Organic Carbon Fate and Transport in a Lowland, Temperate Watershed

Recent research has shown the importance of hydrology to impact the variability of dissolved organic matter transport in streams often using organic carbon measurements and tracers of organic carbon to elucidate DOM provenance. Data driven methods have proven useful at the small watershed scale but tracer signals are difficult to interpret when in-stream produced DOM is pronounced, thus requiring the use of a modeling tool. In lowland stream systems, turnover of autochthonous organic matter and the influence of hydrology on its transport can be a substantial portion of the DOM budget. A modeling framework was developed to account for physical and biological processes including watershed hydrology, fluid hydraulics and sediment transport and deposition to the streambed as well as particulate and dissolved organic matter pools and their deposition, erosion, fixation and decomposition. Seasonal variability simulated with the model showed algal fixation predominance in the early spring followed by decomposition of the particulate pool to DOM and carbon dioxide in the late summer and fall. Model results from a five year simulation showed pronounced annual variability. In years with a high density of hydrologic events during autochthonous growth, the benthic organic matter pool was limited, which in turn impacted later decomposition and DOM export. Further, the model showed that years with less frequent hydrologic events produced benthic organic matter stocks as much as two times greater than years with high density hydrologic events. The model results agreed well with 21/2 years of carbon flux measurements collected from the stream. The modeling tool shows effectiveness for understanding the control of hydrology and in-stream biogeochemistry upon DOM for ecosystem function and OM cycling research in lowland systems.