Potential effects of deep seawater discharge by an Ocean Thermal Energy Conversion plant on the marine microorganisms in oligotrophic waters

Type Article
Date 2019-11
Language English
Author(s) Giraud Mélanie1, 2, 3, Garçon Véronique2, de La Broise Denis1, L'Helguen Stéphane1, Sudre Joël2, Boye Marie1, 4
Affiliation(s) 1 : LEMAR (UMR 6539), IUEM, Technopôle Brest-Iroise, 29280 Plouzané, France
2 : LEGOS (UMR 5566), 31401 Toulouse cedex 9, France
3 : France Energies Marines, 29200 Brest, France
4 : Institut de Physique du Globe de Paris (UMR 7154), 75005 Paris, France
Source Science Of The Total Environment (0048-9697) (Elsevier BV), 2019-11 , Vol. 693 , P. 133491 (12p.)
DOI 10.1016/j.scitotenv.2019.07.297
WOS© Times Cited 5
Keyword(s) Marine microbial ecosystem, Biogeochemistry, Modeling, Artificial seawater discharge in situ experiments, Environmental standards

Installation of an Ocean Thermal Energy Conversion pilot plant (OTEC) off the Caribbean coast of Martinique is expected to use approximately 100,000 m3 h−1 of deep seawater for its functioning. This study examined the potential effects of the cold nutrient-rich deep seawater discharge on the phytoplankton community living in the surface warm oligotrophic waters before the installation of the pilot plant. Numerical simulations of deep seawater upwelled by the OTEC, showed that a 3.0 °C temperature change, considered as a critical threshold for temperature impact, was never reached during an annual cycle on the top 150 m of the water column on two considered sections centered on the OTEC. The thermal effect should be limited, <1 km2 on the area exhibited a temperature difference of 0.3 °C (absolute value), producing a negligible thermic impact on the phytoplankton assemblage. The impact on phytoplankton of the resulting mixed deep and surface seawater was evaluated by in situ microcosm experiments. Two scenarios of water mix ratio (2% and 10% of deep water) were tested at two incubation depths (deep chlorophyll-a maximum: DCM and bottom of the euphotic layer: BEL). The larger impact was obtained at DCM for the highest deep seawater addition (10%), with a development of diatoms and haptophytes, whereas 2% addition induced only a limited change of the phytoplankton community (relatively higher Prochlorococcus sp. abundance, but without significant shift of the assemblage). This study suggested that the OTEC plant would significantly modify the phytoplankton assemblage with a shift from pico-phytoplankton toward micro-phytoplankton only in the case of a discharge affecting the DCM and would be restricted to a local scale. Since the lower impact on the phytoplankton assemblage was obtained at BEL, this depth can be recommended for the discharge of the deep seawater to exploit the OTEC plant.

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Giraud Mélanie, Garçon Véronique, de La Broise Denis, L'Helguen Stéphane, Sudre Joël, Boye Marie (2019). Potential effects of deep seawater discharge by an Ocean Thermal Energy Conversion plant on the marine microorganisms in oligotrophic waters. Science Of The Total Environment, 693, 133491 (12p.). Publisher's official version : https://doi.org/10.1016/j.scitotenv.2019.07.297 , Open Access version : https://archimer.ifremer.fr/doc/00507/61867/