Abstract <p>The effect of the horizontal pressure gradient in inland water bodies (lakes and reservoirs) on the processes of formation of dissolved gas concentrations was studied. The calculation tools were a three-dimensional hydrostatic model and a one-dimensional model based on averaging three-dimensional equations over a horizontal section of a reservoir and supplemented with parameterization of the pressure gradient to account for gravitational oscillations (seiches). The results of the numerical experiments show that the use of parameterization is of fundamental importance for describing the formation of dissolved gas concentrations: the exclusion of the pressure gradient in the model yields results corresponding to the Kato–Phillips formulation and does not allow for correct reproduction of gas distribution in finite-sized reservoirs. Parameterization of the influence of the pressure gradient and horizontal diffusion in the one-dimensional LAKE model allows for sufficiently accurate reproduction of biogeochemical processes in accordance with the reference results obtained using the full three-dimensional model.</p>