Hydrological and Biogeochemical Controls on Transport, Modification and Export of Dissolved Organic Matter in Large Drainage Networks.

English Abstract:

Dissolved organic matter (DOM) is essential to the ecology and chemistry of inland waters as an energy and nutrient source, a regulator of light attenuation and a transporter of heavy metals and other pollutants. The key questions explored in this research project include the controls on DOM movement from the terrestrial landscape and modification of DOM during its transit through streams and rivers and toward the ocean in a large drainage network. We explore the riverine fate of terrestrial DOM subsidies by developing a simple model that routes water and DOM through the 1300 km² Passumpsic River watershed located in northern New England. The Passumpsic watershed is drained by a dendritic channel network comprised of 1,500 first- through fifth-order streams that feed the 75-km long, sixth-order Passumpsic River, a tributary to the Connecticut River. Published scaling laws are used to specify the numbers, lengths, and connectivities of the stream segments, while the routing algorithm describes the precipitation-induced delivery of terrestrial DOM to headwater reaches and the down-network changes in DOM concentrations resulting from mixing with other waters and rate-limited decomposition. Results of model simulations conducted to date underscore the dominant contribution of low-frequency precipitation events to the annual subsidy of terrestrial DOM to the drainage network and reveal that most of this DOM subsidy is utilized in large rivers, far from its source within the drainage network.