Yellowstone Lake, occupied by S. yellowstonensis, sits in a volcanic caldera, and is heavily influenced by superheated water carrying extraordinarily high levels of dissolved nutrients that diatoms need to grow, levels much higher than typical in other lakes occupied by S. niagarae. The soils of its basin though are composed mostly of obsidian sand (glass!!) which will cause very low levels of other nutrients. Altogether it is a very different lake than those typically having S. niagarae. Why is this important?