Pre-classification improves relationships between water clarity, light attenuation, and suspended particulates in turbid inland waters

Abstract

Relationships between water clarity, light attenuation, and concentration of suspended particulates are important in water optics and remote sensing, but are not well described yet, especially for optically complex turbid inland waters. In this study, based on 3-year data from Chinese lakes (Lake Taihu, Lake Chaohu, and Three Gorges reservoir), we propose a new approach to describe the inter-relationships of these bio-optical variables. This approach includes a pre-classification step of the waters into three types based on a semi-analytical parameter C s before establishing the relationships. Our results showed that the pre-classification of waters increased model accuracies both for Z SD (Secchi depth) versus K d (diffuse attenuation coefficient) and K d versus TSM (total suspended matter concentration). The quasi-theoretical model described better the relationship between Z SD and K d than the empirical model. For the K d versus TSM relationship, linear models proved suitable for the Type 2 and Type 3 waters, whereas the power function model gave a better fit for the Type 1 water. Testing of the proposed relations with an independent dataset showed mean absolute percentage errors (MAPE) mostly below 30%. The findings of this study clarify the relationships between Z SD, K d, and TSM, and improve our bio-optical understanding of complex turbid inland waters.