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The geochemistry of trace metals in the Brazos River and the Brazos River estuary
Abstract
This comprehensive seasonal study of the Brazos River and its estuary has provided much new information concerning the behavior of dissolved and particulate trace metals in a river system. Such a study is appropriate because rivers are a significant source of trace metals for the ocean, yet the fate of the metals after entering the ocean is poorly known. Brazos River surface water was sampled biweekly from 9/11/80 to 9/26/81. The Brazos River estuary was sampled in the winter, spring and late summer of 1981. Samples were analyzed for total dissolved Pb, Cu, Fe and Mn by differential pulsed anodic stripping voltammetry (ASV) and flameless atomic absorption spectrophotometry (AAS). Suspended particulate metals, Cd, Pb, Cu, Mn and Fe, were determined by AAS following a HNO(,3)/HF leach. The following ancillary data were collected: river discharge, total suspended matter, pH, major ions, nutrients, chlorophyll a, phaeo-pigments, dissolved and particulate organic carbon (DOC and POC), humic acid and apparent complexation capacity. Brazos River water chemistry was determined to be a function of two inputs: an influx of low salinity water from surface runoff and groundwater, and releases from Whitney Dam of high salinity water originating from evaporitic formations. Dissolved metal concentrations were Pb (0.04-0.9 nM), Cu (6-16 nM), Fe (2-430 nM) and Mn (2-570 nM); the ranges for particulate metal concentrations were Cd (0.03-1.16 ppm), Pb (9-42 ppm), Cu (12-22 ppm), Fe (2.4-3.7%) and Mn (280-1480 ppm). Variations in metal concentrations were related to groundwater input, organic matter and river sediment diagenesis.In the Brazos River estuary, distinct concentrations maxima were found in the 3-10('o)/oo chlorinity range for dissolved Pb (0.06-0.9 nM), Cu (6-42 nM), Fe (5-80 nM) and Mn (2-290 nM). Particulate metal concentrations showed significant seasonal and spatial variations: Cd (0.09-0.57 ppm), Pb (15-43 ppm), Cu (12-32 ppm), Fe (0,5-5.4%) and Mn (250-1990 ppm). Reducing conditions effecting diagenetic remobilization in estuarine sediments are proposed to be an important source of dissolved metal input to estuarine water. Calculations of dissolved riverine metal transport to the ocean which include estuarine metal input are as much as 40 times higher than when estuarine processes are ignored. Variations in complexation capacity (0-0.35 (mu)M Cu) are attributed to changes in DOC origin and concentration, the input of dissolved Cu and competition for complexing sites by Mg ions.
Description
Typescript (photocopy).Collections
Citation
Keeney-Kennicutt, Wendy Lisabet (1982). The geochemistry of trace metals in the Brazos River and the Brazos River estuary. Texas A&M University. Texas A&M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -515426.
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