| 河网水源生态湿地水氢氧同位素分异特征 |
| 摘要点击 6323 全文点击 612 投稿时间：2020-12-24 修订日期：2021-02-09 |
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| 中文关键词 构筑根孔湿地 植物床-沟壕系统 氢氧同位素 水力流程梯度 潜水 嘉兴河网地区 |
| 英文关键词 constructed root-channel wetland plant-bed/ditch system hydrogen and oxygen isotope hydraulic flow gradients subsurface water Jiaxing stream network area |
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| 中文摘要 |
| 为揭示河网水源生态湿地中水力流程沿途和植物床-沟壕系统内部水同位素分异特征，于2019年8月夏季湿雨期，沿水力流程梯度采集嘉兴市石臼漾湿地、贯泾港湿地、海宁市长水塘湿地和泰山港湿地这4个根孔型水源生态湿地上层水样，于2020年1月冬季干冷期采集泰山港湿地植物床-沟壕系统内部沟壕上层水样和植物床潜水样品.测定氘（δD）和δ18 O丰度，运用同位素技术和数理统计方法解析湿地水体水同位素分布和组成特征，并探明植物床-沟壕系统对水同位素分异的影响.结果表明：①河网水同位素时空变化很大程度上受到不同水源补给和蒸发富集作用的影响，湿地敞水区水线与邻近区域大气降水线相比，湿地区水氢氧同位素呈现富集特征；②通过多种数理统计手段结合散点图并做模型假设诊断分析，发现在4个湿地的区域尺度和每个湿地内部的局域尺度，水氢氧同位素丰度及组成在垂向维度和水平维度大多呈现复杂的非线性变化，在区域尺度上，垂向维度的水位高程较水平维度的水力流程长度对水同位素的分布影响更大，而在局域尺度内，水力流程驱动的影响往往更大；③异质性较强的湿地根孔生态净化区相较于其他功能区其水同位素相对更加富集；④由芦苇等根系发达的植物所形成的地下大孔隙网络、富含粘土的基质土壤和植物床上的植物对湿地水氢氧同位素丰度具有显著影响，因此，在植物床-沟壕系统内部，出水侧的低位小沟相较于进水侧的高位小沟其水同位素偏轻；⑤植物床-沟壕系统中水同位素丰度的突变点可能预示着水体净化的拐点；⑥植物床-沟壕系统潜水中氘盈余（d-excess）明显高于沟水相应值，且潜水变异系数远大于沟水，湿地根孔生态净化区的氘盈余呈现夏季湿热雨季偏负、冬季干冷旱季偏正的季节性差异，反映了湿地水汽来源的季节性差异和内部同位素分馏行为的空间差异.研究结果为人们认识人工湿地中水同位素分布特征、水力流态及提升湿地运行效果提供参考依据，并为探索湿地水质提升关键技术提供新思路.本研究表明水同位素技术在剖析湿地水文学方面具有可靠的巨大潜力. |
| 英文摘要 |
| To explore the isotopic distribution and differentiation of water along the hydraulic flow gradients and plant-bed/ditch systems in constructed root-channel wetlands, surface and subsurface water samples were collected from four ecological wetlands, namely Shijiuyang and Guanjinggang in Jiaxing, as well as Changshuitang and Taishangang in Haining. All samples were collected along water flow pathways during the wet and rainy summer season in August 2019, except for those from Taishangang, which were collected within the plant-bed/ditch system during the dry and cold winter season in January 2020. The abundance of deuterium (δD) and δ18 O was determined in each functional area of the wetlands to assess the influence of wetlands on water differentiation. Stable isotope technology and mathematical statistics were used to analyze the distribution of δD and δ18 O in constructed root-channel wetlands and to reveal the influence of plant-bed/ditch systems on stable isotopes of water. A variety of data mining methods were used to examine the differentiation of stable isotopes of water, at various dimensions and scales, including nonparametric Kendall's tau-b correlation, stepwise regression, gray relational analysis, and machine learning (random forest) combined with scatter diagrams and model hypothesis diagnosis analysis. The main results were as follows:① The spatiotemporal variations in water isotopes of stream networks were largely affected by different water supply and evaporation enrichment effects. The slope and intercept of the wetland water line in Jiaxing were both significantly lower than the regional precipitation line of the adjacent Changshu Station (CHNIP). This showed that the wetlands area had undergone hydrogen and oxygen isotope enrichment. The δD values in Shijiuyang wetland water ranged from -52.2‰ to -49.4‰, and δ18 O values ranged from -7.6‰ to -6.9‰. In Guanjinggang wetland water samples, δD ranged from -48.1‰ to -45.1‰, and δ18 O ranged from -6.8‰ to -5.8‰. The δD values in Changshuitang wetland water ranged from -49.8‰ to -48.4‰, and δ18 O ranged from -7.2‰ to -6.6‰. The δD values in Taishangang wetland water ranged from -55.3‰ to -51.6‰, and δ18 O ranged from -7.8‰ to -7.2‰. ② Hydrogen and oxygen isotope abundance and composition of water showed complex nonlinear changes in the vertical and horizontal dimensions at different scales. At the regional scale, water level elevation in the vertical dimension had a greater impact on water isotope distribution than the length of the hydraulic flow pathway in the horizontal dimension. Water isotopes tended to be enriched in low-lying areas with low water levels. At the local scale, the influence of hydraulic process often played a greater role in determining water isotope distributions. The spatial variations of water isotopes were comprehensively determined by the evaporation of regional water and meandering hydraulic processes inside the wetland. ③ Compared with other wetland functional areas, the central constructed root-channel area (middle treatment zone) was more enriched in water isotopes. ④ The underground macropore network formed by plants with developed rhizomes or roots (e.g., Phragmites communis Trin. and Typha orientalis Presl), mineral-rich substrate soil, and aquatic plants in the plant bed had a significant influence on the abundance of hydrogen and oxygen isotopes in the plant-bed/ditch system. Therefore, when water passed through the plant-bed/ditch system, the values of δD and δ18 O in the lower ditch (outlet) were lower than those in the higher ditch (inlet). ⑤ The abrupt change in isotopic contents of the plant-bed/ditch system might indicate an inflection point in water quality purification. ⑥ The deuterium excess (d-excess) in subsurface water of the plant-bed/ditch system was significantly higher than that in ditch water, and the coefficient of variation in subsurface water was considerably greater than that in ditch water. The d-excess in the wetland root-channel ecological purification zone showed significant temporal differences and was negative in the summer and positive in the winter, which reflected the seasonal variation in water vapor sources and the spatial variation in isotope fractionation behavior in wetlands. These results provide some understanding of the distribution of water isotopes in constructed wetlands, which will strengthen their operation and management. This study also provides some ideas regarding new technologies for water quality improvement and shows that water isotope technology may be a reliable method for analyzing wetland hydrology. |
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