Impact of Watershed Characteristics on Surface Water Transport of Terrestrial Matter into Coastal Waters and the Resulting Optical Variability: An example from the Penobscot River, Maine
Collin
Roesler, University of Maine, collin.roesler@maine.edu
(Presenting)
George
Aiken, U.S. Geological Survey, graiken@usgs.gov
Andrew
Barnard, WET Labs, Inc., andrew@wetlabs.com
Thomas
Huntington, U.S. Geological Survey, thunting@usgs.gov
Heidi
Franklin, University of Maine, heidi.franklin@maine.edu
Cristina
Orrico, WET Labs, Inc., cris@wetlabs.com
Coastal waters are physically, biogeochemically, and therefore optically complex as a result of the commingling of waters arising from terrestrial, freshwater and marine ecosystems. Separating the influences of these three ecosystems on the optical properties of the resulting mixture is challenging, particularly given the variability within each. We present the results of a four-year observational program from the Penobscot River, Maine. Approximately monthly samples and in situ optical observations were collected from nearly 20 stations representing major tributaries and main branch locations. Water samples were analyzed for particulate and dissolved biogeochemical (e.g. organic and inorganic carbon and nitrogen, pigments) and optical properties (e.g. absorption, scattering and fluorescence). Seasonal patterns in biogeochemical properties were quantified for each tributary and related to drainage basin land coverage and seasonal discharge. Carbon and nitrogen budgets were quantified for the river. Optical proxies for the dominant biogeochemical properties (i.e. DOC, POC, chlorophyll) were quantified from the discrete optical and biogeochemical observations. These proxies were then applied to optical observations obtained hourly from moored sensors to quantify the variability in riverine biogeochemical inputs into the estuarine waters of Penobscot Bay. Optically, the dissolved organic matter dominates over particulate or algal matter regardless of season and is significantly correlated to DOC. The dynamics of DOC are strongly seasonal and are proportional to discharge. It appears that while there is some transformation of this matter (loss of some fractions and gain of others) in the estuary, it has a large significant impact on the optical properties of the coastal waters throughout the year, leading to overestimation of ocean color derived chlorophyll concentrations, particularly during low chlorophyll seasons.
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