Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, P.R.China.
Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, P.R.China; University of Chinese Academy of Sciences, Beijing 100049, P.R.China.
Water Res. 2021 Dec 1;207:117786. doi: 10.1016/j.watres.2021.117786. Epub 2021 Oct 28.
There are some uncertainties of using chlorophyll a (Chla) concentrations in water surface to address phytoplankton dynamics, especially in large shallow lakes, because of the dramatic vertical migration of phytoplankton. The column-integrated algal biomass (CAB) can reflect the whole water column information, so it is considered as a better indicator for phytoplankton total biomass. An algal biomass index (ABI) and an empirical algorithm were proposed previously to measure algal biomass inside and outside euphotic zone from the Moderate Resolution Imaging Spectrometer (MODIS) data. A long-term CAB time series was generated in this study to clarify the temporal and spatial changes in phytoplankton and address its sensitivity to climatic factors in Lake Chaohu, a shallow eutrophic lake in China, from 2000 to 2018. Overall, the CAB for Lake Chaohu showed significant temporal and spatial dynamics. Temporally, the annual average CAB (total CBA within the whole lake) was increased at rate of 0.569 t Chla/y, ranging from 62.06±8.89 t Chla to 76.03±10.01 t Chla during the 19-year period. Seasonal and periodic variations in total CAB presented a bimodal annual cycle every year, the total CAB was highest in summer, followed by that in autumn, and it was the lowest in winter. The pixel-based CAB (total CAB of a unit water column), ranging from 112.42 to 166.85 mg Chla, was the highest in the western segment, especially its northern part, and was the lowest in the central parts of eastern and central segments. The sensitivity of CAB dynamics to climatic conditions was found to vary by region and time scale. Specifically, the change of pixel-based algal biomass was more sensitive to the temperature change on the monthly and annual scales, while wind speed impacted directly on the short-term spatial-temporal redistribution of algal biomass. High temperature and low wind speed could prompt the growth of total CAB for the whole lake, and the hydrodynamic situations affected by wind and so on determined the spatial details. It also indicated that Lake Chaohu may face more severe challenges with the future climatic warming. This study may serve as a reference to support algal bloom forecasting and early warning management for other large eutrophic lakes with similar problems.
叶绿素 a（Chla）浓度在水表面的应用存在一些不确定性，尤其是在大型浅湖泊中，因为浮游植物的垂直迁移非常显著。水柱综合藻类生物量（CAB）可以反映整个水柱的信息，因此被认为是浮游植物总生物量的更好指标。先前已经提出了藻类生物量指数（ABI）和经验算法，以从中等分辨率成像光谱仪（MODIS）数据中测量光饱和带内外的藻类生物量。本研究生成了一个长期的 CAB 时间序列，以澄清浮游植物的时空变化，并探讨其对中国浅水富营养化湖泊巢湖的气候因子的敏感性，时间范围为 2000 年至 2018 年。总体而言，巢湖的 CAB 表现出显著的时空动态。时间上，巢湖的年平均 CAB（整个湖泊内的总 CBA）以每年 0.569 t Chla 的速度增加，在 19 年期间，范围从 62.06±8.89 t Chla 到 76.03±10.01 t Chla。总 CAB 的季节性和周期性变化呈现出每年两次的双峰年周期，夏季最高，其次是秋季，冬季最低。基于像元的 CAB（单位水柱的总 CAB），范围从 112.42 到 166.85 mg Chla，在西段最高，特别是北部，在东段和中段的中心部分最低。CAB 动态对气候条件的敏感性因地区和时间尺度而异。具体而言，基于像元的藻类生物量的变化对月度和年度尺度上的温度变化更为敏感，而风速直接影响藻类生物量的短期时空再分配。高温和低风速会促使整个湖泊的总 CAB 增长，而风等因素引起的水动力情况则决定了空间细节。这也表明，随着未来气候变暖，巢湖可能会面临更大的挑战。本研究可为其他具有类似问题的大型富营养化湖泊的藻类水华预测和预警管理提供参考。
