Methane emissions from cypress knees in a southeastern floodplain swamp.

Methane emissions were observed from knees of baldcypress (Taxodium distichum) in floodplain swamps of the Ogeechee river, a blackwater river in the lower coastal plain of Georgia, USA Emissions were sampled on 10 dates from March 1988 to September 1989, with small chambers placed over single knees. Methane emission rates from individual knees averaged 0.90 mg/d, corresponding to an average of 0.14 mg m-2 d-1 for the whole floodplain. In the habitat with the highest knee density (0.42 knees/m2), the average rate was 0.55 mg m-2 d-1. Spatial patterns in emissions from knees were similar to those of overall methane emissions from the swamp surface, though because of their low density were a minor contribution (0.42%) to total methane emissions from this system.