Stable ‘Non-Traditional’ Isotopes - Application of Geochemical Tracers to Fluvial Sediment - page 119

from the lake that operated from 1890 to 1985. Zn deposition from the smelter was
thought to be limited, however, until 1917 when a 172m exhaust stack was added
to the facility. The overall approach was to collect, date, and analyze sediments
within a core from the lake, which dated back to about 1,450 YBP. Thapalia et al.
( 2010 ) found that the core could be subdivided into 4 time periods on the basis of
metal concentrations and mass sediment/metal (Zn, Cu, As, and Pb) accumulation
rates (Fig. 5.1 ). These 4 time intervals included (1) a pre-smelting period (pre-dating
1917), (2) a period of smelter operation prior to extensive urbanization within the
catchment feeding the lake ( 1917-1945), (3) a period characterized by smelting

and rapid urbanization within the catchment (

∼

1945-1985), and (4) a period fol-
lowing the closure of the smelter and characterized by relatively stable urban land
use (

∼

66 Zn values (reported using the batch JMC 3-

∼ 1985-2007). Isotopically, ʴ

0749-L standard) varied by 0 over the length of the core. More importantly,

the variations systematically correlated with the timing of smelter operation (pre-
smelter, smelter and post-smelter periods) (Fig. 5.1 ). The

. 50

66 Zn composition of the

ʴ

Fig. 5.1 a Mass accumulation rates (MAR) for Cu and Zn shown for core samples extracted
from Lake Ballinger near Seattle, Washington, USA; b Zn and Cu isotopes data plotted as a
function of depth within the cores (i.e., age). Dashed blue lines refer to the boundaries between
zones 1 (presmelter period), 2 (smelter period), 3 (smelter plus urbanization period), and 4 (post
smelter period). 2 error bars denote precision of external replicates (Reprinted with permission from
Thapalia et al. ( 2010 ) (Copyright 2010 American Chemical Society)