What Is the Role of Fresh Groundwater and Recirculated Seawater in Conveying Nutrients to the Coastal Ocean?

Weinstein, Yishai; Yechieli, Yoseph; Shalem, Yehuda; Burnett, William C.; Swarzenski, Peter W.; Herut, Barak

doi:10.1021/es104394r

Cited by 82 publications

(56 citation statements)

References 28 publications

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“…DIN exported to the seepage face (∼ 142 mol m −1 yr −1 ) was in the range of previous measurements at other sites, such as the Mediterranean coast (France; 530 mol m −1 yr −1 ; Weinstein et al, 2011), the Gulf of Mexico (FL, USA; 414 mol m −1 yr −1 ; Santos et al, 2009) and the Atlantic coast (Aquitania coast, France; 150 mol m −1 yr −1 ; Anschutz et al, 2016). However, in most of these studies, the DIN pool was mainly dominated by NO x , while at Martinique Beach NH + 4 represented more than 90 % of the potential DIN supply to the seepage face.…”

Section: Nitrogen Fluxessupporting

confidence: 72%

Nitrogen transformations along a shallow subterranean estuary

et al. 2017

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Abstract. The transformations of chemical constituents in subterranean estuaries (STEs) control the delivery of nutrient loads from coastal aquifers to the ocean. It is important to determine the processes and sources that alter nutrient concentrations at a local scale in order to estimate accurate regional and global nutrient fluxes via submarine groundwater discharge (SGD), particularly in boreal environments, where data are still very scarce. Here, the biogeochemical transformations of nitrogen (N) species were examined within the STE of a boreal microtidal sandy beach located in the Magdalen Islands (Quebec, Canada). This study revealed the vertical and horizontal distribution of nitrate (NO, dissolved organic nitrogen (DON) and total dissolved nitrogen (TDN) measured in beach groundwater during four spring seasons (June 2011(June , 2012(June , 2013(June and 2015 when aquifer recharge was maximal after snowmelt. Inland groundwater supplied high concentrations of NO x and DON to the STE, whereas inputs from seawater infiltration were very limited. Non-conservative behaviour was observed along the groundwater flow path, leading to low NO x and high NH + 4 concentrations in the discharge zone. The long transit time of groundwater within the beach (∼ 166 days), coupled with oxygen-depleted conditions and high carbon concentrations, created a favourable environment for N transformations such as heterotrophic and autotrophic denitrification and ammonium production. Biogeochemical pathways led to a shift in nitrogen species along the flow path from NO x -rich to NO x -poor groundwater. An estimate of SGD fluxes of N was determined to account for biogeochemical transformations within the STE based on a N-species inventory and Darcy's flow. Fresh inland groundwater delivered 37 mol NO x yr −1 per metre of shoreline and 63 mol DON m −1 yr −1 to the STE, and NH and DON. Our study shows the importance of tidal sands in the biogeochemical transformation of the terrestrial N pool. This local export of bioavailable N probably supports benthic production and higher trophic levels leading to its rapid transformation in surface sediments and coastal waters.

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Section: Nitrogen Fluxessupporting

confidence: 72%

Nitrogen transformations along a shallow subterranean estuary

et al. 2017

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“…It is known that SGW contains elevated amounts of dissolved nutrients, including silicic acid. They estimate a global average of 200 µmol Si kg −1 , which is in the mid-range of a specific study on SGW carried out at Dor on the Israeli coast (Weinstein et al, 2011). Taken together this represents a flux of 9.7 mol Si yr −1 calculated as 25 % of total riverine water flow × 200 µmol Si kg −1 .…”

Section: Submarine Groundwater Flux (Sgw)mentioning

confidence: 89%

“…This was considered reasonable both because of the nature of the sediments, which are deep-sea sediments where bioirrigation was not expected to be a significant process, and because of the shape of the silicic acid profiles, which showed no evidence of being modified by depth-dependent bioirrigation. The molecular diffusion coefficient for silicic acid in seawater measured at 25 • C is 1 × 10 −5 cm 2 s −1 (Wollast and Garrels, 1971). Correcting this for temperature using the Stokes-Einstein relationship (T = 13 • C for ADW) = 0.7 × 10 −5 cm 2 s −1 .…”

