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Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15–0.23 Tg of soot and 0.15–0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

ABSTRACTThe concentration and sources of organic nitrogen (ON) in lake sediments affect lake nitrogen cycles. However, the factors influencing ON accumulation rate (ONAR) are unclear. We collected 3 sediment cores from northern, eastern, and southern Dianchi Lake (DC-N, DC-E, and DC-S, respectively) in July 2014, to study the effects of autochthonous and allochthonous sources of ON. The ON and ONARincreased 2.4–5.1 and 2.6–4.8 times, respectively, from 1900 to 2000, especially since the 1980s, when algal blooms have occurred more frequently. The ON decreased in the order DC-S > DC-N > DC-E, whereas the ONARdecreased in the order DC-N > DC-S > DC-E, suggesting that ONARwas influenced by ON content as well as the depositional environment. The total concentrations of n-alkanes (n-C12to n-C34) ranged from 4719 to 61 960 ng g−1in the 3 sediment cores, with proportions varying with vertical depth. The sources of ON were mainly allochthonous (soil erosion and terrestrial plants) and autochthonous (algal and aquatic plants) in DC-S and DC-N, respectively, and primarily mixed planktonic and terrestrial in DC-E. The stochastic impacts by regression on population, affluence, and technology (STIRPAT) model revealed that a 1% increase in air temperature and nitrogen fertilizer corresponded to an increase in ONARby 23–33% and 20–79% in the Dianchi Lake basin, especially in DC-S and DC-E. However, a 1% increase in urban land area reduced ONARby 2–11%, especially in DC-N. Our study suggests that the spatial and temporal ONARin Dianchi Lake may increase in response to a warmer and wetter climate combined with increasing chemical nitrogen fertilizer application.

The influence of bioturbation induced by bottom‐dwelling macrozoobenthos on nitrogen dynamics in lotic stream sediments remains unclear. In this work, we advance the understanding of faunal bioturbation in lotic environments by developing a fully‐coupled flow and multicomponent reactive transport model and investigate the influence of sediment reworking and burrow ventilation processes on nitrogenous transformations. The model results indicate that sediment reworking and burrow ventilation significantly increase nitrate (NO3−) influx, penetration depth, and reaction rates in the streambed. Denitrification rates were observed up to three times higher in beds with U‐shaped burrows compared to flatbeds. The ratio of mound height to stream water depth ratio (h/H0) is a dominant control on determining the relative importance of the sediment reworking and burrow ventilation processes in modulating nitrogenous reactions. A power‐law scaling framework is ultimately proposed to predict NO3−removal efficiency based on the Damköhler number in bioturbated lotic streambeds. The increase in nitrate (NO3−) levels can harm rivers by causing problems like eutrophication, toxic algal blooms, and low oxygen levels. Microbes, like those involved in denitrification, can help reduce NO3−levels in the riverbed, where surface water and groundwater mix. Creatures like macroinvertebrates that live in the riverbed also play a role in how NO3−moves and is used. We wanted to know if these creatures, by disturbing the sediment and irrigating it, change how NO3−behaves in the riverbed. Our computer modeling showed that having U‐shaped burrows in the sediment can enhance the rate at which NO3−is removed, up to three times more than in flatbed sediments. As the ratio of the mound height to the total depth becomes less than 0.1, the influence of sediment reworking on NO3−influx and consumption rates decreases, and burrow ventilation becomes more important. We also came up with a way to predict NO3−removal efficiency in bioturbated riverbeds under flowing water conditions. These findings underscore the significance of bioturbation in rivers with moving water and have important implications for managing and restoring rivers. Developing a Navier‐Stokes‐Brinkman‐Darcy‐Reaction fully‐coupled approach to study interplay between nitrogen cycling and faunal bioturbationSediment reworking and burrow ventilation processes could significantly alter the nitrogenous transformations in low flow environmentsA power‐law scaling framework can be used to predict nitrate removal efficiency within the bioturbated sediments from the Damköhler number Developing a Navier‐Stokes‐Brinkman‐Darcy‐Reaction fully‐coupled approach to study interplay between nitrogen cycling and faunal bioturbation Sediment reworking and burrow ventilation processes could significantly alter the nitrogenous transformations in low flow environments A power‐law scaling framework can be used to predict nitrate removal efficiency within the bioturbated sediments from the Damköhler number

