1 research outputs found
Riverine Export of Aged Carbon Driven by Flow Path Depth and Residence Time
The flux of terrestrial C to rivers
has increased relative to preindustrial
levels, a fraction of which is aged dissolved organic C (DOC). In
rivers, C is stored in sediments, exported to the ocean, or (bio)chemically
processed and released as CO<sub>2</sub>. Disturbance changes land
cover and hydrology, shifting potential sources and processing of
DOC. To investigate the likely sources of aged DOC, we analyzed radiocarbon
ages, chemical, and spectral properties of DOC and major ions from
19 rivers draining the coterminous U.S. and Arctic. DOC optics indicated
that the majority is exported as aromatic, high molecular weight,
modern molecules while aged DOC tended to consist of smaller, microbial
degradation products. Aged DOC exports, observed regularly in arid
basins and during base flow in arctic rivers, are associated with
higher proportion of mineral weathering products, suggesting deeper
flows paths. These patterns also indicate potential for production
of microbial byproducts as DOC ages in soil and water with longer
periods of time between production and transport. Thus, changes in
hydrology associated with landscape alteration (e.g., tilling or shifting
climates) that can result in deeper flow paths or longer residence
times will likely lead to a greater proportion of aged carbon in riverine
exports