Section: Silicic Acid In Porewatersmentioning

confidence: 99%

Silica cycling in the ultra-oligotrophic eastern Mediterranean Sea

2014

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Abstract. Although silica is a key plant nutrient, there have been few studies aimed at understanding the Si cycle in the eastern Mediterranean Sea (EMS). Here we use a combination of new measurements and literature values to explain the silicic acid distribution across the basin and to calculate a silica budget to identify the key controlling processes. The surface water concentration of ∼ 1 µM, which is unchanging seasonally across the basin, was due to the inflow of western Mediterranean Sea (WMS) water at the Straits of Sicily. It does not change seasonally because there is only a sparse population of diatoms due to the low nutrient (N and P) supply to the photic zone in the EMS. The concentration of silicic acid in the deep water of the western Ionian Sea (6.3 µM) close to the S Adriatic are an of formation was due to the preformed silicic acid (3 µM) plus biogenic silica (BSi) from the dissolution of diatoms from the winter phytoplankton bloom (3.2 µM). The increase of 4.4 µM across the deep water of the EMS was due to silicic acid formed from in situ diagenetic weathering of aluminosilicate minerals fluxing out of the sediment. The major inputs to the EMS are silicic acid and BSi inflowing from the western Mediterranean (121 × 10 9 mol Si yr −1 silicic acid and 16 × 10 9 mol Si yr −1 BSi), silicic acid fluxing from the sediment (54 × 10 9 mol Si yr −1 ) and riverine (27 × 10 9 mol Si yr −1 ) and subterranean groundwater (9.7 × 10 9 mol Si yr −1 ) inputs, with only a minor direct input from dissolution of dust in the water column (1 × 10 9 mol Si yr −1 ). This budget shows the importance of rapidly dissolving BSi and in situ weathering of aluminosilicate minerals as sources of silica to balance the net export of silicic acid at the Straits of Sicily. Future measurements to improve the accuracy of this preliminary budget have been identified.

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“…Other studies highlight that biogeochemical processes occurring in a STE can attenuate high N and P in contaminated terrestrial groundwater prior to discharge to the coastal ocean [Addy et al, 2005;Kroeger and Charette, 2008;Santoro et al, 2008]. For example, attenuation of nitrate contamination in terrestrial groundwater by denitrification has been observed in STEs [Loveless and Oldham, 2010;Weinstein et al, 2011;Erler et al, 2014], resulting in non-conservative net nitrate removal ( Figure 4A). However, studies have also shown net nitrate production and high nitrate concentrations in shallow STEs despite low nitrate concentrations in both terrestrial groundwater and seawater.…”

mentioning

confidence: 98%

“…In systems with high seawater productivity and organic matter content, saline SGD associated with tide-and wave-induced seawater circulating through the STE may release nutrients to the ocean due to the mineralization of marine organic matter [Anwar et al, 2014;Sadat-Noori et al, 2016b;Santos et al, 2009d]. The loads of marine 31 organic matter delivered into a STE are lower where the coastal ocean is oligotrophic, which may result in FSGD rather than saline SGD dominating the nutrient fluxes to the ocean [Weinstein et al, 2011]. Quantifying SGD-derived nutrient fluxes to the ocean requires sitespecific understanding of biogeochemical transformations and groundwater flow processes in a STE.…”

mentioning

confidence: 99%

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Robinson¹,

Xin²,

Santos³

et al. 2018

Advances in Water Resources

217

148

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Sustainable coastal resource management requires sound understanding of interactions between coastal unconfined aquifers and the ocean as these interactions influence the flux of chemicals to the coastal ocean and the availability of fresh groundwater resources. The importance of submarine groundwater discharge in delivering chemical fluxes to the coastal ocean and the critical role of the subterranean estuary (STE) in regulating these fluxes is well recognized. STEs are complex and dynamic systems exposed to various physical, hydrological, geological, and chemical conditions that act on disparate spatial and temporal scales. This paper provides a review of the effect of factors that influence flow and salt transport in STEs, evaluates current understanding on the interactions between these influences, and synthesizes understanding of drivers of nutrient, carbon, greenhouse gas, metal and organic contaminant fluxes to the ocean.Based on this review, key research needs are identified. While the effects of density and tides are well understood, episodic and longer-period forces as well as the interactions between multiple influences remain poorly understood. Many studies continue to focus on idealized nearshore aquifer systems and future work needs to consider real world complexities such as geological heterogeneities, and non-uniform and evolving alongshore and cross-shore morphology. There is also a significant need for multidisciplinary research to unravel the interactions between physical and biogeochemical processes in the STE, as most existing studies treat these processes in isolation. Better understanding of this complex and dynamic system can improve sustainable management of coastal water resources under the influence of anthropogenic pressures and climate change.

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What Is the Role of Fresh Groundwater and Recirculated Seawater in Conveying Nutrients to the Coastal Ocean?

Cited by 82 publications

References 28 publications

Nitrogen transformations along a shallow subterranean estuary

Nitrogen transformations along a shallow subterranean estuary

Silica cycling in the ultra-oligotrophic eastern Mediterranean Sea

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

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