Nutrients in Streams

Dissolved nitrate, ammonia, and total phosphorus data were used from sites on streams that drained watersheds that had primarily agricultural, urban, or forested land use.  These sites were sampled in NAWQA study units begun in 1991 and 1994. Discharge weighted mean  concentrations calculated from monthly samples were used for comparisons. Nitrate, ammonia, and total phosphorus were counted as a contaminant if the discharge weighted mean concentration exceeded the applicable drinking-water or aquatic-life standard or guideline.

Nutrients in ground water 

Dissolved nitrate concentration data were used from shallow wells screened near the top of the water table where land use within 500 meter radius was primarily agricultural, urban, or forested. These wells  were sampled in NAWQA study units begun in 1991 and 1994.  Generally each well was sampled once, however, the average concentration was used if multiple samples were collected from an individual well. Nitrates was counted as a contaminant if the concentration exceeded the drinking-water standard. Detailed procedures for data analysis can be obtained here.