The Wetland Word: Hydric Soil 

Definition:

Soil is more than just a substrate we walk on; it supports life. It provides essential nutrients, plays an important role in carbon and nitrogen cycles, and is home to a multitude of organisms that help decompose organic matter. When soil has been saturated by water, seasonally or year-round like those in wetland habitats, resulting in anaerobic, or low-oxygen, conditions, it is considered hydric. 

Etymology: 

The word “hydro” comes from Ancient Greek ὑδρο- (meaning hudro-) and ὕδωρ (meaning húdōr, or water). The suffix “-ic” arises from Middle English, Anglo-French, and Latin, meaning “one having the character or nature of.” 

“Soil” comes from Anglo-French, but might represent Latin’s solium, which means “seat” or solum, which means “ground.” 

Use/Significance in the Earth Science Community: 

Generally speaking, three characteristics are used to identify a wetland: 

1. Presence of water in or above the soil 

1. Hydric soil 

1. Hydrophytic vegetation 

In wetlands, hydric soil supports the growth and regeneration of vegetation that has adapted to grow in saturated/inundated and low-oxygen conditions. Oftentimes the soil can be used to help identify a wetland type for purposes like wetland delineation. Scientists can study soil to better understand wetland ecosystems and help inform management of these systems, both for conservation and restoration purposes. 

U.S. Geological Survey Use: 

The wetlands lining the coast of Louisiana are home to important fish and wildlife species, protect shorelines from erosion and storm surge, and filter contaminants from the water. However, Louisiana has experienced the greatest coastal wetland loss of any other state in the continental U.S. Federal and state-funded restoration projects are underway to restore hydrologic conditions and rebuild wetlands, and scientists at the USGS Wetland and Aquatic Research Center play a key role in monitoring these projects and providing the information needed to ensure long-term restoration success.  

To do this, USGS scientists conduct vegetation plot surveys and soil measurements at field sites across Louisiana to help assess ecosystem condition. Porewater, or the water found within the pores of the soil, is measured for salinity, temperature, and conductivity to capture water conditions within the soil. They also measure wetland processes that influence marsh condition using tools like soil cores and Rod Surface Elevation Tables, or RSETs. Soil cores capture a vertical profile of the sediment and provide insight into processes affecting land change in the wetland ecosystems. USGS scientists add a layer of white clay over a patch of soil; months later, they insert a copper tube into the ground and use liquid nitrogen to freeze the soil around the outside of the tube. Scientists can then measure how much soil has been added above the white clay layer over time, which helps measure the rate of soil accretion in coastal wetlands. 

For more information on wetland science at the USGS Wetland and Aquatic Research Center, please visit: https://www.usgs.gov/centers/wetland-and-aquatic-research-center-warc/science-topics/wetlands