Factors Regulating the Distribution of Elements in the Sediments of a Seasonally Anoxic Lake in Tropical Taiwan

Abstract

Sixteen metals, both total and acid-leached, and their binding formations were quantified for the sediment column of the seasonally anoxic Great Ghost Lake. Since marked variation in the content of organic matter plays a major role in regulating the distribution of metals in sediments, this study provided insight into the relationship between organic matter and metals in a naturally anoxic water environment. Metals, Al, Cs, Mg, Rb and V, had significant negative correlations with total carbon content (TC) and occurred less often in mobile fractions. These findings indicate that these metals came from lithogenic sources and did not change much during early diagenesis. As a result, signals of these elements, whose origins can be traced back to long-range transport dust, were better preserved. Acid-leached contents of Cs, Mg and Rb also had negative correlations with TC, while both total and acid-leached As and Cd had good positive correlations with TC. Large portions of both As and Cd, were observed in mobile fractions (especially As) and came from organic sources and/or were incorporated into organic matter during early diagenesis (especially Cd). Long-term variations in redox conditions of the lake were induced by climate changes and might have influenced distributions of Sr and redox-sensitive Mn and V in mobile fractions. In addition to natural processes, enrichment of Pb and Cd near the core top was from anthropogenic aeolian sources. Finally, recent aeolian fluxes of Al, As, Ba, Br, Ca, Cd, Ce, Cl, Cr, Cs, Cu, Er, Eu, Fe, Ga, Gd, K, La, Lu, Mg, Mn, Na, Nd, Ni, Pb, Rb, Si, Sm, Sr, Ti, Tm, V, Yb, Zn and Zr were estimated and large amounts of micronutrient Fe (~60 µg cm-2 yr-1 ), of aeolian origin, was also noted.

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