Lakhasly

trace metals.Atmospheric deposition was the most quantitatively important anthropogenic Pb source, which contributed 38-49% of the total sediment pollution and had an average contribution rate of 43.7%.The clusters in farther distances were

mainly chemical fertilizer and livestock manure samples, in- dicating that they did not substantially contribute to watershed

sediment pollution by Pb. On the other hand, the river sedi- ment cluster was very near to the concentrated clusters for

background soil and atmospheric deposition samples.Different Pb sources were also quantitatively discrim- inated by using Isosource.

trace metals. Although the liner correlation between ob-
served and estimated excessive Cr concentrations was

moderate, other trace metals generally had higher R2
values, suggesting acceptable modeling results. For Ni,
Pb, and Cr, the first anthropogenic source (represented
by PC1) was their major anthropogenic source, which
could contribute on average 89.7%, 92.2% and 74.3%
of their excessive concentrations, respectively. However,
excessive Cu and Zn mainly originated from the second
anthropogenic source (represented by PC2), with the

average contribution rates of 95.1% and 92.5%, respec-
tively. The third anthropogenic source (represented by

PC3) was the major anthropogenic source only for Cd,
which contributed on average 97.9% of excessive Cd
concentration in the sediments.
Lead isotopic composition

The 206Pb/207Pb and 208Pb/207Pb ratios were used to charac-
terize Pb isotopic composition. For river sediment, back-
ground soil, chemical fertilizer, livestock manure, and atmo-
spheric deposition samples, their 206Pb/207Pb and 208Pb/207Pb

ratios were measured on average as 1.163 ± 0.003 and 2.453 ±
0.003, 1.168 ± 0.004 and 2.477 ± 0.007, 1.118 ± 0.004 and
2.416 ± 0.013, 1.099 ± 0.008 and 2.354 ± 0.012, and 1.158 ±
0.004 and 2.426 ± 0.005, respectively. To further discriminate
different Pb sources in this watershed, values for the

206Pb/207Pb ratio were plotted against values for the
208Pb/207Pb ratio. As displayed in Fig. 4, different Pb sources
appeared as relatively concentrated clusters according to their
isotopic compositions. The clusters in farther distances were

mainly chemical fertilizer and livestock manure samples, in-
dicating that they did not substantially contribute to watershed

sediment pollution by Pb. On the other hand, the river sedi-
ment cluster was very near to the concentrated clusters for

background soil and atmospheric deposition samples. By

comparison, the river sediments were located closer to water-
shed background soils than to atmospheric deposition sam-
ples, which indicated a major contribution of natural source

and a lesser contribution of anthropogenic sources.

Different Pb sources were also quantitatively discrim-
inated by using Isosource. During the calculation by this

software, source contributions were considered to be
feasible solutions only if the observed and estimated
Pb isotopic ratios for river sediment matched within ±
0.001. Consequently, the contribution of background
soil representing natural source ranged from 51 to
59%, with an average contribution rate of 54.4%.
Atmospheric deposition was the most quantitatively important
anthropogenic Pb source, which contributed 38–49% of the
total sediment pollution and had an average contribution rate
of 43.7%. However, the contributions of chemical fertilizer
and livestock manure were both very low, with the average
contribution rates of 1.0% and 0.8%, respectively.