NOAA/NESDIS Center for Satellite Applications and Research, College Park, Maryland, USA.
Global Science & Technology, Inc., Greenbelt, Maryland, USA.
Integr Environ Assess Manag. 2022 Jun;18(4):921-938. doi: 10.1002/ieam.4597. Epub 2022 May 3.
Phytoplankton growth in estuaries is regulated by a complex combination of physical factors with freshwater discharge usually playing a dominating role controlling nutrient and light availability. The role of other factors, including upwelling-generating winds, is still unclear because most estuaries are too small for upwelling to emerge. In this study, we used remotely sensed proxies of phytoplankton biomass and concentration of suspended mineral particles to compare the effect of river discharge with the effect of upwelling events associated with persistent along-channel southerly winds in the Chesapeake Bay, a large estuary where upwelling and its effects on biogeochemical dynamics have been previously reported. The surface chlorophyll-a concentrations (Chl-a) were estimated from Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data using the Generalized Stacked-Constraints Model (GSCM) corrected for seasonal effects by comparing remotely sensed and field-measured data. Light limitation of phytoplankton growth was assessed from the concentration of suspended mineral particles estimated from the remotely sensed backscattering at blue (443 nm) wavelength b (443). The nine-year time series (2012-2020) of Chl-a and b (443) confirmed that a primary factor regulating phytoplankton growth in this nearshore eutrophic area is discharge from the Susquehanna River, and presumably the nutrients it delivers, with a time lag up to four months. Persistent southerly wind events (2-3 days with wind speed >4 m/s) affected the water column stratification in the central part of the bay but did not result in significant increases in remotely sensed Chl-a. Analysis of model simulations of selected upwelling-favorable wind events revealed that strong southerly winds resulted in well-defined lateral (East-West) responses but were insufficient to deliver high-nutrient water to the surface layer to support phytoplankton bloom. We conclude that, in the Chesapeake Bay, which is a large, eutrophic estuary, wind-driven upwelling of deep water plays a limited role in driving phytoplankton growth under most conditions compared with river discharge. Integr Environ Assess Manag 2022;18:921-938. © 2022 SETAC.
河口浮游植物的生长受多种物理因素的复杂组合调控，其中淡水排放通常起着主导作用，控制着营养物质和光照的可利用性。其他因素的作用，包括上升流产生的风，仍然不清楚，因为大多数河口太小，上升流无法出现。在这项研究中，我们使用浮游植物生物量和悬浮矿物质颗粒浓度的遥感代理，来比较河流排放的作用与与持久的沿通道南向风相关的上升流事件的作用，这些事件在切萨皮克湾已有报道，切萨皮克湾是一个大型河口，上升流及其对生物地球化学动力学的影响之前已被报道。利用可见红外成像辐射计套件（VIIRS）卫星数据，使用广义堆叠约束模型（GSCM）估算表层叶绿素-a 浓度（Chl-a），该模型通过比较遥感和现场测量数据来校正季节性影响。利用从遥感后向散射在蓝色（443nm）波长 b（443）处估算的悬浮矿物质颗粒浓度，评估浮游植物生长的光限制。九年来（2012-2020 年）的 Chl-a 和 b（443）时间序列证实，调节这个近岸富营养区浮游植物生长的主要因素是萨斯奎哈纳河的排放，以及它所输送的营养物质，其时间滞后可达四个月。持续的南向风事件（风速>4m/s，持续 2-3 天）影响了湾内中部的水柱分层，但没有导致遥感 Chl-a 显著增加。对选定上升流有利的风事件的模型模拟分析表明，强南向风导致了明确的横向（东西向）响应，但不足以将高营养物质的水输送到表层以支持浮游植物的爆发。我们的结论是，在切萨皮克湾，这个大型富营养化河口，与河流排放相比，在大多数情况下，风驱动的深层水上升对浮游植物生长的驱动作用有限。
