Mondal Arpita, Banerjee Sandip
Department of Mathematics, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, 247667, India.
Sci Rep. 2023 Oct 10;13(1):17141. doi: 10.1038/s41598-023-43745-z.
The intensity of eddy diffusivity and the spatial average of water velocity at the depths of the water column in oceans and lakes play a fundamental role in phytoplankton production and phytoplankton and zooplankton biomass, and community composition. The critical depth and intensity of turbulent mixing within the water column profoundly affect phytoplankton biomass, which depends on the sinking characteristic of planktonic algal species. We propose an Nutrient-Phytoplankton-Zooplankton (NPZ) model in 3D space with light and nutrient-limited growth in a micro-scale ecological study. To incorporate micro-scale observation of phytoplankton intermittency in bloom mechanism in stationary as well as oceanic turbulent flows, a moment closure method has been applied in this study. Experimental observations imply that an increase in turbulence is sometimes ecologically advantageous for non-motile planktonic algae. How do we ensure whether there will be a bloom cycle or whether there can be any bloom at all when the existing phytoplankton group is buoyant, heavier, motile, or non-motile? To address these questions, we have explored the effects of critical depth, the intensity of eddy diffusivity, spatial average of water velocity, on the concentration as well as horizontal and vertical distribution of phytoplankton and zooplankton biomass using a mathematical model and moment closure technique. We quantify a critical threshold value of eddy diffusivity and the spatial average of water velocity and observe the corresponding changes in the phytoplankton bloom dynamics. Our results highlight the importance of eddy diffusivity and the spatial average of water velocity on seasonal bloom dynamics and also mimic different real-life bloom scenarios in Mikawa Bay (Japan), Tokyo Bay (Japan), Arakawa River (Japan), the Baltic Sea, the North Atlantic Ocean, Gulf Alaska, the North Arabian Sea, the Cantabrian Sea, Lake Nieuwe Meer (Netherlands) and several shallower lakes.
海洋和湖泊水柱深度处的涡动扩散率强度以及水速的空间平均值，在浮游植物产量、浮游植物和浮游动物生物量以及群落组成方面发挥着基础性作用。水柱内湍流混合的临界深度和强度深刻影响着浮游植物生物量，而这取决于浮游藻类物种的下沉特性。在一项微观尺度的生态学研究中，我们提出了一个三维空间中的营养物 - 浮游植物 - 浮游动物（NPZ）模型，该模型考虑了光照和营养限制的生长情况。为了将浮游植物间歇性的微观尺度观测纳入到静止以及海洋湍流中的水华机制中，本研究应用了矩量闭合方法。实验观测表明，对于非游动性浮游藻类而言，湍流增加有时在生态上是有利的。当现有的浮游植物群体是漂浮的、较重的、游动的或非游动的时，我们如何确定是否会出现水华周期，或者是否根本会出现任何水华现象呢？为了解决这些问题，我们使用数学模型和矩量闭合技术，探讨了临界深度、涡动扩散率强度、水速空间平均值对浮游植物和浮游动物生物量的浓度以及水平和垂直分布的影响。我们量化了涡动扩散率和水速空间平均值的临界阈值，并观察浮游植物水华动态的相应变化。我们的结果突出了涡动扩散率和水速空间平均值对季节性水华动态的重要性，并且还模拟了日本三河湾、东京湾、荒川（日本）、波罗的海、北大西洋、阿拉斯加湾、北阿拉伯海、坎塔布连海、荷兰新米尔湖以及几个较浅湖泊等不同现实生活中的水华场景。
