In evaluating the options available to remove nitrogen from the Cape’s estuaries, there are both mechanical and biological solutions to look at as well as “social” actions to reduce inflows. Mechanical solutions would involve sewers and a centralized sewage treatment plant or a complete rethinking of the state’s current state of the art in cesspool specifications, Title 5 systems, and replacement with a local, personalized nitrogen remediation system, composting toilets, and other emerging technologies. Social actions would cover actions such as the regulation of fertilizers.
Biological mitigation is interesting and has a nice “organic” ring to it. The science has been studied for years on the Cape at the Marine Biology Laboratories (MBL) in Woods Hole and at the Waquoit National Estuarine Research Reserve. This would encompass the use of shellfish to filter and process nitrogen and other pollutants, as well as the introduction of seaweed aquaculture. The Cape Cod Times of April 19 reports on the potential of an Asian species of seaweed — gracilaria — to capture nitrogen. Scientists at the MBL are studying the ability of gracilaria to process nitrogen in a study at Waquoit. [Link is to the Cape Cod Times which is pay-walled].
The town of Mashpee studied the ability of oysters to remove nitrogen in 2008. The shellfish constable reported on the effort which took place in the Mashpee River, once regarded as one of the finest sea-trout fisheries in the world and a fishing destination in the mid-19th century by the likes of Daniel Webster. The good news is that clams are good nitrogen-eaters. The bad news is they only make a dent in the problem:
“The 2008 harvest of 520,000 oysters removed about 260 kilograms of nitrogen from the estuary based on analysis of oysters sampled from the river (0.5 g N/oyster). This was about 4% of the 6563 kg of nitrogen reduction needed to meet the Total Maximum Daily Load (TMDL) for nitrogen in the river required by the Massachusetts Department of Environmental Protection (MA DEP 2006, Report #96-TMDL-4). New oyster seed is purchased every year with the goal of harvesting a million oysters a year removing 500 kg of nitrogen. This would be about 8% of the reduction needed to meet the TMDL for nitrogen.”
The Mashpee trial report is here.
(Side note — the Total Maximum Daily Load is the holy number at the center of the discussion. The Conservation Law Foundation sued the Environmental Protection Agency for not setting and enforcing the TMDL standards as set out by the Clean Water Act.)
The use of seaweed to mitigate nitrogen is a news to me. My only reservation is the potential for an invasive species issue such as the one the Cape is suffering from codium, the thick, rubbery seaweed nick-named “deadman’s fingers” and “oyster thief.” That stuff invaded New England in the 1950s from Europe and is now regarded as a pestilence. According to the Cape Cod Times, gracilaria has proven itself in a trial on the Bronx River in New York State, “If the Waquoit plants do as well as their New York cousins, they’ll remove two to four times as much nitrogen from the water as do oysters, another highly touted bionutrient extractor, the fancy term for the process.”
And as an added benefit, the seaweed has commercial value and could become a cash crop.