Incorporating a constructed wetland system into a water pollution emissions permit system: a case study from the Chaohu watershed, China

Water pollution emissions permit systems (WPEPS) and constructed wetland systems (CWS) are widely but independently used to balance regional economic development and ecosystem health. In this paper, a watershed scale framework that incorporates a CWS into a WPEPS is proposed for regional economic and ecosystem health sustainability. A strategy that integrates three allocation principles: per capita emissions, economic utility, and water quality contributions, is established for the initial CWS-incorporated WPEPS emissions permit allocations. To quantitatively verify the effectiveness of the CWS-incorporated WPEPS, a bi-level optimization model is formulated, in which fuzzy random variables are employed to describe the system uncertainties. The model is then applied to a practical case in the Chaohu watershed, China, to assess the effects of changing watershed management targets, from which practical insights are obtained on the initial emissions permit allocation strategies and the CWS coordination effects. It has proved that the integrated watershed management of the CWS-incorporated WPEPS is more able to rationally allocate the limited water pollution emissions permits and better balance the Chaohu watershed economic development to ensure ecological health sustainability. The CWS-incorporated WPEPS model under uncertainty can be used to guide local governments when formulating their sustainable watershed management strategies.