Total alkalinity measurement using an open‐source platform

Abstract

Total alkalinity is a pivotal water quality parameter dictating the response of natural waters to acid–base system perturbations such as ocean acidification and acid mine drainage. Its value as a biogeochemical and ecological variable is enhanced not just by high measurement quality, but also by measurement accessibility. This research demonstrates an instrument that advances the accessibility of high‐precision, high‐accuracy total alkalinity measurement using open‐source, and low‐cost instrumentation. Repeated testing of water samples from Lake Superior demonstrated a measurement precision (standard deviation or SD) of 3.0 μmol kg−1. Analysis of standards and reference materials demonstrated an uncertainty of 5.3 μmol kg−1 as well as robustness to freshwater and saltwater matrices. This instrument adds to the wealth of inorganic carbon measurement technologies in marine and lacustrine settings and stands to enhance the ability of both communities to generate accurate and accessible measurements of total alkalinity.

Underway pCO2 Surveys Unravel CO2 Invasion of Lake Superior From Seasonal Variability

“…Seasonal variation in DIC was evident as a summertime decrease on the order of 20 μmol kg 1 , followed by an autumn increase of c. 10 μmol kg 1 . The pH free distribution fell within the range of values given in Minor and Brinkley (2022), while the mean calculated DIC was 10-40 μmol kg 1 higher than observations given in Zigah et al (2011) and Sandborn et al (2023). The discrepancy may be due to interannual DIC increases, sampling bias in the latter two studies favoring regions or periods of lower DIC, contribution of organic alkalinity, uncertainty associated with equilibrium calculation, or error propagated from uncertainty in A T .…”

“…(2011) and Sandborn et al. (2023). The discrepancy may be due to interannual DIC increases, sampling bias in the latter two studies favoring regions or periods of lower DIC, contribution of organic alkalinity, uncertainty associated with equilibrium calculation, or error propagated from uncertainty in A T .…”

“…(2014). A T is given as μmoles of hydrogen ion equivalent kg −1 in this work, and is largely invariant in Lake Superior (Minor & Brinkley, 2022; Sandborn et al., 2023) except in regions with significant terrestrial influence; no A T ‐conductivity relationship for Lake Superior has been published, so A T was not estimated from underway data.…”

“…Surface-water DIC and pH (free scale) were calculated from measured pCO 2 , SST, and an assumed A T of 840 μmol kg 1 (Figures 2d and 2e) with PyCO 2 SYS, using the carbonate constants of Waters et al (2014). A T is given as μmoles of hydrogen ion equivalent kg 1 in this work, and is largely invariant in Lake Superior (Minor & Brinkley, 2022;Sandborn et al, 2023) except in regions with significant terrestrial influence; no A T -conductivity relationship for Lake Superior has been published, so A T was not estimated from underway data.…”