Globally accelerating fish introductions and fisheries expansion in lacustrine ecosystems have imposed severe threats to endemic fish populations and ecological structures. Quantifying food web architecture and niche enables rigorous evaluation of invasive fishes’ roles in impacting endemic communities and their cascading ecosystem effects. Stable isotope analysis (δ13C and δ15N) of producers and consumers was combined using MixSIAR model to quantify the proportional contributions of basal carbon sources in Fuxian Lake. The trophic position estimation incorporated the carbon-source-weighted δ15N baselines, accounting for isotopic variability in source materials. Multidimensional datasets (carbon source contributions, trophic positions, isotopic niches, and life-history traits) were integrated to quantify the ecological impacts exerted by invasive species on endemic Anabarilius grahami populations. Results indicated pelagic carbon sources dominated (57.8

Phytoplankton are primary bio-indicators of riverine ecosystem functioning, however, their robustness in turbid, fragmented systems remains poorly characterized. This study investigates spatiotemporal dynamics of phytoplankton community composition, biomass, and diversity in the Upper Red River, China, a system defined by sediment overloads and cascading dams. Seasonal field campaigns aim to evaluate the influence of hydro-physical filters (temperature, discharge and turbidity) alongside nutrient forcing. Results reveal a seasonal pattern in phytoplankton biomass, with higher levels during the dry season of lower temperatures. This is likely driven by increased water retention time and hydrological stability in dammed reaches, which appears to facilitate biomass accumulation despite lower nutrient concentrations. During the wet season, extreme turbidity and elevated flow suggest that light limitation and hydraulic flushing may override nutrient availability as primary regulators of biological metrics. Under these conditions, phytoplankton exhibit shifts in Chl-a/biomass ratios consistent with physiological strategies maximizing light-harvesting efficiency in low-light environments. We suggest that metrics like Chl-a can be unreliable indicators of total biomass in turbid environments, as their correlation is affected by community compositional shifts and potential physiological pigment adjustments. Observations indicate that the wet-season flood pulse enhances longitudinal homogenization, acting as a potential reset mechanism temporarily restoring the riverine continuum and mitigating serial discontinuity due to cascading dams. These findings point toward the flow regime as a major determinant of ecological structure in sediment-laden rivers. Effective monitoring of fragmented corridors may benefit from hydro-ecologically integrated indicators like pigment-to-biomass ratios and hydrology-based metrics, rather than over-reliance on nutrient-biomass paradigms.

Global freshwater ecosystems are experiencing widespread ecological degradation and biodiversity loss, creating an urgent need for robust ecological health assessment frameworks. Traditional assessment approaches typically rely on a single taxonomic group, limiting their ability to capture ecosystem degradation because different biological groups exhibit taxon-specific responses and temporal lags to environmental changes. Based on environmental DNA (eDNA) metabarcoding, we developed a multitrophic index of biotic integrity (IBIm) to assess ecological health by integrating bacteria, fungi, eukaryotic algae, and invertebrates of 40 shallow lakes in the Yangtze-Huaihe River basin, China. The effectiveness of the IBIm was supported by its strong associations with environmental gradients and its sensitivity to declines in β-diversity. Compared to single-taxon IBIs, the IBIm showed stronger correlations with multiple physicochemical variables, including dissolved oxygen and ammonia. In addition, lower IBIm values were associated with reduced local contributions to beta diversity (LCBD) across multiple biological groups, indicating a loss of local community uniqueness under degradation. Lake health assessments based on IBIm were more stringent than those based on the water quality index (WQI): only 37.5% of lakes were classified as "Good" by IBIm, compared with 82.5% by WQI. The IBIm framework bridges practical biomonitoring with ecological interpretation of freshwater degradation and provides a promising tool for ecosystem monitoring and management under global change.

