Long-term changes in the distribution of Trapa L. in six Japanese lakes observed by satellite imagery

• Published in: Hozen Seitaigaku Kenkyu = Japanese Journal of Conservation Ecology Vol. 22; no. 1; pp. 171 - 185
• Main Authors: Oyama, Yoichi, Matsushita, Bunkei, Fukushima, Takehiko
• Format: Journal Article
• Language: Japanese
• Published: Kyoto The Ecological Society of Japan 2017; Ecological Society of Japan
• Subjects: Blooms; Distribution; floating-leaved macrophytes; Imagery; Lakes; Landsat; Landsat satellites; Long-term changes; Mathematical models; Near infrared radiation; Normalized Difference Water Index (NDWI); Remote sensing; Satellite imagery; Satellite observation; Satellites; Spaceborne remote sensing
• ISSN: 1342-4327; 2424-1431
• DOI: 10.18960/hozen.22.1_171

In this study, we used Landsat images to observe changes in the distribution of Trapa L., which has a tendency to overgrow in Japanese lakes. Six Japanese lakes in different locations were chosen as study areas (Lakes Sirarutoro, Takkobu-numa, North Inba-numa, South Inba-numa, Suwa and Mikata). The extraction algorithm for Trapa L. was developed based on the Normalized Difference Water Index (NDWI), which uses short-wave infrared and green reflectances, instead of the more commonly used Normalized Difference Vegetation Index (NDVI); NDVI cannot distinguish between Trapa L. and cyanobacterial blooms due to their similar spectral characteristics at near infrared and red bands. Satellite-derived and in-situ estimates of Trapa L. distribution corresponded closely (R2=0.82, N=8). Seasonal observation in Lakes Sirarutoro, North Inba-numa and Mikata revealed that Trapa L. was absent from February to May, rapidly increased in July, with subsequent numbers maintained through September, and rapidly decreased in October. Changes in the distribution of Trapa L. over the past 25 years showed a tendency toward expansion in most lakes.