The fragile balance of the most productive ecosystems

07.24.19 -

By Barbara Jewett, NCSA

According to the National Oceanic and Atmospheric Administration’s National Ocean Service, “estuaries are among the most productive ecosystems in the world. Many animals rely on estuaries for food, places to breed, and migration stopovers. Estuaries and their surrounding wetlands are bodies of water usually found where rivers meet the sea. Estuaries are home to unique plant and animal communities that have adapted to brackish water—a mixture of fresh water draining from the land and salty seawater.”

But, the service notes, estuaries are delicate ecosystems. Researchers have long been aware of that but it’s becoming apparent to the public as estuaries become polluted, such as the one at the mouth of the Mississippi River and the nation’s largest estuary, Chesapeake Bay.

Blue Waters Graduate Fellow Salme Cook of the University of New Hampshire uses ocean models and applies them to shallow coastal environments including estuaries. She is focused on two particular estuaries in New Hampshire that are experiencing water quality degradation.

“There's a lot of reasons for that,” she says. “But one of the areas of research I’m looking at is nutrient release from sediments. When you have an excess amount of nutrients, then you start having problems. We'll get events like algae blooms. What happens with algae is that they take up all these extra nutrients, their population rapidly increases and clouds the water, which blocks sunlight to vegetation that's underneath. And vegetation in estuaries is really, really important. They actually lead to water clarity by slowing water flow which then allows sediment to “fall out” of the water column. They also provide important habitat for juvenile fish populations. But what happens is the algae then die pretty quickly, taking all the oxygen out of the water which leads to other events like fish kills, which are really big issues in areas like Florida and the foot of the Mississippi River.”

People do not think that the fertilizers they spread on their lawns runoff into local watersheds and eventually make their way to estuaries, says Cook, but they do.

She notes that cohesive or fine sediment containing high levels of pollutants are responsible for decreased water clarity and quality on coastlines throughout the world. Environmental managers and scientists that guide legislative policies and conservation efforts are increasingly relying on computer simulations like hers that take into account the hydrodynamics, sediment transport, and associated biogeochemical fluxes, she says.

But these models have limitations, most notably, she points out, access to “computational resources to resolve these processes at the necessary temporal and spatial scales, and availability of observational data to verify model results.” Cook has been using the National Center for Supercomputing Applications’ Blue Waters supercomputer at the University of Illinois at Urbana-Champaign to understand the importance of wind-wave induced sediment transport in driving nutrient fluxes in cohesive sediment environments using a coupled hydrodynamic-sediment transport model.

“The modeling really tells us about this parameter called shear stress, which you can't really measure directly. So we take models and we estimate what the water is doing to the sediment during different stages of a tide or what the waves are doing to the sediment. We estimate shear stress based on theory. And that's what we're really interested in. People are very interested in shear stress and shallow environments, but it's very difficult to model because the ocean models are really meant for larger-scale regional applications. So when you start bringing them into shallow water, they break down a bit, they act funky. So you need to get high resolution, and you need really good maps of the bottom topography.”

Cook points out that researchers have never really modeled and observed shear stress in the New England area, and applied them in this way. And definitely not to the degree she is, of looking at sediment resuspension across an entire estuary.

“And what we're working on now is incorporating waves and that hasn't been done before,” she says. “Blue Waters has been great because it's allowed us to get all of these steps up until waves. And that's the part of the research that I wasn't expecting to do during my Ph.D., but Blue Waters accelerated some of the work that I've done. So now we're working on this new stuff.”

Ecosystem balance led to career balance

Cook says she went into research because “I really love applied research.” With a background in engineering, she’s used to solving problems by building things for a specific application. But working on her Ph.D. “really allowed some of this fundamental scientific foundation for me to really sort of couple the two together.” For example, she says she and her colleagues published a paper earlier this year about a model they had validated. The output from that model went to a local oyster restoration researcher, who used it in their restoration efforts.

“Across the eastern seaboard, we've lost 90 percent of our oyster populations, partly due to disease, but partly because the water quality has really impacted their life cycle,” she explains. “In the Great Bay in New Hampshire, we've had a really huge die-off of oysters. Oysters are really important because they filter large amounts of water and they actually remove nutrients from the water column as well. In Great Bay we have… a researcher [with] his own oyster farm, but he's also looking to pick out areas in the Great Bay to do oyster restoration efforts. It's really important when building an oyster reef to have low sediment in the water column because too much sediment can fill their gills and they can't proliferate and live and thrive. So he picked out a couple of areas, sent me those locations, and I picked them out of the model, sent him data and then he’s using it to plan some of his oyster restoration efforts.”

Cook says it is always been her career goal to do applied research or have her work be applied to solve problems for societal benefit.

“There is this tug between fundamental and applied [research] and you know, if you're doing too applied or if you're too fundamental, and so it's tough to find a good balance. But I think this project has been a really good balance.”

About NCSA

The National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign provides supercomputing and advanced digital resources for the nation's science enterprise. At NCSA, University of Illinois faculty, staff, students, and collaborators from around the globe use advanced digital resources to address research grand challenges for the benefit of science and society. NCSA has been advancing one third of the Fortune 50® for more than 30 years by bringing industry, researchers, and students together to solve grand challenges at rapid speed and scale.

National Science Foundation

Blue Waters is supported by the National Science Foundation through awards OCI-0725070 and ACI-1238993.