Erosion water

Fertilizer Use. The worldwide use of fertilizers has an important, positive effect on the environment. Conservative estimates (112) iadicate that about 30% of world food production is direcdy attributable to fertilizer use. Without fertilizer, therefore, at least 30% mote virgin land would have to be devoted to agriculture, and 30% more labor and other resources would have to be expended. Even more serious would be the effects of land tillage and cropping without nutrient replenishment. Past experience has shown that, under such a condition, crop yields progressively decrease, the land eventually becomes barren, and forces of wiad and water erosion prevail. 

Turbulence and high fluid velocities resulting from normal pump operation accelerated metal loss by abrading the soft, graphitically corroded surface (erosion-corrosion). The relatively rapid failure of this impeller is due to the erosive effects of the high-velocity, turbulent water coupled with the aggressiveness of the water. Erosion was aided in this case by solids suspended in the water. 

Metal loss in these areas had produced a smooth surface, free of deposits and corrosion products. The rest of the internal surface was covered by a thin, uniform layer of soft, black corrosion product. The graphitically corroded surfaces of the pump casing provided soft, friable corrosion products that were relatively easily dislodged by the abrasive effects of high-velocity or turbulent water (erosion-corrosion). 

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). 

A wooden or metal containment box surrounding the treated area is commonly used when a small quantity of test material is to be applied. The box, typically rectangular in shape and partially buried beneath the soil surface, serves to isolate the treated area from surrounding soil and protect against wind and water erosion. A one- to two-nozzle application boom that moves along guy wires or tracks is often used to ensure even application. Radiolabeled materials having two or more label positions often serve as replicates in these studies. 

The ET cover cannot be tested at every landfill site so it is necessary to extrapolate the results from sites of known performance to specific landfill sites. The factors that affect the hydrologic design of ET covers encompass several scientific disciplines and there are numerous interactions between factors. As a consequence, a comprehensive computer model is needed to evaluate the ET cover for a site.48 The model should effectively incorporate soil, plant, and climate variables, and include their interactions and the resultant effect on hydrology and water balance. An important function of the model is to simulate the variability of performance in response to climate variability and to evaluate cover response to extreme events. Because the expected life of the cover is decades, possibly centuries, the model should be capable of estimating long-term performance. In addition to a complete water balance, the model should be capable of estimating long-term plant biomass production, need for fertilizer, wind and water erosion, and possible loss of primary plant nutrients from the ecosystem. 

Development of the Environmental Policy Integrated Climate (EPIC) model and its predecessor, the Erosion Productivity Impact Calculator, began in the early 1980s.69 70 The first version of EPIC was intended to evaluate the effects of wind and water erosion on plant growth and food production. More recent versions also evaluate factors important to other environmental issues. EPIC is a onedimensional model however, it can estimate lateral flow in soil layers at depth. All versions of EPIC estimate surface runoff, PET, AET, soil-water storage, and PRK below the root zone—these complete the hydrologic water balance for an ET landfill cover. 

In addition to a complete water balance, EPIC estimates plant biomass production, fertilizer use, wind and water erosion, loss of nitrogen and phosphorus from the soil, and the effect of nutrient loss from the soil on plant growth. 

The top layer in the landfill profile is the vegetative layer. In the short term, this layer prevents wind and water erosion, minimizes the percolation of surface water into the waste layer, and maximizes evapotranspiration, the loss of water from soil by evaporation and transpiration. The vegetative layer also functions in the long term to enhance aesthetics and to promote a self-sustaining ecosystem on top of the landfill. The latter is of primary importance because facilities may not be maintained for an indefinite period of time by either government or industry. 

More research and demonstration activity should be devoted to water harvesting, which can be considerably useful not only in reducing irrigation requirements but also in the reduction of overland flow and consequently in the protection of soils from water erosion, as well as in leaching soils from salts accumulated with irrigation water. The solution of tied ridges, or diked furrows, to be obtained either by animal energy or when possible with the use of mechanical equipment, has been... 

