长江口盐沼土壤有机质更新特征的滩面趋势

通过对长江口崇明东滩高潮滩、中潮滩以及光滩柱状样的有机元素(C、N)含量与碳稳定同位素组成(δ13C)、粒度组成等的测定,研究盐沼土壤有机质更新特征及其滩面趋势.结果表明,长江口盐沼土壤POC-δ13C相关特征与山地土壤剖面上部土层的基本类似,盐沼土壤有机质主要源于长江流域表层土壤,有机质年龄不足100年.不同高程柱样TN-C/N、POC-TIC与POC-δ13C关系特征表明盐沼土壤有机质更新程度普遍较低,有机质更新特征呈明显的滩面变化趋势.光滩有机质基本反映沉积母质特征,更新程度极低;中、高潮滩有机质更新作用已经发生,随着滩面演变,处于不同更新阶段的有机质组分混杂程度提高.盐沼滩面过程塑造垂向沉积层序,层序中独特的沙、泥纹层构造导致物质上下运移困难,有机质更新作用受到抑制.盐沼滩面过程直接影响有机质的累积与更新,对于有机质更新的时空特征具有显著制约.

Trends of soil organic matter turnover in the salt marsh of the Yangtze River estuary

Soil organic matter (SOM) turnover was studied for the Chongmingdongtan Salt Marsh in the Yangtze River Estuary, based on the analyses of stable carbon isotope (δ¹³C), grain sizes and contents of particulate organic carbon (POC), total nitrogen (TN) and inorganic carbon (TIC) for three cores excavated from high marsh, middle marsh and bare flat. Results indicated that correlations between soil POC contents and δ¹³C values of the salt marsh cores were similar to those of the upper soil layers of mountainous soil profiles with different altitudes. SOM of salt marsh was younger than 100 years, and originated mainly from materials of soil erosion in the catchment basin of the Yangtze River. Diagrams of TN-C/N, POC-TIC and POC-δ¹³C for the cores indicated that turnover degree of SOM from the salt marsh was generally low, and tendencies regarding SOM turnover were clear from bare flat to high marsh. Bare flat showed characteristics of original sediments, with minor SOM turnover. The turnover of SOM was discernable in the high marsh and middle marsh, and the mixing degrees of SOM compartments with different turnover rates increased with evolution of the muddy flat. The exclusive structure of muddy layer and sandy layer originated from dynamic depositional processes on tidal flat made great difficulties for vertical migration of dissolved materials, and SOM turnover was then constrained.