LEMAR (UMR 6539), IUEM, Technopôle Brest-Iroise, 29280 Plouzané, France; LEGOS (UMR 5566), 31401 Toulouse cedex 9, France; France Energies Marines, 29200 Brest, France.
LEGOS (UMR 5566), 31401 Toulouse cedex 9, France.
Sci Total Environ. 2019 Nov 25;693:133491. doi: 10.1016/j.scitotenv.2019.07.297. Epub 2019 Jul 19.
Installation of an Ocean Thermal Energy Conversion pilot plant (OTEC) off the Caribbean coast of Martinique is expected to use approximately 100,000 m h 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 km 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.
在马提尼克岛的加勒比海沿岸安装海洋热能转换（OTEC）试验工厂预计将使用大约 10 万立方米的深海水来运行。本研究考察了在安装试验工厂之前，寒冷富营养的深海水排放对生活在表层温暖贫营养水域中的浮游植物群落的潜在影响。OTEC 引起的深海水上涌的数值模拟表明，在考虑的两个部分的中心，OTEC 上的水柱顶部 150 米范围内，在一个年周期内，从未达到 3.0°C 的温度变化，这被认为是温度影响的临界阈值。热效应应该是有限的，在面积上 <1 公里，温度差为 0.3°C（绝对值），对浮游植物组合产生可忽略不计的热影响。通过现场微宇宙实验评估了由此产生的混合深海水和地表水对浮游植物的影响。在两个孵化深度（深叶绿素 a 最大值：DCM 和透光层底部：BEL）下测试了两种水混合比（2%和 10%的深海水）的情景。在 DCM 中，深海水添加量最高（10%）时，影响最大，导致硅藻和甲藻的发展，而 2%的添加仅引起浮游植物群落的有限变化（相对较高的聚球藻属丰度，但没有明显的群落转移）。这项研究表明，OTEC 工厂将显著改变浮游植物群落，从微微型浮游植物向微型浮游植物转移，只有在排放物影响 DCM 的情况下，而且仅限于局部范围。由于在 BEL 处对浮游植物群落的影响较小，因此建议在排放深海水时选择该深度，以利用 OTEC 工厂。
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