Rainfed apple orchards on the Loess Plateau are chronically constrained by water scarcity and soil nutrient depletion, which severely limit orchard productivity and long-term sustainability. This study aimed to evaluate the effects of an integrated management strategy combining rainwater harvesting (RWH), supplemental irrigation (SI), and partial substitution of chemical fertilizer with organic fertilizer (OF) on soil water and nutrient dynamics, root–shoot development, and yield formation in a typical rainfed apple orchard. A two-year field experiment was conducted from 2022 to 2023 on the Loess Plateau with five treatments: RWH + SI + low-rate OF (WHIOF1), RWH + SI + high-rate OF (WHIOF2), RWH + SI (WHI), RWH alone (WH), and a rainfed control (CK). Soil moisture and nutrient parameters, root and aboveground growth traits, and fruit yield and quality were systematically measured. Mantel tests and partial least squares regression were used to identify the key factors driving yield and fruit quality responses. Compared with CK, the WHIOF2 treatment significantly increased soil water storage in the 0–180 cm profile by30.19

Janthinobacterium strains, which belong to the family Oxalobacteraceae, have attracted considerable attention due to their ability to synthesize violacein and degrade polyphenols. Wild alpine rhododendrons dominate the mountainous vegetation in southwestern China, and their leaf litter decomposition contributes to humification in alpine lakes. The Janthinobacterium strains may play a key role in the decomposition of these leaf litters. In 2025, metagenomic approaches combined with isolation and cultivation methods were applied to investigate microbial resources in stacked decayed leaves from these alpine lakes. The predominant phyla are Pseudomonadota and Actinomycetota with the relative abundances of 47.9% and 39.9%, respectively. The relative abundance of genus Janthinobacterium is only 0.1% in the community, but 11 Janthinobacterium strains were isolated. Based on the ANI and phylogenomic analyses, strains Du111 and Du118 should represent a novel species, for which the name Janthinobacterium foliorum sp. nov. is proposed. The ANI and AAI values between Janthinobacterium aestuarii and Janthinobacterium violaceum are 95.5% and 97.1%, respectively, implying that the recent proposed J. violaceum is the synonym of J. aestuarii. Comparative genomic analyses further reveal that not each of Janthinobacterium strains could produce violacein and prodigiosin, but most Janthinobacterium strains have the potential for participating in the decomposition of lignin and cellulose. This study clarifies the novel role of Janthinobacterium strains, showing that the isolated strains do not represent a novel taxonomic species but have adapted to the alpine microenvironment associated with Rhododendron leaf litter.

Thermal and nutrient fluctuations are known to determine ecological structure in shallow lakes. However, their forcing on algal assembly in large and deep lakes remains largely unclear in subtropical regions. Here, a monthly survey was conducted in 2015 to examine the mechanisms for epilimnetic diatom assembly across 16 sites of Fuxian Lake in subtropical China. In this deep system (maximum depth 158.9 m), there existed a clear seasonality in the dominant diatoms, shifting from colonial Fragilaria crotonensis (January-February) to heavily silicified Aulacoseira granulata (March-April), before small-sized Pantocsekiella ocellata predominated (> 50 %) from May to December when thermal stability was strong. While species turnover over time was notable (2.07 +/- 0.18 SD, n = 16) and driven by nutrient and thermal factors (55.0 % variance), spatial species turnover was lower (1.10 +/- 0.22 SD, n = 12), and nutrient and thermal factors explained much less variance (14.3 %). Specifically, temperature and nutrients independently explained 24.1 % and 17.6 % of the temporal variation, respectively, with a strong interaction (13.3 %). Structural equation modeling (SEM) further suggested that strong thermal stability, enhanced by rising temperature and reduced wind speed, may have significantly shaped diatom assembly. Additionally, rising stability was associated with decreased epilimnetic nutrient concentrations, possibly due to a weaker exchange with bottom-water, which can inhibit diatoms with high nutrient demands. Overall, our in situ observational evidence indicates that thermal stability governs seasonal succession of diatom communities and also interacts with fluctuating nutrients, suggesting that continued warming may seasonally enhance lake-water thermal stability and intensify species turnover in deep subtropical lakes.

