40Phytoplankton biomass and community dynamics in the lake pont-chartrain estuary of southeast louisiana, usa: effects of light and nutrients upon seasonal and spatial patterns

A yearlong study (2002–2003) was conducted in the Lake Pontchartrain Estuary (LPE) of Southeast Louisiana in order to examine the temporal and spatial variability of phytoplankton biomass and community dynamics in relation to nutrients, light climate and other abiotic parameters. Variability was assessed through a north-south transect across the estuary and at five of the major tributaries of the LPE at bi-weekly intervals. Phytoplankton pigmentation was analyzed by HPLC and used to calculate biomass (as chlorophyll a) and to determine the relative abundances of phylogenetic groups and taxa (via CHEMTAX). Microscopic analyses of select samples were used to verify the efficacy of the CHEMTAX method in the waters of the LPE. Water-column up-/down-welling irradiance (PAR) and colored dissolved organic matter (CDOM) measurements were used to characterize the light climate. Results indicate that LPE phytoplankton biomass and community composition are: 1) highly variable at the spatial and temporal scales of this study, 2) can significantly impact the light field of the LPE, and 3) are influenced by macro-nutrient ratios.