  We investigate how nonlocal entanglement, as identified by violations of a
Bell inequality, may be protected during the evolution. Our system consists of
two qubits each embedded in a bosonic reservoir evolving independently and
initially in an entangled mixed state. We show that the violation of the Bell
inequality can be related to the single-qubit population of excited state in
such a way that, by appropriately choosing structured environments that give
rise to sufficiently high values of population trapping, long-time protection
of nonlocal entanglement can be correspondingly achieved.
