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Dynamics of dissolved organic carbon in a stream during a quarter century of forest succession

Dissolved organic carbon (DOC) is a heterogeneous mixture of compounds that makes up a large fraction of the organic matter transported in streams (Webster and Meyer 1997). It plays a significant role in many ecosystems. Riverine DOC links organic carbon cycles of continental and oceanic ecosystems. It is a significant trophic resource in stream food webs (e.g., Hall and Meyer 1998). DOC imparts color to lakes, regulating the amount of ultraviolet radiation reaching lake biota and influencing lake thermal regimes (Schindler and Curtis 1997). Cycling and biotic impact of metals are influenced by DOC concentration; for example, the concentration of methyl mercury in lakes and in lake biota increases with their DOC content (Driscoll et al. 1995). A synthesis of lake research identified colored DOC as a key characteristic of lakes, determining a lake's response to multiple anthropogenic stressors (Williamson et al. 1999). Because DOC regulates so many aspects of aquatic ecosystems, it is important to understand how natural and anthropogenic changes can alter its concentration in lotic ecosystems. DOC transport in streams varies with watershed topography, extent of wetlands, soil type, nature of vegetation, fire history, hydrology, and land use. DOC concentration and transport increase as proportion of the watershed covered by wetlands or peat increases, and as soil carbon (C) content increases (e.g., Aitkenhead et al. 1999). Differences in soils' capacity for C sorption results in differences in stream DOC content (Nelson et al. 1993; see also Quails et al., chapter 5, this volume). DOC export is less in watersheds with lower soil pH (Brooks et al. 1999). Forest type is an important predictor of DOC delivery to Adirondack lakes (Canham et al.