Aquatic systems point-source discharges

It is also used as an electron acceptor by microorganisms. Nitrihcation of ammonia N in soil is a source of nitrate. In addition, nonpoint and point source discharges from terrestrial ecosystems can be a major source of nitrate to wetlands and aquatic systems. In the atmosphere, nitrogen oxides can react with photochemically produced free radicals and produce nitric acid, which contributes to acid rain. Nitrate is also a common fertilizer used in agricultural ecosystems. 

It will have become apparent from the preceding discussions that xenobiotics after discharge from a point source may enter any of the various environmental compartments aquatic systems including biota and sediment, the atmosphere, terrestrial systems including soils, biota, and in the long run possibly the ultimate predator — humans. Considerable effort has therefore been devoted to the development and application of models to evaluate this dissemination in quantitiative terms. These involve the concept of fugacity, and it seems appropriate at the beginning to examine this concept briefly. 

Studies aimed at understanding the sources, fate and effects of environmental contaminants, such as those described in this book, have provided much of the information used by managers and regulators to limit and regulate inputs to the environment as a result of human activities. These inputs include direct discharge to air, soil and water from point sources and more diffuse inputs, from so-called non-point sources, such as agricultural and urban runoff and atmospheric inputs to aquatic systems. Overall, much has been... 

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