Combined anion and cation resins for the collection and analysis of atmospheric deposition: field and laboratory experiments

Voeller, Gabrielle

"Precise methods for the quantification of atmospheric deposition are necessary in order to assess accurately pollution loads to ecosystems. While methods of collection involving aqueous samples are well developed, they require frequent collection, careful handling shortly after field collection. Ion-exchange resin columns have been successfully used as an alternative for collection of NO3- and SO4 2- in a spatially extensive study on which aqueous sampling was not feasible (Weathers et al. 2006). Here, the reliability of ion-exchange resins for measurement of BR-, PO43-, CL-, Na+, Mg2+, and Ca2+ was examined through a combination of field and laboratory studies. Field studies included collection of both throughfall and bulk deposition from June to November, 2006, at sites on Schoodic Point and Mount Desert Island, Maine, both located within Acadia National Park. Additionally, an array of ion-exchange resin columns containing both anion and cation resins were set in an open field along with a set of aqueous bulk deposition collectors from September to November, 2006, in Greene, Maine. Samples from both chromatography and inductivity coupled plasma optical emission spectroscopy (ICP_OES). In order to assist the ion-exchange resin capture efficiency, solutions with varying concentrations of CL-, BR-, SO4 2-, NO3-, PO43-, Na+, Mg2+, Ca2+ were loaded onto blank columns and extracted in conjunction with the samples. Recovery of CL-, BR-, SO4 2-, NO3- was more than 90% of expected values in the lab loading experiment and thus field capture efficiency is likely to be good. Recovery of PO43- ions from the loading experiment was highly variable, making measurement of PO43- unreliable. In Greene, measurements of Na+ in aqueous bulk deposition was lower than that measured by the resins, while Mg2+and Ca2+ measurements in bulk deposition was were higher than those of the resins. These patterns were similar to those found in the lab loading experiment. The most accurate measurements of ion loads (a percent recovery above 90%) can be obtained when between 10 and 40% of the total exchange capacity of the resin beads contained in the column is used. When a load is below 10% of the exchange capacity, it is difficult analytically to differentiate between blanks and laboratory or field loadings. Future work should explore reasons fort he inconsistent recovery of cations. "Research Recommendations: "Future work should explore reasons for the inconsistent recovery of cations." Page 84-101 provides specific details about the parts of the study that worked or did not work and recommendations as to potential future investigations and recommendations. /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/ /SCHOODIC PENINSULA/ GIS-CATEGORY 2 maps roughly depicting locations of sampling available