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Since the industrial revolution, it has been assumed that fossil-fuel combustions dominate increasing nitrogen oxide (NO x ) emissions. However, it remains uncertain to the actual contribution of the non-fossil fuel NO x to total NO x emissions. Natural N isotopes of NO 3 − in precipitation (δ 15 N w-NO3− ) have been widely employed for tracing atmospheric NO x sources. Here, we compiled global δ 15 N w-NO3− observations to evaluate the relative importance of fossil and non-fossil fuel NO x emissions. We found that regional differences in human activities directly influenced spatial-temporal patterns of δ 15 N w-NO3− variations. Further, isotope mass-balance and bottom-up calculations suggest that the non-fossil fuel NO x accounts for 55 ± 7% of total NO x emissions, reaching up to 21.6 ± 16.6Mt yr −1 in East Asia, 7.4 ± 5.5Mt yr −1 in Europe, and 21.8 ± 18.5Mt yr −1 in North America, respectively. These results reveal the importance of non-fossil fuel NO x emissions and provide direct evidence for making strategies on mitigating atmospheric NO x pollution. This study investigates in the importance of non-fossil fuel NO x emissions in the surface-earth-nitrogen cycle. The study shows how changes of regional human activities directly influence δ 15 N signatures of deposited NO x to terrestrial environments and that emissions have largely been underestimated.

The episodic growth of high-elevation orogenic plateaux is controlled by a series of geodynamic processes. However, determining the underlying mechanisms that drive plateau growth dynamics over geological history and constraining the depths at which growth originates, remains challenging. Here we present He-CO 2 -N 2 systematics of hydrothermal fluids that reveal the existence of a lithospheric-scale fault system in the southeastern Tibetan Plateau, whereby multi-stage plateau growth occurred in the geological past and continues to the present. He isotopes provide unambiguous evidence for the involvement of mantle-scale dynamics in lateral expansion and localized surface uplift of the Tibetan Plateau. The excellent correlation between 3 He/ 4 He values and strain rates, along the strike of Indian indentation into Asia, suggests non-uniform distribution of stresses between the plateau boundary and interior, which modulate southeastward growth of the Tibetan Plateau within the context of India-Asia convergence. Our results demonstrate that deeply-sourced volatile geochemistry can be used to constrain deep dynamic processes involved in orogenic plateau growth. Deeply-sourced volatiles are releasing from orogenic plateau regions, providing windows to plateau growth dynamics occurring at variable depths. Here the authors show that mantle-derived volatiles reveal the involvement of mantle dynamics in southeastward growth of the Tibetan Plateau.

River cutoffs and oxbow lakes represent ubiquitous features in alluvial plains, shaped by unidirectional meandering flow. Extensive studies have been conducted on these features as their presence immediately decreases meander sinuosity and plays a significant role in the long‐term eco‐morphodynamic and sedimentary evolution of landscapes they carved in. In contrast, limited attention has been given to meander cutoffs formed in tidal environments by bidirectional currents, and the corresponding hydrodynamical processes within these features are poorly understood. Here, we present new, first‐handed hydroacoustic data collected through a series of fixed‐point and cross‐sectional flow measurements along a chute cutoff located in the microtidal Diaokou Mudflat, the Yellow River Delta, China. The investigated cutoff bend displays higher hydrologically active than the newly‐formed chute channel at low tide, whereas the chute channel gradually become the main conduit for tidal flow propagation with water stage increasing. Specifically, poorly‐developed flow separation zones are compensated by widespread secondary circulation cells that are more pronounced under the influence of turbulences and complex bedforms rather than channel curvatures. Unlike fluvial cutoffs, which tend to be hydrologically disconnected to parent channels by coarse‐grained bed sediment plugging near the entrances, our study case is characterized by the absence of plug bars and widespread bank slumps instead. Consequently, our results support earlier suggestions that tidal cutoffs seldom disconnect from parent channels due to frequent overbank events and flow confluences, which can keep cutoffs active by flushing away fine‐grained, cohesive sediments, especially in mudflat systems. Key Points Hydroacoustic measurements of flow velocities in a mudflat cutoff show critical differences with fluvial counterparts Hydrodynamics of the tidal chute cutoff are correlated to the changes of water depth Poorly‐developed plug bars and frequent flow confluences can keep tidal cutoffs hydrologically‐connected to parent channels

