A combustor includes a combustion chamber having an outer liner and an inner liner and defining a first combustion zone, an annular dome coupled to the outer liner and the inner liner, and a trapped vortex cavity extending from at least one of the outer liner or the inner liner and defining a second combustion zone. A plurality of first mixing assemblies are disposed through the annular dome, and operably inject a first fuel-air mixture into the first combustion zone. A plurality of second mixing assemblies are disposed at the trapped vortex cavity, and operably inject a second fuel-air mixture into the second combustion zone defined in the trapped vortex cavity to produce combustion gases. A steam system includes a steam injector in fluid communication with the trapped vortex cavity. The steam injector operably injects steam into the trapped vortex cavity and the steam mixes with the combustion gases.