Why does the relationship between benthic primary production and lake morphometry vary regionally?

Benthic primary production varies among lakes from 1 to 2000+ mg C m− 2 d− 1, in part owing to variations in basin shape. First principles predict an inverse correlation between benthic primary production and mean to maximum depth ratio, an index of basin shape, but reports of positive correlations suggest that current understanding is incorrect or incomplete. We develop a hypsometric (area–depth) model for littoral area that accounts for habitat disruption due to ice scouring at the lake margin. When this disruption is incorporated, the direction of the relationship between benthic primary production and depth ratio depends on water clarity—regions with clear lakes should have positive correlations, whereas regions with less water clarity should have inverse correlations. Empirical analysis of benthic primary production measurements from four eco-regions characterized by different levels of water clarity supports this prediction. Collectively, our analyses demonstrate how first principles can be used to explain heterogeneous patterns of benthic primary production at broad geographic scales.