Recovery of copepod, but not cladoceran, zooplankton from severe and chronic effects of multiple stressors

Abstract

In the mid-twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L )1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed -Cladocera and Copepoda occurred with equal frequency in area lakes -but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre-neutralization stress.

Freshwater Diatoms as Indicators of Combined Long-Term Mining and Urban Stressors in Junction Creek (Ontario, Canada)

“…The health of Junction Creek was impacted by the contamination and degradation in its watershed, and showed highly impaired biological integrity [1]. Still nowadays, despite pollution control and rehabilitation actions having been undertaken, aquatic ecosystems in the region suggest slow recovery [2][3][4][5][6]. Mining activities are still present in the region, although under significantly more restrictive pollution control and regulation, and intensification of urban development represents a supplementary environmental threat.…”

Calcium and sodium as regulators of the recovery of four Daphnia species along a gradient of metal and base cations in metal contaminated lakes in Sudbury, Ontario, Canada

“…The severity and duration of the historical contamination in Sudbury has complicated ecological recovery, given that so many species disappeared, and potential colonist pools have also been damaged by metal contamination, and possibly by other stressors such as climate change . Still, in response to the local water quality improvements , some zooplankton and fish have recovered in Sudbury lakes (Gunn and Keller, 1990;Yan et al, 2004;Keller et al, 2007). Gunn and Sandoy (2003) argued that biological recovery requires that a number of healthy key organisms and sensitive species, including fish, phytoplankton, zooplankton and benthic invertebrates re-establish viable populations and resume their role in the system, such that the restored community resembles one in similar ecosystems with minimal anthropogenic impact.…”

“…However, a lost species can only recover if there is habitat of sufficient quality for founding populations to persist (Griffith et al, 1989;Keller et al, 1999). Such biological recovery has been both slow and incomplete in Sudbury's urban lakes (Yan et al, 2004. Water quality has improved significantly (Keller et al, 1999;Keller, 2009;Khan et al, 2012) and daphniid colonists have arrived, but most have failed to re-establish populations (Yan et al, 2004;Schartau et al, 2007).…”

“…Such biological recovery has been both slow and incomplete in Sudbury's urban lakes (Yan et al, 2004. Water quality has improved significantly (Keller et al, 1999;Keller, 2009;Khan et al, 2012) and daphniid colonists have arrived, but most have failed to re-establish populations (Yan et al, 2004;Schartau et al, 2007). Acidity is no longer the problem since the majority of Sudbury lakes now have pH >6.0, a safe pH for Cladocera (Havens et al, 1993;Holt andYan, 2003); hence, attention has turned to lingering metal problems.…”

“…There are about 7 species native to the Shield (Hebert, 1995), and, as a group, they are considered to be among the most important pelagic herbivores, maintaining water clarity and providing food for fish. They are also among the most sensitive freshwater invertebrates to adverse water quality conditions (Koivisto and Ketola, 1995;Hairston et al, 2005), therefore, their failure to re-establish populations in many Sudbury lakes is a concern (Yan et al, 2004). Above their required concentrations, essential metals such as Cu become toxic (Mertz, 1981), reducing the survival (Bielmeyer et al, 2005) and reproduction of daphniids (Koivisto and Ketola, 1995), also altering their energy budgets and reducing the accumulation of lipids (Canli, 2006).…”