Unexpected nitrogen flow and water quality change due to varying atmospheric deposition

Atmospheric deposition has a significant impact on the nutritional status and limitations of aquatic ecosystems. However, the impacts have considerable uncertainty due to a lack of quantification of the indirect nitrogen (N) deposition, in terms of atmospheric-land surface-water bodies fluxes. In this study, we combined monitoring N deposition datasets with semi-distributed modeling to characterize the baseline N flow in tributary streams in the Three Gorges Reservoir Region of China, and predicted the varying impacts of indirect N deposition from 2006 to 2015. This study indicated that the indirect N deposition, as an important N source, accounted for 10.47% of the total N flow of tributary streams. The Clean Air Action or Carbon Neutral would induce a reduction of deposition and then reduced the tributary N flux by 0.45 x 10(4)-1.09 x 10(4) T yr(-1). Meanwhile, the declining N deposition would result in the tributary N: phosphorus (P) stoichiometry to 22.04, approaching from P limitation to N limitation. The variation in N/P ratio was smaller in agricultural watersheds than those forest-and grass-dominated watersheds. Our finding indicated that process toward mitigating water quality will be difficult without consideration the indirect impacts of N deposition, and attention should be paid to variations in nutrient limitation and the plankton communities of inland waters due to the variation of regional or global N deposition.

Automated summary

Atmospheric deposition has a significant impact on the nutritional status and limitations of aquatic ecosystems. This study combines monitoring data and modeling to investigate the indirect nitrogen deposition and its varying impacts on tributary streams in the Three Gorges Reservoir Region of China. The findings highlight the importance of considering indirect N deposition in water quality management and the variation in nutrient limitation and plankton communities due to regional or global N deposition.