The Karakoram fault (KKF) is an important strike‐slip boundary for accommodating deformation following the India‐Asia collision. However, whether the deformation is confined to the crust or whether it extends into the mantle remains highly debated. Here, we show that the KKF is overwhelmingly dominated by crustal degassing related to a 4He‐ and CO2‐rich fluid reservoir (for example, He contents up to ∼1.0–1.6 vol.%; 3He/4He = 0.027 ± 0.013 RA (1σ, n = 47); CO2/N2 up to 3.7–57.8). Crustal‐scale active deformation driven by strike‐slip faulting could mobilize 4He and CO2 from the fault zone rocks, which subsequently accumulate in the hydrothermal system. The KKF may have limited fluid connections to the mantle, and if any, the accumulated crustal fluids would efficiently dilute the uprising mantle fluids. In both cases, crustal deformation is evidently the first‐order response to strike‐slip faulting. Plain Language Summary Bubbling hot springs are common in fault zones along which Earth's lithosphere cracks. Chemical and isotopic compositions of spring gases can offer key information on the subsurface connectivity of the deep‐rooting faults that is not easily visible. To assess whether the Karakoram fault (KKF) in western Tibetan Plateau is developing in the crust or extends into deeper mantle, we studied the origin and transport of spring gases and found that the KKF is overwhelmingly dominated by degassing of a crustal fluid reservoir that contains high amounts of helium (He) and CO2. This could be attributed to He‐CO2 mobilization of deforming and fracturing fault zone rocks at crustal depths, suggesting that the KKF is primarily developing in the crust and may have limited fluid connections to the mantle. Key Points New He isotope data show that southern Karakoram fault (KKF) is overwhelmingly dominated by degassing of crustal fluids A crustal 4He‐ and CO2‐rich fluid reservoir is identified and linked to crustal‐scale active deformation driven by strike‐slip faulting KKF may have limited fluid connections to the mantle and requires further evaluation based on He isotope and seismic data

Atmospheric ammonia (NH 3 ) and ammonium (NH 4 + ) can substantially influence air quality, ecosystems, and climate. NH 3 volatilization from fertilizers and wastes (v-NH 3 ) has long been assumed to be the primary NH 3 source, but the contribution of combustion-related NH 3 (c-NH 3 , mainly fossil fuels and biomass burning) remains unconstrained. Here, we collated nitrogen isotopes of atmospheric NH 3 and NH 4 + and established a robust method to differentiate v-NH 3 and c-NH 3 . We found that the relative contribution of the c-NH 3 in the total NH 3 emissions reached up to 40 ± 21% (6.6 ± 3.4 Tg N yr −1 ), 49 ± 16% (2.8 ± 0.9 Tg N yr −1 ), and 44 ± 19% (2.8 ± 1.3 Tg N yr −1 ) in East Asia, North America, and Europe, respectively, though its fractions and amounts in these regions generally decreased over the past decades. Given its importance, c-NH 3 emission should be considered in making emission inventories, dispersion modeling, mitigation strategies, budgeting deposition fluxes, and evaluating the ecological effects of atmospheric NH 3 loading. By integrating nitrogen isotope systematics of ammonia emissions and transformations in the atmosphere, this study quantified the combustion-related ammonia emission and uncovered its importance for mitigating strategies of ammonia pollution.

Hydroelectric reservoirs are highly regulated ecosystems, where the understanding on bacterioplankton has been very limited so far. In view of significant changes in river hydrological conditions by dam construction, hydraulic load (i.e., the ratio of mean water depth to water retention time) was assumed to control bacterioplankton diversity in cascading hydropower reservoirs. To evaluate this hypothesis, we investigated bacterioplankton composition and diversity using high-throughput sequencing and related environmental variables in eleven reservoirs on the Wujiang River, Southwest China. Our results showed a decrease of bacterioplankton diversity index with an increase of reservoir hydraulic load. This is because hydraulic load governs dissolved oxygen variation in the water column, which is a key factor shaping bacterioplankton composition in these hydroelectric reservoirs. In contrast, bacterioplankton abundance was mainly affected by nutrient-related environmental factors. Therefore, from a hydrological perspective, hydraulic load is a decisive factor for the bacterioplankton diversity in the hydroelectric reservoirs. This study can improve the understanding of reservoir bacterial ecology, and the empirical relationship between hydraulic load and bacterioplankton diversity index will help to quantitatively evaluate ecological effects of river damming.

