Long-term biogeochemical study plots (presentation)

Peter M. Groffman
Institute of Ecosystem Studies
Box AB, Millbrook, NY 12545
Phone:(845) 677-5343
FAX: (845) 677-5976
E-mail: groffmanp@ecostudies.org

Richard V. Pouyat
U.S. Forest Service
Room #134, Technology Research Center Building, 5200 Westland Boulevard
University of Maryland, Baltimore County
Baltimore, MD. 21227
Phone: (410) 455-8014
Fax: (410) 455-6500
E-mail: rpouyat@aol.com

Alan Lorefice
Institute of Ecosystem Studies
Box AB, Millbrook, NY 12545
Phone:(845) 677-5343
FAX: (845) 677-5976
E-mail: loreficea@ecostudies.org

Over the last two years, the Baltimore Ecosystem Study (BES) has established a network of long-term permanent biogeochemical study plots. These plots will provide long-term data on vegetation, soil and hydrologic processes in the key ecosystem types within the urban ecosystem. Plots are currently instrumented with lysimeters (drainage and tension) to sample soil solution chemistry, time domain reflectometry probes to measure soil moisture and trace gas flux chambers to measure the flux of carbon dioxide, nitrous oxide and methane from soil to the atmosphere. Measurements of in situ nitrogen mineralization, nitrification and denitrification are made at approximately monthly intervals. Detailed vegetation characterization (all layers) was done in summer 1998.

The current network of study plots includes eight forest plots, chosen to represent the range of forest conditions in the area, and 2 grass plots. The network is being expanded to include more grass plots, urban yards and wetlands.

Here we present preliminary data on nitrogen cycling from the forest plots. Nitrogen mineralization (Figure 1) did not vary among the forest plots, however, nitrification (Figure 2) was markedly higher in the urban than rural plots. These results are consistent with urban-rural contrasts observed in the New York City metropolitan area and raise important questions that we will follow up in future research: Are these patterns caused by differences in soil type, earthworms, N deposition or land use history? These data show the nature and extent of variability within the most natural ecosystem type in the BES area. They will be very useful for comparison with the more heavily human-dominated ecosystems that we are also studying.

Figure 1. Nitrogen mineralization in two urban and two rural forest sites in the Baltimore metropolitan area. There are two plots in urban Leakin and Hillsdale parks and two upland plots (OR-UP) and two mid-slope (OR-MID) plots in rural Oregon Ridge Park. Values are means (with standard error) of all plots over four sampling dates in December 1998 and March, May and June 1999. Mineralization was measured using an in situ intact core method.

Figure 2. Net nitrification in two urban and two rural forest sites in the Baltimore metropolitan area. There are two plots in urban Leakin and Hillsdale parks and two upland plots (OR-UP) and two mid-slope (OR-MID) plots in rural Oregon Ridge Park. Values are means (with standard error) of all plots over four sampling dates in December 1998 and March, May and June 1999. Nitrification was measured using an in situ intact core method.