IUSC:STAR:RAINeD: Rain in the Archive: Innovations in Nitrogen Deposition

One of the main pathways for nutrients to enter ecosystems is through wet deposition – rain and snow precipitation. Elements, including nitrogen, dissolved in precipitation are returned to Earth’s surface where plants and other organisms can access these critical life-sustaining nutrients. The global productivity of forests and the surface water quality of streams, rivers, and lakes is often linked to nutrient deposition. There is a rich history of studying nitrogen wet deposition, but previous research has primarily focused on only two forms of nitrogen – ammonium and nitrate. However, wet deposition includes a third form of dissolved nitrogen: dissolved organic nitrogen (DON). This form of nitrogen is rarely assessed in deposition monitoring programs but can contribute 25-95% of the total nitrogen entering ecosystems via wet deposition. This project will quantify DON in wet deposition using archived samples from the National Atmospheric Deposition Program to understand sources of DON in precipitation, characterize the spatial and temporal variability of DON wet deposition, and investigate the ecosystem consequences of this additional source of nitrogen for organisms including lichens and herbaceous plants. Atmospheric deposition provides an essential source of nitrogen (N) to ecosystems. There is broad consensus that excess N, as the result of atmospheric deposition, has compromised the health of ecosystems at regional and global scales. This project will use archived precipitation samples from the National Atmospheric Deposition Program National Trends Network to quantify concentrations and loads of DON in wet deposition across the United States. Previous analyses with a smaller set of archived samples indicate a high level of sample stability. The preservation and stability of these scientific collections is significant as researchers can now reevaluate concentrations of other solutes creating a more holistic quantification and characterization of nutrient loads to ecosystems. Using these archived samples, the RAINeD (Rain in the Archives: Innovations in Nitrogen Deposition) project will ask three overarching questions: 1) what are the drivers of spatial and temporal variability of DON wet deposition across ecoregions; 2) what is the relationship between concentrations of DON and other measured solutes and can we hindcast time-series of wet deposition DON; and 3) how are temporal estimates of nutrient critical load exceedances modified with the incorporation of DON? The over-arching hypothesis of this project is that biological processes and sources control the seasonality and magnitude of DON wet deposition. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.