This paper describes a rain‐event driven, process‐oriented simulation model, DNDC, for the evolution of nitrous oxide (N2O), carbon dioxide (CO2), and dinitrogen (N2) from agricultural soils. The model consists of three submodels: thermal‐hydraulic, decomposition, and denitrification. Basic climate data drive the model to produce dynamic soil temperature and moisture profiles and shifts of aerobic‐anaerobic conditions. Additional input data include soil texture and biochemical properties as well as agricultural practices. Between rainfall events the decomposition of organic matter and other oxidation reactions (including nitrification) dominate, and the levels of total organic carbon, soluble carbon, and nitrate change continuously. During rainfall events, denitrification dominates and produces N2O and N2. Daily emissions of N2O and N2 are computed during each rainfall event and cumulative emissions of the gases are determined by including nitrification N2O emissions as well. Sensitivity analyses reveal that rainfall patterns strongly influence N2O emissions from soils but that soluble carbon and nitrate can be limiting factors for N2O evolution during denitrification. During a year sensitivity simulation, variations in temperature, precipitation, organic C, clay content, and pH had significant effects on denitrification rates and N2O emissions. The responses of DNDC to changes of external parameters are consistent with field and experimental results reported in the literature.

Simulations of nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soils were carried out with a rain‐event model of nitrogen and carbon cycling processes in soils (Li et al., this issue). Model simulations were compared with five field studies: a 1‐month denitrification study of a fertilized grassland in England; a 2‐month study of N2O emissions from a native and fertilized grassland in Colorado; a 1‐year study of N2O emissions from agricultural fields on drained, organic soils in Florida; a 1‐year study of CO2 emissions from a grassland in Germany; and a 1‐year study of CO2 emissions from a cultivated agricultural site in Missouri. The trends and magnitude of simulated N2O (or N2O + N2) and CO2 emissions were consistent with the results obtained in field experiments. The successful simulation of nitrous oxide and carbon dioxide emissions from the wide range of soil types studied indicates that the model, DNDC, will be a useful tool for studying linkages among climate, land use, soil‐atmosphere interactions, and trace gas fluxes.

Salvage excavations of a nearly complete and remarkably well-preserved skeleton of an American mastodont (Mammut americanum) in Licking County, Ohio, yielded a discrete, cylindrical mass of plant material found in association with articulated vertebrae and associated ribs. This material is interpreted as intestinal contents of the mastodont and paleobotanical analyses indicate that the mastodont diet included significant amounts of low, herbaceous vegetation. Enteric bacteria (Enterobacter cloacae), isolated from a sample of this material, are believed to represent survivors or descendants of the intestinal microflora of the mastodont. This is the first report of the isolation of bacteria associated with late Pleistocene megafauna.

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Red clays associated with Prairie du Chien and Sinnipee (Galena) dolomites and loess were studied stratigraphically and geomorphically at 10 locations. The clay content (< 2 µm, 82 ± 9.1%; < 0.2 µm, 70 ± 10.4%, n = 15) relative to the overlying loess (< 2 µm, 28 ± 4.4%; < 0.2 µm, 16 ± 4.9, n = 4) and the dolomite insolubles (< 2 µm, 47 ± 11%; < 0.2 µm, 34 ± 9.6%, n = 7) indicate fine clay enrichment. Smectite‐rich oriented clay coatings on dolomite sands suggest illuviation. Undisturbed chertlines from dolomite through red clay bodies necessitate a volume‐for‐volume replacement. Periglacial activity during the Wisconsinan frequently produced loess (i), over a mixed zone of loess and red clay (ii), over in‐situ red clay (iii), and dolomite (iv). For the 1‐to 10µm quartz; euhedral grains indicated by x‐ray diffraction I(100)/(101) = 0.23, 0.54, 1.02, 0.70, respectively; nine trace element contents = 2.15 ± 0.40, 1.61 ± 0.18, 0.78 ± 0.10 relative to dolomite (1.0); and oxygen isotopes expressed as δ18O = 18.6, 19.7, 26.9, 26.4%. The values for the mixed zone (ii) fall between those for the loess (i) and insitu red clay (iii). Optical data for the morphology of the fine sand fractions (50–250 µm) were corroborative. The silt and sand of in‐situ red clay (protected in karst depressions and by chert lag gravels) are from the dolomite.