How Do You Know an Ecosystem is Healthy? Ask students how they can tell whether a river or stream is healthy or not. Have them discuss examples they they have seen where they live.

There are many factors used to assess health Water cloudiness Dissolved Oxygen Nutrients (Phosphorus, Nitrogen) Amounts of plants and animals Scientists use different measures to determine whether a river or stream is healthy. These include the cloudiness of the water (turbidity), how much oxygen is dissolved in the water, whether there are too many or too few nutrients, and they examine the amounts and types of organisms present.

Turbidity Measure of floating particles Particles can be silt, soil, floating vegetation and organisms Can be affected by rainfall Can be caused by humans: runoff, erosion, boating The cloudiness of the water can be an indicator of whether a river or stream is healthy. For example, too much soil runoff can prevent plants from making their food and give harmful organisms habitat to live.

Dissolved Oxygen Concentration of Oxygen in the water Important for organisms to live Changes daily and seasonally Must be above a certain amount to support wildlife Decaying material consumes Oxygen Plants and animals need a certain amount of oxygen to live. When organisms die, the oxygen is used up.

Nutrients Nitrogen and Phosphorus are important measures High Nitrogen and Phosphorus amounts can increase the amount of algae Humans can contribute nutrients through too much fertilizer use Nutrients need to be in balance. Too many nutrients can cause certain kinds of organisms to grow too much. When these organisms die, their decay can cause the oxygen level to decrease to a low level, killing organisms that need oxygen to survive.

Amounts and Types of Living Things Some species are important indicators of health Examine ecosystem to look for “normal” conditions Some living things (e.g., algae) will increase in population when the system is out of balance Scientists look for a healthy balance or organisms. They sometimes compare what they find to what has been historically living in that ecosystem to determine what is normal.

References Pinto, G., Bielmyer-Fraser, G.K., Goldberg, N., Ouellette, A., Le, A., Pyati, R., Zoellner, B., Closmann, C. (2018/19). 2019 State of the River Report for the Lower St. Johns River Basin, Florida: Water Quality, Fisheries, Aquatic Life, & Contaminants (LSJR). Prepared for the City of Jacksonville, Environmental Protection Board. https://sjrreport.com.