Finally, after a long, cold winter, the landscape is beginning to change as leaves appear and flowers bloom. This is not an exclusively terrestrial event. In the shallow water of Chesapeake Bay and its many tributaries, underwater grasses are once again making their presence known.
Known as submerged aquatic vegetation or SAV, these plants provide food and shelter for communities of waterfowl, fish, shellfish, and invertebrates. Minnows dart between the plants and graze on tiny organisms that grow on the stems and leaves. Hiding in the grass beds, small fish find refuge from larger, hungrier mouths. Sitting on the bottom, also well-hidden by the plants, a blue crab sheds its shell and patiently waits for its new armor to harden.
For waterfowl, SAV is a valuable food source. In the fall and winter, migrating waterfowl search the sediment for nutritious seeds, roots, and tubers. Resident waterfowl may feed on SAV year round. Microscopic zooplankton consume decaying SAV and, in turn, become food for larger Bay organisms, such as fish and clams. Thus, SAV plays a key role in the Bay’s energy cycle.
Like other green plants, SAV produces oxygen, a precious and sometimes limited commodity in the Bay. The grasses also filter and trap sediment that can cloud the water and bury bottom-dwelling organisms, such as oysters. In addition, they remove and use nutrients, like nitrogen and phosphorus, from surrounding waters.
There are more than 10 species of SAV commonly found in the Bay or nearby rivers. Salinity, water depth, and bottom sediment determines where each species can grow. The ability of SAV to survive is largely determined by the amount of light that reaches the plants. Environmental factors that reduce water clarity, and in turn, the amount of sunlight reaching the plants, are the primary cause of SAV decline.
For example, suspended sediment and other solids can cloud the water, or even cover the plants completely. Sources of sediment include runoff from farmland, building sites, and highway construction. Shoreline erosion also adds sediment to Bay waters. Land development, boat traffic, and loss of shoreline vegetation accelerate natural erosion.
Nutrients, create other problems for SAV. Although vital to all ecosystems, excessive amounts of nutrients stimulate rapid growth of algae, known as blooms. Algae blooms cloud the water, and certain types of algae grow directly on the plants, further reducing available sunlight.
Some of the major sources of nutrients include sewage treatment plants, agricultural fields, and fertilized lawns. Every day, treated sewage effluent is released into rivers and eventually reaches the Bay. Runoff from farm fields and lawns carries with it nutrient-rich fertilizers. Often, runoff also contain herbicides and pesticides that can be toxic to aquatic plants and animals.
During the 1960s, it has been estimated that more than 200,000 acres of SAV grew along Bay and river shorelines. By 1978, a survey of SAV documented only 41,000 acres. Declining water quality, disturbance of SAV beds and alteration of shallow water habitat all contributed to the decline. The absence of SAV translates into a loss of food and habitat for many Bay species.
The U.S. Fish and Wildlife Service, other federal and state agencies, and other organizations monitor SAV distribution each year. By examining aerial photographs, SAV locations are mapped for the entire Bay and its tidal tributaries. By monitoring SAV, biologists can determine which areas need to be protected. And by examining historical distribution, areas where SAV once flourished can be targeted for restoration. SAV are making a comeback. A 1992 survey of reported 70,000 acres of SAV.
Citizens can help by participating in a volunteer SAV survey. Individuals with access to shallow water areas confirm the presence of previously identified SAV beds. Citizens often report SAV beds too small to be seen in the aerial surveys. Frequently, their information is used by local officials in directing the protection and management of waterways and shoreline areas.
SAV reflects the general water quality of an area and can be used to gauge the health of the Bay and its tributaries. Everyone who lives, works, and plays in the Bay watershed directly affects water quality through everyday activities. And, the presence of SAV reflects our stewardship for the Bay and the wildlife it supports.
What You Can Do
- Reduce the amount of fertilizers used in yards. Plant vegetation suited to your soil, moisture and climate conditions. If you must fertilize, follow all directions carefully and never apply before storms.
- Waterfront property owners should avoid using herbicides that may harm delicate SAV plants. Prevent erosion by planting shoreline vegetation.
- Boaters should avoid disturbing SAV beds. Propellers tear rooted vegetation out of bottom sediments.