Nitrates in Iowa Water
Data is provided that shows the nitrate levels in Iowa's wells rising from 2002 to 2017. The provided video examines the filtering capabilities of different soil types.
Possible Guiding, Compelling and/or Anchoring Questions
- What is a hypothesis about why some colors come out and others stay in the soil?
- If red is positively charged and blue is negatively charged, can you infer the overall charge of the soil? Is it positive? Negative? Neutral? What evidence supports your conclusion?
- Why are nitrate levels in Iowa wells trending up?
Iowa has a problem with high nitrate levels in the streams, rivers, and groundwater. Nitrates typically come from farm fertilizers that run off the fields into the surface water or percolate through the soil into the underground water. High nitrate levels are associated with a number of health effects including “blue baby” syndrome. The type of soil can determine how much of the nitrogen in the form of nitrates stay in the soil near the plant or how much may drain out of the soil ending up in waterways. Because nitrate is an anion, it is attracted to cations in the soil. Soils with more anions than cations repel nitrates. The process by which ions are trapped in the soil is called “cation exchange” and it is a measure of soil quality.
This phenomenon can be a starting point for students learning about chemical reactions using the simple principle of opposites attract.
- After viewing the video and making hypotheses, students can research the cations and anions in soil and make predictions about whether or not each will react with nitrates. They should then determine if the nitrate will stay in the soil near the plant (if it is attracted to a cation) or leave the soil and end up in the water (if it is repelled by anions).
- Students who understand more chemistry can predict what the chemical formulas will be when nitrate reacts with the various soil cations. Work on single and double displacement reaction products should follow.
- As an extension, have students bring in soil samples and try the activity depicted in the video. All soils will have slightly different results depending on what is in them (be sure to do this on white paper to see the colors clearly). This can lead to further inferences.
- Students should also look at nitrate levels in Iowa (see map and data linked below) to understand the importance of ion exchange in soils.
- A final activity might be to have a farmer talk to students about his/her efforts to reduce the use of nitrogen on the soil.
- Purdue University: Fundamentals of soil cation exchange capacity: Introduction to cation exchange.
- Iowa WQIS: Live map of nitrates in Iowa waters: This live map shows students what the current nitrate levels are in Iowa.
- AgPhD: How much nitrogen can your soil hold?: Discusses how soil charge affects the nitrate holding capacity of soil and how farmers can ensure that they are applying the correct amounts of fertilizer for the soil capacity.
Iowa Core Alignment
Submitted by DeEtta Andersen.
Thumbnail image obtained from Flickr.