Spatial Distributions of Biogeochemical Parameters in Surface Sediments

The spatial variability of several sedimentological. chemical and biological parameters in the uppermost layer of bed sediment (ULBS) in Lake Kinneret, was studied during the development of anoxic conditions in the hypolimnion (May, 1995). ULBS samples were taken along a transect from the littoral to the pelagic zones, during the crash of the Peridinium gatunense bloom, about 2 months after the onset of stratification and when oxygen in the hypolimnion was almost completely depleted. The 2–3mm of theULBS, collected by SCUBA diver, contained relatively fresh material (as shown by high Chl c content) but differed from that of intact Peridinium cells. In the ULBS, the C:N atomic ratio averaged 8 and was similar all over the lake bottom and the average Chlorophyll a:c ratio was 4 (reaching a value of ∼7 at 5m). These ratios in Peridinium cells were about 14.3 and 2, respectively. In addition, δ 13C in the organic matter from the ULBS was lighter than that of Peridinium. This data suggests that substantial degredation of the organic matter already occurs in the water column. Grain size distribution suggests the occurance of intense focussing processes in Lake Kinneret. Chemical and biological parameters in the ULBS exhibited clear depth dependant patterns, suggesting changes in physical and chemical processes occur. Three different zones can be distinguished in Lake Kinneret bottom sediments, a. The littoral oxic photic zone (down to 5–7m), which is influenced by intensive biodegredation and high turbulence, b. Transition zone (7–20m), with an oxic-photic gradient and developed focussing processes, c. Profundal, anoxic zone (>20m), where all fine, settled, organic rich material concentrates and undergoes anaerobic decomposition.