Patrick Mulholland Oak Ridge National Lab Environ. Sci Lab P.O. Box 2008 Oak Ridge, TN 37831 mulhollandpj@ornl.gov
Amelia K. Ward Center for Freshwater Studies University of Alabama Box 870206 Tuscaloosa, AL 35487
G. Milton Ward Dept. Biological Sciences University of Alabama Box 870206 Tuscaloosa, AL 35487
This NEON Research Design (Observational) addresses the issue of how forested ecosystems will respond to future changes in nitrogen deposition and the interactive effects of N deposition and changes in ozone exposure and climate. It addresses several of the grand challenge issues presented in the NEON ISEP and earlier NEON reports. In particular, it focuses on the response of forested ecosystems to critical air pollutants (N and ozone) which are highly influenced by changes in land use, particularly in the transportation and energy generation sectors, and the interactive effects of air pollutants and climate variability and change. Forests are among the most widespread and socially/economically important ecosystems in the U.S., and N deposition is affecting forests in poorly understood ways. Forests also comprise large portions of the drainages of many rivers discharging to coastal areas experiencing significant problems involving eutrophication and hypoxia. There are important and poorly understood interactive effects of N deposition and climate change (e.g., vegetation shifts, changes in rainfall, increases in winter temperatures that affect dormant season retention) that may alter the response of forest ecosystems to future N deposition.
Forest and stream ecosystem responses to be studied range from ecosystem-scale processes to molecular/genetic measures of microbial processes and diversity. Response variables will include: carbon exchange and ecosystem productivity (forest and stream), soil N cycling and retention, N gas emissions from soil and stream, watershed N retention, forest tree species distributions (canopy and understory), and microbial functional diversity and N cycling enzymes. The Domain toolbox and relocatable platform instrumentation are needed for these measurements. This Design will provide both the regionally distributed data needed for calibration of N biogeochemistry and forest ecosystem response models as well as a better understanding of important mechanisms to more fully parameterize these models.
The primary gradient over which these responses will be studied is N deposition. Observational sites will consist of small forested watersheds (wildland sites) and the streams draining them (1st or 2nd order) across a gradient in N deposition along a transect running in a Southwesterly direction from the Northeastern U.S. (northern New England) to Alabama and to the western portions of Arkansas and Missouri. This transect covers the range of N deposition rates currently impacting deciduous hardwood forests in the eastern U.S. There are 6 nodes along the transect with each node consisting of 2 sites in relatively close proximity (within 100-200 km) and generally similar N deposition rates, but with differences in forest species composition and/or soils/geology that influence their susceptibility to N deposition. The peak in current N deposition is near the center of the transect (Southeastern OH/western PA) and N deposition declines in either direction from this node. Regional differences in population growth and urbanization are expected to result in increases in N deposition along the southern portion of this transect (due to rapid growth in Southeastern U.S.) but remain the same or decrease along the northern end of the transect (Northeastern U.S.).