Possible Effect of Lock and Dam 19 on Phytoplankton Communities of the Upper Mississippi River

Abstract Algal community composition at three sites above and five sites below Lock and Dam 19 on the upper Mississippi River was determined from samples taken during July, August, September, and November of 2003, and April and June of 2004, to compare the above-dam navigation-channel and vegetation-bed phytoplankton communities, and determine what effect the power plant and lock and dam may have on the mixing of these communities. We predicted there would be clear differences in community composition and abundance between the three above-dam locations and a more uniform community composition below the dam due to mixing. No site-specific or predictable patterns to suggest an effect of the power plant or lock and dam were detected. Nonmetric multidimensional scaling ordination supports the idea that temporal factors may play a larger role in structuring localized phytoplankton communities in this section of the upper Mississippi River.