John Melack researches ecological processes in lakes, wetlands and streams, as well as the hydrology and biogeochemistry of catchments. His research combines state-of-the-art measurements, modeling, experiments and remote sensing and examines ecological processes.

He has conducted studies in eastern Africa, tropical South America, Japan, Australia and the United States. His work in the Amazon basin spans more than 40 years, with a current focus on changes in floodplain lakes and the release of methane from wetlands. In California, Melack has spent decades investigating the saline Mono Lake and high-elevation lakes in the Sierra Nevada. He is also involved in an LTER examining linkages among coastal watersheds, near-shore kelp ecosystems and offshore waters in Santa Barbara Channel.