Phosphorus and nitrogen limitation of phytoplankton growth in the freshwaters of North America: a review and critique of experimental enrichments

While P is generally considered to be the primary nutrient limiting algal growth in lakes, limitation of algal growth by N has been observed in freshwater. The most pronounced phytoplankton responses to enrichment occur when both N and P are added together. The role of N and P in constraining algal growth at the whole-lake scale have not been completely separated, but examination of the distribution between treatments of lake-years in which substantial algal growth response occurred indicated that combined N and P enrichment was required to consistently produce substantial algal growth response. A more important role than has previously been recognized for N as a limiting nutrient in freshwaters is indicated. -from Authors