Vegetation Restoration Of The Reclamation Area In The South China Muddy Coast

The vegetation restoration of muddy coast reclamation area in the south China is urgent and difficult,mainly appears in the following aspects.(1)Muddy coast has become a main target of "artificial land" because of its smooth topography,large intertidal zone area,large amount of resources,and rapid deposition speed;(2)Large proportion of reclamation area is muddy coast and the southern shore line changes more than the north,so it is urgently needed to be repaired;(3)The soil in the muddy coastal enclosure is derived from the dredging,that is,the tidal flat sediment,which have characteristics of high salt content and poor ventilation,and has a stress effect on plant growth;(4)Little is known regarding the influences of heavy rainfall in the southern China on soil leaching.If imitate the north or northwest inland large-scale setting up the underground salt bed,landfill and other high-priced practices,will it cause waste of resources?(5)There is no supporting theory for vegetation restoration in the muddy coastal fill area in the south,and are lacks of different types of plant combinations.In order to bring out a practicable plant configuration scheme in muddy coastal fill areas under the condition of heavy rainfall in southern China by investigating the effect of rainwater on soil desalination in different stages of vegetation restoration,and testing the desalination efficiency of different remediation measures.The following work has been done.(1)With the restoration of receding ponds in the south Hangzhou Bay as the main study areas,the changes of 4 seasons in the 5 restoration stages(tidal flat,ponds in use,and restoration of the first,third and seventh year)were investigated by the method of space conversion into time.The survey indexes include soil salinity,moisture content,pH,bulk density,organic matter and other soil physical and chemical factors,groundwater depth and salinity,plant community structure,plant growth and so on.In addition,the local daily precipitation and evaporation in 2017 were recorded too;(2)Taking the construction real estate and park in Qidong,Jiangsu as an example,the soil desalination and plant growth in different years under different projects after the reclamation were observed;(3)Select suitable plants in the muddy coast reclamation area according to the surveys of vegetation restoration in different bays in the South;(4)By comparing the desalination conditions of different restoration measures and stages,this research puts forward suitable desalination measures and plant configuration suggestions.The main results are as follows:(1)According to soil physical and chemical factors and plant manifestation,soil salt content was higher than 6 g/kg,root rotting,root-stem black rot,leaf scorching and so on.The main causes of death of early cultivated plants during vegetation restoration in muddy coastal fill areas were high salinity and low oxygen content in soil.(2)The annual presipatation measured on the south coast of Hangzhou Bay in 2017 was 1762.9 mm,and the evapotranspiration ratio was 0.56.Compared to the initial soil,the desalinization rates of 1 year after restoration of 0-20 cm?20-40 cm and 40-60 cm soil layers were 4.57%,11.69%and 24.30%respectively.2 years later,the desalinization rates of the three layers were 37.50%,34.26%and 29.99%compared with the original ones.And after 7 years,the desalination rates of the 3 sayers were 91.33%,0.88%and 81.40%,respectively.These desalinization rates indicated that the leaching and desalting effect of soil were obvious during vegetation restoration.The elution and desalination effect is obvious.During the period of 0-7 years,the salinity of groundwater decreased from 9 g/kg to 1.3 g/kg.However,the problems toward soil alkalization and low content of soil organic still existed in different remediation stages.Based on the actual desalination rate in Hangzhou Bay,it is estimated that it takes about 5 to 6 years for 0-20 cm layer and 20-40 cm layer to desalinate to 1g/kg,and about 7 years for desalting from 40-60 cm to lg/kg.(3)Despite the plant communities in this area are disturbed based on the analysis of the succession of the plant communities and plant composition of family and genus,it is still a positive succession.The overall growth of Hibiscus hamabo showed a significant improvement at first and then decreased slightly while the growth of Nerium oleander improved gradually.RDA analysis showed that the growth was mainly affected by particle size factors.It was inferred that the direct influence factors should be soil aeration determined by particle size content,but had little effect on salinity and no significant correlation.It is possible that the soil salinity gradient is within the salt tolerance range of the H.hamabo.(4)Through field and literature surveys,266 species(including 2 varieties)of 83 families,204 genera,83 species of muddy shoreline reclamation areas were selected.The target and type of restoration should be ascertained when planting.Considering climate.reclamation and restoration time,micro-environment,etc.are critical to plants selection and allocation.The configuration must be consistent with the scientific nature of succession and the characteristics of coastal environment.(5)The three types of desalination-free physical desalinization measures are "do not raise the topography","do not raise the terrain + dig trenches," and "elevate the terrain + dig drains".Under natural rainfall showers,the highest desalination rate is achieved by the method of "elevate the terrain + dig drains".(6)The way of vegetation restoration in the southern muddy coastal enclosed area,namely,“elevating terrain,river channel and furrow + stage planting.”is recommended rather than adopt the high-cost method such as the replacement of the soil and the other high cost due to the strong rainfall in the south and the low ratio of evapotranspiration.The main plant configurations of different stages are as follows:early reclamation stage should pay full attention to the role of soil improvement,selecting halophytes and green manure plants;in the medium term,interplanting plants with high salt tolerance landscape effect should be considered;lastly,we must pay attention to the overall consideration of all elements of the system and choose animal friendly plants.Vegetation restoration can make full use of the municipal measures of underground drainage pipe,combine with the roadside trees and shrub grass near the main road.Film mulching is needed to prevent secondary salinization when planting arbor.The follow-up study can summarize and integrate engineering techniques such as soil desalination and plant conservation,plant selection and collocation through different types of vegetation restoration cases to form a more practical technical system.