Abstract Aquatic ecosystems have changed dramatically, but the relative roles of external forcings and internal atmospheric variability remain unclear. Here, using Tibetan lake ecological reconstructions and Earth system simulations, we reveal how shared external forcings shaped Tibetan Plateau limnoecology over the past millennium through two distinct pathways. In the temperature-centric pathway, cooling episodes driven by volcanic activity and internal variability likely regulated preindustrial lake conditions. This baseline was disrupted as recent forced warming has shortened lake ice-cover and increased meltwater input, altering lake resources and triggering unprecedented diatom shifts. In the freshening-centric pathway, salinity-tolerant diatoms tracked monsoon-driven precipitation changes and lake freshening, both governed by shifts in the intertropical convergence zone. Preindustrial shifts likely reflected hemispherically asymmetric orbital and volcanic forcings, whereas modern changes have been altered remarkably by Northern Hemisphere industrial aerosol fluctuations and warming-induced meltwater. As multifaceted stressors intensify, Tibetan lake ecosystems may continue diverging from their natural variability.

In recent decades, lakes in arid central Asia have undergone severe ecological and environmental changes due to accelerated climate warming and intense human activities. However, there have been few studies that integrate multi-community dynamics, long-term historical trends, and drivers of ecological change, limiting our ability to effectively manage the evolution of these freshwater ecosystems. In this paper, we analyze high-resolution biotic proxies (subfossil cladocerans and diatoms) from Bosten Lake and Ailike Lake, northwest China, over the past two centuries, and compare these records with other lakes in the region to reveal changes in lake ecosystems. Our results indicate that natural climate variability was the primary driver of a first transition (similar to 1910 CE), whereas anthropogenic forcings predominantly drove a second transition (similar to 1960 CE) in these dryland lakes. After similar to 1960 CE, planktonic eutrophic cladoceran species such as Bosmina longirostris and diatom species including Fragilaria cf. crotonensis, Cyclotella atomus, and Cyclotella meneghiniana became more dominant. Redundancy analysis and variance partitioning analysis suggest that changes in community assemblages were mainly driven by nitrogen loading (TN and/or delta N-15), with additional influences related to lake productivity (Chl-a and TOC) and global warming. Furthermore, another shift in cladoceran composition in Bosten Lake, commencing similar to 1990 CE, from large-sized Daphnia to small-sized Bosmina, was likely caused by increased predation pressure as result of the introduction of commercial fish farming. Our findings highlight the importance of understanding the complex interactions of lake ecological shifts with compounded stressors, both climate and anthropogenic forcings, for sustainable water management strategies, enhancing ecological resilience, and protecting freshwater ecosystems from further degradation.

As primary producers in lake ecosystems, phytoplankton mediate aquatic carbon and nitrogen cycling, with stable isotope signatures archived in their biomass‌ serving as sensitive tracers of climatic fluctuations and anthropogenic impacts on biogeochemical processes. Through comprehensive analysis of phytoplankton carbon and nitrogen isotope signatures across nine Yunnan plateau lakes (2017-2022), we reveal divergent regulatory mechanisms under coupled environmental stressors. The isotopic discrimination of phytoplankton carbon isotope, driven by both growth rate and inorganic carbon pool changes, exhibits temperature sensitivity (+0.43 ‰/ °C), showing monsoon-modulated seasonal patterns where warming enhances 13C enrichment in lacustrine organic matter, potentially reshaping ‌elemental carbon partitioning under climate change. Phytoplankton nitrogen isotope signatures reveal nonlinear responses to watershed urbanization (population density, built-up area), with isotopic deviations from watershed soil nitrogen isotope baselines tracking anthropogenic nitrogen sources (e.g., 15N-depleted agricultural fertilizers vs. 15N-enriched sewage inputs). Projected intensification under climate warming and accelerated urbanization may further amplify dual-isotope (13C and 15N) imprints within lacustrine carbon-nitrogen coupling.‌ Crucially, the dual enrichment of 13C and 15N isotopes elevates baseline signatures at primary trophic levels while reducing energy transfer efficiency via isotope-specific zero-point vibrational effects. These isotope-mediated dynamics decode synergistic interactions between climate variability and human-driven perturbations, establishing an isotopic toolkit for diagnosing carbon-nitrogen coupling and guiding adaptive watershed governance in fragile plateau ecosystems.

