A VALIDATED MODEL FOR DAILY VARIATIONS IN THE FLUX, ORIGIN, AND DISTRIBUTION OF SETTLING PARTICLES WITHIN LAKES

We performed intensive sediment trap studies at different water depths and locations in nine Swedish lakes to determine the flux, distributi on, and origin of settling particulate matter in the pelagic zone. Fro m these data, we developed a dynamic model that includes important mec hanisms controlling fluxes of autochthonous, allochthonous, and resusp ended particles in lakes during both stratification and turnover. The data suggest that during the period of turnover, sediment resuspension is a function of direct wind/wave activities. During these periods, r esuspended particles are quite evenly distributed in the water column. During stratification, however, particles in deeper lakes are enriche d in the hypolimnion. We suggest that these particles are resuspended due mainly to internal water motions. The model describes how much and at which water depths material is resuspended, and how this material is distributed in the water column. This includes the process of sedim ent focusing. The model allows determination of sediment accumulation at different water depths and of the boundary between erosion, transpo rtation, and accumulation of sediment. Furthermore, the model shows th e time dependence of the flux and distribution of sealing particles in relation to changes in wind speed. The model is driven by wind, strat ification, and lake morphometric data that can be determined with good accuracy. Some coefficients describing particle dynamics are also nee ded, e.g. particle settling velocity, vertical water mixing velocity, and sediment resuspension rate. The most uncertain coefficients were s ubjected to sensitivity analyses. The model can explain differences ov er time in the flux, origin, and distribution of sealing particles in different lakes. Because it has earlier been recognized that the flux and distribution of settling particles can be of great importance for the dispersal, burial, biouptake, and ecological effects of nutrients and contaminants, the model may provide valuable information for lake management.