Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA)

Ullman, William J.; Chang, Bonnie X.; Miller, Douglas C.; Madsen, John A.

doi:10.1016/s0272-7714(02)00398-0

Cited by 115 publications

(99 citation statements)

References 35 publications

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“…This finding is consistent with the literature, where this interface is considered an active environment for dilution of incoming groundwater solutes (Sawyer et al, 2013;Li et al, 1999) and for biogeochemical processes, in particular for nitrogen cycle (Jones and Mulholland 2000; Ullman et al 2003;Gomez-Velez et al 2015). However, in an estuarine setting, different scales of groundwater -surface water mixing are present and may synergistically contribute to N attenuation.…”

supporting

confidence: 91%

Nitrogen attenuation, dilution and recycling at the groundwater – surface water interface of a subtropical estuary inferred from the stable isotope composition of nitrate and water

Lamontagne

Cosme²,

Minard³

et al. 2018

Preprint

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Abstract. Estuarine environments have a dynamic groundwater -surface water interface driven by terrestrial 15 groundwater discharge, tidal cycles, waves and other processes. This interface also corresponds to an active biogeochemical environment. An assessment of discharging groundwater with elevated (>300 mg N L -1 ) NH4 + and NO3 -concentrations at such an interface located in a subtropical estuary indicated that 80 % of the N was attenuated, one of the highest N removal rates (>100 mmol m -2 day -1 ) measured for intertidal sediments. The remaining N was also diluted by a factor of two or more by mixing before being discharged to the estuary. Most reaching the riverbed. Whilst porewater NO3 -was more  18 O depleted than its synthetic source, porewater (-3.2 to -1.8‰) was enriched by 1-4‰ relative to rainfall-derived groundwater mixed with seawater. 30Isotopic fractionation from H2O uptake during the N cycle and H2O production during synthetic NO3 -reduction are the probable causes for this enrichment.

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supporting

confidence: 91%

Nitrogen attenuation, dilution and recycling at the groundwater – surface water interface of a subtropical estuary inferred from the stable isotope composition of nitrate and water

Lamontagne

Cosme²,

Minard³

et al. 2018

Preprint

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“…We used NH 4 + , not NO x , for these calculations, because NH 4 + is the N species present in the subto anoxic discharge region of the beach and in the freshwater lens samples. Nutrient efflux of beach sediments can significantly sustain productive benthic communities that inhabit the seepage zone (Hays and Ullman, 2007;Ullman et al, 2003). In our study area, increasing normalized Chl a, POC, and POP concentrations in the seepage zone, especially the beach runnel (Phytobenthos site 6, Fig.…”

Section: Pore Water Discharge Influences Phytobenthos and Nearshore Wmentioning

confidence: 82%

“…3). Thus, the USP at Spiekeroog beach may extend down to greater depths than previously shown in other studies using salinity measurements and/or hydrological modeling (Charette and Sholkovitz, 2006;McAllister et al, 2015;Santos et al, 2008;Ullman et al, 2003). The majority of these studies were, however, carried out in microtidal environments, which may explain why the USP does not reach depths exceeding 5 m.…”

Section: Beach Hydrology and Salinity Gradients Influence The Beach Ementioning

confidence: 83%

“…This will lead to a refined groundwater flow model, to a better understanding of the key processes in biogeochemistry, of the role of organisms for OM degradation, and of the fluxes at the sediment-water interface. To date, most studies on hydrological and biogeochemical processes in subterranean estuaries of beach systems were carried out in microtidal and/or low-energy environments such as semi-protected bay situations (Charette and Sholkovitz, 2006;McAllister et al, 2015;Santos et al, 2008;Ullman et al, 2003). Therefore, a maximum sampling depth of about 5 m was sufficient to resolve the USP at these study sites.…”

Section: Perspectivesmentioning

confidence: 99%

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The drivers of biogeochemistry in beach ecosystems: A cross-shore transect from the dunes to the low-water line

et al. 2017

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This study addresses key processes in high-energy beach systems using an interdisciplinary approach. We assess spatial variations in subsurface pore water residence times, salinity, organic matter (OM) availability, and redox conditions and their effects on nutrient cycles as well as on microbial community patterns and microphytobenthos growth. At the study site on Spiekeroog Island, southern North Sea, beach hydrology is characterized by the classical zonation with an upper saline plume (USP), a saltwater wedge, and a freshwater discharge tube in between. Sediment and pore water samples were taken along a cross-shore transect from the dunes to the low-water line reaching sediment depths down to 5 m below sediment surface. Spatial variations in pore water residence time, salinity, and organic matter availability lead to steep redox and nutrient gradients. Vertical and horizontal differences in the microbial community indicate the influence of these gradients and salinity on the community structure. shoreline. We propose that this nutrient efflux triggers growth of microphytobenthos on sediment surfaces of the discharge zone. A first comparison of nutrient discharge rates of the beach site with a nearby sandy backbarrier tidal flat margin indicates that the beach system might be of less importance in supplying recycled nutrients to nearshore waters than the backbarrier tidal flat area.

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“…This points towards the need for an additional O 2 source in the surface intertidal beach sediments. As reported by Ullman et al (2003), tidal pumping and wave action may provide a constant source of O 2 to sustain nitrification, as well as oxic degradation of the locally produced, labile organic matter higher on the beachface. In line with these observations, the O 2 measurements in the surface intertidal sediments (PZ-3 and PZ-5) indicate higher concentrations, which do not originate from landward transport but are more likely supplied through aeration of the surface beachface sediments at low tide (Fig.…”

Section: Nitrogen Dynamicsmentioning

confidence: 84%

Flow and nutrient dynamics in a subterranean estuary (Waquoit Bay, MA, USA): Field data and reactive transport modeling

Spiteri¹,

Slomp²,

Charette³

et al. 2008

Geochimica et Cosmochimica Acta

135

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A two-dimensional (2D) reactive transport model is used to investigate the controls on nutrient (NO 3 À , NH 4 þ , PO 4 ) dynamics in a coastal aquifer. The model couples density-dependent flow to a reaction network which includes oxic degradation of organic matter, denitrification, iron oxide reduction, nitrification, Fe 2+ oxidation and sorption of PO 4 onto iron oxides. Porewater measurements from a well transect at Waquoit Bay, MA, USA indicate the presence of a reducing plume with high Fe 2+ , NH 4 þ , DOC (dissolved organic carbon) and PO 4 concentrations overlying a more oxidizing NO 3 À -rich plume. These two plumes travel nearly conservatively until they start to overlap in the intertidal coastal sediments prior to discharge into the bay. In this zone, the aeration of the surface beach sediments drives nitrification and allows the precipitation of iron oxide, which leads to the removal of PO 4 through sorption. Model simulations suggest that removal of NO 3 À through denitrification is inhibited by the limited overlap between the two freshwater plumes, as well as by the refractory nature of terrestrial DOC. Submarine groundwater discharge is a significant source of NO 3 À to the bay.

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Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA)

Cited by 115 publications

References 35 publications

Nitrogen attenuation, dilution and recycling at the groundwater – surface water interface of a subtropical estuary inferred from the stable isotope composition of nitrate and water

Nitrogen attenuation, dilution and recycling at the groundwater – surface water interface of a subtropical estuary inferred from the stable isotope composition of nitrate and water

The drivers of biogeochemistry in beach ecosystems: A cross-shore transect from the dunes to the low-water line

Flow and nutrient dynamics in a subterranean estuary (Waquoit Bay, MA, USA): Field data and reactive transport modeling

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