Temporal changes in nitrogen and phosphorus codeficiency of plankton in lakes of coastal and interior British Columbia

Plankton nutrient limitation and deficiency were assessed in six coastal and four interior lakes and reservoirs in British Columbia. Ultimate nutrient limitation was defined as occurring over longer time scales (months to years) and represented the potential attainable biomass or yield. Proximate nutrient deficiency reflected plankton physiological status and, therefore, represented potential limitations of instantaneous growth rates. All lakes and reservoirs were considered to be ultimately P-limited according to total N to total P ratios (TN:TP). However, both P and N deficiencies were found to occur at the same time, suggesting that when deficiency occurs, codeficiency is common. The <3 mum size fraction accounted for a large proportion of P debt, whereas the >3 mum size fraction accounted for most of the ammonium-enhanced response. Thus, plankton size is important for understanding nutrient deficiencies in plankton communities. Our results stress (i) the importance of measuring proximate deficiencies at greater temporal resolution, (ii) that N and P were commonly found to be codeficient, (iii) the need to define nutrient limitation and deficiency in the context of the method used, and (iv) that several concurrent measures of deficiency are required to assess the nutrient status of plankton communities.