An eco-balance approach to the evaluation of historical changes in nitrogen loads at a regional scale

Historical changes in nitrogen flows of a municipality from 1912 to 2002 were analyzed to evaluate the relation between production and environmental pollution. The system comprised human, livestock and farmland subsystems. The indicators used in this study were production, surplus nitrogen (N) on farmland and total systems, and flow indices. Flow indices consist of cycling index (CI), export index (EI), and loss index (LI). CI was defined as the proportion of nitrogen cycled in the system to the total system throughflow, EI as nitrogen exported from the system, and LI as nitrogen lost from the system (sum of field surplus nitrogen, nitrogen in non-utilized excreta, and N2O and NH3 emissions).Complex changes in N flow of human, livestock, and farmland subsystems were analyzed by comparing production to the surplus N on farmland and total systems and flow indices. The relations between production and other indicators were defined as eco-balance. A negative correlation is desirable between the indicators and production in the case of an indicator for environmental damage such as surplus N and LI, whereas a positive correlation is preferred in the case of benefits such as CI and EI.Flow indices simplified the complex changes inside the system. According to the analysis of eco-balance, the investigated period from 1912 to 2002 could be divided into three periods: manure-based period (MBP) from 1912 to 1957, transition period from manure-based to chemical-fertilizer-based period (TP) from 1958 to 1977, and chemical-fertilizer-based period (CBP) from 1978 to 2002. Driving forces of each period were extracted based on the eco-balance.