The role of phosphorus in the growth of Cladophora

Abstract

1.1. An examination of river survey data showed standing crop of Cladophora to be correlated with phosphorus concentration. In general, river water containing less than 1·0 mg l−1 total inorganic P produced only modest growths of Cladophora.2.2. Culture experiments with supplemented river water confirmed the importance of phosphorus by showing that growth of Cladophora in waters upstream of sewage discharges, could be increased to downstream levels by addition of phosphorus.3.3. Growth experiments in synthetic media containing levels of phosphorus from 1 to 7 mg l−1 indicated no significant growth increase above 1 mg P l−1 but a significant reduction below 1 mg P l−1.4.4. In natural water, the maximum level of phosphorus for growth was found to vary, being 2·5 mg P l−1 at 3·2 mg N l−1 NO3 and 0·95 mg P l−1 at 5·25 mg N l−1 NO3.5.5. A 3 × 4 factorial experiment utilizing synthetic media, confirmed an interaction between nitrogen and phosphorus. The highest level of NO3 (7·7 mg N l−1) enhanced growth at the lowest phosphorus level (0.5 mg P l−1) but at higher levels of phosphorus growth was reduced.6.6. The importance of such interactions is discussed briefly in connection with eutrophication and nutrient stripping.