黄河口典型潮沟土壤碳氮分布特征规律

为探究黄河三角洲盐沼土壤碳氮含量在潮沟水系中的时空分布特征,选取黄河口一条典型的潮沟系统,采集一、二、三级潮沟表层土壤,探寻土壤有机碳、总氮与土壤容重、盐度、pH等理化因子的相关关系。结果表明：土壤有机碳和总氮在时空尺度上表现出极大的异质性特征。时间尺度上,土壤有机碳和总氮出现先上升后下降的趋势。空间尺度上,一级潮沟土壤有机碳和总氮平均值（2.9 g·kg^-1、0.36 g·kg^-1）大于二级（1.4 g·kg^-1、0.18 g·kg^-1）、三级（1.6 g·kg^-1、0.21 g·kg^-1）潮沟。相关分析表明,土壤有机碳和总氮与盐度呈显著正相关（P<0.01）,与容重呈显著负相关（P<0.01）。盐沼湿地土壤碳氮含量受土壤水盐条件的影响,而潮沟水系的树状结构对水盐条件的影响是导致土壤碳氮含量时空差异分布的重要因素。

Characteristics of carbon and nitrogen distribution in typical tidal creeks of the Yellow River Delta

Carbon and nitrogen are two key elements in the natural wetland soil. Changes of organic carbon contents in wetland soil significantly affect the structure and function of wetland ecosystems. Soil carbon and nitrogen contents in coastal salt marshes are closely related to hydrological connectivity patterns of coastal wetlands. To explore the spatio-temporal characteristics of soil carbon and nitrogen contents in different tidal creek systems of salt marsh, this research selected a typical, complete tidal creek system with major and minor tributaries in the estuary of the Yellow River. By collecting surface soil (0-5 cm) in the first-, second-, and third-level tidal creek regions, we attempted to explore the relationship between soil organic carbon, total nitrogen contents and soil moisture contents, salinity, bulk density, pH and other physical-chemical factors. Results illustrated that the soil organic carbon and total nitrogen contents presented great heterogeneity on both temporal and spatial scales. On the time scale, the soil organic carbon contents increased firstly and then decreased, the second tidal creek changed the most striking while the third tidal creek showed the least significant. The soil total nitrogen contents presented variability in different grades of tidal creeks. The total nitrogen contents were listed as August > September > July in the first-degree tidal creek, while the contents reached the peak in September of the second and third tidal creeks. The soil carbon and nitrogen ratio reached the peak in August. On the spatial scale, the average contents of the soil organic carbon and total nitrogen (2.9 g·kg^-1, 0.36 g·kg^-1) in the first tidal creek were greater than those of the second tidal creek (1.4 g·kg^-1, 0.18 g·kg^-1) and the third tidal creek (1.6 g·kg^-1, 0.21 g·kg^-1). The longer the lateral distance of the first tidal creek is, the higher the contents of the soil organic carbon and total nitrogen are. The soil organic carbon and total nitrogen contents in the third-degree tidal creek showed a slow downward trend in distance which was opposite to those of the first-degree tidal creek. Correlation analysis showed that there was a significantly positive correlation between soil organic carbon, total nitrogen contents and salinity (P<0.01), and a prominently negative correlation with soil bulk density (P<0.01). In summary, the soil carbon and nitrogen contents of the salt marsh wetland are affected by the soil water and salt conditions, and the tree structure of the tidal water system is crucial to the water and salt conditions of the surrounding soil. The influence of the structural characteristics of the tidal water system on the water and salt conditions is one of the important factors of spatial and temporal differences in soil carbon and nitrogen content.