Grantee Research Project Results
2002 Progress Report: Effects of N Deposition on Gaseous N Loss from Temperate Forest Ecosystems
EPA Grant Number: R827674Title: Effects of N Deposition on Gaseous N Loss from Temperate Forest Ecosystems
Investigators: Groffman, Peter M.
Current Investigators: Groffman, Peter M. , Verchot, Louis V. , Potter, Christopher , Adams, Mary Beth , Fernandez, Ivan , Rustad, Lindsey
Institution: Cary Institute of Ecosystem Studies
Current Institution: Cary Institute of Ecosystem Studies , University of Maine , USDA
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1999 through September 30, 2002
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: $894,361
RFA: Regional Scale Analysis and Assessment (1999) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The objectives of this research project are to: (1) determine the importance of gaseous loss of nitrogen (N) from temperate forest ecosystems; (2) determine the impacts of N deposition on gaseous loss of N from these ecosystems; (3) test a mechanistic model that relates N gas emissions to N availability and soil moisture content; and (4) develop a new and more mechanistic version of the daily National Aeronautic and Space Administration-Carnegie Ames Stanford Approach (NASA-CASA) ecosystem model for N gas emissions that can be applied at the regional level using satellite remote sensing and other spatial data sets in a geographic information system (GIS) format. This new simulation model will be used to assess trends in N cycling over gradients of N deposition in the Northeast United States, as well as project changes in N gas fluxes with changing air pollution.
Progress Summary:
While much effort has gone into determining the fate of atmospheric N in temperate forest ecosystems, many uncertainties remain as to exactly where N is stored and what processes and pathways influence N retention and/or loss. One of the largest areas of uncertainty is gaseous loss. This flux may be large and may be very sensitive to N deposition.
To accomplish our objectives, we sampled gas fluxes (NO, N2O) on a monthly basis over two growing seasons (2000 and 2001) at five sites along an N deposition gradient in the Northeast United States: Fernow Experimental Forest (FN), WV; Catskills State Forest (CS), NY; Hubbard Brook Experimental Forest (HB), NH; Harvard Forest (HF), MA and Bear Brook Watershed (BB), ME. Sampling has occurred in both N fertilized and unfertilized plots at four of the five locations. Monthly sampling has been augmented by several additional sampling efforts to characterize short-term responses of fluxes to rainfall, diurnal temperature changes, and fertilization events. We also have made measurements of factors known to control flux rates (e.g., N pool sizes, turnover rates, denitrification rates, soil temperature, soil pH, and soil moisture).
The flux and ancillary controlling factor data are being used to develop a new and more mechanistic version of the daily NASA-CASA ecosystem model that can be applied across a 10 state region (ME, NH, VT, MA, RI, CT, NY, NJ, PA, WV). This new simulation model will be used to assess trends in N cycling over gradients of N deposition in the Northeast United States and to project changes in N gas fluxes with changing air pollution. We have made monthly measurements of in situ NO and N2O flux at all our sites over two growing seasons using chamber techniques. Chambers consisting of polyvinyl chloride (PVC) ring (20-cm diameter x 10-cm height) and vented PVC covers were placed into the soil to a depth of 2-3 cm in early summer 2000 and have been left in place.
Surface fluxes of NO are being measured using a dynamic chamber technique (Davidson, et al., 1991). At the time of measurement, covers are placed over the base, making a closed chamber. The chambers are then connected to a Unisearch NO2 analyzer with Teflon tubes and air is circulated between the instrument and the chamber. Inside the instrument, NO is oxidized to NO2 by reaction with CrO3. Fluxes are calculated from the rate of increase of NO concentration within the chamber.
Surface fluxes of N2O are measured using a static chamber technique (Davidson, et al., 1993), using the same PVC rings used for the NO measurements. Chamber headspace is sampled through a rubber septum at 10-minute intervals for 30 minutes using nylon syringes. Samples are placed in evacuated vials and returned to the laboratory for N2O analysis by gas chromatography. N2O fluxes are calculated from the rate of increase of N2O concentration within the chamber.
We also have made limited measurements of N2 fluxes using a new soil core recirculation developed with U.S. Department of Agriculture-National Research Initiative Competitive Grants Program (USDA-NRICGP) funding. This system is based on two gas chromatographs equipped with electron capture and thermal conductivity detectors allowing for simultaneous analysis of N2, NO2, and CO2. As a result of sensitivity problems, monthly measurements were not made as planned during 2000 and 2001. We made refinements to this system during the winter of 2001-2002, and have been obtaining flux measurements from two of our sites (Hubbard Brook, Catskills) since the summer of 2002.
