Evaluation of forest disturbance legacy effects on dissolved organic matter characteristics in streams at the Hubbard Brook Experimental Forest, New Hampshire
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Dissolved organic matter (DOM) source and composition are critical drivers of its reactivity, impact microbial food webs and influence ecosystem functions. It is believed that DOM composition and abundance represent an integrated signal derived from the surrounding watershed. Recent studies have shown that land-use may have a long-term effect on DOM composition. Methods for characterizing DOM, such as those that measure the optical properties and size of the molecules, are increasingly recognized as valuable tools for assessing DOM sources, cycling, and reactivity. In this study we measured DOM optical properties and molecular weight determinations to evaluate whether the legacy of forest disturbance alters the amount and composition of stream DOM. Differences in DOM quantity and composition due to vegetation type and to a greater extent, wetland influence, were more pronounced than effects due to disturbance. Our results suggest that excitation-emission matrix fluorescence with parallel factor analysis is a more sensitive metric of disturbance than the other methods evaluated. Analyses showed that streams draining watersheds that have been clearcut had lower dissolved organic carbon (DOC) concentrations and higher microbially-derived and protein-like fluorescence features compared to reference streams. DOM optical properties in a watershed amended with calcium, were not significantly different than reference watersheds, but had higher concentrations of DOC. Collectively these results improve our understanding of how the legacy of forest disturbances and natural landscape characteristics affect the quantity and chemical composition of DOM in headwater streams, having implications for stream water quality and carbon cycling.
KeywordsHubbard Brook Experimental Forest Dissolved organic matter (DOM) Dissolved organic carbon (DOC) Stream Watershed Parallel factor analysis (PARAFAC) Land use
The authors thank Tammy Wooster for sample collection, Ian Halm for logistical support, and Yan Ding for assistance with laboratory analyses. Brian Pellerin and Jamie Shanley provided helpful comments that improved this manuscript. This research was supported by the National Science Foundation through grants to the Hubbard Brook (award #DEB-1114804) and the Florida Coastal Everglades (award #DBI-0620409) Long Term Ecological Research (LTER) programs, the DOI-NPS funded Everglades Fellowship Program (to KC), and through a contribution from the Southeast Environmental Research Center (SERC) Endowment (G. Barley Chair to RJ). This publication is a contribution to the Hubbard Brook Ecosystem Study. The Hubbard Brook Experimental Forest is operated and maintained by the USDA Forest Service, Northern Research Station, Newtown Square, PA. This is SERC contribution number 680.
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