USING WATER LEVEL MANAGEMENT TO REDUCE CYANOBACTERIAL BLOOM TOXICITY IN A NORTHERN LAKE

Lake water level (WL) fluctuations are an important factor driving variation in many ecosystem processes.  Relative to permanently inundated sediments in deeper waters, nearshore sediments that are periodically exposed and re-inundated develop distinct physicochemical characteristics, which we hypothesize alters nitrogen (N) and phosphorus (P) flux from sediments and influences nearshore harmful algal blooms (HABS).  To test this hypothesis we studied Lake Kabetogama (MN, USA), a northern lake where WLs are managed for multiple purposes and that experiences HABs in nearshore areas.  Using intact sediment core experiments, we found that greater WL fluctuations were associated with increases in organic N and P flux from sediments into the water column.  Concurrent experiments on naturally occurring HABs indicate N limitation, and additions of ammonium (but not nitrate) caused decreases in the expression of a cyanotoxin gene (mcyE).  The supply of organic N or P is probably only important for cyanobacteria when more labile forms are depleted, which appeared to be the case for N in our phytoplankton experiment. Possibly, increases in available organic N would prolong the persistence of cyanobacteria blooms, which in our study produced mcyE RNA when N limited.  Using our data to parameterize structural equation models, we predict that, all other things being equal, WL management regimes with greater annual WL fluctuation would result in more N and P supply to the nearshore zone.

Primary Presenter: James Larson, U.S. Geological Survey (jlarson1@alumni.nd.edu)

Authors:

James Larson, U.S. Geological Survey  (jhlarson@usgs.gov)

Sean Bailey, U.S. Geological Survey  (sbailey@usgs.gov)

Ryan Maki, National Park Service  (ryan_maki@nps.gov)

Victoria Christensen, U.S. Geological Survey  (vglenn@usgs.gov)

Erin Stelzer, U.S. Geological Survey  (eastelzer@usgs.gov)

Keith Loftin, U.S. Geological Survey  (kloftin@usgs.gov)

James Smith, U.S. Geological Survey  (james_c_smith@nps.gov)

Jaime LeDuc, Concerned Citizens of Montauk  (leducjaime@gmail.com)

Seth McWhorter, University of Georgia  (mcwhorter.seth@epa.gov)

Susan Wilde, University of Georgia  (swilde@uga.edu)