Spatial distributions of biogeochemical parameters in surface sediments

Abstract

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 tile crash of thePeridmium gatunense bloom, about 2 months after the onset of stratification and when oxygen in the hypolimnion was almost completely depleted. The 2–3mm of the ULBS, collected by SCUBA diver, contained relatively fresh material (as shown by high Chl c content) but differed from that of intactPeridinium 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 inPeridinium cells were about 14 3 and 2, respectively. In addition, δ¹²C in the organic matter from the ULBS was lighter than that ofPeridinium. 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 pholic zone (down to 5–7m), which is influenced by intensive biodegradation and high turbulence. b Transition zone (7–20m), with anoxic-photic gradient and developed focussing processes c. Profundal, anoxic zone (>20m), where all line, settled, organic rich material concentrates and undergoes anaerobic decomposition.