Mechanisms underlying recovery of zooplankton in Lake Orta after liming

Abstract

The goal of this study was to improve the understanding of the large-scale mechanisms underlying the recovery of the zooplankton of Lake Orta from historical contamination, following reduced input of ammonia and metals and the subsequent 1989/90 liming intervention. The industrial pollution had been severe and long-lasting (1929-1990 2001 and 2007 (0.55 and 0.72 for rotifers, 0.85 and 0.86 for crustacean, respectively), much higher than in limed lakes in Sudbury, Canada, and in adjacent Lake Maggiore. We hypothesize this could be related to the lack of Cladoceran predators and zooplanktivorous fish in the pelagic waters of Lake Orta.

When and how? Freshwater mussel recolonization in Lake Orta

“…2)]: acid-base status of Lake Orta had completely recovered, ammonium levels had lowered, falling in the range of those observed in the other subalpine oligotrophic lakes, while nitrate was still >1 mg L -1 . Present concentrations of Fe, Mn, Al and Cu in the water column are as low as those of the nearby Lakes Maggiore and Mergozzo (Rogora et al 2016) while, Ni and Cr, although at low levels, still might pose a threat for biota (Piscia et al, 2016). No data is available on sediment chemistry after 1996 ) when the area colonized was highly enriched in Cu (~2000 mg kg -1 ), Cr (~1000 mg kg -1 ), Pb (~500 mg kg -1 ) and Mn (~1500 mg kg -1 ) with pore water concentrations of Cu and Cr respectively of 0.63 and 0.10 (Guilizzoni et al 2001) the layer deposited between 1996 and 2001 (about 1 cm) was probably not sufficient to isolate organisms from the toxic layers underneath.…”

Lake Orta chemical status 25 years after liming: problems solved and emerging critical issues

“…Hypolimnetic anoxia has also been eliminated which permits the survival of hypolimnetic colonists. On the other hand, the slower decrease of Ni and the presence of Cr, although at low levels, still might pose a threat for biota, as discussed in Piscia et al (2016), also in relation to other chemical variables (e.g., Ca, Na). Solubilization of trace metals from the sediments must be also taken into account, particularly in relation with the oxygen levels in the deeper waters.…”

“…These data permit a longer-term evaluation of both the response of the lake to the restorative interventions, and an assessment of the present state of lake's acid-base and trophic status. This information, coupled with that from the studies about the biological communities (Morabito, 2016;Piscia et al, 2016) contributes to the definition of the lake ecological and chemical status. Furthermore, an in-depth knowledge of the lake chemical and trophic status is a precondition for the planning of any restoration measure, such as fish introduction (Volta et al, 2016).…”

Differentiated Responses of Plankton and Zoobenthos to Water Quality Based on Annual and Seasonal Analysis in a Freshwater Lake

“…Biodiversity, which is one of the fundamental elements of ecosystem functioning [2], has been considered an important indicator that could be applied in biological restoration as well as assessing ecosystem health of a lake [3]. Previous studies of biodiversity in aquatic ecosystems, which refer to phytoplankton, zooplankton, and zoobenthos, focus mainly on the relationships between biological characteristics and environmental variables [4][5], spatiotemporal patterns [6][7][8], and biological restoration [9][10][11]. Yet studies on differentiated response patterns of biodiversity in freshwater lakes on water quality based on annual and seasonal analysis, as an essential work for the biological recovery and management of a lake ecosystem, are few and should be paid more attention.…”