Table 1 The main time periods of Lake Kirkkojärvi ecosystem.
From: Multiple mining impacts induce widespread changes in ecosystem dynamics in a boreal lake
Period | Years | Water characteristics | Sediment chemistry | Cladocera | Diatoms | Interpretation |
|---|---|---|---|---|---|---|
After the accident | 2013–2015 | Lake is meromictic. High salinity prevails. Fe and P are released from the sediment to hypolimnion. | Fe and P exhibit lower concentrations, also Ni and Zn decrease due to decreased pollution. | B. longirostris dominates. | D. tenuis dominates | Lake is clearly impacted by pollution |
Pond accidents | 2012–2013 | Strong stratification. Dam accident derived Ni and Zn stay on top of chemocline. | Ni and Zn peak. Si peaks due to the pollution accident. | B. longirostris dominates. Richness and diversity are low. | D. tenuis increases | Lake is clearly impacted by pollution |
Mining begins | 2008–2012 | Onset of meromixis and anoxia in deep water. Mine-related elements increase. | Zn, Ni, S and Na increase | Bosmina longirostris increases, diversity and richness decreases | Diatoma tenuis increases | Saline water and meromixis affects the system |
Natural | 1971–2008 | Not permanently stratified, chemistry resembles natural conditions | K increases due to forestry | Daphnia dominates. Rich and diverse community | Tabellaria and Aulacoseira spp. dominate. Rich and diverse community | Most likely nearly natural boreal lake |
