Orthophosphate turnover times were measured in 18 small and medium-sized lakes in western Canada. Turnover times in eight thermally stratified lakes were similar to those of other Canadian lakes: moderately rapid (up to 42 min) in the spring, increasing to very rapid (3–16 min) during July and August. Turnover times in the shallow (i.e. those which mixed intermittently during summer) productive lakes were far more variable, ranging from 17 min to 17 h in spring and 2 min to 36 h during July and August. For individual shallow lakes turnover times remained constant for particular summers. One shallow lake was studied over two summers. In the first summer, turnover times were extremely slow (7–36 h) and in the second summer they were extremely rapid (2–11 min). Therefore I suggest that the mechanisms controlling nutrient limitation in shallow productive lakes are not constant, and can vary dramatically from year to year.
Multi-Elements in Waters and Sediments of Shallow Lakes: Relationships with Water, Sediment, and Watershed Characteristics
