Geochemical conditions and nitrogen transport in nearshore groundwater and the subterranean estuary at a Cape Cod embayment, East Falmouth, Massachusetts, 2013–14

Colman, John A.; LeBlanc, Denis R.; Böhlke, John K.; McCobb, Timothy D.; Kroeger, Kevin D.; Belaval, Marcel; Cambareri, Thomas C.; Pirolli, Gillian F.; Brooks, Thomas W.; Garren, Mary E.; Stover, Tobias B.; Keeley, Ann

doi:10.3133/sir20185095

Cited by 3 publications

(4 citation statements)

References 7 publications

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“…In comparing the integrated true flux across sampling month, we estimate that transformations of NO 3 − in the sub‐benthic zone (including removal via denitrification and anammox) reduces the total dissolved inorganic N (NO 3 − + NH 4 + ) flux to the overlying benthic zone by ~ 47% in June and ~ 42% in August. This loss estimate is consistent with numerous past observations of removal via denitrification in subsurface salinity mixing zones (e.g., Kroeger and Charette 2008; Colman et al 2018; Wong et al 2020). Furthermore, transformations occurring in the benthic zone and enclosed water column (potentially including denitrification, nitrification, DNRA, remineralization, and assimilation) further reduce the dissolved inorganic N flux to the estuary by ~ 52% in June and ~ 42% in August.…”

Section: Resultssupporting

confidence: 91%

“…4, 5). The NO 3 − loss mechanisms may include removal via denitrification (e.g., Kroeger and Charette 2008; Colman et al 2018) or anammox, possibly within reducing microsites (e.g., Sawyer 2015) or assimilation into microbial biomass (e.g., Marchant et al 2014). Denitrification could have been enabled by available electron donor DOC (e.g., Szymczycha et al 2017), which was ~ 35–85 μ M at lowest salinity and increased to ~ 310–390 μ M at high salinity; or by dissolved Fe (Böhlke and Denver 1995), or dissolved Mn (Labbé et al 2003), both of which followed a similar trend as DOC with respect to salinity (Brooks et al 2021).…”

Section: Resultsmentioning

confidence: 99%

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Oxygen‐controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer–estuary interface

Brooks

Kroeger

Michael

et al. 2021

Limnology & Oceanography

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Nutrient loads delivered to estuaries via submarine groundwater discharge (SGD) play an important role in the nitrogen (N) budget and eutrophication status. However, accurate and reliable quantification of the chemical flux across the final decimeters and centimeters at the sediment-estuary interface remains a challenge, because there is significant potential for biogeochemical alteration due to contrasting conditions in the coastal aquifer and surface sediment. Here, a novel, oxygen-and light-regulated ultrasonic seepage meter, and a standard seepage meter, were used to measure SGD and calculate N species fluxes across the sediment-estuary interface. Coupling the measurements to an endmember approach based on subsurface N concentrations and an assumption of conservative transport enabled estimation of the extent of transformation occurring in discharging groundwater within the benthic zone. Biogeochemical transformation within reactive estuarine surface sediment was a dominant driver in modifying the N flux carried upward by SGD, and resulted in a similar percentage of N removal (~42-52%) as did transformations occurring deeper within the coastal aquifer salinity mixing zone (~42-47%). Seasonal shifts in the relative importance of biogeochemical processes including denitrification, nitrification, dissimilatory nitrate reduction, and assimilation altered the composition of the flux to estuarine surface water, which was dominated by ammonium in June and by nitrate in August, despite the endmember-based observation that fixed N in discharging groundwater was strongly dominated by nitrate. This may have important ramifications for the ecology and management of estuaries, since past N loading estimates have generally assumed conservative transport from the nearshore aquifer to estuary.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Oxygen‐controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer–estuary interface

Brooks

Kroeger

Michael

et al. 2021

Limnology & Oceanography

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“…The δ 18 O[NO 3 − ] values resulting from nitrification in infiltrating lakebed porewater were substantially lower than those reported for regional groundwater containing NO 3 − presumed to have formed in soils, which more often appear to indicate incorporation of 2H 2 O–O and 1O 2 –O without fractionation effects (e.g., +4 to +6‰; Böhlke et al., 2006; Colman et al., 2018), as described elsewhere (Amberger & Schmidt, 1987; Boshers et al., 2019; Kendall et al., 2007; Xue et al., 2009). Different reaction mechanisms or substrate limitations may have caused different isotopic effects during nitrification in these environments (Boshers et al., 2019), which may be useful for distinguishing NO 3 − from different recharge sources in the Cape Cod aquifer.…”

