OPTIMAL SAMPLING PERIOD FOR PREDICTING PHOSPHORUS AND CHLOROPHYLL CONCENTRATIONS IN NORTH-TEMPERATE LAKES

Because total phosphorus and chlorophyll a concentrations vary seasona lly within north-temperate lakes, estimates of lake trophic status are usually based on several to many sampling visits. However, because su ch effort is not always logistically possible, the empirical relations hips developed between these trophic status indicators may depend upon seasonal patterns of sampling. Clearly, it is desirable to know if so me periods of the year are more likely to produce representative estim ates of total phosphorus and chlorophyll a, or, alternatively, if samp ling in other periods should be restricted or even avoided. Data from north-temperate lakes are used to examine the degree to which single m onthly samples for total phosphorus and chlorophyll a represent season al means. Analyses indicate that the least precise and least accurate estimates of the means occur when single-visit synoptic surveys are co nducted during April. Not until August to September do single sampling visits provide data that approximate those represented by the means g arnered through more frequent sampling.