Spectral Irradiance, Phytoplankton Community Composition and Primary Productivity in a Salt Marsh Estuary, North Inlet, South Carolina, USA

Abstract

We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant col- ors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7-2.1 m −1 with corresponding euphotic zone depths of 1.5-6.7 m. Phytoplankton biomass (as chlorophyll a(chla))variedseasonallywitha summermaximum of16 μg chl a l −1 and a winter minimum of 1.4 μ gc hla l −1 .T he phytoplankton community consisted mainly of diatoms, prasi- nophytes, cryptophytes and haptophytes, with diatoms and pra- sinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest cor- relations with temperature.Light-saturated chla-specific ratesof photosynthesis and daily primary productivity varied with sea- son and ranged from 1.6 to 14 mg C (mg chl a) −1 h −1 (32-803 mg C m −3 day −1 ). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m −3 year −1 .O verall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a rela- tively minor role due to short residence times, strong tidal forcing and vertical mixing.