The Contribution of Ice Cover to Sediment Resuspension in a Shallow Temperate Lake: Possible Effects of Climate Change on Internal Nutrient Loading
Niemistö, Juha P. | Horppila, Jukka
The effect of ice cover on sediment resuspension and internal total P (Tot-P) loading was studied in the northern temperate Kirkkojärvi basin in Finland. The gross sedimentation and resuspension rates were estimated with sediment traps during ice-cover and ice-free periods. After ice break, the average gross sedimentation rate increased from 1.4 to 30.0 g dw m⁻² d⁻¹ Resuspension calculations showed clearly higher values after ice break as well. Under ice cover, resuspension ranged from 50 to 78% of the gross sedimentation while during the ice-free period it constituted from 87 to 97% of the gross sedimentation. Consequently, the average resuspension rate increased from 1.0 g dw m⁻² d⁻¹ under ice-cover to 27.0 g dw m⁻² d⁻¹ after thaw, indicating the strong effect of ice cover on sediment resuspension. To estimate the potential effect of climate change on internal P loading caused by resuspension we compared the Tot-P loading calculations between the present climate and the climate with doubled atmospheric CO₂ concentration relative to the present day values (ice cover reduced from current 165 to 105 d). The annual load increased from 7.4 to 9.4 g m⁻² In conclusion, the annual internal Tot-P loading caused by resuspension will increase by 28% in the Kirkkojärvi basin if the 2 × CO₂ climate scenario comes true.
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