3.2.1. PSR model and indicator system
The Pressure-State-Response (PSR) model is based on the concept of feedback loop. Pressures denote the human activities which will change the state of environmental resources and lead to the societal and policy responses [30]. The PSR model provides a means for selecting and organizing data and indicators in a uniform framework for decision makers and the public and ensures the important factors are not neglected. The PSR framework was used as a starting point for selecting environmental indicators and then was modified for application in a sustainability context. Ecosystem health which determines the overall viability of environments was introduced to the PSR model to correct the inherent limitations [15, 31]. The continuous dynamic interactions between lacustrine wetlands and environment (i.e. pressures and responses) determine whether the state is sustainable (Figure 2). In this way, the indicator system couples environmental and development issues to enable better informed policy decisions and human behavioral changes to be implemented at appropriate levels to achieve sustainability. The sustainability indicators of Yilong Lake are identified based on the conditions in the Yilong Lake area (Table 2).