An integrated assessment system for the carrying capacity of the water environment based on system dynamics

摘要

Implementing an integrated assessment system for the carrying capacity of water environments should include recognizing and eliminating warning signs based on future predictions. However, existing methodologies tend to ignore the warning methods already in place, and current studies fail to quantify water ecology issues adequately. To help solve these problems, the ecological footprint that involves water uses a procedural indicator system, which adopts an early warning methodology system approach. This reconstruction has devised definitions, recognizes hazards, states forecasts status, analyses signs, judges situations, distinguishes levels, and eliminates risks. Based on these procedures, a dynamic system model has been developed, comprising five subsystems with an overarching parent system. These subsystems are population, ecology, water resources, water environment, and water ecology. The simulation involves carrying rates for the water environment, water resource, water ecology, and the level of harmony between society and the environment. All these serve to describe the water environment carrying capacity, i.e., the upper limit of the capacity to supply resources, remove pollutants, and offer sustainable ecological services. To properly quantify the carrying capacity, the water environment carrying rate was assessed by a comprehensive analysis of the water environment, water resources, and water ecological carrying rate. The carrying rates were calculated as the ratios of currently existing pressure to the maximum pressure that can be born. When values are greater than 1, they indicate overload because the actual pressure is greater than the pressure they can bear. The degree of coordination between economy and environment was standardized to range between 0 and 1. The larger the value, the more harmonious the relationship. For this research, the North Canal basin, a basin consisting of several rivers flowing through Beijing, Tianjin, and Hebei in northern China and its surrounding areas, was chosen. The results showed that water environment and resource carrying rates would decline to 2.60 and 0.94, respectively, while the water ecology carrying rate would remain high at 10.98 by the year 2025. In addition, the degree of coordination would increase from 0.65 to 0.79. These statistics mean that the overload statuses will be high for a long time, although they are expected to ease gradually. Besides, the relationship between society and the environment would become more stable. Considering both the overload statuses and the relationship between society and the environment, the warning signs would not vanish. Based on predictions, the measures used were explained from three perspectives, i.e., alleviating pressures, enhancing carrying capacities, and finding a balance between society and the environment. Finally, the effects of the measures were estimated quantitatively.