Levels Of Phosphorus And Nitrogen In Shenandoah River Water

In the period 1936-1941, smallmouth bass nests were counted in the Main Stem and South Fork of the Shenandoah River. Counts were made during the smallmouth bass spawning season when waters were clear, usually May 1-15. Due to eutrofication, the South Fork and Main Stem water now remains clear for only a few days. The enumeration and study of bass nests has been made more difficult due to the sudden development of blooms of algae. High levels of phosphorus and nitrogen in the South and North Forks and the Main Stem are believed to be the cause. Total phosphate ranged from 0.33 to 4.80 parts per million in the South Fork and from 0.23 to 1.50 ppm. in the Main Stem. The highest seasonal averages occurred in the spring and fall. In the North Fork, total phosphate ranged from 0.14 to a maximum of 1.40 ppm., with the highest seasonal averages occurring in the spring and summer. Orthophosphate ranged from 0.30 to 2.30 ppm. in the South Fork, and from 0.14 to 1.04 ppm. in the Main Stem. The North Fork ranged from 0.07 to 1.15. The highest averages occurred in the fall when the South Fork averaged 0.934 ppm. and the Main Stem 0.489 ppm. The highest average in the North Fork occurred in the Spring (0.453 ppm.). Nitrate nitrogen levels were high in all sections of the river and based on past records is increasing steadily. In the South Fork, nitrate nitrogen as N03 ranged from 1.18 to a maximum of 8.93 ppm. Spring and winter had the highest seasonal averages with 5.60 and 6.79; the Main Stem was from 0.82 to a maximum of 7.90 ppm. Spring and winter had the highest averages with 4.488 and 5.626 ppm., respectively. The North Fork had the highest nitrate nitrogen, with levels ranging from 1.087 to a maximum of 11.462 (an amount approaching safety limits for drinking water). Winter had the highest seasonal average, 7.584 ppm. In both the South and North Forks, the average, as well as winter and summer average nitrate and phosphate levels, decreased from their initial high levels in passage downstream. Nitrite nitrogen levels and nitrogen/ phosphorus ratios were also determined.

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