Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Civil and Environmental Engineering


Darwin L. Sorensen


The bioavailable fraction of phosphorus (BAP) in the lower Bear River system waters was investigated. BAP plays a critical role as the limiting nutrient for algal production and eutrophication in proposed reservoirs in the Bear River system. The Bear River system has a hardness rang ing between 180-240 rng/L as CaC03 which significantly affects BAP.

BAP estimation was done by a modified Selenastrum capricornutum Printz Algal Assay Bottle Test. The algal bioassay is considered the best estimator of BAP because no chemical tests or i ndicator parameters are available. Autoclaving and UV radiation were found to be unacceptable means for sterilization because of phosphorus precipitation and inability to kill all the protozoa, respectively. Whole water samples were sterilized by gamma radiation . Hydrogen peroxide formed by gamma radiation was minimized by sparging with nitrogen gas , and adding peroxidase to remove low hydrogen peroxide concentrations. Soluble reactive phosphorus concentrations changed during radiation.

The algal photosynthetic consumption of co2 in the assay procedure raised the pH from 8 to as high as 10, which resulted in significant quantities of phosphorus precipitating with calcium and becoming unavailable. To minimize the effects of precipitation, the following recommendations are made : (1) bubble the bioassay flask with a C02/air gas mixture to minimize pH increase ; and (2) use a high inoculum (105 cells/ml) of S . capricornutum that have been phosphorus starved for several days to maximize luxury uptake.

Bioavailable phosphorus was estimated for each of the sources in Cache County. There are three major point sources (Logan, Hyrum, and Preston wastewater treatment plants) that contribute significant quantities of phosphorus . There are approximately 200 feedlots in the Cache Valley, and approximately 744,000 acres of land in Cache County which contribute runoff to the Bear River system. In Cache County, point sources contribute 2 8 , 20 0 ( 4 6%) kg BAP /yr, livestock runoff contributes 2,500 (4%) kg BAP/yr, and land runoff contributes 28,600 to 33,600 (50%) kg BAP/yr. Bioavailable phosphorus from land runoff was calculated by using export coefficients, which are usually accurate within a factor of two.

A comprehensive phosphorus management plan is required to reduce available phosphorus from all sources to minimize algal blooms in the receiving waters.