The continuous flux of organic carbon (OC) from terrestrial ecosystems into inland water is an important component of the global carbon cycle. The buried OC pool in inland water sediments is considerable, and black carbon (BC) is a significant contributor to this OC pool because of the continuous growth in BC emissions. Therefore, determining the effect of BC on total OC burial and variations in the structure of BC during the burial process will contribute significantly to our understanding of lacustrine carbon cycling. This study investigated BC burial and its structural variations in response to anthropogenic drivers using four dated sedimentary cores from a deep plateau lake in China. The BC burial rate rose from 0.96 ± 0.64 g·m–2·y–1(mean of sedimentary cores pre-1960s) to 4.83 ± 1.25 g·m–2·y–1(after 2000), which is a 5.48 ± 2.12-fold rise. The increase of char was similar to those of BC. The growth rate of soot was 7.20 ± 4.30 times, which is higher than that of BC and char, increasing from 0.12 ± 0.08 to 0.64 ± 0.23 g·m–2·y–1. There was a decreasing trend in the ratio of char and soot at a mean rate of 62.8 ± 6.46% (excluding core 3) in relation to increased fossil fuel consumption. The contribution of BC to OC burial showed a significant increasing trend from the past to the present, particularly in cores 3 and 4, and the mean contribution of the four cores was 11.78 ± 2.84%. Source tracer results from positive matrix factorization confirmed that the substantial use of fossil fuels has promoted BC burial and altered the BC structure. This has resulted in BC with a higher aromatic content in the lake sediment, which exhibits reduced reactivity and increased stability. The strong correlation between BC and allochthonous total OC indicates that the input pathways of the buried BC in this plateau lake sediment were terrestrial surface processes and not atmospheric deposition.

ABSTRACTSimple and inexpensive estimation of the rates and sources of atmospheric nitrogen (N) deposition is critical for its effective mitigation in a region with different land-use types. In this study, the N content and N isotopic composition (δ15N) of moss (Haplocladium microphyllum) tissues and precipitation at six sites with three land-use types (urban, suburban, and rural) were measured in the Yangtze River Delta. A significant linear relationship between moss N content and wet N deposition, and a consistent decrease trend for moss N content and wet N deposition from urban to suburban to rural areas were observed. More negative δ15N of suburban and rural mosses indicated N mainly released from agriculture and effluent, while the less negative δ15N of urban mosses were mainly influenced by fossil fuel combustion and traffic emissions. Although the negative moss δ15N indicates that reduced N dominates wet N deposition, there was no significant correlation between moss δ15N and the ratio of ammonium to nitrate (NH4+/NO3−). These results reveal that the moss N content and δ15N can be used as a complementary tool for estimating the rates and sources of wet N deposition in a region with different land-use types.

AbstractXu X, Liu H, Jiao F, Ren Y, Gong H, Lin Z, and Huang C. 2020. Influence of climate change and human activity on total nitrogen and total phosphorus: a case study of Lake Taihu, China. Lake Reserv Manage. 36:186–202. Climate change and human activities can influence lake total nitrogen (TN) and total phosphorus (TP), affecting the overall health of the lake. These factors must be considered for planning and management of lakes in order to maintain their ecosystem integrity and sustain societal development. Using the Ensemble Empirical Mode Decomposition Method (EEMD) and the nonparametric Mann–Kendall test, the changes of TN and TP and their relationship to climate change and human activities were quantitatively evaluated on multiple time scales ranging from 1952 to 2010 using Meiliang Bay of Lake Taihu (China) for a case study. Patterns of TN change could be divided into 4 time scales: 2.73, 5.89, 25.33, and 45 yr, with an evident increasing long-term trend. Patterns of TP change were divided into 2.49, 6.4, 11.5, and 43 yr time scales with an increasing long-term trend. On short time scales, TN and TP were positively correlated with gross domestic product (GDP) and urban area, and negatively correlated with crop area and animal production. For the long-term trends, TN and TP were positively correlated with temperature, GDP, urban area, and animal production, and negatively correlated with precipitation and crop area. Both TN and TP abruptly changed in 2000, consistent with the abrupt changes in temperature, precipitation, and urban area. Collectively, results revealed that specific human activities in the watershed affected TN and TP in the sediments both on short-term and long-term scales, while global climate change affected TN and TP in the sediments on long-term scales. These results suggest that climate change and human activities must be considered to manage and protect lakes.

