Why is excess nitrogen important?
Although nitrogen is an essential building block of life, the impacts of excess nitrogen "cascade" through Earth systems. For example, in the atmosphere, nitrogen dioxide contributes to particulate matter and ozone formation, whereas in ecosystems excess nitrate can contribute to forest degradation, soil and stream acidification. When exported to coastal systems, excess nitrogen contributes to algal blooms and hypoxia. Thus, understanding the fluxes of reactive nitrogen (i.e., any form available for biotic uptake) across Earth systems is key to mitigating these deleterious impacts. Our research program focuses on three broad research questions:
How does human activity affect spatial patterns of atmospheric nitrogen emissions and deposition?
Ongoing projects are redefining the use of "isoscapes" to assess sources of atmospherically deposited reactive nitrogen to landscapes, watersheds, regions, and continents. We are characterizing the isotopic composition of reactive nitrogen emissions from multiple land uses and human activities. This work, conducted in agricultural, urban, forested, energy production, and maritime settings, is aimed at filling knowledge gaps required for accurate isoscape interpretation. Reactive nitrogen deposition fluxes and isotopic composition are being examined in gases, particulate matter, precipitation, plant biomonitors, and an ice core to assess similarities in spatial and temporal patterns of emissions and subsequent deposition. Research projects are funded by the U.S. Department of Agriculture (CSREES Air Quality Program), grants from the Electric Power Research Institute (EPRI), and an NSF CAREER award.
How do ecosystems respond to anthropogenic alterations to the nitrogen cycle?
Ongoing projects investigate sources and mechanisms for changing ecosystem nutrient status in forested, near-road, and urban settings. We are examining inter-watershed controls on breakthrough of atmospheric nitrogen and assessing how N saturation status influences atmospheric nitrogen export in streamwater. Additionally, we seek to clarify the role of plant uptake in retention of atmospheric nitrogen. Research projects are funded by NSF (Hydrologic Sciences and Ecosystems Studies Cluster), U.S. Forest Service (Northern Global Change Research Program), and the Maryland Department of Natural Resources (Power Plant Research Program).
How does hydrologic connectivity influence reactive nitrogen delivery to aquatic systems?
Current projects aim to advance our understanding of the fate of non-point sources of reactive nitrogen in aquatic systems. Using triple nitrate isotopes, we are examining factors that control nutrient delivery in human-impacted landscapes and determining how hydrological connectivity is a critical factor for proper assessment of watershed nutrient budgets. Research projects are funded by the Pennsylvania Water Resources Research Institute (WRRI), the University of Pittsburgh, a small grant from the Nine Mile Run Watershed Association, and an NSF CAREER award.