Tolerance of estuarine benthic diatoms to high concentrations of ammonia, nitrite ion, nitrate ion and orthophosphate

Abstract

Ten species of benthic diatoms from the Eems-Dollard estuary were cultured unialgally in synthetic media with various concentrations of ammonia (NH4++NH3), nitrite ion, nitrate ion and orthophosphate. Most of the species grew well in media with very high concentrations of nitrite ion (1 to 10 mg-at N l-1), nitrate ion (about 16.9 mg-at N l-1) and orthophosphate (at least 0.9 mg-at P l-1). Ammonia concentrations higher than 0.5 mg-at N l-1 inhibited growth of the cultures. The rate of photosynthesis of diatoms from the field and from cultures was also inhibited by 0.5 mg-at N l-1 of ammonia under certain conditions. Inhibition of photosynthesis by ammonia was strongly enhanced by high irradiance and high pH. It is most unlikely that nitrite ion, nitrate ion and orthophosphate attain concentrations high enough to be inhibitory in the field, but concentrations of ammonia may be high enough for inhibition to occur. However a clear relationship between sensitivity of the diatoms and their occurrence on more or less polluted mudflats was not found.