The Influence of the Atchafalaya River on Wetland and Estuarine Functioning: Management Implications
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PRESENTATION
John Day, Robert Lane, Robert Twilley, Dubravko Justic, Richard Shaw, and James Cowan johnday@lsu.edu
Dept. of Oceanography and Coastal Sciences, School of the Coast and Environment, Louisiana State University, Baton Rouge, LA 70803
Abstract
Atchafalaya River discharge strongly influences the physics, chemistry, and ecology of Fourleague Bay and adjacent areas. Circulation is dominated by river discharge spring when residence time is low. The river introduces high amounts of sediments, nutrients and organic matter.
Sediments initially deposited in the bay are redistributed to wetlands and the near‐shore. Marsh accretion is high. There is net uptake of N by sediments and wetlands during high flow and a net release during low flow. The shallow bay is well‐mixed with oxygenated surface sediments and low rates of P regeneration for most of the year. Stable isotope analyses show the river is an important source or organic material to the system. During high flow, chlorophyll and aquatic primary production (APP) are highest at the fresh‐saline interface, along bay‐margins and in tidal bayous draining into the bay. Light limits APP in fresher areas while nutrients are a more important in higher salinity waters. Annual phytoplankton production is about 400 g C m‐2y‐1. Zooplankton egg production is high (12‐70 eggs female ‐1d‐1), correlated with chlorophyll, and often >50% of daily APP. Both resident and offshore‐spawned, larvae of estuarine‐dependent species show clear salinity responses. Larval fish were transported into and retained within bay. Ontogenetic shifts in habitat utilization with the bay and adjacent bayous appear to follow the seasonality in river discharge and chlorophyll concentration. Most of this work was supported by the Louisiana Sea Grant Program.
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