  We study the effect of system reservoir coupling on currents flowing through
quantum junctions. We consider two simple double-quantum dot configurations
coupled to two external fermionic reservoirs and study the net current flowing
between the two reservoirs. The net current is partitioned into currents
carried by the eigenstates of the system and by the coherences between the
eigenstates induced due to coupling with the reservoirs. We find that current
carried by populations is always positive whereas current carried by coherences
are negative for large couplings. This results in a non-monotonic dependence of
the net current on the coupling strength. We find that in certain cases, the
net current can vanish at large couplings due to cancellation between currents
carried by the eigenstates and by the coherences. These results provide new
insights into the non-trivial role of system-reservoir couplings on electron
transport through quantum dot junctions. In the presence of weak coulomb
interactions, net current as a function of system reservoir coupling strength
shows similar trends as for the non-interacting case.
