An explicit expression for the local power absorption density in a uniformly-magnetized slab plasma is derived from the Vlasov-Maxwell equations, taking into account density and temperature gradients. Using a transformation to Lagrangian coordinates, the kinetic flux of energy due to particle streaming can be separated in a suitable way from the actual power dissipation. Computations using this expression show how equilibrium gradients play a role in the modelling of low-frequency Alfven wave heating, and give a threshold below which the gradient effects are important in a medium-sized Tokamak.