Chemical weathering flux model

Attempts to model chemical weathering of catchments have used a variety of approaches and were originally designed to understand acidification processes. The BIRKENES code (Christophersen et al., 1982) was one of the first developed to model catchment stream chemistry. It used cation-anion charge balance, a gibbsite equilibrium solubility control for aluminum concentrations, a Gapon ion exchange for metals sorption, and rates for sulfate adsorption/ desorption in a two-reservoir model. The model was calibrated by input mass fluxes and output mass fluxes for the Birkenes catchment in Norway to provide the water flux information and to fit empirical parameters. 

PROFILE is a biogeochemical model developed specially to calculate the influence of acid depositions on soil as a part of an ecosystem. The sets of chemical and biogeochemical reactions implemented in this model are (1) soil solution equilibrium, (2) mineral weathering, (3) nitrification and (4) nutrient uptake. Other biogeochemical processes affect soil chemistry via boundary conditions. However, there are many important physical soil processes and site conditions such as convective transport of solutes through the soil profile, the almost total absence of radial water flux (down through the soil profile) in mountain soils, the absence of radial runoff from the profile in soils with permafrost, etc., which are not implemented in the model and have to be taken into account in other ways. 

Air quality modelling at met.no consists of three different systems, all coupled offline to our numerical weather prediction (NWP) models. These are (1) a nuclear emergency system, (2) an urban air quality (AQ) forecasting system and (3) a longterm air quality chemical transport model routinely used in Europe to determine transboundary pollution fluxes. 

Volatile and semivolatile organic chemicals placed on surface soils have very similar chemical process behavior patterns as those shown above for Hg. Numerous laboratory and a few field flux measurements have been performed on this class of chemicals as documented in a recent review. The review was performed to assess the quantity and quality of measured flux data and the availability of process-based emission models. The basic difference between the flux chamber model and the field-scale model is that the former involves a steady-state flux process and the latter is a transient one. The EC models needed for the large time-scale involved with most field applications must consider the so-called weathering effect which characterizes the depletion of the available-for-volatilization chemical mass in the... 

---