|Van Pelt, Robert - Scott|
Submitted to: International Conference on Aeolian Research
Publication Type: Proceedings
Publication Acceptance Date: 7/22/2002
Publication Date: 7/25/2002
Citation: Van Pelt, R.S., Zobeck, T.M., Gill, T.H. 2002. Sediment deposition in an attic near a region of dust provenance: Implications for historic regional dust dispersion and deposition patterns[abstract]. International Conference on Aeolian Research. July 22-25, 2002. Lubbock, Texas. p. 347-351.
Interpretive Summary: Fugitive dust from wind erosion endangers human safety and health. Wind erosion is a winnowing process that removes the finer, more chemically active portions of the soil, and the resulting dust may contain many times the surface soil's concentration of plant nutrients and chemical contaminants such as pesticides and heavy metals. Recently, concerns about nutrient and contaminant transport in surface waters has increased the focus on dust as a source of these materials in watersheds. While current rates of dust deposition in a given watershed may be quantified, past rates are unavailable. Relatively undisturbed attics offer unique archives of historic dust patterns that are rarely cleaned and protect the dust from rain and ultraviolet radiation. If the attic is sufficiently large and is vented at the ends, the deposition pattern may represent regional patterns, allowing qualitative estimates of the physical, chemical, and microbiological nature of dust that has been deposited both locally and at different distances downwind. We sampled the dust at several distances from the gable vent in the relatively undisturbed floor of an attic built in 1954. We found that the total deposition and particle size distribution parameters decreased exponentially with increased distance from the vent. A simple exponential decay function was regressed against the observations with high levels of correlation. The percent organic carbon increase with distance from the vent matched an inverse exponential function with a high level of correlation as well. Both these observations agree well with deposition patterns observed in larger regions downwind from areas where dust is generated. It appears that this and similar attics may provide a physical scale model of a deposition basin that will allow estimates of historic dust-borne transport of mineral, organic, chemical, and microbiological materials from one region to distance-specific areas in another.
Technical Abstract: Fugitive dust emission is a common result of wind erosion in semiarid areas. Recently, research on dust transport, dispersion, and deposition has focused on the nutrients, chemicals, and pathogens that are often transported on dust particles. While many techniques exist for quantifying present day atmospheric load and deposition, there is little information available concerning historic patterns of dust generation, transport, and characteristics. Undisturbed ventilated attics offer an archive of dust that dates back to the time the structure was constructed. We collected dust samples in a second-story attic dating back to 1954 and located several kilometers from the nearest eroding farm fields in Big Spring, TX. Big Spring is located at the southern end of the Southern High Plains, a regionally important dust source area. A total of 13 samples were collected from measured attic floor areas at 1.1 m intervals from the upwind gable to a distance of 13.7 m into the center of the rectangular building. The samples were dried at 60 deg C, sieved through a 60 mesh screen to remove building debris and macro-biological materials, weighed, and split on a spinning riffler to provide uniform samples for analyses. To date, calculations of total deposition expressed as kg m-2 and particle size analysis using a Beckmann-Coulter laser/PID instrument has been performed on the samples. Patterns of total deposition as a function of increasing distance from the gable vent matched a simple exponential decay function with an r2 of 0.996 and median particle diameter decrease with increasing distance from the vent matched the same exponential decay function with an r2 of 0.951. Since these patterns are similar to the deposition patterns noted in regional dispersion and dry deposition of aeolian dust, it would appear that this attic, and others like it, offer archives of not only the aeolian dust passing through and being deposited in the immediate location, but also of areas several kilometers downwind as well.