Data-set of CO2, CH4, N2O dissolved concentrations and ancillary data in Lake Victoria (March 2018, October 2018, and June 2019)

The data-base contains 4 xlsx files:

CTD_Lavigas_123 contains vertical profiles of CTD data (water temperature, specific conductivity, pH, oxygen saturation level (%O2)), partial pressure of CO2 measured with headspace equilibration with a Licor, CH4 and N2O measured with headspace equilibration by gas chromatography on samples collected with a Niskin bottle, obtained in March-April 2018, October-November 2018, and June 2019.

UW_Lavigas_1 contains the continuous measurements in surface waters of partial pressure of CO2 and CH4 measured by equilibration with a Los Gatos Research portable analyzer, plus CTD data and bottom depth, obtained in March-April 2018.

UW_Lavigas_2 contains the continuous measurements in surface waters of partial pressure of CO2 and CH4 measured by equilibration with a Los Gatos Research portable analyzer, plus CTD data and bottom depth, obtained in October-November 2018.

UW_Lavigas_3 contains the continuous measurements in surface waters of partial pressure of CO2 and CH4 measured by equilibration with a Los Gatos Research portable analyzer, plus CTD data and bottom depth, obtained in June 2019.

For vertical profiles (CTD_Lavigas_123) water was collected with a Niskin bottle and two 60 mL borosilicate serum bottles (Wheaton) for the determination of CH4 and N2O were filled with a silicone tubing, allowed to overflow, poisoned with a saturated solution of HgCl2 (100 µL), sealed with butyl stoppers, crimped with aluminum caps, and stored at ambient temperature in the dark. Samples for the determination of pCO2 were collected from the Niskin bottle in 4 polypropylene 60 mL syringes where 30 mL of sample water were equilibrated with 30 mL of ambient air (5 min of vigorous manual shaking). The pCO2 in ambient air and in the equilibrated gas phase were determined with a Li-840 calibrated with N2 and a suite of CO2:N2 commercial mixtures (Air Liquide Belgium) with mixing ratios of 388, 813, 3788, and 8300 ppm CO2. The overall precision of pCO2 measurements was ±2.0%. Concentrations of CH4 and N2O were determined via the headspace equilibration technique (20 mL N2 headspace in 60 mL serum bottles) and measured by GC with flame ionization detection (GC-FID) and electron capture detection (GC-ECD) with a SRI 8610C GC-FID-ECD calibrated with CH4:CO2:N2O:N2 mixtures (Air Liquide Belgium) of 1, 10, 30, 509 and 2011 ppm CH4 and of 0.2, 2.0 and 6.0 ppm N2O, and using the solubility coefficients of CH4 (Yamamoto et al. 1976) and N2O (Weiss & Price 1980). The precision of measurements was ±3.9% for CH4 and ±3.2% for N2O.

In surface waters, pCO2 and the partial pressure of CH4 (pCH4) were measured with a Los Gatos Research (LGR) off-axis integrated cavity output spectroscopy analyzer (Ultraportable Greenhouse Gas Analyzer with extended range for CH4) coupled to an equilibrator (Frankignoulle et al. 2001). The reading of pCO2 and pCH4 from the LGR was compared in the home laboratory to the values from CH4:CO2:N2 mixtures (Air Liquide Belgium) of 1, 10, 30, 509 and 2011 ppm CH4 and 431, 1088, 4,385 and 22,029 ppm CO2. The instrument did not show detectable drift between the start and the end of the fieldwork, and the factory calibration gave satisfactory readings against standards.

Both approaches to measure pCO2 and CH4 show excellent agreement (Borges et al. 2022). Water temperature, conductivity, pH, and dissolved O2 were measured with Yellow Spring Instrument (YSI) multiprobe (YSI EXO-2). Depth was measured with a Humminbird Helix 5 G2.

References

Borges AV, L Deirmendjian, S Bouillon, W Okello, T Lambert, FAE Roland, VF Razanamahandry, NRG Voarintsoa, F Darchambeau, IA Kimirei, J-P Descy, GH Allen, C Morana (2022) Greenhouse gas emissions from African lakes are no longer a blind spot, Science Advances, 8, eabi8716, 1-17

Frankignoulle M., A. Borges & R. Biondo (2001) A new design of equilibrator to monitor carbon dioxide in highly dynamic and turbid environments. Water Research 35/5: 1344-1347

Yamamoto S., J.B. Alcauskas, T.E. Crozier, Solubility of methane in distilled water and seawater. J. Chem. Eng. Data 21, 78-80 (1976).

Weiss R.F., B.A. Price, Nitrous oxide solubility in water and seawater. Mar. Chem. 8, 347-359 (1980).