Bio-physical modeling of the Hudson River plume dynamics from a bio-optical perspective.

Bronwyn Cahill (1,2), Paul Bissett (1), Oscar Schofield (2)

(1) Florida Environmental Research Institute, Tampa, FL, USA
(2) IMCS, Rutgers University, New Brunswick, NJ, USA


The Hudson River plume emanates from the highly urbanized New York / New Jersey Harbor complex, and represents a major pathway for the transport of nutrients and chemical contaminants to the coastal ocean. The fate and transport of this material is controlled not only by plume dynamics but also by biological and chemical processes that are coupled to the dynamics of the plume. As part of the Lagrangian Transport and Transformation Experiment (LaTTE), we use ROMS/EcoSim to model and synthesize LaTTE data from a bio-optical perspective, and examine the impact of buoyant plumes on the ecological dynamics of the Northeast US coast. EcoSim is an ecological/optical modeling system that was developed for simulations of carbon cycling and biological productivity. It includes four phytoplankton functional groups, each with a characteristic pigment suite which vary with the group carbon-to-chlorophyll-a ratio, C:Chla. The properties of each functional group evolve over time as a function of light and nutrient conditions. Other EcoSim components include bacteria, dissolved organic matter, and dissolved inorganic carbon cycling. The interaction between EcoSim’s components describe autotrophic growth of and competition between the four phytoplankton groups, differential carbon and nitrogen cycling, nitrogen fixation and grazing.

Our first simulations focus on April 2005, coincident with the LaTTE 2005 field program, when a high springtime discharge from the Hudson River estuary took place, and variable mean winds predominantly fluctuated between northeasterlies and southeasterlies. Our results show a buoyant bulge of freshwater developing seaward of the Hudson River estuary in response to the high freshwater discharge event. Transport of the freshwater anomaly appears to respond to the prevailing wind direction: northeasterlies transport the freshwater anomaly southwestward along the New Jersey coast; southeasterlies transport the freshwater anomaly northeastward along the coast of Long Island. Oceansat derived chlorophyll between 5th and 21st April 2005 show plumes of high chlorophyll concentrations (> 5 mgl-1) developing along both the New Jersey and Long Island coasts. The ecological response to the freshwater anomaly, as determined by EcoSim, is being examined.