Temporal patterns of dissolved organic matter biodegradability are similar across three rivers of varying size. Issue 6 (18th June 2016)

• Record Type: Journal Article
• Authors: Coble, Ashley A.; Marcarelli, Amy M.; Kane, Evan S.; Toczydlowski, David; Stottlemyer, Robert
• Is Part Of: Journal of geophysical research. Volume 121:Issue 6(2016:Jun.)
• Page Start: 1617
• Page End: 1631
• Publication Date: 2016-06-18
• Subjects: dissolved organic carbon loads -- dissolved organic matter composition -- temporal variability -- temperate tributaries; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2015JG003218
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Dissolved organic matter (DOM) composition may be an important determinant of its fate in freshwaters, but little is known about temporal variability in DOM composition and the biodegradability of DOM in northern temperate watersheds. We measured biodegradable dissolved organic carbon (BDOC) via incubation assays and DOM composition using optical indices on 11 dates in three Lake Superior tributaries. Percent BDOC (%BDOC) and BDOC concentrations were seasonally synchronous across these watersheds, despite that they vary in size by orders of magnitude (1.7 to 3400 km 2 ). Relative to %BDOC, BDOC concentrations were more tightly constrained among sites on any given date. BDOC also varied within seasons; for example, %BDOC on two different dates in winter were among the highest (29% and 54%) and lowest (0%) values observed for each site (overall %BDOC range: 0 to 72%). DOM composition varied the most among tributaries during a summer storm event when BDOC (both as percent and concentration) was elevated but was remarkably similar among tributaries during fall, spring, and winter. Multivariate models identified humic‐like and tryptophan‐like fluorophores as predictors of %BDOC, but DOM composition only described 21% of the overall variation in %BDOC. Collectively, these three rivers exported ~18 Gg C yr −1 as DOC and ~2 Gg C yr −1 as BDOC, which corresponded to 9 to 17% of annual DOC exported in biodegradable form. Our results suggest much of the C exported from these northern temperate watersheds may be biodegradable within 28 days and that large pulses of labile DOM can be exported during storm events and spring snowmelt. Key Points: DOM biodegradability varies synchronously among watersheds varying in size DOM composition was only distinct among different watersheds during storm flow 15.7% of annual DOC export from these northern temperate watersheds was biodegradable