Characteristics of wintertime carbonaceous aerosols in two typical cities in Beijing-Tianjin-Hebei region, China: Insights from multiyear measurements.

In order to investigate the impact of "Blue Sky War" implemented during 2018-2020 on carbonaceous aerosols in Beijing-Tianjin-Hebei (BTH) region, China, fine particulate matter (PM2.5) samples were collected simultaneously in Tianjin and Handan in three consecutive winters from 2018 to 2020. Organic carbon (OC) and elemental carbon (EC) in PM2.5 were measured with the same thermal-optical methods and analysis protocols. Significant reductions in primary organic carbon (POC) and EC concentrations were observed both in Tianjin and Handan, with decreasing rates of 0.65 and 2.95 µg m-3 yr-1 for POC and 0.13 and 0.64 µg m-3 yr-1 for EC, respectively. The measured absorption coefficients of EC (babs, EC) also decreased year by year, with a decreasing rate of 1.82 and 6.16 Mm-1 yr-1 in Tianjin and Handan, respectively. The estimated secondary organic carbon (SOC) concentrations decreased first and then increased in both Tianjin and Handan, accounting for more than half of the total OC in winter of 2020-2021 and with increasing contributions especially in highly polluted days. SOC was recognized as one of key factors influencing EC light absorption. EC in the two cities was relatively more related to coal combustion and industrial sources. The reductions of primary carbonaceous components may be attributed to the air quality regulations targeting coal combustion and industrial sources emissions in BTH area. Potential source contribution function (PSCF) analysis results indicated that the major source areas of OC and EC in Tianjin were the southwest region of the sampling site, while the southeast areas for Handan. These findings demonstrated the effectiveness of air quality regulation in primary emissions in typical polluted cities in BTH region and highlighted the needs for further control and in-depth investigation of SOC formation along with implementation of air pollution control act in the future.

Spatiotemporal dynamics of phytoplankton biomass and community succession for driving factors in a meso-eutrophic lake.

Effects of climate change and nutrient load caused by human activities on lake phytoplankton blooms have attracted much attention globally. However, their roles and synergistic effects on phytoplankton biomass and community historical succession are not well understood, especially for meso-eutrophic plateau lakes. In this study, a multi-year (1997-2022) monthly dataset including hydro-chemical and meteorological indicators of the meso-eutrophic plateau lake Erhai in China, was used to explore the contributions of climate change and nutrients on phytoplankton biomass variation and community succession. Phytoplankton biomass increased from 1997 to 2006, slowly decreased from 2006 to 2015, then increased again from 2015 to 2022, according to a generalised additive model (GAM). Alongside warming, nitrogen, phosphorus and organic matter are key drivers of long-term interannual variation in phytoplankton biomass and historical succession of the phytoplankton community. The extensive blooms in recent years were strongly associated with both organic matter accumulation and global warming. Phytoplankton biomass in northern and southern districts was greater than in central areas, with Cyanophyta and Pyrrophyta dominating in the north and Chlorophyta prevalent in the south. Since 2015, phytoplankton diversity has increased significantly, and biomass has declined in the southern district but increased markedly in the northern district. Spatial heterogeneity was caused by the spatial distribution of nutrients and the buoyancy regulation capacity of cyanobacteria. The results demonstrate that bloom mitigation responds strongly to nitrogen and phosphorus control in meso-eutrophic lakes, therefore preventing and controlling blooms through nitrogen and phosphorus reduction is still an effective measure. Given the accumulation of organic matter in recent years, synergistic control of organic matter and total nitrogen and phosphorus could effectively reduce the risk of cyanobacterial and dinoflagellate blooms.

Accelerated increase in vegetation carbon sequestration in China after 2010: A turning point resulting from climate and human interaction.

