Abstract
Respiration of dissolved organic matter (DOM) in streams contributes to the global CO2 efflux, yet this efflux has not been linked to specific DOM sources and their respective uptake rates. Further, removal of DOM inferred from longitudinal concentration gradients in river networks has been insufficient to account for observed CO2 outgassing. We hypothesize that understanding in-stream dynamics of DOM, which is a heterogeneous mixture spanning a wide range of biological labilities, requires considering that DOM lability decreases during downstream transport. To test this hypothesis, we paired seasonal bioreactor measurements of DOM biological lability with whole-stream tracer data from White Clay Creek, Pennsylvania, USA, and used a particle-tracking model to predict in-stream DOM dynamics. The model simulates continuous inputs of DOM and uses storage time in the stream bioactive regions plus kinetic parameters from bioreactors to assess differential uptake of DOM fractions (i.e., fractionation) in the stream. We compared predictions for in-stream dynamics of bulk DOM concentration (quantified as dissolved organic carbon) and fluorescent DOM components. Our model-data synthesis approach demonstrates that more labile fractions of DOM in stream water preferentially originate and are consumed within short travel distances, causing spiraling metrics to change with downstream distance. Our model can account for local sources of rapidly cycled labile DOM, providing a basis for improved interpretation of DOM dynamics in streams that can reconcile apparent discrepancies between respiratory outgassing of CO2 and longitudinal DOM concentration gradients within river networks.
Original language | English (US) |
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Article number | e2020WR027918 |
Journal | Water Resources Research |
Volume | 57 |
Issue number | 2 |
DOIs | |
State | Published - Feb 2021 |
Funding
This work was supported by National Science Foundation grants EAR‐1344280 to AIP, EAR‐1451372 to RMC, and DEB‐1052716 and EAR‐1452039 to LAK, and the European Commission supported (project ID 734317). We thank J.D. Newbold for sharing data of solute tracer (NaCl) experiments from White Clay Creek. HiFreq: Smart high‐frequency environmental sensor networks for quantifying nonlinear hydrological process dynamics across spatial scales
Keywords
- DOM
- FDOM
- biological lability
- fractionation
- particle-tracking model
- uptake
ASJC Scopus subject areas
- Water Science and Technology