Dissolved organic matter (DOM) is one of the most important biogeochemical components influencing productivity, nutrient cycling, and optical properties of aquatic environments. DOM fuels heterotrophic

Dissolved organic matter (DOM) is one of the largest fluxes of carbon in inland water ecosystems and a central component of riverine metabolism. DOM, which is approximately 50% dissolved organic carbon (DOC) by mass (Dittmar & Stubbins, 2014;Krogh, 1934), is a nutrient and energy source, capable of transporting metals and pollutants, and a driver of light availability in water bodies (Kaplan & Cory, 2016;Schlesinger & Melack, 1981). Large amounts of riverine DOC enter the ocean annually, where it is an important source of reduced carbon (Raymond & Spencer, 2015). Although the amount of DOC entering the ocean is relatively well known, its representative chemical composition, reactivity, and the seasonality of its input are not as