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The relative influence of land cover, hydrology, and in‐stream processing on the composition of dissolved organic matter in boreal streams
Author(s) -
Kothawala Dolly N.,
Ji Xing,
Laudon Hjalmar,
Ågren Anneli M.,
Futter Martyn N.,
Köhler Stephan J.,
Tranvik Lars J.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg002946
Subject(s) - dissolved organic carbon , boreal , environmental science , streams , snowmelt , hydrology (agriculture) , wetland , land cover , surface runoff , ecology , environmental chemistry , land use , chemistry , geology , computer network , geotechnical engineering , computer science , biology
Low‐order boreal streams are particularly sensitive interfaces where dissolved organic matter (DOM) is transported from soils to inland waters. Disentangling the relative influence of key environmental factors suspected to influence stream water DOM composition is highly relevant to predicting the reactivity and fate of terrestrial DOM entering inland waters. Here we examined changes to DOM composition using absorbance and fluorescence, from 17 boreal streams ranging from first to fourth orders, over 14 months, including the rarely studied winter season, and two snowmelt periods ( n = 836). We also analyzed soil pore water samples from three forest soil lysimeters to a depth of 70 cm ( n = 60). Of five identified fluorescing parallel factor analysis components, two (C4 and C5) expressed a clear mire wetland or forest signature, providing distinct molecular markers of dominant land cover. In fact, land cover alone explained 49% of the variability in DOM composition. In contrast, seasonal fluctuations in hydrology only contributed to minor shifts (8%) in the composition of stream water DOM, while in‐stream transformations to DOM composition were undetectable. These findings suggest that low‐order boreal streams act as a passive pipe, since in‐stream processing of DOM is restricted by short water residence times (6 h to 2 days). In addition, we demonstrated the sensitivity of optical approaches to distinguish between key terrestrial sources of DOM in the boreal landscape. By distinguishing the proportional leverage of key environmental controls on headwater stream DOM composition, we are better equipped to predict where and when key DOM transformations occur in the aquatic conduit.