Dissolved Organic Matter Dynamics in a Suburbanizing Watershed: The Importance of Wetlands, People, and Flowpaths

Human development of a watershed often yields fundamental and quantifiable changes in water quality and inorganic nutrient cycling. The effects of suburban development on the cycling of dissolved organic matter (DOM), however, have received relatively less attention, and the understanding of local dissolved organic matter dynamics is rarely a stated goal of watershed management. In this study, we examine the effects of suburbanization on concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as well as the optical properties of DOM using 17 study sites in the Lamprey River watershed, NH that integrate varying levels of human development and population density. We show that concentration of DOC and DON is related to wetland cover but is not correlated with population density. Further, we observed no response in DOC concentration with increased flow at the mainstem site, while DON concentration is diluted. The optical properties of dissolved organic matter, however, showed different trends. Fluorescence Index (FI) decreases with increasing wetland cover and lower population density. We show that in a coastal watershed, while DOM quantity is driven by the presence of wetlands, DOM quality changes with both wetland cover and human development. The decoupling of DOM quantity and quality in this suburbanizing watershed indicate that DOM quality may be an important yet overlooked control on watershed-scale biogeochemical cycling and nutrient export.