China has increased its vegetation coverage and enhanced its terrestrial carbon sink through ecological restoration since the end of the 20th century. However, the temporal variation in vegetation carbon sequestration remains unclear, and the relative effects of climate change and ecological restoration efforts are under debate. By integrating remote sensing and machine learning with a modelling approach, we explored the biological and physical pathways by which both climate change and human activities (e.g., ecological restoration, cropland expansion, and urbanization) have altered Chinese terrestrial ecosystem structures and functions, including vegetation cover, surface heat fluxes, water flux, and vegetation carbon sequestration (defined by gross and net primary production, GPP and NPP). Our study indicated that during 2001-2018, GPP in China increased significantly at a rate of 49.1-53.1 TgC/yr2 , and the climatic and anthropogenic contributions to GPP gains were comparable (48%-56% and 44%-52%, respectively). Spatially, afforestation was the dominant mechanism behind forest cover expansions in the farming-pastoral ecotone in northern China, on the Loess Plateau and in the southwest karst region, whereas climate change promoted vegetation cover in most parts of southeastern China. At the same time, the increasing trend in NPP (22.4-24.9 TgC/yr2 ) during 2001-2018 was highly attributed to human activities (71%-81%), particularly in southern, eastern, and northeastern China. Both GPP and NPP showed accelerated increases after 2010 because the anthropogenic NPP gains during 2001-2010 were generally offset by the climate-induced NPP losses in southern China. However, after 2010, the climatic influence reversed, thus highlighting the vegetation carbon sequestration that occurs with ecological restoration.

Interannual Variation of the East Asia Jet Stream and Its Impact on the Horizontal Distribution of Aerosol in Boreal Spring.

Interannual variation of the aerosol optical depth (AOD) in East Asia has been investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) data and Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) data for 2000-2018. The data analysis focuses on boreal spring when Siberian biomass burning is at its seasonal maximum. The results indicate that the significant increase in organic and black carbon is primarily caused by emissions from biomass burning in East Asia, which leads to significant interannual variations in aerosol loading and pan-Pacific transport. The anomalous large-scale climate variability associated with the East Asia Jet Stream (EAJS) provides favorable conditions for increasing the AOD of organic and black carbon in Northeast Asia and may represent an underlying physical mechanism. When the EAJS shows greater weakening than normal, abnormal high-pressure anomalies are maintained in East Asia, which tend to drive warm advection over Northeast Asia. This warm advection expedites the melting of the Eurasian snow cover, which helps increase surface dryness in late spring and provides favorable conditions for biomass burning. The EAJS index can be predictable with statistical significance up to lead 1 month by the dynamical ensemble seasonal forecasts, suggesting a possible implementation of the empirical AOD forecasts using climate forecast models.

A 4-year field measurement of N2O emissions from a maize-wheat rotation system as influenced by partial organic substitution for synthetic fertilizer.

Soil N2O emissions depend on the status of stoichiometric balance between organic C and inorganic N. As a beneficial management practice to sustain soil fertility and crop productivity, partial substitution of organic fertilizers (OFs) for synthetic fertilizers (SFs) can directly affect this balance status and regulate N2O emissions. However, no multi-year field studies of N2O emissions under different ratios of OFS to SFs have been performed. We conducted a 4-year experiment to measure N2O emissions in a maize-wheat rotation in central China. Six treatments were included: total SF (TS), total OF, no N fertilizer, and ratios of to SF with 1: 2 (LO), 1: 1 (MO), and 2: 1 (HO), based on N content. Two incubation experiments were performed to further interpret the field data. In the first year, cumulative N2O emissions (kg N ha-1) in LO, MO, and HO were 4.59, 4.68, and 3.59, respectively, significantly lower than in TS (6.67). However, from the second year onwards, organic substitution did not reduce N2O emissions and even significantly enhanced them in the fourth year relative to TS. Soil respiration under OF-amended soils increased over the course of the experiment. From the second year onwards, there was no marked difference in mineral N concentrations between OF- and SF-amended soils. OF caused a drop in soil pH. Cumulative N2O was negatively correlated with pH. Long-term organic substitution enhanced N2O emissions produced via denitrification rather than nitrification and resulted in higher temperature sensitivity of N2O emissions than TS. The enhanced N2O emissions from the OF-treated soils were mainly attributable to accelerated OF decomposition, increased denitrification-N2O emissions, and lessened N2O reduction due to lower pH and greater NO3-. These results indicate that OF substitution can reduce N2O emissions in the first year, but in the long-term it can increase emissions, especially as soils warm.