The flux measurements have revealed some interesting findings. Perhaps most novel is the observation that NO fluxes are significant in northeastern forests, and much higher than N2O fluxes, which are frequently the only gas measured. Data from the Harvard Forest site, where two temperate forest stands since 1988, with different levels of N to simulate elevated rates of atmospheric N deposition, illustrate these results quite well. Plots within a red pine stand treated with either low (50 kg N ha-1 y-1) or high (150 kg N ha-1y-1) levels of N displayed consistently elevated NO fluxes (100 - 200 µg N m-2h-1), while only the high-N treatment plot within a mixed hardwood stand displayed similarly elevated NO fluxes (see Figures 1 and 2). Nitrous oxide fluxes in the N-treated plots were generally less than 10 percent of NO fluxes. Net nitrification rates and NO production rates measured in mineral and organic soils in the laboratory displayed patterns that were consistent with field NO fluxes. Treatment of soils with acetylene resulted in inhibition of both nitrification and NO production, indicating that autotrophic nitrification was responsible for the elevated NO production. Soil pH was negatively correlated with annual rates of N deposition. Low levels (3-12 ng N kg-1) of nitrite (NO2-) were detected in mineral soils from both sites. Kinetic models describing NO production as a function of the protonated form of NO2- (nitrous acid [HNO2]), adequately described the mineral soil data. Rates of NO consumption were lower in the Hardwood high-N treatment plots compared to the low-N and control plots. The results indicate that atmospheric deposition may generate losses of gaseous NO from forest soils by promoting rapid nitrification, and that the response may significantly vary between forest types. The lowering of soil pH resulting from nitrification and/or directly from atmospheric deposition also may play a role by promoting abiotic reactions involving HNO2.
Figure 1. Fluxes of (a) NO and (b) N2O during June 2000, through November 2001. Values are the means of three measurements in the control, low-N, and high-N treatment plots at approximately monthly intervals. Symbols indicate if the low-N (#) or high-N (*) plot values significantly are different from the control at any time based on Analysis of Variance with least significant differences multiple range test: # or *, p less than 0.05; ## or **, p less than 0.01.
Figure 2. Total estimated emissions of (a) NO and (b) N2O during June 2000, through November 2001, versus annual N deposition rates in Hardwood and Pine forest plots.
Other field flux data were collected to facilitate our modeling efforts. Special campaigns were carried out to evaluate the effects of fertilization (see Figure 3) and rainfall (see Figure 4) events on flux.
Figure 3. Response of NO flux to NH4NO3 applied on May 29, 2001 in (a) Hardwood and (b) Pine plots.
Figure 4. Response of (a) NO flux and (b) N2O flux to 25-mm of water added on August 17, 2001, and October 27, 2001. Symbols indicate if post-wetting fluxes significantly are different from prewetting fluxes, * p less than 0.05; ** p less than 0.01; and*** p less than 0.001.
Modeling and Extrapolation
Gas fluxes are notoriously variable in time and space. This variability greatly complicates our ability to produce estimates of ecosystem scale annual flux that can be compared with annual N inputs or hydrologic outputs (Groffman, et al., 2000). While many studies produce such estimates by extrapolating point measurements to larger areas and time scales, we will use mechanistic models to produce more refined extrapolations. These models will be developed from the field flux data discussed above, and ancillary data on gross and net N mineralization and nitrification rates. We will use the hole-in-the-pipe (HIP) model as the basis for our mechanistic modeling. The HIP model depicts N gas fluxes as a product of gross N fluxes through the soil microbial community, with variable amounts of different gases being emitted as a function of soil environmental conditions (moisture, pH). We are adapting and modifying the HIP model using new approaches developed by Venterea, et al. (2000) that more accurately depict the links between nitrification, chemical transformations of nitrite, and NO emission.
We will link our mechanistic model with the NASA-CASA model, which is an aggregated representation of major ecosystem carbon and N transformations (including gas fluxes) that can be run at regional scales when driven by a set of gridded coverages at 1 km spatial resolution. The N gas emission components of the NASA-CASA model have been reevaluated in the context of our field measurements. Revisions are underway in the CASA framework, based in part on recent validation/comparison studies (Davidson, et al., 2000; Parton, et al., 2001). The modeling will proceed more rapidly toward regional extrapolation results now that we have two field seasons of measurements to use as calibration checks on flux algorithms.
The following regional driver data sets have been obtained and processed into the NASA Ames:
· Nitrogen Deposition Isopleth Maps, continental United States, 1994-1999 (Source: National Atmospheric Deposition Program, Illinois State Water Survey).
· Daily Climate Drivers, averaged 1961-1990 to include air temperature, precipitation, relative humidity, vapor pressure, and surface irradiance regridded to 8 km resolution for the continental United States. (Source: VEMAP U.S. data CD; Kittel, et al. Journal of Biogeography 1995;22:857-862).
