Organic matter and pigments in surface sediments: Possible mechanisms of their horizontal distributions in a stratified lake

The analysis of spatial changes of organic matter and pigments (chlorophyll a, chlorophyll b, bacteriochlorophyll e, and phaeophytin a) in the uppermost bottom sediments was used to distinguish between sources of settled material in Lake Kinneret (Israel) during thermal stratification. The proportion of phytobenthic chlorophyll a decreased relatively to total chlorophyll a down to zero at 17 m. Bacteriochlorophyll e, derived from Chlorobium phaeobacteroides, was the most abundant pigment below the thermocline. Organic matter content in the sand-free sediment fraction and chlorophyll a to organic matter ratio were the lowest in the bottom area most extensively affected by shoaling internal seiches and where resuspension occurred. The proportion of resuspended matter sharply decreased with bottom depth in the hypolimnion. The importance of degraded materials of planktonic origin apparently increased towards the lake center. These distribution patterns could be achieved by dispersion of the rapidly sinking resuspended particles with fast metalimnetic jets and by focusing of the lighter planktonic particles by water motions in the turbulent benthic boundary layer. Our study showed that analysis of distribution of freshly settled organic components on the bottom may be a useful tool for understanding particle transport mechanisms in lakes.