Gardner

Leonard Gardner

Professor
Low Temperature Geochemistry

B.S., 1958, St. Peter's College;
B.S., 1963, M.S., 1966, Ph.D., 1968, Pennsylvania State University

Research Areas: Aqueous geochemistry and geomorphology; the geochemistry and mineralogy of soils and saprolites; origin of caliche; geologic and geochemical processes in salt marshes; watershed biogeochemistry; modeling of geochemical processes in aqueous systems.

Soil Geochemistry: Estimates of the absolute amounts of element removal (or addition) resulting from rock weathering are usually based on comparisons with an element (usually Ti or Al) assumed to be immobile during weathering. This assumption may or may not be valid. Intense weathering of crystalline rocks in the Piedmont Province of South Carolina has resulted in the formation of thick residual soils, called saprolites, which retain the textural and structural features of the parent rock. On the basis of textural integrity, one can reasonably assume that weathering has proceeded in an isovolumetric fashion; that is, a unit volume of saprolite has evolved from an equivalent volume of parent rock without dilation or compaction. Thus by expressing element concentrations on a volumetric basis (g/cc) one can estimate the loss or gain of elements due to transformation of a volume of parent rock into saprolite. Based on the isovolumetric of soil profiles from a number of sites, I have discovered that both Al and Ti are commonly mobilized during weathering. More importantly, however, isovolumetric data for a saprolite profile can be used to construct an empirical reaction progress diagram for the weathering process. The empirical diagram can be compared with theoretical diagrams in an attempt to discover the stoichiometry of the reactions controlling the weathering process. I have found that simple textbook reactions do not adequately describe rock weathering. Thus this work is being continued in an effort to discover the nature of the reactions involved in the weathering of various rock types.

Salt Marsh Processes: Salt marshes are thought to influence the chemistry and productivity of adjacent coastal waters. Researchers at the Baruch Institute have been monitoring the movement of nutrients and other substances in tidal waters draining the marshes at North Inlet, S.C. Since the export (or import) of chemicals from marshes depends partly on biogeochemical processes in marsh sediments, I have been attempting to ascertain the magnitude and direction of the flux of substances between interstitial waters and surface waters. These studies are based on measurements of the concentrations of various substances (e.g. H 2 S, CO 2' ) in core profiles. Such profiles provide information on the nature and rate of biogeochemical processes such as sulfate reduction and iron sulfide precipitation.

Recent Publications:

Gardner, L.R., 1990, "Simulation of the diagenesis of carbon, sulfur and dissolved oxygen in salt marsh sediments," Ecological Monographs, 91-111.

Gardner, L.R., T. Wolaver, and M. Mitchell, 1988, "Spatial variations in the sulfur chemistry of salt marsh sediments at North Inlet, S.C.," Jour. Mar. Res., 45, 815-836.

Gardner, L.R., P. Shanna, W. Moore, and M. Bollinger, 1987, "Sedimentation and bioturbation in a salt marsh as revealed by 2 1 0 Pb, 137 Cs, and 7Be studies," Limnol. Oceanogr. 32 (2), 313-326.

Gardner, L.R., 1984, "Carbon and oxygen isotope composition of pedogenic CaCO3 from Soil profiles in Nevada and New Mexico, U.S.A., Isotope Geology, v. 2, 55-73. Gardner, L.R., 1980, "Mobilization of Al and Ti during weathering - Isovolumetric geochemical evidence," Chemical Geology, 30, 151-165.

Gardner, L.R., 1. Kheoruenromne, and H.S. Chen, 1978, Isovolumetric geochemical investigation of a buried granite saprolite near Columbia, S.C.," Geochim. Cosmochim. Acta, v. 42,417424.

Gardner, L.R. and 1. Lerche, 1990, "Simulation of sulfur diagenesis in anoxic marine sediments using Rickard Kinetics for FeS and FeS2 formation," Computers and Geoscience, 16, 441-450.

Gardner, L.R., L. Thombs, D. Edwards, and D. Nelson, 1989, "Time series analyses of suspended sediment concentrations at North Inlet, S.C.," Estuaries, 12, 211-221

Gardner, L.R. and C. Gonnan, 1984, "The summertime net transport of dissolved oxygen, salt, and heat in a salt marsh basin, North Inlet, S.C.," Estuarine, Coastal and Shelf Science, v. 19.