App.—List of Acronyms and Glossary * 201 



Submergent — a herbaceous or nonvascular plant, either 

 rooted ornonrooted, which lies entirely beneath the 

 water surface, except for flowering parts in some 

 species. 



Substrate — the bottom surface on which plants grow. 



Swamp — a forested wetland. 



Threatened — nearing endangered status. 



Tundra — a wet arctic grassland dominated by lichens 

 and Sphagnum mosses. It is characterized by a thick 

 spongy mat of living and undecayed vegetation that 



is often saturated with water. 



Turbidity — the cloudy condition of a body of water that 

 contains suspended material, such as clay or silt par- 

 ticles, dead organisms, or small living plants or 

 animals. 



Watershed — the region drained by or contributing 

 water to a stream, lake, or other body of water. 



Water table — the upper surface of ground water in the 

 zone of saturation. 



