I. Nitrogen Deposition within Temperate, Northern Forests
During my PhD, I examined the role of land use on the sources and processing of nitrogen through temperate watersheds by examining the variability of the dual isotopic composition of stream nitrate draining catchments dominated by a singular land use: forested, suburban, and agriculture.
The climate of northern CT and southern MA (i.e. my field sites) means that these landscapes do not experience a seasonal snowpack – rather there are often multiple snow melt event throughout the winter and spring. Examining the seasonal variation in hydrology and the isotopic composition of nitrate illustrated the importance of shifting flow paths – i.e. shallow, presumably shorter flow paths dominate in the winter while deeper, longer flow paths dominate streamflow contributions in the summer, leading to the differences in nitrogen retention within these forested ecosystems.
- Barnes, R. T., P.A. Raymond, K.L. Casciotti. 2008. Dual isotope analyses indicate efficient processing of atmospheric nitrate by forested watersheds in the northeastern U.S. Biogeochemistry, DOI: 10.1007/s10533-008-9227-2
Stephen Sebestyen recently led an effort to compile nitrate isotope data from Northern forest catchments. This data synthesis effort (so valuable) provides insight on transport of unprocessed atmospheric nitrate in catchments that is more generalizable. For example, only three of 85 streams had high fractions (>20%) of unprocessed atmospheric nitrate during baseflow; 25 of those 85 streams had high fractions during stormflow. Overall, the database helps us to identify the regional extent and variability of fractions of unprocessed atmospheric nitrate in waters of the Northern Forest. In the absence of monitoring for nitrate isotopes in sustained catchment monitoring programs, this information is critical to defining the size and trend of chronic nitrogen pollution effects as well as the efficacy of regulatory and management schemes intended to reduce pollution effects on forests and streams. See abstract of Fall 2018 AGU presentation.
II. Nitrogen Deposition within a Montane Environment
We examined how nitrogen and water moves through montane hill-slope soils and the role of aspect in controlling these flowpaths and processes. Snowmelt and rainfall experiments were recently conducted using labeled nitrogen (δ15N) and LiBr tracers to observe the timing and size of nitrogen and water fluxes through north and south facing slopes. Preliminary results suggest that while during snowmelt source dynamics seem to be the most important determinant the movement of nitrate and water during the rainfall experiment was controlled by soil properties, e.g. texture.
Collaborators: Eve-Lyn Hinckley, Suzanne Anderson, Bob Anderson, & Mark Williams (Univ of Colorado, Institute of Arctic & Alpine Research), Brian Ebel (CO School of Mines), Sheila Murphy (USGS). This work is occurring in conjunction with the Boulder Creek Critical Zone Observatory and was funded by a NSF EAR Postdoctoral Fellowship to Dr. Hinckley.
- Hinckley, E.S., B.A. Ebel, R.T. Barnes, R.S. Anderson, M.W. Williams, & S.P. Anderson. 2012. Aspect Control of Water Movement on Hillslopes Near the Rain-Snow Transition of the Colorado Front Range, U.S. Hydrological Processes, doi:10.1002/hyp.9549
- Hinckley, E.S, R.T. Barnes, S.P. Anderson, M.W. Williams, & S.M. Bernasconi. 2014. Nitrogen retention and transport differ by hillslope aspect at the rain-snow transition of the Colorado Front Range, JGR-Biogeochemistry, DOI: 10.1002/2013JG002588
- Hinckley, E.S., B.A. Ebel, R.T. Barnes,S.F. Murphy & S.P. Anderson. 2017. Critical zone properties control the fate of nitrogen during experimental rainfall in montane forests of the Colorado Front Range. Biogeochemistry, DOI: 10.1007/s10533-017-0299-8