Under-ice dynamics of dissolved oxygen from lake Tovel (Italy) based on high frequency data from three winters

In dimictic oligotrophic lakes, under-ice metabolism, dissolved oxygen (DO) dynamics and depletion are poorly understood. Here, we present high frequency (HF) data of under-ice DO dynamics measured at two depths (5 and 25 m) for three winters (January to March 2014, 2015, and 2016) in Lake Tovel, a small, montane lake (1178 m above sea level; area 38 ha; maximum depth 39 m). We assessed i) metabolic rates at a daily scale based on HF data for DO and light for winter 2016, and ii) DO depletion rates at a seasonal scale for all three winters. We applied different methods to estimate lake metabolism (i.e. book keep- ing and inverse modelling); in metabolic calculations, many days with low DO signals, zero light, and a nighttime DO increase had to be considered. We applied rigorous criteria of data management for lake metabolism calculations that resulted in many days with no metabolic rates. In agreement with its oligotrophic state and low dissolved organic car- bon content, Lake Tovel was net heterotrophic. At a seasonal scale, DO concentrations at 5 m declined in 2014, remained stable in 2015 and increased in 2016, and these differences were linked to radiatively driven convective mixing. We hypothesise that coupling physical processes with lake metabolism will bring new insights to DO dynamics in ice covered sys- tems.