基于加权Topsis法综合评价典型滩涂围垦区土壤质量演变

Soil quality evaluation in typical coastal reclamation zones based on weighted Topsis method

滩涂是我国重要的后备耕地资源,为探究围垦开发对沿海滩涂土壤环境的影响,对浙江省慈溪市不同围垦年限多种土地利用方式下的276个土壤/沉积物样品试验检测,结合Norm值优化主成分分析,筛选出有机质(OM)、氧化钙(Ca O)、硫(S)、溴(Br)、硼(B)、铅(Pb)、镉(Cd)7项指标的最小数据集,采用极差标准化和变异系数定权的Topsis法评价土壤质量,为揭示阻碍研究区土壤质量提升的障碍因子提供参考。结果显示:276个土壤/沉积物样本土壤质量综合指数为44.6~74.1,受围垦时间影响差异显著,呈前20 a逐步提高—20~30 a相对平稳—30~50 a急剧提高的趋势。从利用方式来看,土壤质量呈菜地>果园>农田>林地>养殖>潮滩>荒地的趋势。农业活动导致的增肥脱钙脱盐是围垦区土质提升的根本原因,但研究区土壤质量整体仍处于中度贫瘠水平,一级土壤仅占研究区总面积的7.1%,质量较差的四、五级土壤面积超一半。较低的OM和较高的Ca O、Cd是限制垦区土质提升的主要障碍因子。因此,土壤培肥时,合理施用化肥农药是进一步提升滩涂围垦区土壤质量的关键。

Tidal flat is an important reserve of cultivated land resource in China.There is high spatial heterogeneity,properties and environment changes of soil in the transformation from wetland to agricultural soil.In order to evaluate the effect of soil quality under different reclamation durations and multiple land use in a typical coastal area in Cixi County,Zhejiang Province,276 soil/sediment samples from farmland,vegetable land,orchard,forestland,aquafarm,wasteland and tidal flat reclaimed for 0 to 50 years were collected and analyzed.Considering the spatial heterogeneity,principal component analysis was used in combination with norm value,then minimum data set(MDS)with seven indexes was put forward.This included organic matter(OM),calcium oxide(CaO),sulfur(S),bromine(Br),boron(B),plumbum(Pb)and cadmium(Cd)under six reclamation duration and seven utility patterns.About 29.2%of the index accounted for 80.3%of the information.The Topsis method,which combined maximum difference normalization method and variable coefficient fixing weight method,was used to assess the soil quality.Compared with the traditional membership function method,the used method was a much more effective one.Besides,the distance to optimal vector directly was used to explain the obstruction factor,which showed the primary obstacle and was applicable in supervising soil environment and improving soil quality by the local government.The results suggested that the range of soil quality comprehensive indexes for the 276 soil/sediment samples was 44.6–74.1.The trend in the indexes increased sharply in first 20 years and then stabilized in the 20–30 years,and then it again increased sharply for 30–50 years of reclamation.In general,the overall soil quality in the study area was moderate to infertile.The class I soil quality was only 7.1%of the samples.More than half of the soil samples belonged to classes IV or V.Based on land use types,soil quality was ranked in the following order:vegetable field>orchard>farmland>forest>aquafarm>tidal flat>wasteland.Paddy field was better than dry land for the same reclamation period,which indicated that basic paddy farmland was much more environmental friendly in Cixi reclamation district.Irrigation-induced decalcification and desalination effectively improved the quality of reclaimed soil.Meanwhile,low OM and high CaO and Cd primarily limited soil quality.Next were salt content as Br,S and B,followed by heavy metal as Pb.Soil content of Cd increased quickly to critical point of pollution,which was easily enriched in paddy and caused diseases.Reasonable use of chemical fertilizers was a key to further promotion of soil quality in reclaimed tidal areas.