## 1 Introduction  
Of all types of inland surface waters, lakes are the most sensitive to eutrophication. Occupying the lowest place in the field, they are predisposed to capture nutrients and organic compounds flowing from catchment areas. Even in flow-through lakes, the hydraulic retention time resulting from horizontal water exchange is usually sufficient for lakes to have an advantage of accumulation of pollutants over their neutralization. These relationships have been described by the precursors of modern limnology since the middle of the last century [1, 2, 3], when lake ecosystems were called ephemerides on a geological scale. Despite the well-known causes of lake degradation, economic development in most countries intensifies anthropopressure on these ecosystems. The result is the ever-increasing problem of their eutrophication [4]. The main factors determining the rate of lake degradation are the supply of nutrients and the morphometric features of the lake basin. One of the most serious sources of eutrophication of surface waters is agriculture [5, 6, 7, 8]. The catchments, transformed by cultivation and breeding, become efficient suppliers of biogenic and organic matter to the lakes [9]. The rate of nutrient inflow depends on the hydrological situation in the catchment [10, 11]. The denser the river and drainage network, the faster pollutants reach water reservoirs. Non-flow lakes located in agricultural landscape resist degradation for the longest time. In lake districts with a temperate climate, deep lakes--thus stratified in summer--generally undergo eutrophication more slowly than shallow lakes. Due to the restriction of trophogenic processes to the surface layers (usually the epilimnion), they can withdraw some of the indigenous matter through sedimentation to the deeper layers of water. In this way, they reduce the symptoms of eutrophication as the growing season progresses. Shallow lakes, especially polymic ones, are characterized by greater dynamics of matter circulation and greater productivity. Nutrient resources deposited in the bottom layers and in the sediment are more accessible to primary producers [8]. The possibility of periodic retraction of matter to deeper water layers facilitates the self-purification of surface waters, but also affects the risk of deoxidation of the water. This leads to the activation of the phenomenon of \"internal supply\" of phosphorus and nitrogen mobilized from bottom sediments in conditions of reduced redox potential [8; 12; 13]. The impact of these processes on the ecosystem is so strong, it may negate the effect of protective measures taken in catchments and accelerate eutrophication, despite the elimination of external sources of pollution [14]. Therefore, the key goal of the restoration of water reservoirs is to improve the oxygen balance. One of the most commonly used restoration methods is artificial aeration [15; 16]. Artificial aeration is carried out in two ways: (I) with thermal destratification (complete mixing); and (II) without destruction of thermal layers (hypolimnion oxygenation). The first group of methods is aimed at eliminating the thermocline separating the warm waters of the epilimnion from the cold, stagnant layers of the hypolimnion, which consequently unifies the physical and chemical conditions in the entire water column. Destratification of water can be achieved by various methods, but the simplest and least energy-intensive is to discharge compressed air above the bottom in the deepest part of the lake. This method has been used in many lakes around the world [16]. The mechanism of destratification consists of repeated pushing of the bottom waters to the surface by compressed air bubbles. This, in turn, results in temperature equalization and mechanical mixing of the entire mass of water. Air is mainly a transport factor here--the effectiveness of oxygen diffusion into water during the rise of the generated air bubbles is estimated at only a few percent.