The phytoplankton productivity of an acidic lake

The phytoplankton productivity over two years in a lake heavily loaded by acid mine drainage was very low. Algal assays indicated that below pH 5.5 the water, if buffered and fertilized with phosphorus, resulted in log growth. Above pH 5.5 algal log growth could be induced with phosphorus addition only. However, an in situ bag experiment was done in the lake and immediate bloom conditions of the indigenous algae resulted from phosphorus addition only, despite pH values below 5.