The Winogradsky Column & Biofilms: Models for Teaching Nutrient Cycling & Succession in an Ecosystem

Wetlands are among the most productive ecosystems in the world. The high productivity of wetlands is due to their ability to capture large amounts of the sun's energy and store it as chemical energy, as well as to their efficient recycling of what is produced (Niering 1985). The characteristic hydric soils in wetlands reflect the effect of water when present on soil or substrate for extended periods. According to Mitsch and Gosselink (1993) hydric soils that are semipermanently or permanently flooded develop gray or sometimes greenish or blue-gray color as a result of a process known as gleying. This process is the result of the chemical reduction of iron. Another characteristic of soils that are seasonally flooded is mottle formation. Orange/reddish or dark reddish-brown/black mottled spots seen throughout an otherwise gray soil matrix suggest soils with spots of iron and manganese oxides in an otherwise reduced environment. The development of gleys and mottles is mediated by microbiological processes and the rate at which they are formed depends on the presence of sustained anaerobic conditions, appropriate soil temperature (50 C is considered optimum), and the presence of organic matter as a substrate for microbial activity. These chemical transformations in wetland soils illustrate the interaction of nutrients and microbiological activities in ecosystems. One problem faced by biology teachers in teaching nutrient cycling is the lack of suitable exercises that can be conducted in the classroom. We feel that the use of a Winogradsky column