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Technical Report

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Bottom sediments, suspended sediments, and water were sampled along 130 miles of the Buffalo River in northern Arkansas. The water and acid extracts of the suspended sediments and the minus 95 mesh fraction of the bottom sediments were analyzed by atomic absorption spectrometry. All samples were analyzed for Na, K, Mg, Ca, Zn, Cd, Cu, Pb, Fe, Co, Cr, Ni, and Mn. Selected bottom samples also were analyzed by As, Hg, and Zr. Zr was determined by x-ray fluorescence. Li and Sr were determined for selected water and suspended sediment samples. There is a general decrease downstream in Fe, Cu, Cr, Ni, Mn, Pb, K, and Na in the bottom sediments as the drainage area increases in carbonate rock and decreases in shale. The elements Mg, Ca, Zn, and Cd increase in bottom sediments downstream. The values for these elements in the water, especially the major elements, also correspond closely with the geology of the region. Tributaries are sites of abrupt rise and fall of metal values, within a few miles, from background to anomalously high values to background, especially tributaries draining Zn and Pb mineralized areas. The bottom sediments are mainly quartz and chert grains. These grains apparently are coated with hydrous iron oxide which acts as a sorbent for many of the elements and is a dominant transport mechanism for acid extractable Co, Cr, Ni, Cu, Mn, and K. Other acid extractable metals, particularly Mg, Ca, Zn, Cd, and Pb, are mostly in clastic grains. Graphic representation of the Langmuir equation for Mn is consistent with adsorption of Mn by iron in both bottom sediments and suspended sediments. On the basis of the volume of water collected, all the elements except Fe are more concentrated in the water than in the suspended sediments. Fe concentration of the suspended sediments increases with increasing flow because the suspended load is increased. The Mn/Fe ratio of the suspended sediments is approximately equal to or greater than that of the bottom sediments. The Mn/Fe ratio of suspended sediments relative to that of the bottom sediments increases downstream, possibly because of an autocatalytic effect of Mn precipitation. The relationship between sediment and water concentrations is not clear from the data because of the restricted concentration ranges for some elements in the suspended sediment and water. The sediment from the Buffalo River can be used to estimate grossly the concentration of elements in the water.

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