Connecting the Dots

The effects of excessive nitrogen loading on Long Island’s coastal ecosystems

Christopher J. Gobler, Ph.D., Professor, Stony Brook University, School of Marine and Atmospheric Sciences, Stony Brook, NY 11794-5000

Long Island is crowded. With 1.5 million people packed into Suffolk County, there are only a handful of nations in the world that are more densely populated. Unfortunately, most of these people dwell in homes without a modern waste disposal system (e.g. sewers) and thus the nitrogenous waste from more than one million Suffolk residences is leaching out of septic tanks and cesspools and into the groundwater beneath our feet. This unplanned experiment is proceeding quickly, as the recently released Suffolk County Comprehensive Water Resources Management Plan reported rapid and large changes (40 and 200% increase) in the levels of nitrogen in Suffolk County’s groundwater between 1987 and 2005, with measurements in 2013 showing the same rate of change and models indicated these levels will continue to rise for several decades. Nitrogen rich groundwater continually seeps from land into our bays, harbors, and estuaries where it is exacting an unwanted toll. Salt marshes are the marine habitats closest to land, serve as an important habitat for a variety of animals and, as we learned from Hurricane Sandy, serve as a critical first line of defense against coastal storm surge and waves.

Unfortunately, excessive nitrogen loading has contributed to the loss of up to 80% of Long Island’s coastal salt marshes since the 1970s. Excessive nitrogen seepage is also stimulating the growth of multiple strains of harmful and toxic algae such as brown tides, red tides, green tides, rust tides, which were unknown to Long Island three decades ago, but recur annually today. These algae are having a cascading negative impacts on our coastal ecosystems and in some cases can be a human health threat. Eelgrass meadows are critical benthic habitats that sustain our most important shellfish and finfish but are highly sensitive to nitrogen and shading by algae.

As nitrogen levels in groundwater have increased, 90% of Long Island’s eelgrass has vanished and Suffolk County has recently predicted these grasses will be extinct on Long Island in two decades if current nitrogen loading trends continue. Algal blooms stimulated by excessive nitrogen loading can also starve coastal waters of oxygen and make them more acidic, two conditions that are also detrimental to fish and shellfish. For all of these reasons, Long Island fisheries have been on the ropes. In the 1970s, the bay scallop fishery on eastern Long Island and the hard clam fishery on the south shore were the two largest fisheries for these mollusks on the US east coast. Since that time, landings of hard clams and bay scallops on Long Island have diminished more than 90% due to a combination of the woes brought about by excessive wastewater nitrogen outlined above: Algal blooms, seagrass loss, low oxygen, and lower pH. In the end, these trends could directly affect every Long Islander as billions of dollars of our economy are wrapped up in fisheries and tourism and home values have been shown to trend with coastal water quality.