Will Long Island Sound residents make changes to help protect it?

Millions of people live, work and recreate in communities that surround the 1,320-square miles that comprise Long Island Sound. Connecticut and New York have worked for decades to restore water quality and protect the wildlife, habitats, and ecosystem services provided by the Sound.

Yet, water quality monitoring by the Long Island Sound Study, launched as part of the Environmental Protection Agency’s inaugural National Estuary Programs in 1985, shows there is still more to do. Government agencies, universities, community organizations, and environmental groups continue to partner on efforts to conserve the Sound.

For more than seven years, Clark University has been one of those partners, through the research of environmental economist Robert Johnston, director of the George Perkins Marsh Institute, which is affiliated with the School of Climate, Environment, and Society.

Most recently, Johnston has been involved with multiple studies that evaluate how everyday human activities pollute the Sound and how to effectively reduce this pollution. The studies focus on sources of excess nitrogen — a pollutant linked to household sources such as septic systems and lawn fertilizer. An abundance of nitrogen can lead to algae blooms, hypoxia (low oxygen levels), and other changes in the water. Hypoxia can kill fish and other marine life, contribute to “dead zones” in the water, and threaten tourism, recreation, and local economies, among other consequences.

Since 2019, Johnston has been the principal investigator on three federal grants totaling over $1.5 million that aim to reduce two of the largest sources of nitrogen pollution to Long Island Sound: residential lawn fertilization and household septic systems. His research combines large-sample household surveys, high-resolution geospatial information, water-quality and tax assessor data, hydrological modeling, and various statistical models to explain household behavior (such as lawn fertilizer use) and predict the effect of programs that seek to influence those behaviors. These predictions identify the types of policies and programs that are most — and least — effective at reducing nitrogen pollution to the Sound.

Which homeowners will replace aging septic systems — and where?

Johnston’s most recent project, which started in January, will develop a “framework and integrated, spatially-explicit economic-behavioral-hydrological model” to identify effective means to design and target programs that encourage homeowners to replace their aging septic systems with new, more effective wastewater technologies.

“Pollution due to septic systems is a major problem across New England,” he explains, “and traditional systems are not designed to remove nitrogen.”

According to the Long Island Sound Study, “the largest source of nitrogen — about 50 percent — is from human waste, including from discharges of treated sewage in wastewater treatment plants and individual septic tanks from homes.”

“Yet, there’s no systematic, quantitative research that predicts who will choose to upgrade their septic systems in response to the different types of incentives that might be offered,” Johnston says. “Even if a program pays the full monetary cost of upgrading to a nitrogen-removing system, homeowners may still choose not to upgrade due to the inconvenience and desire to avoid construction on their property.”

It’s not only a question of whether homeowners will choose to upgrade their systems, but where.

“In some locations, nitrogen from household septic systems enters Long Island Sound very quickly through rivers and streams,” Johnston explains. “In other locations, it might require decades to slowly reach the Sound through groundwater.”

“Pollution due to septic systems is a major problem across New England, and traditional systems are not designed to remove nitrogen.”

— robert johnston

Predicting effects on Long Island Sound thus requires integrated approaches, he says. “We not only have to predict human behavior — whether and where people might upgrade their septic systems — but how the resulting changes in pollution move through surface and groundwater to the Sound.”

Johnston’s work is part of a two-year, $812,258 grant from the Long Island Sound Study and Connecticut Sea Grant. The project is a collaborative effort with researchers from the University of Connecticut, University of Maryland, and University of Miami.

Encouraging residents to curb lawn fertilizer use

Fertilizer use accounts for about one-third of the nitrogen pollution to Long Island Sound embayments — the bays, harbors, and coves where fresh and saltwater mix. For more than six years, Johnston has worked with marine, environmental, and land-use scientists on the design and targeting of more effective campaigns to reduce the use of household lawn fertilizers.

“For most [nitrogen] sources, we’re moving in a positive direction,” Johnston says. Over 20 years, implementation of the Comprehensive Conservation and Management Plan for Long Island Sound has reduced the annual discharge of nitrogen by 40 million pounds, according to researchers.

“But residential lawn care,” he adds, “is one of the sources of nitrogen that we haven’t yet reduced very well.” Johnston explains, “A key issue here is understanding household behavior — what type of households tend to fertilize the most — and then predicting how those households will respond to different types of policies and programs that aim to reduce their fertilizer use.”

“One of our primary goals is to help target behavior-change campaigns that encourage homeowners to use less fertilizer.”

— robert johnston

Information of this type is necessary to ensure that programs to reduce fertilizer are effective.

“Only about half of households apply lawn fertilizer in the first place,” Johnston says, “and we can identify the types of households that tend to apply most frequently — for example those with newer, larger homes. Policies or programs in areas where fertilizer use is already low will tend to have negligible impact.”

From 2019 to 2022, Johnston studied whether and how often residents fertilize their lawns. Funded by a $370,620 Environmental Protection Agency (EPA)-New York Sea Grant aimed at changing residents’ lawn care practices, Johnston worked with researchers from the City University of New York, University of Maryland, and Florida Atlantic University, integrating surveys of residents and ecological data from their yards.

Pinpointing nitrogen “hot spots”

Now, Johnston is drawing upon that data, along with integrated, high-resolution land-cover data and hydrological models, to predict “how much fertilizer residents are using in different areas and how much of that nitrogen pollution reaches Long Island Sound.” The two-year project, funded by a $405,630 EPA-New York Sea Grant, runs through February 2026.

Johnston and researchers from the University of Connecticut, University of Maryland, and University of Miami are creating an integrated model and associated maps of “nitrogen hot spots” where residential areas use the most nitrogen lawn fertilizer and where that nitrogen is most likely to reach Long Island Sound.

“One of our primary goals is to help target behavior-change campaigns that encourage homeowners to use less fertilizer,” Johnston says. “Where you conduct these campaigns and the type of households you target both have a major impact.”

For instance, he says, many campaigns to decrease fertilizer use target densely populated urban areas, because the density of these areas reduces the cost of reaching each household.

“It’s easy to go door-to-door in an urban area,” explains Johnston. Yet, those campaigns may not have as large an impact on improving the Sound because city residents have smaller lawns and tend to apply fertilizer less frequently.

“The majority of lawn fertilizer is being used in exurban areas,” he adds. Lying beyond the suburbs, exurban areas often include household lots of one to five acres. “Households in these areas tend to apply fertilizer more frequently and apply it to larger lawns.”

Johnston’s research integrates predictive models of household behavior with high-resolution mapping of lawns from 1-meter NOAA Coastal Change Analysis Program land-cover data. Implications for nitrogen pollution entering Long Island Sound are then derived by integrating these fertilizer-use predictions with spatially explicit estimates of nitrogen transport to Long Island Sound, provided by collaborating scientists at the University of Connecticut.

The studies, according to Johnston, “will be used to provide actionable guidance for targeting behavior-change campaigns across the Long Island Sounds watershed.”