Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. But when too much nitrogen enters the water, it can fuel the growth of algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. Nitrogen runs off the land during rain events. Atmospheric nitrogen from industry settles on the water.
How is it measured?
Total nitrogen (TN) samples were collected at 74 stations, bimonthly to monthly, over the entire year. Data from each sampling station was used to calculate a median concentration. An attainment score was subsequently derived using multiple health-based thresholds. TN scores for each sampling station were then averaged by reporting region.
Threshold levels
| Threshold (mg L-1) | Score |
|---|---|
| <0.55 | 100 |
| 0.55–<0.65 | 80 |
| 0.65–<1.0 | 60 |
| 1.0–<1.5 | 40 |
| 1.5–<2.0 | 20 |
| ≥2.0 | 0 |