[1] A new model of phytotoxicity of salt and plant salt uptake is presented and is coupled to an existing three-dimensional groundwater simulation model. The implementation of phytotoxicity and salt uptake relationships is based on experimental findings from willow trees grown in hydroponic solution. The data confirm an s-shaped phytotoxicity relationship as found in previous studies. Uptake data were explained assuming steady state salt concentration in plant roots, passive salt transport into the roots, and active enzymatic removal of salt from plant roots. On the one hand, transpiration strongly depends on groundwater salinity (phytotoxicity); on the other hand, transpiration significantly changes the groundwater salinity (uptake). This feedback loop generates interesting dynamic phenomena in hydrological systems that are dominated by transpiration and are influenced by significant salinity gradients. Generic simulations are performed for the Okavango island system and are shown to reproduce essential phenomena observed in nature.Citation: Bauer-Gottwein, P., N. F. Rasmussen, D. Feificova, and S. Trapp (2008), Phytotoxicity of salt and plant salt uptake: Modeling ecohydrological feedback mechanisms, Water Resour. Res., 44, W04418,
Humic acids, a heterogenic group of natural organic macromolecules with a complex polymeric structure, form a significant part of the soil and water environment. They have a high surface activity, thus they are able to interact with other components in the environment (mineral and microbial
cell surfaces, organic and inorganic compounds). This work is focused on humic acid effects on the growth of microorganisms utilizing phenolic compounds as the sole carbon and energy source. For this purpose a bacterial population Rhodococcus erythropolis and a yeast strain Candida
maltosa were used. Both microorganisms had been adapted to the degradation of phenol and phenolic compounds for many years. However, a toxic effect of these compounds still occurs. The addition of humic acids into the cultivation medium extended toleration of the bacteria to higher concentrations
of phenolic compounds and increased the growth of this microbial population as well. In the case of the yeast, humic acids inhibited the growth. Humic acids easily form an additive layer on the surface of the investigated microorganisms. The generated humic acid layer can probably serve as
a transport barrier and thus influence the growth of microbial populations.
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