Chemical composition of Lake Orta sediments

Abstract

Lake Orta (18.2 km2, 1.3 km3, 143 m max. depth) has been severely polluted since industrialisation of its watershed began in 1926, at which time the lake began to receive industrial effluents containing high concentrations of copper and ammonia. Chromium-, nickel-, and zinc-rich effluents from plating factories have also contributed to pollution levels, and pH -levels dropped below 4.0 as a result of the oxidation of ammonia to nitrates. More than 60 papers have documented the evolution of the chemical characteristics of both water and sediment, and the sudden decline of plankton, as well as benthos and fish. As a remedial action the lake was limed from May 1989 to June 1990 with 10,900 tons of CaCO3. The treatment was immediately effective in raising the pH and decreasing the metal concentrations in the water column, and plankton and fish communities quickly rebounded. However, the chemical characteristics of sediments were influenced by the liming to a much lesser extent. Since 900 tons of copper and the same amount of chromium were contained in the top 10 cm of sediment, it appears likely that the sediment could potentially act as a current and future source of these metals to the water column. This observation has resulted in the implementation of a vigorous monitoring regime to track the post-liming recovery of Lake Orta

When and how? Freshwater mussel recolonization in Lake Orta

“…1) corresponding to the area which was primarily affected by industrial discharges of the Bemberg factory since 1926 (Bonacina, 2001;Baudo and Beltrami, 2001). Average population density was 3.9 ind.…”

Ecological effects of multiple stressors on a deep lake (Lago Maggiore, Italy) integrating neo and palaeolimnological approaches

“…Sedimentary records of the pollution of Lago Maggiore with DDT, trace metals (especially mercury) and persistent organic pollutants (POPs) over the past ca 55 years have been obtained through the analysis of short cores collected during several sampling campaigns starting in 1963 (e.g., Muntau 1981;Provini et al 1995;Guzzella et al 1998;Baudo et al 2002). Detailed distribution maps for macro and trace elements have been drawn up based on the core data (Baudo et al 1981;Viel and Damiani 1985;Rossi et al 1993;Baudo et al 2002;Bettinetti et al 2005;Guzzella et al 2007) and the total burdens of metals and POPs in sediments have been esti- mated (Cenci et al 1991;Provini et al 1995;Guzzella, unpublished data).…”

“…Detailed distribution maps for macro and trace elements have been drawn up based on the core data (Baudo et al 1981;Viel and Damiani 1985;Rossi et al 1993;Baudo et al 2002;Bettinetti et al 2005;Guzzella et al 2007) and the total burdens of metals and POPs in sediments have been esti- mated (Cenci et al 1991;Provini et al 1995;Guzzella, unpublished data). All work to date shows mercury (and other trace metals not shown) and DDT at highest concentrations in sediments deposited during northern Italy's industrial and economic boom of the 1960s (Fig.…”

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

“…Particularly important, also in relation to the effect on the benthic fauna, is the quality of lake sediments: recent studies revealed the presence of toxic residues in the top layer of Lake Orta sediments, which could potentially act as a source of metals to the water column (Baudo and Beltrami, 2001). The presence of trace metals in the sedi-N o n -c o m m e r c i a l u s e o n l y ments also prevent a full recolonization by macrobenthic organisms (Nocentini et al, 2001).…”