Temperate reservoirs are large carbon sinks and small CO sub(2) 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: Freshwater
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1002/gbc.20020

Sediment organic carbon (C) burial and CO sub(2) 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 CO sub(2) sources during a wet summer, but CO sub(2) 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 CO sub(2) sources based on budgets. This is likely because CO sub(2) 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 CO sub(2) emissions. We estimate that Ohio reservoirs bury up to 4 times more OC, but emit