Abstract
Remote sensing accuracy of the dynamic water environment under a changing environment due to climate and anthropogenic impacts should be improved by a deep understanding of the absorption properties pertinent to the water body. Spectral variation of suspended particulate material (SPM) absorption and its changing mechanism during flood periods of Poyang Lake were analyzed in this study. Absorption coefficients were measured and determined by spectrophotometry using the quantitative filter techniques (QFTs) based on field samples from July 12 to September 06, 2017. Two main optical active constituents (OACs) of SPM including nonalgal and phytoplankton algal particulates were quantified and analyzed in detail. The results suggested that, during study periods, Poyang Lake exhibits an overall high level of suspended nonalgal detritus and algal concentration and lower water clarity, showing a strong absorption by total suspended sediments that are closely related with the land-derived nonalgal detritus material which varied significantly with diverse proportions of minerals and organic materials from multiple sources. Due to variations in phytoplankton community pigment composition, concentration, and package effect, there exists a difference between optical absorption capacity on blue (440) and red (675) portions of bands, the former of which had an obvious enhancement due to the increased effect of accessory pigments in suspended phytoplankton particles from July to September. Evidence also presented that the nonlinear dependency of specific phytoplankton particulate absorption on pigment concentration for various trophic statuses in different periods could be unstable due to relative contributions of the package effect and accessory pigments; this could bring uncertainties to the parameterization of optical models and remote sensing algorithms proposed for accurate applications in lake water environment monitoring.
Highlights
Absorption coefficients of optical active constituents (OACs, i.e., particulate and dissolved materials) play an important role in the inherent optical properties (IOPs, i.e., absorption and specific coefficients), largely determining the apparent optical properties (AOPs, i.e., water leaving radiance and remote sensing reflectance) in natural waters [1, 2].erefore, remote sensing inversion accuracy of the dynamic water environment under a changing environment due to climate and anthropogenic disturbances should be improved by a deep understanding of the absorption properties pertinent to the water body under consideration [3–5].Over past decades, variability in absorption coefficients has been thoroughly documented in oceanic waters, where phytoplankton and their derivative products are optically dominant, and other components are often assumed to covary with phytoplankton pigments [6–10]
E main objectives of this study are (1) to separate absorption coefficients of suspended particulate materials in Poyang Lake through controlled laboratory experiments during the flood period, which may have its own characteristics at this time, contributing to a better understanding of the optical behavior of SPM absorption, and (2) to clarify the changing mechanism for corresponding components of absorption, which may facilitate improvements in the parameterization of remote sensing algorithms for the interpretation of remote sensing information
SPM and Chl.a were higher in July than September, representing a decreasing level of suspended sediments in lake columns as water flooded during the study time
Summary
Yuandong Wang ,1,2 Xibin You, Lianfang Yu, Lihong Meng, Xiangming Xu, and Guangxu Liu. Spectral variation of suspended particulate material (SPM) absorption and its changing mechanism during flood periods of Poyang Lake were analyzed in this study. Due to variations in phytoplankton community pigment composition, concentration, and package effect, there exists a difference between optical absorption capacity on blue (440) and red (675) portions of bands, the former of which had an obvious enhancement due to the increased effect of accessory pigments in suspended phytoplankton particles from July to September. Evidence presented that the nonlinear dependency of specific phytoplankton particulate absorption on pigment concentration for various trophic statuses in different periods could be unstable due to relative contributions of the package effect and accessory pigments; this could bring uncertainties to the parameterization of optical models and remote sensing algorithms proposed for accurate applications in lake water environment monitoring
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