A northern Italian shallow lake as a case study for eutrophication control |
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Authors: | Serena Zaccara Alessandro Canziani Valeria Roella Giuseppe Crosa |
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Institution: | (1) Ecology Unit, Department of Biotechnology and Molecular Sciences, University of Insubria, via Dunant 3, 21100 Varese, Italy;(2) Environmental Protection Councillorship of Varese District, Varese, Italy;(3) ARPA, Department of Varese, Varese, Italy |
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Abstract: | Lake Varese (northern Italy) has shown deterioration in water quality since the 1960s and, as a result of the long duration
of direct discharge of untreated sewage into the lake, it was classified as being hypertrophic. To recover the lake water
quality, a series of externally and internally remedial actions were implemented in subsequent years. The applied sewage collecting
system induced a reduction of the external P loads from 50 t P year−1 to 16t P year−1 and the weighted mean annual TP concentration decreased from 352 μg P l−1 to 85 μg P l−1, typical of eutrophic conditions. The hypolimnetic water withdrawals, adopted in the years 2000–2003, allowed a reduction
of the internal P loads of about 3–5 t P. In the same years, 500t O2 were injected at depths of 4.5–8 m during the summer months. In spite of these internal remedial actions, no significant
reduction of the weighted mean annual concentration of the TP could be observed, and during the summer stratification period
no significant reduction of the volumes of anoxic water and of the duration of the anoxia were detected. The anoxic conditions
are still the prevailing force driving the lake P-budget, maintaining the lake in eutrophic status. |
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Keywords: | Eutrophication Shallow lake Remedial actions |
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