CHANGES IN PHYTOPLANKTON PHYSIOLOGY AND MORPHOLOGY IN RESPONSE TO DISSOLVED NUTRIENTS IN LOUGH NEAGH, N IRELAND

SUMMARY. Cell phosphorus and anthrone‐reactive carbohydrate contents were measured over a 6‐month period in the phytoplankton of Lough Neagh, N. Ireland. When all the soluble reactive phosphorus had disappeared from the water column, cell phosphorus contents began to decrease, reaching a minimum value of 0.4% ash‐free dry weight. At this time, cell carbohydrate contents greatly increased and phosphorus sorption assays showed rapid uptake of orthophosphate. Following a presumed sediment phosphorus release, cell carbohydrate and phosphorus uptake rate decreased greatly and there was a subsequent increase in cell phosphorus content to 1.6% ash‐free dry weight. As the cell phosphorus content declined, blue‐green algal filaments became progressively shorter. On the basis of these responses it is likely that phosphorus limitation occurred over a 4‐week period. Copyright © 1979, Wiley Blackwell. All rights reserved