Assessing environmental improvement options from a water quality perspective for an urban–rural catchment

The ability of environmental systems to persist while experiencing sharp discontinuities is an issue of great importance to today's environmental managers and planners. This study quantified the relationship between land use and the total nitrogen (TN) load in a catchment using a mass balance model based on multivariate analysis. This model considered the spatial arrangement of observed data and the quantity of different land-use types to examine the relationship between the environmental improvement effects of various policy measures and the TN load in the Gyaku River basin, Japan. The distribution of the land uses was estimated from LANDSAT/TM data using ISODATA clustering. The aim was to develop concrete controls for improving the environment (i.e., an environmental improvement policy). The TN load was governed largely by the distribution of human-related factors such as industrial wastewater discharge, agricultural production, population density, and livestock density. The optimal environmental state was determined by examining various factors influenced by human activities and natural phenomena. The analysis incorporated previously published data from the early stages of stand development. First, the boundaries of the self-governing bodies that would enforce the proposed measures were located on maps of the environment and settlements in the study catchment. A proposed plan was then developed based on concrete procedures. The study catchment contained a predominantly agricultural area and an urban area. Thus the environmental improvement policy had to consider both urban and rural characteristics of the catchment. The qualitative effects of various measures and combinations of measures were simulated, considering inflows and outflows from both the agricultural and urban areas. This study is particularly useful because many visible aspects of Japanese environmental management are not those that rationally based paradigms of decision making would associate with environmental improvement and resilience.