Date of Award

8-2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Stephen A. Norton

Third Committee Member

Katherine Webster

Abstract

The majority of phosphorus (P) found in the water column of many lakes is recycled from lake sediment. The profundal sediments in cores from two lakes that released low amounts of P (low-P lakes) and one that released high amounts of P (high-P lake) were analyzed to help understand the mechanisms responsible for the difference in P release rates among the lakes. All three lakes had similar hypolimnetic iron (Fe) release rates. Extractions of the profundal sediment involved reductive and non-reductive reagents. The bicarbonate-dithionate (BD) reduction extraction results suggest that a significantly larger fraction of P was associated with the reducible Fe(III) hydroxides in the high-P lake than in the low-P lakes. As such, P release in the high-P lake was more susceptible to changes in the hypolimnetic redox conditions. The extraction procedures provided little evidence for the possibility of bacterial uptake of P during anoxic conditions in the low-P lakes. As such, P release in the high-P lake was more susceptible to changes in the hypolimnetic redox conditions. The extraction procedures provided little evidence for the possibility of bacterial uptake of P during anoxic conditions in the low-P lakes. However, the significant increase in the BD-P fraction with time in the high-P lake suggest that bacteria may be directly involved in the release of P with the onset of anoxia. The released P may then be adsorbed onto Fe(III) hydroxides and released upon reductive dissolution of the mineral. Through monitoring of the BD-P and BD-Fe:BD-P ratios with time it may be possible to predict the hypolimnetic release of P from the sediment of high-P lakes during anoxia. A sediment core form each of the study lakes was used to determine the P fractionation within the sediment at varying depths. Normalized accumulation rates were determined by 210Pb dating of the sediment cores. The low-P lakes had significantly higher concentrations of NaOH-extractable and total extractable Al than the high-P lake over the entire 50 cm core. Even though chemical extractions cannot unambiguously determine P associated with Al form that associated with the sediment organic matter, the results suggest that Al hydroxide may be partly responsible for sequestering P in the sediments of the low-P lakes. The P and Al normalized accumulation rates in the sediment of the cores covary only in one lake. This was a low-P lake, however, the correlation was not statistically significant.

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