Soil extractable nitrate, ammonium, and organic nitrogen (N) are essential N sources supporting primary productivity and regulating species composition of terrestrial plants. However, it remains unclear how plants utilize these N sources and how surface-earth environments regulate plant N utilization. Here, we establish a framework to analyze observational data of natural N isotopes in plants and soils globally, we quantify fractional contributions of soil nitrate ( f NO3- ), ammonium ( f NH4+ ), and organic N ( f EON ) to plant-used N in soils. We find that mean annual temperature (MAT), not mean annual precipitation or atmospheric N deposition, regulates global variations of f NO3- , f NH4+ , and f EON . The f NO3- increases with MAT, reaching 46% at 28.5 °C. The f NH4+ also increases with MAT, achieving a maximum of 46% at 14.4 °C, showing a decline as temperatures further increase. Meanwhile, the f EON gradually decreases with MAT, stabilizing at about 20% when the MAT exceeds 15 °C. These results clarify global plant N-use patterns and reveal temperature rather than human N loading as a key regulator, which should be considered in evaluating influences of global changes on terrestrial ecosystems. Isotopic constraints reveal that soil nitrogen contribution to global plants is temperature-controlled, not by precipitation or nitrogen deposition. As temperatures rise, inorganic nitrogen becomes more important and preferred over organic nitrogen.

A heavy load of nitrogenous compounds reflects nutrient loss and influences water quality in large rivers. Nitrogenous concentrations and dual isotopes of nitrate were measured to ascertain the spatial and temporal distributions of nitrate transformation in the Yellow River, the second-longest river in China. Assessment of the long-term record indicates that [NO 3 − –N] has increased by two-fold over the past three decades. Weekly observation of ammonium over a twelve-year period revealed high concentrations and suggests impairment of water quality, particularly since 2011. The estimated total dissolved nitrogen flux was 7.2 times higher in middle reaches than that at head waters. Anthropogenic nitrogen sources become more important in lower section of the upper reaches and middle reaches because of intensive agricultural activities and urban input. Nitrate in the lower reaches was mainly derived from transportation of upstream nitrate and point sources from cities. The spatial variation of ammonium and nitrate isotopes show that nitrification is a key process governing nitrogen transformation. Riverine biological processes could potentially be responsible for the shift of nitrate isotope signature. The first step to reducing nitrogen load and improving water quality will be containment and careful management of sources from urban input, sewage waste and irrigation runoff.

Mosses, among all types of terrestrial vegetation, are excellent scavengers of anthropogenic nitrogen (N), but their utilization of dissolved organic N (DON) and their reliance on atmospheric N remain uncharacterized in natural environments, which obscures their roles inN cycles. Natural 15N abundance of N sources (nitrate ( ), ammonium ( ) and DON in deposition and soil) for epilithic and terricolous mosses was analyzed at sites with different N depositions at Guiyang, China. Moss assimilation was inhibited substantially by the high supply of and DON. Therefore, contributions of and DON to moss N were partitioned using isotopic mass-balance methods. The N contributions averaged 56% and 46% from atmospheric , and 44% and 17% from atmospheric DON in epilithic and terricolous mosses, respectively. In terricolous mosses, soil and soil DON accounted for 16% and 21% of bulk N, which are higher than current estimations obtained using 15N-labeling methods. Moreover, anthropogenic deposition suppressed utilization of DON and soil N because of the preference of moss for under elevated deposition. These results underscore the dominance of, and preference for, atmospheric in moss N utilization, and highlight the importance of considering DON and soil N sources when estimating moss N sequestration and the impacts of N deposition on mosses.

1. Exotic plant invasion has been changing the vegetation composition and function of terrestrial ecosystems. Nitrogen (N) and phosphorus (P) are often the limiting nutrients for terrestrial plants. However, under invasive pressure, in situ plant N and P usage mechanisms remain poorly understood but are pivotal for a better understanding of plant invasion and coexistence in invaded ecosystems. 2. Nitrogen and P concentrations, natural ¹⁵N abundance (δ¹⁵N values) were investigated in leaves and soils under different invasive pressures (here expressed as the biomass percentages of invasive plants in each plot) for two invasive species (Chromolaena odorata and Ageratina adenophora) in Xishuangbanna in tropical China. 3. Soil N and P concentrations revealed the relatively N-rich but P-poor status of our study site. Under invasion, soil inorganic N (dominated by ammonium) and available P did not increase significantly. The leaf N and P of invasive plants increased, while leaf N increased but P decreased for native species. Natural δ¹⁵N mass balance between leaves and soil inorganic N sources revealed that ammonium dominated N utilization in both natives and invaders. Invasive plants showed ammonium utilization with increasing leaf N levels, while native plants under no invasion showed nitrate utilization with increasing leaf N levels. 4. Synthesis. Increased soil ammonium availability contributed to preferential ammonium utilization by invasive plants and elevated ammonium utilization in natives, but the P competition of natives decreased in invaded ecosystems. These novel insights into nutrient dynamics in invaded ecosystems enhance our understanding of plant invasion and coexistence mechanisms.