Spatial and temporal variability of dissolved organic matter quantity and composition in an oligotrophic subtropical coastal wetland
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Dissolved organic matter (DOM) is an essential component of the carbon cycle and a critical driver in controlling variety of biogeochemical and ecological processes in wetlands. The quality of this DOM as it relates to composition and reactivity is directly related to its sources and may vary on temporal and spatial scales. However, large scale, long-term studies of DOM dynamics in wetlands are still scarce in the literature. Here we present a multi-year DOM characterization study for monthly surface water samples collected at 14 sampling stations along two transects within the greater Everglades, a subtropical, oligotrophic, coastal freshwater wetland-mangrove-estuarine ecosystem. In an attempt to assess quantitative and qualitative variations of DOM on both spatial and temporal scales, we determined dissolved organic carbon (DOC) values and DOM optical properties, respectively. DOM quality was assessed using, excitation emission matrix (EEM) fluorescence coupled with parallel factor analysis (PARAFAC). Variations of the PARAFAC components abundance and composition were clearly observed on spatial and seasonal scales. Dry versus wet season DOC concentrations were affected by dry-down and re-wetting processes in the freshwater marshes, while DOM compositional features were controlled by soil and higher plant versus periphyton sources respectively. Peat-soil based freshwater marsh sites could be clearly differentiated from marl-soil based sites based on EEM–PARAFAC data. Freshwater marsh DOM was enriched in higher plant and soil-derived humic-like compounds, compared to estuarine sites which were more controlled by algae- and microbial-derived inputs. DOM from fringe mangrove sites could be differentiated between tidally influenced sites and sites exposed to long inundation periods. As such coastal estuarine sites were significantly controlled by hydrology, while DOM dynamics in Florida Bay were seasonally driven by both primary productivity and hydrology. This study exemplifies the application of long term optical properties monitoring as an effective technique to investigate DOM dynamics in aquatic ecosystems. The work presented here also serves as a pre-restoration condition dataset for DOM in the context of the Comprehensive Everglades Restoration Plan (CERP).
KeywordsDOM Wetland Spatial and temporal variations EEM-PARAFAC Everglades
This study was funded by the National Science Foundation through the FCE-LTER program (DEB-9910514 and DBI-0220409). The authors thank the Wetland Ecosystem Laboratory at SERC for logistic support, the SERC Water Quality Laboratory for DOC analyses, and Y. Yamashita for assistance with the PARAFAC modeling and helpful discussions. MC thanks the Department of Chemistry & Biochemistry and the FCE-LTER program for financial support, and S. Jiang for assistance with the PCA analyses. Precipitation Data were provided by the Florida Coastal Everglades Long-Term Ecological Research (LTER) Program. Support to RJ through the George Barley endowment fund in SERC is also acknowledged. This is SERC contribution #601.
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