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

Abstract

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 × 104–1.09 × 104 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.