Karl Zeller

Quantifying simultaneous fluxes of ozone, carbon dioxide and water vapor above a subalpine forest ecosystem

Assessing the long-term exchange of trace gases and energy between terrestrial ecosystems and the atmosphere is an important priority of the current climate change research. In this regard, it is particularly significant to provide valid data on simultaneous fluxes of carbon, water vapor and pollutants over representative ecosystems. Eddy covariance measurements and model analyses of such combined fluxes over a subalpine coniferous forest in southern Wyoming (USA) are presented. While the exchange of water vapor and ozone are successfully measured by the eddy covariance system, fluxes of carbon dioxide (CO(2)) are uncertain. This is established by comparing measured fluxes with simulations produced by a detailed biophysical model (FORFLUX). The bias in CO(2) flux measurements is partially attributed to below-canopy advection caused by a complex terrain. We emphasize the difficulty of obtaining continuous long-term flux data in mountainous areas by direct measurements. Instrumental records are combined with simulation models as a feasible approach to assess seasonal and annual ecosystem exchange of carbon, water and ozone in alpine environments. The viability of this approach is demonstrated by: (1) showing the ability of the FORFLUX model to predict observed fluxes over a 9-day period in the summer of 1996; and (2) applying the model to estimate seasonal dynamics and annual totals of ozone deposition and carbon, and water vapor exchange at our study site. Estimated fluxes above this subalpine ecosystem in 1996 are: 195 g C m(-2) year(-1) net ecosystem production, 277 g C m(-2) year(-1) net primary production, 535 mm year(-1) total evapo-transpiration, 174 mm year(-1) canopy transpiration, 2.9 g m(-2) year(-1) total ozone deposition, and 1.72 g O(3) m(-2) year(-1) plant ozone uptake via leaf stomata. Given the large portion of non-stomatal ozone uptake (i.e. 41% of the total annual flux) predicted for this site, we suggest that future research of pollution-vegetation interactions should relate plant response to actively assimilated ozone by foliage rather than to total deposition. In this regard, we propose the Physiological Ozone Uptake Per Unit of Leaf Area (POUPULA) as a practical index for quantifying vegetation vulnerability to ozone damage. We estimate POUPULA to be 0.614 g O(3) m(-2) leaf area year(-1) at our subalpine site in 1996.

A solar radiation algorithm for ecosystem dynamic models

A general algorithm is described for estimating average monthly solar radiation in cal cm−2 day−1 received on mountain slopes that uses basic topographic and climatic information for input, i.e. latitude, elevation, slope aspect and orientation, and average monthly data for ambient temperature, relative humidity and total precipitation. The algorithm is an extension of the methodlogy developed by Lui and Jordan, Klein, and Bonan. We have tested our method against independent data from 69 meteorological stations throughout the northern hemisphere provided by Muller and Zeller. The stations were selected to represent different latitudes, climate zones and elevations. The test showed that the algorithm predicts quite accurately seasonal patterns of solar radiation from the subpolar region down to the tropics and thus can be used with ecological simulation models (e.g. gap-phase succession models or regional landscape models).

Modeling coupled interactions of carbon, water, and ozone exchange between terrestrial ecosystems and the atmosphere. I: Model description

A new biophysical model (FORFLUX) is presented to study the simultaneous exchange of ozone, carbon dioxide, and water vapor between terrestrial ecosystems and the atmosphere. The model mechanistically couples all major processes controlling ecosystem flows trace gases and water implementing recent concepts in plant eco-physiology, micrometeorology, and soil hydrology. FORFLUX consists of four interconnected modules-a leaf photosynthesis model, a canopy flux model, a soil heat-, water- and CO2- transport model, and a snow pack model. Photosynthesis, water-vapor flux and ozone uptake at the leaf level are computed by the LEAFC3 sub-model. The canopy module scales leaf responses to a stand level by numerical integration of the LEAFC3model over canopy leaf area index (LAI). The integration takes into account (1) radiative transfer inside the canopy, (2) variation of foliage photosynthetic capacity with canopy depth, (3) wind speed attenuation throughout the canopy, and (4) rainfall interception by foliage elements. The soil module uses principles of the diffusion theory to predict temperature and moisture dynamics within the soil column, evaporation, and CO2 efflux from soil. The effect of soil heterogeneity on field-scale fluxes is simulated employing the Bresler-Dagan stochastic concept. The accumulation and melt of snow on the ground is predicted using an explicit energy balance approach. Ozone deposition is modeled as a sum of three fluxes- ozone uptake via plant stomata, deposition to non-transpiring plant surfaces, and ozone flux into the ground. All biophysical interactions are computed hourly while model projections are made at either hourly or daily time step. FORFLUX represents a comprehensive approach to studying ozone deposition and its link to carbon and water cycles in terrestrial ecosystems.

O3 and NO2 fluxes over snow measured by Eddy correlation

The fluxes of nitrogen dioxide and ozone, as well as supporting meteorological data, have been measured at a snow covered grassland field site in northern Colorado by eddy correlation. The fluxes of both species are small. The median surface resistance to ozone deposition is greatest during the morning and least during the afternoon. The nitrogen dioxide flux is generally downward overnight and during the morning and upward during the afternoon. Surface NO emissions are thought to strongly influence the observed NO2 flux. The median surface resistance to oxidant (Ox = O3 + NO2) deposition shows no pronounced diurnal variation, but is greater for aged snow (22.8 ± 8.95 cm−1) than for fresh snow (8.1 ± 4.9 s cm−1). Quoted error limits are one standard error of the estimate.

Measurements of upward turbulent ozone fluxes above a subalpine spruce‐fir forest

High rural concentrations of ozone (O 3 ) are thought to be either stratospheric in origin, advected from upwind urban sources, or photochemically generated locally as a result of natural trace gas emissions. Ozone is known to be transported vertically downward from the above-canopy atmospheric surface layer and destroyed within stomata or on other biological and mineral surfaces. However, here we report winter-time eddy correlation measurements of vertical O 3 flux above a subalpine canopy of Picea engelmannii and Abies lasiocarpa in the Snowy Range Mountains of Wyoming that indicate anomalous upward O 3 fluxes. Upward fluxes of 0.5 μg m -2 s -1 (11 kg km -2 day -1 ) were routinely measured during the 1991-92 winter season. Decreasing O 3 concentration from several hours to several days that relate to increasing positive O 3 flux magnitudes and visa versa, suggest O 3 may be temporarily stored in the snow base.

Erratum to: On the average temperature of airless spherical bodies and the magnitude of Earth’s atmospheric thermal effect

[This corrects the article DOI: 10.1186/2193-1801-3-723.].

Modelling Flux-Gradient Relationships for Chemically Reactive Species in the Atmospheric Surface Layer

In atmospheric surface layer studies, the turbulent flux of variable A is approximated by the formula (Stull, 1988; Garratt, 1992):

New Insights on the Physical Nature of the Atmospheric Greenhouse Effect Deduced from an Empirical Planetary Temperature Model

\overline {wa} = - \frac{{\kappa zu * }}{{{\phi _a}(\zeta )}}\frac{{\partial {\rm A}}}{{\partial z}}