Search

Abstract: This paper will discuss TRIPLEX-Flux, a process-based model that estimates net ecosystem production (NEP) as well as analyzing the level of sensitivity of the model''s response by simulating CO2 flux in an existing old black spruce BOREAS site in central Canada. The research objectives were: (1) to test the TRIPLEX-Flux model simulations against flux tower measurements; and (2) to examine parameter and input variable effects on model response via sensitivity analysis. Validation of NEP data at 30min intervals derived from tower and chamber measurements showed that the NEP data from the model corresponded well with the measured NEP from the BOREAS site (R 2 >0.65). Sensitivity analysis demonstrated different levels of sensitivity between morning and noon periods and from the current to doubled atmospheric CO2 concentrations. Additionally, the comparison of different algorithms to calculate stomatal conductance showed that the NEP predicted by the model using the iteration algorithm was consistent with the results using a constant C i/C a of 0.74 for current and 0.81 for doubled CO2 concentrations. Varying parameter and input variable values by ±10% resulted in a similar model response between morning and noon periods (less than or equal to 27.6% and 27.4%, respectively). Most parameters were more sensitive at noon than they were in the morning except for those that were correlated with air temperature, suggesting that air temperature has considerable influence over model sensitivity for these parameters/variables. Air temperature effect was greater under doubled than it was under current atmospheric CO2 concentrations. In contrast, model sensitivity to CO2 decreased under doubled CO2 concentrations. [Copyright &y& Elsevier]

High frequency dissolved oxygen measurements in Mediterranean coastal lagoons show different dynamics on different time scales. In this paper the seasonal and daily dynamics are analysed and discussed and a continuous simulation model is developed to represent them for the salt lake of Fogliano (Italy). Field and laboratory experiments evidenced that primary production slows down in highly oxygenated and irradiated summer days, acting in feedback regime with the oxygen already present in the media, that wind stress contributes in exceeding the oxygen saturation concentration and that there is a firm correlation between oxygen consumption at the sediment layer and overhanging water temperature. Water temperature, solar radiation and wind regime are the forcing functions of the model; the main state variables are dissolved oxygen and detritus in the pelagic and benthic layers, together with carbon dioxide and vegetal biomass. The slow seasonal and fast diel dynamics are both revealed by the model evidencing detailed aspects of oxygen dynamics in a coherent agreement with field observed data trends. [Copyright &y& Elsevier]

A new remote-sensing-based land surface model, named ecosystem–atmosphere simulation scheme (EASS), is introduced in this paper. The principle motivation for formulating EASS is to provide realistic partition of energy fluxes at regional scales as well as consistent estimates of carbon assimilation rates. EASS has the following characteristics: (i) satellite data are used to describe the spatial and temporal information on vegetation, and in particular, we use a foliage clumping index (Ω) in addition to leaf area index to characterize the effects of three-dimensional canopy structure on radiation, energy and carbon fluxes; (ii) energy and water exchanges and carbon assimilation in the soil–vegetation–atmosphere system are fully coupled and are simulated simultaneously; (iii) the energy and carbon assimilation fluxes are calculated with stratification of sunlit and shaded leaves to avoid shortcomings of the “big-leaf” assumption. Model experiments shows that the simulation realism and accuracy by the new strategy are enhanced about 9–14% compared with the “big-leaf model”. Moreover, Ω is useful for accurate separation of sunlit and shaded leaves in the canopy. The accuracy in simulation of energy and carbon fluxes increase about 5–8% by considering the effects of Ω on the radiation interception and the separation of sunlit and shaded leaves; (iv) snow and soil simulations are emphasized by including a flexible and multiple layer scheme. EASS has been tested and validated against multiple-year observed data at several sites. EASS is proved to be overall successful in capturing variations in energy fluxes, canopy and soil temperatures, and soil moisture over diurnal, synoptic, seasonal and inter-annual temporal scales. [Copyright &y& Elsevier]