Sediment characteristics in Waquoit Bay, MA under acidification

We conducted continuous flow through incubations on sediments collected from Waquoit Bay, Massachusetts (USA) at two stations: Metoxit Point and Sage Lot Pond. The objectice of this study was to better understand the impact of moderate (pH 7.3) and extreme (pH 6.3) pH conditions on sediment nutrient and greenhouse gas fluxes. At the end of each incubation we collected samples for sediment chlorophyll-<em>a</em>, sediment phaeophytin, loss on ignition (LOI), percent carbon (%C), percent nitrogen (%N), molar carbon to nitrogen (C:N) ratios, and dissolved iron (DFe). We collected these samples using plastic (polycarbonate) syringe subcorers (20 mL) that we sectioned up to 4 cm in 1 cm increments. Syringes were acid washed except for those used to collect chl-<em>a </em>and phaeophytin. C, N, and LOI samples were stored in plastic centrifuge tubes (50 mL) in a freezer until they were analyzed. Chl-<em>a</em> and phaeophytin samples were stored in DI rinsed plastic centrifuge tubes (50 mL) and stored in a -80 °C freezer. DFe porewater was extracted in a glove bag under anoxic conditions, centrifuged and filtered using 0.2 µm polyethersulfone filters into DI leached and dried 2 mL polycarbonate tubes. We followed methods for sediment % carbon, % nitrogen and C:N using the Protocol Handbook for NICE (Nitrogen Cycling in Estuaries; Dalsgaard et al. 2000). We ran these samples on an Elemental Combustion System 4010 made by Costech Analytical Technologies (Valencia, CA) with a method detection limit of 0.012 mg for C and 0.002 mg for N. LOI was determined using the dry weight after combusting samples at 600 °C for 6 hours. We extracted and analyzed sediment chlorophyll-<em>a</em> and phaeophytin using techniques described by Arar and Collins (1997), Fagherazzi et al. (2014) and Ray et al. (2020). Dissolved Fe concentrations were determined using a method described by Anschutz and Charbonnier (2021) which was adapted for micro-colorimetric assays based on a standard 96-well microplate format and read on an absorbance microplate reader (SpectraMax ABSPlus; San Jose, CA, USA). <strong>Sampling Sites</strong> Metoxit Point = 41° 34' 8.04" N 70° 31' 17.76" W Sage Lot Pond = 41° 34' 8.04" N 70° 30' 30.20" W <strong>Experiment Information</strong> Experiment_Type = For each station we conducted two incubations. The first incubation conducted was the Extreme treatment (pH 6.3) which included 3 control cores and 3 cores acidified to a pH of 6.3. The second experiment conducted was the moderate treatment (pH 7.3). Treatment = The acidification treatment each cores were exposed to: Control = pH 8.0 pH 6.3 = Extreme pH 7.3 = Moderate Core_ID: Number/Letter identifying the core <strong>Abbreviations and Units</strong> Collection_Date = Date of sediment collection (mm-dd-yy) Depth = range in centimeters (cm) Sed_Chla = sediment chlorophyll-<em>a</em> milligram per square meter (mg m-2) Sed_Phaeo = sediment phaeophytin milligram per square meter (mg m-2) C = percent carbon of total mass N = percent nitrogen of total mass C:N = carbon to nitrogen molar ratio LOI = Loss on ignition DFe = dissolved iron in porewater (µmol L-1) <strong>Aknowledgements</strong> We would like to thank the Waquoit Bay National Estuarine Research Reserve (WBNERR) for their support of our research. Sediment cores for this study were collected using WBNERR boats. We are particularly grateful for Dr. Megan Tyrrell and Tonna-Marie Rogers who were instrumental in helping us carry out fieldwork and for making sure we had all the resources necessary for a successful field day. We would also like to thank members of the Fulweiler Lab, Alia Al-Haj, Amanda Vieillard, Catherine Mahoney, Emily Miao, Kwetzpallin Mexika, Melissa Ederington Hagy, Nia Bartolucci, Paulina Azzu, and Ryan Shipley for their help with sample prep, field work and experiments. We also thank Dr. Cédric Fichot and Dr. Nilotpal Ghosh for help with CN sample analysis and instrumentation use. <strong>References</strong> Anschutz P, Charbonnier C (2021) Sampling pore water at a centimeter resolution in sandy permeable sediments of lakes, streams, and coastal zones. Limnol Oceanogr Methods 19:96–114. https://doi.org/10.1002/LOM3.10408 Arar EJ, Collins GB (1997) In Vitro Determination of Chlorophyll a and Pheophytin a in Marine and Freshwater Algae by Fluorescence. Washington, DC Dalsgaard T, Nielsen LP, Brotas V, et al (2000) Protocol handbook for NICE - Nitrogen Cycling in Estuaries:a project under the EU research programe: Ministry of Environment and Energy National Environmental Research Institute … Fagherazzi S, Mariotti G, Banks AT, et al (2014) The relationships among hydrodynamics, sediment distribution, and chlorophyll in a mesotidal estuary. Estuar Coast Shelf Sci 144:54–64. https://doi.org/10.1016/j.ecss.2014.04.003 Ray NE, Al-Haj AN, Fulweiler RW (2020) Sediment biogeochemistry along an oyster aquaculture chronosequence. Mar Ecol Prog Ser 646:13–27. https://doi.org/10.3354/meps13377 <br>