Ecological water replenishment effect of Sanhuanpao wetland in Sanjiang plain
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Abstract:
A serious degradation and significant decrease in wetlands areas in Sanjiang Plain of China have been reported.Water shortage is the key cause of wetland degradation.The natural inflow can not meet the actual water demand of wetland.Thus,it is imperative to replenishment the ecological water of the wetland.There may be conflicts between ecological and agricultural water use in the region,and water resources are preferentially used for agriculture in the region.Therefore,it is necessary to select the appropriate location and timing of water replenishment to make a planned water replenishment,to limit the ecological water resources that can be used to the maximum extent and the wetland can achieve better water replenishment effect.It requires the study of ecological water replenishment schemes based on water replenishment effect analysis. The characteristics of regional water demand and the surrounding hydraulic connection were analyzed,and the reasonable water replenishment period and location were selected to design the water replenishment scheme.Three water replenishment schemes were determined;one-time water replenishment in April (scheme 1),monthly water replenishment on demand from April to October (scheme 2),and staged water replenishment in April and July (scheme 3).MIKE 21 water flow evolution model was constructed through grid division,terrain interpolation,roughness selection,boundary setting,model verification,and other processes to realize the water flow evolution simulation of ecological water replenishment process in Sanhuanpao wetland,and to show the dynamic change process of water replenishment area and water depth.The GIS platform was used for numerical statistics and analysis of the wetland water replenishment effect. In schemes 1 and 3,the water replenishment flow was large and the spread was fast due to the relatively concentrated water replenishment.The flow had flowed to most wetland swamps areas containing the core areas I and II of the wetland before the period of large water demand from May to July.In scheme 2,due to the small amount of water supply on demand each month,the diffusion of small flow could not supply the wetland in time due to a certain lag.Before July,the water area and water depth are small,and the water demand process and water supply process are not synchronized due to the delay of water supply spread.In scheme 1,the water depth in the low-lying area was large in a short time,and a large amount of water supply caused the inundation of some central and northeastern cultivated land,while schemes 2 and 3 did not cause the inundation.The water area of the wetland increased significantly after water replenishment under the three schemes.The water replenishment areas of schemes 1 and 3 exceeded 20 000 hm2 in May,and it could be considered that the water flow had flowed into the whole protected area.Subsequently,the water area of scheme 1 decreased gradually due to evaporation,and the water area of scheme 3 was larger as a whole after water replenishment again.However,the water flow spread in scheme 2 was lagging,the water area increased gradually after water replenishment,and the water area was small in the early stage.Until July,the water area reached a large range,which is about 16 000 hm2.In terms of water depth,scheme 1 had a larger water depth in many areas,and the water depth in most areas of the eastern and western core areas of the reserve was more than 0.4 m.The water depth in different areas was quite different.After concentrated replenishment in April,the water depths of core areas I and II increased rapidly from April to July,reaching 0.62 m and 0.46 m,respectively,which may cause damage to some animal and plant habitats.In scheme 2,the water depth of the wetland increased slowly after monthly replenishment.Before July,the water depth of the two core areas was basically below 0.20 m,which was not enough to meet the water requirements of major birds and vegetation.In the later stage of replenishment,the water depth of more areas was distributed in 0.1-0.2 m,and the distribution of different water depths was gradually uniform.In scheme 3,the water depth increased from April to mid-May,and the water depths in the core areas I and II increased to 0.35 m and 0.28 m,respectively.The water depths in the two areas decreased from the end of the first replenishment to August,and the water depths increased to 0.44 m and 0.30 m,respectively,after the second replenishment.The water depth decreased again due to evaporation consumption.The process could meet the requirements of the suitable water depth for the rare waterfowl and dominant vegetation in the Sanhuanpao wetland. The staged water replenishment scheme in April and July has the best simulation effect.Under three schemes,the average water area of scheme 3 is the largest,which is closer to the recovery target,followed by scheme 1 and scheme 2.In scheme 2,the ondemand replenishment flow has a long spread time,and the process of water demand and replenishment is not synchronized.schemes 1 and 3 can replenishment the water demand of wetland to the water demand area in time,which can overcome the problem of flow hysteresis.However,one-time replenishment of scheme 1 will cause inundation of surrounding irrigation areas,and there are more areas with lower and higher water depths,and the spatial and temporal distribution of different water depths is uneven.The M-type characteristics of water demand process are more consistent under the staged replenishment scheme in April and July.By analyzing the suitable water depth range of rare waterfowl and dominant vegetation in the core area,the change process of water depth after water replenishment in this scheme can better meet the suitable living conditions of organisms in the region and create a suitable habitat environment.
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