Why are all the fish dying? What do algal blooms have to do with it? And how much does the Riverhead Sewer Treatment Plant contribute to nitrogen loading in the Peconic River? RiverheadLOCAL editor Denise Civiletti explains.

Posted by RiverheadLOCAL.com on Tuesday, June 16, 2015

Why are the fish dying?

The menhaden (aka bunker) are dying from lack of oxygen in the local waters of the Peconic River and western Flanders Bay.

Why is the oxygen in the water low?

Oxygen levels in the water are affected by a lot of things, including poor tidal flushing and aeration, the number of fish in a confined area using up oxygen in the water — such as when the blue fish run the bunker up the river — and the levels of microscopic algae in the water.

Why do algae affect oxygen?

Algae photosynthesize in the day, producing oxygen, which is released into the water column. At night, they undergo respiration, consuming dissolved oxygen (DO) in the water column. This respiration can result in short-term dissolved oxygen depression, which is known as “diurnal” dissolved oxygen variation.

What is the relationship between nitrogen and algae in the water?

Excess nutrients, like nitrogen, in the water stimulate aquatic plant growth, including production of microscopic algae.

Where do excess nutrients in the water come from?

Nutrients like nitrogen enter local waters in several ways. Annual nitrogen “loading” in western Flanders Bay results from “non-point” sources

  • Sediment flux
  • Groundwater
  • Atmospheric deposition
  • Stormwater runoff

And “point” sources

  • Riverhead Sewage Treatment plant
  • Peconic River
  • Meetinghouse Creek

What are the biggest sources of nitrogen loading in Flanders Bay?

Non-point sources contribute 81 percent of nitrogen loading (1,760 pounders per day) in western Flanders Bay and 100 percent in eastern Flanders Bay.

Point sources contribute 19 percent of nitrogen in western Flanders Bay. The Riverhead Sewage Treatment Plant contributes 170 lbs. per day or just under 8 percent of the total nitrogen loading per day.

What ‘s the relative nitrogen loading to western Flanders Bay from the various non-point and point sources?

Nitrogen Loading

Groundwater – 1,320 lbs. per day, 61 percent
Sediment flux – 250 lbs. per day, 12 percent
Riverhead Sewage Treatment Plant – 170 lbs. per day, 8 percent
Atmospheric deposition – 160 lbs. per day, 7 percent
Peconic River- 140 lbs. per day, 6 percent
Meetinghouse Creek – 110 lbs. per day, 5 percent
Stormwater runoff – 30 lbs. per day, 1 percent

Why is nitrogen in groundwater?

The sources of nitrogen in groundwater are primarily fertilizers and septic systems.


Source: Peconic Estuary Program Comprehensive Conservation and Management Plan

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