The geochemistry of black water in selected coastal streams of the Southeastern United States

Abstract

An investigation was conducted in a watershed formed by the tributaries of the Little River in South Georgia to study the nature of the humic and inorganic fractions of black water, and their influence on stream water quality. Large amounts of black colored water were sampled during 1983 to 1984 according to streamflow pattern in December, March, June and September. Measurements of air and water temperature and dissolved oxygen were made at the gaging sites, whereas water analysis for conductivity, Cl, NO₃‐N, NH₄‐N, P, total N, and other macro‐ and microelements were conducted in the laboratory. Fulvic (FA) and humic acid (HA) were isolated from the water samples, and analyzed by infrared and ¹³C NMR spectroscopy. Suspended clay from the water samples were collected and determined by x‐ray diffraction analysis. The results showed that black water was characterized by low conductivity and low ion concentrations indicating satisfactory chemical quality. The Na content was half the amount of other rivers in the Southeastern United States, whereas the ? content was similar to the world average. A seasonal fluctuation was noticed for Ca and Mg concentration. The increase of these ions during high streamflow in spring and summer was attributed to agricultural practices in the surrounding lands. Dissolved organic matter (DOM) concentration was highest in December during low streamflow. As DOM content decreased during high streamflow, water pH increased. A large part of the humified DOM was composed of fulvic acid, which was more aromatic in nature than soil‐fulvic acid as determined by ¹³C NMR. The suspended clay had a composition reflecting the clay mineralogy of Tifton soils in the surrounding uplands. It is believed that the Tifton soil, with its low activity clay and hence low CEC, may not be able to buffer the effect of acid leaching of black water.