EXPORT OF TERRESTRIAL DISSOLVED ORGANIC CARBON TO COASTAL RIVERS AS A FUNCTION OF CLIMATE AND LAND-SURFACE PROCESSE

Monthly observations spanning multiple years in seven major rivers in four different climate zones within the U.S. were analyzed for correlations between dissolved organic carbon (DOC) concentration and surface air temperature, precipitation, land cover and discharge. The major watersheds were the Altamaha River (GA), the Apilachicola River (FL), the Columbia River (OR), the Delaware River (NJ), the Sacramento and San Joaquin Rivers (CA) and the Susquehanna River (MD). One minor watershed, the Neponset River (MA) was also analyzed. Results indicate that temperature is the most important variable for DOC export when the variation of annual mean temperatures is large (e.g., >5 ◦C) with sufficient precipitation levels. Land-surface characteristics and discharges are better correlated to DOC concentrations when variations of annual mean temperatures are small (e.g. <2 ◦C). However, results from the small watershed (Neponset) showed that land surface processes vary annual DOC concentrations about ±1.65 mg/L from mean value. DOC flux per square meter was calculated based on incremental temperature increases. The results indicate that an increase of 1 ◦C would result in a 0.476 mg/L increase of in-stream DOC in large watersheds. Climate warming would have a greater impact on riverine DOC yields in cooler climate zones (up to 26% per ◦C) than on those in warmer climate zones (up to 6% per ◦C). This study is the first to examine DOC relationships in watersheds in multiple climate zones. Weak correlations between temperature and DOC found in previous studies may be attributable to the fact that those studies examined small watersheds contained within a single climate zone.