Index-based mapping of floating algae blooms observed on Lake Iznik using Landsat-8 imagery

Abstract

As one of the most important members of the freshwater ecosystem, lakes have been under
pressure in recent years, mainly due to climate change, population growth and anthropogenic
activities, which adversely affect water quality and cause several environmental disasters
such as harmful algal blooms. Remote sensing technologies have been widely used for their
advantages in monitoring rapid changes in freshwater resources at global and local scales. The
main goal of this study is to detect and map the dense floating algae formations observed in
Lake Iznik, the largest freshwater source of the Marmara region, in 2022. For this purpose,
Automatic Mucilage Extraction Index (AMEI), initially proposed for mucilage detection, and
the well-known Normalized Difference Water Index (NDWI) were utilized, and their
performances were compared in mapping algal formations using the Landsat-8 image. The
results showed that the floating algae formations covered 12.1% (about 36.35 km2) of Lake
Iznik on June 5, 2022. In addition, the high-density algal formations were detected with 99%
accuracy, while high- and low-algae formations were detected with 77% accuracy in the AMEI
index map produced with appropriate threshold values. As a result, it can be concluded that
the AMEI, initially formulated by considering the spectral bands of Sentinel-2, can be easily
adapted to Landsat imagery to extract floating algal blooms.