The large-distance dynamics in quarkonium systems is investigated, in the large-Nc limit, through the saturation of Wilson loop averages by minimal surfaces. Using a representation for the quark propagator in the presence of the external gluon field based

Flavor singlet and non-singlet axial Ward identities are investigated using the Wilson formulation of lattice QCD with Clover O(a)-improvement, which breaks explicitly chiral symmetry. The matching at one-loop order of all the relevant renormalization constants with the continuum MS scheme is presented. Our calculations include: (1) the contributions arising from the Clover term of the action; (2) the complete mixing of the gluon operator GG with the divergence of the singlet axial current; (3) the use of both local and extended definitions of the fermionic bilinear operators. A definition of the gluon operator GG on the lattice outside the chiral limit is proposed. Our definition takes into account the possible power-divergent mixing with the pseudoscalar density, generated by the breaking of chiral symmetry. A non-perturbative procedure for the evaluation of such mixing constant is worked out. Finally, the renormalization properties of the composite insertion of the topological charge operator ∫d4x GG(x) relevant for the lattice calculation of the neutron electric dipole moment, induced by the strong CP-violating term of the QCD Lagrangian, are discussed.