Data of dissolved oxygen and carbonate parameters supporting the study entitled with "Export Flux, Biogeochemical Effects, and Fate of Terrestrial Carbonate System: A Case from Changjiang (Yangtze River) Estuary to the East China Sea"

Water samples were collected at two or three different depths (including sea surface and the bottom water) using 5 or 30 L Niskin bottles. The ancillary data of in situ temperature were obtained using a calibrated Conductivity-Temperature-Depth/Pressure unit (SBE-19 plus, Sea Bird Co.) or a calibrated YSI6600 probe. Salinity (Practical Salinity Scale of 1978) was measured with a calibrated WTW’s TetrCon^®925 probe. The dissolved oxygen (DO) samples were collected, fixed and titrated aboard following the classic Winkler procedure at the satisfactory level of <0.5%. A small quantity of NaN₃ was added during subsample fixation to remove possible interferences from nitrites (Wong, 2012). The DO saturation (DO%) was calculated from field-measured DO concentration divided by the DO concentration at equilibrium with the atmosphere which was calculated from temperature, salinity and local air pressure, as per the Benson and Krause (1984) equation. To quantify the effects of net community metabolism, apparent oxygen utilization (AOU) was also calculated by subtracting the field-measured DO concentration from the air-equilibrated DO. Ignoring effects of air-sea exchange and water mixing, an AOU > 0 implies net community respiration, while an AOU < 0 implies net community production. Seawater samples (S > 10) for DIC and TAlk analyses were stored in 60 mL borosilicate glass bottles (bubble free) and 140 mL high-density polyethylene bottles, respectively. They were immediately mixed with 50 μL of saturated HgCl₂, and then sealed and preserved at room temperature until determination. According to Huang et al. (2012), there were no statistical differences for seawater samples between the measuring results from our procedure and from those stored in the borosilicate glass bottles suggested by Dickson et al. (2007). The freshwater, or low-salinity samples (S < 10), were stored in 250 mL Teflon coated glass bottles (Corning Pyrex^®, Corning Inc., USA) together with ground-glass stoppers, mixed with 100 μL of saturated HgCl₂. According to a parallel storage technique study conducted in our 2015 surveys, these Teflon-coated glass bottles are suitable for relatively long-term (<70 days) storage of freshwater carbonate samples (Liu and Zhai, 2016). DIC and TAlk data were collected by commercial analytical systems (Model AS-C3 and AS-ALK1+, Apollo SciTech Inc., USA). Following Cai (2003) and Zhai et al. (2007), DIC was measured by infrared detection following acid extraction of a 0.5–0.9 mL sample with a Kloehn^® digital syringe pump, and TAlk was determined at 25 °C by Gran acidimetric titration on a 15–25 mL sample with a Kloehn^® digital syringe pump, using a precision pH meter and an Orion^® 8102BN Ross electrode for detection. Both DIC and TAlk determinations were referred to Certificated Reference Materials (CRM) from Andrew G. Dickson’s lab at Scripps Institute of Oceanography at a precision of ± 2 μmol kg^–1 (Dickson et al., 2007; Zhai et al., 2007).