Lower Yangtze River Basin Research Articles

Long‐term hydrological assessment of remote sensing precipitation from multiple sources over the lower Yangtze River basin, China

AbstractMulti‐source remote sensing precipitation products are being used more and more frequently for rainfall analysis and hydrological applications around the world. The aim of the present study was to assess the variances and uncertainty of long‐term precipitation and corresponding hydrological simulations from 1984 to 2016 using rain gauge measurements, two satellite rainfall products retrieved from the Climate Prediction Center (CPC) and the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks – Climate Data Record (PERSIANN‐CDR) respectively, along with rainfall reanalysis data from the ERA‐Interim over the lower Yangtze River basin, China. The results indicated overestimation from ERA‐Interim and PERSIANN‐CDR on seasonal rainfall. CPC rainfall estimation had marginal bias with rain gauge measurements among all the remote sensing rainfall products on a daily scale, while the ERA‐Interim tended to overestimate when the rainfall rate was less than 50 mm. On a monthly scale, CPC rainfall estimations were very close to the rain gauge measurements, with a correlation coefficient of 0.96, whilst the ERA‐Interim rainfall products showed significant overestimation in February, March and September. Nevertheless, all remote sensing rainfall products achieved good performance in June and July, showing promising potential to be an alternative to rainfall data for long‐term water resource analysis. Furthermore, ERA‐Interim rainfall products did not perform as well as the other rainfall sources in flow simulations, as evidenced by the large root‐mean‐square error and bias. CPC rainfall products outperformed all other rainfall sources in terms of the Nash–Sutcliffe coefficient at all temporal scales. In addition, the skill scores suggested that the performance of the streamflow simulation improved significantly on a monthly scale, with a higher Nash–Sutcliffe coefficient and smaller total streamflow errors.

Estimation of daily hydrological mass changes using continuous GNSS measurements in mainland China

Surface displacements measured by the Global Navigation Satellite System (GNSS) integrate the elastic response of the solid Earth to regional and local hydrologic loading signals and provide an opportunity for near-real-time monitoring of terrestrial water storage variations. Here, we estimate the spectral information of hydrology-induced vertical surface deformation based on spherical Slepian basis functions and recover the daily changes in continental water storage over mainland China from January 2010 to December 2019. Our inversion results, depending on a sparsely-distributed GNSS network, indicate the largest seasonal fluctuation of hydrological mass loads in southwestern China. The GNSS-inferred equivalent water height has an annual amplitude of up to 314 mm, which is greater than 243 mm from the Gravity Recovery and Climate Experiment (GRACE) and 150 mm from the Global Land Data Assimilation System (GLDAS). We also find notable seasonal water oscillations of 153–166 mm in the middle and lower Yangtze River Basin. This feature appears in the GNSS inversion model and GRACE Mascon solutions but is invisible in the GLDAS model, mostly indicating the existence of significant changes in surface water storage that is unmodeled in the GLDAS model. There is board agreement in the water estimates derived from multiple data sets in South China, in contrast to weak temporal coherence of various water estimates in North China. We also demonstrate the ability of GNSS for tracking the drought and wet periods, which can serve as an independent means to characterize hydrological extremes. Our study emphasizes that a sparse GNSS network can still be considered as a complementary tool to map large-scale spatiotemporal variations of water storage and benefit the hydrological community for assessing water storage changes and hydrological dynamics.

Spatiotemporal characteristics and estimates of extreme precipitation in the Yangtze River Basin using GLDAS data

AbstractThe Yangtze River Basin has periodically been subject to torrential rains and floods. It is of great significance to characterize the extreme precipitation patterns to learn about frequent flood characteristics in the Yangtze River Basin. Commonly, spatiotemporal characteristics of extreme precipitation was studied by regional frequency analysis method with site data. Spatial sparse site data may cause imprecise divisions of homogeneous regions. In this paper, the spatiotemporal characteristics of extreme precipitation was studied by regional frequency analysis with corrected satellite‐based grid precipitation data (Global Land Data Assimilation System, GLDAS) rather than site data. The results show that: (1) The corrected GLDAS daily precipitation data had greatly improved its ability to capture extreme precipitation events in Yangtze River Basin, as the data average accuracy increased from 0.215 before correction to 0.849 after correction. It is feasible to use satellite‐based grid precipitation data to replace the site data for the regional frequency analysis of extreme precipitation. (2) The Yangtze River Basin was categorized into seven homogeneous regions for the annual maximum 1‐day (RX1DAY) index with an automatic subjective adjustment method. (3) The regional growth curves and quantiles of the Yangtze River Basin were drawn for the return period for 2–100 years. (4) Spatial patterns of extreme daily precipitation series with a return period of 100 years indicated that the precipitation amount increases gradually from the upper to the lower Yangtze River Basin, from the “arid zone” to the “wet zone” and then to the “special wet zone”, and the 100‐year return level of RX1DAY varied from 30.3 to 301.8 mm. There were three main precipitation centres, the Sichuan Basin, Dongting Lake Basin, and a great triangle area covering the Poyang Lake Basin and the south foot of Dabie Mountain.

