Trace metal partitioning and potential mobility in the naturally acidic sediment of Lake Caviahue, Neuquén, Argentina

CABRERA, JM; TEMPORETTI, PF; PEDROZO, FL

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2019 vol. 47

0718-7092

LakeCaviahue is a very acid water body (Patagonia, Argentina) due to theinflux of volcanic fluids. Over the past 18 years, the lake has beenprogressively alkalinizing and pH is close to the ferric ironprecipitation threshold (pH>3,0). Should iron precipitate, waterand sediment composition will be altered. To set a baseline, tracemetal partitioning (Cu, Cd, Cr, Pb, Zn and Mn) was studied for threesediment cores (0 to 16 cm depth) at three sampling stations using asequential extraction procedure (SEP) and the acid volatile sulfide /simultaneously extracted metals (AVS/SEM) protocol. The total metalscontent of the sediments ranged between 0 to 408 µgg-1 ofdry sediment, with Pb>Cr>Mn>Cu>Zn>Cd.No Cd was measured above the limit of detection. The sediment wasrichest in Mn and Cr, two non ? toxic metals at the pH / Ehcombination of the lake basin. Total Pb was at a moderatecontamination level although it is associated with the mostrecalcitrant fraction and therefore has low mobility. The sedimentfractions with higher metal content were the oxidizable and residual,the former commonly associated with labile organic matter and pyritewhile the latter are related to recalcitrant organic matter and rockforming minerals. In addition, a high correlation was found betweenCr, Pb and Mn, thus these metals may be subject to analogousprecipitation processes and possibly to co ? variation in thevolcano effluents. Furthermore, no metals were detected in theexchangeable / carbonates fraction, which is the most labile of allthe sediment fractions. The metal content in (SEM) was likewise belowthe toxicity thresholds of two international sediment qualityguidelines and the ratio AVS/SEM was over one, indicative of non ?toxicity. Both results indicate that metal mobility in the acidsediments of lake Caviahue is very low.p { margin-bottom: 0.25cm; direction: ltr; color: rgb(0, 0, 0); line-height: 200%; }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; }p.cjk { font-family: "Droid Sans Fallback"; font-size: 12pt; }p.ctl { font-family: "FreeSans", "Times New Roman"; font-size: 12pt; }a.western:link { }a.ctl:link { }