Sediment trap studies in Lake Superior: Insights into resuspension, cross-margin transport, and carbon cycling

Document Type

Conference Proceeding

Publication Date

1-1-2004

Abstract

As part of the Keweenaw Interdisciplinary Transport Experiment in Lake Superior (KITES) project, sediment traps were deployed at multiple locations along the northern coast of the Keweenaw Peninsula in Lake Superior. Traps were deployed at multiple depths (25 m below water surface to 5 m above sediments) at varying distances from shore (0.5-21 km) during the months May-October over a 3-year period. Material captured in the sediment traps was analyzed for total carbon (C), total nitrogen (N), total phosphorus (P), total copper (Cu), 210Pb, and stable isotope ratios of C and N. Copper in sediment trap material, a tracer for mine residues, indicated transport of material in both directions along the peninsula. Cross-margin transport of material occurred at all trap locations along the coast and in all seasons. The most significant finding was that sediment traps suspended just below the thermocline collected large amounts of resuspended sediments even when the trap was moored in 120-220 m of water (9-21 km from shore). Estimates of the contribution to settling fluxes of organic carbon from resuspended sediments ranged from 10-30% in offshore traps; estimates based on 210Pb agreed well with estimates based on a carbon mixing model. Element ratios suggest that resuspended material in offshore traps originated in near-shore regions. Despite the strong influence of resuspension on the composition of sedimenting material, stable isotope ratios were controlled by processes occurring in the water column. Seasonal variations in isotope ratios may reflect seasonal shifts between predominance by autotrophic and heterotrophic processes in the water column.

Publication Title

Journal of Great Lakes Research

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