Forest Nitrogen Retention in the Chesapeake Bay Watershed: A Role in Water Quality Restoration?

EPA Grant Number: FP917499
Title: Forest Nitrogen Retention in the Chesapeake Bay Watershed: A Role in Water Quality Restoration?
Investigators: Sabo, Robert Daniel
Institution: University of Maryland - College Park
EPA Project Officer: Lee, Sonja
Project Period: August 29, 2012 through August 28, 2015
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2012) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental


What are the main sources of nitrate in streams from forested watersheds? Can a previously declared N-saturated forest respond rapidly to declining N-inputs from wet deposition? Has N-scarcity become more predominant in forests even in the face of chronic atmospheric deposition? How do soil processes, specifically nitrification and mineralization rates, respond to declining wet deposition?


There are two main components to this study: an intensive watershed study and a regional observational network of N-dynamics within forests. The watershed study will measure N processing efficiency based on dual isotopic analysis of 18O and 15N of nitrate in surface water discharge. The research will be conducted in a reported N-saturated watershed to assess declining atmospheric N deposition and possible climate change. Weekly to bi-weekly grab samples will be obtained along with a storm characterization by an ISCO auto-sampler. Along with the dual isotopic analysis, samples will be subjected to traditional water quality analyses (nitrate, ammonium, ANC, closed pH and so forth). The regional observation network will conduct monthly stream water quality monitoring programs, along with the deployment of buried bags to assess nitrification and mineralization rates in forested catchments throughout the Chesapeake Bay Watershed. This regional network will be coordinated through the Ecological Research as Education Network (EREN). N-scarcity also will be assessed through isotopic analysis of 15N in tree rings; EREN schools and the Appalachian Laboratory will collect cores and assess if N-availability of forests have decreased over time.

Expected Results:

This research also will explore how the shifting N deposition patterns affect maturing Central Appalachian forests in the context of N saturation hypothesis and the progressive N limitation hypothesis. It is expected to find a large atmospheric nitrate component in streamwater from forested catchments. The proportion of atmospheric nitrate should decline as wet deposition of anthropogenic nitrate decreases. A previously N-saturated catchment, TNEF, will demonstrate a rapid response in N-export to declining N deposition. The absolute magnitude of nitrification and mineralization should decrease due to declining N-availability and should correspond with a nitrate deposition gradient. Overall, N-scarcity should become more predominant as forests recover and redevelop even in the face of decades of chronic deposition of nitrate. Increased NPP and CO2 enhancement is not suspected to play as large of a role in the declining nitrate export trends observed in forested catchments in the Chesapeake Bay Watershed.

Potential to Further Environmental/Human Health Protection
EPA’s and the Chesapeake Bay Program’s responsibilities in this initiative must be rooted in empirical data from a multifaceted study that provides information from small, intensive watershed studies to broad geospatial and temporal-scaled studies that adequately assess forest responses to climate change and shifting meteorological inputs. This study aims to assess the unexpected and indirect benefits of clean air legislation. Atmospheric N accounts for 25 to 80 percent of the N load entering the Bay today. Forests have decreased their nitrate exports during the past decade, coinciding with the Clean Air Act Amendments of 1990. This decline not only makes forested streams less likely to suffer from acidification episodes but also allows them to provide higher quality water further downstream. This may aid EPA and Mid-Atlantic States greatly in restoring the eutrophic Chesapeake Bay. Ultimately, local municipalities must incorporate proper accounting of N-export from their forests to make cost-effective decisions that support public health and environmental integrity. Nutrient reductions are key for the Bay, which currently suffers from periodic harmful algal blooms and deadzones. These phenomena endanger residents and visitors to the Bay’s shores and expose seafood consumers to unacceptable risks. In conclusion, proper understanding of N-dynamics within forests will allow proper predictions of forests’ response to shifting meteorological inputs of N and climate change.

Supplemental Keywords:

nitrate, forested watersheds, atmospheric deposition

Progress and Final Reports:

  • 2013
  • 2014
  • Final