Konza Prairie

Pamela Sullivan is relatively new to CEOAS, having joined the faculty in fall of 2019. Her office is still a little spare, with empty walls and boxes needing to be unpacked. But she doesn’t feel a pressing need to hang pictures on the wall.

“All that matters to me with respect to office aesthetics is that I get to see these rhododendrons outside my window. They’re going to be spectacular,” she says, with a laugh.

Sullivan loves plants, but particularly loves how plants and everything else in the Earth’s “critical zone” are connected. The critical zone, she explains, is the slice of Earth that sustains life. The zone extends from the top of the vegetation canopy, whether that means a Pacific Northwest rainforest or a Midwest crop of corn, to the depths of the groundwater.

One thing – the main thing – that connects all the dots in the critical zone is water. Sullivan, an ecohydrologist, has focused much of her research attention on the role of water in influencing critical zone systems and, conversely, examining how groundwater is affected by other elements of the system and by climate change. She asks how groundwater storage and quality is affected by land cover and land use. She asks how changes in groundwater dynamics affect the physical landscape. She asks how and why soil erosion differs from system to system. She works in scales ranging from the pores between soil grains to the entire North American continent. The more work she does, the more she finds that everything is connected.

Because climate change is altering so many of the processes that take place in the critical zone, there has never been a more important time to undertake these holistic studies of ecosystem function. Sullivan says the examples of how climate change is potentially affecting ecohydrology are endless, leading to lists of questions. “What do warming temperatures mean for the solutes that are leaving our soils and going into our streams? What does it mean when we change the amount of evapotranspiration of the forest in these systems? What does it mean if the nutrient cycles in these systems have changed, and what do those changes mean for the soils?” she asks.

A perfect example: for her doctoral research at Florida International University, Sullivan studied tree islands in the Everglades, elevated mounds in the midst of the system’s extensive waterways that serve as critical habitat for all kinds of species needing to keep dry, from trees to birds to panthers. These features are endangered; some areas have lost up to 99% of their tree islands. Using measurements at natural and artificially constructed islands, Sullivan found that the existence of the trees helped build island soils.

“We found that the process of evapotranspiration, in which trees take in water and the excess is evaporated through the leaves and other aerial parts, results in the accumulation of particular ions and nutrients in the groundwater that supports greater accretion of soil, building the islands,” she explains. As the islands grow, the trees also affect the interactions between the islands’ groundwater and the surface water around them. So trees beget larger islands, which beget groundwater changes. Groundwater changes beget more changes in soil chemistry and accretion. The whole system is cyclical.

Before coming to Oregon State, Sullivan was at the University of Kansas, where she studied the region’s iconic tallgrass prairies using the Konza Prairie Long-Term Ecological Research site as a living laboratory. In one study, she and colleagues examined the impacts of the encroachment of woody plants on the chemistry of prairie streams. This invasion occurs relatively rapidly in the prairie without regular burning from forest fires or controlled burns (including by native Americans, who appear to have used fire in this system extensively). The prairie grasses that typify the system have shallow root systems, while the woody plants root deeper, burrowing through the ground and creating flowpaths for groundwater both near the surface and deeper. Sullivan found that these deeper roots encourage greater dissolution of minerals from the surrounding soils, changing the chemistry of the groundwater. The shallow-rooted grasses create more turnover of carbon near the surface of the soil. These distinctions lead to differences in chemical weathering of the soil, with implications for soil formation, water quality and even climate change.

Sullivan is looking forward to diving into Pacific Northwest ecosystems, with plans to initiate studies in the HJ Andrews Experimental Forest and possibly in the volcanic landscapes of central Oregon.

Sullivan’s research has implications for water quality and availability, soil erosion, and other issues that touch significantly and constantly on human lives. Her work can also feed into larger models of global climate change. For example, “When you change where groundwater is stored near the surface, it changes where evapotranspiration takes place. This process can be a driver of climate circulation. So if we don't have this parameter, we might fail to calculate cloud dynamics in our atmosphere correctly. And if we fail to do the cloud dynamics properly, then there are more cascading effects for climate models,” Sullivan explains.

This year, the year of the global coronavirus pandemic, Sullivan might not get to see those rhododendrons outside her office window bloom. But bloom they will, and they will be connected to the soil they are planted in, the rain that falls on them, the groundwater below them and the climate all around. So Sullivan will be connected to those rhodies too, as she continues her research program as best she can from home. After all, as her work demonstrates, everything is connected.

Posted May 12, 2020 by Nancy Steinberg

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