Bioindicator for the Sources and Drivers of Carbon Dioxide and Dissolved Methane Concentrations in Urban Rivers

Abstract

Rivers draining urban areas are reported to be a noteworthy source of atmospheric greenhouse gases (GHGs), yet the drivers of carbon dioxide partial pressure (pCO₂) and dissolved methane (dCH₄) remain unclear in urban rivers. This study identified key controls of biotic and abiotic drivers across urbanization gradients. pCO₂ and dCH₄ increased with urbanization intensity, alongside sewage-associated biotic variables (Bacteroidales abundance, RAB; Methylocystis abundance) and abiotic factors (electrical conductivity, dissolved organic carbon, total dissolved nitrogen, total dissolved phosphorus, chlorophyll a). In highly urban segments, abiotic factors explained 87% of pCO₂ variation, while RAB explained 95% of dCH₄ variation, pointing to sewage inputs as a major methane source. Seasonally, pCO₂ showed comparable averages but a wider range in the wet season. Dissolved oxygen was negatively correlated with pCO₂, explaining 65% (wet) and 58% (dry) of the variation, indicating biological metabolic control. The negative relation between dCH₄ and methane monooxygenase (MMO) abundance suggests biological oxidation regulation. A significantly lower dCH₄ in the wet season was linked to higher MMO and faster flow. Overall, including biological factors and bioindicators improves understanding of pCO₂ and dCH₄ sources and drivers in urban rivers.