A MODIS-Based Novel Method to Distinguish Surface Cyanobacterial Scums and Aquatic Macrophytes in Lake Taihu

Abstract

Satellite remote sensing can be an effective alternative for mapping cyanobacterial scums and aquatic macrophyte distribution over large areas compared with traditional ship's site-specific samplings. However, similar optical spectra characteristics between aquatic macrophytes and cyanobacterial scums in red and near infrared (NIR) wavebands create a barrier to their discrimination when they co-occur. We developed a new cyanobacteria and macrophytes index (CMI) based on a blue, a green, and a shortwave infrared band to separate waters with cyanobacterial scums from those dominated by aquatic macrophytes, and a turbid water index (TWI) to avoid interference from high turbid waters typical of shallow lakes. Combining CMI, TWI, and the floating algae index (FAI), we used a novel classification approach to discriminate lake water, cyanobacteria blooms, submerged macrophytes, and emergent/floating macrophytes using MODIS imagery in the large shallow and eutrophic Lake Taihu (China). Thresholds for CMI, TWI, and FAI were determined by statistical analysis for a 2010-2016 MODIS Aqua time series. We validated the accuracy of our approach by in situ reflectance spectra, field investigations and high spatial resolution HJ-CCD data. The overall classification accuracy was 86% in total, and the user's accuracy was 88%, 79%, 85%, and 93% for submerged macrophytes, emergent/floating macrophytes, cyanobacterial scums and lake water, respectively. The estimated aquatic macrophyte distributions gave consistent results with that based on HJ-CCD data. This new approach allows for the coincident determination of the distributions of cyanobacteria blooms and aquatic macrophytes in eutrophic shallow lakes. We also discuss the utility of the approach with respect to masking clouds, black waters, and atmospheric effects, and its mixed-pixel effects.

Determination of the Downwelling Diffuse Attenuation Coefficient of Lake Water with the Sentinel-3A OLCI

“…An increase in the SPM concentration results in an increase in the light attenuation in the water, which results in a decrease in the transparency and eutrophic depth of the water and thereby affects the spatial and seasonal distributions of aquatic vegetation [65,66]. As a shallow lake, the high dynamic ratio index (the square root of the surface area divided by the average depth, 25.6 km/m) of Lake Taihu indicates that winds are the main driving force for sediment resuspension.…”

Spatial heterogeneity of food web structure in a large shallow eutrophic lake (Lake Taihu, China): implications for eutrophication process and management

“…The difference of physical conditions within Lake Taihu decided the key component of basal source in the algae-dominated zone is algae, not submerged macrophyte. Previous studies have pointed out that the macrophyte-dominated zone also have received large amount of nutrient inputs (Liang et al 2017). For instance, enclosure culture in East Taihu Bay (the region Site 5 located) reached its peak from 1998 to 2008 (Wang et al 2019).…”

Detecting and Quantifying a Massive Invasion of Floating Aquatic Plants in the Río de la Plata Turbid Waters Using High Spatial Resolution Ocean Color Imagery

“…In turn, the red band is affected by chlorophyll-a absorption of the floating vegetation (decreasing reflectance) and by particle scattering for increasing turbidity (increasing reflectance). The threshold was defined by analysis of a 2-year time series of images over the region of highest turbidity in the following [13]. Thus, a threshold of 0.08 in the Rayleigh-corrected reflectance in the RED was set to differentiate highly turbid water pixels from vegetated pixels.…”

“…Different indexes have been developed to detect floating aquatic vegetation using remote sensing data that make use of their strong near infrared (NIR) reflectance similar to that of land vegetation [5][6][7][8][9][10][11]. These indexes have been originally mainly for clear waters, but their applicability in turbid waters is not straightforward as has been already mentioned in [12] and further analyzed in [13].…”