Exploring algal-nutrient relationships along the freshwater-marine continuum

Cyanobacteria harmful algal blooms (CHABs) have become an increasing concern in coastal North Carolina over recent decades.  While CHABs are typically thought of as a freshwater problem, these blooms and their associated toxins can be found in brackish and saline waters along the freshwater-marine continuum.  In this project, we develop a Bayesian hierarchical (multilevel) model to explore how chlorophyll-nutrient relationships vary along the Pamlico River Estuary, and extend these relationships to cyanobacteria abundance using phytoplankton community data (biovolume, cell count).  In particular, we explore the spatially varying associations of salinity, temperature, critical nutrient ratio (nitrogen: phosphorus), and hydrologic inflows with algal abundance.  These relationships are tested individually, and then combined into a comprehensive model that is found to explain ~ 60% of chlorophyll variability across space and time. Further, results suggest nitrogen is the limiting nutrient ~ 90% of the time.  We then apply the model to predict the sensitivity of chlorophyll and cyanobacteria concentrations to changes in nutrients and environmental variables.  Modeling results are presented for different seasons, hydrologic conditions, and along the freshwater-marine continuum.  Results can be used to forecast when CHABs are most likely, and when and where nutrient reductions will be most effective

Presentation Preference: Oral

Primary Presenter: Daniel Obenour, NC State University (drobenour@ncsu.edu)

Authors:

Daniel Obenour, NC State University  (drobenour@ncsu.edu)

Parisa Noorbeh, NC State University  (pnoorbe@ncsu.edu)

Bigyapti Nepal, NC State University  (bnepal@ncsu.edu)

Elizabeth Fensin, NC Dept. of Environmental Quality  (elizabeth.fensin@deq.nc.gov)

Astrid Schnetzer, NC State University  (aschnet@ncsu.edu)