The genus Undibacterium is an important member of Oxalobacteraceae and most species of this genus were isolated from freshwater environments. The recent study based on the genomic analyses revised the taxonomic status of 23 Undibacterium species and proposed that these species should be assigned into four genera (Undibacterium, Neoundibacterium, Affinundibacterium and Paraundibacterium), respectively. During the investigation of microbial resources inhabited in alpine lakes from the southwestern China in 2023, 25 strains show the highest 16S rRNA gene sequence similarities with Undibacterium species were isolated. Utilizing the genomes of these 25 strains and 26 Undibacterium species, the phylogenies among these strains are reconstructed based on the core and pan-genome, respectively. The phylogenomic trees show that the 26 Undibacterium species should be divided into six clades and each clade should represent an independent genus. As the clades 2, 3, 4 and 5 proposed in this study have been revised in other study, the genera Cognatundibacterium and Pseudundibacterium are proposed in this study to accommodate the clades 1 and 6, respectively. The detailed genomic annotations reveal that all the 25 isolated Undibacterium-related strains harbor complete amino acids metabolisms and genes encoding DNA replication and repair, homologous recombination proteins, two-component and phosphate transport systems in response to the oligotrophic, high UV radiation and phosphorus-limited environments of alpine lakes. This study clarifies the role of Undibacterium-related strains in alpine lakes and demonstrates that isolating more strains is of great benefit to the bacterial taxonomy.

Lakes are crucial terrestrial carbon sinks for the Earth's surface systems,where the burial and transfor-mation of total organic carbon(OC)and inorganic carbon(IC)are strongly influenced by watershed surface processes.In alpine regions with limited direct human impact,long-term warming trends can enhance key proce-sses,such as algal growth and the mineralization of organic matter,thereby altering OC and IC accumulation and burial dynamics.We examined spatial patterns,synergistic relationships and controlling factors of carbon burial under regional warming across six alpine lakes in northwestern Yunnan(deep lakes:Dinggongniang Co,Gaigong Co Na,Wodi Co;shallow lakes:Dinggong Co,Bigu Tianchi,Shudu Lake),by employing multiple proxies inclu-ding total nitrogen,chlorophyll,OC and IC contents,combined with climate reconstruction data.Results showed that 1.14℃ increase in temperature over the past 150 years had significantly reshaped carbon sequestration across lakes.The response magnitude of primary productivity to temperature increases in shallow lakes(Bigu Tianchi:39％;Shudu Lake:58％;Dinggong Co:30％)was significantly greater than in deep lakes(Dinggongniang Co:14％;Gaigong Co Na:7％;Wodi Co:20％).Distinct carbon cycling processes were observed between lake types.In deep lakes,algal contributions to OC were negligible while enhancing synchronous OC-IC deposition,indicating stratification simultaneously inhibited autochthonous carbon burial while promoting organic matter preservation.Con-versely,there were strong chlorophyll-OC correlations with weakened OC-IC coupling in shallow lakes,revealing algal-dominated organic carbon production coupled with enhanced mineralization processes.Furthermore,atmos-pheric deposition altered inorganic carbon burial regimes through nitrogen enrichment in alkaline waters(Dinggong-niang Co,Gaigong Co Na,Wodi Co,Shudu Lake,Bigu Tianchi).Elevated pH promoted carbonate precipitation and IC accumulation,while acidic inputs suppressed IC burial in acidic lake(Dinggong Co)and modified OC-IC burial relationship.Overall,the carbon burial processes in alpine lakes exhibited different responses to regional environmental changes,which were strongly related to lake depth,pH,and other limnological characteristics.

