Date of Award

Spring 5-1-2021

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Ocean Science and Engineering

Committee Chair

Wei Wu

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Patrick Biber

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Kevin Dillon

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Robert Leaf

Committee Member 4 School

Ocean Science and Engineering


Changes in climate and atmospheric acidic deposition alter biogeochemical cycles in forested ecosystems. I investigated the responses of vegetation, soil, and hydro-related processes to changes in climate and acidic deposition at five high-elevation forests in the southeastern U.S. using a biogeochemical model - PnET-BGC model. I focused on change-points and thresholds concepts that were less studied in forest ecosystems as well as seasonal variability of responses and extreme events. I applied principal component analysis (PCA) to reduce the dimensionality of data. I developed a Bayesian multi-level model to derive key biogeochemical variables response to temperature and precipitation (local) and latitude and elevation (regional) with uncertainty accounted for. The first principal components (PC1s) explain 50-60% and 40-50% of the variance in the 17 main biogeochemical variables simulated from the model at the Coweeta Basin (CWT) and Shenandoah National Park (SNP) respectively. PC1s at CWT are highly correlated to transpiration, gross and net primary production (GPP and NPP), soil base saturation, soil Al:Ca ratio, and stream chemistry (Ca2+ and K+), while PC1s at SNP are highly correlated to NPP, transpiration, and stream base cations. The key biogeochemical processes show strong seasonality in their response to future climate change. Higher latitudinal sites have earlier but fewer change-points than lower latitudes from 1931 to 2100. Vegetation at higher-elevation forests appears more sensitive to climate change, while soil and streams are more sensitive at the lower-elevation forests. Flooding and drought will become more frequent, and soil and stream will become more acidic under climate change. Regional analysis demonstrates that temperature tends to drive key biogeochemical variables more significantly than precipitation. Winter shows the least sensitivity to climate change in NPP, transpiration, and acid neutralization capacity 3 (ANC) at all five sites. In addition, latitude and elevation influence the sensitivity of these biogeochemical variables to temperature and precipitation at some degree. Change in acidic deposition will likely shift the biogeochemical processes response to climate change differently, depending on biogeochemical processes, season, and the direction and magnitude of change in acidic deposition. The effect is minimal for NPP, and summer and winter will have the largest shifts.