Science as Inquiry
Science in Personal and Social Perspectives
If they can't swim, they die. Fish and shrimp are able to escape the suffocating grasp of the hypoxic (low-oxygen) waters in the Gulf of Mexico, but animals like clams, snails, and worms are trapped in the "dead zone," an area which has grown as large as the state of New Jersey (approximately 7,000 square miles) in recent years. It's a marine horror scene, and we should all take notice because it's happening in other coastal areas, too. More than half of the estuaries in the country experience oxygen depletion during the summer, and a third experience a complete loss of oxygen. The hypoxia in the Gulf, however, is the most dramatic case.
To date, scientists trace the cause of the problem to high levels of nutrients, particularly nitrogen. About two-thirds of the nation's harvested cropland and the treated sewage of 27% of the U.S. population empty into the Mississippi River, and eventually into the Gulf. The nutrients discharged feed algal blooms in the spring and summer, which periodically die and sink to the bottom. Large amounts of oxygen are then consumed by the bacteria that decompose the dead algae. Sometimes, so much oxygen is consumed that there is not enough left in the water to sustain life. This dreadful condition persists until an event such as a tropical storm or a cold front mixes the oxygen-depleted lower waters with the upper waters and brings relief.
Take a look at some of the data collected by scientists who have been monitoring the dead zone for many years. We have chosen a data set for you based on type and consistency of data collected and ease of reading. Go to the Nutrient Enhanced Coastal Ocean Productivity (NECOP) Program's home page. Scroll down to the table of "NECOP Projects by Year" and click on 1994. Go to the "Transect C" section and click on "View Transect C Data". A transect line is an imaginary line perpendicular to the coastline, recorded using latitude and longitude measurements. This data set contains water quality measurements taken at certain stations along the transect line on 9 different dates between March and October of 1994.
We are going to look at one particular station, station 6B, on each of the dates. Divide your class into 9 groups, and assign each one a date. Have each group graph dissolved oxygen (mg/L) versus depth (meters). Each graph will contain 21-32 data points. Click here for step by step Microsoft Excel graphing instructions.
What observations can you make? Do you see any trends over time? Generally, the minimum oxygen level required to sustain aquatic life is 5 ppm (parts per million), and when it falls below 2 ppm, anything that can swim leaves the area. What percentage of the measurements had dissolved oxygen readings of 5 ppm or less? How about 2 ppm or less? What do you think happened between the July 1 and August 17 measurements? How do you explain the September 13 measurements?
Your graphs should serve as a dramatic illustration of the hypoxia problem. There is a need to tackle this problem and prevent more of our precious marine environment from becoming barren underwater wasteland and unproductive fisheries. Can you think of potential solutions to the Gulf of Mexico hypoxia problem?
For more classroom activities, visit the Gulf of Mexico Program's Educator and Student Resources page, and look for lessons related to watersheds. More resources on the Bridge include The Watershed Game (for grades 4-8) and Watershed Education Resources on the Internet from GREEN.
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