Technical Abstract: Many ecological problems occur with increased inputs of reactive nitrogen (Nr) into the environment. Excessive Nr is directly associated with the need for food production. The importance of managing Nr is quite broad and extends to numerous issues associated with excessive Nr in the environment. Numerous transformations of Nr into its various combination and bonding with H, O, and C contribute to its transport both by water and through the air. Because of the mobility of the various forms of Nr, ecosystem boundaries are crossed and intended beneficial effects often become unintended detrimental effects for adjacent ecosystems or even within the system that the use of Nr was intended to benefit. Within the terrestrial system, when Nr is separated from C, its most common partner (Asner et al. 1977), Nr can be transformed into many mobile forms by processes that include nitrification, denitrification, and nitrous and nitric oxide formation. The transformation of Nr can result in, for example, the interaction of nitrogen oxides and ammonium with fine particulates and ozone, leaching of nitrate and nitrite in water, and/or volatilization of and aerial transport of ammonia. The ecosystems addressed include the ‘terrestrial’, ‘aquatic’, and ‘atmospheric’ ecosystems as well as the ‘human biological’ ecosystem (i.e. human health) which may also be impacted by Nr. Society is placing an increasingly higher priority upon improved management of Nr because of the concerns that they perceive exist between the management of Nr and human health.