Phosphorus Distribution In Soils And Sediments From Coastal Areas In Eastern China

Reclamation of coastal land is one of the most common ways to obtain available land resources in China. The human activity and intervention play important roles in the evolution of reclaimed soils. As one of the major nutrients for crops, phosphorus (P) also influences the aquatic environment quality of coastal areas. Thus, it is important to do research on the variation and distribution of total P (TP) and P forms in reclaimed soils from coastal areas in the scale of hundred years. In this study, coastal reclaimed areas (Dafeng, Rudong, Cixi and Yueqing Bay coastal reclaimed areas) in Eastern China were chosen to systematic collect surficial soil and sediment samples. The samples in different reclaimed history areas from Dafeng, Rudong and Cixi reclaimed areas, were used to conclude and generalize the variation mechanisms of TP contents after tidal land reclamation. Different medium samples (reclaimed soils, river sediments and intertidal sediments) from Yueqing Bay were collected to investigate distribution patterns and discrepancies of TP and P forms. Our findings could make suggestions for sustainable utilization of reclaimed soil resource to a certain extent. Upon this study, conclusions were exhibited as followed:1. After reclamation, contents of Cl, Na2O and CaO, and values of pH decreased significantly, and the trend of OM was opposite in soils and sediments from all the coastal reclaimed areas (Dafeng, Rudong and Cixi reclaimed areas). The variation of particle size was consistent between Dafeng and Rudong reclaimed areas that with the increase of reclamation years, contents of clay and silt kept rising but opposite to the sand ones. Cixi reclaimed area had the different variation of particle size that at the beginning of reclamation history, contents of clay and silt decreased and then kept rising with the development of reclamation history, and contents of sand were opposite. Contents of MgO, Al2O3, SiO2, K2O, CaO and TFe2O3 were all correlated to the particle size distribution.2. With the increase of reclamation history, contents of TP were increasing in soil samples from Dafeng, Rudong and Cixi reclaimed areas. However, the accumulation speed and original contents of TP were different among the three reclaimed areas, possibly ascribing to the discrepancies of material sources, land-use options, planting crops, P fertilizer applications, etc. Due to the continuous and excessive input of P fertilizer, contents of TP were accumulating in such reclaimed areas.3. The results of geo-statistics showed that the ratio of nugget and sill value of TP in soil and sediment samples from Dafeng reclaimed area was only 6.6%, explaining the high spatial autocorrelation. The ratio of nugget and sill value of TP in soil and sediment samples from Rudong reclaimed area was 100%, showing the weakly spatial autocorrelation due to the discrepancies of land-use types, planting crops, P fertilizer applications, etc. The ratio nugget and sill value of TP in Cixi reclaimed area was 38.8%, exhibiting the medium spatial autocorrelation because of the interaction of structural factors and random factors.4. Among the three types of mediums (reclaimed soils, river sediments and intertidal sediments) from the Yueqing Bay reclaimed area, there were markedly distinct contents of Ex-P, Fe-P, Ca-P and Org-P rather than De-P and TP. Although TP in different mediums were no significant difference, they were correlated to different P species and the relative abundances of P species were unlike. In reclaimed soils, contents of TP were correlated to contents of De-P and the relative contents of P species were De-P>Ca-P>Fe-P>Org-P>Ex-P; in river sediments, TP was positively correlated to Fe-P and Org-P, and the relative contents of P species were De-P>Fe-P>Org-P>Ca-P>Ex-P; in intertidal sediments, TP had no correlation with any P species, and the relative contents of P species were in accordance with the ones of reclaimed soils.5. The variations of physical and chemical properties, anthropogenic P inputs, rapid soil evolution causing by the reclamation activities, etc. possibly led to the discrepancies of contents of TP and P species in mediums from different reclaimed areas.6. Influenced by the anthropogenic reclamation, intertidal sediments rapidly evolve into cultivated soils in coastal reclaimed areas. P fertilizer application, crop cultivation, evolution of soil properties, etc. resulted in the increase of TP contents with the development of reclamation history. However, the contents of available P had no significant increase in such scales of reclamation history. Thus, we concluded that reasonable plan of P fertilizer application to maintain nutrient balance and to assure the supply of available P in soils was the basic guidance of sustainable development of reclaimed soil resources.