Sentinel-2 and Landsat-8 Observations for Harmful Algae Blooms in a Small Eutrophic Lake

Miao Liu,Zhigang Cao,Dan Wu,Xiaomei Su,Hong Ling

doi:10.3390/rs13214479

Abstract

Widespread harmful cyanobacterial bloom is one of the most pressing concerns in lakes and reservoirs, resulting in a lot of negative ecological consequences and threatening public health. Ocean color instruments with low spatial resolution have been used to monitor cyanobacterial bloom in large lakes; however, they cannot be applied to small water bodies well. Here, the Multi-Spectral Instrument (MSI) onboard Sentinel-2A and -2B and the Operational Landsat Imager (OLI) onboard Landsat-8 were employed to assemble the virtual constellation and to track spatial and seasonal variations in floating algae blooms from 2016 to 2020 in a small eutrophic plateau lake: Lake Xingyun in China. The floating algae index (FAI) was calculated using Rayleigh-corrected reflectance in the red, near-infrared, and short-wave infrared bands. The MSI-derived FAI had a similar pattern to the OLI-derived FAI, with a mean absolute percentage error of 19.98% and unbiased percentage difference of 17.05%. Then, an FAI threshold, 0.0693, was determined using bimodal histograms of FAI images for floating algae extraction. The floating algae had a higher occurrence in the northern region than the southern region in this lake, whilst the occurrence of floating algae in summer and autumn was higher than that in spring and winter. Such a spatial and seasonal pattern was related to the variability in air temperature, wind speed and direction, and nutrients. The climatological annual mean occurrence of floating algae from 2016 to 2020 in Lake Xingyun exhibited a significant decrease, which was related to decreases in nutrients, resulting from efficient ecological restoration by the local government. This research highlighted the application of OLI-MSI virtual constellation on monitoring floating algae in a small lake, providing a practical and theoretical reference to monitor aquatic environments in small water bodies.

Highlights

With the dual effects of climate warming and intensified human activities, lake eutrophication and cyanobacterial bloom are extending across the globe [1,2,3,4], in particular in some shallow lakes, such as Lake Taihu (China), Lake Erie (U.S.), Lake Peipsi (Estonia), and Lake Bogoria (Kenya)
Cyanobacteria could release Microcystin, which could threaten the safety of the drinking water and the health of animals on land and of human beings [6]
The Microcystin concentration in waters has been a critical indicator for evaluating the quality of drinking water by the World Health Organization (WHO), the Environmental

Summary

Introduction

With the dual effects of climate warming and intensified human activities, lake eutrophication and cyanobacterial bloom are extending across the globe [1,2,3,4], in particular in some shallow lakes, such as Lake Taihu (China), Lake Erie (U.S.), Lake Peipsi (Estonia), and Lake Bogoria (Kenya). Widespread cyanobacterial blooms pose an urgent demand to manage, mitigate, and restore perspectives in these inland water ecosystems. The aggregation of cyanobacteria in the surface water forms cyanobacterial scums, reducing the penetration of light radiation into the water column and impacting the growth of other phytoplankton, zooplankton, and fishes, significantly weakening the ecological functions of inland lakes [4,5]. Cyanobacteria could release Microcystin, which could threaten the safety of the drinking water and the health of animals on land and of human beings [6]. The Microcystin concentration in waters has been a critical indicator for evaluating the quality of drinking water by the World Health Organization (WHO), the Environmental.

Objectives

Methods

Results

Discussion

Conclusion