OOS 4-3
An introduction to the National Atmospheric Deposition Program: Lessons from a continental-scale monitoring network
Since 1978, the National Atmospheric Deposition Program (NADP) has tracked the status and changes in the many different chemical compounds within precipitation across the continent. The NADP monitors the removal of pollutants from the atmosphere; but more importantly, it monitors the addition of chemical compounds into the Biosphere and ecosystems of North America. Our primary charge has been to provide data for the determination of both spatial and temporal trends in chemical species and mercury wet-deposition fluxes for North America. And over the 37 years of monitoring, we have shown the value of consistent monitoring techniques, high quality assurance standards, and rigorous attention to procedures and data validation. This has allowed us to reliably quantify both small and large trends in several chemical species.
Results/Conclusions
It is clear that the addition of acidic compounds to ecosystems has dropped drastically over the past three decades, but that certain regions are still experiencing high acidic compound loading. Our data also show that nitrogen deposition is increasing, and in particular to very sensitive ecosystems. The nitrogen increases are dominated by increases in ammonium. We have also quantified the mercury input to ecosystems over North America and slight but quantifiable trends in this deposition. While mercury deposition is not important to human health while in the atmosphere, it is of extreme importance to human health as it moves through ecosystems.
Given the new deposition observations of nitrogen and acid compounds planned by the National Environmental Observation Network (NEON), a comparison study is being developed for side-by-side comparison of measurements, operational procedures and tower/ground differences in observations. This collaboration will increase our understanding of anthropogenic pollutant loading impacts on sensitive ecosystems.