Andres Schmidt

High-frequency analysis of the complex linkage between soil CO 2 fluxes, photosynthesis and environmental variables

High-frequency soil CO(2) flux data are valuable for providing new insights into the processes of soil CO(2) production. A record of hourly soil CO(2) fluxes from a semi-arid ponderosa pine stand was spatially and temporally deconstructed in attempts to determine if variation could be explained by logical drivers using (i) CO(2) production depths, (ii) relationships and lags between fluxes and soil temperatures, or (iii) the role of canopy assimilation in soil CO(2) flux variation. Relationships between temperature and soil fluxes were difficult to establish at the hourly scale because diel cycles of soil fluxes varied seasonally, with the peak of flux rates occurring later in the day as soil water content decreased. Using a simple heat transport/gas diffusion model to estimate the time and depth of CO(2) flux production, we determined that the variation in diel soil CO(2) flux patterns could not be explained by changes in diffusion rates or production from deeper soil profiles. We tested for the effect of gross ecosystem productivity (GEP) by minimizing soil flux covariance with temperature and moisture using only data from discrete bins of environmental conditions (±1 °C soil temperature at multiple depths, precipitation-free periods and stable soil moisture). Gross ecosystem productivity was identified as a possible driver of variability at the hourly scale during the growing season, with multiple lags between ~5, 15 and 23 days. Additionally, the chamber-specific lags between GEP and soil CO(2) fluxes appeared to relate to combined path length for carbon flow (top of tree to chamber center). In this sparse and heterogeneous forested system, the potential link between CO(2) assimilation and soil CO(2) flux may be quite variable both temporally and spatially. For model applications, it is important to note that soil CO(2) fluxes are influenced by many biophysical factors, which may confound or obscure relationships with logical environmental drivers and act at multiple temporal and spatial scales; therefore, caution is needed when attributing soil CO(2) fluxes to covariates like temperature, moisture and GEP.

Direct measurement of CO2 and particle emissions from an urban area

From July 9 th through September 24th, 2009, turbulent particle number fluxes and CO 2 fluxes were measured above the city area of Munster, north-west Germany. The goal was to characterize the respective vertical fluxes in the urban boundary area. The measurements were conducted at a height of 65 m a.g.l. on a military radio tower at 10 Hz temporal resolution. Fluxes were calculated applying the eddy covariance method. To determine the impact of traffic emissions on particle number fluxes and CO 2 fluxes, hourly traffic activities for 45° sectors, related to the tower, were calculated. Averaged diurnal and sectoral fluxes are consistently directed upward, implying that the urban area of Munster acts continuously as particle (number) and CO 2 source. Traffic activities vary in the course of the day and within the 45° sectors. The latter is attributable to differences in land use between the sectors. In the course of the day, two peaks are discernible, during the morning and the evening rush hours, respectively. Averaged diurnal particle (number) fluxes are correlated significantly to traffic activity. Accordingly, traffic related emissions are the main sources for urban particle (number) fluxes. Averaged sectoral CO 2 fluxes also correlate fairly well with sectoral traffic activities. In addition, daytime photosynthesis is a controlling variable for the CO 2 flux, leading to lower upward fluxes in daytime. The contribution of the photosynthetic activity of the vegetation in the urban area to the CO 2 flux is quantified. Further, the contribution of traffic related emissions to the CO 2 flux is computed by applying emission factors for carbon dioxide to the traffic activity. They contribute in daytime about 40 to 50 % to the CO 2 flux, whereby, nightly contributions are minimal.

Bayesian optimization of the community land model simulated biosphere-atmosphere exchange using CO2 observations from a dense tower network and aircraft campaigns over Oregon

AbstractThe vast forests and natural areas of the Pacific Northwest compose one of the most productive ecosystems in the Northern Hemisphere. The heterogeneous landscape of Oregon poses a particular challenge to ecosystem models. This study presents a framework using a scaling factor Bayesian inversion to improve the modeled atmosphere–biosphere exchange of CO2. Observations from five CO/CO2 towers, eddy covariance towers, and airborne campaigns were used to constrain the Community Land Model, version 4.5 (CLM4.5), simulated terrestrial CO2 exchange at a high spatial and temporal resolution (1/24°; 3 hourly). To balance aggregation errors and the degrees of freedom in the inverse modeling system, the authors applied an unsupervised clustering approach for the spatial structuring of the model domain. Data from flight campaigns were used to quantify the uncertainty introduced by the Lagrangian particle dispersion model that was applied for the inversions. The average annual statewide net ecosystem productiv...

Carbon cycle dynamics within Oregon’s urban-suburban-forested-agricultural landscapes

Land management strategies within urban-suburban, agricultural, and forested landscapes can have significant impacts on local and regional carbon and water cycles thereby contributing or mitigating effects of global climate change. Decision makers’ plans for bioenergy production have long-term implications, though lack fundamental understanding of impacts on ecosystems and atmospheric greenhouse gases. We quantify the interactions and feedbacks between proposed actions, ecosystem processes, and changes in climate on local and regional scales. This is particularly important as strategies for limiting CO2 emissions are often implemented by states.