Controls on Dissolved Organic Carbon Bioreactivity in River Systems

Area of Science:

• Environmental Science
• Biogeochemistry
• Hydrology

Background:

• Inland waters are crucial for global carbon cycling, transforming and storing dissolved organic carbon (DOC).
• The bioreactivity of DOC, its susceptibility to microbial degradation into CO2, is poorly understood in relation to water residence time (WRT) and landscape factors.
• Understanding DOC bioreactivity is vital for predicting carbon fluxes from terrestrial to aquatic ecosystems.

Purpose of the Study:

• To investigate how water residence time (WRT) and landscape properties influence the bioreactivity of dissolved organic carbon (DOC) in Swedish river systems.
• To differentiate between short-term and long-term bioreactive DOC pools and their environmental drivers.
• To assess the implications of changing DOC bioreactivity for carbon cycling in inland waters.

Main Methods:

• Studied 15 Swedish catchments with diverse geographical and environmental characteristics.
• Conducted short-term (0-6 days) and long-term (1-year) DOC decay experiments.
• Analyzed the influence of WRT and landscape properties (e.g., phosphorus loading) on DOC bioreactivity.

Main Results:

• Short-term bioreactive DOC was linked to high aquatic primary productivity, stimulated by phosphorus from surrounding landscapes.
• The proportion of long-term bioreactive DOC increased significantly with longer WRT.
• Photo-transformation of terrestrial DOC may increase its long-term bioreactivity, indicated by lower aromaticity.

Conclusions:

• DOC bioreactivity in inland waters is complex and varies with water residence time.
• Increasing WRT paradoxically leads to a greater proportion of long-term bioreactive DOC, a previously overlooked pattern.
• This finding has significant implications for understanding the fate of carbon in freshwater systems and its contribution to atmospheric CO2.