Nutrient flux in the Rhode River: Tidal transport of microorganisms in brackish marshes

Abstract

Concentrations of bacteria, chlorophyll a, and several dissolved organic compounds were determined during 11 tidal cycles throughout the year in a high and a low elevation marsh of a brackish tidal estuary. Mean bacterial concentrations were slightly higher in flooding (7·1 × 10 6 cells ml −1) than in ebbing waters (6·5 × 10 6 cells ml −1), and there were no differences between marshes. Mean chlorophyll a concentrations were 36·7 μg l −1 in the low marsh and 20·4 μg l −1 in the high marsh. Flux calculations, based on tidal records and measured concentrations, suggested a small net import of bacterial and algal biomass into both marshes. Over the course of individual tidal cycles, concentrations of all parameters were variable and not related to tidal stage. Heterotrophic activity measured by the uptake of 3H-thymidine, was found predominantly in the smallest particle size fractions (< 1·0 μm). Thymidine uptake was correlated with temperature ( r = 0·48, P < 0·01), and bacterial productivity was estimated to be 7 to 42 μg Cl −1 day −1.