The effect of plants on the dynamics of sulfur species and zinc in wetland sediments

To gain a better understanding of how the presence of plants and their seasonal growth cycle affects the biogeochemistry of sulfur species in wetland sediments, and how this in turn affects the mobility of heavy metals, this research concentrates on the systematic analysis of pore water chemistry and sediment composition via comparative in situ measurements of vegetated and non-vegetated sediments.; The field measurements shows that the oxygen release from the roots into the sediments can reoxidize the reduced solid phase sulfide (i.e. AVS) that is present in the sediments and substantially elevate SO4 2- concentrations in the rhizosphere during the growing season. Evaporation-induced advection increases the flux of solutes (i.e. SO 42-, Zn2+) from the overlying water column into the rhizosphere. The increased precipitation of metal sulfide following microbial sulfate reduction in the deeper vegetated sediments may significantly enhance the removal of trace metals from the contaminated overlying water.; Results show that the elevated SO42- concentrations in the vegetated sediments are gradually decreasing throughout the growing season, although the concentrations remain higher than in the non-vegetated sediments. As a solid phase, the immobility of AVS is determined to be the primary factor that limits the continuous increase of SO4 2- concentrations during the growing season. To investigate the cause for the decrease of SO42- concentrations in response to plant growth, a mathematical model is developed with dynamic formulations for the rhizosphere available AVS. The model successfully explains the seasonal trend of SO42- concentrations throughout the growing season and couples the biogeochemical dynamics of the rhizosphere to the fate and transport of trace metals in the sediments. The availability of AVS in the rhizosphere depending on plant growth may limit the quantity of oxidized AVS to some extent, which greatly reduces the release of trace metals into the rhizosphere. The significantly decreased rhizosphere available AVS contributes to the stability of trace metals in the sediments.; Consequently, both the seasonal sulfur dynamics measured in the vegetated sediments and their application to a model will be useful in determining the fate and dynamics of trace metals and, furthermore, useful in the risk assessment and management of wetlands contaminated with trace metals.