Canopy leaching

In the simulations here, there are two components to I atmospheric deposition, taken here as 1.5 mmol m year , and canopy leaching, which is calculated on the basis of the canopy P content assuming a rate of 6 mmol year in 1730 (see Sec. 3.1.3). To estimate kp in our standard cases, we assume that the input of phosphorus through atmospheric deposition was exactly balanced by leaching losses in 1730. This is somewhat at odds with several observations suggesting that much of the atmospherically derived P deposited onto tropical forests is retained rather than being leached out of the system (Sec. 3.1.2). Nevertheless, as was discussed in Sec. 3.1.1 almost all of this atmospherically derived P... 

When a forest system is subjected to acid deposition, the foliar canopy can initially provide some neutralizing capacity. If the quantity of acid components is too high, this limited neutralizing capacity is overcome. As the acid components reach the forest floor, the soil composition determines their impact. The soil composition may have sufficient buffering capacity to neutralize the acid components. However, alteration of soil pH can result in mobilization or leaching of important minerals in the soil. In some instances, trace metals such as Ca or Mg may be removed from the soil, altering the A1 tolerance for trees. 

The pesticide component of SWRRB takes into account the fate of the chemical applied under field conditions For example, the amount of pesticide actually reaching the ground after application over a plant canopy is calculated. Further, field dissipation of the chemical by photolysis on leaf surfaces as well as degradation in the soil is accounted for with the pesticide component of SWRRB. Leaching of the pesticide below the top 1cm of soil is also computed and runoff corrected for such losses. Further, adsorption of the pesticide to soil surfaces and sediment is taken into account by SWRRB. 

Many petrels and shearwaters approach their nest burrow, often located under forest cover, at night. When Leach s petrel Occanodroma leucorrhoa) return to their nest, they first hover over the spruce-fir canopy near their burrow. Then they plummet to the ground several meters downwind from their nest site and walk upwind to their burrows (Fig. 4.6). In still air, they landed closer to the burrow and followed a more roundabout route than in wind. With external nares plugged or olfactory nerves transected, displaced birds did not return to their burrows for 1 week. In a laboratory two-choice apparatus, breeding petrels... 

Dowdy, R.H., J.A. Lamb, J.L. Anderson, D.C. Reicosky, and R.S. Alessi (1995). Atrazine and alachlor leaching under com/soybean canopies. In Clean Water-Clean Environment - 21st Century, Conference Proceedings of American Society of Agriculture Engineers, Vol. 1. St. Joseph, MI, pp. 65-68. 

Most of the ecosystem nutrient losses occurred during the plantation establishment phase because of the removal of forest debris at clearing and soil dismrbance during mechanized operations. Despite the potential improvement in Ca levels and maintenance of Mg levels as mentioned for Gmelina, both the extraction of nutrients during harvesting, and leaching losses prior to canopy closure, lead to a depletion of key nutrients, particularly potassium, that must be replaced by fertilization if yields are to be maintained (Sanchez et al. 1985, Russell 1987). 

It will not leach out, even when exposed to a continuous hose stream. It is recommended for use on welding curtains, canopies, dividers, awnings and tents. Properly treated materials will meet the requirements of NFPA 701-75 and will repel water. 

A more detailed model is shown in this Fig. 5b. The throughfall Fa of Fig. 5a is replaced by the partial fluxes stem flow (Fu) and canopy drip (Fu). There are also included additional fluxes as Utter fall F e, dry deposition to soil Fse and internal fluxes of the system as uptake by roots and flow to the crown Fee, leaching of leaves Fse and flow from roots to soil F9e. 

The influence of acid rain on the environment is related to the various properties of different ecosystems and varies depending upon physic-chemical characteristics of soil, vegetation type, stemflow and throughfall interactions of rainwater with canopy of different botanic species. For instance, it is well known in Japan that soils close to the stems of Japanese cedar (Cryptomeria japonica) trees are strongly acidic. This is partly due to the leaching of hydrogen ions from the stems. Soil solutions close to a stem (10cm) are markedly acidic (pH 4.5) and contain 47 /zM of total Al in... 

However, if the pesticide is sprayed onto a developing canopy, then some of the pesticide will be intercepted by the plant and will be unavailable for leaching. The source term obviously cannot be estimated accurately without post-application sampling, which is why landowner records are important. Estimation of the source term is critical for the interpretation of all subsequent data collection efforts, as well as for modeling purposes (if that will be part of the use of field data). 

Yet, many forest ecosystems are exposed to acid deposition far exceeding their critical loads. Although these forest ecosystems appear healthy, there may be a sudden detrimental change once the current buffering capacity is depleted. Cation leaching both from the forest canopy and forest soils is observed in some forest ecosystems. Continuous exposure to high levels of acid deposition can lead the forest to be in nutrient imbalance and thereby undermine forest health. 

Biological exchange processes in the forest canopy are absorption or leaching, e.g., irreversible stomata uptake or leaching of elements originating from root uptake. 

AN EVALUATION OF POTENTIAL ROLES OF LEACHING FROM THE CANOPY... 

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