Spectro-fluorometric characterization of dissolved organic matter (DOM) in a Mid-Atlantic watershed
Date
2013
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
Spatial and seasonal pattern of dissolved organic matter (DOM) was
characterized using a unique combination of hydrologic flow path analyses and
spectro-fluorometric tools. The study was conducted over a four year (2008-11) period
in a headwater forested watershed located in the Piedmont region of the mid-Atlantic
USA. Sampling was conducted for stream water and variety of watershed sources
which include throughfall, litter, soil waters, riparian, shallow, and deep ground waters
during base flow and storm flow conditions. Ultraviolet and fluorescence
measurements were performed to generate excitation-emission matrices (EEMs). A
site specific parallel factor analyses (PARAFAC) EEMs model for DOM was
developed and compared against a generic model. Discriminant analyses indicated that
the site-specific model was more sensitive to subtle differences in DOM and was able
to provide a greater level of differentiation in DOM among the watershed sources.
This allowed better insights into how DOM evolved as it moved through the
watershed. Spatial analyses indicated that DOM derived from catchment with
increased wetland coverage was more humic and aromatic. No influence of drainage
area was present in base flow DOM response. Attenuated DOM response during storm
flow conditions with drainage area was observed. Water flow paths appeared to be key
drivers in shaping DOM response in storm conditions. Seasonal patterns of DOM were
evaluated for stream water during base flow and storm flow conditions and for
multiple watershed sources. Overall, seasonal pattern in stream water DOM was more
pronounced for storm flow versus base flow. Similarly among watershed sources, seasonality in DOM sources was more apparent in surficial versus groundwater DOM
sources. This pattern confirmed our primary hypothesis that sorption of DOM (to
mineral soil surfaces) along deeper hydrologic flow paths damped the seasonal DOM
signal. Seasonal “hot” moments such as autumn leaf fall appeared to have a strong
influence on seasonal DOM patterns that was apparent in storm runoff occurring
immediately following autumn leaf inputs. In conclusion, this study clearly
demonstrated the value and benefits of using a suite of optical indices to characterize
DOM.