The densities of bacteria, picophytoplankton, heterotrophic nanoflagellates and ciliates in Lake Kasumigaura (Japan) monitored monthly since 1996

This data paper describes the densities of the bacterioplankton, picocyanobacteria, eukaryotic picoplankton, heterotrophic nanoflagellates (HNFs) and ciliates in the water of Lake Kasumigaura, a shallow, eutrophic lake that is the second largest in Japan. All of these planktonic organisms are components of a microbial loop and are countable using an epifluorescence microscope. These data represent the results of monthly collections from April 1996 through March 2010 at two sites on the lake, and this data set is unique among the available published data papers concerning lakes or plankton and continues to be freely available. The monitoring was performed as a component of the Lake Kasumigaura Long-term Environmental Monitoring program conducted by National Institute for Environmental Studies (NIES) since 1977 and includes water quality, plankton, and benthos. The data have been used for ecological studies and for studies on the management of water quality.