Major Scientific Achievements of the First China-Japan Cooperative GAME/HUBEX Experiment: A Historical Review

In the summers of 1998 and 1999, Chinese and Japanese scientists cooperatively conducted the first large-scale energy and water cycle experiment (WCRP/GEWEX/GAME/HUBEX: World Climate Research Program/Global Energy and Water Cycle Experiment/Asian Monsoon Experiment/Huaihe River Basin Energy and Water Cycle Experiment) in the Huaihe River basin, Anhui Province of China. The main objective of this field experiment (HUBEX) was to investigate the multiple-scale structure characteristics, life cycles, and genesis and development mechanisms of the Meiyu system in East Asia as well as the cause of related flooding disasters. It was a joint China–Japan cooperative meteorological and hydrological observation experiment. On the basis of intensive observations, scientists from the two countries conducted follow-up investigations through collating and compiling data and performing scientific analysis during the following five years. It can be concluded that the HUBEX project has yielded comprehensive and remarkable achievements. This paper introduces the major scientific results derived from this field experiment and the ensuing investigations, and reassesses their merits and shortages for the purpose of providing useful experience and proposing new research targets as well as prospects for the initiation of a new joint scientific Meiyu experiment in the middle and lower Yangtze River basin.

Double increase in precipitation extremes across China in a 1.5 °C/2.0 °C warmer climate

Paris Agreement's 1.5 °C or 2.0 °C global warming targets call for human concerns on warming climate on human society and environment in general. Here we analyzed spatiotemporal patterns and related impacts of precipitation extremes on human society across China using NEX-GDDP (NASA Earth Exchange Global Daily Downscaled Projections) dataset. We found increasing trends of almost all extreme precipitation indices except consecutive dry duration (CDD). Additional 0.5 °C warmer climate from 1.5 °C to 2.0 °C global warming targets can double increase of extreme precipitation indices. Specifically, the increase of Rx5day (Max 5-day precipitation amount) is from 3.98% to 7.63%, the increase of R95pTOT (precipitation in very wet days) is from 19.41% to 34.42% and the increase of PRCPTOT (annual total wet-day precipitation) is from 3.89% to 8.23%, showing that additional 0.5 °C warmer climate can potentially increase flood risks across China. While, we also found regional differences in responses of extreme precipitation to warming climate. Extreme precipitation in the Qinghai Tibet Plateau, the Western Arid and semiarid zone and in the lower Yangtze River basin is in higher sensitivity to warming climate. Constraint of temperature increase of below 1.5 °C but not 2.0 °C will avoid 4.34% to 73.96% impacts of extreme precipitation on human society. It is particularly important for China since that more than half of territory of China is under exposure to high flood and drought disasters.

Whole genome sequence analysis reveals genetic structure and X-chromosome haplotype structure in indigenous Chinese pigs

Chinese indigenous pigs exhibit considerable phenotypic diversity, but their population structure and the genetic basis of agriculturally important traits need further exploration. Here, we sequenced the whole genomes of 24 individual pigs representing 22 breeds distributed throughout China. For comparison with European and commercial breeds (one pig per breed), we included seven published pig genomes with our new genomes for analyses. Our results showed that breeds grouped together based on morphological classifications are not necessarily more genetically similar to each other than to breeds from other groups. We found that genetic material from European pigs likely introgressed into five Chinese breeds. We have identified two new subpopulations of domestic pigs that encompass morphology-based criteria in China. The Southern Chinese subpopulation comprises the classical South Chinese Type and part of the Central China Type. In contrast, the Northern Chinese subpopulation comprises the North China Type, the Lower Yangtze River Basin Type, the Southwest Type, the Plateau Type, and the remainder of the Central China Type. Eight haplotypes and two recombination sites were identified within a conserved 40.09 Mb linkage-disequilibrium (LD) block on the X chromosome. Potential candidate genes (LEPR, FANCC, COL1A1, and PCCA) influencing body size were identified. Our findings provide insights into the phylogeny of Chinese indigenous pig breeds and benefit gene mining efforts to improve major economic traits.

