Development and application of an in-situ alkalinity sensor

• Main Author: Shangguan, Qipei
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2019
• Subjects: sami
• Online Access: https://scholarworks.umt.edu/gsrc/2019/posters/28

Total Alkalinity (AT) in aquatic environments is an extremely useful parameter in identifying and assessing both physical and biogeochemical processes, such as water mixing and dissolution/precipitation of calcium carbonate minerals. AT is also one of the most commonly measured parameters to characterize the inorganic carbon cycle. Determination of AT typically involves a titration where acid is added to a water sample and the resulting pH is measured using a pH electrode. Each analysis typically takes ~15 minutes or less. Large-scale research programs require large investment of capital and labor to produce enough AT data, which severely limits our observational ability. Continuous AT monitoring from moorings, autonomous floats or other platforms can produce high-resolution AT data with reduced cost, time and manpower. SAMI-alk (Submersible Autonomous Moored Instrument for alkalinity) is a robust sensor, developed in our lab, which is capable of performing in-situ measurements hourly over a one month period. This sensor utilizes a novel tracer monitored titration method where a colorimetric pH indicator quantifies both pH and relative volumes of sample and titrant, circumventing the need for gravimetric and volumetric measurements. SAMI-alk can be now deployed in various aquatic environments (ocean, river, etc) through adjusting the ionic strength of the titrant. The SAMI-alk was mounted on a buoy from June 3-22, 2013 on the northeast coast of Oahu, Hawaii. A total of 340 SAMI-alk measurements were made during this period. These AT data, which displayed strong diel cycles with high temporal resolution, greatly improved our understanding of the dynamics of coral productivity (published in Environ. Sci. Technol., 2014, 48 (16), pp 9573–9581). The SAMI-alk was also deployed in the Clark Fork River at Galen Rd, Montana from October 26 to November 05, 2017. A total of 115 measurements were made (unpublished data), which revealed that riverine AT had strong correlations with conductivity. More quality assessment of ...