  We solve for the evolution of the vertical extent of the convective region of
a neutron star atmosphere during a Type I X-ray burst. The convective region is
well-mixed with ashes of nuclear burning and its extent determines the rise
time of the burst light curve. Using a full nuclear reaction network, we show
that the maximum vertical extent of the convective region during photospheric
radius expansion (RE) bursts can be sufficiently great that: (1) some ashes of
burning are ejected by the radiation driven wind during the RE phase and, (2)
some ashes of burning are exposed at the neutron star surface following the RE
phase. We find that ashes with mass number A ~ 30 - 60 are mixed in with the
ejected material. We calculate the expected column density of ejected and
surface ashes in hydrogen-like states and determine the equivalent widths of
the resulting photoionization edges from both the wind and neutron star
surface. We find that these can exceed 100 eV and are potentially detectable. A
detection would probe the nuclear burning processes and might enable a
measurement of the neutron star gravitational redshift. In addition, we find
that in bursts with pure helium burning layers, protons from (alpha, p)
reactions cause a rapid onset of the 12C(p, gamma)13N(alpha, p)16O reaction
sequence. The sequence bypasses the relatively slow 12C(alpha, gamma)16O
reaction and leads to a sudden surge in energy production that is directly
observable as a rapid (~ ms) increase in flux during burst rise.