Section: Discussionmentioning

confidence: 74%

“…NO 3 production zones in the lake-water recharge area provide an opportunity for evaluating in situ isotope effects of nitrification in a saturated natural freshwater environment. Colman et al, 2018), as described elsewhere (Amberger & Schmidt, 1987;Boshers et al, 2019;Kendall et al, 2007;Xue et al, 2009). Different reaction mechanisms or substrate limitations may have caused different isotopic effects during nitrification in these environments (Boshers et al, 2019), which may be useful for distinguishing NO 3 from different recharge sources in the Cape Cod aquifer.…”

Section: Stable Isotope Effects Of Nitrification During Lake-water Re...mentioning

confidence: 99%

Spatial, Seasonal, and Diel Controls of Nitrogen‐Carbon‐Oxygen Cycling During Lake‐Water Infiltration to an Aquifer

Smith,

Repert,

Underwood

et al. 2024

JGR Biogeosciences

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Many freshwater lakes are groundwater flow‐through systems. Although lakes commonly are considered to be sinks for nitrogen inputs, relatively little is known about carbon and nitrogen export from lakes to groundwater. The current study focused on lake‐bottom biogeochemical processes accompanying the transport of nitrogen, dissolved oxygen (O2), and dissolved organic carbon (DOC) during lake‐water recharge from a groundwater flow‐through lake. Lake‐water and porewater (15–100 cm below lakebed) samples were collected along transects within the lake downwelling zone. Infiltrating porewater O2 and DOC concentrations decreased with depth while nitrate (NO3−) concentrations increased, indicating nitrification of organic matter within the profiles. The depth of NO3− production and transport was seasonally dependent. In winter, NO3− and O2 were exported beyond 100‐cm depth; whereas in summer, shallow nitrification zones were underlain by deeper NO3− reduction zones, and diel patterns of O2 and NO3− penetration depths were observed. Microbial community compositions and stable isotope profiles (δ15N[NO3−], δ18O[NO3−], δ18O[O2]) were consistent with apparent C–N–O reaction stoichiometries indicating O2 reduction and nitrification in shallower porewater, followed by varying NO3− reduction at depth. Maximum porewater NO3− concentrations (∼10–20 μM) were limited by infiltrating O2 concentrations and C/N ratios of reacting organic matter. Lake‐water level variations caused changes in shoreline position and porewater velocities, while variations in lake‐water temperature, DOC, and O2 contributed to changes in reaction rates and depth of O2 and NO3− penetration into the lakebed. The quality of groundwater recharged by lake water reflected temporally and spatially varying physical and biogeochemical processes in the sediment porewater.

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Evaluating the effects of replacing septic systems with municipal sewers on groundwater quality in a densely developed coastal neighborhood, Falmouth, Massachusetts, 2016–19

McCobb¹,

Barbaro²,

LeBlanc³

et al. 2021

Scientific Investigations Report

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Land disposal of sewage wastewater through septic systems and cesspools is a major cause of elevated concentrations of nitrogen in the shallow coastal aquifers of southern New England. The discharge of nitrogen from these sources at the −0.76 milligram per liter per year; specific conductance: −12.1 microsiemens per centimeter at 25 degrees Celsius per year; dissolved oxygen: 0.82 milligram per liter per year); however, the rate at which the water-quality improvements will result in decreases in nitrate mass loads to the coastal ponds primarily depends on groundwater traveltimes and the rate of flushing of wastewater constituents from the aquifer.

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Geochemical conditions and nitrogen transport in nearshore groundwater and the subterranean estuary at a Cape Cod embayment, East Falmouth, Massachusetts, 2013–14

Cited by 3 publications

References 7 publications

Oxygen‐controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer–estuary interface

Oxygen‐controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer–estuary interface

Spatial, Seasonal, and Diel Controls of Nitrogen‐Carbon‐Oxygen Cycling During Lake‐Water Infiltration to an Aquifer

Evaluating the effects of replacing septic systems with municipal sewers on groundwater quality in a densely developed coastal neighborhood, Falmouth, Massachusetts, 2016–19

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