| Title | Hypolimnetic oxygen depletion in a deep oligomictic lake under climate change |
| Abstract | Dissolved oxygen (DO) concentration is a fundamental metric to describe climate-related alterations in deep lakes. Increasing water temperatures enhance thermal stratifcation, leading in temperate basins to a growing isolation of deep waters.
This leads to the depletion of hypolimnetic DO, which adds up to limited nutrient circulation and restricted replenishment
of the trophogenic layers. With vanishing convective mixing, it is commonly believed that the only source of hypolimnetic
DO replenishment will be represented by deep intrusions of cold oxygenated waters from the tributaries. In this study, we
frst analyse the 1993-2020 long-term observed trends of DO concentrations in the subalpine deep oligomictic Lake Maggiore (Italy/Switzerland). Then, through an algorithm calculating daily intrusion depths and mass discharges of DO for the
major tributaries, we show that deep insertions are suppressed for increasing winter water temperatures and residual thermal
stratifcation. Turbulent entrainment is proved fundamental for DO replenishment, leading to mass discharges of DO released
into the deep hypolimnion up to more than two orders of magnitude larger than the original ones from the tributaries. Last,
we discuss the results of simulations made through a one-dimensional coupled ecological-hydrodynamic model about the
possible efects of a full turnover on DO concentrations in the deep hypolimnion. Two cases are displayed, with the turnover
taking place either now or with an anoxic hypolimnion deriving from decades of isolation due to severe climate warming.
Through this study, climate warming is shown to be a fundamental driver of DO in Lake Maggiore, its depletion harming
both water quality and the ecosystem. |
| Source | Aquatic sciences (Electron. ed.) |
| Keywords | Oxygen replenishment · Oxygen dynamics · River intrusion · Turbulent entrainment · Lake modelling · Complete mixing |
| Journal | Aquatic sciences (Electron. ed.) |
| Editor | Birkhäuser, Basel, Svizzera |
| Year | 2022 |
| Type | Articolo in rivista |
| DOI | 10.1007/s00027-022-00902-2 |
| Authors | Claudia Dresti, Michela Rogora, Andrea Fenocchi |
| Text | 472516 2022 10.1007/s00027 022 00902 2 Oxygen replenishment · Oxygen dynamics · River intrusion · Turbulent entrainment · Lake modelling · Complete mixing Hypolimnetic oxygen depletion in a deep oligomictic lake under climate change Claudia Dresti, Michela Rogora, Andrea Fenocchi National Research Council of Italy, Water Research Institute CNR IRSA , Largo Tonolli 50, 28922 Verbania, Italy National Research Council of Italy, Water Research Institute CNR IRSA , Largo Tonolli 50, 28922 Verbania, Italy Department of Civil Engineering and Architecture, University of Pavia, Via Ferrata 3, 27100 Pavia, Italy Dissolved oxygen DO concentration is a fundamental metric to describe climate related alterations in deep lakes. Increasing water temperatures enhance thermal stratifcation, leading in temperate basins to a growing isolation of deep waters. This leads to the depletion of hypolimnetic DO, which adds up to limited nutrient circulation and restricted replenishment of the trophogenic layers. With vanishing convective mixing, it is commonly believed that the only source of hypolimnetic DO replenishment will be represented by deep intrusions of cold oxygenated waters from the tributaries. In this study, we frst analyse the 1993 2020 long term observed trends of DO concentrations in the subalpine deep oligomictic Lake Maggiore Italy/Switzerland . Then, through an algorithm calculating daily intrusion depths and mass discharges of DO for the major tributaries, we show that deep insertions are suppressed for increasing winter water temperatures and residual thermal stratifcation. Turbulent entrainment is proved fundamental for DO replenishment, leading to mass discharges of DO released into the deep hypolimnion up to more than two orders of magnitude larger than the original ones from the tributaries. Last, we discuss the results of simulations made through a one dimensional coupled ecological hydrodynamic model about the possible efects of a full turnover on DO concentrations in the deep hypolimnion. Two cases are displayed, with the turnover taking place either now or with an anoxic hypolimnion deriving from decades of isolation due to severe climate warming. Through this study, climate warming is shown to be a fundamental driver of DO in Lake Maggiore, its depletion harming both water quality and the ecosystem. Published version Dresti et al. 2022 Dresti et al 2022.pdf Articolo in rivista Birkhauser 1420 9055 Aquatic sciences Electron. ed. Aquatic sciences Electron. ed. Aquat. sci. Electron. ed. Aquatic sciences. Electron. ed. AS Electron. ed. michela.rogora ROGORA MICHELA claudia.dresti DRESTI CLAUDIA |
