TEMPORAL AND SPATIAL GRADIENTS IN PHYTOPLANKTON PIGMENTS IN THE TAR-PAMLICO RIVER ESTUARY

Abstract

Phytoplankton form the base of most aquatic food webs, and their biomass and the composition of their communities directly impact upper trophic levels. Phytoplankton chlorophyll a concentrations in aquatic environments have been long used to estimate phytoplankton biomass, and the concentrations of accessory chlorophylls and carotenoids used to diagnose the taxa composing the phytoplankton community of an area. In this study, the photopigments present in water samples collected at eleven sites from October to December 2016 along the Tar-Pamlico River estuary were measured using high performance liquid chromatography (HPLC). From the concentrations of these pigments, phytoplankton biomass and community composition was estimated along the spatial gradient of the freshwater end of the Tar-Pamlico River estuary to the mouth of the Tar-Pamlico River. Chlorophyll a concentrations were found to be significantly lower in upstream stations than downstream stations. Concentrations of accessory pigments varied between stations and dates sampled, but no consistent trends were observed over time or space. Changes in pigment concentrations were compared to environmental characteristics such as water temperature, salinity, and dissolved nutrient content to determine the magnitude of their influence on the phytoplankton community. No strong correlations were observed between any combination of these factors and pigment concentrations of samples.