Responses of stream nitrate and DOC loadings to hydrological forcing and climate change in an upland forest of the northeastern United States

Abstract

[1] In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070-2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (À2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.

Event controlled DOC export from forested watersheds

“…7). Similarly to a recent study conducted within a Vermont watershed (Sebestyen et al 2009), we could have expressed this as a seasonal relationship. Researchers have also found a relationship between 60 day antecedent air temperature and DOC concentration for a watershed in Norway (Futter and de Wit 2006), and the number of growing degree days and DOC export from watersheds in Canada (Creed et al 2008).…”

“…9, a one degree increase in water temperature during an event will increase DOC fluxes by 5.5%. Despite grouping a large number of watersheds across a range of latitude and longitude, an r 2 of 0.92 for event fluxes approximates r 2 values for multiple regressions of DOC export from the Sleepers watershed in Vermont (Sebestyen et al 2009, r 2 = 0.91) and a study of 33 catchments in Canada (r 2 = 0.89), where the percentage of wetlands coverage the explained variance (Creed et al 2008). Thus, although it ''is impossible to predict the entire pattern of solutes during storms with satisfactory precision'' in even a single watershed (Butturini et al 2008), it appears that the response of DOC export to hydrologic events across a range of forest types and climate is controlled by similar processes.…”

“…The general conclusion that the DOC-export response to climate change will depend on interactions between multiple processes that operate on different time scales is supported by two recent studies. Sebestyen et al (2009) focused on hydrologic controls of DOC export from a forested watershed in Vermont and predicted that changes in precipitation patterns associated with projected climate change would lead to an increase in DOC export. A second study, which emphasized processes that control DOC pool size and involved application of a terrestrial ecosystem model to a watershed in nearby New Hampshire, concluded that decreases in litterfall and soil OC mineralization would lead to lower DOC export under future climate (Campbell et al 2009).…”

Regulation of stream water dissolved organic carbon (DOC) concentrations during snowmelt; the role of discharge, winter climate and memory effects

“…Ågren (anneli.agren@seksko.slu.se) climate has been predicted to result in an increase in stream DOC concentrations in many regions (De Wit and Wright, 2008;Köhler et al, 2009;Sebestyen et al, 2009). Much less is known about the snowmelt period, which is the most important hydrological period of the year in many seasonally snow covered regions.…”

Connecting silvan and lacustrine ecosystems: transport of carbon from forests to adjacent water bodies

“…The largest DOC loads are, however, connected with extremely high rain events in the summer (Boyer et al 1997), when abundant fresh DOC is available. More rapid decomposition due to higher temperatures transforming plant litter to more easily dissolving compounds together with abundant rains can increase DOC transport from soils to adjacent water bodies (Köhler et al 2009, Sebestyen et al 2009). …”