Dissolved organic matter characterization and metal speciation in boreal streams

环境中的微量金属可能给水生生物和人类带来益处，也可能带来风险。它们可能是自然产生的，也可能部分或全部是人为污染造成的。然而，仅考虑总金属浓度以评估风险/效益已不再适当。相反，有必要确定一种元素的物理化学形式（即物种），因为同一种金属的不同形式可能从必需到无害到剧毒。金属形态的建模允许探索金属在水中的流动性、运输、毒性和生物利用度的过程。然而，由于金属络合的主要配体溶解有机物（DOM）的存在，其在天然水生生态系统中的应用往往受到限制。在建模计算中，通常假设所有dom，无论其性质和来源如何，对复杂的微量金属的行为都相似。特定环境中DOM的多样性和可变性取决于DOM的潜在来源以及流域的水文条件。为了预测金属形态如何影响水生环境中金属的命运和生物利用度，需要更好地了解DOM循环。北方防护罩生态区是安大略省一个特别重要和敏感的地区，它的大多数河流和湖泊都位于这里。在这个项目中，将开发一个金属形态模型，并根据实地观察进行测试，以预测金属形态将如何影响北方河流中水生金属的命运和生物利用度。在安大略省中南部的两条北方河流中，将调查DOM的时空变化以及金属形态的时空变化。将设计实验室实验来研究DOM动力学和组成对金属结合性能的影响。这些实验结果将被纳入一个描述DOM在金属形态形成中的重要性的模型。该模型将允许综合DOM-金属关联的总体影响及其变化，因为DOM的定性和定量特征在研究系统中有所不同。

Trace metals in the environment can provide either benefits or risks to aquatic life and humans. They may arise naturally or result partly or wholly from man-made pollution. It is no longer adequate, however, to consider only the total metal concentration in order to assess risk/benefit. Rather, it is necessary to determine the physicochemical forms (i.e. speciation) of an element because different forms of the same metal can range from essential to innocuous to strongly toxic. The modeling of metal speciation permits exploration into the processes of mobility, transport, toxicity and bioavailability of metals in water. Its application to natural aquatic ecosystems, however, is often limited due to the presence of dissolved organic matter (DOM), the main ligand for metal complexation. It is normally assumed in modeling calculations that all DOMs, regardless of their nature and origin, behave in a similar way toward complex trace metals. The diversity and variability of DOM within a specific environment depend on the potential origins of the DOM as well as on the hydrological conditions in the watershed. A better understanding of DOM cycling is required to predict how metal speciation will affect fate and bioavailability of metals in aquatic environments. The boreal shield ecozone is a particularly important and sensitive region of Ontario where most of its streams and lakes are located. In this project, a metal speciation model will be developed and tested against field observations to predict how the metal speciation will affect fate and bioavailability of water-borne metals in boreal streams. The spatial and temporal change in DOM, as well as those in the metal speciation, will be investigated in two boreal streams of south-central Ontario. Laboratory experiments will be designed to investigate the influence of DOM dynamics and composition on metal binding properties. These experimental results will be incorporated into a model that describes the importance of DOM in metal speciation. This model will allow a synthesis of the overall effects of the DOM-metal associations and of their changes as the qualitative and quantitative character of the DOM varies in the study systems.