Ecological Effects of Deposited S and N Compounds: Effects on Aquatic Biota

Soft waters of upland streams and lakes are those most susceptible to change. Few, if any, ecological effects have been described resulting directly from enhanced S and N inputs to aquatic environments. Effects relate largely to changing levels of acidity-alkalinity; whether the stress effects relate to hydrogen alone or to related inhibition or enhancement of other ion uptake is rarely certain. Enhanced acidity also results in changing metal ion concentrations and speciation in freshwaters. The faunal and floral responses to these chemical changes are varied but in general a decrease in species diversity occurs which may lead to significant changes in community structure and in trophic relationships within the ecosystem. These latter changes may themselves play an important role in governing the presence or absence of many species.