Aquatic carbon fluxes dampen the overall variation of net ecosystem productivity in the Amazon basin: An analysis of the interannual variability in the boundless carbon cycle.

The river-floodplain network plays an important role in the carbon (C) cycle of the Amazon basin, as it transports and processes a significant fraction of the C fixed by terrestrial vegetation, most of which evades as CO2 from rivers and floodplains back to the atmosphere. There is empirical evidence that exceptionally dry or wet years have an impact on the net C balance in the Amazon. While seasonal and interannual variations in hydrology have a direct impact on the amounts of C transferred through the river-floodplain system, it is not known how far the variation of these fluxes affects the overall Amazon C balance. Here, we introduce a new wetland forcing file for the ORCHILEAK model, which improves the representation of floodplain dynamics and allows us to closely reproduce data-driven estimates of net C exports through the river-floodplain network. Based on this new wetland forcing and two climate forcing datasets, we show that across the Amazon, the percentage of net primary productivity lost to the river-floodplain system is highly variable at the interannual timescale, and wet years fuel aquatic CO2 evasion. However, at the same time overall net ecosystem productivity (NEP) and C sequestration are highest during wet years, partly due to reduced decomposition rates in water-logged floodplain soils. It is years with the lowest discharge and floodplain inundation, often associated with El Nino events, that have the lowest NEP and the highest total (terrestrial plus aquatic) CO2 emissions back to atmosphere. Furthermore, we find that aquatic C fluxes display greater variation than terrestrial C fluxes, and that this variation significantly dampens the interannual variability in NEP of the Amazon basin. These results call for a more integrative view of the C fluxes through the vegetation-soil-river-floodplain continuum, which directly places aquatic C fluxes into the overall C budget of the Amazon basin.

Responses of community structure and diversity to nitrogen deposition and rainfall addition in contrasting steppes are ecosystem-dependent and dwarfed by year-to-year community dynamics.

BACKGROUND AND AIMS: Long-term studies to disentangle the multiple, simultaneous effects of global change on community dynamics are a high research priority to forecast future distribution of diversity. Seldom are such multiple effects of global change studied across different ecosystems. METHODS: Here we manipulated nitrogen deposition and rainfall at levels realistic for future environmental scenarios in three contrasting steppe types in Mongolia and followed community dynamics for 7 years. KEY RESULTS: Redundancy analyses showed that community composition varied significantly among years. Rainfall and nitrogen manipulations did have some significant effects, but these effects were dependent on the type of response and varied between ecosystems. Community compositions of desert and meadow steppes, but not that of typical steppe, responded significantly to rainfall addition. Only community composition of meadow steppe responded significantly to nitrogen deposition. Species richness in desert steppe responded significantly to rainfall addition, but the other two steppes did not. Typical steppe showed significant negative response of species richness to nitrogen deposition, but the other two steppes did not. There were significant interactions between year and nitrogen deposition in desert steppe and between year and rainfall addition in typical steppe, suggesting that the effect of the treatments depends on the particular year considered. CONCLUSIONS: Our multi-year experiment thus suggests that responses of community structure and diversity to global change drivers are ecosystem-dependent and that their responses to experimental treatments are dwarfed by the year-to-year community dynamics. Therefore, our results point to the importance of taking annual environmental variability into account for understanding and predicting the specific responses of different ecosystems to multiple global change drivers.

Decreased snowpack and warmer temperatures reduce the negative effects of interspecific competitors on regenerating conifers.

