Distribution and variability of nitrogen and phosphorus in the alluvial, High Plains, Rush Springs, and Blaine aquifers in western Oklahoma

Abstract

INTRODUCTION Aquifers are the primary source of water for drinking and agricultural purposes in western Oklahoma. Health concerns about consuming nitrogen and an increased reliance on ground water for drinking necessitate a better understanding of the cause and effect of contamination from nutrients. The purpose of this project was to compile nutrient data from the National Water Information System data base for the alluvial, High Plains, Rush Springs, and Blaine aquifers and to provide this information in a report for future projects and for the facilitation of nutrient source management. PURPOSE AND SCOPE This report provides graphic, tabular, and area! information on the distribution and variability of nitrogen and phosphorus ion concentrations in ground water from alluvial aquifers in the surficial terrace and alluvium located along rivers and their tributaries west of longitude 98°W. in Oklahoma and from three bedrock aquifers, High Plains, Rush Springs, and Blaine (fig.l). The scope of the work consisted of: (1) compiling ground-water-quality data concerning nitrogen and phosphorus ions, (2) constructing boxplots illustrating data variability, (3) constructing maps for each aquifer showing locations of wells where nitrogen and phosphorus ions were measured in ground water and where concentrations of nitrate (NO3) and nitrite (NO^, reported in milligrams per liter (mg/L) as nitrogen (N), exceed the maximum contaminant levels (MCL's) for drinking water established by the U.S. Environmental Protection Agency (EPA) and State of Oklahoma, and, (4) calculating summary statistics. All site and nutrient data used for this report were retrieved from the U.S. Geological Survey's data base, National Water Information System. Data compiled were restricted to groundwater samples within specified aquifer boundaries; samples from springs and surface water were not used. As no restriction was placed on date or time of sampling, multiple analyses were available for some sites and in these cases the most recent analysis was used. No restriction was placed on type of well or use of water, which vary for each aquifer depending upon water quality, well yield, and need. A total of 1,133 analyses were used for this report. NITROGEN AND PHOSPHORUS The nutrients nitrogen and phosphorus are essential chemical compounds necessary for life and critical for plant nutrition; however, excessive concentrations of these nutrients in water can have undesirable effects. Ground water and surface water are vulnerable to contamination when nutrients are leached from sources in the soil and percolate downward into the underlying aquifer or flow overland into rivers, lakes, and ponds. Problems occur when nutrients accumulate in surface waters, causing eutrophication, or in ground water used for drinking, where nitrogen can pose a health risk. Nitrogen, an essential element for biological processes, is commonly found in waste products from septic tanks, cesspools, animal feed lots, barnyards, and bats (from accumulations of guano) (Hem, 1985). Other sources include municipal and industrial wastewater, nitrogen-based fertilizers, and atmospheric fallout (from combustion of fossil fuel). Nitrogen also occurs naturally in soils from the decomposition of organic material, in some instances at concentrations high enough to cause significant ground-water contamination (Kreitler, 1975). Nitrogen in ground water exists primarily as the ions ammonium (NH4), nitrite (NO2), and nitrate (NO3). Nitrate, the most chemically stable form of nitrogen in the nitrogen cycle and the most mobile in water, is more likely to be the ion found in waters used for drinking, whereas NH4 and NO2 are most often found in oxygen-depleted waters close to the source of contamination. Phosphorus is found in naturally occurring sources such as phosphorus-containing rocks, waste products from large concentrations of ducks and cattle, fallout from the atmosphere, and tree leaves (U.S. Environmental Protection Agency, 1986). However, in most populated regions, including Oklahoma, the most important sources of phosphorus are man-made, such as domestic and industrial sewage and fertilizers. 2 Distribution and Variability of Nitrogen and Phosphorus