Member Institutions:

• Bowling Green State U.
• Cleveland State U.
• Kent State U.
• Medical College of Ohio
• Miami U.
• The Ohio State U.
• Ohio U.
• University of Cincinnati
• University of Toledo
• Wright State U.
• Youngstown State U.

Research Interests

Dr. Heath is a biochemical limnologist, currently conducting most of his research in the Great Lakes and Great Lakes coastal wetlands. Over the past twenty years, his research has investigated biochemical adaptations of planktonic organisms to environmental stresses and has especially focused on P-dynamics and recycling mechanisms. He has conducted much of his work on the significance of dissolved organic phosphorus compounds (DOP) in satisfying nutritional requirements of organisms at the base of the food web. He and his students have worked extensively on the significance of phosphatases released by zooplankton and adaptively produced by algae and bacteria under P-limitation. He has also conducted research on a class of DOP compounds that are apparently humic-iron-phosphorus complexes that release phosphate when irradiated with low doses of UV-light, such as are found in sunlight at the surface of a lake. Currently he and his students investigate those factors that alter the efficiency of nutrient cycling in these oceanic-scale ecosystems.

Several of his current projects involve carbon- and phosphorus dynamics in planktonic communities at the base of the food web, involving a comparison of the microbial food web structure and function as related to C- and P-fluxes between algae, bacteria, protozoans and microcrustaceans in Lake Erie plankton communities. This study, conducted in the western basin of Lake Erie, found that ZM grazing perturbs the normal algal-bacterial coupling and release much phosphate and ammonium. A related investigation is investigating the hypothesis that these ammonium and phosphate releases from ZM may diminish the P-limitation of phytoplankton communities and may be responsible for stimulating the recent appearance of cyanobacteria, such as Microcystis spp. in Lake Erie plankton communities. These studies are funded by NOAA National Sea Grant R/ZM-25 and by the Lake Erie Protection Fund. A study that began on 1 March 1998, will investigate the effects of ZM on the microbenthic food web structure and the activities of microbenthic organisms.

In collaboration with investigators in the Departments of Chemistry and Geology, Dr. Heath, is funded by NOAA to investigate the origin, fate and significance of UV-sensitive iron-containing humic DOP compounds in the P-dynamics of a coastal wetland. This study, supported by NOAA/Sea Grant College Program, conducts field and laboratory investigations of natural organic matter and its structure (determined by chromatography, and atomic force microscopy) to determine those processes that may result in controlling the availability of P as a function of the oxidation state of the iron, as it is photoreduced to Fe2+ and auto-oxidizes to Fe3+.

Selected Publications

• Hwang, S-J. and R. T. Heath. 1997. Bacterial productivity and protozoan bacterivory in coastal and offshore communities of Lake Erie. Can. J. Fisheries Aquat. Sci. 54: 788 - 799.
• Hwang, S-J. and R. T. Heath. 1997. The distribution of protozoa across a trophic gradient, factors controlling their abundance and importance in the plankton food web. J. Plankton Res. 19: 491 - 518.
• Hernandez, I., S-J Hwang, and R.T. Heath. 1996. Measurement of phosphomonoesterase activity with a radiolabelled glucose-6-phosphate. Role in the phosphorus requirement of phytoplankton and bacterioplankton in a temperate mesotrophic lake. Arch. Hydrobiology 137: 265 - 280.

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