Simulation Of Vegetation Change And Its Ecology Effect In Yangtze Estuarine Wetlands

In the past several decades, the natural drives, such as global climate change, sea level rising, sediment and runoff changes of the Yangtze River and vegetation succession, and anthropic drives, such as the Jiuduansha Nature Reserve’s setting up, reclamation, deep water navigation channel and sea bridges’ construction exerted a great influence on the ecosystem service of coastal wetlands in the Yangtze Estuary. In order to investigate the possible impact on the coastal wetland in the Yangtze Estuary by these great changes, we based on the results of classifying remotely sensed images of 1980,1990,2000 and 2010, then analysised the changing of the coastal wetlands systematicly. After that, we use Dyna-CLUE model and CA model to simulate the saltmarsh wetland landscape change, aim to different district we set up different time, different methods and different scenarios as (1) in 2020 we select East Chongming Island and Nanhui nearshore using the Dyna-CLUE model and set up current trend, ecological protection and strength reclamation scenarios; and in order to predict the change of Jiuduansha Nature Reserve we choose CA model and set up only one scenario the ecological protection. With the previous result of wetland’landscape we evaluate relative ecosystem service functions like carbon storage, sediment accumulation and wave attenuation; (2) during 2030-2100, we modified the CA model and set up the scenarios of the current trend, different sea level rise(according to the fifth IPCC report), the first extreme conditions(the coastal wetlands in the Yangtze Estuary suffer from the half rate of silting and the highest sea level rise), the second extreme conditions(the coastal wetlands in the Yangtze Estuary suffer from one quarter rate of silting and the highest sea level rise) to simulate the landscape change in the Yangtze estuary. Then we evaluate the possible impact of these changes will have on relative ecosystem service functions like carbon storage, sediment accumulation and wave attenuation. The main results showed that:1. Under different scenarios of reclamation, the wetlands of the Yangtze estuary will develop in different levels by 2020. The area of wetlands under the scenario of ecological protection will be much more larger than that under the scenario of existing reclamation strength and intensified reclamation mode. So if the strength of reclamation could decrease properly, it would be better for the development and protection of the salted marsh. The total area of natural wetlands will be 163 km2 by 2020 under the scenario of ecological protection, of which the area of Spartina alterniflora, Scirpus mariqueter and Phragmites australis will be 75 km2,32 km2 and 56 km2. The total area of the scenario of existing and intensified reclamation well be 151 km2 and 100 km2. Under these two scenarios, the area of Spartina altemiflora and Phragmites australis will be 151 km2 and 100 km2, both of which are larger than the area of Scirpus mariqueter. Because of the development of vegetation is better for sediment, the area of wetlands of ecological protection scenario will increase most quickly. The area of Spartina alterniflora will decrease under the scenario of existing and intensified reclamation, which indicates that reclamation Moderately will be benefit to control the invasion of Spartina alterniflora.2. The simulation between 2030 and 2100 showed that under the scenario current trend the area of vegetation will be 440 km2,645 km2 and 1031 km2. Under the different kinds of sea level rise, the saltmarsh vegetation growth nearly the same, however the input sedimation will influence the growth. Considering the sea level rise is not significant comparing with the deposition rate, under different sea level rise the area of wetlands will be similar by 2030-2100. But the decresing of runoff and sediment from the Yangtze River will have an affect on the development of vegetation. As the level of sea level rising is much less than the deposition rate, the area change under different scenarios are similar. For example, the total area of wetlands will be 300 km2,400 km2 and 820 km2 by 2030,2050 and 2100 under the forth scenario (the highest level of sea level rising). However, the result under the scenario of half runoff and sediment will be quite deifferent. The total area of wetlands of 2030,2050 and 2100 will stablly be 298 km2,305 km2 and 309 km2. And under the scenario of one quarter deposition rate, the area of vegetation will decrease again, and the number will keep stable at about 278 km2 between 2030-2100.3. The ability of carbon storage, sediment accumulation and wave attenuation at the Yangtze estuary between 2030 and 2100 change significantly. Considering under the scenarios of different sea level rise the area of vegetation is not change significantly so we take the highest sea level rise as the example to introduce. Under the scenarios of two extreme conditions the area of vegetation and its structure will not change significantly so we focus on the first extreme condition.(1) We estimate that under the existing trend that in Qidong nearshore, East Chongming Island, East Hengsha nearshore, Jiuduansha and Nanhui nearshore, the ability of carbon storage of the Yangtze estuarine wetlands will be 94* 104 t, 144×104 t and 241×104 t by 2030,2050 and 2100. During this period the total amount of suspended particulate matter adhered by vegetation will increase, from 33 441 t in 2030 to 113 572 t in 2100; however the amounts of sediment accumulation present the same trend at this time as 26×106 m3,42×106 m3 and 66x 106 m3. Because the different sea level rise showed little affect on the ecosystem services, so we take the highest sea level rise as the example. In 2030,2050 and 2100 the ability of carbon storage of the Yangtze estuarine wetlands will be 74×104 t, 93×104 t, and 183×10 4 t. During this period the total amount of suspended particulate matter adhered by vegetation will increase, from 21 468 t in 2030 to 90 362 t in 2100; however the amounts of sediment accumulation present the opposite trend as 15×106 m3,14×106 m3 and 13×106 m3, respectively. Under the scenario of the first extreme condition, the decrease of incoming sediment and half silting rate as well as the highest sea level rise, in 2030,2050 and 2100 the ability of carbon storage of the Yangtze estuarine wetlands will be 71×104 t,76×104 t, and 82×104 t. The total amount of suspended particulate matter adhered by vegetation will increase a bit, from 24 451 t in 2030 to 32 190 t in 2100; however the amounts of sediment accumulation present the opposite trend as 16×106 m3,15×106m3、14× 106 m3, respectively.(2) We estimate that the ability of wave attenuation by salt marsh will increase from 2030 to 2100 under the scenario of current trend. Under normal tides, the length of seawall without enough vegetation protection will decrease from 261 km in 2010 to 124 km in 2100. The length of seawall without enough vegetation protection under storm surge scenario will decrease from 336 km in 2010 to 124 km in 2100. Under the scenario of highest sea level rise, under normal tides the length of seawall without enough vegetation protection will decrease to 152 km and under storm surge conditions the length of seawall without enough vegetation protection will decrease to 156 km. Under the scenarios of extreme conditions, the decrease of incoming sediment and half silting rate as well as the highest sea level rise will pose greater influence, under normal conditions the length of seawall without enough vegetation protection will increase to 323 km and under storm surge conditions the number will further increase to 352 km.Overall, under the scenario of current trend the result of simulation showed that the area of saltmarsh wetland in the Yangtze estuarine will increase in 2030 and 2100, and the vegetation structure will change seriously. Meanwhile, the ability of carbon storage, sediment accumulation and wave attenuation will all increase. However under the scenario of sea level rise, this trend will not change but the speed will change. The result of extreme conditions would provide scientific basis for wetland resource protection and the trade-off among different ecosystem services.