The persistence and distribution of species under changing climates can be affected by both direct effects of the environment and indirect effects via biotic interactions. However, the relative importance of direct and indirect climate effects on recruitment stages is poorly understood. We conducted a manipulative experiment to test the multiway interaction of direct and competition-mediated effects of climate change on vegetation dynamics. Following stand-replacing fire in California mixed-conifer forest, we seeded two conifer species, Pinus ponderosa and Abies concolor, in two consecutive years, one relatively normal and the other with an unusually wet and snowy winter followed by a hot summer. We additionally manipulated snow amount and competitive environment for both years. We found the effects of the snowpack treatment were contingent upon other abiotic factors (year of seeding) and biotic factors (shrub competition). Under ambient snowpack, shrubs reduced recruitment of P. ponderosa seedlings, but this negative effect disappeared with reduced snowpack. Additionally, the effects of shrubs on seedlings differed between cohorts and by life stage. In a warmer future, decreased snowpack may increase seedling emergence, but hotter and drier summers will decrease seedling survival; the effects of shrubs on conifers may become less negative as temperatures increase.

Viability of cyclic populations.

Theory on viability of small populations is well developed and has led to the standard methodology of population viability analysis (PVA) to assess vulnerability of single species. However, more complex situations involving community dynamics or environmental change violate theoretical assumptions. Synthesizing concepts from population, community, and conservation ecology, we develop a generic theory on the viability of cyclic populations. The interplay of periodic population decline and demography causes varying risk patterns that aggregate during cycles and modify the temporal structure of viability. This variability is visualized and quantitatively assessed. For two standard viability metrics that summarize immediate extinction risk and the general long-term conditions of populations, we mathematically describe the impact of population cycles. Finally, we suggest and demonstrate PVA for cyclic populations that respond to, e.g., seasonality, interannual variation, or trophic interactions. Our theoretical and methodological advancement opens a route to viability analysis in food webs and trophic meta-communities and equips biodiversity conservation with a long-missing tool.

Multiyear greenhouse gas balances at a rewetted temperate peatland.

Drained peat soils are a significant source of greenhouse gas (GHG) emissions to the atmosphere. Rewetting these soils is considered an important climate change mitigation tool to reduce emissions and create suitable conditions for carbon sequestration. Long-term monitoring is essential to capture interannual variations in GHG emissions and associated environmental variables and to reduce the uncertainty linked with GHG emission factor calculations. In this study, we present GHG balances: carbon dioxide (CO2 ), methane (CH4 ) and nitrous oxide (N2 O) calculated for a 5-year period at a rewetted industrial cutaway peatland in Ireland (rewetted 7 years prior to the start of the study); and compare the results with an adjacent drained area (2-year data set), and with ten long-term data sets from intact (i.e. undrained) peatlands in temperate and boreal regions. In the rewetted site, CO2 exchange (or net ecosystem exchange (NEE)) was strongly influenced by ecosystem respiration (Reco ) rather than gross primary production (GPP). CH4 emissions were related to soil temperature and either water table level or plant biomass. N2 O emissions were not detected in either drained or rewetted sites. Rewetting reduced CO2 emissions in unvegetated areas by approximately 50%. When upscaled to the ecosystem level, the emission factors (calculated as 5-year mean of annual balances) for the rewetted site were (±SD) -104 ± 80 g CO2 -C m-2  yr-1 (i.e. CO2 sink) and 9 ± 2 g CH4 -C m-2  yr-1 (i.e. CH4 source). Nearly a decade after rewetting, the GHG balance (100-year global warming potential) had reduced noticeably (i.e. less warming) in comparison with the drained site but was still higher than comparative intact sites. Our results indicate that rewetted sites may be more sensitive to interannual changes in weather conditions than their more resilient intact counterparts and may switch from an annual CO2 sink to a source if triggered by slightly drier conditions.

Interannual variation in nitrous oxide emissions from perennial ryegrass/white clover grassland used for dairy production.

