Turner Designs fluorometers (Model 10-AU) were used to investigate the relationship between physical mixing processes and phytoplankton dynamics in Toolik Lake, an Arctic Tundra Lake located on the North Slope of Alaska. A field fluorometer equipped to measure rhodamine dye was used to determine the vertical and horizontal movement of inflowing waters during storms and lake mixing events. In vivo fluorescence measurements were made simultaneously with a second fluorometer to determine the impact of these physical events on phytoplankton distributions in the lake. Coupled with DCMU additions, the in vivo fluorescence measurements provided additional information on the degree and nature of phytoplankton nutrient/light limitation. In the laboratory we used two additional 10-AU fluorometers; one was used for chlorophyll a determinations and another for ammonium assays employing a newly developed fluorometric technique (Holmes et al. in press). All of the fluorometers worked flawlessly. We were very impressed with their rugged design and stability. In addition, the Water Puppy pump was a joy to use and greatly assisted with the in-vivo measurements and in collecting water samples.