极端洪涝脉冲对黑龙江水中可溶铁形成的影响

Extreme flood-waterlog events play the important role in formation of river hydrochemistry, and the influence mechanism of flooding and inundating on water quality need to be discussed in depth. The concentrations of dissolved iron of Heilongjiang River raised obviously during the extreme flood of the Songhua River in 1998. We speculate that the match of explosive release and export of dissolved organic matter(DOM) from forest and marsh, and suspended particulate(SS) from farmland during the period of the extreme flood-waterlog of 1998, accelerated the forming of Fe-DOM complex and promoted the reduction and dissolution of iron oxides in SS. The mechanism is likely the key dynamic of the abnormity of dissolved iron concentrations of Heilongjiang River in 1998. We plan to conduct field monitoring, sample collecting and simulation experiment. Samples will be separated by ultrafiltration technique, assayed by fluorescence, infrared and other techniques. The research contents designed are listed as follows: ① The content and component of DOM and dissolved iron in flood in different watershed among forest, marsh, grassland and farmland; ② The release of DOM and dissolved iron in the marsh and typical soils after inundated; ③ The influence of mineral constituent of suspended particulate on the forming of complex of iron and DOM; ④ The formation of dissolved iron during mixing of Songhua River and Heilongjiang River. It is great significance to reveal the formation mechanism of dissolved iron under the condition of flood-waterlog pulse. The results are helpful to know the influence of flood pulse on river water quality and the process of dissolved iron transportation from watershed into ocean. It can also provide scientific basis for the processing operation of drinkingwater works along rivers during the flood period.

极端暴雨-洪涝事件是河流水化学格局形成的重要水文要素，但洪涝对水质影响的机制还需进一步阐明。98松花江极端洪涝过程中，黑龙江水中可溶铁含量明显上升，我们推测洪涝脉冲导致森林和湿地中DOM的爆发性输出，高浓度悬浮物（SS）和DOM的耦合加速了江水中Fe-DOM络合物的生成，增加了SS中铁氧化物的还原、溶解，可能是黑龙江可溶铁浓度异常的主要原因。拟采用现场监测、采样分析和实验室模拟方法，利用超滤、荧光光谱、红外光谱等技术，研究DOM主要源区（森林、湿地、草地和农田）暴雨径流中DOM与可溶铁含量与组成、湿地及典型土壤淹水后DOC与可溶铁的释放、悬浮物中矿物组成对可溶铁形成的影响、松花江与黑龙江水混合过程中可溶铁的形成，揭示洪涝脉冲影响下河水中可溶铁的形成机制。研究结果对深入认识寒区洪涝脉冲对河流水质的影响、河流溶解铁向海洋的输送通量波动具有重要意义，也可为沿江自来水厂洪水期工艺运行提供科学依据。

铁是海洋浮游植物生长的限制元素，是影响海洋生产力和减缓温室效应的重要因子。黑龙江流域铁的生物地球化学循环过程非常活跃，一直是东北亚地区的研究热点。极端洪涝事件发生频率增加对黑龙江流域可溶性铁的形成及输送将产生重要影响。本项目研究了流域性、局域性及极端春汛3种洪涝过程中江水中可溶性铁的含量、形态和输出特征，揭示了影响可溶性铁含量变化的因素，探讨了沼泽湿地、森林两大生态系统可溶性铁的输出特征，分析了极端洪涝过程中黑龙江流域可溶性铁的形成机制。主要研究成果包括：（1）2013年流域性极端洪水期间，黑龙江、松花江水中可溶性铁的平均浓度分别为1.11和0.69mg/L，输出通量分别为18.1万吨和3.6万吨，显著高于平水年夏汛期的浓度和通量；局域性洪水过程中，松花江可溶性铁平均浓度为0.25mg/L，显著高于以往报道的夏汛期浓度；极端春汛期间江水中可溶性铁浓度（0.28mg/L）与正常年份相比没有显著性差异。可溶性铁形态均以低分子量络合态铁为主；悬浮物含量、DOM类型及含量是影响可溶性铁释放量的主要因素。（2）在极端降水过程中，毛苔草、小叶章湿地和水稻田水中可溶性铁含量分别为2.08、2.89和3.98mg/L，均显著高于正常年份雨季时的含量，水中DOC的含量也同步升高；各湿地水体中可溶性铁均以低分子量铁为主；淹水深度、DOC、干湿交替是影响湿地土壤可溶性铁释放的主要因素。（3）极端洪水过程中，森林流域（雅鲁河）河水中可溶性铁含量（0.24mg/L）显著升高，低分子量络合态铁为其主要形态，流量和DOM是影响森林河流可溶性铁形成及输送的主要因素。（4）极端洪涝过程是黑龙江流域可溶性铁形成和陆海输送的主要驱动力。极端洪涝过程中，地表径流及沉积物再悬浮作用使得悬浮物含量激增，沿江湿地水文连通性改善使得湿地向河流输入大量DOM，悬浮物及DOM含量升高是可溶性铁形成的主要驱动力。