Conclusion
(1) Groundwater exploitation will form a cone of depression, and the water level around it will flow toward the center of the pumping well, which leads to the inversion of the groundwater hydraulic gradient between the wetland and the piedmont plain, and the base flow of the piedmont plain aquifer recharging the wetland decreases rapidly. A groundwater divide is formed between the wetland and the piedmont plain. With the increase in pumping time, the cone of depression continuously expands, and the groundwater divide gradually moves toward the wetland until it expands to the wetland boundary. At this time, the surface water of the wetland begins to recharge the piedmont plain groundwater and induces infiltration from the wetland to the piedmont plain. After pumping stops, the water level of the original cone of depression gradually rises due to recharge from the western boundary, and the lowest point of the cone of depression level gradually moves toward the wetland until the groundwater flow direction in the study area returns to west–east.
(2) The impact of groundwater overexploitation on wetland degradation is mainly divided into two parts. One part is the reduced base flow from the piedmont plain aquifer to the wetland, which leads to the reduction in groundwater recharge received by the wetland. The other is the expansion of the cone of depression, which induces the groundwater in the wetland to infiltrate into the piedmont plain aquifer, leading to a reduction in wetland surface water. The reduction in base flow tends to occur rapidly and correspondingly with groundwater exploitation, while induced infiltration has a certain lag. At the beginning of pumping, the effect of reduced base flow on wetland degradation dominates, but with pumping time, the effect of induced infiltration on wetland degradation exceeds that of reduced base flow. After stopping pumping, the effect of induced infiltration on wetland degradation responds immediately and decreases rapidly, while the effect of reduced base flow on wetland degradation still increases briefly for some time and then slowly decreases but its effect lasts for a long time.
(3) The different hydraulic conductivities of aquifers also have an impact on wetland degradation. The effect of reduced base flow on wetland degradation is proportional to the hydraulic conductivity, and the effect of induced infiltration on wetland degradation decreases with increasing hydraulic conductivity. In general, according to the numerical simulations under different hydraulic conductivities, the total water reduction of wetlands increases with increasing hydraulic conductivity. In actual wetland areas, if groundwater exploitation is not restricted or artificial supply measures are not taken, the amount of wetland water will gradually decrease until it is exhausted.