Study On Changing Characteristics Of Soil Physicochemical Properties During Degradation Process Of The Flooding Wetland In Gahai

Wetland is a unique ecosystem that formed by land and water interactions, and ithas special ecological environment effect and function, which plays an important rolein adjusting the global climate change. In recent years, its serious deterioration hasbecome one of the major ecological problems in China. Wetland soil has specialphysicochemical properties, which play an important role in maintaining the balanceand succession of wetland ecosystem. Studying changes of soil physicochemicalproperties during the wetland degradation not only help us understand the causes ofwetland degradation, but also provide a theoretical basis for the protection of wetlands.Flooding wetland is one of the important types of wetlands and an important partof the land and water natural landscape. Flooding is an important factor of maintainingflooding wetland ecological system. The area of flooding wetland of Gahai is12281hm2, which accounts for28%of total wetland area of Ghai. It is extremelyimportant to adjust ecological environment of Gahai wetland. The research choseflooding wetland of Gahai as the study subject and analyzed the changes of soilphysicochemical properties during the degradation process by using the principle ofrestoration ecologyl and method of combining field survey with laboratory analysis tomaster the response of soil for wetland degradation. By the research, the conclusionswere as follows:(1) In the degradation process of Gahai’s flooding wetlands,0-40cm, soil bulkdensity gradually increased with the increasing degree of degradation and porositygradually decreased. The average bulk density of soil was moderate degradation（0.61g/cm3）＞severe degeneration（0.56g/cm3）＞mild degeneration (0.39g/cm3)＞non-degradation (0.36g/cm3). Soil capillary porosity was non-degradation（29.07%）＞moderate degradation （26.86%）＞mild degeneration （24.85%）＞severedegeneration（22.27%）. Venting quality was non-degradation（28.92%）＞moderatedegradation（28.26%）＞mild degeneration（24.60%）＞severe degeneration（23.70%）.While non-capillary porosity was severe degeneration（3.35%）> moderate degradation（3.06%）> non-degradation（2.90%）> mild degeneration（2.21%）.(2) As the aggravation of degradation，water holding capacity and storagecapacity Gahai wetlands decreased gradually.0-40cm, the average maximum waterholding capacity of soil was non-degradation（90.16%）＞mild degeneration（69.20%） ＞moderate degradation（49.78%）＞severe degeneration（45.53%）. Capillary waterholding capacity was non-degradation（80.96%）＞mild degradation（63.52%）＞moderate degradation（44.63%）＞severe degeneration（39.61%）.Water content wasnon-degradation（80.60%）＞mild degeneration（62.93%）＞severe degeneration（34.10%）＞moderate degradation（34.03%）, what’s more, the soil water holdingcapacity and water content of non-degraded and degraded wetlands has significantdifference. The average soil capillary storage water capacity was non-degradation（3507.50t/hm2）＞moderate degradation（3326.46t/hm2）＞mild degradation（3113.24t/hm2）＞severe degradation（2928.95t/hm2）.Non-capillary storage watercapacity showed severe degradation （431.01t/hm2）＞moderate degradation（431.01t/hm2）＞non-degradation（303.81t/hm2）＞mild degradation（255.22t/hm2）.(3) After the degradation of wetland, soil nutrient lost and fertility declined. Inthe process of flooding wetland degradation, the wetland soil available N, P, K, totalamount of N, P, K, the content of SOC and MBC were all decreased with thedegradation of wetland. It showed non-degradation＞mild degradation＞moderatedegradation＞severe degradation. Compared with the non-degradation floodingwetlands, the soil average total N of mild degradation, moderate degradation andsevere degradation decreased by13.30%、29.88%、30.67%, total P decreased by14.73%、26.50%、28.70%, total K decreased by0.17%、5.05%、8.06%, SOC decreasedby7.71%、16.40%、17.63%, MBC decreased by22.05%、40.07%、52.62%. The soilC/N ratios of all degraded flooding wetlands were higher than non-degraded wetland.As the degradation of wetland, the mineralization rate of C, N and other soil nutrientelements accelerated. And a large number of nutrient elements lost because ofmineralization.0~40cm, the change range of soil N of non-degraded flooding wetlandsin the vertical direction were greater than degraded wetlands. The difference of soil pHand salinity between the non-degradation and degradation was significant(P＜0.05).Compared with non-degradation flooding wetlands, soil pH value of milddegradation, moderate degradation and severe degradation decreased by2.02%、2.40%、2.52%, salinity increased by33.33%、133.33%、166.67%.(4)As the degradation of flooding wetland of Gahai, wetland soil became tightgradually, vent ability and water permeability declined gradually, the water conservation function of soil and soil fertility decreased, soil environment becameharsh, and soil quality developed towards the direction of malignancy.