Responses of phytoplankton to varied resource availability in large lakes of the Greater Yellowstone Ecosystem

Abstract

We assessed phytoplankton dynamics in three lakes in the Greater Yellowstone Ecosystem to better understand the connections between changing environmental conditions and aquatic communities. This work primarily describes the connections between resource availability and phytoplankton seasonal succession in these lakes. We hypothesized that algal species efficient at utilizing a given resource (including N, P, Si, and light) would be correlated with low relative concentrations of those resources. The lakes generally exhibited moderate resource limitation, which is characteristic of lakes in subalpine and subarctic regions. Although in proximity, the lakes all exhibited different resource relationships: Lewis Lake was most P limited, Jackson Lake was most N limited, and Yellowstone Lake exhibited a moderate degree of N limitation along with periodic Si limitation. Mixing depths and light penetration were also variable among lakes. In 1996, spring diatom biomass was dominated by Stephanodiscus minutulus, Asterionella formosa, Aulacoseira subarctica, and Synedra sp. Relative abundances and dominance varied among the lakes. A. formosa and Synedra sp. abundances were positively correlated with total N: total P (TN:TP) levels in an analysis of data from all three lakes. A. subarctica was negatively correlated with TN:TP and all light: nutrient ratios. Species exhibiting late season maxima included Cyclotella bodanica, Fragilaria crotonensis, and Stephanodiscus niagarae. C. bodanica abundances corresponded to high-light/low-N situations, whereas S. niagarae maxima were found in high-TN:TP/low-light conditions. F. crotonensis abundances were most strongly positively correlated with total Si:TP and TN:TP. Environmental correlations were generally in good agreement with the measured physiological requirements of these species. Additionally, local population maxima of major species of diatoms never coincided.