A validated model for daily variations in the flux, origin, and distribution of settling particles within lakes

Abstract

We performed intensive sediment trap studies at different water depths and locations in nine Swedish lakes to determine the flux, distribution, and origin of settling particulate matter in the pelagic zone. From these data, we developed a dynamic model that includes important mechanisms controlling fluxes of autochthonous, allochthonous, and resuspended 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, resuspended particles are quite evenly distributed in the water column. During stratification, however, particles in deeper lakes are enriched 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 sediment focusing. The model allows determination of sediment accumulation at different water depths and of the boundary between erosion, transportation, and accumulation of sediment. Furthermore, the model shows the time dependence of the flux and distribution of settling particles in relation to changes in wind speed. The model is driven by wind, stratification, and lake morphometric data that can be determined with good accuracy. Some coefficients describing particle dynamics are also needed, e.g. particle settling velocity, vertical water mixing velocity, and sediment resuspension rate. The most uncertain coefficients were subjected to sensitivity analyses. The model can explain differences over time in the flux, origin, and distribution of settling 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.Settling particles have often been considered to be the major transport media for nutrients, toxic metals, and organic contaminants, and they are known to be important for the removal of bioavailable nutrients and pollutants from the water column (Salomons and Forstner 1984;Allan 1986;Allard et al. 1991; Baudo et al. 1991). To determine spatial distribution patterns, sedimentation and resuspension, biological uptake, and ecological effects of nutrients and pollutants, information is needed about the flux of carrier particles, in particular about the amount, the composition, and the distribution of settling particulate matter (SPM; see notations). It is quite common to study characteristics of SPM with sediment traps (Eadie et al. 1984;Rosa 1985; Bloesch and Uehlinger 1986), and the processes of sediment distribution are well known (Hilton 1985; Hilton et al. 1986). Nevertheless, fluxes of SPM in lakes are not completely understood, most likely because there are still uncertainties in quantifying the ...

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