Temperate reservoirs are large carbon sinks and small CO2 sources: Results from high-resolution carbon budgets

• Published in: Global biogeochemical cycles 2013-03, Vol.27 (1), p.52-64
• Main Authors: Knoll, Lesley B., Vanni, Michael J., Renwick, William H., Dittman, Elizabeth K., Gephart, Jessica A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; budgets; carbon; Carbon dioxide; Carbon dioxide emissions; Carbon sinks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects; Geochemistry; Inland waters; Land use; Organic carbon; Reservoirs; Sinkholes; Summer; Synecology; Watersheds
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1002/gbc.20020

Sediment organic carbon (C) burial and CO2 fluxes in inland waters are quantitatively important in regional and global carbon budgets. Estimates of C fluxes from inland waters are typically based on limited temporal resolution despite potential large variations with season and weather events. Further, most freshwater C budget studies have focused on natural soft‐water lakes, while reservoirs and hard‐water systems are globally numerous. Our study quantifies C fluxes in two hard‐water, human constructed reservoirs (Ohio, USA) of contrasting watershed land use (agriculture vs. forest) using high‐resolution mass balance budgets. We show that during a dry summer, C retention and export via the dam were reduced compared to a wet summer. Both reservoirs were net CO2 sources during a wet summer, but CO2 sinks during a dry summer. Despite weather‐related summer differences, annual C fluxes within each reservoir were similar between years. Both reservoirs appear to be net autotrophic despite often being CO2 sources based on budgets. This is likely because CO2 fluxes in our hard‐water reservoirs were more strongly associated with DIC than DOC. Using our C fluxes and statewide watershed land use, we determined the regional importance of Ohio reservoirs in OC burial and CO2 emissions. We estimate that Ohio reservoirs bury up to 4 times more OC, but emit