## 2 Data and Methods  
### Field-Measured Dataset  
Three field surveys were performed in Lake Chaohu in 2013 (28 May, 19-24 July, and 10-12 October) [7]. Water samples were obtained from 9 depths (surface, 0.1, 0.2, 0.4, 0.7, 1.0, 1.5, 2.0, and 3.0 m) using an ad hoc vertical collection device. The samples of water surface (0 m) were collected directly using a water sampler. The Ch\(\hbar\) value was measured using a Shimadzu UV-2600 spectrophotometer after filtering with Whatman GF/C glass-fibre filters (pore size of 1.1 \(\upmu\)m) and extraction pigment using 90% acetone extraction [42; 43]. For suspended particulate inorganic matter (SPIM), water samples were filtered using the pre-combusted and pre-weighted 47 mm Whatman GF/F glass fiber filters. The filters were then dried at 105 \({}^{\circ}\)C for 4-6 h, SPIM was derived gravimetrically by burning organic matter from the filters and weighting the filters again [44]. Water samples were filtered using 0.22-\(\upmu\)m pore-size filters, and absorption coefficient of colored dissolved organic matter (\(a_{g}(\lambda)\), 280 nm to 700 nm with 1 nm interval) was measured using a Shimadzu UV-2600 spectrophotometer. Additional information regarding the measurements and processing methods used to derive Ch\(\hbar\)a, SPIM, and \(a_{g}(\lambda)\) can be found in previous studies [21; 45; 46].  
Ch\(\hbar\)a values showed a large range (max/min ratio = 268.78) and variability (standard deviation (SD)/mean = 2.62). The CV (coefficient of variation = SD/mean) of Ch\(\hbar\)a(z) vertical profiles ranged from 4% to 239% with an average value of 67% [7]. The Ch\(\hbar\)a(z) vertical profiles were classified into 4 classes: Vertically uniform (Class 1), Gaussian (Class 2), exponential (Class 3), and hyperbolic (Class 4) [7]. In this study, Gaussian distribution type was analyzed, as the exponential and hyperbolic types were usually measured in the cases with high content of algal blooms.  
Gaussian functions with maximum values on the water surface was used to describe Ch\(\hbar\)a(z) profiles:  
\[\mathrm{Ch}\hbar\mathrm{a(z)}=\mathrm{C_{0}}+\frac{\mathrm{h}}{\sigma\sqrt{2 \pi}}\exp[-\frac{1}{2}(\frac{z}{\sigma})^{2}], \tag{3}\]  
where \(\mathrm{C_{0}}\) is the background value of Ch\(\hbar\)a(z) in the water column, and \(\mathrm{h}\) and \(\sigma\) determine the vertical variations of Ch\(\hbar\)a(z).  
Mean CV of vertical profiles of SPIM and dissolved organic carbon (DOC) was 28% (8-64%) and 14% (6-34%), respectively, which was obvious lower than that of Ch\(\hbar\)a(z) profiles. Note that the vertical profiles of \(a_{g}(\lambda)\) were not measured in this study, so the vertical profiles of \(a_{g}(\lambda)\) were assumed to be vertical uniform according to the vertical variation of DOC. SPIM and \(a_{g}(\lambda)\) were set to be vertically homogeneous with the average value of field measurements in Lake Chaohu (Table 2).  
\begin{table}
\begin{tabular}{c c c} \hline
**Input Parameters** & **Default Values** & **Variable Values** \\ \hline \(\lambda\) (nm) & 400–750, every 5 nm & \(\backslash\) \\ Wind speed (m/s) & 2.25 & \(\backslash\) \\ \(\theta\)(\({}^{\circ}\)) & 30 & 15–75, every 15\({}^{\circ}\) \\ SPIM (mg/L) & 30 & 0–60, every 5 mg/L \\ \(a_{g}\)(440) (m\({}^{-1}\)) & 0.85 & 0–4.0, every 0.5 m\({}^{-1}\) \\ \(\mathrm{S_{g}}\) (nm\({}^{-1}\)) & 0.019 & \(\backslash\) \\ \(\mathrm{C_{0}}\) & 0–40, every 5 & \(\backslash\) \\ h & 1–76, every 5 & \(\backslash\) \\ \(\sigma\) & 0.2–1.4, every 0.2 & \(\backslash\) \\ \hline \end{tabular}
\end{table}
Table 2: Input parameters of Ecolight simulation: Solar zenith angle (\(\theta\)), suspended particulate inorganic matter (SPIM), absorption coefficient of colored dissolved organic matter (CDOM) at 440 nm (\(a_{g}\)(440)), and spectrum shape of CDOM absorption coefficient (\(\mathrm{S_{g}}\)). \(\mathrm{C_{0}}\), h, and \(\sigma\) are structure parameters of Ch\(\hbar\)a(z) profiles.