| Global climate has changed dramatically, which is caused by the increase of greenhouse gases, and global warming is one of the most significant global climate change performance. Global warming and its impact are the most serious environmental problems currently that human face, in which soil carbon pool plays an essential role. Therefore, all countries and regions around the world undertake with varying degrees the study of soil organic carbon in order to improve or solve global environmental and ecological problems caused by global climate change.The soil organic carbon and its labile C can sensitively reflect the changes of soil carbon pool, so this research based on the typical natural tidal wetlands and the different time series farmland derived from wetland on south coast of the Hangzhou Bay, was carried out to survey natural wetlands and different reclamation history farmland, then collect soil samples of mudflat under Phragmites australis, Spartina alterniflora, Scirpus mariqueter, and blare mudflat, and different reclamation history (10,40,60,120 a) farmland respectively, analyzing the changes of soil organic carbon (SOC), soil dissolved organic carbon (DOC), soil readily oxidizable carbon (ROC) and light fraction organic matter (LFOM). Besides, it was also carried out by using Geostatistics and Geographical Information System(GIS) technologies to explore spatial variability of soil organic carbon content in different soil layers (0～20,20～40,40～60,60～80,80～100,0～100 cm) in Cixi City, on south coast of the Hangzhou Bay. Results show that:0-50 cm soil layer, the average SOC content in mudflats under Phragmites australis, Spartina alterniflora, Scirpus mariqueter, and blare mudflats were in the followed by 3.87～5.29 g·kg-1,6.15～6.78g·kg-1,4.33～5.06 g·kg-1,4.21～5.25 g·kg-1 and the SOC content of Spartina alterniflora was higher than the other types in the same soil layer; The DOC and LFOM mean content ranges of Spartina alterniflora were 90.69～104.24 mg·kg-1, 2.00～2.95 g·kg-1 respectively, and higher than Phragmites australis, Scirpus mariqueter, Blare mudflats in the same soil layer, however, the ROC content of blare mudflats (2.06～2.30g·kg-1) was higher than the other vegetation types; The ratios of DOC and ROC to SOC between Phragmites australis, Spartina alterniflora, and Scirpus mariqueter varied considerably in different layers, the DOC proportion of blare mudflat was relatively lower and its ROC proportion was relatively higher than the other types.The variations of organic carbon active fractions were similar to soil organic carbon substantially and it still existed differences in different reclamation history farmland. Soil organic carbon and its active fractions showed an increasing trend with reclamation time increasing, but the increase was diminished after 40 a and their contents tended to be relative stable afterwards. As to 0-10 cm soil layer, soil organic carbon, dissolved organic carbon, readily oxidizable carbon and light fraction organic matter increased 40.43%, 14,23%,25.47%,13.68%, respectively. Soil organic carbon and its active fractions content were mainly distributed in 0-20 cm soil layer, but dissolved organic carbon presented slightly difference. The ratio of dissolved organic carbon to soil organic carbon reduced with reclamation time increasing, however, the proportions of readily oxidizable carbon increased. Soil organic carbon was significantly positive related to its active fractions and they all showed significantly positive correlated with total nitrogen, soil moisture content.The average contents of soil organic carbon in the soil layers varied from 3.49 to 7.95 g·kg-1 in the Cixi area, with variation coefficients ranging from 54.51% to 67.34%, indicating a moderate degree of variability. Geostatistical analysis reveals that the value of nugget effect varied from 0.141 to 0.372, displaying strong spatial correlation, and that the optimal semi-variance models for the soil layers from the surface down to the bottom of a soil profile were Gaussian, exponential, exponential, Gaussian and spherical model respectively; The results of Kriging demonstrate that soil organic carbon displayed an increasing trend from beach to inland in all the soil layers, and a decreasing trend with soil depth in a soil profile, and was distributed in the surface soil layer (0-20 cm) like a band in parallel with the coastline. Both different land use patterns and different reclamation history intensified spatial variability of soil organic carbon.All the findings indicating that the invasion of Spartina alterniflora can further improve wetlands carbon sequestration capacity; with increasing reclamation period soil organic carbon content increased but its stability may decline; the labile organic carbon could sensitively indicate soil organic carbon dynamics characteristics; the spatial variability of soil organic carbon is mainly caused by structural factors in Cixi City. The results are able to provide soil organic carbon reference to the study to understand characteristics of the distribution of organic carbon in soils on south coast of the Hangzhou Bay. |
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