Physical and Chemical Characteristics of Bottom Soil Profiles in Ponds at Auburn, Alabama, USA and a Proposed System for Describing Pond Soil Horizons

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Abstract
Soil cores were taken from each of three, 2‐, 23‐, and 52‐yr‐old research ponds (650–1,010 m2area) at Auburn, Alabama. Many physical and chemical variables changed in intensity with increasing depth in cores. Compared to original compacted pond soil, sediment contained more moisture; had lower bulk density (3); possessed higher percentages of silt and clay; had greater porosity, specific surface area, and cation exchange capacity; and contained greater concentrations of organic matter and nutrients. Sediment organic matter was highly decomposed as evidenced by low proportions (5–15%) of carbon and nitrogen associated with the light fraction (soil retained on a 53‐μm sieve). Sediment depth at 100‐cm water depth increased with pond age (11.7 cm, 28.3 cm, and 48.3 cm in 2‐, 23‐, and 52‐yr‐old ponds, respectively), but sediment composition did not change greatly over time. Successive layers in cores were as follows: 1) water near the soil‐water interface with a high concentration of solids; 2) high moisture content sediment with dry bulk density 3; 3) lower moisture content sediment with bulk density between 0.3 and 0.5–0.7 g/cm3; 4) rapid transition of bulk density from 0.5–0.7 g/cm3to 1.4 g/cm3; 5) original compacted soil with bulk density of 1.4–1.7 g/cm3. We propose that these five layers be referred to as F (flocculent layer), S (stirred or mixed sediment), M (mature, bulk, un‐mixed sediment), T (transitional layer), and P (original, undisturbed pond bottom) horizons, respectively. Superficial, oxidized sediment is termed an Sohorizon, and the reduced part of the S horizon is termed an Srhorizon. The upper part of the T horizon is an MT horizon when it is similar to the M horizon, or a FT horizon when it resembles the P horizon. A system for delineating horizons in pond soil profiles will be valuable in future attempts to classify pond soils.