NUTRIENTS

Nutrients in surface water are essential for aquatic plant and animal life, but large nutrient concentrations can have adverse ecological effects. In general, sources of nutrients include wastewater treatment plants, fertilizer, manure, plant decay, and atmospheric deposition (Hem, 1989). Concentrations of nutrients analyzed in samples collected during the study at the three intensive fixed sites are shown in tables 5-7. Concentrations of nutrients in equipment blank samples were small compared to concentrations in environmental samples. Small concentrations of some nutrients detected in field blanks could cause a positive bias in small nutrient concentrations in environmental samples. The small concentrations of nutrients in field blanks probably were from residual contamination in the collection and processing equipment. The nutrients of most concern are nitrite plus nitrate nitrogen and phosphorus.

Nitrite plus nitrate nitrogen is a concern for drinking water because excessive concentrations of nitrate can cause methemoglobinemia (blue baby syndrome), which restricts oxygen transport in the bloodstream of infants (Hem, 1989). The maximum contaminant level (MCL) for dissolved nitrite plus nitrate nitrogen in U.S. Environmental Protection Agency (EPA) drinking water regulations is 10 milligrams per liter (mg/L) for water delivered to any user of a public water system (U.S. Environmental Protection Agency, 1996). Boxplots of the distribution of dissolved nitrite plus nitrate nitrogen concentrations for the three intensive fixed sites are shown in figure 5. Median concentrations were 1.97 mg/L at the agriculture indicator site, 0.551 mg/L at the urban indicator site, and 10.6 mg/L at the integrator site.

Nitrite plus nitrate nitrogen concentrations were graphed for the three intensive fixed sites to show any concentration fluctuations over time or seasonal patterns (fig. 6). Nitrite plus nitrate nitrogen concentrations at all three sites did not indicate seasonal patterns. Nitrite plus nitrate nitrogen concentrations at the integrator site, which is downstream from three municipal wastewater treatment plants, often exceeded the MCL for drinking water.

Nitrite plus nitrate nitrogen concentrations were smaller in samples collected during storm events (larger discharge) than during base flow at the agriculture indicator site (table 5). Nitrite plus nitrate nitrogen concentrations in storm-event samples at the urban indicator site did not vary from concentrations in base-flow samples (table 6). Nitrite plus nitrate nitrogen concentrations also were smaller in samples collected during storm events than during base flow at the integrator site (table 7). Nitrite plus nitrate nitrogen concentrations in base-flow samples at the agriculture indicator site did not seem to vary with discharge, but nitrite plus nitrate nitrogen concentrations in base-flow samples at the urban indicator site generally increased with increasing discharge (fig. 7). In contrast, nitrite plus nitrate nitrogen concentrations in base-flow samples at the integrator site generally decreased with increasing discharge (fig. 8).

Phosphorus often is associated with eutrophication, which is the enrichment of a body of water with nutrients that results in accelerated algal or plant production (Hem, 1989). Eutrophication can result in fish kills, unpleasant odors, loss of recreational value, and other water-quality related problems (Land and others, 1998). The EPA recommends that total phosphorus concentrations not exceed 0.10 mg/L in streams not discharging directly into reservoirs and not exceed 0.05 mg/L in streams discharging directly into reservoirs (U.S. Environmental Protection Agency, 1986). Boxplots of total phosphorus concentrations for the three intensive fixed sites are shown in figure 5. Total phosphorus concentrations at the agriculture indicator site exceeded 0.10 mg/L only in two samples collected during storm events (table 5). Total phosphorus concentrations at the urban indicator site ranged from <0.010 mg/L to 0.545 mg/L and also were greater in samples collected during storm events (table 6). Total phosphorus concentrations in all samples collected at the integrator site exceeded 0.10 mg/L (but were less than 3.0 mg/L) (table 7).

Back to: Table of Contents

Forward to: Pesticides