Occurrence, spatial distribution and risk assessment of organophosphate esters in surface water from the lower Yangtze River Basin

Organophosphate esters (OPEs) are extensively used as flame retardants and plasticizers in China; however, their potential carcinogenicity causes great concern. To date, their environmental distribution in water samples from the lower Yangtze River Basin still remains uncharacterized. This study systematically investigated the occurrence and spatial distribution of 13 OPEs, as well as their associated potential risks, in water samples from the lower Yangtze River and its 88 major inflowing rivers. The total OPE (ΣOPEs) concentrations ranged from 55.6 to 5071 ng/L, with a median of 144 ng/L. Among them, halogenated OPEs were the dominant group with an average of 61.6%, and tris(1-chloro-2-propyl) phosphate (12.6–450 ng/L, median: 53.38 ng/L) and tris(2-choroethyl) phosphate (11.0–1202 ng/L, median: 36.4 ng/L) were the most abundant OPEs. Significantly different concentrations were found with spatial variations (p < 0.01), and were higher in southern cities than in northern cities of the lower Yangtze River Basin. Principal component analysis with multiple linear regression and Spearman correlations showed that the main sources were likely emission of vehicular and marine traffic. Ecological risk analysis showed that the risk quotient (RQ) values of samples remained below 1, but the percentage of 0.1 < RQ ≤ 1 was 26.9%, indicating a medium risk of OPEs in water samples. Moreover, ethylhexyl diphenyl phosphate predominantly contributed to the ecological risk, accounting for >89.2% of the total ecological risk of ΣOPEs. However, the total non-carcinogenic and carcinogenic risks of ΣOPEs were negligible at the detected concentrations, even in a high exposure scenario. The risks from major inflowing rivers of the lower Yangtze River were almost one order of magnitude higher than those of the mainstream lower Yangtze River.

Monitoring Long-Term Lake Level Variations in Middle and Lower Yangtze Basin over 2002–2017 through Integration of Multiple Satellite Altimetry Datasets

Satellite altimetry has been effectively used for monitoring lake level changes in recent years. This work focused on the integration of multiple satellite altimetry datasets from ICESat-1, Envisat and Cryosat-2 for the long-term (2002–2017) observation of lake level changes in the middle and lower Yangtze River Basin (MLYB). Inter-altimeter biases were estimated by using the gauged daily water level data. It showed that the average biases of ICESat-1 and Cryosat-2 with respect to Envisat were 6.7 cm and 3.1 cm, respectively. The satellite-derived water levels were evaluated against the gauged data. It indicated significantly high correlations between the two datasets, and the combination of three altimetry data produced precise water level time series with high temporal and spatial resolutions. A liner regression model was used to estimate the rates of lake level changes over the study period after the inter-altimeter bias adjustment was performed. The results indicated that ~79% of observed lakes (41/52) showed increasing trends in water levels with rates up to 0.203 m/y during 2002–2017. The temporal analysis of lake level variations suggested that ~60% of measured lakes (32/53) showed decreasing trends during 2002–2009 while ~66% of measured lakes (79/119) exhibited increasing trends during 2010–2017. Most of measured reservoirs displayed rapidly rising trends during the study period. The driving force analysis indicated that the temporal heterogeneity of precipitation can be mainly used to explain the observed pattern of lake level changes. The operation of reservoirs and human water consumption were also responsible for the lake level variations. This work demonstrated the potential of integrating multiple satellite altimeters for the long-term monitoring of lake levels, which can help to evaluate the impact of climate change and anthropogenic activities on regional water resources.

