Interannual drought length governs dissolved organic carbon dynamics in blackwater rivers of the western upper Suwannee River basin

• Published in: Journal of geophysical research. Biogeosciences Vol. 118; no. 4; pp. 1636 - 1645
• Main Authors: Mehring, A. S., Lowrance, R. R., Helton, A. M., Pringle, C. M., Thompson, A., Bosch, D. D., Vellidis, G.
• Format: Journal Article
• Language: English
• Published: Hoboken, NJ Blackwell Publishing Ltd 01-12-2013; Wiley
• Subjects: Carbon; Carbon cycle; Carbon dioxide; climate change; Correlation; Discharge; Dissolved organic carbon; DOM; Downstream; Drought; Droughts; Earth sciences; Earth, ocean, space; EEM; Environmental impact; Exact sciences and technology; Freshwater; High temperature; Hydrology; Marine and continental quaternary; Microorganisms; Mineralization; River basins; River discharge; River flow; Rivers; Surficial geology; United States; Georgia; experimental studies; rivers; stream transport; river discharge; concentration; carbon cycle; North America; mineralization; fluorescence; drought; temperature; export; dissolved organic carbon
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2013JG002415

The Little River (LR) in southern Georgia, U.S., has experienced lengthening droughts since monitoring began in 1972. We evaluated the impacts of drought on riverine carbon cycling using a 9 year data set of dissolved organic carbon (DOC) coupled with laboratory experiments in the LR, as well as long‐term data sets in three additional rivers within the Suwannee River basin. Longer drought periods reduced downstream DOC export but also led to higher DOC concentrations in the following hydroperiod. Within a hydroperiod, DOC concentration was positively correlated with temperature and negatively correlated with river discharge but also negatively correlated with total discharge during the previous hydroperiod. Among hydroperiods, DOC concentration was more strongly correlated with antecedent hydrological conditions than with current hydrological conditions across broad spatial scales: in three additional rivers within the Suwannee River basin (Alapaha, Withlacoochee, and Okapilco) and in headwater and downstream reaches of the LR. Microbial DOC consumption and CO2 production were elevated when DOC concentration was high. Despite dramatic hydrologic changes, DOC composition appeared stable, with optical analyses suggesting that LR DOC is primarily composed of three terrestrial humic‐like fluorescence groups. If the current climatic trend of intensifying droughts, elevated temperatures and decreased discharge continue, our results suggest the net effect may be for a more localized riverine carbon cycle with reduced downstream transport of DOC, but higher local mineralization rates due to elevated DOC concentrations.
Key Points
Post‐drought [DOC] was significantly higher in 4 southeastern blackwater rivers
[DOC] was more correlated with past than with current hydrological conditions
Increased drought may lower export, but raise DOC concentration & mineralization