Monitoring the changes of redox potential, pH and electrical conductivity of the mangrove soils in northern Taiwan.

The redox potential (Eh), pH and electrical conductivity (EC) of the marsh soils of the Chuwei mangrove, located in the estuarine of the Tansui River in northern Taiwan were monitored for two years (from October 1995 to September 1997). The soils of selected pedons were studied, and the soils were classified based on Keys to Soil Taxonomy. The soil pH values tended to be neutral due to the impact of seawater on the mangrove marsh. The amounts of organic carbon found in this study area were much less than those generally encountered in the wetland soils of temperate regions in the world. The base saturation percentages of the soils were almost 100%, the exchangeable Na being particularly predominant. The concentrations of various cations of water in this ecosystem were in the order of Na+ > Mg2+ > K+ = Ca2+, and those of anions of water were in the order of Cl- > SO4(2-) > NO3- > PO4(3-). In spite of seasonal flooding changes, highly reduced states (100 to -200 mV of Eh values) existed throughout the two-year study. The spatial and temporal variations of the Eh values of the surface soil (0-20 cm) were higher than those of the subsoils (20-100 cm). The EC values of the soils from the surface to a depth of 100-cm were generally more than 20 dS/m. The marsh soils of the Chuwei mangrove were, thus, classified as Halic Endoaquents or Halic Fluvaquents.