Grantee Research Project Results
2003 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, 2002 through September 30, 2003
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 Aeronautics 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, and to project changes in N gas fluxes with changing air pollution.
Progress Summary:
Although much effort has gone into determining the fate of atmospheric N in temperate forest ecosystems, many uncertainties remain as to 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 (nitric oxide [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 (FEF), WV; Catskills State Forest (CS), NY; Hubbard Brook Experimental Forest (HB), NH; Harvard Forest (HF), MA; and Bear Brook Watershed (BB), ME. Sampling took place in both N fertilized and unfertilized plots at four of the five locations. Monthly sampling was augmented by several additional sampling efforts to characterize short-term responses of fluxes to rainfall, diurnal temperature changes, and fertilization events. We also took measurements of factors known to control flux rates (e.g., N pool sizes and 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 for N gas emissions that can be applied across a 10-state region (ME, NH, VT, MA, RI, CT, NY, NJ, PA, WV) using satellite remote sensing and other spatial data sets in a GIS format. This new simulation model is being 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 made monthly measurements of in situ NO and N2O flux at all of our sites over two growing seasons using chamber techniques. Chambers consisting of polyvinyl chloride (PVC) rings (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 were measured using a dynamic chamber technique (Davidson, et al., 1991). At the time of measurement, covers were placed over the base, creating a closed chamber. The chambers then were connected to a Unisearch NO2 analyzer with Teflon tubes and air was circulated between the instrument and the chamber. Inside the instrument, NO was oxidized to NO2 by reaction with CrO3. Fluxes were calculated from the rate of increase of NO concentration within the chamber.
Surface fluxes of N2O were measured using a static chamber technique (Davidson, et al., 1993), using the same PVC rings that were used for the NO measurements. Chamber headspace was sampled through a rubber septum at 10-minute intervals for 30 minutes using nylon syringes. Samples were placed in evacuated vials and returned to the laboratory for N2O analysis by gas chromatography. N2O fluxes were calculated from the rate of increase of N2O concentration within the chamber.
We also took limited measurements of N2 fluxes using a new soil core recirculation that we have developed with U.S. Department of Agriculture (USDA)-National Research Initiative Competitive Grants Program funding. This system is based around two gas chromatographs equipped with electron capture and thermal conductivity detectors allowing for simultaneous analysis of N2, N2O, and CO2.
The flux measurements to date have revealed some interesting and novel findings. Perhaps most novel is the observation that NO fluxes are significant in northeastern forests, and much higher than N2O fluxes, which is frequently the only gas measured. Data from the HF site, where two temperate forest stands have been fertilized since 1988 with different levels of N to simulate elevated rates of atmospheric N deposition, illustrate these results quite well (see Figure 1, Venterea, et al., 2003). Plots within a red pine stand, which were treated with either low (50 kg N ha-1 y-1) or high (150 kg N ha-1 y-1) levels of N displayed elevated NO fluxes (100-200 µg N m-2 h-1), while only the high-N treatment plot within a mixed hardwood stand displayed elevated NO fluxes. Nitrous oxide fluxes in the N-treated plots generally were less than 10 percent of NO fluxes. The estimated total NO emissions were similar in the Hardwood and Pine high-N plots, representing 3.0 percent and 3.7 percent, respectively, of total N inputs to the high-N plots during June 2000–November 2001. The integrated NO mass flux from the Pine low-N addition plot represented the greatest proportion (8.3 percent) of total N inputs. Estimated emissions of NO from the Hardwood and Pine control plots represented 1.3 and 2.3 percent, respectively, of total inputs. Total N2O emissions were less than 5 percent of total NO emissions and less than 0.3 percent of total N inputs in all plots. Soil NO fluxes were of the same order of magnitude as the other major N loss mechanism in these plots (i.e., NO3- leaching below the root zone). Typical summertime NO fluxes (100-200 µg N m-2 h-1) were equivalent to 15-45 percent of annual NO3- leaching losses in the high-N plots, and were more than 100 percent of NO3- losses in the Pine low-N plots estimated for 1996 (Magill, et al., 2000).
Figure 1. 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 (Venterea, et al., submitted)
Ancillary measurements of soil N transformations produced several interesting findings related to the mechanisms of N gas production and N saturation in HF Soils (Venterea, et al., submitted). Gross NO production rates increased in a manner that was consistent with nitrification rate increases, and represented 5-16 percent of nitrification rate in organic soils exhibiting symptoms of N saturation. Laboratory NO consumption rates were equivalent to half-lives less than 20 seconds, and estimates of field subsurface NO production indicated that greater than or equal to 96 percent of the NO produced was consumed prior to being emitted at the soil surface. Diffusion-reaction model simulations were consistent with laboratory and field results in suggesting that NO production combined with rapid transformation may have contributed up to 25 percent of total gross NO3- production. Model simulations also suggested that gaseous NO diffusion will influence the proportion of NO that is converted to NO3- and the transport of NO3- through the soil profile.
