"August 1971." Includes bibliographical references (pages 75-76).

Bioassays for nutrient availability were evaluated to define conditions and limits under which each method can give meaningful results. The biological availability of algal nutrients in a water sample and the algal response to changes in the growth-limiting nutrient were measured. Factors other than insolubility prevent the nitrogen or phosphorus of certain samples of aerobic lake muds from being readily available for algal growth. The facts, that live algae and aquatic weeds do not share their adequate or surplus nutrients with nutrient-limited algae and that lake muds do not provide readily available nitrogen or phosphorus, indicate that once lake waters are stripped of available nutrients by plant production, further plant production will depend upon nutrients from continuous sources, such as wastewater effluents. Phosphorus-starved cells of Anabaena rapidly increase their capacity to reduce acetylene to ethylene when they receive phosphorus. This response may be used as a bioassay for detecting available phosphorus in aquatic ecosystems.