Three streams with watersheds of different land uses (urban, agricultural, and forested) were chosen for this study. A composite sample of diatoms was obtained from small rocks in a riffle of each stream and identified to genera. Water chemistry measurements included chloride, sulfate, nitrate, conductivity, pH, alkalinity and temperature.Conductivity, chloride, and sulfate were significantly higher in the urban watershed and lowest in the forested watershed. However, the forested watershed had the highest levels of nitrate, which may have come from groundwater or organic matter decomposition. Alkalinity, pH andtemperature did not vary among watersheds.Diatom diversity was significantly higher in the forested watershed. Several diatom genera, Amphora, Cymbella and Gyrosigma, were positively correlated with nitrate and negatively correlated with conductivity, chloride and sulfate, which indicate their potential use as indicators of water quality. / Department of Natural Resources and Environmental Management

Several species of the diatom genus Thalassiosira Cleve, were observed in freshwater phytoplankton samples collected from a fifty-two kilometer reach of the San Joaquin River in the vicinity of Stockton, California, USA. The study was conducted between the South Airport Way bridge near Vernalis and the Stockton Deep Water Ship Channel during fall and summer of both 2005 and 2006. The entire reach is freshwater habitat with the lower twenty-eight km strongly influenced by tidal flow reversals driven by the San Francisco Estuary. Ninety four whole water samples were collected from surface waters during the months of July, August, September and October in 2005 and the months of July and August in 2006. Six species of Thalassiosira were identified using scanning electron and light microscopy: T. weissjlogii (Grunow), T. gessneri Hustedt, T. lacustris (Grunow), T. visurgis (Grunow), T. decipiens (Grunow), and T. incerta (Makarova). Of the species observed, only T. weissjlogii has been previously reported in the freshwater portion of the San Joaquin River. The other five species have been previously reported from sites in the San Joaquin- San Francisco Estuary characterized as brackish, suggesting they are distributed in waters of various salinities ranging from freshwater to brackish within the river and estuary.