Lake topography and wind waves determining seasonal-spatial dynamics of total suspended matter in turbid Lake Taihu, China: assessment using long-term high-resolution MERIS data.

Yunlin Zhang,Kun Shi,Xiaohan Liu,Boqiang Qin,Yongqiang Zhou,Francois G Schmitt

doi:10.1371/journal.pone.0098055

Abstract

Multiple comprehensive in situ bio-optical investigations were conducted from 2005 to 2010 and covered a large variability of total suspended matter (TSM) in Lake Taihu to calibrate and validate a TSM concentration estimation model based on Medium Resolution Imaging Spectrometer (MERIS) data. The estimation model of the TSM concentration in Lake Taihu was developed using top-of-atmosphere (TOA) radiance of MERIS image data at band 9 in combination with a regional empirical atmospheric correction model, which was strongly correlated with the in situ TSM concentration (r 2 = 0.720, p<0.001, and n = 73). The relative root mean square error (RRMSE) and mean relative error (MRE) were 36.9% and 31.6%, respectively, based on an independent validation dataset that produced reliable estimations of the TSM concentration. The developed algorithm was applied to 50 MERIS images from 2003 to 2011 to obtain a high spatial and temporal heterogeneity of TSM concentrations in Lake Taihu. Seasonally, the highest and lowest TSM concentrations were found in spring and autumn, respectively. Spatially, TSM concentrations were high in the southern part and center of the lake and low in Xukou Bay, East Lake Taihu. The lake topography, including the water depth and distance from the shore, had a significant effect on the TSM spatial distribution. A significant correlation was found between the daily average wind speed and TSM concentration (r 2 = 0.685, p<0.001, and n = 50), suggesting a critical role of wind speed in the TSM variations in Lake Taihu. In addition, a low TSM concentration was linked to the appearance of submerged aquatic vegetation (SAV). Therefore, TSM dynamics were controlled by the lake topography, wind-driven sediment resuspension and SAV distribution.

Highlights

Large eutrophic shallow lakes are spatially and temporally complex environments because of the dynamic interactions of physical, chemical and biological factors [1,2,3]
There was a high determination coefficient .0.6 through the near-infrared wavelength range of 705 to 850 nm, which showed that the total suspended matter (TSM) concentration could be estimated accurately using Rrs(l, 0+) in this wavelength range; this result had previously been found for Lake Taihu and other turbid waters [14,19,27]
A simple band model of TSM estimation was initially calibrated using in situ TSM concentrations from 2005 and Medium Resolution Imaging Spectrometer (MERIS) band 9 TOA radiance corrected by the former regional empirical atmospheric correction model, which had a relatively high modeling accuracy (r2 = 0.720, p,0.001, and n = 73)

Summary

Introduction

Large eutrophic shallow lakes are spatially and temporally complex environments because of the dynamic interactions of physical, chemical and biological factors [1,2,3]. Such lakes are often characterized by high and varying concentrations of total suspended matter (TSM) that result from terrestrial inputs and sediment resuspension [3,4]. Measurements of TSM would be required to have high spatial and temporal resolution (order of tens of meters and tens of minutes, respectively). Obtaining representative and successive measurements of environmental factors through traditional point sampling has proven to be problematic within these varying environments, especially when the data are extrapolated over large lake scales based on measurements at only a few sites

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Results

Discussion

Conclusion