Transition of Carbon-Nitrogen Coupling along an Anthropogenic Disturbance Gradient in Subtropical Small Mountainous Rivers
Abstract
Relationship between DOC and DIN and their stoichiometric ratio regulating various biogeochemical reactions reflects the condition of balanced carbon and nitrogen in aquatic environments. Little is known to the relationship between DOC and DIN along a human disturbance gradient in subtropic mountainous rivers. Here, we investigated the DOC, NO3-, and NH4+ in 42 Taiwan rivers with different levels of human disturbance. Results showed that the concentrations of the three nutrients were generally low, yet the DOC and DIN exports were much higher than the global average, which indicate a strong hydrologic regulation and continuous supply. As stoichiometric ratios, Taiwan rivers are generally under carbon-limited conditions. Thus, NO3- in excess of microbial demand should accumulate following energetic constraints in well-oxygenated rivers. Human activities lead to higher concentration and export of DOC, NO3-, and NH4+. An elevated concentration combined with gentle slope in highly-disturbed watersheds may lower down DO concentration and pose the threat of eutrophication. When DO became lower than 6.5 mg L-1 in water columns, the dominant influence on DOC-DIN patterns would shift from energy to redox constraints. Under this condition, an inverse DOC- NO3- pattern would emerge and the excess N was accumulated as NH4+ rather than NO3-. This study provided empirical evidence for the transition and drivers of riverine DOC-DIN patterns along an anthropogenic gradient and furthered our understanding of aquatic carbon-nutrient dynamics.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H13G..02H