Changes and drivers of freshwater mussel diversity patterns in the middle and lower Yangtze River Basin, China

The Yangtze River Basin (Changjiang Basin) hosts one of the most diverse freshwater mussel assemblages on Earth. However, due to human activities this fauna is dramatically imperiled in this region, highlighting the need for urgent conservation measures. To better protect and conserve these taxa, it is crucial to understand the main drivers that control the diversity patterns, as well as the anthropogenic influence on these patterns. Here, we estimated distinct diversity metrics (i.e. species richness and alpha, gamma, and beta diversity) to analyze the spatial freshwater mussel diversity changes across 16 tributaries and lakes from the middle and lower Yangtze River Basin, in two periods: past 1962–2012 and present. For the past, mussel records were compiled from previous studies, for the present, we surveyed 565 sites for freshwater mussel presence and abundance within the 16 selected areas. We also assessed several climatic and geographical parameters to try to identify the main factors that modulate species composition across the study area. We show that from the historical to the present periods, species diversity experienced a significant decrease, registering, per river/lake, an average of 5.4 extirpations of species native to China and 3.9 of the Yangtze River Basin endemics. The gamma diversity of the whole study area and the alpha diversity of each of the studied rivers and lakes have also decreased during this period. The beta diversity values indicated a significant trend towards taxonomic homogenization over the last decades. Poyang and Dongting Lakes should be considered for protection given due to their high diversity and species loss given that nestedness in these lakes represented the main component of beta diversity.

Summer Monsoon Rainfall Patterns and Predictability over Southeast China

AbstractThis study advances the use of the Self‐organizing Map (SOM) to identify the summer monsoon rainfall patterns over Southeast China (SEC), using 272 gauge records from May to August. Three distinct rain belts over the Huai River basin (HRB), the Lower Yangtze River basin (LYRB) and the South Coast region (SCR) are found. Their subseasonal variability strongly agrees with the northward progression of the East Asian Summer Monsoon (EASM) front in a stepwise fashion. We find that precipitation in the SCR and HRB rain belts exhibit significant changes in the mid‐1990s, while the 1990s is the most active decade for the LYRB rain belt. Promising predictability of average daily rainfall over these three regions is obtained, with about 39% to 50% of the total variance explained by the circulation informed regression models. Both leave‐one‐year‐out cross‐validation and blind prediction verify the regression performance. The western North Pacific Subtropical High phases, mid‐latitude blocking high anomaly over northeast China and upper‐level divergence in SEC are found to best explain the variability of the rain belts. The newly proposed Russia‐China wave patterns (western/central Russia → north of Tibetan Plateau → SEC) and teleconnection between the El Niño‐Southern Oscillation and the rain belts also offer additional predictability. Findings from this work may advance the understanding of the EASM rain belts, and offer insights to the source of bias for numerical simulations of daily summer monsoon rainfall in the region.

E-commerce promotes trade in invasive turtles in China

AbstractFreshwater habitats in China are potentially suitable for invasive alien turtle species and, consequently, raising turtles in aquaculture facilities and the trade in turtles this supplies pose risks to habitats and native wetland communities when exotic turtles escape or are released deliberately. Online trade (e-commerce) is making an increasing contribution to turtle sales in China, seemingly driving demand and thus potentially exacerbating the risk of release. We document the scale and spatial pattern of online sales of non-native turtles over 90 days on China's Taobao.com e-commerce site. The majority of sales were in the ecologically sensitive middle and lower Yangtze river basin (82.35% of &gt; 840,000 slider turtles Trachemys scripta elegans, and 68.26% of &gt; 100,000 snapping turtles, Chelydridae spp.). These species are native to the Americas. Concurrently, over 2008–2018, we found 104 mentions of feral turtle issues listed on Baidu News where, among the 53 prefectures mentioned, issues with invasive turtle populations also focused predominantly in the middle and lower Yangtze river basin. Although circumstantial, this association suggests that the substantial online sale of alien turtles could be having detrimental effects in China's Yangtze river basin. It is important to safeguard these wetland habitats, which are of global importance, by improving policies for detecting and regulating invasive alien turtle issues and by warning consumers about the ecological hazard of their purchases.

