (223Ra, 224Ra, 228Ra) that we used to derive fluxes (water, nutrients) associated with terrestrial groundwater discharge and/or seawater circulation through the nearshore permeable sediments and coastal aquifer. Field work was conducted at different periods of the year to study the temporal variability of the chemical fluxes. Offshore transects of 223Ra and 224Ra were used to derive horizontal eddy diffusivity coefficients that were subsequently combined with surface water nutrient gradients (NO2− + NO3−, DSi) to determine the net nutrient fluxes from SGD. The estimated DSi and (NO2− + NO3−) fluxes are 6.2 ± 5.0 *103 and 4.0 ± 2.0 *103 mol d−1 per km of coastline, respectively. We attempted to further constrain these SGD fluxes by combining horizontal eddy diffusivity and 228Ra gradients. However, SGD endmember selection in this area (terrestrial groundwater discharge vs. porewater) adds further uncertainty to the flux calculation and thus prevented us from calculating a reliable flux using this latter method. Additionally, the relatively long half-life of 228Ra (5.75 y) makes it sensitive to specific circulation patterns in this coastal region, including sporadic intrusions of Rhône river waters that impact both the 228Ra and nutrient surface water distributions. We show that SGD nutrient fluxes locally reach up to 20 times the nutrient fluxes from a small river (Huveaune River). On a regional scale, DSi fluxes driven by SGD vary between 0.1 and 1.4% of the DSi inputs of the Rhône River, while the (NO2− + NO3−) fluxes driven by SGD on this 22 km long coastline are between 0.1 and 0.3% of the Rhône River inputs, the largest river that discharges into the Mediterranean Sea. Interestingly, the nutrient fluxes reported here are similar in magnitude compared with the fluxes quantified along the sandy beach of La Franqui, in the western Gulf of Lions (Tamborski et al., 2018), despite the different lithology of the two areas (karst systems vs. unconsolidated sediment).