Nitrous oxide (N2 O) emissions are subject to intra- and interannual variation due to changes in weather and management. This creates significant uncertainties when quantifying estimates of annual N2 O emissions from grazed grasslands. Despite these uncertainties, the majority of studies are short-term in nature (<1 year) and as a consequence, there is a lack of data on interannual variation in N2 O emissions. The objectives of this study were to (i) quantify annual N2 O emissions and (ii) assess the causes of interannual variation in emissions from grazed perennial ryegrass/white clover grassland. Nitrous oxide emissions were measured from fertilized and grazed perennial ryegrass/white clover grassland (WC) and from perennial ryegrass plots that were not grazed and did not receive N input (GB), over 4 years from 2008 to 2012 in Ireland (52°51'N, 08°21'W). The annual N2 O-N emissions (kg ha(-1); mean ± SE) ranged from 4.4 ± 0.2 to 34.4 ± 5.5 from WC and from 1.7 ± 0.8 to 6.3 ± 1.2 from GB. Interannual variation in N2 O emissions was attributed to differences in annual rainfall, monthly (December) soil temperatures and variation in N input. Such substantial interannual variation in N2 O emissions highlights the need for long-term studies of emissions from managed pastoral systems.

Dry-season length affects the annual ecosystem carbon balance of a temperate semi-arid shrubland.

Semi-arid ecosystems have been shown to dominate over tropical forests in determining the trend and interannual variability of land carbon (C) sink. However, the magnitude and variability of ecosystem C balance remain largely uncertain for temperate semi-arid shrublands at the decadal scale. Using eddy-covariance and micro-meteorological measurements, we quantified the interannual variation in net ecosystem production (NEP) and its components, gross primary production (GPP) and ecosystem respiration (Reco, i.e., the sum of autotrophic and heterotrophic respiration), in a semi-arid shrubland of the Mu Us Desert, northern China during 2012-2022. This shrubland was an overall weak C sink over the 11 years (NEP = 12 ± 46 g C m-2 yr-1, mean ± SD). Annual NEP ranged from -66 to 77 g C m-2 yr-1, with the ecosystem frequently switching between being an annual C sink and a C source. GPP was twice as sensitive as Reco to prolonged dry seasons, leading to a close negative relationship between annual NEP and dry-season length (R2 = 0.80, P < 0.01). Annual GPP (R2 = 0.51, P = 0.01) and NEP (R2 = 0.58, P < 0.01) were positively correlated with annual rainfall. Negative annual NEP (the ecosystem being a C source) tended to occur when the dry season exceeded 50 d yr-1 or rainfall dropped below 280 mm yr-1. Increases in dry-season length strengthened the effects of low soil moisture relative to high vapor pressure deficit in constraining NEP. Both GPP and NEP were more closely correlated with C uptake amplitude (annual maximum daily values) than with C uptake period. These findings indicate that dry-season extension under climate change may reduce the long-term C sequestration in semi-arid shrublands. Plant species adapted to prolonged dry seasons should be used in ecosystem restoration in the studied area to enhance ecosystem functions.

Spatial and temporal variation in the diet of the Pacific sand lance Ammodytes hexapterus in waters off the coast of British Columbia, Canada.

Variation in the diet of the Pacific sand lance Ammodytes hexapterus was examined in three years (2009-2011) at four sites in British Columbia, Canada. There were 12 major taxa of prey in diets, eight of which were Crustacea, with copepods being by far the dominant taxon in all 12 site-years. Of the 22 copepod taxa recorded, only Calanus marshallae and Pseudocalanus spp. occurred in all collections, and these two calanoid species dominated diets in terms of frequency of occurrence and total numbers of prey (Pseudocalanus spp. in most collections), and total prey biomass (C. marshallae in all collections). Based on an index of relative importance, C. marshallae was the primary prey at the two southerly sampling sites (Pine and Triangle Islands) and Pseudocalanus spp. at the two northerly sites (Lucy Island and S'Gang Gwaay). Based on an index of dietary overlap, the species composition of the copepod component of A. hexapterus diets overlapped very strongly at the northerly and the southerly pairs of sites in both a cold-water La Niña year (2009) and a warm-water El Niño year (2010), but overall there was more homogeneity amongst all four sites in the La Niña year.