Stable carbon isotope signatures of cellulose in macrophytes collected from three eutrophic lakes in China

Aquatic plants are essential for maintaining the diversity and stability of a lake ecosystem. Stable carbon isotopes (δ13C) of macrophytes have been widely used as a powerful tool to study ecological processes and paleoenvironmental evolution in lakes. Varying results are obtained when using the δ13C of macrophytes to study the changes in the lake environment at different spatio-temporal scales. Thus, sample preparation and subsequent laboratory analyses are crucial for studying environmental changes using the isotopic signal retained in the macrophytes, and are essential for the interpretation of isotope-environment relationships. This study analyzed the δ13C of different tissue components of macrophytes in three lakes of the lower Yangtze River basin, and a correlation analysis was performed on aquatic environments influencing the δ13C values in the different tissue components of macrophytes. The test results showed the difference between the δ13C values of the whole sample and cellulose. Relative analyses indicated that the major factors contributing to the δ13C variability in macrophytes were pH and the concentration of dissolved inorganic carbon (DIC). The δ13C of α-cellulose (δ13CAC) is more sensitive to environmental variables than that of the whole sample (δ13CW) and holocellulose (δ13CHC). The results of this study imply that extraction of α-cellulose is a prerequisite for research on the changes in lake environment using δ13C of macrophytes. This study aims to provide theoretical and data basis for further research on the environmental and ecological change using stable carbon isotopes of aquatic plants.

Predicting June Mean Rainfall in the Middle/Lower Yangtze River Basin

We demonstrate that there is significant skill in the GloSea5 operational seasonal forecasting system for predicting June mean rainfall in the middle/lower Yangtze River basin up to four months in advance. Much of the rainfall in this region during June is contributed by the mei-yu rain band. We find that similar skill exists for predicting the East Asian summer monsoon index (EASMI) on monthly time scales, and that the latter could be used as a proxy to predict the regional rainfall. However, there appears to be little to be gained from using the predicted EASMI as a proxy for regional rainfall on monthly time scales compared with predicting the rainfall directly. Although interannual variability of the June mean rainfall is affected by synoptic and intraseasonal variations, which may be inherently unpredictable on the seasonal forecasting time scale, the major influence of equatorial Pacific sea surface temperatures from the preceding winter on the June mean rainfall is captured by the model through their influence on the western North Pacific subtropical high. The ability to predict the June mean rainfall in the middle and lower Yangtze River basin at a lead time of up to 4 months suggests the potential for providing early information to contingency planners on the availability of water during the summer season.

Attribution of Lake Warming in Four Shallow Lakes in the Middle and Lower Yangtze River Basin.

Many physical, chemical, and biological processes in lakes depend on lake water temperature. However, attribution of the warming rate in a shallow lake is not well understood yet. Here, we evaluated a one-dimensional lake model FLake by observed daily lake surface water temperature (LSWT) at four typical lakes in the Middle and Lower Yangtze River basin and then attributed LSWT warming to climate variables during the period 1979-2017. We found that FLake could capture well the seasonal/interannual variation of observed LSWT. During the 39-year study period, LSWT significantly warms at a rate of 0.26-0.28 °C per decade, 24-35% slower than the air temperature. Increased solar radiation and air temperature contributed to most (>80%) of the LSWT warming. The warming trend of LSWT in the spring is the largest among the four seasons, 2-4 times the warming rate of the other seasons. Brightening in the spring contributes 50-64% of the largest spring warming. The future air warming plus the brightening trend with the Clean Air Act in China would amplify LSWT warming and, thus, advance and/or deteriorate algae blooms, especially in spring.

On the sensitivity of seasonal and diurnal precipitation to cumulus parameterization over CORDEX-EA-II

The ability of the Weather Research and Forecasting (WRF) model in simulating the seasonal and diurnal cycles of rainfall over the Coordinated Regional Climate Downscaling Experiment East Asia Phase II (CORDEX-EA-II) domain is validated against the Tropical Rainfall Measuring Mission (TRMM) datasets. A focus is placed on the role of convective parameterization (CP) schemes. A set of numerical experiments at a 25 km resolution for 1998–2009, using six different CPs, is performed to evaluate the physics-dependency of simulation results. All CPs simulate realistic summer mean precipitation and its northward propagation, with the best performance in the Simplified Arakawa-Schubert (SAS). The biases in the seasonal evolution of rainfall are related to the deficiency in simulated low-level winds and the northward propagation of the cyclonic vorticity. The simulated earlier peak time in other CPs is delayed by about 1–2 h by the Kain-Fritsch with a modified trigger function (KFMT), although this scheme shows a disadvantage in the magnitude. The performance of different CPs in simulating diurnal rainfall cycles is dependent on regions, and none of them performs better than the others for all the sub-regions. The initiation of simulated convection is weakly physics-dependent. However, the timing and magnitude of stratiform precipitation differ among the six experiments. A further analysis shows that the dry biases over the lower Yangtze River basin are a result of the weakened southwesterly water vapor transport, while the excessive afternoon rainfall in the Kain-Fritsch (KF) simulation is attributed to the largest positive perturbation in the lower level atmosphere, especially the enhanced vertical transport of humidity.

