Flow and discharge of groundwater from a snowmelt-affected sandy beach

Chaillou, Gwénaëlle; Lemay-Borduas, Frédérike; Larocque, Marie; Couturier, Mathilde; Biehler, Antoine; Tommi-Morin, Gwendoline

doi:10.1016/j.jhydrol.2017.12.010

Cited by 16 publications

(19 citation statements)

References 46 publications

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“…In addition, external contamination from wastewater or sceptic tank seepages cannot be completely excluded. Nevertheless, the absence of traces of NH + 4 contamination in the landward part of the beach and the stable isotopes of water reported by Chaillou et al (2017) do not support an anthropogenic NH + 4 input.…”

Section: Ammonium Production Along the Stementioning

confidence: 73%

“…Under these hydrologic conditions, the saline circulation cell and its associated mixing zone are spatially limited, and the inland hydraulic gradient is the main control of total SGD (Heiss and Michael, 2014;Robinson et al, 2007a). Based on the stable isotopes of water along the STE, Chaillou et al (2017) confirmed the contribution of only two water endmembers (i.e. fresh meteoric groundwater and seawater) and the absence of additional sep-tic tank seepages.…”

Section: Study Areamentioning

confidence: 89%

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Nitrogen transformations along a shallow subterranean estuary

Couturier¹,

Nozais²,

Rao³

et al. 2016

Preprint

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Abstract. The transformations of chemical constituents in subterranean estuaries (STE) control the delivery of nutrient loads from aquifers to the coastal ocean. It is important to determine the processes and sources that affect nutrient concentrations at a local scale in order to accurately estimate 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 microtidal boreal sandy beach located in the &#206;les-de-la-Madeleine (Qu&#233;bec, Canada). This study reveals the vertical and horizontal distribution of nitrate (NO3&#8722;), nitrite (NO2&#8722;), ammonia (NH4+), dissolved organic nitrogen (DON) and total dissolved nitrogen (TDN) measured in beach groundwater during four spring seasons (June 2011, 2012, 2013 and 2015) when aquifer recharge is maximal after snow melt. Inland groundwater supplied high concentrations of NOx&#8722; and DON to the STE, whereas inputs from seawater were very limited. Non-conservative behaviour was observed along the groundwater flow path, leading to low NOx&#8722; and high NH4+ concentrations in the discharge zone. The long residence time of groundwater within the beach (~&#8201;82 days), coupled with oxygen-depleted conditions and high carbon concentrations created a favourable environment for N transformations such as heterotrophic denitrification and ammonium production. An estimate of SGD fluxes of N was determined to account for biogeochemical transformations within the STE. Fresh inland groundwater delivers 37.54&#8201;mol&#8201;m&#8722;1&#8201;y&#8722;1 of NOx and 63.57&#8201;mol&#8201;m&#8722;1&#8201;y&#8722;1 of DON to the STE, and NH4+ input was negligible. But the N load to coastal waters is dominated by NH4+ and DON, due to N transformations along the flow path. NH4+ represents 99&#8201;% of the DIN flux to coastal waters, at 42.80&#8201;mol&#8201;m&#8722;1&#8201;y&#8722;1. Since N fluxes to the coastal bay (88&#8201;mol&#8201;m&#8722;1&#8201;y&#8722;1) are slightly lower than N fluxes from fresh inland groundwater (102&#8201;mol&#8201;m&#8722;1&#8201;y&#8722;1), the STE appears to be a sink of terrestrially-derived N. The net transformations of N in the STE led to N removal along the groundwater flow path along the groundwater flow path.

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Section: Ammonium Production Along the Stementioning

confidence: 73%

Section: Study Areamentioning

confidence: 89%

Nitrogen transformations along a shallow subterranean estuary

Couturier¹,

Nozais²,

Rao³

et al. 2016

Preprint

View full text Add to dashboard Cite

show abstract

“…Based on the stable isotopes of water along the STE, Chaillou et al (2018) confirmed the contribution of only two water end-members (i.e., fresh inland groundwater mainly originated from snow melt and seawater) and the absence of additional septic tank seepages, which could act as a source of OC into beach groundwater. The surficial runoff cannot be totally excluded.…”

Section: Source Of the Doc In The Study Beach Based On  13 C-doc Signaturesmentioning

confidence: 75%

“…A few recent studies have focused on the biogeochemistry of the STE (Couturier et al, 2017(Couturier et al, , 2016 and the calculation of groundwater flows (Chaillou et al 2018(Chaillou et al , 2016 at the Martinique Beach site. The shallow superficial unconfined beach aquifer releases both fresh groundwater and recirculated seawater to the coastal embayment.…”

Section: A C C E P T E D Mmentioning

confidence: 99%

Interactions between iron and organic carbon in a sandy beach subterranean estuary

et al. 2018

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Understanding the behavior of terrestrially derived dissolved organic carbon (DOC) through subterranean estuaries (STEs) is essential for determining the carbon budget in coastal waters.However, few studies exist on the interaction of organic carbon (OC) and iron (Fe) in these dynamic systems, where fresh groundwater mixes with recirculated seawater. Here, we focused on the origin and behavior of DOC, and we quantified the relative proportion of OC trapped by reactive Fe-hydroxides along a sandy beach STE. The  13 C-DOC signal in beach groundwater seems to respond rapidly to OC inputs. Our results show a terrestrial imprint from the aquifer matrix dominated by the degradation of particulate organic carbon (POC) issue from an old soil horizon composed of terrestrial plant detritus ( 14 C dating ~800 to 700 years B.P) which is buried below the Holocene sand. Even though the system can be sporadically affected by massive inputs of marine OC, this transient marine imprint seems to be rapidly evacuated from the STE. As reported in soil and in marine mud, Fe-OC trapping occurs in the sandy sediment of the STE. At the groundwater-seawater interface, newly precipitated reactive Fe-hydroxides interact with and trap terrestrial OC independently of the DOC origin in beach groundwater. The molecular fractionation of DOC along the STE and preferential trapping of terrestrial compounds favor the in situ degradation and/or export of non-Fe-stabilized marine-derived molecules to coastal waters. These findings support the idea that the sandy beach STE acts as a transient sink for terrestrial OC at the land-sea interface and contributes to the regulation of marine vs. terrestrial carbon exports to coastal waters.

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Section: Study Areamentioning

confidence: 89%

Nitrogen transformations along a shallow subterranean estuary

et al. 2017

View full text Add to dashboard Cite

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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Flow and discharge of groundwater from a snowmelt-affected sandy beach

Cited by 16 publications

References 46 publications

Nitrogen transformations along a shallow subterranean estuary

Nitrogen transformations along a shallow subterranean estuary

Interactions between iron and organic carbon in a sandy beach subterranean estuary

Nitrogen transformations along a shallow subterranean estuary

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