Nutrient and dissolved gas fluxes across the sediment-water interface under normoxic conditions in Waquoit Bay, Massachusetts (USA)

On 7 occasions over the course of 3 years (2011-2013) we conducted hypoxic static core incubations on sediments and water collected in Waquoit Bay Massachusetts (USA) from four stations: Childs River Estuary, Metoxit Point, South Basin, & Sage Lot Pond. The goal of this study was quantify sediment metabolism under water column hypoxia in a shallow, temperate estuarine system. As part of that study, we compared the hypoxic flux rates to normoxic flux rates. Here we provide a comprehensive dataset of dissolved nutrient (i.e., inorganic nitrogen, phosphorus, and silica) and gas (i.e., di-nitrogen, nitrous oxide, and methane) fluxes across the sediment-water interface measured from static core incubations under normoxic conditions. Note that normoxic fluxes for O2, NH4+, PO43-, N2O, N2, are published (Foster & Fulweiler 2014; Foster & Fulweiler 2016), as are the normoxic fluxes for DSi & CH4 (Foster & Fulweiler 2019).

We collected triplicate or quadruplicate sediment cores in PVC tubes (10 cm inner diameter, 30 cm height) from the side of a boat using a pole corer equipped with a one-way valve (Fulweiler et al. 2010; Foster & Fulweiler 2014). We also collected in situ bottom water from each site and filtered onboard (nominally to 0.2μm). We then transported cores and water back to our Boston University laboratory and placed them in a water-bath inside an environmental chamber set to ambient bottom water temperatures. We conducted static core incubations in the dark to determine fluxes across the sediment-water interface (e.g., Banta et al. 1995; Giblin et al. 1997; Fields et al. 2014). Core lids were equipped with magnetic stir bars (Dornblaser et al. 1989) which provided gentle (45 rpm) mixing of the overlying water with minimal suspension of sediments (Hopkinson et al. 2001; Renaud et al. 2008; Heiss et al. 2012). For each time point we collected water samples from the cores through an outflow port and water was replaced simultaneously through an inflow port to balance the volume and minimize atmospheric exchange.

Dissolved inorganic nutrient concentrations were determined with high-resolution digital colorimetry on a SEAL Auto Analyzer 3 with segmented flow injection using standard techniques and chemical analyses (Solorzano 1969; Johnson & Petty 1983; Grasshoff et al. 1999). We directly measured N2 on a quadrupole membrane inlet mass spectrometer (MIMS) using the N2/Ar technique developed by Kana et al. (1994). On four occasions we also collected additional duplicate water samples for the analysis of dissolved greenhouse gases, N2O and CH4. We directly measured dissolved N2O and CH4 using a headspace equilibration technique (Kling et al. 1991; Foster & Fulweiler 2016). We analyzed the vial headspace (after water sample – headspace equilibration) using a gas chromatograph (Shimadzu GC-2014) equipped with a flame ionization detector (FID, for CH4) and an electron capture detector (ECD, for N2O). We measured oxygen concentrations using an optical Luminescent Dissolved Oxygen sensor (Hach LDO 101).

Note that on one occasion (6 Aug 2012), absolute N2O flux rates were 1-3 orders of magnitude greater than on the other dates and were significant outliers in the dataset (Foster & Fulweiler 2016). These data are designated with a star (*). In addition, on 2 dates in 2012 there was an issue with the instrument analysis of N2, therefore they are designated as having a measurement issue (m.i.) and were not able to be used in our analyses. Nutrient and greenhouse gas parameters were not measured (n.m.) prior to 2012. In a few instances flux rates we could not determine (c.n.d.) flux rates because there was not predictable linear relationship between concentration change and time.

Please email with questions: sqfoster@bu.edu

CRE = Childs River Estuary (41° 34.805’ N 70°31.826’ W, 1.2 m deep, bottom water salinity 27.3-29.7 psu)

MP = Metoxit Point (41° 34.134’ N 70° 31.272’ W, 2.2 m deep, bottom water salinity 29.6-31.3 psu)

SB = South Basin (41° 33.404’ N 70° 31.442’ W, 1.8 m deep, bottom water salinity 30.6-31.3 psu)

SLP = Sage Lot Pond (41° 33.270’ N 70° 30.584’ W, 1.2 m deep, bottom water salinity 28.9-30.4 psu)

Incubation Temperature = degrees Celsius

O2 uptake = di-oxygen per mole O2 (micromoles per meter squared per hour)

NH4+ Flux = ammonium (micromoles per meter squared per hour)

DSi Flux = silica (micromoles per meter squared per hour)

PO43- Flux = phosphate (micromoles per meter squared per hour)

N2-N Flux = di-nitrogen gas per mol N (micromoles per meter squared per hour)

N2O Flux = nitrous oxide (nanomoles per meter squared per hour)

CH4 Flux = methane (nanomoles per meter squared per hour)

Date = dd (day) - month - yy (year)

* = outlier value

m.i. = measurement issue

n.m. = not measured

c.n.d. = could not determine

There are numerous people who contributed to this project. We would like to thank the Waquoit Bay National Estuarine Research Reserve (WBNERR) for their continued multi-year support of our research. All water and sediment samples for this study were collected using WBNERR boats. We are particularly grateful to the following WBNERR employees who assisted with the fieldwork: MK Fox, A Lescher, J Mora, C Weidman. We would also like to thank several Fulweiler Lab members and Boston University Marine Program (BUMP) students for their assistance with fieldwork and the laboratory-based core incubation experiments: S Andrews, A Banks, S Buckley, K Czapla, S Donovan, D Forest, E Heiss, J Luthringer, M McCarthy, S. Newell, MK Rogener, R Schweiker, K Yoshimura. MK Rogener and E Heiss also helped analyze samples for N2/Ar concentrations on the Membrane Inlet Mass Spectrometer (MIMS). K Czapla and A Al-Haj conducted analyses for nutrient concentrations using a SEAL auto-analyzer. We also thank Boston University Earth and Environment Department for use of their facilities and their general academic and logistical research support.

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