Focusing on Water
Water has been a continuous theme in Mary Engels’ life.
Engels was an avid swimmer growing up in Aurora, Oregon, and spent 10 years as a river guide. She has studied coral reefs and spent eight years educating undergraduates about oceanography with the Sea Education Association (SEA).
In 2012, water led her to the University of Idaho to pursue a doctorate in water resources, which she will complete in summer 2019.
Fresh Water Availability
Engels began working with SEA in 2004 after earning a master’s degree in geology and geophysics from the University of Hawaii-Manoa. SEA is a study abroad opportunity that allows undergraduate students the opportunity to spend a semester at sea to learn about marine and maritime environments. Engels served as a shipboard scientist for three years before becoming the science coordinator, based in Woods Hole, Massachusetts, where she facilitated the science program, hired scientists to work on SEA’s two sailing research vessels, and managed the shipboard labs.
“I didn’t have a clear picture of where I was going when I got done with my master’s,” she said. “It was serendipity that I ended up with SEA and got a sideline education in oceanography.”
As she explored the Pacific Ocean and many of the small, remote islands within it, she became intrigued by the issue of fresh water on the islands.
“In the process of sailing around to a lot of these remote places, these tiny remote islands, you come to realize the thing that is going to drive people off those islands is the lack of fresh water,” Engels said. “When you see that first hand, it’s really drives home the importance of water in general.”
From the Pacific to Idaho
After eight years with SEA, Engels knew she needed to get a Ph.D. if she wanted to progress any further in her career. She began looking for water-related programs in the Western United States and discovered the water resources program at U of I.
“When I was thinking about going back to school, I was really interested in the role water plays in different systems, and the water resources program here is an interdisciplinary program, which was super appealing to me — to get the policy, and the law, as well as the hard science perspectives,” she said.
Engels decided to center her doctoral research on the water dynamics of small islands, like those she visited with SEA. Specifically, she compared how coconut trees — which are an invasive species — and native tree species, Pisonia grandis, utilize available fresh water. She focused her work on Palmyra Atoll, a northern line island located south of Hawaii.
“I was interested in trying to understand how vegetation changes are altering water movement through soils on these islands,” Engels said. “Small islands don’t have traditional aquifers. When it rains the fresh water percolates through the islands and sits in the bulk of the island as a unique thin lens. For humans, these lenses are the only source of fresh water between rain events and coconuts are able to tap this water source directly because of their deep roots.”
In contrast, Pisonia grandis is known for its very shallow root system and for building an organic Jemo soil cap, which can get as deep as half a meter. Seabirds roost and nest in the Pisonia grandis trees but not nearly as often in coconut trees. Because of the seabirds roosting in Pisonia grandis trees, the Jemo soils underneath are very nutrient-rich.
“The seabirds are this nutrient vector bringing marine nutrients to the islands and makes it a livable ecosystem,” Engels said. “Most of these islands are nutrient poor, so seabirds are an important component of changing that.”
Engels has discovered that the Jemo soil has very important water management implications for Pisonia grandis. Because the organic soil is so different physically from the coral sand and rubble underneath, a capillary barrier forms at the contact between the organic soil cap and coral sand below. This barrier results in water being retained in the organic soil layer where the shallow roots of Pisonia grandis can access it. Unless the whole system is saturated, this barrier effect prevents water from flowing down through the sand and into the freshwater lens.
“It seems to be its evolutionary niche for this tree,” she said. “It has significant ecosystem consequences because it’s a rich organic soil with high concentration of nutrients, and these nutrients in turn feed other plants and marine organisms on and around the island.”
Native vegetation, including Pisonia grandis, is often cleared to make room for coconut trees, which are one of the only production crops able to grow on small tropical islands. Engels hopes her research will help inform management decisions.
“Coconuts are so important for the humans on these islands that I’m not sure I would tell them not to plant coconuts, but my recommendations would be along the lines of being strategic about where you plant coconuts and if you for some reason are no longer actively farming these coconuts, maybe consider restoration both from the water perspective and the nutrient perspective,” she said.
Engels has accepted an assistant professor position with the U of I College of Natural Resources and will continue to research how these different tree species use water, the physical structure of soil that allows them to use water differently and how that influences water storage on the islands. Engels is also working to develop a method to use freely available imagery from NASA’s Landsat satellites to identify different tree species in these remote locations.
Wherever her research leads her, Engels is most concerned with making a difference.
“I think the thing I’m most interested in having from my career is research that is used, that makes an actual difference in near-real time,” she said.
Article by Amy Calabretta, College of Agricultural and Life Sciences
Published in May 2019