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The formation of chemical and biological heterogeneity in lakes can be favored by physical and morphometric constrains. This study describes the results of four whole-lake field campaigns carried out in Lake Como (north Italy) during thermal stratification. The aim was to analyze the distribution of chemical-biological variables in a multi-basin lake as a result of internal and external physical drivers and constrains. Lake Como has a y-like shape encompassing three main sub-basins: northern, south-eastern, and south-western. Field data underlined: the presence of chemical-biological gradients between the south-western basin and the rest of the lake and the propagation of a fresher water-plume (formed by the two main northern inflows) into the northern basin and then into the south-western closed arm. The use of a three-dimensional hydrodynamic model showed a periodic movement of this plume that tends to enter the south-western basin first and then to return toward north, moving forward and back through the junction of the three arms. The entrance into the eastern basin, instead, occurs only secondarily. Wavelet transform analysis revealed common periodicity between the plume movement and the action of different external and internal lake-stressors, including: the discharge of the main inflow (period centered at 1, 3.3, and 6.5 day), the wind intensity (0.5 and 1 day) and the two main basin-scale internal wave motions: (3.3 day and 7.1 day). The periodic movement of the fresher water-plume enhances the water exchange and reduces the chemical-biological gradients between the western closed basin and the main lake, playing a crucial role in distributing both inorganic and organic materials at the lake basin-scale.

The internal wave-field of a Y-shaped lake (Lake Como, North Italy) was investigated over a 3-year long period applying wavelet time-frequency analysis to temperature and wind data time series, recorded at the edge of each of the three arms. The comparison with the results from a modal model allowed to identify the presence of both first and second vertical modes of oscillations. The field data analysis underlined a heterogeneous baroclinic response with the eastern arm decoupled from the remaining part of the lake constituted by the northern and western arms (north-south west transect). This disjoined response is expected to enhance the water exchange between the northern and the western arm, with relevant consequences on the inter-basins water exchanges and on the distribution of chemical and biological species. In the north-south west transect the analysis of the low power signals in winter underlined a residual internal wave activity ascribed to the first vertical free mode of oscillation (V1H1). © 2014 Elsevier Ltd.

The internal wave-field of a Y-shaped lake (Lake Como, North Italy) was investigated over a 3-year long period applying wavelet time-frequency analysis to temperature and wind data time series, recorded at the edge of each of the three arms. The comparison with the results from a modal model allowed to identify the presence of both first and second vertical modes of oscillations. The field data analysis underlined a heterogeneous baroclinic response with the eastern arm decoupled from the remaining part of the lake constituted by the northern and western arms (north-south west transect). This disjoined response is expected to enhance the water exchange between the northern and the western arm, with relevant consequences on the inter-basins water exchanges and on the distribution of chemical and biological species. In the north-south west transect the analysis of the low power signals in winter underlined a residual internal wave activity ascribed to the first vertical free mode of oscillation (V1H1).