SBU Study Shows Record Number of Harmful Algal Blooms and Dead Zones in Long Island Waters
Scientists at Stony Brook University have completed their assessment of Long Island’s surface water quality, finding a record-setting 36 distinct ‘dead zones’ or regions with less than three milligrams of oxygen per liter during the Summer of 2024.
From June through September, every major bay and estuary across Long Island was afflicted by harmful algal blooms (HABs), oxygen-starved dead zones, and/or fish kills. Excessive delivery of nitrogen from onsite wastewater has been established as a root cause of these disturbing events.
While the study and its findings only apply to Long Island waters, other regions around the country are having the same water quality issue in its fresh and salt waters, such as the many waterways connected to the Chesapeake Bay.
“It has become clear that, absent aggressive change, Long Island should expect the wide-spread occurrence of low oxygen zones and HABs during summer and these events could worsen with climate change,” said Chris Gobler, SUNY distinguished professor and principal investigator of the research in Stony Brook’s School of Marine and Atmospheric Sciences (SoMAS) at a press conference October 22 on the shores of Great South Bay in Patchogue, NY.
The New York State Department of Environmental Conservation (NYSDEC) states that waters suitable for the propagation and survival of fish, shellfish, and wildlife should not have excursions to less than three milligrams of oxygen per liter, as oxygen is required for the survival of all marine life. Consequently, six fish kill events documented across the south shore of Long Island this summer all occurred in locations where dissolved oxygen levels had fallen below far below this threshold.
HABs were widespread in 2024. There were more than two dozen lakes and ponds that experienced outbreaks of blue-green algal (or, cyanobacterial) blooms, a serious concern for both human and animal health. Blue-green algae make toxins that can be harmful to humans and animals and have been linked to dog illnesses and dog deaths across the U.S. and on Long Island.
In all cases, cyanobacteria, which makes gastrointestinal or neurological toxins, were present during the blooms of 2024. The south fork of Long Island was called out for having 17 water bodies with these toxic blooms this summer. For the past eight years, Suffolk County has had more lakes with blue-green algal blooms than any other of the 64 counties in New York State, a distinction that is likely to be repeated in 2024.
Across marine water bodies, more than 25 locations experienced HABs. On the upside, no shellfish beds were closed due to HABs in 2024. On the downside, some of the events of 2024 were more intense and widespread than in the past. For example, world records for blooms were shattered.
The HABs did not stop there. In August, a rust tide began on the east end of Long Island, starting in Shinnecock Bay and ultimately spreading through most of the Peconic Estuary. Rust tide is caused by the alga Cochlodinum (aka Margalefidinium), which is ichthyotoxic, meaning it can kill fish and has been responsible for fish and shellfish kills on Long Island.
According to Gobler, climate change threatens to make all of these events worse in the future. Beyond warmer temperatures intensifying dead zones and prolonging warm-water HABs, such as rust tides and blue-green algal blooms, climate change is bringing more intense rainfall events that deliver high levels of nitrogen, he explained.
This was abundantly clear on August 19, when a record-setting rainfall event delivered more than 10 inches of rain to some parts of Long Island and both HABs and bacterially induced shellfish bed closures followed.
“While some folks referred to the August 19 event as a 1-in-1,000-year event, the truth is that this marks the third time this decade Long Island has experienced 10+ inches of rain in 24 hours and the science shows we should expect more of this in the future. Since these events deliver excess nitrogen to coastal zones, they are a clarion call to double down on nitrogen load reductions to protect coastal ecosystems in the future,” said Gobler.
Despite the gloomy news, there were some signs of hope in the data. For example, in the Long Island Sound, the largest dead zone in the northeastern U.S. has continued to shrink since nitrogen reductions were achieved there.
Over the years, the occurrence of HABs and dead zones has contributed to the collapse of critical marine habitats such as seagrass, major fisheries on Long Island such as bay scallops and hard clams, and coastal wetlands that help protect waterfront communities from the damaging impacts of storms. Excessive nitrogen coming from household sewage that seeps into groundwater and ultimately, into bays, harbors, and estuaries or, in some cases, is directly discharged into surface waters, is a root cause of the maladies of 2024. Excessive nitrogen stimulates algal blooms that can, in turn, remove oxygen from bottom waters as they decay. Suffolk County and Nassau County recently completed ‘subwatershed studies’ this decade that both identified wastewater as the largest source of nitrogen to surface waters and set goals for reducing nitrogen loading from septic systems as a defense against these impairments.
The report on the Summer of 2024 was compiled by the Gobler Laboratory of Stony Brook University that has been monitoring and sampling Long Island’s waters on a weekly basis every summer since 1999. Data was also generated by the New York State Department of Environmental Conservation and the Long Island Sound Study, which is funded by the U.S. Environmental Protection Agency.