Comparison of spectrophotometric and electrochemical pH measurements for calculating freshwater pCO2
Comparison of spectrophotometric and electrochemical pH measurements for calculating freshwater pCO2
复制标题
DOI：
10.1002/lom3.10501
复制
发表时间：
2022-07
期刊：
影响因子：
--
通讯作者：
Fischer L. Young;Q. Shangguan;C. Beatty;Makenzy D. Gilsdorf;M. DeGrandpre
中科院分区：
文献类型：
--
作者：
Fischer L. Young;Q. Shangguan;C. Beatty;Makenzy D. Gilsdorf;M. DeGrandpre
内陆沃茨在全球碳循环中发挥着重要作用，通过下游输出和与大气交换二氧化碳，对陆地碳通量作出了重大贡献。然而，淡水无机碳通量仍然存在很大的不确定性。一个促成因素是碳酸盐系统计算中的不确定性，该计算用于根据淡水系统的pH值和碱度估计CO2分压（pCO 2）。不确定性主要源于低离子强度系统中玻璃pH电极测量引起的不准确pH值。本研究比较了基于指示剂的分光光度法和电化学pH测量及其在计算淡水pCO 2中的应用。我们的研究发现，与pCO 2参考方法相比，基于pH电极的pCO 2估计值高估了230 ± 200 μatm（n = 54），而基于指示剂的分光光度法pCO 2 pH估计值在100-1600 μatm范围内为58 ± 33 μatm（n = 34）。此外，我们发现当离子强度假设为零时，计算的pCO 2误差约为参考pCO 2的20%。使用自主分光光度pH和pCO 2传感器进行的19天现场研究发现，计算的pCO 2平均误差为−70 ± 57 μatm（n = 1685）。虽然我们的重点是河流CO2，但这些发现和随后的结论适用于所有淡水系统。分光光度pH测量将改善未来淡水pCO 2的计算，并更好地量化内陆沃茨在全球碳预算中的作用。
Inland waters have an important role in the global carbon cycle, contributing significantly to terrestrial carbon fluxes through downstream export and exchange of CO2 with the atmosphere. However, large uncertainties in freshwater inorganic carbon fluxes remain. One contributing factor is uncertainty in carbonate system calculations for estimating the partial pressure of CO2 (pCO2) from pH and alkalinity in freshwater systems. The uncertainty stems largely from inaccurate pH values caused by glass pH electrode measurements in low ionic strength systems. This study compares indicator‐based spectrophotometric and electrochemical pH measurements and their application for calculating freshwater pCO2. Our study found that, compared to a pCO2 reference method, pH electrode‐based estimates of pCO2 were overestimated by 230 ± 200 μatm (n = 54) where indicator‐based spectrophotometric pH estimates of pCO2 were 58 ± 33 μatm (n = 34) over the range of 100–1600 μatm. Furthermore, we found that when ionic strength was assumed to be zero, calculated pCO2 error was ~ 20% of the reference pCO2. A 19‐d field study using autonomous spectrophotometric pH and pCO2 sensors found an average error in calculated pCO2 of −70 ± 57 μatm (n = 1685). Although, our focus is on riverine CO2, these findings and subsequent conclusions apply to all freshwater systems. Spectrophotometric pH measurements will improve future freshwater pCO2 calculations and better quantify inland waters' role in the global carbon budget.