What’s Going On in Our Water

This June we were appalled to read about fish kills in the Peconic Estuary, turtle kills, and harmful algal blooms in the Peconics and Shinnecock Bay. This was especially shocking to me since for many years I used these waters as clean “reference” sites for studies on effects of pollution in fish, crabs, and shrimp living in the waters of northern New Jersey.

The cause of our local problems is excess nutrients, especially nitrogen. While nitrogen is an essential nutrient (a part of all proteins and nucleic acids) and a fertilizer that is important for agricultural productivity, when too much of it gets into the water it is a pollutant.

The sources of nutrients include sewage, animal wastes, and fertilizers that are discharged or run off from agricultural areas. On land, excess nitrogen flows from agricultural fields and suburban lawns, entering freshwater and going down to estuaries via streams and rivers, altering water chemistry and ecology. Synthetic fertilizer was a benefit in terms of crop yield but is an ongoing environmental problem, primarily because of runoff into aquatic ecosystems. The increased use of commercial fertilizers has increased nitrogen inputs tenfold in many parts of the world.

Waste from septic tanks enters estuaries through seepage into groundwater, which moves slowly into estuaries. In eastern Suffolk we rely mostly on individual septic tanks rather than centralized sewage treatment plants. Most of those systems were built many years ago. Where there is more residential development and more septic tanks in the neighborhood (and where isn’t that happening?), more nitrogen seeps into groundwater and nearby water bodies.

Nutrient enrichment promotes excessive growth of algae (fertilizing the algae), mostly microscopic phytoplankton blooms. Small increases in these algae can increase productivity in food webs and sustain more fish and shellfish. However, like too much of anything, overstimulation of algal growth can degrade water quality and threaten human health and living resources. When algal blooms die off, the dead cells sink to the bottom, where they stimulate bacteria to decompose them. The decomposition process uses up dissolved oxygen from the water. If the aeration of water by mixing is less than the bacterial metabolism, the bottom waters will lose oxygen and become hypoxic (low oxygen) or anoxic (no oxygen), creating stressful or lethal conditions.

The dissolved oxygen was down to zero in the Peconic during one of the fish kills this June. Hypoxia is a major problem in many estuaries, especially in late summer and early fall, and has been increasing globally. The fact that these incidents occurred so early in the summer indicates the local problem is particularly severe.

Low oxygen reduces the abundance and diversity of adult fish and reduces the growth rate of newly settled lobsters, crabs, shellfish, and juvenile flounder. Species that cannot move or move slowly may die in low-oxygen water. Fish larvae are poor swimmers and become more vulnerable to predation. Animals generally deal with low oxygen by reducing their activity in order to consume less oxygen. This often means feeding for shorter periods and eating less food.

In many areas hypoxia is so severe that they are called “dead zones” because nothing (aside from bacteria) can live there. Areas with oxygen sufficient to sustain some life (below two or three milligrams per liter) have reduced bottom (benthic) communities, made up of very small animals. When the benthic community is stressed, only small, short-lived worms remain; animals like crustaceans and mollusks (shellfish) can no longer survive. Hypoxia tends to be overlooked until conspicuous fish kills occur.

The turtles in the Peconic were not killed by low dissolved oxygen, since they breathe air. They were killed by toxins from some of the phytoplankton. Some phytoplankton species produce toxins that can impair respiratory, nervous, and other functions, and even kill fish, shellfish, seabirds, and mammals.

Harmful algal blooms have been called “red tides” or “brown tides” because of water discoloration when they occur, though many do not discolor the water. Their economic impacts can be severe if shellfish harvest and fishing are closed. Reports of such blooms have been increasing worldwide and often correlate with nitrogen inputs.

This year we have been revisited by a brown tide in Great South Bay and Moriches Bay, a fairly regular recurrence on eastern Long Island since the 1980s. But this year we also had a bloom of Alexandrium, which produces the toxin saxitoxin, in Shinnecock. While brown tide can cause ecological problems, it is not a human health concern. On the other hand, saxitoxin causes paralytic shellfish poisoning when people eat shellfish that have accumulated the toxin from the plankton they feed on. Such poisoning can make people very sick because, as the name implies, it causes paralysis. If the diaphragm is paralyzed, a person can’t breathe and can die.

Reducing the nitrogen inputs into our estuaries is an urgent necessity that will not be easy. I recently heard that there is a requirement for homeowners to have their septic tanks tested — something we never knew about for the 40 years we’ve had our house. Our officials should communicate with towns on Cape Cod that are experiencing similar problems in their estuaries from similar septic tank sources. Like the East End, they derive considerable economic benefit from the attraction of their coastal areas and healthy marine environment.

There is no quick fix for this; it will require considerable effort and expense. It also will take time for improvements to be seen after we curb the nitrogen inputs.

Judith S. Weis is a professor emerita of biology at Rutgers University who lives part time in Springs. She will be giving a talk about her newest book, “Marine Pollution: What Everyone Needs to Know,” at the South Fork Natural History Museum in Bridgehampton at 11 a.m. on Aug. 8.