| Abstract |
In order to examine the response of stream phytoplankton communities to acidification, three artificial streams along the Mississippi River were sampled at biweekly intervals. This study took place at Monticello, Minnesota, during late spring-early summer, 1979. One stream served as a control with an ambient pH of 8.1, and two streams were maintained at pH 6.3 and 5.3 by the addition of sulfuric acid. The streams provided a unique replicate system whereby physical and chemical parameters could be controlled and continually monitored in a field situation. The phytoplankton samples were filtered onto membrane filters and the constituent phytoplankton species were enumerated. The diversity of phytoplankton was similar throughout all three pH regimes. However, phytoplankton community similarity decreased over the course of the six week experimental period. Biomass, measured by in vivo chlorophyll fluorescence and as the density of the algal cells, showed a similar pattern. The pattern of algal community development differed across the pH treatments. The phytoplankton at pH 6.3 and 8.1 attained their maximum biomass during the first month of sampling (June). There is a lag in the population maxima of phytoplankton at pH 5.3, possibly due to a slower division rate caused by a less than ideal pH environment. Species composition was nearly identical across the pH range, dominated by diatoms in each stream. The most extreme pH value, pH 5.3, seemed to be a sublethal value for the diatoms existing there. |
