Study Shows Factors Driving Inland Water CO2 Emissions

Carbon emissions from lakes, rivers, and reservoirs include a huge proportion of the carbon cycle worldwide. New studies on carbon release from inland waters in China have concentrated on single rivers or lakes, and the fundamental factors driving carbon dioxide (CO₂) emissions remain vague.

Currently, a team of researchers headed by Prof. Zhang Yunlin from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences collected metadata from various studies containing measured data on the efflux of CO₂ from inland waters and acquired a total of 1,405 measurements, including 625 lake sites, 658 river sites, and 122 reservoir sites sampled mainly between 2010 and 2020, and examined the effluxes of CO₂ and drivers throughout the inland waters in China.

This study has been published in the October 10^th issue of Global Change Biology.

From various data-sharing forums, the team acquired a series of data products, including land cover and land use, gross primary productivity (GPP), and net primary productivity (NPP) at spatial resolutions of 30 m and 1 km.

Next, they obtained data on catchment agricultural and urban land use, gross domestic product (GDP), NPP, population density, topsoil pH, topsoil organic carbon, and precipitation.

Through analyzing these data products, we unravel the driven mechanisms of CO₂ efflux from lakes, reservoirs and rivers in China.

Professor Zhang Yunlin, Study Lead Author, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences

 The scientists discovered markedly higher CO₂ efflux from rivers than from reservoirs and lakes. The effluxes of CO₂ from lakes and rivers grew considerably with the increasing catchment urban land use, and CO₂ effluxes of reservoirs and lakes grew considerably with increasing catchment agricultural land use.

The effluxes of CO₂ from reservoirs, lakes, and rivers grew with increasing population density and catchment GDP. In comparison, there were no major relationships between the CO₂ efflux and catchment yearly NPP, pH of topsoil, topsoil organic carbon concentration, or catchment precipitation.  

Earlier studies have learned that compared to less inhabited areas, the growth in population density results mainly in the eutrophication of inland waters caused by the discharge of industrial, agricultural, and housing effluents, along with nonpoint sources of organic carbon.

In eutrophic waters, the main production is usually increased with high quantities of bio-labile organic matter, supporting microbial degradation and thereby strongly increasing the CO₂ production and release from inland waters.

These outcomes indicate that anthropogenic disturbances concerning urbanization and agricultural land use can impact CO₂ releases from inland waters more than catchment productivity, which earlier had been recognized as the key driver for CO₂ releases from inland waters in less populated areas.

This study showed that the occurrence of anthropogenic disturbances in catchments, signified by GDP, agricultural and urban land use, and population density, were positively associated with the emission of CO₂.

It emphasized the significance of in-situ creation of CO₂ through the degradation of household emissions, nonpoint source- and algal-organic carbon in catchments draining thickly populated regions compared with CO₂ being straightaway delivered via inflowing catchment streams.

Journal Reference:

Wang, J., et al. (2022) Urbanization in developing countries overrides catchment productivity in fueling inland water CO₂ emissions. Global Change Biology. doi.org/10.1111/gcb.16475.