Using modeled runoff to study DOC dynamics in stream and river flow: A case study of an urban watershed southeast of Boston, Massachusetts

The origin, function, and fate of dissolved organic carbon (DOC) in stream flow are not well-understood. This study explores the environmental factors controlling the spatial and temporal variation of DOC in terrestrial ecosystems of a watershed southeast of Boston, Massachusetts. Our hypothesis is that environmental factors: stream flow, land cover type, vegetation density, and drainage area are significant in estimating DOC export from an urban watershed. The hypothesized environmental factors were statistically correlated to the variation of the sampled in-stream DOC concentrations at annual, seasonal, and daily scales. For the purpose of scaling up to a large watershed that lacks dense gauged hydrological data or for projection of future scenarios, we examined the effectiveness of using simulated stream flow for studying terrestrial DOC dynamics. Our results demonstrated that all hypothesized environmental factors except vegetation density were particularly strong predictors in watersheds with a large proportion of developed (urban) area. The resulting linear model is able to explain about 76% (R2 = 0.76) and 64% (R2 = 0.64) of the variance of in-stream DOC concentrations at seasonal and annual scales respectively. Results suggest that more frequent DOC sampling than once each month is required to establish the quantitative relationship between simulated stream flows from a Soil Water Assessment Tool (SWAT) and in-stream DOC concentrations at daily scale. Using a hydrological model is effective for studying the impacts of climate and human activities on DOC export to aquatic ecosystems at appropriate scales.