3.1. Evaluation of supply services
After World War II, in order to quickly restore urban economy, the process of urbanization has been accelerated. Humans are eager to obtain materials from the nature and accumulate resources, thus leading to serious environmental problems such as sharp decline in biodiversity, river pollution, and green space destruction. Governments and some scholars of various countries have begun to pay attention to environmental quality in order to provide sustainable supply resources for urban development through restoring water bodies and green spaces. River health evaluation index systems and green space health evaluation systems have been successively established.
In 1981, based on the concept that a good water ecosystem must have a perfect biological community structure, with the biological integrity index (IBI) was first proposed for evaluating the quality of water environments. After 16 indices of species composition were quantified, including the indices of nutritional structure and individual health status, the water environment quality was divided into 6 levels according to the characteristics of biological integrity (Karr, 1991). In 1984, the River Invertebrate Prediction and Classification Project (RIVP-ACS) was proposed (Wright et al. , 1998) to predict the biomass of macroinvertebrates in a river without any human disturbance with different characteristics of various areas and then the predicted biomass value was compared with the actual monitored value of macroinvertebrates in the river to evaluate the health status of the river. In 1994, the Australian River Evaluation Program (AUSRIVAS) (Simpson et al. , 1999) was proposed to predict the theoretical biomass in a river with the hydrological indices (habitat structure, water flow state, and continuity), physical and chemical parameters, indices of invertebrates and fish aggregates, water quality indices, and ecotoxicological indices.
In general, the evaluation based on these indices can obtain intuitive results. The obtained biomass reflects the available resource from a water body, and provides the basis for subsequent fishing or protection. In these evaluation systems, only the changes in biomass in water bodies, especially invertebrate biomass, are considered, but whether invertebrates are index species for the habitat is not considered. Therefore, these systems cannot accurately reflect the stress on river ecosystems.
In green space evaluation, the symptoms of land diseases can be evaluated with key indices such as erosion, fertility loss, hydrological anomalies, infrequent outbreaks or inexplicable local extinctions of certain species, and degradation of agricultural products and forestry products (Carmony, 1992). However, due to the economic development, both greening construction and environmental protection should be considered equally. Green coverage rate, green space rate, and park area per capita should be introduced to the evaluation index system so as to improve evaluation results (Zhang, 2010). Existing green space evaluation index systems often only focus on the quantity of green spaces and ignore the quality of green spaces, so they cannot meet the requirements for building a high-quality ecological city in the new era. Therefore, in the future subsequent evaluation system, quantitative and qualitative indices of water bodies and green spaces should be selected and the interaction between water bodies and green spaces should be comprehensively considered to reflect the complex structure and functions of the blue-green fusion space.