Methane Emission from a Tropical Wetland in Ka'au Crater, O'ahu, Hawai'i

Abstract

Abstract: Natural tropical wetlands constitute an important but still poorly studied source of atmospheric methane, a powerful greenhouse gas. We measured net methane emission, soil profiles of methane generation and oxidation, and related environmental parameters in a tropical wetland occupying the Ka'au extinct volcanic crater on the Hawaiian island of O'ahu. The wetland has a fluctuating water table with dynamics that can be reproduced using precipitation data and a simple model. Median net methane flux was 117 mg m-2 day-1 and is consistent with measurements at other tropical sites. Net methane flux in the Commelina diffusa—dominated vegetation pattern (honohono) was significantly higher than that of the invasive Psidium cattleianum—dominated pattern (strawberry guava). Net methane emission in the honohono vegetation pattern was also significantly higher during the “wet” season compared with the “dry” season, although we did not find a clear correlation between net methane emission, water table level,...