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Temporal patterns of dissolved organic matter biodegradability are similar across three rivers of varying size
Author(s) -
Coble Ashley A.,
Marcarelli Amy M.,
Kane Evan S.,
Toczydlowski David,
Stottlemyer Robert
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003218
Subject(s) - dissolved organic carbon , tributary , temperate climate , chemistry , organic matter , seasonality , total organic carbon , environmental chemistry , environmental science , hydrology (agriculture) , ecology , biology , cartography , geotechnical engineering , organic chemistry , engineering , geography
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.