A Satellite-Based Assessment of the Distribution and Biomass of Submerged Aquatic Vegetation in the Optically Shallow Basin of Lake Biwa

Shweta Yadav,Masayuki Tamura,Yosuke Yamashiki,Kanako Ishikawa,Minoru Yoneda,Junichi Susaki

doi:10.3390/rs9090966

Shweta Yadav, Masayuki Tamura + Show 4 more

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https://doi.org/10.3390/rs9090966

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Journal: Remote Sensing	Publication Date: Sep 18, 2017
Citations: 29	License type: CC BY 4.0

Affiliation: Kyoto University, Lake Biwa Museum

Abstract

Assessing the abundance of submerged aquatic vegetation (SAV), particularly in shallow lakes, is essential for effective lake management activities. In the present study we applied satellite remote sensing (a Landsat-8 image) in order to evaluate the SAV coverage area and its biomass for the peak growth period, which is mainly in September or October (2013 to 2016), in the eutrophic and shallow south basin of Lake Biwa. We developed and validated a satellite-based water transparency retrieval algorithm based on the linear regression approach (R2 = 0.77) to determine the water clarity (2013–2016), which was later used for SAV classification and biomass estimation. For SAV classification, we used Spectral Mixture Analysis (SMA), a Spectral Angle Mapper (SAM), and a binary decision tree, giving an overall classification accuracy of 86.5% and SAV classification accuracy of 76.5% (SAV kappa coefficient 0.74), based on in situ measurements. For biomass estimation, a new Spectral Decomposition Algorithm was developed. The satellite-derived biomass (R2 = 0.79) for the SAV classified area gives an overall root-mean-square error (RMSE) of 0.26 kg Dry Weight (DW) m-2. The mapped SAV coverage area was 20% and 40% in 2013 and 2016, respectively. Estimated SAV biomass for the mapped area shows an increase in recent years, with values of 3390 t (tons, dry weight) in 2013 as compared to 4550 t in 2016. The maximum biomass density (4.89 kg DW m-2) was obtained for a year with high water transparency (September 2014). With the change in water clarity, a slow change in SAV growth was noted from 2013 to 2016. The study shows that water clarity is important for the SAV detection and biomass estimation using satellite remote sensing in shallow eutrophic lakes. The present study also demonstrates the successful application of the developed satellite-based approach for SAV biomass estimation in the shallow eutrophic lake, which can be tested in other lakes.

Highlights

There has been considerable interest in submerged aquatic vegetation (SAV), as it is intricately involved in the aquatic food web and significantly influences the freshwater ecosystem [1,2,3,4].On the other hand, the rampant overgrowth of invasive SAV species in natural lakes and streamsRemote Sens. 2017, 9, 966; doi:10.3390/rs9090966 www.mdpi.com/journal/remotesensingRemote Sens. 2017, 9, 966 has received much attention recently from water engineers and research scientists [5,6,7,8,9]
The study shows that water clarity is important for the SAV detection and biomass estimation using satellite remote sensing in shallow eutrophic lakes
The present study demonstrates the successful application of the developed satellite-based approach for SAV biomass estimation in the shallow eutrophic lake, which can be tested in other lakes

Summary

Introduction

There has been considerable interest in submerged aquatic vegetation (SAV), as it is intricately involved in the aquatic food web and significantly influences the freshwater ecosystem [1,2,3,4].On the other hand, the rampant overgrowth of invasive SAV species in natural lakes and streamsRemote Sens. 2017, 9, 966; doi:10.3390/rs9090966 www.mdpi.com/journal/remotesensingRemote Sens. 2017, 9, 966 has received much attention recently from water engineers and research scientists [5,6,7,8,9]. The massive overgrowth of invasive SAV species is associated primarily with the anthropogenic nutrient enrichment in freshwater ecosystems, and it is likely to have an impact, environmentally or economically. Invasive aquatic plants alter the nutrient cycles, degrade water quality, dominate native species, and obstruct navigation, fishery and other recreational activities [5,6,16]. In Japan, over 40 alien aquatic plant species have already been naturalized and have proliferated in many lakes and river beds [17]. Egeria Densa ( known as Brazilian waterweed) which is a submerged aquatic plant with relatively fast growth rate, thrives in low light conditions to a water depth of 4 m, and can invade freshwater systems with its dense canopy formation [18]

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