las comunidades de peces del río guadiamar y el accidente minero ...

II.2- Habitat-fish community relationships in the
Guadiamar River basin (SW Spain) 8 years after a toxic
spill: is the spill still important?
Abstract
The Guadiamar River basin (SW Iberian Peninsula) suffered one of the most
environmentally harmful toxic spills worldwide on April 25th 1998, when a tailing pond
broke and released 4 m 3 of acid water and 2 m 3 of mud rich in heavy metals.
Immediately, removal works started and a recovery program was designed for the
affected area. Eight years later, every stream in the catchment was sampled to find the
most influential variables for native and exotic fish, and to establish whether the spill is
still exerting an influence on the fish community. GLMs were performed to analyze the
relationship between fish species richness and diversity and environmental variables.
The remaining effect of the toxic spill was assessed by comparing Guadiamar basin
values with those of six similar basins that were not affected by the spill. Native fish of
the Guadiamar basin prefer environments with low human influence, locations far away
from reservoirs, a large drainage area and the presence of natural shelters in the river
channel. For native fish, variables at both the catchment and site scales were equally
relevant. Exotic fish were mainly favoured by site-scale factors downstream from the
reservoir, where the alteration of the river channel and accumulated disturbances give
them an advantage versus natives. In summary, eight years after the accident richness
and diversity of the Guadiamar fish community are more influenced by anthropogenic
impacts than by the long-term influence of the toxic spill. This work highlights that
studies that aim to monitor the long-term effects of pollution events should take into
account the previous and current impacts of other anthropogenic factors, such as
upstream reservoirs or humanized land uses.
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