Date of Award

Spring 1998

Project Type

Dissertation

Program or Major

Natural Resources

Degree Name

Doctor of Philosophy

First Advisor

William H McDowell

Abstract

Interactions between dissolved organic carbon (DOC) and mineral soils were examined in field and laboratory experiments. Specific emphasis was given to factors influencing DOC mobility and element release during mineral weathering and soil formation. Soil chemical and physical properties controlling equilibrium concentrations of DOC (DOC$\rm\sb{np})$ in coarse-textured forest soils were investigated using laboratory batch reactors and the initial mass isotherm approach. The influence of DOC concentration on release of metals and silica was investigated in four soil parent materials. One of four acid treatments (0.001 N HNO$\sb3$ and three concentrations of forest floor leachate) or distilled water were added to soil columns every third day for one year. Chemical composition of solutions and soil materials were analyzed before and after solution percolation to assess net release or retention of DOC and inorganic constituents. Results of laboratory column and batch investigations were compared to trends in weathering and DOC retention in a field site in Berlin, NH. In soil B horizons, DOC$\rm\sb{np}$ was correlated with soil pH, % OC, and some forms of extractable Al and Fe. Soil properties correlated with DOC$\rm\sb{np}$ values in B horizon soils were not generally correlated with DOC$\rm\sb{np}$ values in E horizons. DOC$\rm\sb{np}$ values were not correlated with soil surface area. Laboratory derived trends in DOC$\rm\sb{np}$ values were in agreement with patterns of DOC concentrations in field soil solutions. In the column study, release of Si, Al, Ca, and Mg from soil materials increased with increasing DOC input. Changes in soil chemical properties (pH, loss-on-ignition, extractable Al and Fe) following leaching were consistent with podzolization. The most dramatic changes in soil chemical properties were found in soils leached with high concentrations of DOC. Comparison of solution and soil measures of organic carbon retention indicate that only about 50% of the DOC lost from solution was measured as soil organic carbon at the end of the experiment. This finding shows that microbial decomposition is a significant factor regulating organic carbon concentrations in mineral soils and that soil solution data alone do not yield a complete picture of organic carbon dynamics.

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