Increasing Outbreak of Cyanobacterial Blooms in Large Lakes and Reservoirs under Pressures from Climate Change and Anthropogenic Interferences in the Middle–Lower Yangtze River Basin

In recent decades, the increasing frequency and severity of cyanobacterial blooms in recreational lakes and water supply reservoirs have become a great concern to public health and a significant threat to the environment. Cyanobacterial bloom monitoring is the basis of early warning and treatment. Previous research efforts have always focused on monitoring blooms in a few specific lakes in China using moderate resolution imaging spectroradiometer (MODIS) images, which are available for the years 2000 onward. However, the lack of overall information on long-term cyanobacterial blooms in the lakes and reservoirs in the middle–lower Yangtze River (MLYR) basin is an obstacle to better understanding the dynamics of cyanobacterial blooms at a watershed scale. In this study, we extracted the yearly coverage area and frequency of cyanobacterial blooms that occurred from 1990 to 2016 in 30 large lakes and 10 reservoirs (inundation area &gt;50 km2) by using time series Landsat satellite images from Google Earth Engine (GEE). Then, we calculated the cyanobacterial bloom area percentage (CAP) and the cyanobacterial bloom frequency index (CFI) and analyzed their inter-annual variation and trends. We also investigated the main driving forces of changes in the CAP and CFI in each lake and reservoir. We found that all reservoirs and more than 60% of lakes exhibited an increasing frequency and coverage area of cyanobacterial blooms under the pressures of climate change and anthropogenic interferences. Reservoirs were more prone to be affected by fertilizer consumption from their regional surroundings than lakes. High temperatures increased blooms of cyanobacteria, while precipitation in the lake and reservoir regions somewhat alleviated blooms. This study completes the data records of cyanobacterial blooms in large lakes and reservoirs located in hotspots of the MLYR basin and provides more baseline information before 2000, which will present references for water resource management and freshwater conservation.

Weakened growth of cropland-N2 O emissions in China associated with nationwide policy interventions.

China has experienced rapid agricultural development over recent decades, accompanied by increased fertilizer consumption in croplands; yet, the trend and drivers of the associated nitrous oxide (N2 O) emissions remain uncertain. The primary sources of this uncertainty are the coarse spatial variation of activity data and the incomplete model representation of N2 O emissions in response to agricultural management. Here, we provide new data-driven estimates of cropland-N2 O emissions across China in 1990-2014, compiled using a global cropland-N2 O flux observation dataset, nationwide survey-based reconstruction of N-fertilization and irrigation, and an updated nonlinear model. In addition, we have evaluated the drivers behind changing cropland-N2 O patterns using an index decomposition analysis approach. We find that China's annual cropland-N2 O emissions increased on average by 11.2GgN/year2 (p<.001) from 1990 to 2003, after which emissions plateaued until 2014 (2.8GgN/year2 , p=.02), consistent with the output from an ensemble of process-based terrestrial biosphere models. The slowdown of the increase in cropland-N2 O emissions after 2003 was pervasive across two thirds of China's sowing areas. This change was mainly driven by the nationwide reduction in N-fertilizer applied per area, partially due to the prevalence of nationwide technological adoptions. This reduction has almost offset the N2 O emissions induced by policy-driven expansion of sowing areas, particularly in the Northeast Plain and the lower Yangtze River Basin. Our results underline the importance of high-resolution activity data and adoption of nonlinear model of N2 O emission for capturing cropland-N2 O emission changes. Improving the representation of policy interventions is also recommended for future projections.

