Modeling Functional Organic Chemistry in Arctic Rivers: An Idealized Siberian System
Researchers from Los Alamos National Lab and New Mexico Institute of Mining and Technology, with collaborators from Oak Ridge National Laboratory, the Naval Postgraduate School, and the International Arctic Research Center examined the biogeochemical evolution of riverine organic macromolecules from highland to Arctic plume outlets via a reduced Lagrangian kinetic model. An idealized 3000km river system was adopted which comprises soil and delta processing, and tributaries flowing from Arctic sub-ecological systems. The biophysical impact due to injected macromolecules and low molecular weight products have been examined along with their extent of coastal spreading.
Our analysis suggests that along the main stem chemistry is relatively slow, but dilution from river tributaries plays a crucial role in determining the outlet concentration. In addition to fresh cytosol contents and humics, tributaries carry the signature of lignin phenol to distinguish tundra vs taiga sources. Microbial and photochemical losses help to determine the final coastal value for most species, but reactive evolution is distinct for various functions with a special contribution from post and pre-processes (soil and delta). Some species for example the proteins surpass threshold values for biophysical influence. Functional groups are transported that can impact light attenuation and vertical heat distribution, for example as the colored dissolved organic.
As major carriers for organic carbon to the Arctic ocean, boreal rivers form an important link between land and ocean processes. The fate of specific riverine organic molecules has been studied as they mobilize functional groups that determine biophysical properties such as surface adsorption, light attenuation, and nutrient release. Our reduced lagrangian model includes the main river course plus pre- and post-processes in soil and delta, tributaries that connect wetlands, tundra, and taiga ecosystems. We studied organic chemical evolution by performing several sensitivity tests accounting for coastal/reduced turnover rates and upper/lower limit initial DOC input from the northern ecological system. The temporal variation of DOC turned out to be relatively small, but the tributary mixing factor was significant. Transformation of each chemical species and the relative contribution from regional sub-ecologies turned out to be distinct. Tributaries also moved signature molecules such as lignin phenols enabling differentiation of tundra vs taiga. The outlet concentration of colored dissolved organic material is a sum of fractions of humics and individual structures such as amino acids and proteins. Concentrations rise above the values for biophysical influence such as absorption (light attenuation) and for surfactant structures for adsorption. The extent of coastal spreading was tested through a regional box model by calibrating against salinity and color.