TESTING DUST COLLECTION AND RECOVERY METHODS FOR GEOCHEMICAL ANALYSIS: IMPLICATIONS TO LANDSCAPE EVOLUTION AND GROUNDWATER CHEMISTY

Dust (dry deposition) is an important geological material that contributes to soil formation and has been proposed to affect landscape evolution, formation of terra rossa in karst, and shallow groundwater chemistry. Although there are many successful methods to collect dust, extracting dust from containers while minimizing sample loss remains a challenge. Most methods use as much as 1L of distilled water, acknowledging that some components may be lost and mineralogy may change during evaporation to recover the solids. In this study, we experimented with different methods of extracting a known mass of fine-grained material from a MWAC (Modified Wilson and Cooke) dry deposition collector (internal inlet and outlet diameters of 2.7 cm and volume of ~470 cm³; 2-234 mg) and a standard NADP dry deposition bucket (DDB; 700 mg). We tested five methods of dust extraction from the MWAC and one method in the DDB. Overall, these five methods resulted in 40% to 97% dust recovery, by weight. Although Method 3 (wiping with a Kimwipe®) yielded the highest recovery, it was complicated by finding an effective way to remove the dust from the Kimwipe®. Method 5, using a paintbrush to remove the dust and then dissolving remaing material in distilled-deionized water, was thus judged to be the most effective overall (95% recovery). We applied Method 3 to test extraction from the DDB, and achieved a recovery of 96%, with a nearly linear decrease, from 33% to 6%, in the amount of material recovered on the five Kimwipes® used. We also tested whether simulated windspeeds of 1 to 5.3 m sec^-1 could mobilize small scraps of paper or dust in the DDB. Although we observed some movement of scraps of paper at windspeeds as low as 1.95 m sec^-1, no material left the bucket even at the highest windspeed. A year of dust collection at the Konza Prairie Long-Term Ecological Research Site, northeastern Kansas in directionaly-oriented MWAC collectors, resulted in total (organic and inorganic) dust mass of about 1 gm. The largest amount of dust was collected in the NW-SE-oriented MWAC and the NE-SW-oriented MWAC during summer-to-fall, and late winter-to-spring, respectively. We will also present information on the mineralogy and geochemistry of the dust, and propose implications for chemical weathering and groundwater chemistry.