Cullen Wilson

Date of Award

2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Ivan J. Fernandez

Second Committee Member

Stephen A. Norton

Third Committee Member

Robert G. Wagner

Abstract

Modern wastewater processing methods create large volumes of biosolids in order to meet U.S. environmental standards for water discharge. The reuse of biosolids has received attention for the potential economic and environmental benefits, and the potential risks. Biosolids are commonly treated with lime to minimize pathogen and trace element contamination risks. Beneficial reuse of lime-treated biosolids in forest ecosystems requires a greater understanding of the immediate and continuing effects on soil pH, and on soil and foliar chemistry. Soils in a northeastern hardwood forest were amended with lime-treated biosolids at a Maine state regulated maximum loading rate and at two higher loading rates (4.5, 6.7 and 13.5 Mg CaCO3 equivalency ha-1). At the highest loading rate, O horizon soil pH peaked six weeks after amendment at a salt solution pH (pHs) of 6.49 compared to 3.59 in the unamended control. O horizon pHs remained elevated over the control by an average of 1.80 units for the remainder of the study period (>2 years after amendment). Upper B horizon soils amended at the highest loading rate averaged a 0.43 unit pHs increase over the control during the study period. B horizon pHs continually increased throughout the study period, reaching a maximum of 4.50, compared to 3.91 in the control. In the O and upper B horizons, amendment led to decreased extractable concentrations of pH-affected elements (Al, H, Fe, Mn), decreased exchangeable acidity, and increased exchangeable Ca. Hardwood tree species growing in amended soil had increases in foliar B, and for two species, decreases in the C/N ratio. Foliar Ca, Na and Al correlated (+0.58 ≤| r |≤+0.86) with both their respective soil exchangeable concentrations and soil pH (especially in the upper soil). The implication of these correlations is that amendments could increase tree growth in future growing seasons. The highest amendment rate in this study increased soil pH, though it remained below the circum-neutral zone that is potentially optimal for plant nutrient uptake. Changes in soil and foliar nutrients suggested that nutrient imbalances had not occurred due to the amendments.

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