Nutrient-chlorophyll-Secchi relationships under contrasting grazer communities of temperate versus subtropical lakes

Abstract

Published data for total phosphorus (TP), total nitrogen (TN), chlorophyll (Chl), and water transparency (Secchi depth) for 420 lake-years in temperate North America and Europe and subtropical Florida were analyzed to test the hypothesis that subtropical and temperate lakes produce similar nutrient-Chl-Secchi relationships regardless of regional contrasts in seasonal, physical, chemical, and biological characteristics. We also tested the hypothesis that similarities in nutrient-Chl-Secchi relationships between temperate and subtropical lakes are expected only when the size or community structure of zooplankton remains constant. TP-Chl relationships were not significantly different for small zooplankton dominated temperate and subtropical lakes, but large herbivore (LH) dominated temperate lakes exhibited significantly lower Chl yield to TP than either subtropical small herbivore (SH) or temperate SH lakes. Although both nitrogen and phosphorus were important in determining the patterns and strengths of nutrient-Chl relationships in subtropical and temperate lakes, no particularly different role of TN or TP in determining Chl yield in the subtropical versus temperate lakes was observed. Unlike the nutrient-Chl relationships, Secchi depth seemed to decline as a function of both Chl and TP from subtropical SH to temperate SH to temperate LH lakes. Overall, the subtropical and temperate lakes seemed to produce similar general patterns of nutrient-Chl-transparency relationships, although mostly under the dominance of small zooplankton communities.