Partial coupling and differential regulation of biologically and photochemically labile dissolved organic carbon across boreal aquatic networks

[摘要] Despite the rapidly increasing volume of research on the biological andphotochemical degradation of DOC (dissolved organic carbon) in aquatic environments, little is knownof the large-scale patterns in biologically and photochemically degradable DOC(BDOC and PDOC, respectively) in continental watersheds, and on the linksthat exist between these two key properties that greatly influence the flowof carbon from continents to oceans. Here we explored the patterns in theconcentrations and proportions of BDOC and PDOC across hundreds of boreallakes, rivers and wetlands spanning a large range of system trophic status andterrestrial influence, and compared the drivers of these two reactive poolsof DOC at the landscape level. Using standardized incubations of naturalwaters, we found that the concentrations of BDOC and PDOC covaried acrossall systems studied but were nevertheless related to different pools ofdissolved organic matter (DOM; identified by fluorescence analyses) inambient waters. Concentrations of nutrients and protein-like fluorescent DOM(FDOM) explained nearly half of the variation in BDOC, whereas PDOC wasexclusively predicted by DOM optical properties, consistent with thephotochemical degradability of specific FDOM pools that we experimentallydetermined. The concentrations of colored DOM (CDOM), which we use here as aproxy of terrestrial influence, almost entirely accounted for the observedrelationship between FDOM and the concentrations of both BDOC and PDOC. Theconcentrations of CDOM and of the putative biolabile fluorescence componentshifted from complete decoupling in clear-water environments to strongcoupling in darker streams and wetlands. This suggests a baselineautochthonous BDOC pool fueled by internal production that is graduallyoverwhelmed by land-derived BDOC as terrestrial influence increases acrosslandscape gradients. The importance of land as a major source of bothbiologically and photochemically degradable DOC for continental watershedsresulted in a partial coupling of those carbon pools in natural freshwaters,despite fundamental contrasts in terms of their composition and regulation.

[学科分类] 地球化学与岩石