By: Alisa Fried, AWS Stewardship Intern*
The presence of underwater grasses provides various benefits to the river and the organisms that live in and around it.
Until recently, it seemed that submerged aquatic vegetation (SAV), also known as underwater grasses, were scarse in the Anacostia River due to high turbidity in the water and other severe water quality problems. However, since as late as 2013, SAV populations have been coming back to the river, demonstrating an improvement in overall river health. Water clarity has been improving for the last couple of years or so creating more suitable conditions for these wonderful plants that are great indicators of the river's health. Currently, one of the most prevalent SAV species in the Anacostia is the non-native Hydrilla (Hydrilla verticillata). While there is current disagreement on whether or not this non-native species is a problem for biological diversity and overall ecosystem wellbeing, some scientists believe that the plant is helping to provide habitat and food for aquatic organisms and encouraging the return of waterfowl to the river.
Coontail (Ceratophyllum demersum) growing within one of our exclosures at Buzzard Point, right by the confluence with the Potomac River.
AWS has been on the look for SAV growth in the Anacostia River for several years, ine the last couple of years there has been a clear resurgence of SAV, especially near the confluence with the Potomac River where water clarity is better. In the summer of 2015 AWS installed three PVC exclosures to propagate Wild Celery (Vallisneria americana) at Buzzard Point, right by the confluence with the Potomac River. There, the most recent figures from our SAV surveys within our exclosures show significant SAV growth. These exclosures provide a good opportunity to monitor SAV growth. According to the data collected on July 19, 2016, each plot has 100% coverage of SAV within them! The dominant species present is hydrilla, which is present in each plot and accounts for an average of 79% of the total coverage. The second most prominent species is Wild celery, a native species, with an average of about 11% coverage in the three plots. Other species found within the exclosures include Coontail (Ceratophyllum demersum), Water stargrass (Heteranthera dubia), Spiny naiad (Najas minor), Small pondweed (Potamogeton pusillus) and Southern naiad (Najas guadalupensis). That's seven species of SAV growing in them!
Water stargrass (Heteranthera dubia) is a native submerged aquatic plant with showy star-shaped flowers.
Wild Celery (Vallisneria americana) seen from above the water's surface, this native underwater grass was propagated by AWS in the Anacostia River.
Small pondweed (Potamogeton pusillus), another native species, provides habitat for fish, turtles and aquatic insects.
Spiny naiad (Najas minor) is an introduced but non-invasive underwater grass that has naturally dispersed to our SAV exclosures.
Hydrilla (Hydrilla verticillata) is an abundant non-native species in the river's SAV beds. Long hated by boaters because it tangles the outboard motor propellers, new studies show that it is not as bad as we thought it was and it actually provides valuable ecosistem services like habitat for fish and wildlife.
The presence of SAV provides various benefits to the river and the organisms that live in and around it. SAV provides habitat for various aquatic animals, including mussels, snails and fish. Young fish depend on this vegetation to provide food and protection from predators. The increase in waterfowl populations has been linked to the growth of SAV, which provides habitat for the aquatic organisms that birds feed on. Overall, the return of SAV populations in the Anacostia River indicate the increase of river health and allow for the resurgence of various aquatic and semi-aquatic organisms.
Our SAV "cages" or exclosures are working as seed sources for the underwater grasses to further spread and expand up and down the Anacostia River's bed.
*Alisa Fried is a native Baltimorean and a junior at St. Mary’s College of Maryland where she studies Spanish and Environmental Studies.
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