The need for comprehensive and consistent treatment of the nitrogen cycle in nitrogen cycling and mass balance studies: I. Terrestrial nitrogen cycle.
A review of conceptual models that scientists use to characterize the nitrogen (N) cycle and to conduct N mass balance studies at global, regional and local scales is presented. Large uncertainties in processes and process rates make it difficult to conduct precise N mass balances and the dominant conceptual model has changed in recent decades. An earlier conceptual model recognized explicitly that human activities, especially agriculture, have both depleted terrestrial N and increased the fixation of atmospheric N in biologically available forms. The current conceptual model does not include adequate treatment of the depletion of the terrestrial N reservoir, the resulting transfer of N to the hydrosphere and atmosphere, or the cycling of terrestrial N below the plow layer. Thus, it delivers an unrealistically limited view of human influences on the N cycle. It is recommended that a comprehensive and consistent treatment of terrestrial N cycling be developed to better facilitate scientific explanation of historical N-related environmental changes and more closely balance N budgets on a range of geographical and temporal scales. Improved N-cycle models will provide an improved scientific basis for answering important resource management and policy questions.
Illinois State Water Survey, Champaign 61820, USA. ekrug@sws.uiuc.edu
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D017753:Ecosystem; D004784:Environmental Monitoring; D005843:Geography; D008962:Models, Theoretical; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D013997:Time Factors
D009584:Nitrogen