Question

why are bubbles from the bottom of the pond increase in volume when they reach the surface of water​

Answer 1

The pressure under a liquid surface varies with depth. As depth increases, pressure increases. Thus, when a bubble rises from below the surface it encounters less pressure. This causes the volume to increase and the bubble rises in size as it rises from a depth

Answer 2

This is called evaporation which confidences to form tiny water droplets and into air bubbles