Summary of the Article on Phase Change in Lakes, Snow, and Soil:

### Phase Change Processes

The article describes the process of phase change in the lake, snow, and soil, which is similar to the approach used for vegetated land units (Chapter 2.6). The key aspects are:

#### Melting
- If the temperature is below freezing and liquid water remains, or if the temperature is above freezing and ice remains, phase change can occur.
- The available energy for melting, Q_avail, is calculated based on the temperature difference and the heat capacity.
- The mass of melt, M, is the minimum of the available ice mass and the energy available for melting divided by the latent heat of fusion.
- The remaining heat, Q_rem, is used to adjust the layer temperature.

#### Freezing
- The available energy for freezing, Q_avail, is negative.
- The mass of freezing, M, is the maximum of the negative of the liquid water mass and the available energy divided by the latent heat of fusion.
- The remaining heat, Q_rem, is used to adjust the layer temperature.

#### Snow over Unfrozen Lake
- If there is snow water, W_sno, over an unfrozen top lake layer, the available energy in the top lake layer is used to melt the snow.
- The snow thickness is adjusted downwards proportionally to the amount of melt, maintaining a constant density.

The article provides the detailed equations and calculations for these phase change processes in the lake, snow, and soil layers.