Steve Pacella

Steve Pacella loves the ocean and everything in it. But a trio of grey whales was making him very, very nervous.

The whales were feeding in Puget Sound close to where he had deployed some fairly sensitive and expensive instruments to measure water quality for his research with the U.S. Environmental Protection Agency’s Office of Research and Development in Newport, Oregon. The instrument package, one of several sitting on the bay’s bottom, was crucial to learning about nutrient loading and its connection to ocean acidification in the estuary. He hadn’t lost one of these benthic instrument packages yet, but the whales were big and the instruments were small. He watched in trepidation as the whales churned up the mud.

“I never knew this, but gray whales like to eat burrowing shrimp. And there are shrimp beds near one of our deployment sites. One swipe of the tail …” Pacella muses.

Luckily, the whales finished their meal and the instruments were left intact. Pacella breathed a sigh of relief. The instruments would continue collecting water quality data, and Pacella’s project would march ahead, unhindered by the whales. That’s a good thing, because this groundbreaking research is providing new insights into how estuaries are impacted by global climate change.


The Puget Sound study was one of a series of projects that Pacella (Ph.D. 2018) has been working on with partners at EPA and the College of Earth, Ocean, and Atmospheric Sciences for a decade, starting as an EPA intern fresh out of college. The team has been exploring whether and how nutrient loading – excess nitrogen, phosphorus and other elements coming mostly from human activities – in estuaries affects ocean acidification, a consequence of global climate change that has been garnering scientific and public attention, but hasn’t been examined much in shallow estuarine settings. Estuaries, where fresh water from rivers meets the ocean, are crucial habitats for the young of many commercially important species of fish and shellfish and serve many other functions that sustain human communities.

Pacella first came to EPA in 2008 as a contractor, having earned an undergraduate degree from Boston University. The serendipitous job opening on the other side of the country began an association with EPA that took him through two graduate degrees at Oregon State and ultimately to a highly rewarding job with the agency.

His initial work at EPA involved ecosystem modeling using a technique called inverse analysis, which allows characterization of an ecosystem where only patchy or highly variable data are available. This work snowballed into a master’s degree in environmental science under the mentorship of EPA-Newport’s Ted DeWitt.

When that project wrapped up, Pacella again found himself looking for the next step. He was accepted to CEOAS, and with the help of his old friends at EPA, he found the perfect opportunity in the form of EPA’s Student Career Experience Program. SCEP funds scientists to work part-time with the agency while they simultaneously pursue a degree. Pacella worked with his advisor, CEOAS Associate Professor George Waldbusser, and CEOAS’s Burke Hales and EPA’s Cheryl Brown on a project to examine connections between human-caused nutrient pollution and OA in estuarine seagrass meadows in Puget Sound.

Estuaries are notoriously variable places for many reasons. For one thing, aquatic plants respire and photosynthesize in the light of day, consuming carbon dioxide, and only respire at night, producing carbon dioxide like we do when we exhale. Because high CO2 leads to low pH, an indication of increased acidity, estuarine pH naturally declines at night and climbs during the day. This variation led to the conventional wisdom that estuaries are far less sensitive to ocean acidification than the open ocean – the thought was that estuarine variability would probably swamp any signal of additional acidification resulting from human activities.

But Pacella and colleagues realized that another factor was at play in estuaries: nutrient loading, which fuels plant productivity. When those plants, whether microscopic phytoplankton or seagrasses, die off, decomposition results in increased CO2 in the water, and more CO2 means a more acidic environment. And of course, estuaries are already being acidified, like the rest of the marine environment, by excess CO2 in the atmosphere from global carbon emissions.

By taking extensive water quality samples in the Sound and carrying out some unique modeling, Pacella and his colleagues helped to upend the conventional wisdom about OA in estuaries. They found that estuaries may actually be more susceptible than the open ocean to ocean acidification, as human sources of CO2 lower the ecosystem’s ability to absorb natural fluctuations of the greenhouse gas.

“The interaction between the global CO2 ocean acidification signal and the natural variability from the biology of the system amplifies the low pH at night. The nighttime lows are getting lower because the whole effect is worse than the sum of the parts,” he explains. “So actually estuaries may be more vulnerable to OA than the open ocean.”

This work could have important management implications. “If we can parse out the natural and human components of low-pH events, we can start to understand which management levers might be more or less effective,” he says.

After finishing his Ph.D., it was time for another transition for Pacella. Although he had other options, he chose to stay at EPA in Newport, where he is continuing his work on ocean acidification in estuaries, now focused in Tillamook Bay. (Here, the whales leave his equipment alone; instead he battles barnacles and other encrusting organisms that grow on the instruments.) He would also like to broaden what he’s learned in Washington and Oregon to other U.S. estuaries. “I think we have a great opportunity to take these lessons learned about the factors that control OA vulnerability in estuaries and ask, what other systems seem to have those characteristics? Which systems do we think will be more or less vulnerable?”

Pacella speaks glowingly about the education and support he received from CEOAS throughout his graduate career. “CEOAS was an awesome program for me,” he says. “I was blown away by the caliber and diversity of the science. I felt like I came out of the program with an understanding of the Earth system not just from an oceanographic perspective, but geologically, atmospherically. I appreciated the holistic approach.”

Pacella reflects on his decade of work with EPA with satisfaction and pride. “I love being able to do fundamental science that is guided by the agency’s mission,” he says. “It makes me think about the bigger picture and how this work might actually be used at the local or federal level.”

“Ultimately we’re trying to come up with a good scientific foundation on which to base hard decisions for a lot of people,” he continues. “And I like being able to contribute to that.”

By Nancy Steinberg
Posted October 28, 2019

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