· Monthly Satellite Advanced Very High Resolution Radiometer (AVHRR) leaf area index (LAI) and fraction of photosynthetically active radiation (FPAR) Source: EOS MODIS Team, Boston University 8 km resolution for the continental United States, 1982-1998.
· Land Cover Type, 1 km and 8 km Land Cover Classification for the continental United States, mid-1990s. (Source: University of Maryland, DeFries, et al. International Journal of Remote Sensing 1998;19:3141-3168).
Several new model algorithms are in the implementation and evaluation stage for improved simulations of NO and N2O emissions from Northeast United States forest soils. The NASA-CASA model will generate predicted nitrification rates in forest soils, which can be used in turn to predict NO and N2O emission fluxes from soil surfaces as a function of simulated soil water content, temperature, pH, bulk density, and texture. Field measurements of these parameters at the five Northeast United States experimental sites will be used to make model calibration checks of the trace gas algorithms.
Because results from field measurements at Northeast United States forest sites indicate that tree species composition plays an important role in controlling soil N mineralization rates and trace gas emissions, we are evaluating several potential sources for regional representation of forest species coverage. For example, the U.S. Environmental Protection Agency (EPA) has produced new vegetation maps at 1 km for the entire United States as part of their Biogenic Emissions Inventory System (BEIS), including all major Northeast United States forest species. We are in the process of evaluating this EPA map product for integration with our other GIS map layers for the 10 Northeast states in the United States. We plan to couple this forest cover map with a new species-level data set for leaf nitrogen content, which we also have generated in the past year from 7 months of literature-based research.
Because results from field measurements at Northeast United States forest sites indicate that soil properties play an important role in controlling soil N mineralization rates and trace gas emission model input parameters. The 1 km State Soil Geographic (STATSGO) soil data attributes that we will evaluate and use in our regional N gas modeling include soil texture class, sand-silt-clay fractions, porosity, depth to bedrock, bulk density, and soil pH.
References:
Davidson EA, Vitousek PM, Matson PM, Riley R, Garciá-Méndez G.
Soil emissions of nitric oxide in a seasonally dry tropical forest of México.
Journal of Geophysical Research 1991;96(15):439-445.
Davidson EA, Matson PM, Vitousek PM, Riley R, Dunkin K, Garciá-Méndez G. Processes regulating soil emissions of NO and N2O in a seasonally dry tropical forest. Ecology 1993;74(1):130-139.
Davidson EA, Keller M, Erickson HE, Verchot LV, Veldkamp E. Testing a conceptual model of soil emissions of nitrous an nitric oxides. Bioscience 2000;50(8):667-680.
Groffman PM, Brumme R, Butterbach-Bahl K, Dobbie KE, Mosier AR, Ojima D, Papen H, Parton WJ, Smith, KA, Wagner-Riddle C. Evaluating annual nitrous oxide fluxes at the ecosystem scale. Global Biogeochemcial Cycles 2000;14(4):1061-1070.
Parton WJ, Holland EA, Del Grosso SJ, Hartman MD, Martin RE, Mosier AR, Ojima DS, Schimel DS. Generalized model for NOx and N2O emissions from soils. Journal of Geophysical Research 2001;106(D15):17403-17420.
Venterea RT, Rolston DE. Mechanistic modeling of nitrite accumulation and nitrogen oxide gas emissions during nitrification. Journal of Environmental Quality 2000;29(6):1741-1750.
Venterea RT, Groffman PM, Verchot LV, Magill AH, Aber JD, Steudler PA. Nitrogen oxide gas emissions form temperate forest soils receiving long-term nitrogen inputs. Global Change Biology (submitted, 2002).
Future Activities:
In the next year, we will complete our N2 flux measurements, finalize our mechanistic models, and begin regional extrapolation work.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 15 publications | 5 publications in selected types | All 4 journal articles |
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Venterea RT, Lovett GM, Groffman PM, Schwarz PA. Landscape patterns of net nitrification in a northern hardwood-conifer forest. Soil Science Society of America Journal 2003;67(2):527-539. |
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Supplemental Keywords:
scaling, regional analysis, landscape analysis, nitrous oxide, nitrification, microbial., RFA, Scientific Discipline, Air, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Environmental Chemistry, climate change, VOCs, Fate & Transport, Ecological Effects - Environmental Exposure & Risk, Forestry, Regional/Scaling, fate and transport, ecological exposure, nitrogen deposition, N deposition, forest ecosystems, forest inventory and analysis, modeling, biogeochemical, air pollution, regional scale impacts, sulfur compounds, atmospheric pollutant loads, GIS, nitrogen compounds, air quality, atmospheric models, nitrogen, acid rain, scaling methodsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.