This study quantifies planktonic autotrophy and heterotrophy in the Beinan River, a tectonically active mountainous catchment in SE Taiwan. Metabolic rates were higher in the wet season, reflecting strong net heterotrophy. Scaled to the catchment, planktonic CO₂ production (~7.9 x 10⁷ mol yr^-1) accounts for ~3.8% of total catchment CO₂ flux. Microbial communities shifted seasonally, showing planktonic metabolism is a vital part of the riverine carbon cycle.

In marsh soils, oxygen concentrations are high close to plant roots and decline to near zero within millimetres. Microorganisms do not decompose organic matter in proportion to oxygen. Many models nevertheless use a single average oxygen concentration. Using Elbe River soils, we compared this approach with a calculation over the full range. The single average overestimated carbon dioxide release by about 12 %. Marsh soils may therefore store more carbon than models predict.