New Zealand Journal of Marine and Freshwater Research abstracts

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AVAILABILITY OF SOIL AND SEDIMENT PHOSPHORUS TO A PLANKTONIC ALGA

R. H. S. McColi

Ecology Division, Department of Scientific and Industrial Research, P.O. Box 30466, Lower Hutt, New Zealand

Abstract Chlorophyll production by Chlorella vulgaris Beij. var. vulgaris was used to estimate alga-available phosphorus in clays, soils, and lake sediments suspended in water at concentrations appropriate to lake inflows during floods (100 -500 g/m³). Chlorella apparently used 24-81% of 0.5MH₂SO₄ extractable phosphorus in clays from topsoils, about 25% from lake sediments, and 0.3-1.0% from, subsoils low in phosphorus and with high phosphorus retention. The presence of suspended soil material did not reduce the availability to Chlorella of inorganic phosphorus added to the cultures. Increasing the Chlorella population by adding inorganic phosphorus resulted in an apparent increase in availability of phosphorus from the soil, possibly as a result of enzymic mineralisation of organic soil phosphorus. The amount of available phosphorus in lake sediments was not a reliable guide to the trophic condition, of the lake. Suspended material from sediments, soils, and especially clay eroded from fertilised topsoils may provide phosphorus for algal growth in. lakes. If allqphanic clays are applied to lakes to sorb phosphorus and hence control eutrophication, the particles must settle out before planktonic algae in the photic zone can use the adsorbed phosphorus.

*Present address: Soil Bureau, DSIR, Private Bag, Lower Hutt, New Zealand. N.Z. Journal of Marine and Freshwater Research 9 (2): 169-82
(Received 30 September 1974)

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