The ionic effects on the dynamics and conformation of DNA in silt-like confinement are investigated. Confined lambda-DNA is considered as a model polyelectrolyte, and its longest relaxation time, diffusivity, and size are measured at a physiological ionic strength between 1.7-170 mM. DNA properties change drastically in response to the varying ionic environment, and these changes can be explained by blob theory with an electrostatically mediated effective diameter and persistence length. In the ionic range we investigate, the effective diameter of DNA that represents the electrostatic repulsion between remote segments is found to be the main driving force for the observed change in DNA properties. Our results are useful for understanding the manipulation of biomolecules in nanofluidic devices.