Diurnal and annual variations of physical and chemical parameters in a marsh within Okefenokee Swamp were examined during 1777 and 1978. Temperature, conductivity, oxygen, carbon dioxide, potassium, sodium, magnesium, and calcium were affected by physical and biotic factors that operated on different temporal scales. Temperature, carbon dioxide, and oxygen showed diurnal and seasonal patterns that are typical of shallow marshes. Conductivity was less than 80 μmphos cm-1and varied with O2and temperature. Dissolved cation concentrations, especially those of K+and Ng++, were low. Diurnal changes in K+and Na++concentrations were statistically significant and seemed to be related to biotic uptake and release.