Chemical Properties of Lakes: Introduction to the Lake Multi-Scaled Geospatial and Temporal Database (LAGOSNE)

This lesson was adapted from educational material written by Dr. Kateri Salk for her Fall 2019 Hydrologic Data Analysis course at Duke University.

Introduction
Trophic states are based on lake fertility. The root “trophy” means nutrients; therefore, lakes are classified based on the amount of available nutrients for organisms. More fertile lakes have more nutrients and therefore more plants and algae. There are four lake trophic states:

“Oligo” means very little; therefore, oligotrophic means very little nutrients (Phosphorus and Nitrogen). In oligotrophic lakes, oxygen is found at high levels throughout the water column. Cold water can hold more dissolved oxygen than warm water, and the deep region of oligotrophic lakes stays very cold. In addition, low algal concentration allows deeper light penetration and less decomposition.

“Meso” means middle or mid; therefore, mesotrophic means a medium amount of nutrients (Phosphorus and Nitrogen). Mesotrophic lakes behave differently than oligotrophic lakes in that they stratify, meaning they separate into layers in the summer (more on lake stratification). 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.

“Eu” means true; therefore, eutrophic literally means true nutrients or truly nutrient rich (Phosphorus and Nitrogen). Eutrophic lakes are found in southern Minnesota 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.

Hypereutrophic lakes are at the extreme end of the eutrophic range with exceedingly
high nutrient concentrations and associated biomass production. In temperate regions
the fish communities are dominated by roach and bream. Anoxia or complete loss of oxygen often occurs
in the hypolimnion during summer stratification.

For more information on lake trophic states, please visit http://www.lake.wateratlas.usf.edu/library/learn-more/learnmore.aspx?toolsection=lm_tsi and http://www.manitowoccountylakesassociation.org/oligotrophic-vs-mesotrophic-vs-eutrophic/.

Learning Objectives

After successfully completing this exercise, you will be able to:

1. Navigate and explore the LAGOSNE database and R package
2. Evaluate lake water quality using the trophic state index
3. Analyze spatial and temporal patterns of water quality across the northeast U.S.