Who Killed SAV? Background
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This lesson is adapted from "Who Killed Ese-Vee?" in the Chesapeake Bay Foundation's Bay Grasses in the Classes curriculum. The lesson is intended as a follow-up to Grasses, Grasses Everywhere.
Submerged aquatic vegetation (SAV) provides an essential link in the balanced health of the Chesapeake Bay and its tributaries. Like grass in the schoolyard, SAV requires light, water, and nutrients to survive. In turn, these grasses produce the oxygen necessary for the survival of underwater organisms. Underwater grasses, such as wild celery, eelgrass, and widgeon grass, provide shelter for fish, shellfish, and many other invertebrates. SAV provides food for waterfowl as well as for the animals it shelters. SAV helps to maintain water quality and clarity, working as a natural filter to trap sediment. SAV roots provide stability to the bottom of the Bay and its tributaries, playing a vital link in preventing erosion and further sediment pollution. SAV absorbs nutrients for its own benefit, and this in turn benefits the underwater environment by helping to keep nutrient levels in check.
Since the 1960s, over half of the Bay's SAV has disappeared. It is impossible to pinpoint one single cause of this decline, but it seems likely that the very pollutants SAV removes from the water are partly to blame. Excessive amounts of sediment cloud the water and block out the sunlight vital for the survival of underwater grasses. Likewise, excessive nutrients cause large algal blooms, which block out the sunlight. Hurricanes and dredging have also contributed to the decline. In this lesson, students will research these natural and human factors in order to defend or prosecute each "suspect."
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