Question

How would you distinguish a mesotrophic lake diatom assemblage from a eutrophic assemblage in a sediment core?

Answer 1

Mesotropic lake

Meso means middle or mid. Therefore, mesotrophic means a medium amount of nutrients. Mesotrophic lakes usually have clear water with some algal blooms in late summer.

Mesotrophic lakes are great fishing lakes.

Mesotrophic lakes stratify, meaning they separate into layers in the summer. The top layer of water becomes warm from the sun and contains algae. Since the by-product of photosynthesis is oxygen, oxygen concentration remains high at the surface of the lake. The bottom layer remains cooler and can become anoxic in mid-summer. This change occurs because as all the algae and other organisms die and are decomposed at the bottom of the lake, oxygen gets used up. Since this bottom layer of water does not mix with the top layer of water in the summer, oxygen cannot be replenished. The implications of anoxia are that no fish or other organisms can live where there is no oxygen; therefore, in late summer, fish move shallower where there is still oxygen available.

Eutrophic lake

Eu means true. Therefore, eutrophic literally means true nutrients or truly nutrient rich. Eutrophic lakes are found in places where the soils are more fertile and where there is a lot of farmland. Eutrophic lakes are shallow and have murky water and mucky, soft bottoms. They also have a lot of plants and algae.