Some reductions from a Lax integrable system and their Hamiltonian structures

A Lie algebra is constructed and an isospectral problem with eight potentials is designed. From which, corresponding hierarchy of nonlinear evolution equation is derived and the integrable couplings of AKNS, D-AKNS, TD, Levi, Li, Ma and Fan hierarchies are deduced, and they are integrable in sense of Liouville. For each reduction case the relevant Hamiltonian structure is established by means of quadratic-form identity.