Catchment liming creates recolonization opportunity for sensitive invertebrates in a smelter impacted landscape

The response of a sensitive indicator species to the effects of catchment liming was assessed in a lake severely impacted by atmospheric emissions from a metal smelter in Sudbury, Canada. The lake chemistry recovered following the closure of the local smelter and major reductions (approximately 95%) in acid and metal emissions from other area smelters, leading to recolonization of the lake with fish and other biota. However, the littoral macrobenthos community remain severely impoverished. The catchment liming sustained improved stream water quality for 20 years after the initial aerial treatment and created a littoral zone hot spot for the recolonization of Hyalella azteca . Colonization at delta sites of untreated catchment drainage areas, in the same lake, were low and highly variable, and these sites appeared to be impacted from soil erosion and episodic release of acid and metals. This study demonstrated the need to both reduce air pollutants and to conduct land reclamation in severely damaged watersheds, before lake ecosystems themselves can be fully recovered.