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Processes described above result in sediment forming distinct layers with respect to bulk density (weight of soil per unit
volume, usually given in grams dry soil per cubic centimeter)(Figure 2), organic matter concentration (Figure 3), and color.
A core taken through the sediment and extending into the original bottom soil is called a profile. Layers in the profile are
known as horizons. Munsiri et al. (1995) described these horizons and assigned letters to them to facilitate discussion
(Figure 4). For practical purposes, the F and S horizons are most important in aquaculture because they exchange substances
with overlaying water to influence water quality (Munsiri et al., 1995; Boyd, 1995). Research conducted in ponds at PD/A CRSP sites and vicinity has demonstrated that aquaculture ponds typically develop profiles shown in Figure 4 and attain equilibrium concentrations of soil organic matter within a few years. A procedure for classifying pond soil based on the characteristics of horizons has been formulated (Boyd et al., 2002), but pond soil classification is beyond the scope of this report.
The word soil is used for the weathered surface layer of the earth’s crust in which plants grow, various animals burrow,
and humans have frequent contact. Sediment is used to refer to geological material that has been suspended and transported by water to another place where it settles from the water and forms a deposit. In many places, the soil was formed by sedimentation. All aquaculture pond bottoms become covered with sediment, and this sediment can be considered an aquaculture pond soil. In describing various physical, chemical, and biological processes occurring in the pond bottom, it is convenient to refer to bottom deposits as sediment. However, in the discussion of management of pond bottoms, we usually will refer to the sediment layers in the bottom of an aquaculture pond as pond soil.
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