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Chemical Ecology Evidence for Phosphate as the Only Factor Limiting Algal Growth in Lake Kinneret

1972; Wiley; Volume: 10; Issue: 4 Linguagem: Inglês

10.1002/ijch.197200085

1869-5868

M. Halmann,

Environmental Science and Water Management

Abstract Experiments on the growth of the natural populations of algae and of other microorganisms as a function of the supply of various nutrients was carried out for Lake Kinneret water sampled at about 2 week intervals during January‐June 1972. The addition of orthophosphate caused a rapid rise in biomass, which, after several days, increased to 2‐5 times that in untreated water, as measured by the increase in turbidity and protein content. On the other hand, the addition of sodium or potassium nitrate, ammonium chloride, ferrous ethylenediamine sulfate, sodium silicate or vitamin B12 had no noticeable effect. The plot of biomass produced versus the concentration of added phosphate is a steeply rising function in the range of 0.1 to 1.0 μ molar orthophosphate, which levels off at higher phosphate concentrations, reaching saturation above about 2 μ molar phosphate. Thus, in the range of its natural concentration in Lake Kinneret, 0.09‐0.5 μ molar, orthophosphate is the limiting factor. Above 2 μ molar phosphate, nitrate becomes the limiting factor, as was shown by experiments in which both phosphate (>2 μ molar) and nitrate were added, resulting in extremely abundant algal growth. A model of the reduction of nutrient input was achieved by laboratory experiments, in which the lake water was diluted with distilled water (by 1/4), thus resulting in an approximately proportional (to about 1/4) decrease in biomass. The effect of restoring the natural concentration of either nitrate or orthophosphate was then measured. Added nitrate had no effect, while added phosphate caused a rapid increase in biomass, which after 2‐4 weeks came close to that in the natural lake water. These results indicate that during the spring of 1972, phosphorus has been the only element limiting algal growth in the lake.