In a general way, the overall movement of phosphorus on the continents can be considered as the constant water erosion of rock and transport of P in both particulate and dissolved forms with surface runoff to river channels and further to the oceans. The intermediate transformations are connected with uptake of P as a nutrient by... 

Approximately 44 000 t of arsenic are annually removed from soils (Matschullat, 2000), 303. Major processes that eliminate arsenic from soils include microbial volatilization (up to 26,200 tyear-1 (Matschullat, 2000), 300-301), plant uptake, wind and water erosion, and leaching into precipitation, irrigation water, and groundwater (Matschullat, 2000 Bar-Yosef, Chang and Page, 2005). 

Researchers working for the Nebraska Agricultural Experiment Station developed the stubble-mulch or crop residue mulch practice, a highly effective method of soil erosion control (Douley and Russel, 1939). Stubble mulching used subsurface tillage implements that left crop residues on the soil surface and provided some protection against wind and water erosion (Zingg and Whitfield, 1957). 

Alekin O.A. (1978) Water erosion of land surface. In U.S.S.R. Committee for the Internatl. Hydrol. Decade World Water Balance and Water Resources of the Earth, Studies and Reports in Hydrology, 25, UNESCO Press, Paris, 663 pp. 

Finally, it must be noted that the evolution of tolerance is a necessary condition for the evolution of a population able to colonize a mine, but it may not be sufficient. Mines differ from normal habitats in many ways apart from mere metal contamination the soil structure is usually worse, and the organic content less, so that the soils dry out quickly the soils are frequently very deficient in nitrogen and phosphorus and other essential elements and wind and water erosion may mean that seedling establishment is very difficult (Baker and Proctor, 1990). The result is that plants have to be able to adapt to all these conditions as well as to the metal contamination in practice, only those species which show at least some preadaptation to these harsh conditions are going to be able to evolve tolerant races. It may well be that it is this factor, rather than the evolution of tolerance per se, that is most important in determining which species are able to evolve tolerant races. Such arguments may be relevant when comparing the evolution of tolerance in mine environments and aerially-contaminated sites such as those around smelters, where soil conditions and selective forces are markedly different (Baker, 1987). 

Water erosion has been fairly well characterized in the U.S.A., but has generally received less attention in other countries. Four main factors influence the degree to which water erosion occurs chmate, soil, topography, and vegetative cover. One may assume a value for each of these factors, which by itself may indicate a soil-loss problem. 

Barrows, H.L. and Kilmer, V.J., 1963. Plant nutrient losses from soils by water erosion. Adv. Agron., 15 303—316. 

Many metal(loid)-contaminated sites require the establishment of a plant cover (phytostabilization) to minimize wind and water erosion of topsoil and to... 

In a general way, the overall movement of phosphorus on the continents can be considered as the constant water erosion of rock and transport of P in both particulate and dissolved forms with surface runoff to river channels and further to the oceans. The intermediate transformations are connected with uptake of P as a nutrientby biota and interactions between river waters and bottom sediments. The majority (up to 90%) of eroded P remains trapped in the mineral lattices of the particulate matter and will reach the estuaries and ocean without entering the biological cycle. The smallest soluble part of eroded phosphorus is readily available to enter the biological cycle (Figure 28). 

Figure 2. Conceptual scheme of a small catchment ecosystem. Fluxes of element i between a hydrological basin and its surroundings Wi, total weathering of rocks Pi, wet atmosphere deposition Di, dry deposition Ai, possible anthropogenic inputs (e.g. fertilization) Ri, surface and subsurface runoff of soluble substances Mi, possible water erosion of solid substances Bi, biomass export (harvesting) (Moldan and Cherny, 1994).

Natural sources of vanadium release to water include wet and dry deposition, soil erosion, and leaching from rocks and soils. The largest amount of vanadium release occurs naturally through water erosion of land surfaces. It has been estimated that approximately 32,300 tons of vanadium are dissolved and transported to the oceans by water, and an additional 308,650 tons are thought to be transported in the form of particulate and suspended sediment (Van Zinderen Bakker and Jaworski 1980). 

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