Posted on March 10, 2025 in Environmental Sciences Initiative
Georgie Humphries is a fourth-year Ph.D. candidate in the Earth and Environmental Sciences program at the CUNY Graduate Center, based at the Environmental Sciences Initiative at the CUNY ASRC, and affiliated with the Queens College School of Earth and Environmental Sciences (SEES). Before joining the CUNY ASRC as a master’s student, she earned her bachelor’s degree in Environmental Science from SUNY Purchase, with a minor in biology and a concentration in policy. While completing her undergraduate degree, she moved back to the Independent Republic of Cyprus, where she worked with the Cyprus Sustainable Tourism Initiative researching plastic and microplastic waste. This experience inspired her to investigate the effects of urbanization on bodies of water, particularly its impact on ecological relationships between microbes.
Under the mentorship of Dianne Greenfield, an associate professor of Biological Oceanography at the CUNY ASRC and SEES, Humphries studies the associations between phytoplankton and bacteria as they relate to ecological stressors such as nutrient enrichment, hypoxia, and harmful algal blooms. These blooms present not only serious environmental concerns, but economic and health concerns as well— some algal species can produce toxins that can cause ecosystem impacts, accumulating in shellfish and leading to shellfish poisoning. Bacteria then decompose decaying blooms, which reduces oxygen levels in the water, contributing to hypoxia.
“Though microscopic, both phytoplankton and bacteria are critical for cycling nitrogen and carbon. More research is showing that their interactions are important for the ecological and biogeochemical functions of estuaries, but research on these associations in urban estuaries is sparse,” Humphries explains.
Last year, she published her first dissertation chapter in Aquatic Microbial Ecology, characterizing the abundance and taxonomic groups of phytoplankton and bacteria in the Western Long Island Sound, a body of water heavily impacted by urbanization and wastewater runoff. Her findings revealed that dinoflagellates—an algal taxonomic group of concern due to some species’ ability to produce biotoxins—were positively associated with bacterial abundances throughout the study area. She also observed that closer to shore, where wastewater is input directly, both phytoplankton and bacteria were more prevalent. Additionally, levels of dissolved organic matter, a primary food source for microbes, were higher along the shoreline.
“We found that most of the algal species in this area are dinoflagellates as opposed to other types of phytoplankton, and many dinoflagellates produce toxins that, in addition to ecosystem effects, can cause humans to become quite sick through shellfish poisoning,” said Greenfield. “Clams, mussels, and oysters are really important to local fisheries, so this research is critical for addressing both public health and economic concerns.”
Humphries’ research involves collecting water samples using various methods, from paddleboards to boats, followed by biogeochemical and microbial analysis. She identifies taxonomic groups of bacteria and algae through metabarcoding and microscopic visualization using epifluorescent and light microscopy. Currently, Humphries is expanding her research to examine microbial associations in other urban estuaries that differ in physical and geographic characteristics. She aims to determine whether specific urban stressors drive similar microbial interactions across locations or if phytoplankton-bacterial associations are unique to local conditions.
“We still don’t know if these associations are specific to certain New York urban estuaries like Western Long Island Sound, or if they are seen more broadly across other estuaries facing wastewater inputs, like Flanders Bay, which I’m exploring now,” said Humphries. “By studying these associations, we can better understand if wastewater is the primary driver of the significant increases in microbial communities that we’re seeing in urban estuaries.”
Beyond her primary research, Humphries has received multiple fellowships and was recently featured in Nautilus. She is also conducting research on nature-based solutions for coastal resiliency at the CUNY Science and Resiliency Institute at Jamaica Bay, where she now serves as a research assistant. This project is funded by a U.S. Coastal Research Project Award under Brett Branco, an associate professor of Earth and Environmental Sciences at Brooklyn College.
Through her research, Humphries helps illuminate the complex relationships between urbanization, microbial communities, and water quality, advancing our understanding of how the built environment influences coastal ecosystems.