Gopal Bhatt Lewis C. Linker Jesse Bash Paul Capel Gary W. Shenk Douglas A. Burns 2021 <p><span>The Chesapeake Bay watershed has been the focus of pioneering studies of the role of atmospheric nitrogen (N) deposition as a nutrient source and driver of estuarine trophic status. Here, we review the history and evolution of scientific investigations of the role of atmospheric N deposition, examine trends from wet and&nbsp;<a title="Learn more about dry deposition from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/dry-deposition" data-mce-href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/dry-deposition">dry deposition</a>&nbsp;networks, and present century-long (1950–2050) atmospheric N deposition estimates. Early investigations demonstrated the importance of&nbsp;<a title="Learn more about atmospheric deposition from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/atmospheric-deposition" data-mce-href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/atmospheric-deposition">atmospheric deposition</a>&nbsp;as an N source to the Bay, providing 25%–40% among all major N sources. These early studies led to the unprecedented inclusion of targeted decreases in atmospheric N deposition as part of the multi-stakeholder effort to reduce N loads to the Bay. Emissions of nitrogen oxides (NO</span>_x<span>) and deposition of wet nitrate, oxidized dry N, and dry ammonium (NH</span>₄⁺<span>) sharply and synchronously declined by 60%–73% during 1995–2019. These decreases largely resulted from implementation of Title IV of the 1990 Clean Air Act Amendments, which began in 1995. Wet NH</span>₄⁺<span>&nbsp;deposition shows no significant trend during this period. The century-long atmospheric N deposition estimates indicate an increase in total atmospheric N deposition in the Chesapeake watershed from 1950 to a peak of ~15&nbsp;kg&nbsp;N/ha/yr in 1979, trailed by a slight decline of &lt;10% through the mid-1990s, and followed by a sharp decline of about 40% thereafter through 2019. An additional 21% decline in atmospheric N deposition is projected from 2015 to 2050. A comparison of the Potomac River and James River watersheds indicates higher atmospheric N deposition in the Potomac, likely resulting from greater emissions from higher proportions of agricultural and urban land in this basin. Atmospheric N deposition rose from 30% among all N sources to the Chesapeake Bay watershed in 1950 to a peak of 40% in 1973, and a decline to 28% by 2015. These data highlight the important role of atmospheric N deposition in the Chesapeake Bay watershed and present a potential opportunity for decreases in deposition to contribute to further reducing N loads and improving the trophic status of tidal waters.</span></p> application/pdf 10.1016/j.atmosenv.2021.118277 en Elsevier Atmospheric nitrogen deposition in the Chesapeake Bay watershed: A history of change article