Ph.D., University of Wisconsin, Madison (1971)
M.S., University of Wisconsin, Madison (1964)
B.S., University of Wisconsin, Stevens Point (1963)

Research Interests

Water Chemistry/Ecosystem Dynamics
Nitrogen dynamics in water column and sediments, nutrient-organism interactions in coastal ecosystems, relationships between nitrogen inputs and oxygen removal in coastal environments such as the “Dead Zone,” Dissimilatory nitrate reduction to ammonium (DNRA) as a mechanism to retain available N in coastal regions.

Nitrogen cycling is important in coastal and estuarine ecosystems because nitrogen is transformed to a variety of forms, by autotrophic and heterotrophic processes in the water and sediments, and is a nutrient that often limits the growth of phytoplankton and other plants in these relatively shallow systems. Internal regeneration is an important process providing nitrogen to plants whereas denitrification causes available nitrogen to be lost from estuarine and coastal ecosystems.

Major goals are to understand and quantify the biotic mechanisms and rates of nitrogen remineralization and the fate of nitrogen compounds in the water and at the sediment-water interface. This information is needed to understand nitrogen biogeochemistry and to quantify the relative importance of internal nitrogen regeneration processes compared to inputs from other sources in these productive ecosystems. Nitrogen regeneration and transformation rates in the water and at the sediment-water interface are measured with 15-N as an isotopic tracer. Ammonium concentrations and isotope ratios are measured by high performance liquid chromatography. Denitrification rates are determined using a Membrane Inlet Mass Spectrometer. Nitrogen cycling studies have been conducted in Texas coastal ecosystems, Florida Bay, the Mississippi River Dead Zone, The Great Lakes, Lake Taihu, China, and other shallow coastal environments and wetlands.