Dynamics of phytoplankton productivity and exopolysaccharides (EPS and TEP) pools in the Seine Estuary (France, Normandy) over tidal cycles and over two contrasting seasons

Type Article
Date 2017-10
Language English
Author(s) Morelle Jerome1, 2, Schapira MathildeORCID3, 4, Claquin Pascal1, 2
Affiliation(s) 1 : Univ Caen Normandie, Normandie Univ, F-14032 Caen, France.
2 : UPMC, UCBN, UMR BOREA, CNRS 7208,IRD 207,MNHN, F-14032 Caen, France.
3 : IFREMER, LER N, Ave Gen Gaulle, F-14520 Port En Bessin, France.
4 : IFREMER, LER, MPL, NT, Rue Ile Yeu BP 21105, F-44301 Nantes 03, France.
Source Marine Environmental Research (0141-1136) (Elsevier Sci Ltd), 2017-10 , Vol. 131 , P. 162-176
DOI 10.1016/j.marenvres.2017.09.007
WOS© Times Cited 14
Keyword(s) Phytoplankton, Microphytobenthos, PAM fluorometer, Electron transport rate

Exopolysaccharides (EPS) play an important role in the carbon flux and may be directly linked to phytoplankton and microphytobenthos production, most notably in estuarine systems. However the temporal and spatial dynamics of estuarine EPS are still not well understood, nor how primary productivity triggers this variability at these different scales.

The aim of this study was to investigate the primary productivity of phytoplankton and EPS dynamics in the Seine estuary over a tidal cycle in three different haline zones over two contrasted seasons. The other objectives was to investigate the origin of pools of soluble carbohydrates (S-EPS) and transparent exopolymeric particles (TEP) in phytoplankton, microphytobenthos or other compartments. High frequency measurements of productivity were made in winter and summer 2015. Physical and chemical parameters, biomass and EPS were measured at hourly intervals in sub-surface waters and just above the water sediment-interface.

Our results confirmed that high frequency measurements improve the accuracy of primary productivity estimations and associated carbon fluxes in estuaries. The photosynthetic parameters were shown to be strongly controlled by salinity and by the concentrations of suspended particle matter at the smallest temporal and at spatial scales. At these scales, our results showed an inverse relationship between EPS concentrations and biomass and productivity, and a positive relationship with sediment resuspension. Additionally, the distribution of EPS appears to be linked to hydrodynamics with the tide at daily scale and with the winter at seasonal scale. At spatial scale, the maximum turbidity zone played an important role in the distribution of TEP.

Our results suggest that, in the Seine estuary, between 9% and 33% of the S-EPS pool in the water column can be attributed to phytoplankton excretion, while only 0.4%–1.6% (up to 6.14% in exceptional conditions) originates from the microphytobenthos compartments. Most EPS was attributed to remobilization of detrital carbon pools in the maximum turbidity zone and in the sediment or allochthonous origin.

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