长江中游下荆江段漫滩系统土壤氮空间分布特征研究

Study on the Spatial Distribution Characteristics of Soil Nitrogen at the River-Floodplain System of Lower Jingjiang Reach of Middle Yangtze River

【目的】对比研究河段尺度土地利用方式与水文地貌单元不同组合模式下土壤氮分布的差异性。【方法】选取长江中游下荆江段7种典型组合模式下的15个样地,0~20cm土层每隔5cm环刀采样,然后测定土壤的全氮含量及容重,并计算土壤氮密度和储量。【结果】0~20cm土层的土壤全氮含量及氮储量在芦苇地中较在薏杨林地中高,且在江心洲人工芦苇地中最大,在堤岸薏杨林地最小。不同地貌单元0~20cm土壤全氮含量及氮储量的对比则是同为芦苇地以在江心洲最高,然后依次是河漫滩、堤岸;同为薏杨林地以在故道中最高,然后依次是河漫滩、堤岸。在土壤全氮含量及氮密度的垂向分布上,农林活动增强了0~10cm土层土壤氮的相对富集、加大了垂向变异,江心洲人工芦苇地的垂向分布特征体现了大洪水间歇期土壤氮的阶段性累积过程,不同组合模式下土壤氮的差异性在0~10cm土层较大、>10~20cm土层较小。【结论】河流漫滩系统土壤氮不仅受到土地利用的影响,还与水文地貌性质如洪水脉冲、侵蚀与堆积特性等有关。

[Purposes]It aims to explore the relation of soil nitrogen distribution to the combining modes of land use and hydrogeomorphic units within a river-floodplain system.[Methods]Fifteen positions representing seven typical combining modes at the lower Jingjiang reach of middle Yangtze River were selected for soil sampling.Soil samples were collected from the depth 0-20 cm at 5 cm intervals by using soil sample rings.Soil total nitrogen content and bulk density were then determined,and soil nitrogen density and stock was calculated.[Findings]The soil nitrogen content and stock at depth 0-20 cm were larger in reed lands than in poplar lands,and were highest in the reed lands of channel islands and lowest in the poplar lands of levee banks.The comparison between different hydrogeomorphic units indicated that the soil nitrogen content and stock for reed lands were highest at channel islands,less at floodplains,and lowest at levee banks.For poplar lands,the highest soil nitrogen content and stock were observed at oxbow-lake areas,lower at floodplains,and the lowest at levee banks.The vertical distribution of soil nitrogen indicated that the agricultural and afforestation activities have enhanced the relatively enrichment of soil nitrogen at the 0-10 cm depth,and that The differences in soil nitrogen content and density between different combining modes were larger at the 0-10 cm depth than at the 〉10-20 cm depth.[Conclusions]The soil nitrogen within a river-floodplain system was not only affected by land uses,but was also connected with the hydrogeomorphic characteristics such as flood pulses and erosion-deposition features.