Narragansett Bay was reported last summer to be the cleanest it’s been in the last 150 years, an announcement that was met with acclaim by many but also with consternation by others. The controversy was the focus of a recent symposium at the University of Rhode Island Graduate School of Oceanography.
Improved water clarity may be a boon for swimmers, said Al Eagles of the Rhode Island Lobstermen’s Association, but to fishermen “if the water’s that clear, to me it’s dead.”
“The bay has evolved and it’s changed, but it’s always been productive,” said Michael McGiveney, president of the Rhode Island Shellfisherman’s Association. But after reductions to nutrient discharges to the bay thanks to wastewater treatment improvements, he said, fishermen worry that the loss of nitrogen means that while the water is cleaner, “there’s not enough food for the shellfish to be productive.”
McGiveney was speaking at the 2017 Ronald C. Baird Sea Grant Science Symposium, which focused on ecological changes in Narragansett Bay and their implications.
Nitrogen is a vital food source for phytoplankton, which in turn feed shellfish and other aquatic life. Fishermen on the stakeholder panel at the symposium starkly described declines in their target species – including shellfish, lobster, and crab. They called on symposium participants, as fellow stewards of the bay, to come up with solutions.
“I don’t think Narragansett Bay is dying in any way, but I do think the choices we’ve made have caused some significant changes,” said Robinson Fulweiler, an associate professor at Boston University who has done extensive work examining nitrogen processes in Narragansett Bay. “Some of these choices we’ve actively made and others indirectly through larger scale regional processes.”
The Choices We’ve Made
Nearly 55 percent of total nitrogen discharge entering Narragansett Bay from wastewater treatment facilities has been curbed, surpassing the 50 percent goal set in 2004 by the Governor’s Narragansett Bay and Watershed Planning Commission.
These reductions were aimed at 11 of 19 facilities in the state that are near the most impacted areas – the upper bay, Greenwich Bay, and the Providence and Seekonk Rivers – as well as six facilities in Massachusetts along the Blackstone and Ten Mile Rivers. Separate efforts by the Environmental Protection Agency were undertaken in the Taunton River and Mount Hope Bay.
While some speakers described the August 2003 fish kill in Greenwich Bay as being a catalyst for nutrient reductions, “the [Rhode Island Department of Environmental Management] did not regulate nutrients because of the fish kill,” stressed Angelo Liberti, chief of surface water protection at DEM, who discussed the state’s efforts to reduce pollution in the Bay from wastewater discharge.
In that event, 1 million fish died, primarily menhaden, as well as benthic species (those inhabiting the seafloor), due to severely low oxygen levels.
“Since the early 80s, it’s been documented by the University of Rhode Island, the Narragansett Bay Project, that there were significant portions of the upper bay suffering the effects of excessive nitrogen, excessive algae growth, and low dissolved oxygen,” he said. “There were other fish kills. They weren’t massive fish kills, and there remain fish kills today, but it wasn’t all about [just one] fish kill.”
The event, however, was the first to be noted in the history of Narragansett Bay since 1898, according to Fulweiler. So while not the first incident, it did spark greater public attention to water quality and other habitat issues.
Poor water quality in Narragansett Bay has led to beach and fishing closures, as well as extensive loss of eelgrass – a crucial food and habitat resource for many species. The upper portions of the bay near industrial and urban waterfronts north of Prudence Island and Greenwich Bay are especially impacted.
These differences are attributed to greater concentrations of population in urban areas of the upper bay that equate to more nutrients from stormwater runoff and wastewater discharge, as well as poorer circulation in embayments in these regions.
“The 2003 fish kill in Greenwich Bay [occurred not because] there was simply an excess of nitrogen and productivity [of phytoplankton], but rather there was an unusual circumstance of physical conditions that helped make this happen,” said Fulweiler, referring to a gyre that was discovered in this sub-estuary of Narragansett Bay.
This circulation dynamic traps water flowing in, and any pollutants it contains, for extended periods of time, causing the area to be more vulnerable to nutrient accumulation from wastewater discharge and associated hypoxic (low oxygen) conditions.
“Even though we can dial back the nitrogen, we can still have low oxygen events because of the physics of the systems, as well as any legacy impacts Narragansett Bay is holding onto,” she said, acknowledging the accumulation of nutrients and toxins in the bay’s sediments over the last few hundred years since the Industrial Revolution.
Nitrogen itself is not a toxin and is essential for many things to grow and thrive. However, too much nitrogen in the system has been linked to large algal blooms that block sunlight and increase organic matter resulting in loss of eelgrass, as well as low dissolved oxygen levels due to the decay of phytoplankton that robs the water of oxygen that is crucial for fish and shellfish – ultimately changing the local environment.
These impacts, as various studies indicate, are most acute during the summer months (between May and October) when warmer temperatures, increased precipitation, and nitrogen loads from effluent coalesce to exacerbate these conditions.
“We talk too much about oxygen and not enough about the ecosystem benefits of reducing primary productivity,” said Liberti. “That was the goal. Reduce primary productivity to allow more sunlight to penetrate the seagrass [and grow better habitat] and improve the diversity of aquatic life in the bay.”
The 50 percent nitrogen reduction goal was largely based on the MERL (Marine Ecosystem Research Lab) experiments at the University of Rhode Island’s Graduate School of Oceanography (GSO), added Liberti. These experiments used mesocosms, controlled miniature environments simulating the conditions of the bay, to observe ecological responses to various conditions such as nutrient loading from the effluent.
