黄河三角洲内陆到潮滩土壤中碳、氮元素的梯度分布规律

黄河三角洲是我国典型的通过黄河冲积泥沙填海造陆形成的近代沉积区。区域受到黄河冲积、沉积等自然过程和农业耕种熟化等人类活动的双重影响。本研究通过在黄河三角洲地区内陆到河口海湾不同距离采集典型土壤类型剖面发生层样品，探讨土壤有机碳、总氮等生源要素的空间分布规律，为阐明我国典型海岸带地区陆源碳、氮的输送及循环特征提供基础依据。研究结果表明，黄河三角洲内陆与河口地区呈现出完全不同的土壤碳、氮分布规律。表层土壤碳、氮含量在黄河沿岸及三角洲南部均表现出由陆向海逐级递减的空间分布特征，而在黄河刁口流路和清水沟流路沿行水方向有梯度升高的趋势。内陆地区土壤碳、氮与盐分呈一定的负相关关系，表明土壤碳、氮主要受到耕作熟化过程的影响；而在河口地区两者呈显著的正相关关系（p〈0.01），表明靠近海湾地区土壤碳、氮积累可能受到细颗粒泥沙沉积和滩涂湿地厌氧等环境影响。表层土壤碳、氮比变幅在3.6~8.6之间，说明该地区土壤有机质分解较快，不利于有机碳的积累。土壤剖面中，一些特殊发生层如红色夹黏层、黑色泥炭层对土壤碳、氮的富集具有明显的作用，其中红色夹黏层的土壤碳、氮含量接近耕层土壤。总之，黄河三角洲土壤在耕作垦殖、泥沙沉积等综合作用下形成的空间分布格局以及剖面特征发生层是影响碳、氮封存、释放和增汇等循环过程的关键驱动因素。

Gradient distributions of nitrogen and organic carbon in the soils from inland to tidal flat in the Yellow River Delta

The Yellow River Delta （YRD） is a typical fluvial plain that formed by the Yellow River alluvial sediments. The soils of the area are heavily influenced by natural processes （e.g., alluviation and deposition of the Yellow River） and human activities （e.g., long-term cultivation）. The objective of this study was to reveal the spatial distribution characteristics of soil organic carbon （SOC） and total nitrogen （TN） in the YRD region based on the pedogenetic horizon samples from the typical soil sections of inland to tidal flat. The study could be helpful to understand the transport and cycling of terrestrial organic carbon and nitrogen in estuarine-coastal zone. The results showed that distinct distribution patterns of soil carbon and nitrogen were observed in the inland and estuary areas. The concentrations of TN and SOC in surface soils gradually decreased seaward along the Yellow River and in the southern part of the delta, while an increasing trend could be found along the Qingshuigou and Diaokou course. A negative correlation of SOC and TN with salt content was found in the soils of the inland areas, implying the influence of cultivation on the accumulation of SOC and TN. However, an inverse relationship was found in the estuary, which implied that fine particle sediment and reduction condition might make an impact on the accumulation of SOC and TN in the soils of the tidal flat area. The ratio of carbon to nitrogen （C/N） in the soil was relatively lower than that in other farmlands. This meant that the soil environment was favorable to the accumulation of nitrogen and decomposition of soil organic matter. The depth distribution of SOC and TN indicated that the special pedogentic horizons, such as red clay layer in the depth of〉60 cm and peat layer in the topsoil of tidal flat, played an important role in the enrichment of SOC and TN in the Yellow River Delta. Therefore, spatial distribution pattern and special pedogentic horizons of the soils in YRD formed by cultivation and sediment