High-resolution measurements of chromophoric dissolved organic matter (CDOM) in the Neponset River Estuary, Boston Harbor, MA

The Neponset River Estuary is a small, tidally dominated urban system that is fringed with Spartina spp. salt marsh and drains the second largest river into Boston Harbor, MA. High-resolution measurements of chromophoric dissolved organic matter (CDOM) were taken with a towed instrument package, the MiniShuttle, to explore tidal and seasonal variations in the sources and distributions of CDOM in the estuary. A mid-estuary source of CDOM was apparent on all surveys representing 10–50% of the freshwater CDOM source to the system. Presumably this source results from the degradation of salt marsh derived organic matter within the estuary. The strength of this source peaked in late summer, an observation that is consistent with this interpretation. Two-dimensional (tow-yo) data shows that the constricting Granite Avenue Bridge displays a major influence on circulation in the estuary. Further, large-scale tidal mixing and variations in the freshwater endmember on the time scale of hours make interpretations difficult. High-resolution measurements show that a fluctuating freshwater endmember and a constant CDOM source from the fringing salt marsh during August, 2002 are consistent with observations.