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 dry deposition networks, and present century-long (1950–2050) atmospheric N deposition estimates. Early investigations demonstrated the importance of atmospheric deposition 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_x) and deposition of wet nitrate, oxidized dry N, and dry ammonium (NH₄⁺) 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 NH₄⁺ 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 kg N/ha/yr in 1979, trailed by a slight decline of <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.

切萨皮克湾流域一直是大气氮 (N) 沉积作为营养源和河口营养状态驱动因素作用的开创性研究的焦点。在这里，我们回顾了关于大气 N 沉降作用的科学研究的历史和演变，检查了干湿沉降网络的趋势，并提出了长达一个世纪（1950-2050 年）的大气 N 沉降估计。早期调查表明大气沉降作为海湾氮源的重要性，在所有主要氮源中提供 25%–40%。这些早期研究导致空前地包括有针对性地减少大气 N 沉降，作为多方利益相关者努力减少海湾 N 负荷的一部分。氮氧化物（NO _x) 和湿硝酸盐、氧化干 N 和干铵 (NH ₄ ⁺ ) 的沉积量在 1995-2019 年期间同步急剧下降 60%-73%。这些下降主要是由于实施了 1990 年清洁空气法修正案的第四章，该修正案于 1995 年开始。湿 NH ₄ ⁺在此期间沉积没有明显的趋势。长达一个世纪的大气 N 沉降估计表明，切萨皮克流域的大气 N 总沉降从 1950 年增加到 1979 年约 15 kg N/ha/yr 的峰值，随后在 1979 年中期略有下降，<10% 1990 年代，随后到 2019 年急剧下降约 40%。预计从 2015 年到 2050 年，大气 N 沉降量将再下降 21%。波托马克河和詹姆斯河流域的比较表明，波托马克河的大气 N 沉降量较高，可能是由于该流域较高比例的农业和城市土地排放量增加所致。大气氮沉降从 1950 年切萨皮克湾流域所有氮源中的 30% 上升到 1973 年的 40% 的峰值，到 2015 年下降到 28%。