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| DOI：10.13522/j.cnki.ggps.2022336 |
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| Using Remote Sensing to Monitor Aquatic Vegetation and Algal Blooms in Lakes in Yellow River Basin |
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CHEN Yonggui, ZHU Yuxiang
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Henan Collage of Surveying and Mapping, Zhengzhou 451464, China
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| Abstract: |
| 【Background and objective】Global warming and anthropogenic activities will change ecological functions of lakes, resulting in eutrophication and algal blooms, for example. Monitoring the change in aquatic vegetation and algae is important to improve lake management but difficult, especially at large scale. Remot sensing can plug this gap and in this paper, we study the feasibility of using it to acquire vegetation dynamics in lakes.【Method】The studied site is Ulansuhai lake in the upper reach of the Yellow River basin. Emergent and submerged vegetation as well as floating algae were calculated based on spectral feature analysis of the spectral data acquired from the Landsat8 imageries. A decision tree classification model was constructed to analyze the aquatic vegetation and algal blooms. A MNDSI spectral index was proposed to identify the aquatic vegetation and yellow moss algal blooms; a NDWI spectral water index was used to extract water bodies that were free of vegetation and algae. An improved enhanced vegetation index (AEVI) was used to extract the emergent vegetation; a modified macroalgal index (MFAI) was used to distinguish the submerged vegetation from the yellow moss algal blooms. The accuracy of the method was tested against ground-truth data. 【Result】The spectral index combined with the decision tree classification model is effective to distinguish the aquatic vegetation from the yellow moss algal blooms. Using the Landsat8 imageries acquired from 1986 to 2018 revealed that the emergent vegetation taxa grew slowly, and the coverage area of the submerged vegetation showed periodic changes, decreasing 1986 to 2013 and increasing after 2013. The yellow moss algal bloom did not show identifiable trends, with their outbreaks occurring irregularly from 1986 to 2018. |
| Key words: groups of aquatic vegetation; yellow algal blooms; spectral index; decision tree; Ulansuhai Lake |
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