FREQUENCY-DISTRIBUTIONS AND TRANSFORMATIONS OF LAKE VARIABLES, CATCHMENT-AREA AND MORPHOMETRIC PARAMETERS IN PREDICTIVE REGRESSION-MODELS FOR SMALL GLACIAL LAKES

There are more than 83 000 lakes in Sweden and about 81 000 of these c all be characterized as small, glacial lakes. Similar proportions betw een small, glacial lakes and other lake types ought to exist also for lakes in other parts of the world influenced by the latest glaciation, e.g. North America, Russia and Finland. Most lakes on the earth belon g to this population of lakes. All lakes from this population cannot b e thoroughly investigated, only a sample of lakes. A key question then is: how will empirical models based on data from the sample of lakes predict for other lakes from the population? It is not possible to ans wer that question unless several sub-questions are first addressed. Th is work concerns one of those, does the frequency distribution of the sample represent the frequency distribution of the population? The wor k addresses this issue from the perspective of predictive empirical mo dels for lake management and research. This work presents comprehensiv e data sets on a battery of practically useful standard lake variables from more than 900 lakes. All these lakes are Swedish, but they cover a wide range of geographical, geological and climatological character istics and the results should be widely applicable for all lakes from this lake type. General recommendations on suitable transformations fo r empirical models are presented for 12 water variables (pH, total-P, colour, hardness, etc.), 13 catchment area characteristics (bedrocks, soils, etc.) and 17 lake morphometric features (size and form paramete rs). This paper also presents case studies demonstrating the importanc e of selecting the right transformations for predictive empirical mode ls. New models for Secchi depth, lake pH, colour and total phosphorus are presented to illustrate the practical utility of the results conce rning transformations. The effects of sample size on transformations c hoices are also evaluated. (C) 1997 Elsevier Science B.V.