Watershed DOC Uptake Occurs Almost Entirely in Lakes and Reservoirs: A New Model for Connected River, Lake and Reservoir DOC Cycling
Abstract
River networks transport dissolved organic carbon (DOC) from terrestrial uplands to the coastal ocean. The extent to which a reach, lake, or reservoir within a river network uptakes DOC depends on the stream order, the seasonal conditions, and the flow, with important implications for watershed greenhouse gas dynamics and ecosystem health. At the watershed scale, it remains unclear whether DOC uptake is dominated by biological processes such as respiration, or abiotic processes like photomineralization. The partitioning of DOC uptake in lakes vs dam reservoirs vs rivers is also unclear. In this study, we present the first model that unifies the year-round controls on DOC cycling for an entire river network, including the effects of river-lake-reservoir connectivity, to elucidate the importance of biotic vs. abiotic controls on DOC uptake in lakes, reservoirs and rivers. We present the Catchment Uptake and Sinks by Season, Order, and Flow for DOC (CUPS-OF-DOC) model, which quantifies terrestrial DOC loading, gross primary productivity (GPP), and uptake via microbes and photomineralization. The model is applied to the heavily dammed Connecticut River Watershed in the United States, and accounts for cascading reach- and reservoir/lake-scale DOC cycling across ninety-eight scenarios spanning combinations of flows, seasons, and stream orders. We show that riverine DOC uptake is relatively constant with stream order, but the proportion of DOC uptake that is from photomineralization varies. Photomineralization dominates in rivers in most flow conditions and stream orders, especially in winter. Whole-watershed DOC uptake occurs mostly via biomineralization in lakes and reservoirs, with rivers accounting for less than 10% of DOC uptake during the growing season, despite accounting for more than 90% of the open water surface area.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H53C..01M