Changes in phytoplankton community after brackishing in Lake Koyama-ike in Tottori Prefecture, western Japan

Abstract

We compared community structure in phytoplankton and water variables in epilimnetic waters in Lake Koyama-ike located in western Japan, between before and after brackishing project in 2012. Monthly-monitored data, with three replicated years each (i.e., before: 2009~2011, after: 2012~2014), were analyzed statistically to detect changes in the flora and water variables. Whereas insignificant effects of the brackishing on total abundances of phytoplankton (i.e., chl-a, cell density), it modified the community structure from freshwater-inhabitants dominated (e.g., Anabaena affinis , Cyclotella meneghiniana , Microcystis aeruginosa , Planktothrix agardhii ,) to brackish water and seawater-species dominating community (e.g., Cylindrotheca closterium , Heterocapsa rotundata , Skeletonema costatum ). Further, the brackishing resulted in an obviously increased salinity (1,800 ~8,000 mgCl^-1 l^-1) but limited changes in nutrient concentrations (i.e., decrease in ammonium (0.01 ~0.06 mgNH 4⁺ l^-1) and insignificant changes in other nutrients) in epilimnetic waters.