Soil Cores

What can we learn from soil cores?

Soils and sediment can tell us a lot about the health of a wetland, including nutrient concentrations, average productivity, and flooding patterns. There’s a rich history in every soil sample that scientists can piece together if they know what to look for.

Soil cores are a method of collecting soils that allow the observer to get a vertical profile within a layer of sediment or soil. [1] Depending on the desired characteristic, cores can be a foot of material from the surface or they can be over 6 feet tall starting 20 feet below the surface. Each study using a core sample can tell a diverse story. For example, cores in coastal wetlands can be used at CRMS sites to measure accretion on top of marker horizons in an RSET-MH apparatus , in swamps to gauge the oxidation potential of soils, or in marsh to quantify the living root mass that provides structural integrity to platforms. Sediment types, decomposition, and bulk density can also be measured.

Knowing the quality of soils that you’re working with is important in planning for success in the restoration field. Poor soil quality will have lower success in repopulating native flora, as we discussed in our Wetland Wednesday post here. Soil cores lead us to a better understanding of processes that we may not be able to see and to predict the future of ecosystems. Soil testing is a crucial part of conservation and will be a vital tool in the fight to protect our coast.

 

Featured image from http://uwmyvatn.blogspot.com/2012/07/the-grass-is-always-greenerin-midge.html

[1] https://kb.osu.edu/bitstream/handle/1811/513/1/(98)%202.11%20Soils.pdf

Stress Part II: Flooding and Hypoxia

Wetland inhabitants must also deal with flooding stress. All parts of a plant must have oxygen, which causes problems when a plant is rooted in hypoxic soils and it is flooded. Gases diffuse about 10,000 times more slowly through water than through air, and wetland soils are often inundated and hypoxic. This poses an issue for supplying roots with enough oxygen since they don’t have any around them. Some root systems will have adventitious roots, which means they extend above the surface of the water or soil to allow gas exchange with the atmosphere.[1] Red mangroves have prop roots, black mangroves have pneumatophores, and both supply oxygen directly to the root system rather than relying on transport all the way from the leaves to the roots.[2]

Hypoxia can be caused by eutrophication and decomposition. Hypoxia and anoxia are dangerous to most plants and animals because most cannot live only with anaerobic (without oxygen) respiration. Bacteria can sometimes live in anoxic conditions by using different electron receptors that are more plentiful in wetland soils like sulfates. Plants can sometimes cope with hypoxia thanks to adaptations like aerenchyma development in their roots. Aerenchymous tissues are much more porous to allow gases to diffuse up to 30 times more easily through a plant! In animals, lungs can allow some fish, mammals, and aquatic gastropods (snails) to live in hypoxic waters, but many fish have gills that are not adapted to hypoxia. The Gulf of Mexico along Louisiana’s coast boasts one of the largest hypoxic zones in the world with a peak area of over 8,500 square miles in 2017, where many commercial fisheries have seen a large decline in fish catch. [3]

Photo from NOAA, Dead Zone 2017

Works Cited:

[1] Gilman, Sharon. “Plant Adaptations.” ci.coastal.edu/~sgilman/778Plants.htm.

[2] “Adaptations.” Adaptations :: Florida Museum of Natural History, http://www.floridamuseum.ufl.edu/southflorida/habitats/mangroves/adaptations/.

[3] “Gulf of Mexico ‘Dead Zone’ Is the Largest Ever Measured.” Gulf of Mexico ‘Dead Zone’ Is the Largest Ever Measured | National Oceanic and Atmospheric Administration, web.archive.org/web/20170802173757/http:/www.noaa.gov/media-release/gulf-of-mexico-dead-zone-is-largest-ever-measured.

Featured image is of Rhizophora mangle (red mangrove) from Flickr by barloventomagico

Salinity Stress and Tolerance

Living in any habitat comes with hurdles that make it harder for plants and animals to thrive. We call these hurdles “stress”. Coastal wetlands demonstrate several kinds of stresses to both plants and animals. Through many years of evolution, plants and animals have adapted to living with these stresses, also called being “stress tolerant”. Adaptations can be in physical structure changes or on the smaller scale (cellular). Some stresses that come with living in coastal wetlands include salinity (the amount of salt or ions in the water), inundation (flooding at least above the ground, sometimes even higher than the whole plant), and hypoxia (low dissolved oxygen in the water). [1]

Salt water intrusion has been increased by dredging navigation channels among other impacts. Saltwater intrusion makes fresh bodies of water more saline than they usually are. The problem with this is that the plants that live in such places are adapted to live in fresh water and generally cannot deal with increases in salinity more than 1 or 2 parts per thousand (ppt). For reference, the Gulf of Mexico’s average salinity is approximately 36ppt. Some plants, though, can live in full-strength sea water. For example, the black mangrove (Avicennia germinans) has several adaptations that let it keep its cells safe from high salinity. Like smooth cordgrass (Spartina alterniflora), black mangroves excrete salt onto their leaves to get it out of their systems.[2] Some fish have similar adaptations in their gills that allow them to keep their internal salt concentrations at safe levels.

Salt Crystals accumulate on A. germinans leaves (Photo by Ulf Mehlig, found on Wikimedia Commons)

 

Works Cited:

[1] Bradford, Nick. “Stressed Wetlands.” NEEF, 10 May 2016, http://www.neefusa.org/nature/land/stressed-wetlands.

[2] Gilman, Sharon. “Plant Adaptations.” ci.coastal.edu/~sgilman/778Plants.htm.

Featured image is of A. germinans from Wikimedia commons, courtesy of Judy Gallagher