Measurements at other sites along our regional N deposition gradient confirm the results observed at HF. In high- and low-elevation plots at the FEF, and in hardwood- and softwood-dominated plots at BB, NO emissions in N-amended watersheds were higher than emissions in the respective reference watersheds (see Figure 2). Peak emission rates ranged from approximately 1 µg NO-N m-2 h-1 in the softwood plots at BB to 100 µg NO-N m-2 h-1 in the high- and low-elevation plots at FEF, compared to less than 0.1 - 20 µg NO-N m-2 h-1 in the control watersheds. Laboratory measurements indicated that nitrification was the dominant source of NO production in soils from both forests. These results from two different ecosystems provide additional evidence that elevated soil NO emissions are a characteristic response in forests subjected to persistent N inputs.
Figure 2. NO Fluxes in Control and N-Amended Plots at: (a) FEF, and (b) BB (mean ± standard error, n = 2). Bars with different letter designations are significantly different based on least significant difference (LSD) comparisons of N-amended versus unamended soils within each site and elevation or species with confidence level indicated as follows: * = P < 0.10; ** = P < 0.05; *** = P < 0.01. May 2001 data from FEF high-elevation plots and August 2000 data from BB softwood control plots were not obtained.
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, in press). Although many studies produce such estimates by extrapolating point measurements to larger areas and time scales, we are using mechanistic models to produce more refined extrapolations. These models are being developed from the field flux, ancillary gross, net N mineralization, and nitrification rate data discussed above.
We are using 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 (see Figures 2 and 3).
Figure 3. Conceptual Diagram Showing How Atmospheric Deposition Leads to Increased Soil:Atmosphere NO Flux in Two Ways: (1) by Adding N That Increases Nitrification Rates and Nitrite Production; and (2) by Increasing Soil Acidity, Which Stimulates Chemical Decomposition of Nitrite to NO
We will link our mechanistic model with the NASA-CASA model, which is an aggregated representation of major ecosystem C 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 (see Figure 4). 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 is rapidly proceeding toward regional extrapolation results, now that we have two field seasons of measurements to use as calibration checks on flux algorithms.
Figure 4. The NASA-CASA Ecosystem Carbon and Nitrogen Process Model Showing How Landscape and Regional Scale Data Can be Used to Drive N Gas Flux Models
The following regional driver data sets have been obtained and processed into the NASA Ames GIS:
· 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 (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 northeastern 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 experimental sites will be used to make model calibration checks of the trace gas algorithms.
Because results from field measurements at northeastern 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, including all major northeastern forest species. We are in the process of evaluating this U.S. EPA map product for integration with our other GIS map layers for the 10 northeastern states. We plan to couple this forest cover map with a new species-level data set for leaf N content, which we also have generated in the past year from several months of literature-based research.
Because results from field measurements at our forest sites indicate that soil properties play an important role in controlling soil N mineralization rates and trace gas emissions, we are evaluating the USDA national STATSGO map, also called the NATSGO product, for updated model input parameters. The 1-km STATSGO 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. Geophysical Research 1991;96:15439-15445.
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;74:130-139.
Venterea RT, Groffman PM, Verchot LV, Magill AH, Aber JD, Steudler PA. Nitrogen oxide gas emissions from temperate forest soils receiving long-term nitrogen inputs. Global Change Biology 2003;9:346-357.
Magill A, Aber J, Berntson G, McDowell W, Nadelhoffer K, Melillo J, Steudler P. Long-term nitrogen additions and nitrogen saturation in two temperate forests. Ecosystems 2000;3:238-253.
Venterea RT, Rolston DE. Mechanistic modeling of nitrite accumulation and nitrogen oxide gas emissions during nitrification. Journal of Environmental Quality 2000;29:1741-1751.
Davidson EA, Keller M, Erickson HE, Verchot LV, Veldkamp E. Testing a conceptual model of soil emissions of nitrous and nitric oxides. BioScience 2000;50:667-680.
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–Atmospheres 2001;106(D15):17403-17419.
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 Biogeochemical Cycles 2000;14:1061-1070.
Future Activities:
The final months of work will focus on modeling and extrapolation- producing landscape- and regional-scale estimates of flux, and on preparing papers for publication.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 15 publications | 5 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Venterea R, Lovett G, Groffman P. Landscape patterns of nitrification and nitrous oxide production in a northern hardwood forest. Agronomy 2001. |
R827674 (2003) |
not available |
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Venterea RT, Groffman PM, Verchot LV, Magill AH, Aber JD. Gross nitrogen process rates in temperate forest soils exhibiting symptoms of nitrogen saturation. Forest Ecology and Management 2004;196(1):129-142. |
R827674 (2003) R827674 (Final) |
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Supplemental Keywords:
scaling, regional analysis, landscape analysis, nitrogen, N, nitrous oxide, nitrification, microbial, N deposition, acid rain, nitrogen oxides, N cycle, environmental, biogeochemistry, ecology, modeling, Northeast., 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 methodsRelevant Websites:
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http://www.hubbardbrook.org Exit
Progress 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.