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

We assessed phytoplankton dynamics in three lakes in the Greater Yellowston e Ecosystem to better understand the connections between changing environme ntal conditions and aquatic communities. This work primarily describes the connections between resource availability and phytoplankton seasonal succes sion in these lakes. We hypothesized that algal species efficient at utiliz ing a given resource (including N, P, Si, and light) would be correlated wi th low relative concentrations of those resources. The lakes generally exhi bited moderate resource limitation, which is characteristic of lakes in sub alpine and subarctic regions. Although in proximity, the lakes all exhibite d different resource relationships: Lewis Lake was most P limited, Jackson Lake was most N limited, and Yellowstone Lake exhibited a moderate degree o f N limitation along with periodic Si limitation. Mixing depths and light p enetration were also variable among lakes. In 1996, spring diatom biomass w as 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 correlate d 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: n utrient ratios. Species exhibiting late season maxima included Cyclotella b odanica, Fragilaria crotonensis, and Stephanodiscus niagarae. C. bodanica a bundances corresponded to high-light/low-N situations, whereas S, niagarae maxima were found in high-TN: TP/low-light conditions. F. crotonensis abund ances were most strongly positively correlated with total Si:TP and TN:TP. Environmental correlations were generally in good agreement with the measur ed physiological requirements of these species. Additionally, local populat ion maxima of major species of diatoms never coincided.