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.