  We use 3D hydrodynamic simulations of the long-term evolution of neutron star
merger ejecta to predict the light curves of electromagnetic transients that
are powered by the decay of freshly produced r-process nuclei. For the dynamic
ejecta that are launched by tidal and hydrodynamic interaction, we adopt grey
opacities of 10 cm$^2$/g, as suggested by recent studies. For our reference
case of a 1.3-1.4 $M_\odot$ merger, we find a broad IR peak 2-4 d after the
merger. The peak luminosity is $\approx 2\times 10^{40}$ erg/s for an average
orientation, but increased by up to a factor of 4 for more favourable binary
parameters and viewing angles. These signals are rather weak and hardly
detectable within the large error box (~100 deg$^2$) of a gravitational wave
trigger. A second electromagnetic transient results from neutrino-driven winds.
These winds produce `weak' r-process material with $50 < A < 130$ and abundance
patterns that vary substantially between different merger cases. For an adopted
opacity of 1 cm$^2$/g, the resulting transients peak in the UV/optical about 6
h after the merger with a luminosity of $\approx 10^{41}$ erg/s (for a wind of
0.01 $M_\odot$) These signals are marginally detectable in deep follow-up
searches (e.g. using Hypersuprime camera on Subaru). A subsequent detection of
the weaker but longer lasting IR signal would allow an identification of the
merger event. We briefly discuss the implications of our results to the recent
detection of an nIR transient accompanying GRB 130603B.
