National Water-Quality Assessment (NAWQA) Program

U.S. Geological Survey
Water-Resources Investigations Report 99-4007

Review of Phosphorus Control Measures in the United States and Their Effects on Water Quality

By David W. Litke


Historical information on phosphorus loadings to the environment and the effect on water quality are summarized in this report, which was produced as part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. Phosphorus is a water-quality constituent of concern because it is often the limiting nutrient responsible for accelerated eutrophication in water bodies.

Phosphorus inputs to the environment have increased since 1950 as the use of phosphate fertilizer, manure, and phosphate laundry detergent increased; however, the manufacture of phosphate detergent for household laundry was ended voluntarily in about 1994 after many States had established phosphate detergent bans. Total phosphorus concentrations in raw wastewater effluent contained about 3 milligrams per liter of total phosphorus during the 1940's, increased to about 11 milligrams per liter at the height of phosphate detergent use (1970), and have currently declined to about 5 milligrams per liter. However, in some cases, tertiary wastewater treatment still is needed to effectively improve water quality of streams.

Downward trends in phosphorus concentrations since 1970 have been identified in many streams, but median total phosphorus concentrations still exceed the recommended limit of 0.1 milligram per liter across much of the Nation. Data from the NAWQA Program are representative of a variety of phosphorus-control measures, and, therefore, may be used to evaluate the effects of various control strategies. Current areas of concern include: evaluation of the effects of increased manure loadings of phosphorus on soil phosphorus and, subsequently, on ground water and subsurface runoff; determination of point-source and nonpoint-source components of phosphorus loads by geographic modeling and hydrologic separation techniques; and development of methods or indices to evaluate nutrient impairment in streams and rivers to serve as a basis for developing phosphorus criteria or standards.

Table of Contents

Purpose and Scope
Phosphorus in the Environment
Phosphorus Sources and Sinks
Phosphorus and Eutrophication
Phosphorus Control Measures
Phosphate Detergent Bans
Effluent Phosphorus Limits
Nonpoint-Source Controls on Phosphorus
Effects of Phosphorus Control Strategies on Water Quality
Extent of Eutrophication
Reductions in Phosphorus Concentrations and Loads
Improvements in Eutrophic Conditions
Use of National Water-Quality Assessment Program Data to Evaluate Effects of Phosphorus Controls
Description of NAWQA Water-Quality Data
NAWQA Findings

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For further information about this report, contact the National Water-Quality Assessment Program office.

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