Effects of ammonia in pulp mill effluents on estuarine phytoplankton assemblages: field descriptive and experimental results

A field descriptive and field/laboratory experimental program was carried out to evaluate the effects of ammonia (NH3) discharged by a pulp mill on estuarine plankton. Field data indicated that ammonia concentrations in the receiving system (Amelia Estuary; range, 0.19-0.43 mg l(-1)) were significantly higher than those taken in the reference system (Nassau Estuary; range, 0.090. 0.11 mg l(-1)). Significantly reduced chlorophyll a concentrations were noted in the Amelia system, and these varied inversely with ammonia concentrations. There were periodic reductions of light transmission in areas affected by mill effluents and in upper areas of both estuaries due to postulated urban storm water runoff. Field surveys indicated that whole water and net phytoplankton numbers and species richness were significantly lower in the Amelia system. Zooplankton numbers were significantly lower at various Amelia stations, whereas there were no significant differences in zooplankton species richness between the two study areas. The field results indicated that the most likely system-wide differences of water quality that could account for the noted biological responses were the relatively high ammonia concentrations in the Amelia system. Field ammonia levels in the Amelia system were significantly associated with observed impairment of key indices of phytoplankton assemblages in areas affected by mill discharges, especially during summer periods of maximal impact. Laboratory microcosm experiments with Skeletonema costatum indicated adverse effects of ammonia on chlorophyll indicators. Microcosm results indicated that ammonia had a stimulatory effect on S. costatum at mean concentrations of 0.06 mg l(-1) with initial adverse effects of ammonia within a range of 0.1-0.24 mg l(-1) and major effects at concentrations >0.46 mg l(-1). Mesocosm experiments with ammonia indicated stimulatory effects from 0.11 to 0.14 mg l(-1) with inhibition of phytoplankton growth at 0.20 mg l(-1). The difference between stimulatory effects and