In the semi-arid Loess Plateau of China, afforestation frequently leads to soil water depletion, threatening ecosystem sustainability. Although mixed-species plantations are encouraged to enhance resource use efficiency, their effects on deep soil water and root distribution strategies remain unclear. This study compared soil water content (SWC), deep soil water deficit (SWD), and fine root distribution in pure and mixed plantations of Robinia pseudoacacia, Platycladus orientalis, and Hippophae rhamnoides to assess whether species mixing intensifies consumption for deep soil water. Soil moisture and root samples were collected with a maximum depth of 20 m across five stand types in August 2018 and during the 2019 growing season. Results showed that mixed stands exhibited shallower water depletion depth and lower SWC below 2 m than pure stands, but a more severe deep soil water deficit, with observed SWD exceeding the expected values by 12% in the R. pseudoacacia-P. orientalis mixture (MRP) and 22% in the H. rhamnoides-P. orientalis mixture (MHP), indicating intensified water consumption below 2 m. In the MRP, the maximum rooting depth was shallower than in the corresponding pure stands. Within the mixture, species-specific root plasticity was observed: the normalized fine root length density (FRLD) of P. orientalis was four times greater in mixture than in pure stand, whereas that of R. pseudoacacia was 62% lower, suggesting divergent foraging strategies. Correlation analyses indicated that SWC was differently associated with root traits between pure and mixed stands, with relationships varying by soil depth. Mixed-effects models confirmed that both plantation type and soil depth significantly influenced FRLD and Root dry weight density (RDWD), while specific root length (SRL) was mainly affected by plantation type and its interaction with depth. These findings demonstrated that mixed-species afforestation intensifies deep soil water competition. Therefore, sustainable management should prioritize the selection of species with complementary root foraging strategies and the optimization of planting densities in semi-arid regions.

In dryland agroforestry systems, large-scale afforestation for ecological restoration often compromises groundwater sustainability, yet the roles of tree species traits (e.g., rooting depth) and soil-vegetation interactions remains unclear. We conducted a field study on the Loess Plateau, comparing 14 deep-rooted afforestation species (13 trees, 1 shrub) with adjacent shallow-rooted crops (maize, wheat, millet, etc.) across 32 paired sites. Using soil water profiling, root mapping, and tritium tracing, we found that deep rooting (4.8-28 m) reduced soil water storage by 0-2131 mm and groundwater recharge by at least 67.2 % compared to shallow-rooted vegetation. Rooting depth explained 72 % of recharge variation, outperforming climate and soil factors. Moreover, the adverse effect of rooting depth on recharge was strongly modulated by soil texture, as coarser-textured soils weaken this impact by enhancing deep percolation. These findings provide a scientific basis for selecting lowwater-demand tree species (e.g., shallow-rooted Ziziphus jujuba) to maintain groundwater recharge in dryland agroforestry systems. Our results quantify the trade-off between afforestation goals and groundwater security, offering actionable insights for climate-smart land-use planning.

Lakes are considered excellent archives for the reconstruction of sedimentary processes and related hydroclimatic variations. Dian Lake in south-western China was selected to demonstrate the impacts of Indian summer monsoon-induced water and sediment availabilities on land surface changes and human behaviours. A new sediment core from Dian Lake in the vicinity of Hebosuo village was analyzed by grain size composition, geochemical content, and minerals to detect land-lake processes that responded to hydroclimatic variations and human impacts through the Holocene. Our data suggest that Dian Lake levels during the last 9.8 cal. ka BP were controlled by the variations of the Indian summer monsoon moisture supply according to the displacements of the Intertropical Convergence Zone. A low lake level stage of similar to 4 m lower than present was determined between 3.1 and 1.73 cal. ka BP, allowing the residents of the Dian culture to occupy the low terrains for settlement and farmland cultivation. With lake level rise at around 1.73 cal. ka BP (220 CE) the high input of clay-fine silt-sized sediments rich in rubidium and barium indicates intensified soil erosion in the Dian Lake basin. Former paddy farmlands and mountain slopes were drained by artificial and natural channels towards the lake in response to strengthened rainfalls covering low terrains by coarse and red alluvial sediments that fostered the residents to abandon the lowlands in the southern basin until 1368 CE. However, the surface erosion process during this period promoted the elevation of the south-eastern delta so that it could be re-occupied since Ming Dynasty. The Indian summer monsoon influence comparable to the modern pattern was responsible for lake level rise to the present level since then but also triggered high seasonality in flood and drought events to foster manual regulation of flood discharge during the last centuries.

