Effects of clay mineral turbidity on dissolved organic carbon and bacterial production

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Effects of inorganic turbidity from clay minerals on allochthonous dissolved organic matter (DOM), its consumption by bacteria and photodegradation by solar radiation were investigated. In controlled experiments of adsorption of DOM of six specific leaf leachates onto montmorillonite, kaolinite, and clay extracted from drainage basin soil, up to 31 mg C of leaf leachate was adsorbed g clay–1. A suspension of clay adsorbed preferentially the chromophoric portion of dissolved organic carbon (DOC) and enhanced photochemical decomposition of CDOM and DOC under experimental conditions representative of the surface of the water column. Significant amounts of DOM were desorbed from the clay-organic aggregates into water of low ionic strength and low concentrations of DOM. Solar radiation decomposed chromophoric organic matter adsorbed onto suspended clay in part to low molecular organic products and to CO2. Montmorillonite clay significantly decreased (>90%) bacterial production, unless the clay had appreciable adsorbed DOM. With organic matter adsorbed, the addition of montmorillonite or of natural clay minerals resulted in significant increases (+100%) in bacterial production. This increase indicated that clay-organic matter aggregates can play an important role in the transport of terrestrial organic matter to aquatic environments and that this organic matter adsorbed to clay particles is available to bacteria through desorption.

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