National Water-Quality Assessment Historical Nutrient Monitoring Locations

NAWQA Program's retrospective database contains point locations for over 22,000 surface-water samples collected from 1980 to 1990. The U.S. Geological Survey compiled this historical water-quality and ancillary data from its NWIS system, state agencies, and the EPA's STORET database. Data was aggregated by study-unit personnel to determine preexisting conditions and assess nitrate contamination risk.

Use Cases

• Analyze spatial distribution of nitrate and ammonia concentrations across monitoring locations to identify contamination risk areas.
• Model relationships between land-use classifications (e.g., Forest, Agricultural, Urban) and aggregated nutrient groups like total phosphorus.
• Assess temporal trends in orthophosphate and total nitrogen levels using the reported year of sampling for 1980-90 data.
• Correlate ancillary features like soil hydrologic group or nitrogen input to land surface with historical water-quality samples.
• Map integrated land-use designations for sites with drainage areas greater than 10,000 square miles against nutrient concentration data.

Strengths

• Over 22,000 surface-water samples provide a substantial historical record.
• Data aggregation into standardized nutrient groups (e.g., ammonia as N, total phosphorus) improves cross-study comparability.
• Includes ancillary data on land use, soil type, and nitrogen inputs compiled from national-scale maps and study units.

Limitations

• Sampling, preservation, and analytical techniques varied across sources and time, introducing potential measurement inconsistency.
• Temporal coverage is limited to 1980-1990, representing a specific historical period.
• Land-use classification uses broad Anderson Level I categories, which may lack detail for mixed-use sites.

Provenance

Source

U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program.

Collection Method

Compilation from USGS NWIS, state water-resource agencies, and EPA STORET database, with ancillary data from NAWQA Study Units and digital maps.

Time Range

1980-1990.

Freshness

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Geography

United States, focusing on the first 20 NAWQA Study Units.