  We consider the moduli space of flat $SO(2n+1)$-connections (up to gauge
transformations) on a Riemann surface, with fixed holonomy around a marked
point. There are natural line bundles over this moduli space; we construct
geometric representatives for the Chern classes of these line bundles, and
prove that the ring generated by these Chern classes vanishes below the
dimension of the moduli space, generalising a conjecture of Newstead.
