Article

Wetlands

, Volume 34, Issue 3, pp 413-425

Thresholds in the Response of Free-Floating Plant Abundance to Variation in Hydraulic Connectivity, Nutrients, and Macrophyte Abundance in a Large Floodplain River

  • Shawn M. GiblinAffiliated withWisconsin Department of Natural Resources, Mississippi River Monitoring Field Station Email author 
  • , Jeffrey N. HouserAffiliated withUpper Midwest Environmental Sciences Center, US Geological Survey
  • , John F. SullivanAffiliated withWisconsin Department of Natural Resources
  • , Heidi A. LangrehrAffiliated withWisconsin Department of Natural Resources, Mississippi River Monitoring Field Station
  • , James T. RogalaAffiliated withUpper Midwest Environmental Sciences Center, US Geological Survey
  • , Benjamin D. CampbellAffiliated withWisconsin Department of Natural Resources, Mississippi River Monitoring Field Station

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Abstract

Duckweed and other free-floating plants (FFP) can form dense surface mats that affect ecosystem condition and processes, and can impair public use of aquatic resources. FFP obtain their nutrients from the water column, and the formation of dense FFP mats can be a consequence and indicator of river eutrophication. We conducted two complementary surveys of diverse aquatic areas of the Upper Mississippi River as an in situ approach for estimating thresholds in the response of FFP abundance to nutrient concentration and physical conditions in a large, floodplain river. Local regression analysis was used to estimate thresholds in the relations between FFP abundance and phosphorus (P) concentration (0.167 mg l−1), nitrogen (N) concentration (0.808 mg l−1), water velocity (0.095 m s−1), and aquatic macrophyte abundance (65 % cover). FFP tissue concentrations suggested P limitation was more likely in spring, N limitation was more likely in late summer, and N limitation was most likely in backwaters with minimal hydraulic connection to the channel. The thresholds estimated here, along with observed patterns in nutrient limitation, provide river scientists and managers with criteria to consider when attempting to modify FFP abundance in off-channel areas of large river systems.

Keywords

Mississippi River Free-floating plants Duckweed Nitrogen Phosphorus Connectivity