The effects of the disposal of copper mine tailings on the littoral meiofaunal
assemblages of the Chañaral area of northern Chile were studied. Tailings
disposal has taken place along this stretch of coastline since 1938. The tailings,
derived from the Potrerillos (now closed) and El Salvador mines, were sent down
the dry river bed of the Rio Salado to be deposited in Chañaral Bay resulting in
the formation of an extensive tailings beach. In 1975 the tailings were redirected
from the Rio Salado via a tailings canal to a new dumping point at Caleta Palito,
ten kilometres north of Chañaral Bay. Again a large tailings beach formed in the
littoral zone between Caleta Agua Hedionda and Caleta La Lancha. In 1990,
after court action, a tailings settlement dam was constructed at Pampa Austral
where the solid component of the tailings was allowed to settle out. Since then
only 'clear water' tailings have been delivered to the coast at Caleta Palito.
A sediment quality triad (SQT) approach was used to examine the effects of the
tailings, supported by laboratory experiments designed to look at each of the
perturbing components of the tailings individually. The first element of the SQT
was an analysis of the physicochemical nature of the beaches studied. The
concentrations of labile metals, assumed to be equivalent to the bioavailable
metals, were measured in both the porewater and overlying seawater using the
diffusion gel technique (DGT). An analysis of the sediment structure was also
conducted. The second element of the SQT was an analysis of the meiofaunal
assemblage structure on each of the beaches studied using both univariate and
multivariate (PRIMER) techniques. The third element of the SQT was the use of
whole assemblage meiofaunal bioassays conducted in microcosms. Finally, to
provide supporting information, a series of laboratory microcosm experiments
were conducted to identify the effects of copper alone and the physical impact of
the tailings on meiofaunal assemblages. Twelve sites were used for the study,
and were divided a priori into three groups. The first group comprised the
reference sites (Las Piscinas, Torres del Inca and Playa Zenteno) which lay
sufficiently far to the south as to be unaffected by the tailings dumping. The
second group comprised the northern sites within the Parque Nacional Pan de
Azucar (Puerto Pan de Azucar, Frente Isla Pan de Azucar and Playa Blanca),
these sites on visual inspection did not appear to be impacted by the tailings
dumping. The third group comprised those sites located around the dumping
points (Caleta La Lancha, Caleta Agua Hedionda, Palito 1 000m Norte, Playa
Palito, Palito 2000m Sur and Playa Chañaral) which on visual inspection showed
clear signs of impact by the tailings dumping.
Though a number of metals could be associated with the tailings discharge at
Caleta Palito by their distribution in the seawater samples, only in the case of
copper was there a clear association with the tailings distribution in both the
seawater and porewater samples. The concentrations of copper in the seawater
and porewater were highly correlated and it is assumed that the tailings on the
beaches was the source of copper in the adjacent seawater. When compared to
the reference sites, the meiofaunal assemblages at the impacted sites (the third
group) had significantly lower densities and diversities; at the northern sites only
the densities were lower. The two groups of meiofauna that proved to be most
sensitive to the effects of tailings dumping were the foraminiferans and the
harpacticoid copepods. Otoplanid turbellarians were identified as characteristic
of those beaches impacted with tailings. BIOENV (PRIMER) analysis of the
data indicated that the combination of porewater copper and the amount of
tailings present were mostly responsible for the observed structure of the
meiofaunal assemblages. The bioassay of the sediments indicated that the
sediments from the northern sites were not toxic to the test meiofaunal
assemblages, but confirmed the toxicity of the sediments from the impacted sites. The response of the meiofaunal assemblages to increased bioavailable copper was confirmed using the laboratory microcosm experiments. The effects of the physical impact of the tailings, primarily a reduction in interstitial space,
depended upon the group under consideration. For the foraminiferans the
increased surface area resulted in an increase in the population density, however
the reverse was the case for the harpacticoid copepods. The effects of the
reduction of interstitial space for the polychaete Saccocirrus were negative,
physically incapable of burrowing it tended to congregate on the surface of the
sediment were it was exposed to an increased risk of predation and loss of
position in the littoral zone.
Using the SQT methodology to summarise the findings of this research I was
able to further divide the impacted sites into two groups. The most severely
impacted sites were those beaches composed only of tailings (Caleta La Lancha,
Caleta Agua Hedionda and Playa Chañaral) where both the increased
concentration of bioavailable copper and the reduction of interstitial space were
acting on the resident meiofaunal assemblages. The less severely impacted sites
were those where there were tailings present but where the tailings had not
completely smothered the beach (Palito 1000m Norte, Playa Palito and Palito
2000m Sur); at these sites the bioavailable concentrations of copper were
generally lower and the reduction in the interstitial space less severe.
This research supports the use of the sediment quality triad as none of the
individual components alone was able to predict the overall level of pollution-induced degradation at the sites studied. The combination of all three
components provides a much more comprehensive picture of the state of the sites than would any one component alone.