Frequently only limited information on predictions of liming effects on natural chemical conditions is available; thus one may be limited to a single method. All three methods for predictions described here have limitations. The use of data from a period before the treatment requires constancy over time. This seems to be the case for the Ca~*/Mg~* and Si, but certainly not for organic matter, colour, organic N and total-P. Reference objects need to represent the affected lake. But with a higher degree of representation, the availability of reference lakes declines. For the same reason, models have to be based on data for illustrative objects. In the case of liming the calculation of direct effects on Ca and alkalinity seem to work satisfactory. This evaluation indicates that liming lowers total-P by 1-2μg/l. For total-P more work is needed to get good estimates of pretreatment conditions. Even more difficult are predictions of "unlimed" organic matter and nitrogen.
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