Air normally moves through interconnected pores by forces such as changes in atmospheric pressure, the flushing action of rainwater, and by simple diffusion.
When this anaerobic environment continues for long periods during the growing season, quite different biological and chemical reactions begin to dominate, compared with aerobic soils.
[1] The plants found in hydric soils often have aerenchyma, internal spaces in stems and rhizomes, that allow atmospheric oxygen to be transported to the rooting zone.
This term is part of the legal definition of a wetland included in the United States Food Security Act of 1985 (P.L.
"[5] The NTCHS hydric soil definition is used by the U.S. Army Corps of Engineers and the Environmental Protection Agency in their joint responsibilities in the administration of Section 404 of the Clean Water Act (1972).