| Title | Hypolimnetic withdrawal coupled with oxygenation as lake restoration measures: The successful case of Lake Varese (Italy) |
| Abstract | Lake Varese is a relatively small lake, belonging to the drainage basin of lake Maggiore (northern Italy). It has had a long history (since 1960s) of water quality deterioration as the result of cultural eutrophication. In 1967 a restoration project was designed, including a sewerage network, an O-ring sewage diversion system, and a centralised wastewater treatment plant with phosphorus and nitrogen control. Since the 1990's, the lake has been the object of a cooperative research program supported by the European Commission, the Italian Ministry of the Environment, the Lombardy Region, and the Varese Province. The subsequent studies revealed that the lake responded to the decreased external nutrient loads. Besides, mathematical models predicted a rather long period (30 years) to attain the restoration goal, recognising the importance of internal P loading from sediments. Also, it was predicted that the application of in-lake measures would be beneficial in accelerating lake recovery. Recently, two measures have been suggested, i.e. hypolinmetic withdrawal in the deepest section (maximum depth: 26 m) and oxygenation in the shallower section, during summer stratification. Lake Varese constitutes the first case in Italy where in-lake methods are used to counteract the problems caused by excessive nutrient enrichment in a relative large system (lake surface: 14.52 km). In this paper, preliminary results of the first two years of operation (2000/2001) are summarised. The results are greatly encouraging. Lake water quality characteristics are as follows: Secchi transparency increased from 3.2 m to 4.9 m; annual mean total P concentrations decreased from 180 mg/m to 70 mg/m; average chlorophyll values decreased from 40 mg/m to 17 mg/m; the frequency of nuisance algal blooms declined to half in comparison to the 1990's and the algal density declined by a factor of 4, and anoxia periods decreased in time and space. Moreover, it has been evaluated that nutrient loads from lake Varese, due to the selected water discharges, did not affect the total nutrient budget of lake Maggiore and the downstream water quality. © Asociación Española de Limnología. |
| Source | Limnética (Internet) 24, pp. 123–132 |
| Keywords | environmental restoration; eutrophication; hypolimnion; oxygenationalgae |
| Journal | Limnética (Internet) |
| Editor | Asociación Ibérica de Limnología, Madrid, Spagna |
| Year | 2005 |
| Type | Articolo in rivista |
| Authors | Premazzi G.; Cardoso A.-C.; Rodari E.; Austoni M.; Chiaudani G. |
| Text | 480341 2005 Scopus 2 s2.0 28044447231 environmental restoration; eutrophication; hypolimnion; oxygenation algae Hypolimnetic withdrawal coupled with oxygenation as lake restoration measures The successful case of Lake Varese Italy Premazzi G.; Cardoso A. C.; Rodari E.; Austoni M.; Chiaudani G. European Commission, Joint Research Centre, Institute for Environment and Sustainability, 21020 Ispra, , Italy; Department of Biology, University of Milan, 20100 Milan, , Italy Lake Varese is a relatively small lake, belonging to the drainage basin of lake Maggiore northern Italy . It has had a long history since 1960s of water quality deterioration as the result of cultural eutrophication. In 1967 a restoration project was designed, including a sewerage network, an O ring sewage diversion system, and a centralised wastewater treatment plant with phosphorus and nitrogen control. Since the 1990 s, the lake has been the object of a cooperative research program supported by the European Commission, the Italian Ministry of the Environment, the Lombardy Region, and the Varese Province. The subsequent studies revealed that the lake responded to the decreased external nutrient loads. Besides, mathematical models predicted a rather long period 30 years to attain the restoration goal, recognising the importance of internal P loading from sediments. Also, it was predicted that the application of in lake measures would be beneficial in accelerating lake recovery. Recently, two measures have been suggested, i.e. hypolinmetic withdrawal in the deepest section maximum depth 26 m and oxygenation in the shallower section, during summer stratification. Lake Varese constitutes the first case in Italy where in lake methods are used to counteract the problems caused by excessive nutrient enrichment in a relative large system lake surface 14.52 km . In this paper, preliminary results of the first two years of operation 2000/2001 are summarised. The results are greatly encouraging. Lake water quality characteristics are as follows Secchi transparency increased from 3.2 m to 4.9 m; annual mean total P concentrations decreased from 180 mg/m to 70 mg/m; average chlorophyll values decreased from 40 mg/m to 17 mg/m; the frequency of nuisance algal blooms declined to half in comparison to the 1990 s and the algal density declined by a factor of 4, and anoxia periods decreased in time and space. Moreover, it has been evaluated that nutrient loads from lake Varese, due to the selected water discharges, did not affect the total nutrient budget of lake Maggiore and the downstream water quality. © Asociacion Española de Limnologia. 24 Published version http //www.scopus.com/record/display.url eid=2 s2.0 28044447231 origin=inward Articolo in rivista Asociacion Iberica de Limnologia 1989 1806 Limnetica Internet Limnetica Internet Limnetica Internet Limnetica. Internet Limnetica on line Internet martina.austoni AUSTONI MARTINA |
