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Scientists Study Subaqueous Soils
August 30, 2019

The study of underwater soils – or subaqueous soils – is a fairly new field. Prior to the late 1990s, soil that was under water was commonly considered to be little more than accumulated sediment from upland runoff. However, as soil scientists began to study this emerging area further, they realized that underwater soils share many characteristics with soils on land. By 1998, a subaqueous soil survey had begun and subaqueous soils were officially a field of study.

Now, according to information provided by the Soil Science Society of America, research led by Barret Wessel, Ph.D., a soil scientist at the University of Maryland (UMD), is investigating the use of subaqueous soils as the basis for aquaculture in support of rural coastline communities.

Subaqueous soils are soils that are permanently under water. They are typically under only a few meters of water, but deeper areas are being explored as well. They contribute to healthy ecosystems in marshes and estuaries, as well as tidal basins and coastal areas.

According to Dr. Wessel, some underwater soils were originally formed in upland environments. They were later “drowned” by rising sea levels, preserving bright colors and structure in the soil profile. Others formed under water in sediments. With the accumulation of organic matter and minerals like pyrite, they became soils. Whatever the manner of their creation, it is important to understand how subaqueous soils change across submerged landscapes. This understanding can lead to best management practices. Ordinary upland soils are mapped and ranked in terms of their suitability to support food crops. Dr. Wessel’s lab at the University of Maryland is developing similar interpretations for subaqueous soils and how they can support oysters and other shellfish “crops” in the Chesapeake Bay.

As can be easily imagined, gathering soil samples for subaqueous soil research presents more challenges than their more dry counterparts. The researchers have been able to adapt a tool usually used in concrete construction to assist with gathering these samples. A concrete vibrator, intended to shake the bubbles out of freshly poured concrete, has been modified to allow the “vibracore” to shake aluminum core tubes so vigorously that they slide into the squishy seafloor. With a tripod and the right boat, they can be pulled out with intact soil samples inside.

Once the soil samples are acquired, testing is done to determine what is going on in the soil and ways to manage the area. Testing includes some tactile aspects such as estimating fluidity of subaqueous soils by squeezing handfuls and rating how easily they flow through your fingers, or smelling the samples to determine if hydrogen sulfide or petroleum odors are present. This “smell test” can reveal how the sulfur cycle is operating in these soils, or if they have been contaminated by chemical spills.

Dr. Wessel emphasizes that the study of subaqueous soils is a vitally important part of the new Coastal Zone Soil Survey. Historically, soil surveyors weren’t very interested in marsh soils, and consequently the soil maps along both the submerged and the exposed sides of our coasts often convey very little useful information. Map units were often described simply as “Tidal marsh, soft” or “Water.” At the time these surveys were made this description was sufficient, but now that climate change threatens our coastlines and our agricultural systems it is clear we need more information.

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