The four large Swedish lakes Vänern, Vättern, Mälaren and Hjälmaren differ in many respects, not least in drainage area characteristics and basin morphometry (1). The differences also include water quality. Since nutrient chemistry of phosphorus (P) and nitrogen (N) in the lakes is of major concern, it has been treated by several authors (2–13). The hydrochemical studies started in 1964 and in ...