Study on Spatial Variability and Assessments of Soil Nutrients and Heavy Metals in Intertidal Zones
|School||Nanjing Agricultural College|
|Keywords||soil nutrients sediment heavy metals spatial variability nutrient assessment pollution assessment|
Intertidal zones are important land resources which contain plenty of agricultural reclamation areas and aquafarm areas in our country. The study on spatial variability and assessments of soil nutrients in reclamation areas and sediments heavy metals in aquafarm areas of intertidal areas, could improve the efficiency of nutrient use, promote the precision fertilizer in the reclamation area, and strengthen environmental protection in aquafarm areas. Moreover, comprehensive, accurate and objective understanding of the utilization of Jiangsu intertidal zones is not only the foundation of scientific and information-based management but also the precondition of the sustainable use and development in these areas.This study selected Wangzhu reclamation area of Dafeng and Rudong aquafarm area in Jiangsu province as experimental regions, while geographic information system (GIS) and geostastistical methods are combined to study the spatial variability of soil nutrients in Wangzhu reclamation area and heavy metals of sediment in Rudong aquafarm area, meanwhile, the research of comprehensive evaluation of nutrients and pollution evaluation assessments were carried out. The major results were as follows:1. The study on spatial variability of soil nutrients was carried out in Wangzhu reclamation area. The results showed that:The ratios of nugget and sill of Organic matter (OM) and Total phosphorus (TP) were 14.3% and 19% respectively, demonstrating a strong spatial correlation individually; while those of soil pH, Total nitrogen (TN), Total potassium (TK) and Available potassium (AK) ranged from 29.8% and 49.9%, indicating a medium spatial correlation individually. According to the spatial distribution maps of soil nutrients, the characteristics of spatial variability and the levels of various soil nutrients can be intuitively mastered. The content of OM was at moderate and low level, while that of Available nitrogen (AN) was at very low level, however, the contents of AK and Available phosphorus (AP) were high. Therefore we suggested that a bulk of nitrogen (N) and organic fertilizer application was needed, but not for potassium (K) and phosphorus (P) fertilizer in this sampling area.2. Fuzzy comprehensive evaluation and spatial interpolation methods were carried out to evaluate the soil nutrients in Wangzhu reclamation area. The result showed that: The region with Integrated nutrients index (INI) 0.6 and level of soil nutrients over two was only 0.1% in the total area; the region with INI 0.4-0.6 and level three was 49.3%; the rest of the total area was 50.6% with INI below 0.4 and level four. The results generated spatial distribution map of soil nutrients levels, from the figure, we can learn that the nutrients level of the eastern and north-west districts were at middle while the other districts were at low level.3. The study on spatial variability of heavy metals of sediment was carried out in Rudong intertidal aquafarm area. The results showed that: Copper (Cu), zinc (Zn) and cadmium (Cd) had a medium spatial correlation individually and lead (Pb) had a weak spatial correlation and the ranges of Cu and Cd were greater than those of Pb and Zn. According to the spatial distribution maps, the content of Cu was decreasing gradually from south and north regions to central region, the content of Zn had high values in the southern and central regions, and the contents of Pb and Cd had high values in the northern and central regions. Based on the research of spatial variability of heavy metals, combining with potential ecological risk index method, the comprehensive quantitative pollution assessments on Cu, Zn, Cd and Pb of sediments were carried out. The results generated a spatial distribution map of comprehensive ecological risk index for heavy metals in sediments. It was found that the whole survey area belonged to the light ecological risk and the ecological risk level of the region near the sewage outfall was heavier in the map, which consistent with the actual situation. It proved that the use of GIS and geostatistics methods could reflect the situation of the heavy metals pollution in sediments correctly and intuitively. Thus, it provided a guideline for the practical application of the heavy metal pollution assessments.