Grain Size Distributions Of Soils And Sediments And Their Relationship With Major And Micro Elemental Compositions In A Typical Reclaimed Coastal Area

Grain size distribution of soil and sediment is a very important parameter. The analysis of grain size distribution can provide the basis for understanding the physical, chemical and biological characteristics of soil and sediment. The article takes an example of Dafeng City which is a typical reclaimed zone of tidal flats in Jiangsu Province. We divided the study area into A, B, C, D, E five sections on the basis of reclaimed history, representing intertidal zone,10years,30years,60years and95years of reclamation separately. By analyzing the particle size distributions(PSD) of surface soils and tidal sediments, this article aimed to reveal the impact of reclamation age and land use on the PSD, and discuss the correlation between PSD and chemical compositions of soils and sediments. The main conclusions are:1. According to the international standard of soil texture classification, the soil textures of reclamation district mainly are loam and clay loam, which the proportions are42%and39%separately. From the district A to E, which the direction is from sea to land, the silt contents of samples increasing, and sand contents decreasing. The variation of silt and sand contents from district A to C is significant, but from district C to E non-significantly. In addition, the variation law of clay content is not obvious in the study area, and the difference among reclamation areas is non-significant.2. Owning to the impact of hydrodynamic and plant, the clay and silt contents of intertidal sediments increase from sea to bank, which the sand contents decreasing. So, the grain size of sediment is tapering in this direction. 3. The analysis result of PSD difference among different land use styles and reclamation zones of different years was:From district C to E, the silt content of agricultural soil increase gradually and sand content decrease with the increasing reclamation years, but the variation is very small. In the district C, the silt contents of fishpond samples significantly below the dry farm and paddy samples which the PSD between them have no obvious variance, while the sand contents are higher. For the whole study area, the order of silt contents of different sample types from large to small is farmland, fishpond and tidal flat, while the sand contents on the contrary and the clay contents have no obvious difference. Hence, the spatial distribution of PSD of soil and sediment influenced mainly by land use while the reclamation ages affect weakly.4. The correlation analysis of grain size and constant element content showed that the concentration of CaO had non-significant correlation with silt content and the degree of correlation between organic material and clay was significant. Except CaO and OM, the remaining elements had highly significant correlation with clay, silt and sand. The Na20and SiO2tended to be enriched in sand fraction, and the rest elements tended to be enriched in fine grain fraction.5. The regression analysis between constant element and grain size showed: Through simple regression and multiple stepwise regression, the concentration of constant elements can forecast the clay, silt and sand content well. The constant elements can be the indicators instead of the grain size contents of soils and sediments.6. The correlation analysis between PSD and concentration of trace elements showed that most elements presented significant or highly significant positive correlation with clay contents except P, Sr and B. The concentration of trace elements increased with the increasing of clay content.7. The correlation between grain size content and concentration of elements such as Cr, Co, Ni, Cu, Zn, Pb, Cd, As and Hg which are closer with human activities shows differences in tidal flat and reclamation zone. Cr concentration by clay in reclamation zone is greater than which in intertidal zone, while the other eight elements present well correlation with clay and silt fraction for intertidal sediments. The enrichment role of elements by clay from strong to weak is Cu>Zn>Ni>Co>Hg>Pb>As>Cd>Cr separately for intertidal sediments, which for reclamation district soil samples is Ni>Cr>Co>Cu>Pb>Zn>As>Cd>Hg. 8. On the basis of significant concentration of trace elements by clay and gradually eliminate method, the article dicussed the quantitative method of distinguishing the samples of abnormal trace elements contents. And take an example of Cu, achieving good result and accurately indentifying the abnormal element points and reasons by applying the new method.