HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Weeks, E. P. Articles by McMahon, P. B. Search for Related Content PubMed Articles by Weeks, E. P. Articles by McMahon, P. B. GeoRef GeoRef Citation Agricola Articles by Weeks, E. P. Articles by McMahon, P. B. Related Collections Field-Scale Studies Landscape-Atmosphere Interactions Diffusion

Nitrous Oxide Fluxes from Cultivated Areas and Rangeland: U.S. High Plains

U.S. Geological Survey, Box 25046, MS 413, Lakewood, CO 80225

View larger version (33K): [in this window] [in a new window]   FIG. 1. Map of the High Plains Aquifer showing locations of the vadose zone study sites.

View larger version (49K): [in this window] [in a new window]   FIG. 2. Profiles of NO3 extracted from vadose zone sediment cuttings and NO3 concentrations in groundwater (after McMahon et al., 2006). Note the break in the x-axis scale at the UMA and GNT sites. Horizontal dashed lines in each plot represent water table depths at indicated times. In groundwater, concentrations plotted on a mass basis were calculated from concentrations measured on a volume basis (in parentheses) and porosity and bulk density data from McMahon et al. (2003). Zones of high NO3 are commonly associated with indicated zones of N2O production.

View larger version (56K): [in this window] [in a new window]   FIG. 3. Lithology and construction details for a typical High Plains vadose zone well installation; NHP = Northern High Plains; CHP = Central High Plains; SHP = Southern High Plains.

View larger version (19K): [in this window] [in a new window]   FIG. 4. Concentrations of chlorofluorocarbons CFC-11, CFC-12, CFC-113, and SF6, in North American air as a function of time (modified from Busenberg and Plummer, 2000, Fig. 6).

View larger version (27K): [in this window] [in a new window]   FIG. 5. (A) Chlorofluorocarbon and SF6 concentrations measured in August 2001 samples from the Central High Plains rangeland site CNG (symbols) compared with simulated profiles (lines) for porosity, moisture content, and tortuosity data shown in Table 2; and (B) measured N2O profiles compared with the simulated profile assuming that steady 0.17 kg N2O-N ha–1 yr–1 production occurs in the top 1 m of the profile. X in line represents mean and range of groundwater equivalent equilibrium concentration in water-vapor-saturated air (GW EEC).

View larger version (30K): [in this window] [in a new window]   FIG. 6. (A) Chlorofluorocarbon and SF6 concentrations measured in August 2003 samples from the Northern High Plains rangeland site IMP (symbols) compared with simulated profiles (lines) for porosity, moisture content, and tortuosity data shown in Table 2; and (B) match of simulated (lines) seasonally distributed root-zone N2O production of 0.04 kg N2O-N ha–1 yr–1 to measured concentrations. X in line represents mean and range of groundwater (GW) equivalent equilibrium concentration in water-vapor-saturated air.

View larger version (31K): [in this window] [in a new window]   FIG. 7. (A) Chlorofluorocarbon and SF6 concentrations at the Northern High Plains irrigated corn site UMA measured in May 2003 compared with simulated profiles for porosity, moisture content, and tortuosity data shown in Table 2; and (B) comparison of simulated to measured N2O concentrations for root-zone production of 2.3 kg N2O-N ha–1 yr–1 occurring seasonally. X in line represents mean and range of groundwater equivalent equilibrium concentration in water-vapor-saturated air (GW EEC).

View larger version (32K): [in this window] [in a new window]   FIG. 8. (A) Chlorofluorocarbon and SF6 concentrations at the Northern High Plains irrigated corn site GNT measured in May (filled symbols) and August 2003 (open symbols) compared with simulated profiles for porosity, moisture content, and tortuosity data shown in Table 2; and (B) comparison of simulated (solid line) to measured N2O concentrations for steady root-zone production of 1.3 kg N2O-N ha–1 yr–1. Inset shows mismatch between shallow and deep data. X in line represents mean and range of groundwater equivalent equilibrium concentration in water-vapor-saturated air (GW EEC).

View larger version (30K): [in this window] [in a new window]   FIG. 9. (A) Chlorofluorocarbon and SF6 concentrations at the Central High Plains Conservation Reserve site CAL-121 measured in August 2001 compared with simulated profiles for porosity, moisture content, and tortuosity data shown in Table 2; and (B) comparison of simulated to measured N2O concentrations for production of 0.017 kg N2O-N ha–1 yr–1 at the 15- to 17-m zone and 0.004 kg N2O-N ha–1 yr–1 at the water table, beginning in 1990 with an initial concentration of 4000 nm3 m–3. X in line represents mean and range of groundwater (GW) equivalent equilibrium concentration in water-vapor-saturated air.

View larger version (28K): [in this window] [in a new window]   FIG. 10. (A) Chlorofluorocarbon and SF6 concentrations measured in July 2002 at the Southern High Plains irrigated cotton site JRW compared with simulated profiles for porosity, moisture content, and tortuosity data shown in Table 2; and (B) comparison of simulated to measured N2O concentrations for root-zone production of 0.074 kg N2O-N ha–1 yr–1 and water table production of 0.009 kg N2O-N ha–1 yr–1. X is a single measurement of groundwater (GW) equivalent equilibrium concentration in water-vapor-saturated air.