Historical impacts of mercury mining and stocking of non-native fish on ichthyofauna in the Idrijca River Basin, Slovenia

Abstract

Mercury mining in Idrija has profoundly changed environmental conditions in the Idrijca River basin. Impacts of mining-related activities on the river system and its ichthyofauna from circa 1490 until World War I were analysed. Literature and archival sources were both studied. Heavy water pollution with mercury and its components, the floating of wood using splash dams in order to create artificial flood waves, fishing and stocking of non-indigenous fish species were the factors identified contributing to major impacts on ichthyofauna. Fish statistics make clear that after four centuries of mercury production ichthyofauna in the Idrijca was by no means the most industrially affected one in Carniola and that there were huge differences among various sections of the Idrijca and its tributaries. We presented the history of fish hatcheries operating from 1876 onward in order to reduce the damage inflicted by mercury mining and related activities and reviewed its impacts on hybridization between marble and brown trout. Introduction of non-native fish was the major threat for the ichthyofauna in comparison to the other mentioned impacts of mercury mining, conducted over long periods but with comparably minor consequences for the survival of the native ichthyofauna.

Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss)

“…Most of the Idrijca River basin is dominated by native marble trout, introduced brown trout, their hybrids Salmo sp. and rainbow trout, but several other fish species also occur (Torkar & Zwitter, 2015).…”

“…Hybridisation with brown trout stocked for angling, displacement by alien rainbow trout ( Oncorhynchus mykiss Walbaum, 1792), habitat alterations (barriers, channelization, erosion control structures, etc . ), water extraction and pollution may be the major threats to marble trout (Berrebi et al ., 2016; IUCN, 2006; Razpet et al ., 2007; Torkar & Zwitter, 2015; Vincenzi et al ., 2012). By the end of the 20th century, the marble trout was on the brink of extinction, with only a handful of genetically pure lineages remaining in small isolated streams (Berrebi et al ., 2000; Povž, 1995).…”

Minerías artesanales para la extracción de oro mediante el uso de mercurio: Estado del arte del impacto ambiental en los medios agua, aire y suelo

“…Situación en el continente Europeo: Según Torkar y Zwitter [14], en la cuenca del Río Idrija en Eslovenia, la minería de mercurio comenzó alrededor del año 1490. Idrija fue una de las minas de mercurio más importantes en Europa, obteniendo el reconocimiento como la segunda mina de mercurio más importante de ese continente en el período moderno.…”

“…Posteriormente, se estimó que unos 37 000 toneladas de mercurio fueron emitidos en el medio ambiente desde el cual miles de toneladas quedaron acumuladas en los sedimentos aluviales del Río Idrijca, y el curso medio y bajo del Río Soca. Torkar y Zwitter [14] señalan que antes de que las actividades mineras comenzaran las secciones de las corrientes en la cuenca del río Idrijca podrían haber estado contaminadas con cantidades restringidas de mercurio nativo. Posteriormente, las actividades del procesamiento del mineral fueron las fuentes más importantes de contaminación.…”

Historic Milestones of Human River Uses and Ecological Impacts

“…Several studies exist, for instance, for the mining of mercury in support of large-scale gold and silver exploitation and production since the sixteenth century in Europe and America. Recently, Torkar and Zwitter (2015) investigated the long-term effects of the Slovenian mercury mine in Idrija and the resulting pollution of Idrijca River on fish. Polluted sediments were swept downstream and finally accumulated in the sediments of the northern part of the Gulf of Trieste (Gosar 2008;Foucher et al 2009).…”