Dynamic biogeochemical watershed models are the only practical approach that can predict concurrent exposure to multiple environmental factors and consider interactive effects between climate change, atmospheric deposition and CO2 fertilization effect. Therefore, they could be powerful tools to help to understand the long-term effects of climate change on ecosystems. In this study, we are using a biogeochemical model (PnET-BGC) coupled with long-term measurements to evaluate the effects of potential future changes in temperature, precipitation, solar radiation and atmospheric CO2 on pools and fluxes of major elements at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. Future emissions scenarios were developed from monthly output from two atmosphere-ocean general circulation models (AOGCMs; HadCM3, PCM) in conjunction with potential lower and upper bounds of projected atmospheric CO2 (550 and 970 ppm by 2099, respectively).
AOGCM results over the 21st century indicate an average increase in temperature ranging from 1.9 to 6.9°C with simultaneous increases in precipitation ranging from 12.5 to 13.9% above the long term mean (1970-1999). Long-term measurements and watershed modeling results show a significant shift in hydrology with earlier spring discharge (snowmelt), greater evapotranspiration and longer growing season (due to CO2 fertilization), and later snowpack development. Model results also show an increase in NO3- leaching over the second half of the century due to increases in net mineralization and nitrification. The extent of this response is dependent on the fertilization effect that increasing atmospheric CO2 has on forest vegetation. The watershed responses of other major elements such as SO42- and Ca2+, and chemical characteristics such as pH and ANC varied based on future climate scenarios. Model projections also suggest marked decreases in soil exchangeable calcium, magnesium and potassium with simultaneous decline in soil base saturation and Ca/Al ratio over the next century.