Intercontinental sampling campaign of river GHG fluxes

This study investigated river GHG fluxes in four rivers: the Cuenca River in Ecuador (South America), the Gilgel Gibe River in Ethiopia (Africa), the Cau River in Vietnam (Asia), and the Zwalm River in Belgium (Europe). These rivers span diverse hydroclimatic zones, geomorphological characteristics, land use and cover (LULC) types, and population densities.  The Cuenca and Zwalm Rivers shared similar mean annual precipitations and temperatures (MAP and MAT, respectively), however the Cuenca experiences higher PET and lower minimum temperatures than Zwalm due to its higher altitude. A similar pattern is observed between the Gilgel Gibe and Cau Rivers, with the former’s higher altitude leading to increased PET and a drier ecosystem, while the latter’s lower altitude leads to higher maximum temperatures. Sampling points were classified based on surrounding LULC within a 1 km radius using the European Space Agency (ESA) LULC map (Zanaga et al., 2022). Sampling point distributions by LULC classes are described in the database.

Five sampling campaigns were performed between February 2022 and October 2023. An equal number of sampling sites (~39) were investigated for the Gilge Gibe, Cau and Cuenca Rivers, while for the Zwalm River, two seasonal campaigns (winter and summer) were conducted across 20 sites. Gas samples were collected by using the floating chamber (FC) technique for analyzing riverine GHG emissions as described in Ho et al. (2021). At each site, three gas samples were collected from the FC’s headspace at 0, 20, and 40 min after its placement. These samples were extracted through a butyl rubber stopper with a 20 ml syringe and immediately transferred into pre-conditioned 12-ml Exetainer® vials (purged three times with helium and evacuated). Vials were stored in dark containers before being transported and analyzed at the ISOFYS in Ghent University and in ETH Zurich. GHG fluxes were estimated from the slope of the linear regression of measured concentrations versus time, and the properties of the FC, using the following equation (Ho et al., 2021):

(1)

In addition to GHG fluxes, we also collected biochemical, geomorphic, LULC and meteorological data. In-situ measurements of water temperature, pH, electroconductivity (EC), salinity, and dissolved oxygen (DO) were recorded using a WTW-3430 multiprobe (WTW GmbH, Weilheim, Germany). Turbidity was measured with a YSI 6920V2-2 multiprobe (YSI Xylem Inc., Yellow Springs, Ohio, USA). Both multiprobes were calibrated prior to sampling. Flow velocity was determined using a Handheld flowtherm NT.2 (Höntzsch, Germany). Water samples from all sites were collected, stored in cool, dark containers, and refrigerated until analysis. Ammonium (NH4+), nitrate (NO3-), nitrite (NO2-) and total nitrogen (TN) concentrations were measured using Spectroquant® Kits. Total organic carbon (TOC) and total inorganic carbon (TIC) were analyzed with a Shimadzu TOC V CPN-analyzer and autosampler. Meteorological data was initially gathered from stations near the sampling sites. In case of missing meteorological data, we supplemented with information from the ERA5-Land dataset (Muñoz Sabater, 2019). Basin areas, river slopes, and topography were obtained via Digital Elevation Maps from the Shuttle Radar Topography Mission (SRTM) (USGS, 2020).

References:

Ho, L., Jerves-Cobo, R., Eurie Forio, M.A., Mouton, A., Nopens, I., Goethals, P., 2021. Integrated mechanistic and data-driven modeling for risk assessment of greenhouse gas production in an urbanized river system. J. Environ. Manage. 294. https://doi.org/10.1016/j.jenvman.2021.112999

Muñoz Sabater, 2019. ERA5-Land hourly data from 1950 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). https://doi.org/10.24381/cds.e2161bac

USGS, 2020. Digital Elevation Shuttle Radar Topography Mission (SRTM) 1 Arc-Second Global Non-Void Filled United States Geological Surv. https://doi.org/10.5066/F7K072R7

Zanaga, Van Den Kerchove, Daems, De Keersmaecker, Brockmann, Kirches, Wevers, Cartus, Santoro, Fritz, Lesiv, Herold, Tsendbazar, Xu, Ramoino, Arino, 2022. ESA WorldCover 10 m 2021 v200. https://doi.org/10.5281/zenodo.7254221