Potential Restoration of Bivalves in the Lower Charles Basin
Can adding native bivalves to the Charles River ecosystem improve the water quality?
Prior to the building of the dam at Science Park in 1910, the lower Charles River Basin was a tidal estuary with an abundant population of saltwater bivalves. The abundance of these bivalves is evident in a 1902 photograph of the Cambridge Embankment and mud flats showing people clamming along the seawall. Today, the river is a very different environment, no longer tidal, largely freshwater although some saltwater comes in through the locks. In the ensuing years, the river has experienced decades of pollution followed by environmental remediation. While the water quality continues to improve, the biggest threats today are remaining sources of e. Coli bacteria contamination, elevated levels of phosphorus and nitrogen from runoff, and annual blooms of cyanobacteria (blue-green algae).
Altering the environment of the Lower Charles Basin from a tidal estuary to a nominal freshwater lake led to a sharp decline in the bivalves typically found in saltwater estuaries. However, freshwater bivalves have likely been present in the upper Charles River as well as many of the tributaries leading to the main stem of the river for centuries. While these bivalves may have established colonies in the main stem of the river and the Lower Charles Basin, increased levels of pollution in the 20th century undoubtedly killed them off. Now that the river is cleaner, is it possible to reintroduce native bivalves to the river and can such a reintroduction lead to improvements in water quality?
There have been many studies that indicate that bivalves are efficient filter feeders, each one processing as much as 10-20 gallons a day. The bivalves improve the water quality by (1) controlling the algae population, (2) reducing turbidity, enhancing sunlight penetration which can promote beneficial aquatic vegetation and habitat, (3) reducing nitrogen in the water, and (4) reducing carbon dioxide levels in the water by fixating the carbon in their shells. We are not alone in thinking that bivalves may be a solution to water quality in our river. The city of Philadelphia is spending more than $8M to build a mussel hatchery and re-establish a vibrant population of bivalves to improve the water quality of the Delaware River.
While our project is still in the embryonic stage, working with Carolina Bastidas of MIT Sea Grant, we have done some field survey work to find bivalves that may already be living in the river. The good news is that there are bivalves in the river. There are native fingernail clams and invasive Asian clams in many places along the main stem of the river. Both of these species are small, less than an inch in diameter. We've also observed some 4-6 inch mussels, although we're still working to identify the specific species.
Looking forward, at some point, we'll need to apply for a research permit which would include a well-defined proposal that would identify the specific bivalve species that we would intend to introduce, the specific location that we would plant the bivalves, and proposed metrics and testing to monitor any changes in the water quality. The permitting process is likely to take 6-12 months if successful. In parallel, we need to be looking for sources of funding to support the project, especially potential sources outside of CRAB.
