TECHNICAL REPORTS Atmospheric Pollutants and Trace Gases Monitoring Nitrogen Deposition in Throughfall Using Ion Exchange Resin Columns: A Field Test in the San Bernardino Mountains

deposition fluxes for the array of dry-deposited gaseous and particulate forms of N, in addition to wet deposition Conventional throughfall collection methods are labor intensive and fog or cloudwater deposition of N. Determining the and analytically expensive to implement at broad scales. This study was conducted to test an alternative approach requiring infrequent sample deposition of these many compounds to complex recipicollection and a greatly reduced number of chemical analyses. The ent ecosystem surfaces under dynamic meteorological major objective of the study was to determine the feasibility of using conditions is a daunting task on the local scale and parion exchange resin (IER) to measure N deposition in throughfall with ticularly impractical and cost prohibitive over extensive field deployment periods of 3 to 12 mo. Nitrogen deposition measurelandscapes. As a result, total N deposition estimates to ments in bulk throughfall collected under pine (Pinus sp.) canopies ecosystems are generally highly uncertain or nonexistent. and in forest clearings were compared between co-located convenWhere N deposition data are available, a variety of aptional throughfall solution collectors and IER throughfall collectors proaches, such as the inferential method, simulation modusing mixed bed IER columns. Deposition data were collected for eling, and throughfall (Lovett, 1994) have been used to 1 yr at a high deposition site (Camp Paivika, CP) and a relatively low determine N deposition or some components of total N one (Barton Flats, BF) in the San Bernardino Mountains in southern California: Annual throughfall deposition values (kg ha 1 of NH4–N deposition. Deposition fluxes in precipitation (wet deNO3–N) under large ponderosa pine trees (Pinus ponderosa Laws.) position) are frequently monitored because this is the were 145.8 and 143.9 at CP and 17.0 and 15.0 at BF according to the least complex and most reproducible component to meaIER and conventional methods, respectively. Analogous values for sure. However, in areas of significant fog or dry deposibulk deposition in forest clearings were 15.6 and 12.3 at CP and 4.0 tion (or both), wet deposition is the smallest component and 3.3 at BF. It was concluded that the IER collectors can be used for of total deposition inputs, particularly in ecosystems routine monitoring of deposition in throughfall and bulk deposition, with high leaf area index values, where plant canopies provided that field blanks are used to account for background levels serve as efficient scavengers of air pollutants in wet and of N in the IER columns, which at times are slightly elevated, possibly dry forms (Fenn et al., 2003). from slow release of amine groups from the anion exchange resin Because it is generally not feasible to monitor atmoduring field exposures. spheric concentrations and deposition of the suite of important atmospheric pollutants over an extensive number of sites, alternative approaches are needed to estiB of the widespread and largely detrimental mate N deposition inputs. The use of passive monitors for aspects of elevated atmospheric N deposition, quantiobtaining average concentrations of gaseous pollutants fication of ecosystem N inputs from air pollution is needed. is now recognized as a vital methodology for measuring Quantification of deposition inputs fosters greater ungaseous pollutant exposure in forests and other areas derstanding of cause and effect relationships between without electric power and where the cost of maintainpollutants and ecosystem responses and is critical for ing multiple active monitors is prohibitive (Bytnerowicz identifying terrestrial and aquatic resources most at risk et al., 2002; Krupa and Legge, 2000). However, total N from N enrichment and acidification effects. Measuring deposition fluxes cannot be determined solely from gastotal N deposition to forests or other ecosystems is a chaleous pollutant concentrations; considerable meteorolenge due to the technical difficulties and expense assological data, pollutant deposition velocity values, and inciated with measuring atmospheric concentrations and formation on plant community characteristics also are required (Baumgardner et al., 2002). M.E. Fenn and M.A. Poth, USDA Forest Service, Pacific Southwest Throughfall is an attractive alternative method for esResearch Station, Forest Fire Laboratory, 4955 Canyon Crest Dr., timating atmospheric deposition to forests and other ecoRiverside, CA 92507. M.A. Poth, current address: USDA-CSREES, National Research Initiative Competitive Grants Program, Stop 2241, systems (Thimonier, 1998). Deposition of N in through1400 Independence Ave. SW, Washington, DC 20250. Received 19 fall is the hydrologic flux of N from the canopy to the Feb. 2004. *Corresponding author ([email protected]). forest floor. Throughfall measurements of N deposition Published in J. Environ. Qual. 33:2007–2014 (2004). © ASA, CSSA, SSSA Abbreviations: BF, Barton Flats; CP, Camp Paivika; IER, ion exchange resin; SBM, San Bernardino Mountains, California, USA. 677 S. Segoe Rd., Madison, WI 53711 USA