Spatial modelling of the regulating function of the Huangqihai Lake wetland ecosystem

The regulating function is the least understood but probably most valuable service provided by an ecosystem. To estimate the impact of externalities on the regulating function of a wetland, we modelled the interdependence between activities that affect wetland characteristics and land utilization patterns. Nature-based solutions (NBS) can provide benefits for society, the economy and nature. The NBS solution for wetland bioremediation is proposed through a combination of ecosystem value provided by nature-based or artificial arable land. We constructed a model to simulate the dynamic spatial and temporal changes in the regulating function of a wetland to study the impact of agricultural and fishing activities on the functions and services of a wetland ecosystem. The model was used to determine the relationship between land use change, wetland range, water quality, and fish stocks. Huangqihai Lake (HQHL) is a relatively isolated lake in an area interlaced with agriculture and pasture zones. From 1973 to 2014, the “shrinkage” of the water area of HQHL approached 60%. Under the influence of humans and natural disturbances, the HQHL wetland faced enormous ecological risks, water pollution, area reduction, sharp biodiversity reduction, and fish extinction. The phosphorus (P) concentration seems to be a key factor affecting both the reed growth in the nearshore areas of the Huangqihai Lake wetland and the breeding of phytoplankton in the core lake water area. Dividing this value by the 25,821 ha of the core wetland area affected by the reclamation, the cost per unit of lost fish production is USD$166/ha/yr. After deducting the externalities of the fishery, the net sustainable income from the conversion is USD$1717/ha. The spatial distribution of nutrient load externalities varies with the use of wetlands. In terms of fishery value, the additional nutrient load associated with the conversion of wetland uses would result in a reduction of at least 8% of the maximum sustainable yield. The conversion of wetland uses resulted in the loss of nutrient buffering functions. To compensate for the farmland's nutrient load buffer service, the government should provide arable land farmers USD$8.1 M/yr. It is theoretically feasible to implement an ecosystem service payment system that can effectively compensate for the loss of nutrient buffer function caused by the conversion of wetlands. The approach based on BNS we described may also have value in other ecosystems where regulatory functions include similar mechanisms.