What’s to Blame for Decreased Productivity in Narragansett Bay?

Climate Change or Clean Water?

In the talks at the 2017 Ronald C. Baird Sea Grant Science Symposium, two causes vied for recognition as the primary driver of changes to sea life—reductions in effluent discharges from wastewater treatment plants and climate change.

John King, University of Rhode Island geological oceanographer and climate change expert, was tasked with answering, how much of this change is climate change?

“I was instructed that I was supposed to be ‘hopeful’ in my approach to this,” King said early on in his remarks. “As many of you know, when I give talks on this, usually people leave the talks feeling like they’ve lived at Chernobyl for a number of years after it blew up.”

King went on to show a range of climate scenarios based on whether emissions remain at present levels, are curtailed, or increase, as indicated on his slide in gray.

“Here’s me being hopeful,” he said, “I hope like [heck] we don’t end up in the gray area because if we do, we’re … just rearranging some deck chairs here today. If we end up in that area, it’s ALL about climate change,” which, he said, would “obliterate other signals.”

Right now, he said, climate change and nutrient inputs “are both pretty important.”

Other speakers pointed out that warming waters in recent years have contributed to increasing numbers of demersal species in the water column that eat phytoplankton from the winter-spring phytoplankton bloom before those nutrients have a chance to fall to the seafloor and feed bottom-dwelling species.

King said that in sediment core samples taken from the Narrow River, the presence and abundance of certain bacteria demonstrate that warming waters do foster more growth than cooler waters.

Slices of those sediment cores from the Medieval Warm Period, for instance, showed more primary productivity than those from the subsequent Little Ice Age that spanned the early 14th century to the mid-19th century. And, King said, “When you have a warm climate and a little bit of fertilizer added to the system, that’s when the productivity seems to take off the most.”

He warned, however, against viewing climate change temperature increases as having linear effects— thinking, for instance, that if two degrees of warming has one impact, that four degrees of warming will simply have twice that impact.

“There are thresholds in the climate system,” he said, “and if you exceed the thresholds, big changes can happen with relatively small changes [in temperature].”

He pointed out that nutrient reductions would not have a linear effect either, as nutrients already present in the seafloor do cycle back into the system, so the impacts of further reducing effluent inputs to the bay would not be immediately obvious. Sediment cores, however, serve as a predictive tool as well as provide historic insight—continuing to monitor them as temperature and nutrient conditions change, and comparing those changes to known circumstances going back hundreds of years, can help scientists and resources managers predict ecological changes in the bay.

As for making management decisions based on these data, he said, there is no straightforward answer. While environmentalists might seek to return to a more “pristine” system, those conditions might be “less desirable to fishermen.”

Still to be determined, he said, is “What do we want the bay to be?”

 

Testing the Future

Returning to an Eden of pristine water and optimal fish production is not a realistic expectation for what can be achieved in Narragansett Bay, warned Wally Fulweiler, associate professor of biology at Boston University, at the Baird Sea Grant Science Symposium.

Fulweiler, who has been studying nutrients and seafloor sediment in the bay for over a decade, was, however, optimistic about what researchers and stakeholders could learn about bay processes to make the best decisions possible.

“I think we have a chance to be one of the first estuaries in the nation to … work together to quantify the impacts of climate change and decreased nutrient loading, two major human interventions.”

Like King, Fulweiler stated that as nutrients from wastewater discharges decrease, the seafloor, or benthos, would be increasingly important as a source of nutrients that would feed both benthic species and be cycled into the water column to serve as food there. This happens in a process known as nitrogen fixation, in which bacteria— in this case in the benthos—metabolize nitrogen gas, deposited from the atmosphere or elsewhere, into biologically usable forms, such as ammonium.

In addition, she said, nutrient-rich deep water comes into the bay from Rhode Island Sound; determining which source is more important will require study. She also emphasized the value of continuing the long-standing monitoring of bay conditions.

“Without this, we could not have this workshop today to talk about changes or predict what’s going to happen in the future,” she said. Fulweiler called for a return to the use of mesocosms, tanks at the URI Graduate School of Oceanography that were used to replicate bay ecosystems and determine how they would respond to varying conditions.

With these mesocosms, she said, scientists could begin to “test the future”—for instance, to see “what happens when you add nutrients or change temperature.” King later added his support for use of the tanks to help make decisions regarding future interventions. “You can’t really start just messing with what the wastewater treatment plants are doing without understanding how the system works,” he said. “You screw up something in the tank, you drain it and you try again. You trigger some sort of a threshold effect in the bay that is … unintended … that would really be significant.”

Christopher Kincaid, URI professor of oceanography, commented that computer models can capture events that can’t be replicated in the tanks. Fulweiler said that information from experiments in the tanks can feed into the models and that the two “should work together” to provide a clearer picture of bay changes.

Fulweiler also emphasized the importance of the observations of the fishermen, aquaculturists, and others in the audience as providing crucial “eyes on the bay.”

“You can provide information that we don’t get,” she said, “You have an intimate knowledge of the bay that we don’t have. As harmful algal blooms occur, new activities such as kelp farming emerge, and species changes take place in the bay.” She added that “citizen science” will become even more important to observing and understanding Narragansett Bay.

– Monica Allard-Cox | Rhode Island Sea Grant

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. 

 

 

 

 

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