pH profiles in estuarine sediments exposed to acidification

We collected twelve sediment cores from two sites in Waquoit Bay (Massachusetts, USA): Metoxit Point (MP) in August 2021 and from Sage Lot Pond (SLP) in September of 2021. We collected the cores using a pull corer which maintains the vertical structure of the sediment cores and preserves the delicate sediment-water interface (Foster and Fulweiler 2019). We transported the cores back to Boston University within 7 hours of collection and placed them in an environmental chamber set to 29 (±1) °C. To better understand the impact of pH of sediment biogeochemical cycling we conducted continuous flow through incubations with treatments representing control (pH 8.0), moderate (pH 7.3) and extreme pH conditions (pH 6.3). Site water was treated with ambient air and CO2 to reach appropriate pH conditions. Before and after each incubation we collected triplicate sediment pH profiles from each core using a dual mounted motorized micromanipulator profiler and the Sensor Trace Pro v. 3.0.6 control software (Unisense, Aarhus, Denmark). We used a Unisense pH-100 microelectrode (100 µm diameter) to collect pH measurements at 500 µM increments with a maximum profiling depth of 2 cm. We calibrated the pH probe daily with a 2-point method (Unisense, Aarhaus, Denmark) using laboratory standard buffers at pH 4.01 and pH 7.00 (Hach, USA). Email questions and comments to [e-mail] Sampling Sites: 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 Profiling Information: Depth_mm = sampling depth in millimeters Pre_All_pH = mean pH in all cores pre incubation Pre_All_SE = pH standard error in all cores pre incubation Post_Ctrl_pH = mean pH in control cores post incubation Post_Ctrl_SE = pH standard error in control cores post incubation Post_Mod _pH = mean pH in moderate (pH 7.3) treated cores post incubation Post_Mod_SE = pH standard error in in moderate (pH 7.3) treated cores post incubation Post_Ext _pH = mean pH in extreme (pH 6.3) treated cores post incubation Post_Ext_SE = pH standard error in in extreme (pH 6.3) treated cores post incubation Acknowledgements: 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, Kwetzpallin Mexika, Melissa Ederington Hagy, Nia Bartolucci, Paulina Azzu, and Ryan Shipley for their help with sample prep, field work and experiments. References: Foster SQ, Fulweiler RW (2019) Estuarine Sediments Exhibit Dynamic and Variable Biogeochemical Responses to Hypoxia. J Geophys Res Biogeosciences 124:737–758. https://doi.org/10.1029/2018JG004663 Funding This work was funded by MIT SeaGrant through grants to RWF and by the NOAA Margaret A. Davidson Graduate Fellowship awarded to CIM. CIM received additional support from the Mount Holyoke Alumnae Fellowship, the Warren-McLeod Graduate Fellowship from the Boston University Marine Program, and from Boston University’s Department of Earth & Environment.