Cladocerans are widely distributed in aquatic ecosystems and are sensitive to environmental changes; hence, they are commonly used to trace ecological changes in aquatic environments. However, the distribution of cladocerans in northern China is poorly known. We investigated the occurrence of cladocerans in 136 water bodies (including lakes and reservoirs), with varying hydro-chemical and climatic gradients, in northern China and western Mongolia. We identified 38 cladoceran taxa in the surface sediments of 88 different water bodies, while the remaining lakes, mainly saline, had no cladocerans. The spatial distribution characteristics of cladoceran species and the environmental factors determining their community composition were investigated using canonical correspondence analysis. The results demonstrate that water depth, trophic status, and water salinity were the top three variables influencing the composition of cladoceran taxa. Transfer functions between the surface sediment cladocerans and lake level and nutrient (NH4) levels in 62 lakes (26 lakes lacked environmental data) were established via multivariate statistical analyses. Using the subfossil cladocerans of Jili Lake, lake level and nutrient values were reconstructed for the past 100 years. The results agree overall with the observational data, and they reveal that the changes in the cladoceran community reflected mainly lake level fluctuations before 1988 CE, and mainly nutrient changes thereafter. Our research clarifies, for the first time, the environmental significance of modern Cladocera in the lakes of northern China and western Mongolia, and it provides a foundation for the future reconstruction of long-term changes in the ecological environment of lakes.

Eutrophication has become prominent in many lakes of the world, resulting in a continuous rise of suspended particulate organic matter (POM) that can be of vital consequence for water quality and carbon cycling. While the accumulation and decomposition of POM can enhance nutrient cycling at a rate depending on the property of lake-water organic carbon, it is important to identify the source of suspended POM for evaluating eutrophication and carbon burial. Here we analyzed the distribution of stable isotopic ratios (δ13C and δ15N) and the carbon/nitrogen ratio (C/N) in suspended POM in a shallow eutrophic lake of subtropical China, for apportioning the POM sources using Bayesian mixing model. Specifically, we collected seasonal samples of lake-water POM (>0.7 μm) from 20 sites in Yilong Lake from September 2020 to June 2022, as well as six types of modern samples covering the main carbon sources in the catchment. The spatial surveys showed that in the dry year (low water level) the δ13C of POM was more enriched in the western basin than those in the central and eastern basins, while the seasonal surveys showed the most enriched δ13C of POM in September. However, this spatio-temporal heterogeneity disappeared in the wet year (high water level). It was also found that the δ13C, δ15N and C/N values of POM varied significantly with those of phytoplankton across sites and seasons. Application of the MixSIAR model further showed that phytoplankton was the predominant source of POM in Yilong Lake (79.8 ± 13.4 %), but with large annual difference, 68.9 ± 10.3 % in the dry year and 90.7 ± 3.7 % in the wet year. In comparison, the contribution of the other five endmembers was much more moderate. In particular, the proportion of allochthonous organic carbon in POM was relatively low, with terrestrial plants and soils contributing 6.1 ± 4.8 % and 4.3 ± 2.5 % of POM, respectively. Our quantitative evidence for the dominance of the autochthonous source (i.e., phytoplankton) in lake-water POM over time and space suggested a determining role of eutrophication in the composition of lake organic carbon. Therefore, the coupling of algal blooms with organic carbon cycling in inland waters can be enhanced with continuous catchment development and regional warming.

Arsenic contamination has become an important environmental issue of some water bodies in China under the background of economic development and basin exploitation. However, limited attention has been paid to the effects of arsenic pollution prevention and ecological restoration. Phytoplankton is the key primary producer in lake ecosystems. Arsenic can directly affect the phytoplankton growth, species succession and primary productivity, and has become a sensitive indicator of arsenic pollution and its ecological effects. Lake Yangzong has a long history of arsenic pollution and subsequent remediation efforts. We conducted a seasonal survey on phytoplankton and environmental factors of Lake Yangzong covering the south, central and north parts of the lake from 2015 to 2019. The survey data were used to identify the spatio-temporal pattern and driving factors of phytoplankton biomass, and to evaluate the mechanism of phytoplankton biomass changes and effect of eco-restoration under arsenic pollution and treatment. The results showed that the phytoplankton was mainly composed of Cyanophyta. The phytoplankton biomass was in a range of 0.7-30.4 mg/L, with the lowest value in 2016 ((3.0±1.8) mg/L) and the highest value in 2017 ((10.5±8.9) mg/L). The phytoplankton biomass showed significant seasonal variations, but did not show significant spatial difference. The correlation analysis showed that the phytoplankton biomass had a significantly negative correlation with arsenic concentration and transparency, but had a significantly positive correlation with water temperature and pH. The multivariable linear regression model further showed that temperature and arsenic were the key environmental factors in driving the change of phytoplankton biomass. Thus, the arsenic residues in water body still inhibit phytoplankton growth after remediation in heavy metal polluted lakes, indicating that heavy metal pollutants may have long-term effects due to sediment release and enduring ecotoxicological impacts.

