Integration of water quantity and quality in environmental flow assessment in wetlands

Abstract

Hydrological regime is a driving factor in wetland ecosystems. Its excessive alteration will lead to severe degradation of wetlands. Assessment of environmental flows is essential for wetland protection, recovery, and restoration. In order to solve the existing problems of traditional methods, such as rarely considering water quality and ecosystem status, a new method was developed to assess the environmental flows of wetland that will reflect the synergistic effect of water quality and quantity on ecosystems. The proposed method was applied to the Baiyangdian wetland, the largest shallow lake and wetland complex in the North China Plain. The main steps are as follows: 1) Based on the maximum distance cluster results of water quality data and organism data, the Baiyangdian wetland was divided into five regions. The key species were distinguished by a series of simulated removal experiments using the Ecosim model. 2) Integrating the typical monthly average water level and the surface water quality standards of Classes III, IV, and V, 21 integrated scenarios were designed. Aquatox model was applied to analyze the response of phytoplankton, zooplankton, zoobenthos under different circumstances of water levels, NH3, NO3-, PO43-, BOD5 and other environmental factors, illustrating the temporal and spacial distribution of biomass, the status of structure and functions of ecosystem under the synergistic effect of water quality and quantity scenarios. 3) Based on the variation trend of assessment indicators such as total primary production/total respiration, total biomass/total production, biomass of zooplankton/biomass of phytoplankton in different regions, and the weighting factors for each region, finally we concluded that 6.70m can serve as the minimum ecological water level in Baiyangdian, and 7.19-9.55m can serve as the range of appropriate ecological water levels. These ecological water level results can guarantee the stability of the ecosystem structure and balance without having the reverse succession, which also has an ecological significance.