Wetland Wednesday
October 7, 2020
One of the biggest challenges new wetland delineators face is how to sort through all of the hydric soil indicators. There about 100 of them and it is easy to get lost. To help you manage this we have developed a key system that gets you to the right indicators by asking a few focused questions.
To start, the user needs to understand how the indicators are arranged. They are grouped based upon particle size and component materials. The size classes have been identified by the USDA as sand, silt and clay. In addition there is non-texture related soil indicator grouping that can overlap with mineral soils as well as organic soils.
The “A” group is to be used for All Soils regardless of texture class. This group includes all of the organic soil indicators. However, there are some indicators that have nothing to do with the soil texture. An example of this is the hydrogen sulfide (A4) indicator. If you smell rotten eggs in the soil within 12 inches you pass this indicator.
The other “A” indicators mostly focus on the amount of organic matter in the soil. The more organic matter in the soil indicates a low level of decomposition that is usually due to a high amount of water at the surface. So the first question on our key is, “Do we have a lot of organic matter?”
The next question separates the sand from the loam soils. If there is a lot of sand, then you have the sand “S” indicators. If the soil is predominantly silt or clay, then we are looking at a “F” indicator.
The “S” indicators include factors that are related to high organic matter. They also have redoximorphic features like oxidized rhizospheres and gleyed matrix colors.
The “F” indicators are focused on your Munsell Soil Color Chart. Redox concentrations and depletions are key features of this group. There is also a major focus on the soil color value. There is a major divide between dark surface layers and the other colors. This is reflective of values less than or equal to 3.
There are some general ground rules for soil colors. In most cases the predominate color (matrix) should have a chroma less than or equal to 2. However, there are many exceptions to this. Most of these exceptions relate to the landform the soil is found in.
To start our key, begin with texture. Is it an A, S or F soil? Second, is the soil chroma less than or equal to 2? If not, are there landform exceptions? Finally, what is the soil color value? Is it greater than 3 or less than or equal to 3? This opens up those tricky dark surface layer indicators.
This month we are offering are hydric soil indicator webinar that includes a nice graphical key. You can find our more about this webinar here.