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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #287173
Title: Exploring lag times between monthly atmospheric deposition and stream chemistry in Appalachian Forest using cross-correlation

Author
item DEWALLE, DAVID - Pennsylvania State University
item Buda, Anthony

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2016
Publication Date: 9/10/2016
Citation: Dewalle, D.R., Buda, A.R. 2016. Exploring lag times between monthly atmospheric deposition and stream chemistry in Appalachian Forest using cross-correlation. Atmospheric Environment. 146:206-214.

Interpretive Summary: Documenting the recovery of surface waters in response to reductions in nitrogen and sulfur in rainfall is a key priority of long-term monitoring programs in headwater streams, but in many cases, successful trend detection is masked or delayed by short-term variations in rainfall chemistry. We evaluated a simple statistical method for identifying and interrelating short-term variations in nitrogen and sulfur in rainfall and stream water in four forested watersheds located in the mid-Appalachian region of Pennsylvania. Results showed that the method could be used to document short-term changes in the amounts of nitrogen and sulfur delivered in rainfall, as well as determine the time needed for these changes to appear in the stream water chemistry signal. Study findings suggest that the method will enhance the analysis and interpretation of long-term water quality data sets in forested and agricultural watersheds.

Technical Abstract: Although long-term reductions in surface water nitrogen and sulfate concentrations have been widely observed in response to reductions in atmospheric deposition, documenting and inter-relating transient variations in deposition and stream time series has proven problematical due to low signal-to-noise ratios. We used analysis of cumulative sums of residuals (CUSUM residuals) from long-term linear regression trends to document transient variations in monthly atmospheric wet deposition and stream chemistry on four forest basins (approximately 1100 ha) in the Mid-Appalachians during 1978-2009. We also cross-correlated CUSUM residual time series with wet deposition, precipitation, and pollutant concentration time series to determine inter-relationships between these variables, as well as to estimate lag times between deposition and stream chemistry data sets. Transient variations in wet deposition CUSUM residuals for SO4 and inorganic N at three regional monitoring sites showed some common features among monitoring sites, as well as localized variations in precipitation amounts, pollutant concentrations and their interactions. CUSUM residuals in monthly wet deposition appear to have been propagated to stream nitrate-N and sulfate time series with variable lag times (mean lag times approximately equal to 4-6 y). Determination of lag times between transient variations in atmospheric deposition and stream chemistry time series using CUSUM residuals was limited by length of the time series and by how well the available deposition data represented catchment conditions. Overall, while streams are generally showing slow recovery due to long-term reductions in atmospheric emissions, stream chemistry in these relatively-undisturbed forest ecosystems also appears responsive to transient variations in atmospheric wet deposition.