Phosphate in Lakes and Rivers

In lakes and rivers the soluble phosphate content is very variable and this can be accompanied by much phosphate absorbed on suspended clay particles as well as that present in fish, algae and other living matter. 

Unlike in the ocean where phosphate is precipitated as a calcium salt, in lakes (and to a lesser extent in rivers), insoluble iron and aluminium salts may also be involved. Reactions are complicated and are affected not only by the composition of the input water, but by climate and the numerous types of suspended matter which can already be present in the lake. Acid sediments favour the formation of aluminium and iron phosphates, but with neutral or alkaline conditions, calcium salts are likely to predominate. 

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