ENVIRONMENTAL CONTROLS OF PHYTOPLANKTON BLOOM DYNAMICS IN THE NEUSE RIVER ESTUARY, NORTH-CAROLINA, USA

Spatial and temporal patterns of phytoplankton growth, biomass, primar y productivity, and community composition were linked to environmental variables to identify key factors promoting algal blooms in the moder ately eutrophic Neuse Estuary. Diagnostic photopigments (carotenoids), used to examine phytoplankton community structure, explained 83.3% (n = 567) of the variation in phytoplankton biomass (chlorophyll a). Pri ncipal factor analysis identified hydrological forcing variables (sali nity, K-d, NOx, and NH4+) that explained 71% of total variability asso ciated with phytoplankton biomass. Phytoplankton carbon-specific growt h rates (mu(Chl)), measured using chlorophyll a C-14-labeling, ranged from 0.01 to 0.83-day(-1) (0.27 +/- 0.22, mean +/- SD) and decreased d ownstream. A regression model (R-2 = 0.41, P < 0.01), derived from 25 months of biweekly sampling of 13 environmental variables, was used to predict mu(Chl) and construct spatiotemporal contour plots of phytopl ankton growth. Enhanced growth (bloom initiation) occurs in the upper riverine portion of the estuary, biomass accumulates (proliferation an d full bloom) in the central portion, and productivity (but not mu(Chl ), overall, tracks phytoplankton abundance. Management strategies for stemming eutrophication should target processes and conditions associa ted with bloom initiation in the riverine rather than the estuarine po rtion of the system.