The light and dark bottle method is a way of measuring primary productivity in an aquatic ecosystem.

It involves having two bottles, one transparent and one covered, and measuring the changes in dissolved oxygen levels over time. Using some simple calculations, it's possible to determine NPP, GPP and R for the ecosystems. It's a fairly simple experiment that can be done in more school labs.

NPP and GPP are explained in depth in this previous video:    • Primary Productivity Explained