My question is whether semi-permanently submerged sites that are only intermittently exposed only during exceptionally dry years could be considered subaqueous by Soil Taxonomy (e.g. Wassents). Currently, such sites are mapped as undifferentiated ponded map units or as water. It would seem that Wassents and Wassists would have been logical replacements for such map units, but the truth is, some of these do dry out once in a while. It would be nice to have some taxonomic criteria to allow us to map these hydro regimes (besides a phase).
Taken literally, it appears that the keys only allow for a subaqueous site to be exposed for no more than a 3 hours on any given day every year, when in fact, some sites might not exposed at all for 24 hours a day, 365 days a year for all but a few exceptional years. Why does the standard allow periodic emergence with a periodicity of hours, but excludes a possible periodicity of years? Perhaps, the original intent is to exclude any establishment of emergent vegetation that cannot germinate under water?
As an example, in some areas of the humid eastern US we have annual plant communities occurring on sandy pondshores of sandy lake plains or coastal plains. But some species like Rhynchospora nitens (http://bonap.net/TDC/Image/Map?taxonType=Species&taxonId=9155&locationType=County&mapType=Normal; http://michiganflora.net/species.aspx?id=1138) seem to show up on exceptionally dry years when the bottoms of such lakes and ponds are exposed. Most years these lakes support a submergent community with species like Brasenia schreberi, while annuals like Rhynchospora nitens remain dormant as seeds on the bottom. Their ecological niche seems to depend on the exclusion of other emergent vegetation through a long term submersion. In southwest Michigan, they occur as wetter inclusions in Newton (acid wet sands) map units.
Greg J. Schmidt
Ecological Site Inventory Specialist
Natural Resources Conservation Service
3260 Eagle Park Dr. NE, Suite 104
Grand Rapids, MI 49525
cell - (517) 285-7911
e-mail - greg.schmidt@mi.usda.gov
Ecological Site Descriptions - https://esis.sc.egov.usda.gov/
