If you’re looking to buy land to build or grow crops, you know that soil is an incredibly important factor, and today we’re going to talk about one specific type of soil: hydric soil.
These are soils that develop under sufficiently wet environments.
They support the growth and regeneration of vegetation that are adapted to grow in water or wet conditions.
Most often, hydric soils exist in wetlands, which are highly important parts of our ecosystem.
Keep reading to learn more!
1. What is hydric soil?
The National Technical Committee for Hydric Soils defines hydric soil as:
“soils that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part.”
In other words, soil that is frequently flooded or ponded for a long duration (longer than 7 days) during the growing season is hydric soil.
In addition, anaerobic conditions must exist.
2. What does this mean exactly?
If the above definition is confusing, let’s break down the key components.
“that formed under” – there are drained hydric soils, and this phrasing indicates that the presence of drainage systems does not alter the status of hydric soil.
“saturation, flooding, and ponding” – tells us that there are three environments that produce hydric soils.
Saturated conditions occur when there is a high water table.
Flooded conditions are found in areas where overflowing streams, high tides and runoff consistently inundate the soil.
Ponded conditions are produced in enclosed environments when the water inflow is higher than the outflow.
“during the growing season” – this phrasing is applied differently for different applications.
We will discuss this in more detail later.
“develop anaerobic conditions” – this means that the soil must lack oxygen for sufficient time to support water-loving plants.
“in the upper part” – tells us that most of the biological activity in the soil must occur near the soil surface.
When this happens, only a short period of wetness is needed to use up all of the oxygen and create anaerobic conditions.
3. What’s the purpose of hydric soil?
There are numerous agricultural and nonagricultural applications of hydric soil analyses.
Assistance in land-use planning
Assessment of potential wildlife habitat
However, of perhaps greater importance to land buyers, hydric soils are often an indicator that wetlands are present.
Since there are laws that protect wetlands and restrict building on them, you will want to know whether they are on your property.
4. What are the field indicators of hydric soils?
Field indicators are an efficient on-site means of confirming the presence of hydric soil.
They are designed to identify soil that meets the hydric soil definition without further data collection.
These indicators are listed in the “Field Indicators of Hydric Soils in the United States,” which was written by the USDA National Resources Conservation Service soil survey staff.
This is the sole approved source document for hydric soil identification and delineation by the Natural Resources Conservation Service, US Army Corps of Engineers, Environmental Protection Agency, and US Fish and Wildlife Service.
The indicators provide us a method to prove or disprove the presence of hydric soil based on something felt, seen, or smelled and not estimated or guessed.
Indicators are based on biogeochemical processes that occur when soil is saturated or inundated.
These field indicators are essential for hydric soil identification.
5. What are biogeochemical processes?
Biogeochemical processes are processes that alter soil due to the interaction of its chemical composition and the animal/plant life it supports.
Hydric soil indicators are based on several biogeochemical processes that occur when soils are saturated or inundated.
Here are some examples:
Twelve indicators are based on iron reduction, transformation, and differential accumulation.
These include A13, A14, A15, S4, S5, F2, F3, F8, F9, F18, F19, and F20.
Nineteen indicators are based on carbon accumulation and differential decomposition.
These include A1, A2, A3, A5, A6, A7, A8, A9, A10, S1, S2, S3, S7, S8, S9, F1, F11, F13, and F17.
Carbon and Iron
Four different indicators are based on carbon accumulation and differential decomposition and iron reduction, translocation, and differential accumulation.
These include A11, A12, F6, and F7.
Carbon and/or Iron
One indicator is based on carbon accumulation and differential decomposition and/or iron reduction, translocation, and differential accumulation. It is S6.
Carbon and Iron/Manganese
One indicator is based on carbon accumulation and differential decomposition and iron/manganese reduction, translocation, and differential accumulation. It is F16.
One indicator is based on iron/manganese reduction, transformation, and differential accumulation. It is F12.
One indicator is based on sulfur reduction. It is A4.
One indicator is based on the precipitation of calcium carbonate by algae. It is F10.
6. What are some examples of field indicators?
Is this a bit too technical for you?
Don’t worry, some field indicators used to identify the above biogeochemical processes are more straightforward.
A few example indicators are as follows:
Presence of organic soils
A layer of “muck” that is saturated for 30 consecutive days during the growing season.
Sulfidic material on site
The presence of hydrogen sulfide, which produces a distinctive rotten eggs smell.
A Munsell Soil Color book can be used to classify hydric soils based on the soil color.
Soils that are gray, or bluish to greenish-gray are indicators of anaerobic conditions.
Soil listed on the National, State or County hydric soils list
If the soil is listed on a hydric soils list, it’s a good indication that it is hydric.
Iron or manganese concretions
These are concentrations of chemical compounds produced by biochemical processes that are near the surface of the soil.
Such compounds can look like rust, are often gray or dull orange, and can be easily broken apart.