The coastal zone represents a critical intersection of naturally ecological and socio-economic processes. The abundance of data, models, and knowledge derived from various sources in coastal zones facilitates us to integrate them to better understand the evolution of coastal environments. This paper proposes a comprehensive framework of Coastal Zone Information Model (CZIM) to integrate multi-domain coastal information. The core idea of CZIM is to integrate multi-discipline coastal data, models, and knowledge for standardized governance, so as to carry, express, and apply coastal information by the digital system approaching the coastal digital twin. The CZIM framework includes four aspects: coastal data governance, model integration, knowledge engineering, and system construction. We perform a detailed literature review to illustrate the demands and challenges related to those four. The components of each aspect and their interlinks are introduced subsequently, and the future challenges of constructing coastal digital twins relying on CZIM are discussed. CZIM aims to strengthen the ability to organize, manage and apply refined coastal information to support more efficient, scientific, and intelligent decision-making in response to gradually volatile forces from both human activities and natural events, now and in the future. This paper provides a valuable reference for the next generation of coastal digitization in the target of the coastal digital twin.

The boom in dam construction and continuous river‐lake exchange has had a profound impact on the transmission and transformation of riverine dissolved inorganic carbon (DIC). An in‐depth understanding of the change mechanisms of DIC concentrations and sources driven by dam operation and lake recharge is crucial for regulating greenhouse gas emissions and evaluating the impact of DIC on the global carbon cycle. This study investigated dam‐ and lakes‐driven DIC via the concentration and δ13C of DIC, combined with anions, cations, δD and δ18O in the main stream of the Yangtze River. DIC showed a decreasing trend from upper reach (2,262.31 ± 113.69 μmol kg−1) to lower reach (1,771.61 ± 89.36 μmol kg−1). Carbonate dissolution proportion (from 36.45% to 28.44%) and atmospheric CO2proportion (from 37.51% to 22.94%) of DIC decreased from upper reach to lower reach, whereas soil CO2proportion of DIC (from 26.01% to 48.63%) increased. The control of dam operation on DIC biogeochemical process was revealed from different time scales. From the perspective of short‐term seasonal changes (from 2020 to 2021), the mineralization of organic matter in the dry season strengthened CO2degassing and calcite precipitation, reducing the DIC and increasing the proportion of soil CO2. Meanwhile, longer periods of runoff retention provided sufficient time for water–rock reactions in the wet season and increased the DIC and carbonate dissolution source in the reservoir area. On a long‐term scale (from 2009 to 2021), a decrease in pH driven by sediment mineralization contributed to an annual increase in DIC in the reservoir. The flow of lakes mixed into the mainstream was revealed by the enrichment of δ18O, and river‐communicating recharge decreased the DIC and carbonate dissolution source. We show that dam operation and lake inflow change DIC concentrations and sources and therefore need to be considered in the transmission and transformation processes of DIC in the river‐ocean continuum.

Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus (TP) and total nitrogen (TN) were both at high concentrations, ranging from 697.5–3210.0 mg/kg and 1263.7–7155.2 mg/kg, respectively. Inorganic phosphorus (IP) and total organic nitrogen (TON) were the main constituents, at percentages of 59%–78% and 74%–95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm2·yr) in 2014. As the most reactive forms, nitrate nitrogen (NO3-N) and ammonia nitrogen (NH4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71 597.6 t and a TN pool of 81 191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44 468.0 t and 5429.7 t, respectively, for the last century.

