  We are concerned with the isentropic compressible Navier-Stokes system in the
two-dimensional torus, with rough data and vacuum : the initial velocity is in
the Sobolev space H^1 and the initial density is only bounded and nonnegative.
Arbitrary regions of vacuum are admissible, and no compatibility condition is
required. Under these assumptions and for large enough bulk viscosity, global
solutions have been constructed in [7]. The main goal of the paper is to
establish that these solutions converge exponentially fast to a constant state,
and to specify the convergence rate in terms of the viscosity coefficients. We
also prove exponential decay estimates for the solutions to the inhomogeneous
incompressible Navier-Stokes equations. This latter result extends to the torus
case the recent paper [9] dedicated to this system in smooth bounded domains.
