The effect of hydropower production on benthic macroinvertebrates in two rivers in Costa Rica

Little information exists about the consequences of hydropower production in tropical areas, especially during the operational phase. In Latin America, hydroelectric energy is the primary method of fulfilling growing electrical demands. Most large dams (>15m in height) currently under construction or consideration are in the tropics. We investigated the effects of large hydroelectric dams on benthic-macroinvertebrate communities in two Costa Rican rivers. We measured physical-chemical characteristics and sampled benthic-macroinvertebrates from March 2003 to March 2004 in the Peñas Blancas and San Lorenzo Rivers. We also sampled the undammed Chachagua River. The physical-chemical characteristics were similar among the study sites. Taxa richness did not change significantly in areas affected by hydroelectric production. Community composition was different above and below the dam in the Peñas Blancas River. In the San Lorenzo River, the site below the turbine house showed less abundance than the site above, likely due to hydropower production discharge. We also documented the effects of the October 2003 sediment purge on benthic-macroinvertebrates in the Peñas Blancas River. This study shows that mitigation techniques can reduce environmental damage from hydropower production.