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Use case 3 Shallow lakes with low transparency due to sediment resuspension

Turbid lakes are often shallow. They are turbid because the windwaves can resuspend sediment from the bed. These lakes have a high risk to increase in trophic state (eutrophication) and for cyanobacterial blooms. A distinct type of lake in this category are those fed by glaciers.
Because of their vulnerability, some of the lakes in this category are under severe environmental pressure. This seems to be mainly related to their geophysical location (Africa, Middle East) in areas where there is less money available for protection measures. Because in the same areas the lakes are important for all kinds of socio-economic services, the environmental degradation is followed by socio-economic problems.

In case the river inflow is dominated by the optics of TSM and not by the absorption of chlorophyll and CDOM, the effect on the optics of the lake is the same as for re-suspension events: the backscattering is relatively high and the water therefore appears bright. The colour of these lakes is generally described as brown/green, although glaciers fed lakes turn gray.

Within GLaSS, the following shallow lakes with high resuspension have been selected:

Used case 3

Examples and current work

Markermeer

Large wind-exposed shallow lakes are often turbid because lakebed sediments can be whirled up to the water surface under moderate winds. Local influence of the wind became clear when examining satellite remote sensing data. Retrieved surface Total Suspended Matter (TSM) maps from remote sensing matched resuspension predicted from wind and water depth. These findings contribute to the understanding of the Markermeer ecosystem, and support assessment of measures to mitigate high turbidity and reverse unfavorable ecological trends, which has parallels in shallow lakes management all over the world.

Selection 422 Selection 423 Selection 424

TSM concentrations (in mg/l) for different wind directions and speeds. (Left) High surface TSM concentrations in the northeast under the influence of westerly winds, versus (Centre) a clear directional TSM signal resulting from northeasterly winds followed by (Right) lower concentrations caused by settling when the wind is abating (Eleveld, 2012)

Himalayan lakes

Nepal field

In October 2014 a field campaign was carried out by GlaSS partner CNR. Find more photos, details and initial results in this presentation.

Deliverable 5.4 Shallow lakes with low transparency due to sediment resuspension;

References

  • Eleveld, M. A. (2012). Wind-induced resuspension in a shallow lake from Medium Resolution Imaging Spectrometer (MERIS) full-resolution reflectances. Water Resources Research 48(4), W04508, doi:10.1029/2011WR011121