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Title: Simulating microbial denitrification with EPIC: Model description and evaluation

Here, microbial denitrification occurs in anaerobic soil microsites and aquatic environments leading to production of N 2O and N 2 gases, which eventually escape to the atmosphere. Atmospheric concentrations of N 2O have been on the rise since the beginning of the industrial revolution due to large-scale manipulations of the N cycle in managed ecosystems, especially the use of synthetic nitrogenous fertilizer. Here we document and test a microbial denitrification model identified as IMWJ and implemented as a submodel in the EPIC terrestrial ecosystem model. The IMWJ model is resolved on an hourly time step using the concept that C oxidation releases electrons that drive a demand for electron acceptors such as O 2 and oxides of N (NO 3 -, NO 2 -, and N 2O). A spherical diffusion approach is used to describe O 2 transport to microbial surfaces while a cylindrical diffusion method is employed to depict O 2 transport to root surfaces. Oxygen uptake by microbes and roots is described with Michaelis-Menten kinetic equations. If insufficient O 2 is present to accept all electrons generated, the deficit for electron acceptors may be met by oxides of nitrogen, if available. The movement of O 2, CO 2more » and N 2O through the soil profile is modeled using the gas transport equation solved on hourly or sub-hourly time steps. Bubbling equations also move N 2O and N 2 through the liquid phase to the soil surface under highly anaerobic conditions. We used results from a 2-yr field experiment conducted in 2007 and 2008 at a field site in southwest Michigan to test the ability of EPIC, with the IMWJ option, to capture the non-linear response of N 2O fluxes as a function of increasing rates of N application to maize. Nitrous oxide flux, soil inorganic N, and ancillary data from 2007 were used for EPIC calibration while 2008 data were used for independent model validation. Overall, EPIC reproduced well the timing and magnitude of N 2O fluxes and NO 3 - mass in surficial soil layers after N fertilization. Although similar in magnitude, daily and cumulative simulated N 2O fluxes followed a linear trend instead of the observed exponential trend. Further model testing of EPIC+IMWJ, alone or in ensembles with other models, using data from comprehensive experiments will be essential to discover areas of model improvement and increase the accuracy of N 2O predictions under a wide range of environmental conditions.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [6] ;  [5] ;  [7] ;  [7]
  1. Univ. of Maryland, College Park, MD (United States); Texas A & M Univ., College Station, TX (United States)
  2. Univ. of Northern British Columbia, BC (Canada)
  3. Texas A & M Univ., College Station, TX (United States)
  4. Univ. of Maryland, College Park, MD (United States)
  5. Pacific Northwest National Lab./Univ. of Maryland, College Park, MD (United States)
  6. Univ. of Natural Resources and Applied Life Sciences, Vienna (Austria)
  7. Michigan State Univ., East Lansing, MI (United States); Michigan State Univ., Hickory Corners, MI (United States)
Publication Date:
Report Number(s):
PNNL-SA-126008
Journal ID: ISSN 0304-3800; KP1601050
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Ecological Modelling
Additional Journal Information:
Journal Volume: 359; Journal Issue: C; Journal ID: ISSN 0304-3800
Publisher:
Elsevier
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; microbial respiration; nitrous oxide; gas transport equation; fertilizer nitrogen; Michaelis-Menten kinetics; Environmental Policy Integrated Climate
OSTI Identifier:
1393740