Leaching Aboveground

When soil contaminated by organic chemicals has been excavated for aboveground washing, the procedure involves both physical and chemical processes to achieve solid and liquid separation. The first stage involves separation of large particles by 

Throughout the process, water, surfactant, and NAPL are recovered (as much as possible) for reuse and/or recycling. Many of the aboveground leaching facilities are essentially closed-loop systems. In most cases, the resulting clean soil can be used for backfill, landscaping, or similar purposes. 

---

Any variety of configurations of injection wells, horizontal wells, trenches, infiltration galleries, aboveground sprayers or leach fields, and extraction wells, open ditches, or subsurface collection... 

Soil washing involves the leaching of contaminants by the flushing of water through the contaminated soil. Soil washing can be accomplished either in place or aboveground as discussed below. 

Fig. 7.1 Total nutrient stocks and in plant biomass plus soil in rain forest, newly planted Pinus caribaea (6 months old), P. caribaea, and Gmelina arborea plantations at the end of the first rotation (9.5 and 8.5 years old, respectively), and second rotation P. caribaea (1.5 years old) at Jari (Sanchez et al. 1985). H = harvest loss from trees taken when clearing the rain forest for the plantations L = leaching. Total nutrient stock is defined as the sum of all the nutrients in plant biomass (aboveground, litter, detritus, roots) plus total N, available P (extracted by the Mehlich method), and exchangeable K, Ca, and Mg in the top meter of the soil.

Mass balance and isotopic tracer approaches have been used to quantify N fluxes associated with marsh plant growth and death. One study in a very productive, medium form of S. alterniflora from a Georgia salt marsh shows that total uptake of N by roots of S. alterniflora was 34.8 g N m year. Of this 43% was lost by death or leaching from aboveground plant parts, while the rest was lost by death of roots and rhizomes. Total transfer of N from below-to aboveground tissues was 33 g N m ... 

Figure 2 Conceptual model of carbon cycling in the litter-soil system. In each horizon or depth increment, SOM is represented by three pools labile SOM, slow SOM, and passive SOM. Inputs include aboveground litterfall and belowground root turnover and exudates, which will be distributed among the pools based on the biochemical nature of the material. Outputs from each pool include mineralization to CO2 (dashed lines), humification (labile slow passive), and downward transport due to leaching and physical mixing. Communition by soil fauna will accelerate the decomposition process and reveal previously inaeeessible materials. Soil mixing and other disturbances can also make physically protected passive SOM available to microbial attack (passive slow).

Plants contribute to soluble phosphorus not only after their death but also while they are still alive, as older tissues leach. Uptake of phosphorus by vegetation maintains low soluble phosphorus concentration in the soil profile. A large portion of phosphorus stored in belowground biomass is usually not accounted for in mass balance studies. Most of the emphasis is placed on aboveground... 

Activation of the soil microbiota leads to rapid cascades of decomposition of below- and aboveground litter produced during the previous growing season, and active fluxes of gases derived from soil respiration (CO2, NO, NjO) (Matson and Vitousek, 1995). In these processes significant amounts of nutrients are released which can be leached or taken up by newly formed fine roots. Much research is still required to understand the synchronization of events related to water supply, particularly processes of decomposition and release of nutrients and trace gas fluxes. 

---