PHYTOPLANKTON ASSEMBLAGE DYNAMICS IN RELATION TO ENVIRONMENTAL CONDITIONS IN A RIVERINE LAKE

Understanding drivers of phytoplankton assemblage structure is essential given the ecological, aesthetic, and health consequences that vary among taxonomic groups. In this study we examined phytoplankton assemblage structure over a three-year period in Lake Pepin, a natural riverine lake on the Upper Mississippi River. Phytoplankton samples along with a suite of limnological variables were collected from April to October, at 4 sites along a longitudinal gradient of the lake spanning 35 kilometers. To investigate potential relationships, mechanisms, and drivers between environmental conditions and phytoplankton assemblage structure a distance-based linear model was utilized. We found over 100 phytoplankton taxa and assemblage structure varied between years, months, and sites. 32.6% of the total variation in phytoplankton assemblages was explained by a combination of chemical, hydrological, and physical variables. Additionally, we noted a one-year absence of the common diatom, Stephanodiscus hantzschii, that may have been related to an unusual spring of warm water temperature and very low soluble reactive phosphorus concentrations that suggests a possible nutrient limitation for this species in a large river system. Insights into the relationships between environmental conditions and individual and co-occurring species of phytoplankton should aid in developing a greater predictability of assemblages and may enable large river scientists and managers to better anticipate and address water quality conditions under changing climate and hydrologic regimes.

Primary Presenter: Robert Burdis, Minnesota Department of Natural Resources (robert.burdis@state.mn.us)

Authors:

Robert Burdis, Minnesota Department of Natural Resources  (robert.burdis@state.mn.us)

Nicole Ward, Minnesota Department of Natural Resouces  (nicole.ward@state.mn.us)

John Manier, USGS-Upper Midwest Environmental Sciences Center  (jmanier@usgs.gov)