Organic matter variability and implications for metal bioavailability in urban watersheds

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Water is a vital resource in Canada, but the discharge of metals from point and non-point sources in urban environments can have a detrimental affect on aquatic biota. The negative impacts can be reduced by binding of metals to dissolved organic matter (DOM). DOM occurs in all aquatic environments and is formed by natural processes. At high concentrations, it gives water a "tea''-like colour. Metal binding to DOM can be quantified by metal speciation determinations. Metal speciation is a set of experimental techniques used to measure and/or predict the distribution of total metal among some subset of its possible chemical forms. Some forms of metal are more bioavailable than other forms; thus, metal speciation is being taken into account in environmental legislation using computer models. A major input variable to toxicity prediction is dissolved organic carbon (DOC) concentration as an approximate measure of DOM but there is an open question of the temporal and spatial variability of DOM and if toxicity prediction/regulatory models need to consider quality as well as quantity of organic carbon. Quality can be considered as some measure proportional to the molecular nature of the organic matter. In the program proposed here a "cradle to grave" analysis of organic matter variability will be performed. The Grand River in Southern Ontario will be used as a model system. This river starts from a large wetland headwater (Luther Marsh) in a rural area and moves through increasing urbanization towards Lake Erie. In a complete survey of organic matter transformation and quality variability it is important to include the impacts of water treatment processes. Most of the cities along the Grand River bring in drinking water upstream and discharge treated sewage effluent downstream. The next city downstream takes in the water containing this sewage derived organic matter for their drinking water treatment and so on. The significant questions to be addressed in this research program are (1) what does this constant processing and reprocessing of organic matter do to its quality? and (2) what are the implications for metal bioavailability?