Phosphorus Fractionation and Distribution across Delta of Deer Creek Reservoir

• Main Author: Casbeer, Warren C.
• Format: Others
• Published: BYU ScholarsArchive 2009
• Subjects: eutrophication; nutrient budget; nutrient (re)cycling; sediment delta head cutting; Civil and Environmental Engineering
• Online Access: https://scholarsarchive.byu.edu/etd/2004; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3003&context=etd

Eutrophication of reservoir systems, which causes deterioration of water quality through increased algal growth, is detrimental to our sustainable water supply and additionally impairs other beneficial reservoir uses. Limiting the amount of phosphorus (P) entering the system has been the key management tool for this problem, as P is the main limiting nutrient for plant and algal growth. These efforts have focused on controlling input of P from point sources, such as effluents from wastewater treatment plants, dairies, and industrial factories. Even in systems (such as reservoirs) with significantly reduced external P loading, however, there has been continued eutrophication and slower than expected recovery of reservoirs in water quality restoration projects. Other nutrient sources have been studied to explain this phenomenon. The continual eutrophication has been potentially attributed to availability of nutrients from deposited sediments. This is referred to as nutrient recycling, as nutrients previously trapped within sediments may become available within the water column. Deer Creek Reservoir (DCR), a significant water supply in Utah, has had greatly improved water quality after reduction of external P loading. However, there are still large algal blooms at times as well as other water quality issues without clearly attributable causes. Part of the explanation might lie within the deposited sediments, which are present both on the sediment delta and within the reservoir. This thesis provides data that can help researchers understand what role sediment has in the continuation of water quality problems at DCR. Sediment samples were taken across the delta to define both the spatial extent and distribution of P and chemical form, or ‘pool’, of the P. The pools can be used to estimate the ability of the sediment-bound P to move into the water column under various conditions. Results reported here indicate that significant amounts of P are found within these sediments, though not all of it can easily become available for algal growth. We characterized P distribution by taking 91 samples on 6 transects across the exposed delta. Transects were separated by 200 m and samples were taken eery 100 m along the transects. The samples were all analyzed for water soluble P content, and 19 samples were additionally characterized for KCl-, NaOH-, HCl-, and organic (by digestion) P fractions. Total P was determined for these as well by summation. The data showed that water soluble P ranged from 2.28E-03 and 9.81E-03 mg P g−1 dry sediment and showed a decreasing trend along the reservoir. KCl-P ranged from 2.53E-03 and 1.10E-02, NaOH-P from 5.30E-02 to 4.60E-01, HCl-P from 1.28E-01 and 1.34E+00, and organic (residual) P from 8.23E-01 to 3.23E+00 mg·g−1.