湖泊碳埋藏模式及其动态变化对陆地碳汇通量与全球碳收支估算具有重要影响,然而现有湖泊碳埋藏评估主要基于有机碳的埋藏模式,缺乏对无机碳埋藏以及有机碳-无机碳协同变化过程的系统评估.本文通过对云南岩溶区异龙湖开展沉积物岩芯样品的多指标分析和湖盆 3 个点位的记录对比,结合 210Pb、137Cs年代学序列,识别了1900年以来异龙湖有机碳和无机碳埋藏通量的变化历史和空间特征,并甄别了二者协同变化的主要特征及其转化路径.结果表明,近百年来流域开发导致的营养盐长期输入(如沉积物氮和磷的持续富集)显著提高了异龙湖的内源初级生产力,表现为1900～2020年间沉积物藻类色素含量持续增加,蓝藻叶黄素浓度由～7.02μg/g 显著增加到～38.99μg/g.同期有机碳和无机碳的埋藏通量均出现持续的上升趋势,且两者的同步变化特征显著(r=0.98～0.99,P<0.001).回归分析表明,藻类生物量是碳埋藏通量上升的主要驱动因子(R2=0.33～0.91,P<0.001),指示了藻类光合作用以及"生物碳泵"效应对碳埋藏过程的驱动作用.在流域地表物质输入强度总体下降(如磁化率信号和沉积物C:N比值的减小)的背景下,藻类生物量和内源有机碳的持续上升导致了有机质矿化过程中自生碳酸盐的转化作用明显增加(如无机碳δ13C信号的持续下降),进而促进了有机碳与无机碳埋藏通量的协同增长.上述结果表明,水体富营养化过程促进形成了有机碳和无机碳埋藏通量同步增加的长期模式,加强了异龙湖有机碳和无机碳埋藏过程的耦合作用.因此在人类活动与气候变化持续的背景下,对岩溶地区湖泊碳埋藏模式的科学评估需要关注无机碳埋藏过程及其对陆地碳汇通量的动态影响.

Deep-rooted vegetation transpires a considerable amount of deep soil water with different ages in the unsaturated zone. However, the tradeoffs between new water of transpiration (temporally originating from post-planting precipitation) and old water of transpiration (temporally originating from pre-planting precipitation) across the vegetation lifespan are poorly understood. In this study, we collected soil samples from beyond 28 m soil depth on the Loess Plateau of China to investigate the influence of deep-rooted vegetation on the age of soil water and analyze the proportion of new and old water of transpiration in the unsaturated zone under grassland, 22-year-old apple orchard, and 17-year-old peach orchard. Water isotopes (2H, 18O, and 3H), solutes (chloride, nitrate, sulfate), and soil water content were used to identify the critical water ages in the unsaturated zone (one-year water age, water age corresponding to stand age, and the maximum water age of transpiration), and to determine soil water deficit, soil evaporation loss fraction, and potential groundwater recharge. The results showed that soil water mainly moved as piston flow in these soil profiles, and deep soil water largely came from heavy precipitation. Deep-rooted vegetation restrained new pore water velocity and potential groundwater recharge. New pore water velocity declined from 0.40 m yr-1 to 0.14 m yr-1 and 0.34 m yr-1 for apple and peach, respectively. Deep-rooted vegetation decreased groundwater recharge by 9.46 % for apple and 7.04 % for peach, compared to grassland. Over the vegetation lifespan, annual average transpiration was 500.56 mm yr-1 and 468.89 mm yr-1 with maximum water age of 63 years and 45 years for apple and peach, respectively. The transpiration of deep-rooted vegetation mainly used new water (94.97 % for apple and 97.47 % for peach). The total old water of transpiration was 553 mm for apple and 209 mm for peach. Our results identify the temporal sources of vegetation water use, offering new insights into the transpiration process of deep-rooted vegetation.