When we incorporated the concept of subaqueous soils into Soil Taxonomy, the very short daily period of exposure to the atmosphere was, as you would expect, designed for the upper elevation limit in tidal settings along the coast. We were aware that some potential inland soils that could be considered subaqueous soils, have very long cycles (decades to centuries) where the surface water recedes and the soils are exposed to the atmosphere, possibly for years during the dry part of the cycle. A great example is Devil's Lake, in North Dakota. It was mapped many years ago as a regular terrestrial soil survey. At the time, no one knew it would become a lake due to natural processes. Since then the regional hydrology has changed and it is now a permanent lake. This is now known to be part of a very long term regional hydrological cycle. We didn't know how to handle this in Soil Taxonomy, so we simply didn't address it at the time we set up the Wassents and Wassists. A very challenging problem is how do you know when this kind of cycle is the case? Without special studies it isn't something easily discerned in the course of soil survey work. An important thing to consider as you think about the possibilities here is what soil genetic processes might be involved and how would they be expressed. It is my opinion that nearly all diagnostic horizons can not be formed in a truly subaqueous system. Without periods of drying you can't form the structure required for most diagnostic horizons and you can't illuviate material from one layer to another. So for example as we have currently defined the "Wass" suborders they are very simple, little developed soils (only Entisols and Histosols). It doesn't seem like diagnostic horizons such as mollic epipedons, argillic or spodic horizons, fragipans, etc. can form. But if you have special circumstances such as at Devil's lake, they have formed. There you have soils that formed terrestrially now drowned such as Mollisols and Alfisols. Another example can be seen in coastal areas where sea level has risen. I have personally observed soils in Florida salt marshes that once were terrestrial Spodosols, but now are permanently submerged. A special kind of paleosol. We currently have no provision in Soil Taxonomy to handle these kinds of situations. As more work is done to map and classify soils in the subaquatic environment, experience will hopefully lead to asking the right questions and finding solutions to these issues.
