The sedimentary chironomids and pigments in two Yangtze floodplain (China) lake sediment cores since 1800s CE. The sediment cores were dated using lead-210 with the constant rate of supply (CRS) model. Chironomids were ananlyzed following standard procedures. About 10 g wet samples were firstly deflocculated using 10% potassium hydroxide (KOH) in a 75 °C water bath for about 15 minutes. Then, sediments were gently washed through 212 μm and 90 μm sieves with water after which the residues on the sieves were backwashed into a sorting tray. Chironomid head capsules were picked out individually using fine forceps under a dissecting microscope. The chironomid head capsules were identified using a microscope at ×100/×400 magnification. At least 50 head capsules were picked out from each sample to make the results and interpretations statistically robust.

The sediment cores were dated using lead-210. Chironomid samples were prepared and analysed following the methods presented in Brooks et al., (2007). Sedimentary pigments (including canthaxanthin and UVR index) were analyzed using a high performance liquid chromatography (HPLC). The concentration of canthaxanthin was calibrated using total organic carbon. The UVR index calculated by dividing the concentration of UVR-absorbing pigments relative to the sum of alloxanthin, diatoxanthin and lutein-zeaxanthin and multiplying by 100.Elements (TP, Zn and Al) were analyzed using an inductively coupled plasma-atomic emission spectrometry (ICP-AES) after digesting with a mixture of acid (HF:HCl:HNO3:HClO4, 3:0.5:6:0.5, v/v).