Nutrients (nitrogen and phosphorus) are the building blocks for life, but too much in a natural system can lead to problems. Our communities contribute excess nutrients to the Sound from wastewater, septic systems, fertilizer, and fossil fuel burning. Nitrogen fertilizes excessive growth of plant-like organisms (phytoplankton and seaweed), leading to algae blooms. As these organisms and the animals that feed on them respire, die, and decompose, oxygen in the water is depleted. Our other indicators capture the impact of high nutrient inputs (low DO, high chlorophyll a, low water clarity). When conditions are very bad, we sometimes see fish kills and harmful algal blooms.

Mystic Aquarium and Clean Up Sound and Harbors (CUSH) surveying seaweed in Long Island Sound.

How is it measured?

Total nitrogen and total phosphorus were measured at approximately 23 stations up to 33 times during the period of interest (January to December). Total nitrogen is the amount of nitrate, nitrite, ammonia and Total Kjeldahl Nitrogen in the water. Total phosphorus is the amount of dissolved phosphate and organophosphate in the water. 

Threshold Levels

Total Nitrogen ThresholdTotal Phosphorus ThresholdOverall Score Calculation
> 1.2 mg/L> 0.13 mg/LFail (0%)
0.8-1.20.09-0.13Poor (20%)
0.6-0.80.07-0.09Marginal (40%)
0.5-0.60.05-0.07Fair (60%)
0.4-0.50.03-0.05Good (80%)
< 0.4< 0.03Pass (100%)