鄱阳湖湿地土壤-植物-地下水稳定氧同位素组成分析

近年来,鄱阳湖水位持续走低,极端干旱事件频繁发生,湿地生态系统结构与功能遭受破坏。为此,于2014年鄱阳湖湿地保护区两个断面分层采集0~100 cm土壤,并采集优势种植物和河湖水以及地下水数据,运用稳定同位素技术,分析了土壤-植物-河湖水-地下水稳定同位素变化特征,并探寻它们之间的补给关系。结果表明,两断面土壤水氧同位素变化范围分别为–10.48‰~–5.23‰和–12.39‰~–6.55‰,算术平均值分别为–8.36‰和–8.63‰。断面一表层(0~30 cm)土壤水氧重同位素较富集,且随深度增加而减小;断面二表层(0~40 cm)土壤水中氧同位素组成基本无变化。断面一的地下水主要是受降水补给,断面二可能是受降水和河湖水共同补给。鄱阳湖湿地两断面优势种植物虉草叶片水的氧同位素值最大,为–0.9‰,其次是灰化苔草和芦苇,分别为–4.23‰和–5.25‰。

ANALYSIS OF STABLE OXYGEN ISOTOPE OF SOIL-PLANT-GROUNDWATER IN POYANG LAKE WETLAND

Poyang Lake is the largest freshwater lake in China and is also the largest single area of habitat for migratory birds. The water level of Poyang Lake continues to decline, and extreme droughts have frequently occurred in recent years, so that the structure and function of the wetland ecosystem are destroyed. In this paper, stable oxygen isotopes were used as a tracer to identify composition of soil water, lake water, ground water and plant water. The focus was on characterizing the variation with depth of the stable oxygen isotope composition and identifying the main sources of oxygen in soil water profiles, groundwater and plant water, understanding the mechanisms of water movement among them. Soil water sampled at 10 cm intervals over the top 100 cm at two sites in the Poyang Lake wetland, and water samples collected from the plants, lake and river water and ground water were analyzed for stable oxygen isotope composition, to explore the recharge and discharge of relationship between them. The results indicate that the range of the stable oxygen isotope value of soil water from two sites varied from –10.48‰ to –5.23‰ and –12.39‰ to –6.55‰, respectively, average value of which were –8.36‰ and –8.63‰. The value of δ¹⁸O at depth of 0 to 30 cm at one site declined with increasing soil depth, however, the value of δ¹⁸O at depth of 0 to 40 cm at another site had unchanged with increasing soil depth. The value of δ¹⁸O of groundwater at one site was smaller than that of Xiu River, at another site was nearly close to that of the Gan River. Thus, the groundwater at one site was mainly influenced by precipitation, at another site by precipitation, lake and river water. The average value of δ¹⁸O of the domain plant Phalaris arundinacea Linn leave at two sites in Poyang Lake wetland were the largest, –0.9‰, Crex cinerascens, –4.23‰, and Phragmites Adans the smallest, –5.25‰. The value of δ¹⁸O of the same plant leave was different at different sample points at same site, maybe due to different characteristics of migration of primary elements such as Ca, Mg at different geomorphological positions(depression, slope) inducing the different impact on plant transpiration. This study provided reference data that could make a useful contribution to the assessment of ecosystem in the Poyang Lake.