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This article in JEQ

  1. Vol. 26 No. 3, p. 815-829
     
    Received: Apr 30, 1996
    Published: May, 1997


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doi:10.2134/jeq1997.00472425002600030032x

Acidification Effects on Trace Element Chemistry in Agricultural Evaporation Pond Sediments

  1. Mitchell J. Herbel,
  2. Randy A. Dahlgren,
  3. Kenneth K. Tanji * and
  4. Suduan Gao
  1. Dep. of Land, Air and Water Resources, Univ. of California, Davis.

Abstract

Abstract

Evaporation ponds have been used to dispose of saline agricultural drainage waters in the western San Joaquin Valley of California for approximately 20 yr. Through evaporation, high concentrations of trace elements have accumulated in pond waters, evaporite minerals, and bottom sediments resulting in a toxicity hazard to wildlife. Acidification of pond waters (pH ≈ 4–5) is proposed as a means of inhibiting biological productivity, thereby discouraging wildlife from using these ponds as a feeding ground. This investigation uses a pH-stat equilibration (72 h) of pond sediment suspensions to evaluate the effectiveness of sulfuric acid (H2SO4) and FeSO4 as acid sources and the effect of these acid treatments on soluble trace element concentrations at pH 4 and 5. Acid extraction of pond sediments with 1 M HCl showed the following release of potentially labile trace elements: Al≈Fe>>B >Mn>>As,Cu,Mo,Zn>>Se. Titration of brine/sediment suspensions to pH 4.0 showed that the buffering capacity of the brine water and sediments were about equal. During a 72 h pH star, minor acid additions were required to maintain the target pH of 4.0. Relative to non-acidified controls, soluble trace element concentrations in the pH 4 H2SO4 treatment increased for Fe, Mn, Al, Zn, B, and As, remained constant for Cu, Se, and Zn, and decreased for Mo. Similar results were shown for the FeSO4 treatment at pH 4 with the exception of small increases for Cu and Zn and a decrease of Se. The effect of a brine matrix on trace element release/retention showed only minor differences compared to deionized water. The FeSO4 treatment was the most effective acidifying agent and resulted in the lowest soluble concentrations of the most potentially hazardous trace elements (As, Mo, and Se).

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