Planktonic nutrient regeneration and cycling efficiency in temperate lakes

Planktonic nutrient regeneration is a fundamental process that maintains mo st of the primary productivity in marine and fresh-water environments. Howe ver, there is no robust predictive model to describe the pattern and effici ency of nutrient cycling across aquatic systems. Based on rather weak evide nce, the efficiency of nutrient regeneration is believed to decline along a gradient of productivity, so that nutrient-poor environments are assumed t o be more efficient at cycling their nutrients than are nutrient-rich envir onments(1-5), Here we measure phosphorus regeneration directly and show tha t cycling efficiency does not vary with phosphorus concentration. In additi on, we confirm that the phosphorus supply for lake plankton comes primarily from within the plankton community, rather than from external loading or f rom larger organisms such as fish.