For up to 40 students (in 10 groups) Time Required: 2 hrs, which can be conducted over two consecutive lab periods. The experiment will measure dissolved oxygen concentration in water samples using the Winkler technique. The primary productivity of an ecosystem will also be determined. Requirements: Pond water; grow lights; pipets; burettes; flasks; beakers; gloves; goggles; sulfuric acid; linear graph paper; eyedroppers; plastic window screens; 50 sealable containers or BOD bottles; filter paper; aluminum foil. CONTENTS: Sodium iodide, Sodium hydroxide, Manganese sulfate, Starch solution, Sodium thiosulfate, Nitrogen enrichment solution concentrate, Phosphorus enrichment reagents, Complete reagent use instructions.