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TRACING RIVER INFLUENCES ON PHYTOPLANKTON DYNAMICS IN TWO LOUISIANA ESTUARIES
Author(s) -
Wissel Björn,
Gaçe Arian,
Fry Brian
Publication year - 2005
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/04-1714
Subject(s) - estuary , phytoplankton , environmental science , oceanography , drainage basin , hydrology (agriculture) , nutrient , ecology , geology , geography , biology , cartography , geotechnical engineering
To evaluate effects of river inputs on estuarine phytoplankton, we compared particulate organic matter (POM) dynamics in two neighboring estuaries from the Mississippi River delta. The two estuaries, Barataria Basin and Breton Sound, have been isolated from the Mississippi River at their upstream ends for most of the last century due to levee construction, but for the last 13 years, Breton Sound has been reconnected to the Mississippi River via a gated diversion at Caernarvon, Louisiana. Thus, Barataria Basin was the reference estuary and Breton Sound was the river‐impacted estuary. We focused on POM because it was relatively easy to collect and analyze, and because POM dynamics gave a good ecosystem‐level overview of phytoplankton responses to riverine nutrient forcing and hydrologic forcing. A combination of C:N and PO 13 C analyses indicated that most POM was phytoplankton with smaller contributions of sediment. Estuarine concentrations of particulate organic carbon (POC) and nitrogen (PON) were typically higher than end‐member freshwater or marine inputs, indicating the importance of within‐system phytoplankton growth likely fueled by rapid nutrient regeneration in these warm, shallow and well‐mixed estuarine systems. Isotopic analyses generally showed typical estuarine gradients in the reference Barataria Basin estuary, but the river‐influenced upper Breton Sound had elevated PO 13 C and PO 15 N values useful for following the spatial extent of river impacts. Rapid river‐assisted flushing in Breton Sound probably prevented widespread development of algal blooms in response to introductions of the nutrient‐rich river water, but study of some isolated lakes suggested that when longer residence times apply, introduction of river water to coastal estuaries can lead to eutrophic conditions and in some cases, harmful algal blooms. Overall, routinely monitoring amounts and isotopic compositions of POM proved an effective way to trace linkages between river inputs and downstream estuarine phytoplankton dynamics.