Department of Marine Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, 27695-8208, USA.
Institute of Marine Sciences, University of North Carolina At Chapel Hill, Morehead City, NC, 28557, USA.
Sci Rep. 2020 Dec 16;10(1):22026. doi: 10.1038/s41598-020-79157-6.
Picophytoplankton (PicoP) are increasingly recognized as significant contributors to primary productivity and phytoplankton biomass in coastal and estuarine systems. Remarkably though, PicoP composition is unknown or not well-resolved in several large estuaries including the semi-lagoonal Neuse River Estuary (NRE), a tributary of the second largest estuary-system in the lower USA, the Pamlico-Albemarle Sound. The NRE is impacted by extreme weather events, including recent increases in precipitation and flooding associated with tropical cyclones. Here we examined the impacts of moderate to extreme (Hurricane Florence, September 2018) precipitation events on NRE PicoP abundances and composition using flow cytometry, over a 1.5 year period. Phycocyanin-rich Synechococcus-like cells were the most dominant PicoP, reaching ~ 10 cells mL, which highlights their importance as key primary producers in this relatively long residence-time estuary. Ephemeral "blooms" of picoeukaryotic phytoplankton (PEUK) during spring and after spikes in river flow were also detected, making PEUK periodically major contributors to PicoP biomass (up to ~ 80%). About half of the variation in PicoP abundance was explained by measured environmental variables. Temperature explained the most variation (24.5%). Change in total dissolved nitrogen concentration, an indication of increased river discharge, explained the second-most variation in PicoP abundance (15.9%). The short-term impacts of extreme river discharge from Hurricane Florence were particularly evident as PicoP biomass was reduced by ~ 100-fold for more than 2 weeks. We conclude that precipitation is a highly influential factor on estuarine PicoP biomass and composition, and show how 'wetter' future climate conditions will have ecosystem impacts down to the smallest of phytoplankton.
微微型浮游植物（PicoP）越来越被认为是沿海和河口系统初级生产力和浮游植物生物量的重要贡献者。然而，在包括半泻湖 Neuse 河口（NRE）在内的几个大型河口系统中，PicoP 的组成部分尚不清楚或尚未得到很好的解决，NRE 是美国下游第二大河口系统 Pamlico-Albemarle Sound 的支流。NRE 受到极端天气事件的影响，包括最近与热带气旋相关的降水增加和洪水。在这里，我们使用流式细胞术在 1.5 年的时间内研究了中度到极端（2018 年 9 月的佛罗伦萨飓风）降水事件对 NRE PicoP 丰度和组成的影响。富含藻蓝蛋白的类似 Synechococcus 的细胞是最主要的 PicoP，达到约 10 个细胞 mL，这突出了它们作为这个相对长停留时间河口关键初级生产者的重要性。在春季和河流流量增加后，还检测到短暂的微微型真核浮游植物（PEUK）“爆发”，使得 PEUK 周期性地成为 PicoP 生物量的主要贡献者（高达约 80%）。约一半的 PicoP 丰度变化可以用测量的环境变量来解释。温度解释了最多的变化（24.5%）。总溶解氮浓度的变化，表明河流流量增加，解释了 PicoP 丰度变化的第二大因素（15.9%）。佛罗伦萨飓风带来的极端河流流量的短期影响尤为明显，PicoP 生物量减少了约 100 倍，持续了两周多。我们得出的结论是，降水是影响河口 PicoP 生物量和组成的高度影响因素，并展示了“更湿润”的未来气候条件将如何对最小的浮游植物产生生态系统影响。
