Gradients of organic matter quality, mineralization and sequestration in Cook's Bay of Lake Simcoe, Canada

Carbon sequestration in lakes represents a globally relevant carbon sink. Important controls thereof are functions of lake morphometry and productivity, organic matter origin and quality, and organic and inorganic matter burial in sediments. To understand the relative importance of these controls, we investigated organic and inorganic carbon sequestration and burial efficiency by means of 210Pb dating of sediments and determination of in situ carbon sedimentation in elongated Cook's Bay of Lake Simcoe, a large Canadian hard water lake. Spectroscopic and elemental analysis of dissolved and particulate organic matter suggest that along the studied transect the influence of the major tributary on the quality of settling organic particles and dissolved organic matter was significant only at the shallow inlet of the bay, which had generally autochthonous character. Also sediment incubations confirmed similar organic matter decomposability throughout the bay. Thus, organic matter quality played a minor role for organic carbon sequestration, which ranged from 2.5 to 46.7 g m−2 yr−1 and was lower than organic carbon sedimentation of 34-96 g m−2 yr−1. The organic carbon burial efficiency of 7.3-89% did not follow a progressing spatial pattern but was lower both at the shallow and deep end of the bay and significantly related to non-carbonate, inorganic sedimentation (R2 = 0.97). The study suggests that in this lake system the influence of organic matter quality on C sequestration is limited, as well as temperature. However, sedimentation rate controls the duration of exposure to terminal electron acceptors and hence, C sequestration and organic carbon burial efficiency.