7. How do you determine what the growing season is?
As we saw above, to identify hydric soil, you must use “during growing season” data.
The growing season is the portion of the year when soil temperatures are above biologic zero (5 degrees Celsius or 41 degrees Fahrenheit) at 50 cm (19.7 inches).
The following growth season months are assumed for each of the actual mean annual soil temperatures and soil temperature regimes of Soil Taxonomy.
No permafrost and
22 degrees Celsius or higher Isohyperthermic: January to December
22 degrees Celsius or higher Hyperthermic: February to December
15 to 22 degrees Celsius Isothermic: January to December
15 to 22 degrees Celsius Thermic: February to October
8 to 15 degrees Celsius Isomesic: January to December
8 to 15 degrees Celsius Mesic: March to October
Lower than 8 degrees Celsius Frigid: May to September
Lower than 8 degrees Celsius Isofrigid: May to September
Soil Taxonomy Requirements Cryic: May to August
-10 degrees Celsius or lower Hypergelic: July to August
-4 to -10 degrees Celsius Pergelic: July to August
+1 to -4 degrees Celsius Subgelic: July to August
8. What is the hydric soil list?
These lists were created by the National Technical Committee for Hydric Soils using the NASIS (National Soil Information Systems) database selection criteria.
This database shows map units that meet the criteria for hydric soils.
Note: map units are characterized by soil types that generally make up at least 20% of the unit area.
The database has a number of agricultural and nonagricultural applications.
Some of these applications include assistance with and/or land-use planning, conservation planning, and assessment of potential wildlife habitats.
The national list of hydric soils is maintained in a computer file and updated yearly.
Hydric soil lists are created by soil scientists based on local experience and knowledge.
However, just because the soil is present on a list doesn’t mean that the soil is, in fact, hydric.
It is only an interpretive rating, which bases its information on published soil surveys and other estimated soil properties.
9. Why are hydric soils important?
The environmental conditions that help to create hydric soils also favor the formation of wetlands.
Wetlands play an important role in the environment overall.
While they sometimes serve as a barrier for humans, they’re critical habitat for rare and endangered species of flora and fauna.
They also occur at relatively low elevations, which means they can help to filter out polluted waters that run into them.
They’ll retain excessive nutrients and serve as a vital ecosystem.
Wetlands can also be used for valuable recreation space.
From nature appreciation and hunting to fishing and canoeing, wetlands are now protected in the United States as a means of conserving and rehabilitating these spaces.
Overall, hydric soil and wetlands go hand in hand.
In fact, it is one of three required indicators for wetland identification.
In order for an area to be defined as a wetland, it must have hydrophytic vegetation, hydric soils, and wetland hydrology according to the Corps of Engineers Wetlands Delineation Manual and the National Food Security Act Manual.
10. Why must you be aware of hydric soils when purchasing land?
If you purchase land to build, develop, or grow crops, then you must be aware of where the hydric soils are.
These soils do not have enough oxygen.
While you may be able to grow cattails, sedges, and water lilies, you won’t be able to farm or use the land as you otherwise intend.
By identifying hydric soil in advance, you can avoid potentially costly mistakes.
In addition, both the federal government and states are highly protective of streams, wetlands, and wet soils.
There are a number of regulations that limit and otherwise restrict development on wetlands, which you must be aware of as a land buyer.
You can read more about building on wetlands in our blog posts on building on wetlands and wetland mitigation.
Hydric soils are an important component of wetlands, a distinct and protected ecosystem.
If you’re looking at land that has wetlands, then this is a critical element that you should be aware of.
You must know how to treat hydric soil properly or consider alternative land to purchase.
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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.
4 thoughts on “What is Hydric Soil? 10 Things (2023) You Should Know”
I have a question we are looking at buying a home and recently learned of hydric soil on the property. Is there any reason we shouldn’t buy this home. We will not be farming on the property.
Hell Debbie, are there federal or state-designated wetlands on the property? If so, you will want to be very careful since there are a lot of regulations in place that protect wetlands. If not and you want to build on the property, you may still want to speak with a geotechnical engineer to see what implications the hydric soil may have for the building’s foundation.
Thank you for responding so quickly but the home we are looking at was built in 2008 on that land so we won’t be building. Are there any other concerns we should have, i.e., sulfur odors, damage to the home because of the soil? Or flooding? If there is an odor is will it come into the house? The home has stones along the driveway and I’m wondering if that is where the hydric soil is? Any reason we should be concerned about putting in an offer on this home.
Hello Deborah, I would recommend having an engineer take a look at the property. I can’t really speak about the odor since this is going to vary from site to site (you may want to ask the current owner), but my understanding is that the primary concern with hydric (or wet soils in general) would be settlement and flooding. Since the home was built recently, it’s possible that precautions were taken to mitigate these concerns, but this is why it would be a good idea to have an inspector or engineer look at the property.