Hydrologic and biogeochemical influences on carbon processing in the riparian zone of a subarctic stream

• Published in: Freshwater science 2015-03, Vol.34 (1), p.222-232
• Main Authors: Rinehart, Amanda J., Jones, Jeremy B., Harms, Tamara K.
• Format: Article
• Language: English
• Subjects: Acetates; Biogeochemistry; Groundwater; Groundwater–Surface-Water Interactions; Microorganisms; Plumes; Riparian areas; Riparian soils; Soil water; Streams; Watersheds
• ISSN: 2161-9549; 2161-9565
• DOI: 10.1086/679595

Small streams and their adjacent riparian zones contribute disproportionately to the processing and transport of C compared to the catchment area and, thereby, may alter the flux of dissolved organic C (DOC) from aquatic ecosystems. We examined the factors influencing C uptake and CO2 production in the riparian zone of a boreal stream. We tested the hypothesis that enhanced water velocity increases the supply of DOC and nutrients to microorganisms and, therefore, enhances DOC mineralization in the riparian zone. We measured in situ DOC mineralization rate in the riparian zone of a headwater stream at locations that varied with respect to the water velocity of shallow ground water. We added acetate as a tracer to measure C uptake in shallow ground water and monitored CO2 production during tracer experiments. We assessed relationships of these measures of C dynamics with the time that the tracer remained in shallow ground water surrounding the injection site (plume residence time), pre-injection DOC concentration, nutrient availability, and aromaticity of dissolved organic matter. Acetate uptake rate varied 2 orders of magnitude from −0.002 to −0.19/min, whereas CO2 production rate varied 5-fold from 0.01 to 0.06/min. Acetate uptake rate was negatively correlated with mean plume residence time, indicating that rapid water velocity increased C decomposition in the riparian zone. Moreover, Damköhler numbers (Da) were generally