Professor recognized for research on environmental impact of large cities

APRIL 6, 2021 — Cities can have a negative impact on the environment far beyond their infrastructure, specifically on surrounding rivers and streams. That was one of the key conclusions in a study conducted by a group of 10 environmental scientists, including Matthew Troia, assistant professor of environmental science at UTSA.

Their findings were submitted in the paper, “U.S. cities can manage national hydrology and biodiversity using local infrastructure policy,” published in the Proceedings of the National Academy of Sciences of the United States of America.

Their research was recognized by the Ecological Society of America (ESA), who awarded Troia and his fellow authors the 2021 Sustainability Science Award. According to the ESA, the research team demonstrated a novel approach to integrating ecosystem and social sciences, embodying the mission of ESA’s Sustainability Science Award.

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“Biodiversity has important intrinsic value. If we lose some fish species to extinction, we can’t get them back.”

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An alarming discovery from their research is that cities across United States have significantly altered at least 7% of streams, which influence habitats for over 60% of North America’s fish, mussel and crayfish species. Additionally, city infrastructures have contributed to local extinctions in 260 species and currently influence 970 indigenous species, 27% of which are in jeopardy.

“The primary finding is that the energy requirements from cities are impacting freshwater biodiversity,” Troia said. “With cities expanding outward, we’re changing the land use. Every bit of the landscape is by definition part of a watershed, so rain falling on the landscape is going to end up in a stream or river and runoff from the city is going to impact streams, rivers and the species living in them.”

One city found to have a broader impact on biodiversity is Atlanta. That city’s infrastructure impact extended across four major river basins covering 12,500 stream kilometers. The report identified more than 100 local aquatic species now extinct. In contrast, the research team found Las Vegas, a city with a similar size to Atlanta, impacts less than 1,000 stream kilometers, leading to only seven local extinctions.

“The southeastern United States is what we call a freshwater biodiversity hot spot,” Troia explained. “There’s a lot of fresh water species that have been extirpated and it’s likely the consequence of urban development and construction of dams.”

In addition to its biodiversity impact findings, Troia and team received the Science Sustainability Award for highlighting ways policy makers can make better choices about land use, water management, and electricity production. The group promotes integrated planning and decision-making for greater sustainability of cities, along with the water and energy sheds that support them.

“Where state, federal, or global regulations have failed to ensure future water sustainability, cities provide alternative platforms to make the necessary changes, including implementing local regulations and energy taxes, incentivizing renewable investments, and coordinating policies among cities and utilities,” the paper cited.

To accomplish this, Troia and his research partners suggest cities attain water sustainability by adopting strategies to minimize reliance on infrastructures such as dams that impose significant hydrologic alterations to rivers and properly managing storm flows.

“Biodiversity has important intrinsic value. If we lose some fish species to extinction, we can’t get them back,” Troia said. “Every species to some extent plays an important role in the ecosystem, whether its role is a predator or as a prey item for larger fish and animals. Losing biodiversity can have impacts on the ecosystem and humans rely on the ecosystem for clean water, nutrient cycling, carbon sequestration, and other services.”

The lessons from Troia’s research have implications in Texas. With most cities in the Lone Star State growing, particularly along the I-35 corridor, we could experience biodiversity issues similar to what’s taking place in the Southeast, if urban sprawl is not managed correctly.

“My job as an ecology professor at UTSA is to teach the next generation on how losing biodiversity is going to have negative impacts on humanity,” Troia said. “If we see spring-associated fish or salamanders in Central Texas starting to decline, that might be an indicator we’re using too much water or we’re altering the quality of the water. Both are really going to affect people because we really rely on water, particularly in semi-arid places like Texas.”

This is where Troia and his team feel there’s an opportunity for city leaders to step up their strategic planning for water sustainability. They conclude this will require large-scale, transformative, and likely, expensive solutions. Innovative policy considerations are also necessary, such as creating new basin treaties merging city governance with external institutions managing water infrastructure.

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Troia took part in this research project with the Environmental Sciences Division of Oak Ridge National Laboratory in Tennessee. In the spring 2021 semester at UTSA, he’s teaching ichthyology and continuing his research on freshwater biodiversity.

— Bruce Forey

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