Soils surface

Settling and rainout are important mechanisms of contaminant transfer from the atmospheric media to both surface soils and surface waters. Rates of contaminant transfer caused by these mechanisms are difficult to assess qualitatively however, they increase with increasing soil adsorption coefficients, solubility (for particulate contaminants or those adsorbed to particles), particle size, and precipitation frequency. 

Acker, m, field, land acre. -bau,m, agriculture, farming, -bauchemie, /. agricultural chemistry. -bauwissenschaft, /. science of agriculture, -beere, /, dewberry (esp. Rubus caesius). -boden, m. arable soil, surface soil, -bohne,/, field bean, broad bean (Vida/aba). -doppen,/.pf. valonia. 

Visual inspection is an essential primary step. Such inspections should provide data on surface soils, surface waters, and slopes. 

Elements Crustal Abundance Mean in Oregon Rock Types Western Surface Soils Total Recoverable uses Mean DEO Max ... 

Much of the surface soil erosion and hence nutrient loss occurs when deforestation and biomass burning removes and/or consumes the organic materials that protect the soil surface. Significant losses may occur by dry ravel or overland water erosion associated with precipitation events. Under a shifting cultivation system in a tropical deciduous forest ecosystem in Mexico, Maass et al. 61) reported first year losses of N, P, K, and Ca were 187, 27, 31, and 378 kg ha" respectively. In contrast, losses in adjacent undisturbed forests were less than 0.1 kg ha for all nutrients except Ca (losses were 0.1-0.5 kg ha for Ca). 

Figure 6-7 illustrates the runoff paths for HOF and SOF, as well as for subsurface stormflow and groundwater flow. Subsurface stormflow is a moderately rapid runoff process in which water flows to a stream through highly permeable surface soil layers (without reaching the water table). Note in Fig. 6-7 that while HOF and subsurface stormflow may occur over a large fraction of an infiltration-limited hillslope, SOF occurs over a smaller portion adjacent to the stream. 

As an example, the migration of clay from the surface of a soil to a lower horizon results from several processes occurring when certain soil and environmental properties exist. First, claysized minerals must form, usually requiring weathering to have occurred. Clay minerals formed in the surface soil can then go into suspension when salt concentrations in solution are low. Seasonal rains can move the clay down... 

The infiltration problem caused by water quality is also related to the structural stability of the surface soil (see below). 

Bradley PM, FH Chapelle, JE Landmeyer, JG Schumacher (1994) Microbial transformation of nitroaromatics in surface soils and aquifer materials. Appl Environ Microbiol 60 2170-2175. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

The method above, however, is not suitable when one needs a precise study of the vertical distribution of pesticides. Generally, the concentration of pesticides in paddy sediment is highest at the surface. Special care is required to avoid contamination with surface soil when the sediment is collected. The sediment core should be collected in two stages. First, a pipe with a diameter greater than that of the core sampler is inserted in the sediment and then water inside the pipe is removed gently with a syringe, pipet, etc. Next, a layer of surface soil (1-3 cm) is taken with a spatula or a trowel and then subsurface soil is collected with a core sampler to the desired depth see also Figure 4. 

Special care is required to prevent contamination with surface soil when the sediment is collected to study the vertical distribution of a pesticide. The method described earlier (Section 3.1.1) is strongly recommended. 

In most cases, if soil samples are needed, only surface samples are collected. An exception would be harvesting root crops where all residues in the top 6 in of soil would be sampled. A typical surface soil sampler is shown in Figure 2. It is the residue adsorbed on small particles (<150 o.m), which could cling to moist skin, which causes the most exposure to workers. After sampling, place a flag in the center of each sampled location to mark the area against future sampling. After the surface layer has been collected, the soil is sieved to collect the fraction <150 lam and the remainder of the soil is discarded. Maintain separate sieves and collectors for treated and control plots to prevent contamination of the control samples. 

Chernobyl 241Am, in five samples of surface soil collected 1.5-15 km from the Chernobyl accident in July 1987, was predominantly in the 0.005-0.25 mm size fraction of soil, which comprised 65% of the mass (Berezhnoi et al. 1991). 

Bikini Atoll. Surface soil collected at 20 sites on Bikini Atoll in 1972 contained 1.2-45 pCi/g of241 Am (Nevissi et al. 1976). This level will increase for several decades as a result of ingrowth from 241Pu before it begins to decrease. Bikini Atoll was the site of 23 nuclear detonations between 1946 and 1958. 

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