Core IdeasEffects of improved N management on net GWP and GHG intensity were investigated.Fertilizer production and irrigation were the main contributors to GWP.Optimized chemical N and manure N can decrease net GWP and GHG intensity relative to conventional N.Improved N management could realize food security and net GWP mitigation concomitantly. Agricultural production is one of the main sources of greenhouse gas (GHG) emissions globally. Net global warming potential (net GWP) and greenhouse gas intensity (GHGI) were investigated in a maize–wheat rotation from 2011 to 2014 on the North China Plain by summarizing the net exchange of CO2equivalent (CO2–eq) from direct and indirect GHG emissions. The experiment included four managements: no N input (N0), conventional chemical‐N management (Ncon), optimized chemical N management (Nopt), and balanced chemical‐N management incorporated with dairy manure (MNbal). Cumulative N2O emissions were significantly increased by N input rates. Soil organic carbon (SOC) content increased linearly in all treatments with 0.11 to 0.46 g C kg–1yr–1at 0 to 20 cm. The energy consumption associated with chemical N‐fertilizer production and irrigation was the main contributor to GWP. Compared with Ncon, a 45% decrease in chemical‐N input by Noptbrought about a 33% decrease in net GWP, but a 10% decrease in grain yield, and thus only reduced 25% of GHGI. A 40% decrease in total N application in the MNbaltreatment saved chemical N by 66% and increased soil organic carbon sequestration by 45%, increased grain yield by 18%, and finally, decreased net GWP and GHGI by 48 and 56%, respectively, relative to the Ncontreatment. We conclude that the incorporation of dairy manure with chemical N is a promising strategy for reducing net GWP and ensuring food security concomitantly in these intensive maize–wheat cropping systems on the North China Plain.

Light scattering properties in such a highly turbid productive lake as Lake Taihu in China were examined through 118 samples collected during three cruises in November 2006, March 2007, and November 2007. The particulate scattering and backscattering coefficients were observed using WETLabs AC-S and ECO-BB9. A power model with a spectral exponent of −0.729 was used to simulate the particulate scattering coefficient (b_p) spectra. It has a better performance than the linear model. Scattering parameters are more closely related to inorganic suspended matter (ISM) concentration than to other water components, such as total suspended matter (TSM), organic suspended matter (OSM), and chlorophyll a (Chla). This indicates that ISM dominates the scattering signal in the lake. Three discrepancies with oceanic/coastal waters are observed: (a) the backscattering ratio (b˜_bp) decreases with an increase in the ISM concentration because of a highly strong contribution by ISM to b_p; (b) the mass-specific scattering coefficient (b_p ^m) exhibits a wider range of variability than that reported in previous studies, which can be attributed to considerable variation in the OSM and ISM distributions; (c) the particle size distribution slope (ξ) is mostly larger than 4.0 in Lake Taihu, whereas it is usually within 3.5-4.0 for marine particles. In addition, the bulk refractive index (n¯_p) calculated according to the Twardowski et al. model [J. Geophys. Res. 106, 14129 (2001)JGREA20148-0227] indicates that some stations (n¯_p<1.07) can be regarded as organic-particle dominant. Other stations with high ISM concentrations have a very small n¯_p value mostly within 1.10-1.17. Overall, the knowledge on the scattering properties gained in this study broadens our understanding of water optics in highly turbid productive water columns.

Combustion-derived black carbon (BC) is an important component of sedimentary carbon pool. Due to different physicochemical properties, determining the source of char and soot is crucial for BC cycling, especially for nonhomologous char and soot in the Tibetan Plateau (TP). This study analyzed the sequestration and source of BC, char, and soot in the Dagze Co (inner TP) sediment core via the content and δ13C, revealing the biomass and fossil fuel driving on nonsynchronous char and soot and their response to local anthropogenic activities and atmospheric transmission. The results showed that BC concentration increased from 1.19 ± 0.35 mg g–1(pre-1956) to 2.03 ± 1.05 mg g–1(after 1956). The variation of char was similar to BC, while nonhomologous growth was detected in char and soot (r= 0.29 and p> 0.05). The source apportionment showed that biomass burning for 71.52 ± 10.23% of char and promoted char sequestration. The contribution of fossil fuel combustion to soot (46.67 ± 14.07%) is much higher than char (28.48 ± 10.23%). Redundancy analysis confirmed that local anthropogenic activities significantly influenced BC burial and atmospheric transport from outside TP-regulated BC burial. The contribution of biomass and fossil fuels to nonsynchronous char and soot is conducive to understanding the anthropogenic effect on BC burial in the TP.