| Soil physical and chemical properties change rapidly after tidal flat reclamation. Revealing the characteristics of these changes is essential for the sustainable use of soil on reclaimed land. In this paper, a typical reclamation area of Cixi City in Zhejiang province was chosen as the study area. According to the historical maps and interpretation results from remote sensing, the area was devided into six zones with different reclamation time.276 surface samples and 10 profiles were collected by using the grid method. Soil physical and chemical properties were tested in the laboratory to study the evolution of soil properties under different reclamation time and different land-use as well as the impact factors, which lead to the evolution. The main conclusions are as follows:(1) In the early time of reclamation, the clay content of surface soil decreased significantly, by the sediments of 28.8% drop to 16.1%, and soil texture became rough. The soil silt content of reclamation area showed a rising trend and sand content decreased with the reclamation time increasing, and soil texture became finer. Compared with the new reclamed area, the silt sand content of surface soil reclamaed for over 23 years increased significantly, by 45.1% rising to 53.3%; sand content decreased significantly, by 38.7% declining to 32.5%.(2) After reclamation, the salt content decreased sharply. Reclamed for 1-11 years, the salt content decreased by 70.7% to 5.02 g kg-1. Soil salt content of reclamation area decreased slowly with the reclamation time,and when the reclamation time is over 43 years, the salt content fell to 2.56 g kg-1, which is still greater than 1 g kg-1. Distribution of soil salt content was mainly affected by the length of reclamation year, and local area was affected by land-use.(3) At the early period of reclamation, the pH value increased from 8.36 to 8.74. Soil pH of reclamation area decreased linearly with increasing reclamation time, pH of soil reclamed for more than 10 years has dropped to less than 8.5. In the areas of same reclamation time, land-use has no significant effect on soil pH.(4) The source of the tidal flat sediments may be closely related to the Yangtze River. At the early stage of reclamation, major elements (except Na2O and CaO) content change significantly. Major elements of reclamed soil did not change significantlywith reclamation years increasing.(5) After reclamation, soil organic matter and total nitrogen content decreased first and then increased. The content of organic matter decreased from 12.4 g kg-1 to 8.8 g kg-1, which decreased by nearly 30%. For 30 years after reclamation, the content of organic matter increased to 15 g kg-1 and remained relatively stable. Total phosphorus content continued to increase with the growth of reclamation years, by the 0.68 g kg-1 of new reclamation area rose to 1.14 g kg-1 of reclamation over 43 years. The effect of land-use on total phosphorus content, organic matter is not significant in the same year reclamation area.(6) At the beginning of the reclamation, the content of heavy metals decreased significantly. Soil heavy metal elements content of reclamation area had the trend of accumulationwith increasing duration of reclamation, but they were not more than secondary standard of the national soil environmental quality standard "(GB 15618-1995). Soil heavy metal content of reclamation were observed in the surface layer and the Cd and Hg of surface were significantly enriched.(7) Evolution of soil physical and chemcial properities in reclamaed area on short-term scale is mainly affected by particle size effect, outside material input, bioaccumulation and desalinization. Particle size effect had great impact on Cu, Zn, Pb, Cr and As; organic matter had greater impact on the enrichment of Cd and Hg. |
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