Sediment loading to the Great Lakes results from a variety of activities in the watershed, including some agricultural and forestry practices, run-off from roads and other impervious surfaces, construction, mining, and other physical disturbances. Not all sediment loading is due to human activities, some loading is natural for the Great Lakes basin. One recent model suggests the annual sediment load in the Great Lakes basin is as high as 65 million tons.1
Sediment loading has significant impacts on aquatic resources.
- Increased turbidity in the water column makes it difficult for organisms to feed through reduced visibility and alters algae growth patterns because of reduced light availability for photosynthesis.
- It adversely affects fish spawning habitat, especially for species that require gravel or cobble spawning habitats.
- Soil particles often transport absorbed contaminants, including nutrients, pesticides, and toxic compounds into the lakes.
- Excessive sedimentation increases need for dredging to maintain appropriate water depths in harbors, bays, and navigation channels.
- High sediment loads impact the recreational quality of Great Lakes waters.
Mapping suspended sediments as a Great Lakes stressor
Annual loads of suspended sediments were obtained from several sources.2-5
- Canadian tributaries to Lake Huron, Lake Erie, and Lake Ontario: averages for 1972-2005
- Canadian tributaries to Lake Superior: averages for 1990-2009
- U.S. tributaries: averages for 1-2001.
- Some Lake Erie tributary data: 1997-2001.
Annual sediment loads to the Great Lakes from major tributaries.
Estimates of sediment loading to the Great Lakes from major tributaries were propagated spatially based on the assumption that river loads fall to 10% of their initial levels within 10 km of the river mouth, consistent with satellite images of river plumes, and to 1% within 30 km. We acknowledge that sediment transport may differ among locations due to natural embayments and man-made harbor structures.
Spatial distribution of sediment loading as a stressor in the Laurentian Great Lakes (Inset: Western Lake Erie).