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Abstract In 2021, the Ocean Thematic Centre of the European Research Infrastructure “Integrated Carbon Observation System” conducted an international partial pressure of carbon dioxide (pCO2) instrument intercomparison. The goal was to understand how different types of instrumentation for the measurement of oceanpCO2compare to each other. During the two‐week long experiment, we installed various instruments in a tank facility using natural sea water (North Sea). These included direct air–water equilibration systems and membrane‐based flow‐through instruments along with submersible sensors and instruments that are normally installed on buoys and autonomous surface vehicles. In situ instruments were installed inside the tank and the flow‐through instruments were fed the same water using a pumping system. We changed the temperature (between 10°C and 28°C) and the seawaterpCO2(between 250 and 800μatm) to observe instrument responses over a wide range. Since there is no reference for surface oceanpCO2measurements, we agreed on a set of instruments serving as intercomparison reference. All data from the different instruments were then compared against the intercomparison reference during periods of stable temperature andpCO2. The study provides important information to enhance future ocean carbon monitoring networks, but makes no direct recommendation for the use of any specific sensor. A major finding is that equilibration through direct air–water contact appears to be more consistent and independent of external factors than equilibration through a membrane or photometric detection. We found several instruments with no temperature measurements at the location of equilibration or with uncalibrated temperature sensors introducing significant uncertainty in the results.
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Lotic‐SIPCO2 : Adaptation of an open‐source CO2 sensor system and examination of associated emission uncertainties across a range of stream sizes and land uses
Abstract River networks play a crucial role in the global carbon cycle, as relevant sources of carbon dioxide (CO2) to the atmosphere. Advancements in high‐frequency monitoring in aquatic environments have enabled measurement of dissolved CO2concentration at temporal resolutions essential for studying carbon variability and evasion from these dynamic ecosystems. Here, we describe the adaptation, deployment, and validation of an open‐source and relatively low‐cost in situpCO2sensor system for lotic ecosystems, the lotic‐SIPCO2. We tested the lotic‐SIPCO2 in 10 streams that spanned a range of land cover and basin size. Key system adaptations for lotic environments included prevention of biofouling, configuration for variable stage height, and reduction of headspace equilibration time. We then examined which input parameters contribute the most to uncertainty in estimating CO2emission rates and found scaling factors related to the gas exchange velocity were the most influential when CO2concentration was significantly above saturation. Near saturation, sensor measurement ofpCO2contributed most to uncertainty in estimating CO2emissions. We also found high‐frequency measurements ofpCO2were not necessary to accurately estimate median emission rates given the CO2regimes of our streams, but daily to weekly sampling was sufficient. High‐frequency measurements ofpCO2remain valuable for exploring in‐stream metabolic variability, source partitioning, and storm event dynamics. Our adaptations to the SIPCO2 offer a relatively affordable and robust means of monitoring dissolved CO2in lotic ecosystems. Our findings demonstrate priorities and related considerations in the design of monitoring projects of dissolved CO2and CO2evasion dynamics more broadly.
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- PAR ID:
- 10501075
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- Volume:
- 22
- Issue:
- 4
- ISSN:
- 1541-5856
- Format(s):
- Medium: X Size: p. 191-207
- Size(s):
- p. 191-207
- Sponsoring Org:
- National Science Foundation
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