Department of Marine Ecology, IMEDEA (UIB-CSIC), Miquel Marques 21, 07190, Esporles, Balearic Islands, Spain.
Department of Marine Ecology, IMEDEA (UIB-CSIC), Miquel Marques 21, 07190, Esporles, Balearic Islands, Spain.
Sci Total Environ. 2024 Dec 10;955:177123. doi: 10.1016/j.scitotenv.2024.177123. Epub 2024 Oct 21.
Along some Mediterranean coastal areas and other world regions, nutrient and chlorophyll concentrations often show gradient increases of up to one order of magnitude perpendicular to the coast. This nearshore stripe, extending a few hundred meters from the coast, is enriched by submarine groundwater discharges (SGD) containing elevated nutrient concentrations that may eventually sustain high biomass phytoplankton blooms. During a survey carried out in the summer of 2018, we examined the short-term (hours) variability of the phytoplankton biomass (measured as chlorophyll; Chl) in response to environmental changes associated with SGD and wind forcing in the nearshore waters of Palma Beach (Mediterranean Sea). Continuous CTD records revealed a general salinity decline indicative of SGD along the shoreline. Large and pulsed salinity fluctuations (i.e. 2-3 psu variations, 1-4 h) were observed each day that were consistent with offshore advection episodes of the lower salinity water retained in the nearshore (peak crosshore velocity 5-6 cm s). Chl near the shoreline was markedly higher than offshore (3.55 ± 1.29 and 0.68 ± 0.27 mg m respectively) but recurrently fluctuated in the afternoon to up to >7 mg m. Primary production estimations showed that despite the higher production in the nearshore (50.29 ± 10.98 μmol O L d, 4-fold offshore values) productivity per unit chlorophyll did not significantly vary (p > 0.01) therefore suggesting that, at this time scales, high biomass episodes in the nearshore are driven by an accumulation mechanism. Statistical analysis (CCA) demonstrates that Chl variability is largely explained (93 %) by variations in wind and current velocity. Our results provide evidence that the dynamics of this nearshore environment are modulated by the interplay between the shoreward wind-induced flow and the offshore directed density flow. This mechanism could explain the occurrence and episodic nature of high biomass blooms in the nearshore, as well as be an important factor influencing the microbial community structure at the coastal zone.
在一些地中海沿海地区和其他世界区域，营养物和叶绿素浓度经常在垂直于海岸的方向上呈现出高达一个数量级的梯度增加。这个近岸带从海岸延伸几百米，富含含有高营养物浓度的海底地下水排放（SGD），这些营养物最终可能维持高生物量浮游植物的大量繁殖。在 2018 年夏天进行的一项调查中，我们研究了近岸水域浮游植物生物量（用叶绿素表示）对 SGD 和风生流引起的环境变化的短期（数小时）变化。连续 CTD 记录显示，沿海岸线的一般盐度下降表明存在 SGD。每天都会观察到大而脉冲的盐度波动（即 2-3 psu 的变化，1-4 小时），这与保留在近岸的低盐度水的离岸平流事件一致（峰值横流速度为 5-6 cm s）。近岸的叶绿素明显高于离岸（分别为 3.55±1.29 和 0.68±0.27 mg m），但下午经常波动，高达>7 mg m。初级生产力估算表明，尽管近岸的生产力更高（50.29±10.98 μmol O L d，是离岸值的 4 倍），但单位叶绿素的生产力没有显著变化（p>0.01），因此表明，在这个时间尺度上，近岸高生物量事件是由积累机制驱动的。统计分析（CCA）表明，叶绿素变化在很大程度上可以用风速和水流速度的变化来解释（93%）。我们的结果提供了证据，表明这种近岸环境的动态是由岸上风引起的流动和离岸方向的密度流之间的相互作用调节的。这种机制可以解释近岸高生物量大量繁殖的发生和间歇性，并且是影响沿海地区微生物群落结构的一个重要因素。