Speciation and source changes of atmospheric arsenic in Qingdao from 2016 to 2020 - Response to control policies in China.

Arsenic (As) is a toxic pollutant in the atmosphere. The atmospheric As concentration is high over the East Asian continent. At present, there is less research on the long-term trend of atmospheric arsenic pollution, which is not conducive to understanding its behavior. Total suspended particulate matter (TSP) samples were collected in Qingdao in autumn and winter from 2016 to 2020 to analyze total arsenic (TAs), As(V) and As(III). The interannual variation patterns, influencing factors and health risks of arsenic concentrations in aerosols were discussed. The results showed that As(V) is the dominant species of arsenic in aerosols. The average concentration of TAs gradually decreased and the proportion of As(III) increased during autumn and winter from 2016 to 2020. The levels of TAs, As(V) and As(III) in aerosols increased during the heating period and on polluted days. Negative correlation between TAs/TSP and TSP indicated that higher concentrations of TSP in the atmosphere would reduce the content of TAs in particulate matter. The increase of secondary aerosol particles played a dilution effect. Mobile source emissions, biomass and coal combustion were main sources of atmospheric arsenic. The distribution range of large potential sources of atmospheric arsenic decreased from 2016 to 2020, and concentrated, mainly in parts of Shandong province and its offshore areas. Local sources contributed the most to atmospheric arsenic pollution in Qingdao in autumn and winter. TAs, As(V) and As(III) posed a low non-carcinogenic risk and a negligible carcinogenic risk to adults and children. This study reveals the influence of strict air pollution control policies on the speciation and source of arsenic in aerosols.

Interannual variations in the nutrient cycle in the central Bohai Sea in response to anthropogenic inputs.

In recent decades, there has been growing concern regarding the effects of human activities on the coastal nutrient cycle. However, interannual variations in the coastal nutrient cycle in response to anthropogenic nutrient input have rarely been quantified. In this study, a hydrodynamic-ecological model capable of describing the nitrogen and phosphorus cycles was used to analyze interannual variations in the nutrient cycle in the central Bohai Sea, a typical semi-enclosed sea in the Northwest Pacific. The results showed an increasing trend of dissolved inorganic nitrogen and particulate nitrogen from 1998 to 2017, whereas different forms of phosphorus showed no obvious interannual variations. The annual nutrient budgets were also quantitatively estimated from 1998 to 2017. This indicates that atmospheric nitrogen deposition plays an important role in interannual variations in the nitrogen cycle. A large amount of nitrogen from anthropogenic inputs was mainly removed by sedimentation processes instead of increasing the standing stock of nitrogen in the sea. With the reduction of anthropogenic inputs, the model showed that a variety of forms of nitrogen concentration decreased linearly, whereas phosphorus concentration increased slightly. Therefore, although environmental governance can effectively alleviate water eutrophication, it is necessary to avoid the situation where the dissolved inorganic nitrogen concentration in the sea becomes too low for phytoplankton to grow, which may determine the primary productivity and eventually affect fishery resources.

Yessotoxins in Mollusks of the Galician Coast from 2014 to 2022: Variability, Biotransformation, and Resistance to Alkaline Hydrolysis.

