The random redistribution of sediment by wind in a lak

The total sedimentation rate was measured fortnightly for a year in a large shallow lake (Lough Neagh, Northern Ireland, surface area 383 km(2), mean depth 8.9 m) at five sites using 10 sediment traps. The total sedimentation rate included both primary and secondary sedimentation. As the annual average total sedimentation rate, 53.2 +/- 44.1 g m(-2) d(-1), is more than 25 times the primary value, secondary sedimentation due to wind-induced resuspension is very important. The average of the largest 30% of wave mixed layer (WML) values, a function of wind speed and effective fetch, strongly correlates with the total sedimentation rate (r(2) values of 0.69 and 0.98 at two westerly sites) at most of the sites. As the WML value approaches the water depth, then the orbital motion of the waves and the associated turbulence cause sediment disturbance and resuspension. Changing WML values, then, provide a basis to describe the "random redistribution" (RR) of sediment in lakes and these resuspension events can occur as frequently as 2-3 times every two weeks. This study provides, for the first time, clear results and a description of the process of RR of sediment in a lake, particularly the link between wind and sediment resuspension.