“They dosed the tanks and measured ecological responses. We looked at those analyses and the cost of implementation and came up with an adaptive management approach to implement this 50 percent reduction,” he said, noting that these reduction regulations are enforced primarily in the warmer months (May to October) – a time in the bay when nitrogen discharge plays an important role in hypoxia.
But it’s more than just nitrogen that’s been decreased, said Candace Oviatt, a professor at the University of Rhode Island’s Graduate School of Oceanography (GSO) specializing in biological oceanography.
“Phosphorus in the bay has been decreased since the 1990s when we started to take phosphate out of detergents,” she said.
Phosphorous, just like nitrogen, is important for plant growth and primary productivity that is essential for life in the bay but is also detrimental in excess. And just like nitrogen, phosphorous also decreased by about an additional 50 percent when the reduction measures were implemented, noted Oviatt.
“It’s even better than that because the [other] wastewater treatment plants in the watershed also introduced treatments to reduce nitrogen. So the total decrease (of both nitrogen and phosphorous) is closer to 60 percent,” she said.
An Artificial Bay
Though great strides have been made in reducing nutrient loads from wastewater treatment facilities, have these reductions been entirely beneficial to the health of the bay?
“You have to remember that the nutrients in the bay are three times higher than historically before the colonists came to Rhode Island,” said Oviatt, pointing out that before the reduction, nutrient levels were four to five times higher.
The bay that we know, said Fulweiler, could be described as an artificial bay because the level of productivity is not entirely natural, but rather is affected by the nutrients from wastewater discharge.
Up until the late 1800s, all waste (agricultural, industrial, residential etc.) was kept to the land until early sewage systems were introduced.
“As soon as we added water to the system, we began taking all of [those waste products] and flushing them into Narragansett Bay,” said Fulweiler, noting that unlike other estuaries, the amount of nutrients entering Narragansett Bay have stayed pretty much the same (prior to the reductions) since the mid-50s and 60s when area population growth leveled off.
Temperature, rain, and wind are also important factors that play a role in the amount and distribution of nutrients entering Narragansett Bay. Though the impacts are not straightforward, Fulweiler and Oviatt believe that the combination of climate conditions and nutrient changes have contributed to the 30 percent decline of primary productivity in the bay.
For example, warmer winters due to increasing temperatures mean more cloudy days, which limit the ability of phytoplankton to grow.
“Phytoplankton are light limited,” explained Fulweiler. “So, if we’re going to amp up the temperature and have more cloudy days, and the phytoplankton are waiting for that light to turn on, and that light turns on later and later, then you have less opportunity for them to bloom.”
This bloom, which is often referred to as the winter-spring bloom, is fostered by conditions that include lots of sunlight and nutrients and lack of predators. This event is important for kickstarting biological activity in the bay. Increasing temperatures may mean more cloudy days, but it also could mean more predators, such as zooplankton that feed on phytoplankton.
Fulweiler suggests that their metabolic rate could be increasing and they could be chewing down that phytoplankton in such a way that would prevent a bloom from occurring. In this way, less organic matter would reach the seafloor in support of the benthic community.
Wind is also a factor. Fulweiler noted that wind has been decreasing in a New England-wide phenomenon, which means less mixing of the water column and lower dissolved oxygen as well as lower levels of nutrients mixing up from the bottom waters to help grow phytoplankton. Additional climate-related factors include precipitation, which has increased nearly inch every year since 1865.
“We’re warming the water, have more precipitation, and have less wind available,” she said. “All of that will change the ecosystem.”
Fulweiler also notes that researchers have been observing a decline in productivity long before nutrient reduction measures were in place. A long-term data set (one of the oldest in the world that was started by the late Ted Smayda, a research professor at GSO) illustrates that since the 1970s there’s been a strong decline in chlorophyll – a marker in primary production from phytoplankton.
“In the upper Providence estuary, there is no doubt it is heavily nitrogen influenced and a lot of productivity, with resulting negative consequences like low oxygen conditions,” said Fulweiler. “Additionally, in the lower, mid-lower parts of the bay, they are almost being fed by that Providence River estuary, and we see that primary productivity was decreasing long before the nutrient mitigation.”
Areas that have shown a decrease in the winter-spring bloom, according to Oviatt, include Conimicut Point at the mouth of Providence River, T Wharf at the south end of Prudence Island, and at the docks at GSO. Greenwich Bay, she said, still maintains a substantial winter-spring bloom that may be attributed to the circulation dynamics of the gyre.
However, the overall trend, she said, “is that we’re going to have a warmer bay and there isn’t going to be a winter-spring bloom whether we have nutrients in the bay or not.”
“The bay is always changing. I’ve never known an average year in Narragansett Bay. Every year is new and different,” said Oviatt. “And whether we like it or not it’s going to keep changing. We just try to keep track of it and tell you what’s going on as well as we can.”
More information about the Baird Symposium, including links to videos of the morning and afternoon sessions and the PowerPoint presentations, is available online. Results will be used to inform the upcoming Rhode Island Sea Grant research request for proposals and the Rhode Island Coastal Resources Management Council’s Narragansett Bay Special Area Management Plan.
The symposium was sponsored by GSO, Rhode Island Sea Grant, the URI Coastal Resources Center, and the van Beuren Charitable Foundation.
– Meredith Haas | Rhode Island Sea Grant Research Communications Specialist