Impacto de los drenajes ácidos en los ecosistemas acuáticos producidos por la minería del carbón en El Bierzobioacumulación de metales pesados y evolución de las comunidades biológicas

Resum

El Bierzo carboniferous basin is an important mining area where this activity and its legacy left over decades, have altered the aquatic ecosystems of the region. The Boeza River, main fluvial channel studied that ends up at the Miño River, receives polluted water from its tributary the Tremor River. Not only there are several spoil dumps along the riverside of the Tremor River, but also it gets the waters contaminated due to mining activities from the Rodrigatos Stream and those from La Silva Stream, whose problem is caused by meteorization of the sulfurous dumps left after the contruction of the A-6 highway. In the present study, the quality of both river water and sediment has been studied by their physico-chemical analysis and heavy metal concentrations. The results show that river areas with or close to pollution sources have higher heavy metal concentrations than the fluvial stretch considered as control. In addition, water quality has been analysed by the use of biological indicators based on the tolerance of the macrobenthic community to pollution. IBMWP (Iberian Biomonitoring Working Party) and EPT (Ephemeroptera, Plecoptera and Trichoptera insect orders) indexes have pointed out a dangerous contamination of La Silva Stream, and a moderate one of Rodrigatos Stream and lower reaches from the Tremor River, while upper reaches of this river and Boeza River find theirselves in good conditions, especially the control point. At the same time, heavy metal concentrations in macrobenthic and trouts (Salmo trutta) communities have been measured. In that way, it has been observed that those metals which are in high concentrations in the affected river reaches, are also in high proportions within the organisms studied. Therefore, the existence of bioaccumulation is checked. Finally, the Rodrigatos Stream is a special scenario to study the recolonization by macroinvertebrates of the riverbed, considering that various restoration activities have been taken place inside its basin, among which stands out the construction of a passive system to eliminate heavy metals by decantation of a mine drainage that poured into the stream. With the passing of time, when mining activities have been reduced, the Rodrigatos Stream has been able to recuperate part of the macrobenthic fauna more tolerant to heavy metal pollution. Furthermore, the passive treatment system has been satisfactory in the retention of some important heavy metals like Al and Fe.