Humate in coastal sands of northwest Florida

Abstract

Layers of dune and beach sand along the north coast of the Gulf of Mexico are cemented or impregnated with a conspicuous dark-brown to black water-solute organic substance herein called humate. The humate-cemented sand, generally 6 inches to 3 feet thick but as much as 15 feet thick in some places, forms one or several irregular layers in the subsurfaces of broad land areas at a depth of a few inches to 35 feet. Humate accumulates in surface soil layers, in and beneath marsh deposits, in shore and beach sands or bayous and bays, commonly near the mouths of tea-colored streams and near ground-water seepages, and as a type of organic sediment in bodies of brackish or saline water. The average ash-free composition of the humate is 55.00 percent carbon, 4.4 percent hydrogen, 38.5 percent oxygen, 1.4 percent nitrogen, and 0.7 percent sulfur, which closely resembles the composition of lignin, humic acids, dopplerite, and some peat and lignite deposits. Infrared spectra, amount of benzene-extractable hydrocarbons, and spectrographic analysis for contained metals confirm this similarity. This northwest Florida humate is derived by leaching from decaying plant material, or humus, on the land surface; surface and subsurface waters transport the soluble andmore » colloidally dispersed humic substances to subsurface sand environments or to brackish or saline water bodies where flocculation or precipitation of humate is triggered by various physical-chemical mechanisms. Observations and experiments in the field and in the laboratory demonstrate some of the processes of humate formation, including flocculation or precipitation by adsorption of cations, complexing with clay colloids, and lowering of pH.« less