How are the careers of an oceanographer and hydrologist similar? how are they different?

In oceanography you study the marine life and ecosystems, and also ocean circulation along with tectonic plates. A hydrologist studies the volume and stream flow. But they are smialar because they both study the chemical property of the water. 

Oceanography is a branch of earth Science that studies the oceans, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries. 
Hydrology is the study of the movement, distribution, and quality of water throughout the Earth, including the hydrological cycle and water resources.