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).

本研究采用5L或30L尼斯金采水器（Niskin bottles），在2至3个不同深度（包括海面及底层海水）采集水样。原位温度的辅助数据通过经校准的电导率-温度-深度/压力仪（型号SBE-19 plus，Sea Bird公司）或经校准的YSI6600型探头获取。盐度（采用1978年实用盐度标度）通过经校准的WTW TetrCon®925型探头测定。溶解氧（Dissolved Oxygen，简称DO）样品按照精度优于0.5%的经典温克勒（Winkler）滴定法，在船上完成采集、固定与滴定操作。分样固定过程中加入少量叠氮化钠（NaN₃）以消除亚硝酸盐可能带来的干扰（Wong, 2012）。溶解氧饱和度（DO%）通过现场实测溶解氧浓度除以与大气平衡状态下的溶解氧浓度计算得到；后者可根据温度、盐度及当地大气压强，依据Benson与Krause（1984）提出的公式计算得出。为量化净群落代谢的影响，表观氧利用量（Apparent Oxygen Utilization，简称AOU）通过用大气平衡态溶解氧浓度减去现场实测溶解氧浓度计算得到。忽略海-气交换与水团混合的影响时，表观氧利用量大于0代表群落净呼吸作用，小于0则代表群落净生产作用。用于溶解无机碳（Dissolved Inorganic Carbon，简称DIC）和总碱度（Total Alkalinity，简称TAlk）分析的盐度大于10的海水样品，分别储存在60 mL无气泡硼硅酸盐玻璃瓶与140 mL高密度聚乙烯瓶中。样品中立即加入50 μL饱和氯化汞（HgCl₂）溶液，随后密封并在室温下保存直至测定。据Huang等人（2012）的研究，本实验流程的测定结果与Dickson等人（2007）建议的硼硅酸盐玻璃瓶储存方法的测定结果之间无统计学差异。淡水或盐度小于10的低盐水样储存在带有磨砂玻璃塞的250 mL聚四氟乙烯涂层玻璃瓶（Corning Pyrex®，美国Corning公司）中，并加入100 μL饱和氯化汞溶液。根据2015年本团队开展的平行储存技术研究，此类聚四氟乙烯涂层玻璃瓶可用于淡水碳酸盐样品最长70天的中长期储存（Liu与Zhai, 2016）。溶解无机碳与总碱度的数据通过商用分析系统（型号AS-C3与AS-ALK1+，美国Apollo SciTech公司）获取。参考Cai（2003）与Zhai等人（2007）的方法，溶解无机碳的测定流程为：取0.5~0.9 mL样品，通过Kloehn®数字注射泵完成酸萃取后采用红外检测法；总碱度则在25 ℃下，取15~25 mL样品，通过Kloehn®数字注射泵完成Gran酸碱滴定，并采用精密pH计与Orion® 8102BN Ross电极进行检测。溶解无机碳与总碱度的测定均以斯克里普斯海洋研究所Andrew G. Dickson实验室提供的有证标准物质（Certificated Reference Material，简称CRM）为校准基准，测定精度为±2 μmol·kg⁻¹（Dickson等人, 2007; Zhai等人, 2007）。