Annual Phytoplankton Primary Production Estimation in a Temperate Estuary by Coupling PAM and Carbon Incorporation Methods

Abstract

Phytoplankton primary production varies considerably with environmental parameters especially in dynamic ecosystems like estuaries. The aim of this study was to investigate short-term primary production along the salinity gradient of a temperate estuary over the course of 1 year. The combination of carbon incorporation and fluorescence methods enabled primary production estimation at short spatial and temporal scales. The electron requirement for carbon fixation was investigated in relation with physical-chemical parameters to accurately estimate primary production at high frequency. These results combined with the variability of the photic layer allowed the annual estimation of primary production along the estuary. Phytoplankton dynamics was closely related to salinity and turbidity gradients, which strongly influenced cells physiology and photoacclimatation. The number of electrons required to fix 1 mol of carbon (C) was ranged between 1.6 and 25 mol electron mol C−1 with a mean annual value of 8 ± 5 mol electron mol C−1. This optimum value suggests that in nutrient replete conditions like estuaries, alternative electron flows are low, while electrons transfer from photosystem II to carbon fixation is highly efficient. A statistical model was used to improve the estimation of primary production from electron transport rate as a function of significant environmental parameters. Based on this model, daily carbon production in the Seine estuary (France) was estimated by considering light and photic zone variability. A mean annual daily primary production of 0.12 ± 0.18 g C m−2 day−1 with a maximum of 1.18 g C m−2 day−1 in summer was estimated which lead to an annual mean of 64.75 g C m−2 year−1. This approach should be applied more frequently in dynamic ecosystems such as estuaries or coastal waters to accurately estimate primary production in those valuable ecosystems.

Dynamics of exopolymeric carbon pools in relation with phytoplankton succession along the salinity gradient of a temperate estuary (France)

“…The Surprising high values recorded in winter were attributed rather to freshwater chlorophyll detrital matter than living phytoplankton (Morelle et al 2018).…”

“…In these conditions, the mean sampling depth at the WSI is 13.2 ± 1.4 meters. The physical-chemical parameters are described and interpreted in a previous paper (Morelle et al 2018) and a slight summary of their dynamics is given in this paper.…”

“…The dynamics and the high density of phytoplankton in terms of chla coincides with high species richness, high primary production (PP), and high productivity values (Morelle et al 2018).…”

Uncertainties in variable fluorescence and 14C methods to estimate primary production: a case study in the coastal waters off the Korean peninsula

“…Many regional studies have shown that Φ e,C in natural communities correlates with environmental factors such as macro-and micronutrients, temperature, salinity, light intensity, water transparency, and chl a (Lawrenz et al 2013, Schuback et al 2017, Morelle et al 2018. Mostly these relationships are empirical rather than mechanistic.…”

“…The main principle of these methods is to follow the change in the quantum yield of chlorophyll fluorescence and to derive photosynthetic parameters related to the activities of photosystem II (PSII; Kolber et al 1998). Pulse amplitude modulation and fast repetition rate fluorometry (FRRF) are among the commonly used fluorometric methods to estimate photosynthetic parameters and gross primary production in lakes and oceans (Suggett et al 2001, Melrose et al 2006, Morelle et al 2018. Fluorometric methods for determining primary production are non-intrusive, instantaneous, and sensitive, and they can measure the fluorescence variables in real time (Kolber et al 1998).…”