Print PageClimate observations and indicators in the northeastern United States provide evidence of a warming trend that is consistent with global climate change. These changes include seasonal increases in air temperature and precipitation, which have affected streamflow regimes. Most notably, decreases in snow depth and duration have resulted in an earlier streamwater snowmelt peak and more muted spring freshet. Recent regional changes in climate have also resulted in earlier bloom dates and an extended growing season. The effect of shifting patterns of streamflow and plant nutrient uptake has the potential to alter streamwater nutrient flux, ultimately influencing water quality. The center of stream flow volume, defined as the date which half of the total volume of stream water passes by a stream gage for a given time period, is often used as a hydrological indicator of climate change. We extended this concept to nutrient flux and calculated center-of-mass dates for elements exported in stream water at the Hubbard Brook Experimental Forest in New Hampshire. The objective of this study was to evaluate whether climate-induced shifts in streamflow and phenology have altered the timing of nutrient export over the last 46 years of measurement.
Results/Conclusions
Climatic trends in the Hubbard Brook Valley are similar to regional trends and show significant annual air temperature increases of 0.02 °C per year over the last 50 years of measurement. Despite annual increases in precipitation, the total amount of winter precipitation has not changed significantly, which when combined with warmer winter air temperatures, has led to significant declines in snowpack depth and duration. As a result, snowmelt occurs earlier, which has altered the timing of streamflow, as indicated by a two week advance in the winter/spring center-of-volume date over the last 50 years. These changes in streamflow, combined with temperature-related changes in phenology, have altered the timing of streamwater nutrient export. Shifts in the center-of-mass date for more conservative solutes, such as silicon, tend to mirror shifts in streamflow timing. For biologically reactive solutes, such as nitrate, shifts to earlier center-of-mass dates are even more pronounced. This shift in the timing of nutrient export may have important biotic implications if nutrient availability and use disconnect. Organisms that respond to environmental cues other than climate (e.g. photoperiod) may be affected most because they lack the ability to shift rapidly with changes in climate.
