Biogeochemical+cycle+demo

How do you demonstrate biogeochemical cycling in the lab. 'Closed aquariums' typically don't work well. Besides, you wouldn't see anything happening, just be told a story about why it works. Winogradsky columns are cool and gives some things to discuss. The layering pattern explanations may be too difficult here. And these columns can take months to develop and have a significant failure rate. But still a classic on the college campus. The Stella computer modeling program could be desinged to let students make the connecitons and set the flows through the cycles. At $1000 per school, we'd have to find several other uses for the program for this to be viable.