Nutrient dependence of primary productivity in lakes1

An analysis of growing season measurements of daily primary productivity, chlorophyll, water chemistry, and transparency from 58 north temperate lakes shows a strong correlation between volumetric rates of photosynthesis, chlorophyll, and nutrients. Mean daily rates of photosynthesis per unit volume euphotic zone, v̄ , are correlated with mean chlorophyll concentration ( r 2 = 0.80). The mean daily rate of photosynthesis at optimal depth, Ā opt , is highly correlated with mean total P( r 2 = 0.95), and with mean total N( r 2 = 0.91). In contrast, integral rates of photosynthesis are linked less tightly to nutrient concentration because of their simultaneous dependence on transparency. The Dillon‐Rigler phosphorus loading model is extended to predict volumetric rates of photosynthesis ( v̄ and Ā̄ opt ) in lakes where the N:P balance indicates control by phosphorus (N:P ⩾ 13).