Text S7. Diatom analysis
Diatom is a widely used proxy of variations in water quality, including levels of salinity in coastal and estuarine environments (Zong et al., 2013). A total of 67 sediment samples were analyzed; 12 from KhqS, 20 from KHQ-14, and 35 from XS-1603. Diatoms were identified under oil immersion at 1000x using an OLYMPUS BX-51 microscope. Only samples that yielded in excess of 300 diatom valves were included; numbers of diatom valves in the vast majority of samples from XS-1603 fell well below this standard. As a result, no detailed analysis of diatoms from XS-1603 is presented here, although statistically significant counts were obtained for five samples from above -2.0 m OD in the core. In the current research, diatom species are classified into one of six habitat groupings: marine plankton, marine epiphytes, marine/brackish epipelon, brackish plankton, freshwater plankton and freshwater benthos/epiphytes. Zonation of diatom assemblages is carried out with CONISS module in Tilia. The diatom fragments (<1/2 valve) which cannot be identified as one valve were counted.
Diatoms indicative of freshwater conditions, such as Aulacoseira Canadensis (Hustedt) Simonsen, Aulacoseira granulata (Ehrenberg) Simonsen, are common species in disturb river and estuary.Cyclotella distinguenda Hustedt and Cyclotella meneghiniana Kützing are often found in freshwater river and lake.Actinocyclus ehrenbergii Ralfs, Actinoptychus undulates(Bailey) Ralfs and Coscinodiscus spp. (mainly Coscinodiscus radatius , Coscinodiscus subtilis ), Melosira sulcata(Ehrenberg) Kützing are the most common of the marine taxa present, while Diploneis smithii (Brébisson) Cleve, Cyclotella stylorum Brightwell and Cyclotella striata Grunow in Cleve & Grunow are abundant brackish-water indicators.