Diatom preparation followed a standard procedure (Battarbee, 1986), and followed Renberg's (1990) recommendation of bulk preparation using a water-bath. Microspheres were added to each sample to determine diatom concentration (Battarbee and Kneen, 1982). The concentration of microspheres added was 2 ml of 5.01x10^6 per 0.01 g dry weight of sediment. The samples were then diluted, placed on a cover slip and mounted to the microscope slide using Naphrax®. Diatoms were identified and counted at 1000x magnification. Identification was aided by the website “Diatoms of the United States” (Spaulding, 2014) and identification keys (Krammer and Lange-Bertalot, 1991, 1999a,b). At least 300 diatom frustules were counted per slide.