三峡库区淹没消落区土壤氮素形态及分布特征

利用分级浸取分离法对三峡水库腹心地带(巫山-重庆主城区段)淹没消落区土壤中的不同形态氮含量进行了测定,并对各形态氮之间及氮形态与土壤理化特征之间的相关性进行了分析.结果表明:研究区域内,淹没消落区土壤全氮(TN)含量在676.0~1769.7 mg·kg^-1之间,均值为1182.3 mg·kg^-1,TN主要由可转化态氮(TF-N)和非可转化态氮(NTF-N)组成,占TN的百分比分别为46.3%、53.7%;消落区土壤中TF-N组分在适宜的环境条件下会成为水体的二次污染源,其对水体富营养化的影响不容忽视.淹没消落区土壤弱酸可浸取态氮(WAEF-N)、有机态和硫化物结合态氮(OSF-N)在TF-N中占的比例较高,分别为47.3%、33.9%,表明WAEF-N和OSF-N直接影响着淹没消落区土壤TF-N的含量;从各形态氮含量及相对含量的变化范围来看,均表现为WAEF-N>OSF-N>铁锰氧化态氮(IMOF-N)>离子交换态氮(IEF-N).相关性分析结果表明,TN与NTF-N的相关性显著(p<0.01),与IMOF-N及OSF-N含量之间也具有显著相关性(p<0.05),表明TN的增加主要来自NTF-N,其次是IMOF-N及OSF-N;TF-N与WAEF-N、OSF-N之间显著正相关(p<0.01), 与IMOF-N也具有显著相关性(p<0.05),表明TF-N的增加主要来源于这3种形态的氮.TN与有机质(SOM)之间显著正相关(p<0.01),TF-N、OSF-N与SOM之间也呈正相关关系(p<0.05),表明它们可能具有相似的来源或SOM的输入对消落区土壤氮形态的分布有一定的影响.

Nitrogen forms and their distribution characteristics in the soils of water-level-fluctuationg zone in the central Three Gorges Reservoir

The contents of various nitrogen forms in the soils sampled from water-level-fluctuating zone (WLFZ) in the central Three Gorges Reservior were investigated in this study. Correlation coefficients between nitrogen forms and sample geochemical characteristics, including soluble organic matter (SOM), pH, oxidation-reduction potential (ORP), and water content of the soil were analyzed. It indicated that total nitrogen(TN) contents in soils varied from 676.0mg·kg^-1 to 1769.7mg·kg^-1, and the average level was 1182.3mg·kg^-1. The nitrogen forms in the soils consisted of non-transferable nitrogen (NTF-N) and transferable nitrogen (TF-N) in all samples, and the average ratio were 53.7% and 46.3% in TN, respectively. The TF-N in soils of WLFZ would become potential pollution sources of water under special environmental conditions. Therefore, the potential effect of nitrogen on water eutrophication in soils of WLFZ could not be neglected. The ratios of weak acid extractable form (WAEF-N) and organic matter-sulfide form nitrogen (OSF-N) in TF-N were high, up to 47.3% and 33.9%, respectively. In terms of the range of various nitrogen forms content and their ratios in TN, the nitrogen forms in the soils could be ordered as WAEF-N > OSF-N > iron-manganese oxides form (IMOF-N) > ion-extractable form (IEF-N). TN has significantly positive correlations with NTF-N(p<0.01), IMOF-N and OSF-N(p<0.05), indicating that the increase of NTF-N, IMOF-N and OSF-N content can lead to the increase of TN content. Furthermore, TN, TF-N, OSF-N was significantly positively related to SOM (p<0.01; p<0.05), indicating that TN, TF-N, OSF-N and SOM probably came from the same pollution source.