The presence of yessotoxins (YTXs) was analyzed in 10,757 samples of Galician bivalves from 2014 to 2022. Only YTX and 45-OH YTX were found. YTX was detected in 31% of the samples, while 45-OH YTX was found in 11.6% of them. Among the samples containing YTX, 45-OH YTX was detected in 37.3% of cases. The maximum recorded levels were 1.4 and 0.16 mg of YTX-equivalentsg-1, for YTX and 45-OH YTX, respectively, which are well below the regulatory limit of the European Union. The YTX and 45-OH YTX toxicities in the raw extracts and extracts subjected to alkaline hydrolysis were strongly and linearly related. Due to the lack of homo-YTX in Galician samples, the effect of alkaline hydrolysis on homo-YTX and 45OH-Homo-YTX was only checked in 23 additional samples, observing no negative effect but a high correlation between raw and hydrolyzed extracts. Hydrolyzed samples can be used instead of raw ones to carry out YTXs determinations in monitoring systems, which may increase the efficiency of those systems where okadaic acid episodes are very frequent and therefore a higher number of hydrolyzed samples are routinely analyzed. The presence of YTX in the studied bivalves varied with the species, with mussels and cockles having the highest percentages of YTX-detected samples. The presence of 45-OH YTX was clearly related to YTX and was detected only in mussels and cockles. Wild populations of mussels contained proportionally more 45-OH YTX than those that were raft-cultured. Spatially, toxin toxicities varied across the sampling area, with higher levels in raft-cultured mussels except those of Ría de Arousa. Ría de Ares (ARE) was the most affected geographical area, although in other northern locations, lower toxin levels were detected. Seasonally, YTX and 45-OH YTX toxicities showed similar patterns, with higher levels in late summer and autumn but lower toxicities of the 45-OH toxin in August. The relationship between the two toxins also varied seasonally, in general with a minimum proportion of 45-OH YTX in July-August but with different maximum levels for raft-cultured and wild mussel populations. Interannually, the average toxicities of YTX decreased from 2014 to 2017 and newly increased from 2018 to 2021, but decreased slightly in 2022. The relationship between 45-OH YTX and YTX also varied over the years, but neither a clear trend nor a similar trend for wild and raft mussels was observed.

Biodiversity and Interannual Variation of Harmful Algal Bloom Species in the Coastal Sea of Qinhuangdao, China.

For the frequent occurrence of harmful algal blooms (HABs) in the Qinhuangdao coastal sea (QCS) of the Bohai Sea in summer, we tested the hypothesis that high-biodiversity HAB species exist in the area, and a series of censuses of HAB species were conducted in the QCS in the summers of 2014-2019. Through morphological identification, we found 100 algae species representing 42 genera in 3 phytoplankton phyla in this study, among which Bacillariophyta was the most dominant phylum. We also found that the population density of Dinoflagellata increased from 2016 to 2019. In total, 59 HAB species were annotated in this study, including 39 of Bacillariophyta, 18 of Dinoflagellata and 2 of Ochrophyta, of which 13 HAB species were reported in the Bohai Sea for the first time, and most HAB species were widely distributed in the QCS in summer. Notably, four dominant HAB species displayed unique temporal and spatial distribution characteristics, while their distribution ranges and population densities increased from 2014 to 2019. The distributions of five environmental factors were different in the QCS, while the temperature, salinity, and dissolved inorganic nitrogen might be the key environmental factors influencing the distribution of dominant HAB species in the summer. In conclusion, this study provides a detailed evaluation of phytoplankton diversity and interannual variation in the QCS. The existence of a high level of biodiversity of algal bloom species suggests the need for long-term monitoring in order to further study and prevent potential HABs.

Effects of drought, disturbance, and biotic neighborhood on experimental tree seedling performance.