Long-term changes of water quality in aquaculture-dominated lakes as revealed by sediment geochemical records in Lake Taibai (Eastern China)

The rapid development and exploitation of the Yangtze River basin in order to ensure human food security and increase living space in recent decades has resulted in significant potential for degradation of water quality in the river and in hundreds of lakes. Understanding how lake environments have evolved to their present state under a variety of external influences is crucial for evaluating their current status and anticipating future scenarios of environmental changes. However, the lakes along the middle reaches of the Yangtze River (MRY) are as yet little studied. Here, we described the long-term anthropogenic environmental transformations of a small lake (Lake Taibai) in the MRY area, based on a detailed quantitative geochemical analysis of the aliphatic hydrocarbons, nutrients (N and P), biogenic silica (BSi), and major and trace elements present in a dated sediment core retrieved from the lake. Our data revealed that levels of short-chain n-alkanes, αβ-hopanes and the trace elements arsenic (As) and cadmium (Cd) were all low for the entire record in sediments prior to ca. 1970, reflecting unpolluted natural state of the lake. Pronounced anthropogenic effects began to appear in sediments deposited in the subsequent years ca. 1970–1990, during which the levels of all these components were elevated, most likely driven by input of nitrogen (N) and phosphorus (P) containing chemical fertilizers, pesticides and diesel oil respectively. Since ca. 1990, changes of short-chain n-alkane levels in the sediment suggested the lake had undergone dramatic eutrophication in which existing anthropogenic stressors were exacerbated by technological advances that extended the use of chemical fertilizer into aquaculture. This pattern contrasted with an otherwise comparable lake in the lower Yangtze River basin, Lake Changdang, in which trace element and petroleum pollution were much more prominent due to dramatic urbanization and industrialization of the catchment.

Changes in Forest Net Primary Productivity in the Yangtze River Basin and Its Relationship with Climate Change and Human Activities

Net Primary Productivity (NPP) is a basis of material and energy flows in terrestrial ecosystems, and it is also an important component in the research on carbon cycle and carbon budget. This paper evaluated the spatial distribution pattern and temporal change trends for forest NPP simulated by the LPJ (Lund-Potsdam-Jena) model and NDVI (normalized difference vegetation index) in the Yangtze River basin from 1982 to 2013. The results revealed that: (1) the spatial distribution of the forest NPP and NDVI in the Yangtze River basin has gradually decreased from the southeast coast to the northwest. The forest NPP and NDVI in the mid-lower Yangtze were higher than that of the upper Yangtze; (2) the forest NPP and NDVI in most areas of the Yangtze River basin were positively correlated with the temperature and precipitation. Moreover, the correlations among the temperature with the forest NPP and NDVI were stronger than that of correlations among precipitation with forest NPP and NDVI. Moreover, the extreme drought event in the year of 2004–2005 led the NPP to decrease in the middle and lower Yangtze River basin; (3) human activity such as major ecological projects would have a certain impact on the NPP and NDVI. The increase in forest areas from 2000 to 2010 was larger than that from 1990 to 2000. Moreover, the increasing rate for the NDVI was higher than that of NPP, especially after the year 2000, which indicates that the major ecological projects might have great impacts on the vegetation dynamics. Moreover, more attention should be paid on the joint impacts of human activity and climate change on terrestrial NPP and NDVI.

Influence of Three Gorges Dam on Downstream Low Flow

Low flow is a seasonal phenomenon which is a critical requirement for utilization of water resources under rapidly changing environmental conditions. The operation of the Three Gorges Dam (TGD) has had a great influence on downstream low flow in the Yangtze River. In this paper, the characteristics of low flow in the main Yangtze River were analyzed during the dry season before and after the TGD operation during the period of 1956–2016. The results show that: (1) the operation of the TGD has changed the spatial and temporal distribution of streamflow in the middle and lower Yangtze River and the annual mean low flow has increased significantly since the TGD operation. (2) The operation of the TGD could advance the date of the start of dry season in the lower Yangtze River basin. The start dates of the dry season in the Yichang, Hankou and Datong stations were advanced by 14 days, 10 days and 9 days, respectively. (3) The minimum streamflow in the lower Yangtze River has increased notably since the TGD operation. The minimum streamflow was raised by 42.91%, 13.76% and 6.06% at the Yichang, Hankou and Datong stations, respectively. The increasing number of dams in the world might have the potential effects on downstream low flow. More attention should be paid to investigating the influence of dam construction on low flow in rivers all over the world.