By Scott C. Yaich, Ph.D.
The 19th-century explorer and geographer John Wesley Powell defined a watershed as "a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community." Powell wisely recognized that all living things in a watershed, including waterfowl and people, are united by and dependent on its central element—water
And in many ways watersheds are indeed living communities. Much like the network of capillaries and veins that carry blood to the heart, a typical watershed consists of many small, ephemeral channels that flow together to form progressively larger streams and rivers, which ultimately empty into lakes or oceans.
Watersheds come in all shapes and sizes. Some can be as unremarkable as the area drained by a normally dry streambed that joins a creek. At the other extreme, the Mississippi River watershed encompasses 40 percent of the continental United States and carries an average of almost 400 billion gallons of water past New Orleans and into the Gulf of Mexico
Wetlands are a vital component of healthy watersheds. Many wetlands are located in the floodplains of rivers and streams and play an important role in flood control in addition to supporting an abundance of fish and wildlife. Even so-called "geographically isolated" wetlands, such as prairie potholes and playa lakes, are connected to the watershed through underlying groundwater.
The health of a watershed can often be assessed simply by examining its water. For example, over the decades water quality in Chesapeake Bay was degraded by heavy loads of sediment and nutrients discharged into the estuary by the Susquehanna and Potomac rivers and other tributaries. Sediment clouded the water, and nutrient pollution caused algal blooms. With less sunlight penetrating the murky water, beds of submerged aquatic vegetation (SAV) declined by more than 80 percent from historical levels, significantly reducing forage for wintering waterfowl and devastating fish and shellfish populations.
Liquid Assets Along Colorado's lower South Platte River, Ducks Unlimited is working with private landowners, municipalities, and other partners to provide vital habitat for waterfowl and to improve watershed health by creating "recharge wetlands." River water is diverted into adjacent wetland basins during times of high river flows, normally in winter. The water stored in these basins then infiltrates and recharges the underlying aquifer, seeping through the ground to reach the river and augment flows during summer, when water is needed to irrigate crops as well as to provide aquatic habitat for federally endangered species. Landowners who restore recharge wetlands receive "water credits," which help offset other irrigation costs.
"As a result of recharge wetlands, we are able to supply water to farms and major municipalities along Colorado's Front Range, where an anticipated 1 million more people will live by 2050. We have to find solutions that meet our diverse water needs if waterfowl and the environment are to be sustained in the face of growing urban populations," says Greg Kernohan, DU's manager of conservation programs in Colorado. "We are demonstrating that a single wetland project can provide benefits to agriculture, municipalities, and the environment."