Forest biodiversity is likely maintained by a complex suite of interacting drivers that vary in importance across both space and time. Contributing factors include disturbance, interannual variation in abiotic variables, and biotic neighborhood effects. To probe ongoing uncertainties and potential interactions, we investigated tree seedling performance in a temperate mid-Atlantic forest ecosystem. We planted seedlings of five native tree species in mapped study plots, half of which were subjected to disturbance, and then monitored seedling survival, height growth, and foliar condition. The final year of data collection encompassed a drought, enabling comparison between intervals varying in water availability. Seedling performance was analyzed as a function of canopy cover and biotic neighborhood (conspecific and heterospecific abundance), including interactions, with separate generalized linear mixed models fit for each interval. All species exhibited: (a) pronounced declines in height growth during the drought year, (b) detrimental effects of adult conspecifics, and (c) beneficial effects of canopy openness. However, despite these consistencies, there was considerable variation across species in terms of the relevant predictors for each response variable in each interval. Our results suggest that drought may strengthen or reveal conspecific inhibition in some instances while weakening it or obscuring it in others, and that some forms of conspecific inhibition may manifest only under particular canopy conditions (although given the inconsistency of our findings, we are not convinced that conspecific inhibition is critical for diversity maintenance in our study system). Overall, our work reveals a complex forest ecosystem that appears simultaneously and interactively governed by biotic neighborhood structure (e.g., conspecific and/or heterospecific abundance), local habitat conditions (e.g., canopy cover), and interannual variability (e.g., drought).

Interannual variations of Sargassum blooms in the Yellow Sea and East China Sea during 2017-2021.

Golden tide, caused by Sargassum horneri, is becoming another periodic and trans-regional harmful macroalgal bloom in the Yellow Sea (YS) and East China Sea (ECS) other than the green tide. In this study, we employed high-resolution remote sensing, field validations, and population genetics to investigate the spatiotemporal development pattern of Sargassum blooms during the years 2017 to 2021 and explore the potential environmental factors that influence them. Sporadic floating Sargassum rafts could be detected in the middle or northern YS during autumn and the distribution area then occurred sequentially along the Chinese and/or western Korean coastlines. The floating biomass amplified significantly in early spring, reached its maximum in two to three months with an evident northward expansion, and then declined rapidly in May or June. The scale of the spring bloom was much larger than the winter one in terms of coverage, suggesting an additional local source in ECS. The blooms were mostly confined to waters with a sea surface temperature range of 10-16℃, while the drifting pathways were consistent with the prevailing wind trajectory and surface currents. The floating S. horneri populations exhibited a homogenous and conservative genetic structure among years. Our findings underscore the year-round cycle of golden tides, the impact of physical hydrological environments on the drifting and blooming of pelagic S. horneri, and provide insights for monitoring and forecasting this emerging marine ecological disaster.

Meteorology-driven PM2.5 interannual variability over East Asia.

Atmospheric fine particulate matter (PM2.5) is a human health risk factor, but its ambient concentration depends on both precursor emissions and meteorology. While emission reductions are used to set PM2.5-related health policies, the effect of meteorology is often overlooked. To explore this aspect, we examined PM2.5 interannual variability (IAV) associated with meteorological parameters using the long-term simulation from the Community Earth System Model (CESM1), a global climate-chemistry model, with fixed emissions. The results are subsequently contrasted with the MERRA-2 reanalysis dataset, which inherently considers emission and meteorology effects. Over continental East Asia, the CESM1 domain-average PM2.5 IAV is 6.7 %, mainly attributed to humidity, precipitation, and ventilation variation. The grid-cell PM2.5 IAVs over southern East China are larger, up to 12 % due to the more substantial influence of El Niño-induced meteorological anomalies. Under such climate extreme, sub-regional PM2.5 concentration may occasionally exceed WHO air quality guideline levels despite the compliance of the long-term mean. The simulated PM2.5 IAV over continental East Asia is ~25 % of that derived from the MERRA-2 data, which highlights the influence of both emission and meteorology-driven variations and trends inherent in the latter. Although emission-driven variability is significant to PM2.5 IAV, in remote areas downwind of major source regions in East Asia, North America, and Western Europe, the MERRA-2 data revealed that meteorological variations contributed more to PM2.5 IAV than emission variations. Thus, when setting policies for complying with the WHO PM2.5-related air quality guideline levels, the highest annual PM2.5 associated with climate extremes should be considered instead of that based on average climate conditions.