- Water-Quality Monitoring Networks (WQN)
- Nonpoint and Point Sources of Nitrogen
- Selected Constituents and Their Importance
- Stream Water Quality in the Conterminous United States
Statistical summary tables for field measurements and selected nitrogen and phosphorus constituents can be viewed. The period of record for the information presented varies from state to state and is defined in each table. The frequency of data collection varies from weekly, to monthly, to yearly, or can be based on discharge.