Ross earns NSF CAREER award to study fresh, saltwater mixing in estuaries

Grant and Award Announcement

UNIVERSITY OF MAINE

The way fresh and seawater mix in an estuary influences its water circulation, physics and quality, which affect ecosystems and aquaculture. Scientists understand the dynamics of the process in estuaries with simple topographies, but Lauren Ross seeks to better understand them in more complex ones, like the Penobscot River Estuary in eastern Maine. 

The National Science Foundation awarded Ross, an assistant professor of hydraulics and water resources engineering at the University of Maine, a more than $600,000 CAREER Award to improve scientists’ understanding of how estuary shape, river discharge and tides influence fresh and saltwater mixing. The award is the organization’s most prestigious for early career faculty.

Salt water from the sea blends with fresh water from rivers at the mouths of estuaries, which forms a brackish water that flows back into the sea. Ross says the extent of the mixing process can influence how long particles, such as contaminants, excess nutrients and larvae, remain in an estuary, as well whether it experiences hypoxia — or low oxygen levels. Tides can increase the amount of mixing, further affecting the movement of waterborne materials.  

Previous studies into the dynamics of fresh and saltwater blending focus primarily on partially-mixed estuaries, meaning they experience moderate freshwater inflow from rivers, and estuaries with basic dimensions, Ross says. As a result, current research provides less insight into estuaries with complicated topographies like irregular and fluctuating depth and width, headlands and constructions, and estuaries that have relatively large or small freshwater inputs from rivers, all of which can create more or less mixing.

Ross, therefore, will use on-site data and numerical model simulations to quantify the mixing processes in more complex estuaries from across the world. Her research will encompass the Penobscot River Estuary, which experiences moderate river input and tides; the Reloncavi Fjord in the Chilean Patagonia, which has large river input and small tides, and the Gironde Estuary in southwest France, which has large river input and tides. Exploring a variety of estuaries can provide insight into how tides, freshwater input and topography affect the mixing process.

“The interface and exchange of ocean and river water in estuaries greatly influences the hydrodynamics, circulation patterns and transport of material, but we don’t yet fully understand the exchange process,” she says. “I aim to better understand this process and in turn use it to help negotiate and implement pollution and seafood management strategies in estuaries in complicated topographic settings, partly by refining approaches for determining timescales for transport of water borne materials like pollutants, larvae, and harmful algal blooms.” 

Ross has dedicated much of her scientific career toward investigating the physics of estuaries, particularly its flow and the mechanisms that influence it. 

Her recently published research includes quantifying the dynamics of the Jordan River in Down East Maine to understand how they affect particle movement, and creating a framework for reviewing tidal turbine placement in estuaries. Ross also is working on developing a tool to predict how biotoxins from algal blooms travel through estuarine and coastal waters. She has conducted previous studies in the Penobscot River Estuary, Reloncavi Fjord and Gironde Estuary, and plans to use data from them for her CAREER Award project. 

Ross has already created models for the three estuaries, which will produce simulations for her and two graduate students to analyze for their results. 

The ones for the Reloncavi Fjord and Penobscot River Estuary, however, need validation using on-site data. 

One graduate student will help verify the accuracy of the Penobscot model by tasking high school students from Maine Ocean School in Searsport with collecting data from 12 spots in the estuary continually over the course of the five-year-long project. The other graduate student will use publicly available data for the Reloncavi Fjord to validate their model. 

After completing her study, Ross will create and share lesson plans about her findings for high school math and science classes, which she says should teach students about “the differences among the three estuaries, explain simple tidal and volume conservation theory and introduce data visualization tools.” 

Ross also plans on sharing the findings from her research on the Penobscot River Estuary in a yearly Summer Lecture Series at the UMaine Hutchinson Center in Belfast, Maine starting in 2022.

“Estuarine ecosystems are important to us commercially and recreationally, but they are also very delicate ecosystems,” Ross says. “I believe it is important to educate our community and the next generation of scientists and coastal managers on these vital coastal environments as early as possible.”