Ammonia in estuaries and effects on fish

Abstract

This review aims to explore the biological responses of fish in estuaries to increased levels of environmental ammonia. Results from laboratory and field studies on responses of fish to varying salinity and their responses increased ammonia will be evaluated, although studies which examine responses to ammonia, in relation to varying salinity, pH and temperature together are rare. In a survey of British estuaries the continuous measurement of total ammonia showed values that ranged from background levels increasing up to c. 10 mg N l−1 although higher values have been noted sporadically. In outer estuaries pH values tended to stabilize towards sea water values (e.g. c. pH 8). Upper reaches of estuaries are influenced by the quality of their fresh waters sources which can show a wide range of pH and water quality values depending on geological, climatic and pollution conditions. In general the ammonia toxicity (96 h LC50) to marine species (e.g. 0·09–3·35 mg l−1 NH3) appears to be roughly similar to freshwater species (e.g. 0·068–2·0 mg l−1 NH3). Ammonia toxicity is related to differences between species and pH rather than to the comparatively minor influences of salinity and temperature. In the marine environment the toxicity of ionized ammonia should be considered. The water quality standard for freshwater salmonids of 21 μg l−1 NH3–N was considered to be protective for most marine fish and estuarine fish although the influence of cyclical changes in pH, salinity and tempera…