Real-time chemical mapping of a river using OA-ICOS Technology

The carbon cycling and conversion to CO₂ or CH₄ follows specific dynamics in coastal ecosystems that combine water and sediments. In order to better understand this accelerated cycle, a group of marine scientists from Whoods Hole Oceanographic Institution (USA) have developed the gas-powered autonomous surface vehicle (ASV) “ChemYak” equipped with various in-situ sensors for water composition analysis and meteorologic measurements.

The ASV allows to perform carbon cycle mapping in the coastal zone with high spatial and temporal resolution, and accurately follow preplanned routes even in remote locations, with precise speed control.

The ASV was fitted with LGR’s membrane-based Dissolved Gas Extraction System (DGES) coupled with an Ultraportable Greenhouse Gas Analyzer (U-GGA-915) to perform real-time measurements of dissolved CO₂ and CH₄ in coastal waters. The LGR instrumentation was preferred over other commercial sensors for dissolved methane analysis, thanks to its superior accuracy and response time.

Dissolved Gas Extraction System (left) and Ultraportable Greenhouse Gas Analyzer (right)

In attached article “Rapid Mapping of Dissolved Methane and Carbon Dioxide in Coastal Ecosystems Using the ChemYak Autonomous Surface Vehicle”, the marine scientists describe an application example of the complete measurement system for coastal water composition mapping in the North River estuary, 30 miles south of Boston (MA, USA). The ASV was deployed in both the main estuary channel and the smaller Cove Brook tidal creek during a 1-day field test.

ChemYak ASV equipped with various chemical and weather sensors (Nicholson et al.)

The paper provides a detailed and thorough illustration of the combined efficiency of the DGES coupled to U-GGA-915 for in-situ analysis of dissolved gases. In particular, it describes precisely the procedure to characterize the gas extraction efficiency of the DGES.

Data generated with the DGES + U-GGA-915 showed that dissolved CH₄ and CO₂ values increased upriver, reflecting a net flux to the atmosphere from the North River estuary. Authors also observed that levels of CH₄ and CO₂ in the 1-km Cove Brook section were significantly higher than in the main North River channel.

Mapping of partial CO₂ and CH₄ pressure through North River main estuary and Cove Brook tidal creek (Nicholson et al.)

They also demonstrated that the relationship between salinity and water chemistry was clearly distinct between the main channel and side channel, indicating a distinct freshwater end-member, influenced by an additional source of CO₂ and CH₄.

Dissolved CO₂ and CH₄ concentratrion in main channel and Cove Brook side channel of North River as a function of salinity (Nicholson et al.)

This work represents the first use of an ASV utilized for dissolved CH₄ measurements. The authors concluded that the various sensors aboard the ChemYak allowed to collect high-quality continuous data, providing orders of magnitude more data than if characterization had been conducted by water sample collection. In addition, all chemical analysis was done in situ and not in the laboratory, greatly expediting generation of deployment results. This ASV-base approach opens up future opportunities for adaptive sampling using real-time sensor feedback and coordinated, multivehicle operations.

PRECIPITATION ANALYSIS WITH LGR ISOTOPIC WATER ANALYZER

The stable isotopic compositions of rainfalls is affected by complex meteorological and geographical factors, such as atmospheric conditions at the moisture source and precipitation site, moisture transport trajectories, altitude of condensation and latitude. Therefore, stable isotopes of water (²H, ¹⁸O and more recently ¹⁷O) can be used as natural tracers in ecohydrological and meteorological research, providing information on precipitation formation and transport mechanisms.

In the attached report “Stable isotope variations of daily precipitation from 2014–2018 in the central United States“, hydrogeologists from Indiana University-Purdue University Indianapolis (IUPUI) presented a four-year daily precipitation isotope dataset collected at mid-latitudes (Zionsville, Indiana, USA) and measured with LGR Water Vapor Isotope Standard Source (WVISS) and Triple Water Vapor Isotope Analyzer (TWVIA-912).

Water Vapor Isotope Standard Source (WVISS) and Triple Water Vapor Isotope Analyzer (TWVIA-912)

The influencing factors of the precipitation formation at the study site are complex and caused by different water vapor sources (Continental, Pacific, Atlantic, Gulf of Mexico, and Arctic). The procedure for sampling, measuring, calibrating and post-processing the data is detailed in the report. Multiple standards were used to validate the measurements and the precision values were compared with reported values in the literature.

δ²H, δ¹⁸O, δ¹⁷O, d-excess and ¹⁷O-excess values of daily precipitation from

June 2014 to May 2018 in Indianapolis, Indiana, U.S. (Tian & Wang)

The authors concluded that the precisions of the three individual isotopes (δ²H, δ¹⁸O and δ¹⁷O) was in line with finding from previous studies. In addition, they observed that the precision of  ¹⁷O-excess –which is a relatively new tracer- is comparable with Isotopic Ratio Mass Spectrometry (IRMS) which has long been considered as the reference method for isotopic analysis. The dataset is made it available to researchers around the world who may use it as a reference for site comparisons and for assessing global hydrological models.

Additional information on the research efforts of that group at IUPUI is provided in that educational video from Professor Wang, that features the LGR TWVIA-912 analyzer in action:

https://www.youtube.com/watch?v=Mt7C0VZbKvU&feature=youtu.be