Sources and transformations of chromophoric dissolved organic matter in the Neponset River Watershed

Abstract

[1] The major source of chromophoric dissolved organic matter (CDOM) in coastal waters is often terrestrial dissolved organic matter originating in coastal watersheds and delivered to the ocean by rivers or streams. While studies of carbon cycling in large rivers dominate the literature, small rivers deliver the bulk of the freshwater to coastal waters ($60%). However, the variability of organic matter fluxes in small rivers requires high spatial and temporal resolution measurements to adequately represent the processes controlling distributions and fluxes. In this study, CDOM was measured monthly for 2 years at 15 sampling sites throughout a small, coastal, urban watershed ($300 km 2 ), the Neponset River Watershed, and CDOM variability was found to depend on land use type, discharge/precipitation, and growing degree days (temperature). Forest, wetland, residential, industrial, and golf course CDOM end-members were measured and differentiated using CDOM fluorescence, CDOM absorbance, absorbance slopes, total organic carbon and total nitrogen, and photo-and biological lability. Simple statistical models of CDOM end-member behavior could explain 40-70% of the observed seasonal variability. Using these simple relationships, trends in total CDOM loading behavior can be predicted under various scenarios of land use change and global warming. Overall, detailed measurements of CDOM throughout the Neponset River Watershed yield new insights into the watershed processes that affect terrestrial CDOM delivery to coastal oceans.

Sources, fluxes, and behaviors of fluorescent dissolved organic matter (FDOM) in the Nakdong River Estuary, Korea

“…It is well known that a single sampling event is not enough to capture the full range of natural variability in DOM abundance over all seasons (Stedmon et al, 2006;Huang and Chen, 2009;Markager et al, 2011;Dai et al, 2012;Moyer et al, 2015). Overall, our results show that monthly variations are significant.…”

“…Stedmon et al (2006) demonstrated that stronger correlations were observed between DOC and FDOM as humic substances derived from terrestrial DOM are more colored than DOM produced in situ. In general, terrestrial DOM occurring in rivers originates mainly from plant decomposition and leaf litter in the form of humic substances (Huang and Chen, 2009). As such, Gueguen et al (2006) showed that humic materials are more effectively leached from soils during August and September under high temperatures.…”

“…The magnitudes of DOC and FDOM fluxes from rivers are generally dependent on rainfall, discharge, and temperature (Maie et al, 2006;Jaffé et al, 2004;Huang and Chen, 2009). In the estuarine mixing zone, intensive biogeochemical processes occur through photooxidation, microbial degradation, or physicochemical transformations (i.e., flocculation, sedimentation; Bauer and Bianchi, 2011;Moran et al, 1991;Benner and Opsahl, 2001;Raymond and Bauer, 2001).…”

A Chromophoric Dissolved Organic Matter (CDOM) Observatory

“…Our data set of over 40 months of 30 samples distributed throughout the watershed has allowed us to understand the dependence of CDOM endmember values on land use, season and discharge. A simple model can use these parameters to predict the endmembers with an r 2 of 0.4 to 0.7 (Huang and Chen, 2009). This same simple model has been applied to the Hudson Watershed with approximately the same reliability (Huang et al, 2011).…”

“…The CDOM degradation and production terms (from incubations) are being incorporated into the 10 m Boston Harbor model to better simulate CDOM distributions in the harbor. The rates are parameterized to temperature and salinity based on the regression relationships derived from the monthly measurements in the Neponset Estuary and several cruise measurements in the Hudson River (Huang and Chen, 2009;Huang et al 2011a). …”