Shifting Flow Paths: How Disturbance Drives Millennial Carbon Export
Barnes, Rebecca T. 1
1 Environmental Science, Colorado College
The flux of terrestrial C to rivers has increased relative to pre-industrial levels and a fraction of this flux is aged dissolved organic C (DOC). Once in rivers, C is stored in sediments, exported to the ocean, or (bio)chemically processed and released as CO2. Potential sources and processing of DOC shift with disturbance; such as changes land cover or warming temperatures. Using radiocarbon ages, chemical, and spectral properties of DOC and major ions from nineteen rivers draining the coterminous U.S. and Arctic, the spatial and temporal dynamics of aged carbon export were explored. 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 or longer 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.