Natural and anthropogenic controls on particulate metal(loid) deposition in Bolivian highland sediments, Lake Uru Uru (Bolivia)

Abstract

Mining in the Bolivian Altiplano is important and has historically provided much of the world’s Ag, Sn, and Sb. This study aims to better understand the effects of important recent increases in Bolivian mining on the deposition of metals and metalloids in sediment near Oruro, Bolivia’s fifth largest city, with special attention to natural and anthropogenic factors as well as early diagenesis, which could have broader implications in other high-elevation environments that have or will be affected by increased mining activities. To better assess the depositional trends of elements in sediments, five sedimentary cores collected in Lake Uru Uru and the Cala Cala Lagoon (nearby Oruro) were studied and analysis of the physicochemical variables coupled with radiometric dating indicate that (a) sediment deposited in Lake Uru Uru was likely sourced from local outcrops of Tertiary volcanics, Paleozoic shales, and ore and waste piles from mining activities material; (b) sedimentation rates in Lake Uru Uru were close to 3 mm·year−1, 1 mm higher than the ancient Tauca paleolake (~11,000–30,000 years ago); (c) early diagenetic effects have affected the distribution of Mn, As, and Cd in the sedimentary archive; and (d) the deposition of Ag, Sb, and Pb in the studied sediment has largely been related to historical trends in Bolivian Sn mining methods and production.

Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation

“…Furthermore, the synergistic effect of mining (i.e., acid mine drainage (AMD)) and urban effluents from both the Oruro and Huanuni areas (Figure 1) to this shallow lake were proven to enhance Hg methylation, with the sediment being the main source of MMHg during the dry season [19]. Historical and current mining (e.g., Au, Ag, and Sn) and smelting activities in the region have led to the contamination of the lake by various metals, including Hg [19,20]. In addition, the recent urban development has resulted in the almost permanent eutrophication of this shallow aquatic ecosystem [21].…”

“…Historical and current mining (e.g., Au, Ag, and Sn) and smelting activities in the region have led to the contamination of the lake by various metals, including Hg [19,20]. In addition, the recent urban development has resulted in the almost permanent eutrophication of this shallow aquatic ecosystem [21].…”

“…where Jsed (ng.m −2 d −1 ) is the diffusive flux from the sediment, Ø is the porosity (Ø = 0.78 [20]), Dsed is the diffusive coefficient in sediment (2 × 10 −6 cm 2 s −1 and 1.2 × 10 −5 cm 2 s −1 for Hg(II) and MMHg ionic/molecular diffusion coefficient in water [35]), and ∂C/∂z is the linear concentration gradient through the SWI. Positive Jsed indicates an upward-directed flux (efflux from the sediment into the overlying water column), and negative Jsed indicates a downward-directed flux (influx from the water column into the sediment).…”