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Inland water bodies, being the most active biogeochemical cycle reactors, play a pivotal role in the global carbon cycle and CO2 budget. This study integrates existing observation dataset of CO2 flux (fCO2) in rivers, lakes and reservoirs in China, to elucidate their spatial-temporal patterns and key influencing factors and to reappraise the significance for regional carbon balance. It showed that, the fCO2 in rivers, lakes and reservoirs in China presented significant variability with large range of −379.3–4947.6, −160.1–785.0 and −74.0–1603.1 mg CO2 m−2 h−1, respectively. The median of the fCO2 in rivers was of 228.5 mg CO2 m−2 h−1, observably higher than these in lakes and reservoirs (26.0 and 28.3 mg CO2 m−2 h−1, respectively). The fCO2 in rivers and reservoirs exhibited similar decreasing trend from south to north as a result of universal climate restraint, the averaged fCO2 in Pearl River and Yangtze River basins showed much higher than that in Northeastern rivers. While, the averaged fCO2 in the Mongolia-Xinjiang lake district and the Northeast lake district were higher than other lake districts, followed by the Qinghai-Xizang lake district, and the Eastern and Yungui lake district were generally low, contradicting the climatic restriction. The water primary production enhancement resulting from human activities was the main driver of spatial variation in the fCO2 in lakes. Meanwhile, the fCO2 in rivers presented seasonal pattern with higher wet season than dry season, while opposite patterns were found in lakes and reservoirs. Seasonal temperature, precipitation and water primary production were main factors. Furthermore, it showed pH was a key factor indicating the variability of the fCO2 levels either in rivers, lakes or in reservoirs. In lakes, the fCO2 is closely linked to chlorophyll a (Chl-a) and dissolved oxygen (DO), whereas, the fCO2 in rivers is primarily associated with organic carbon (OC) and total nitrogen (TN), highlighting the diverse controlling mechanisms of fCO2 in various inland water types. In addition, we found that water body sizes play an important role in regulating the fCO2 levels, and small waters act as hotspots of CO2 flux. Additionally, widespread urbanization and agricultural activities may enhance CO2 emissions from rivers but potentially mitigating that from lakes. Nevertheless, the comprehensive impact of these factors on CO2 emissions in inland water requires further evaluation. Based on the extrapolation method, we re-estimated that the total CO2 emission of inland waters in China is approximately 117.3 Tg yr−1, which could offset 4.6%–12.8% of the total land carbon sink in China. [ABSTRACT FROM AUTHOR]

Global climate change will modify precipitation and temperatures' temporal and spatial distribution, trigger more extreme weather events, and impact hydrological processes. The Yangtze River basin is one of the world's largest basins, and understanding future climate changes is vital for water resource management and supply. Research on predicting future climate change in the upper Yangtze River basin (UYRB) and introducing machine learning algorithms to analyze the impact of climate factors, including extreme weather indicators, on surface runoff is urgently needed. In this study, a statistical downscaling model (SDSM) was used to forecast the future climate in the UYRB, and the Mann–Kendall (MK) or modified Mann–Kendall (MMK) trend test at a 5% level of significance was applied to analyze temporal trends. The Spearman rank correlation (SRC) test at a 5% level of significance and random forest regression (RFR) model were employed to identify the key climatic factors affecting surface runoff from annual precipitation, annual temperature, maximum 5-day precipitation (R×5Day), number of tropical nights (TR), and consecutive dry days (CDD), and the RFR model was also used to predict future runoff. Based on the results, we found that, compared to the selected historical period (1985–2014), the mean annual precipitation (temperature) during the mid-term (2036–2065) increased by 18.93% (12.77%), 17.78% (14.68%), 20.03% (17.03%), and 19.67% (19.29%) under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively, and during the long term (2071–2100), increased by 19.44% (12.95%), 22.01% (21.37%), 30.31% (30.32%), and 34.48% (37.97%), respectively. The warming and humidification characteristics of the northwestern UYRB were more pronounced. The key climatic factors influencing surface runoff were annual precipitation, maximum 5-day precipitation (R×5day), and annual temperature. Because of warming and humidification, surface runoff in the UYRB is expected to increase relative to the historical period. The surface runoff during the mid-term (long term) increased by 12.09% (12.58%), 8.15% (6.84%), 8.86% (8.87%), and 5.77% (6.21%) under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively. The implementation of sustainable development pathways under the low radiative forcing scenario can be effective in mitigating climate change, but at the same time, it may increase the risk of floods in the UYRB. [ABSTRACT FROM AUTHOR]

Forest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems. [ABSTRACT FROM AUTHOR]

Currently, air pollution becomes a wide-concerned global environmental problem. In Shandong Province of North China, the air quality deterioration has greatly restricted the development of society and threatened human health. In this study, air quality index (AQI) and 6 pollutants monitored in 2019 are analyzed associated with socioeconomic factors, aiming to identify the characteristics and driving factors of air pollution. Our results show that great seasonality and spatial heterogeneity exists for AQI and pollutants. The variation patterns result from mechanisms of pollutants formation, and are mainly dependent on the coal burning-dominated energy production and climatic periodicity. Correlation analysis shows that AQI decreases with the increase of factors of city size, resource and energy consumption, transportation and economy, but is weakly related to population. The ratio of energy supply for different purpose also influences the air pollutants. The increased proportion of electric supply for productive use will result in anabatic pollution caused by particle matters, oxynitrate and oxysulfide. This study provides useful information for the better control of air pollution and insights for the making of environmental-friendly strategies for energy supply. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial–temporal variability of soil water content is critical for water management and restoration of vegetation in semi‐arid areas. Using the temporal stability method, we investigated soil water relations and spatial–temporal variability of volumetric soil water content (VSWC) in the grassland–shrubland–forest transect at a typical semi‐arid subalpine ecosystem in the Qilian Mountains, northwestern China. The VSWC was measured on 48 occasions to a depth of 70 cm at 50 locations along a 240‐m transect during the 2016–2017 growing seasons. Results revealed that temporal variability in VSWC in the same soil layer in the three vegetation types and averaged across vegetation types tended to exhibit similar patterns of a decrease with increasing soil depth. Temporal stability in each vegetation type was stronger with an increase in soil depth. However, the results of temporal stability determined with standard deviation of relative difference (SDRD) disagreed with those based on the Spearman's rank correlation coefficient; the forest site had the highest Spearman rank correlation coefficient while the shrubland—the smallest SDRD in the 0–20 cm soil layer. Correlation analyses of VSWCs between two vegetation types indicated that soil water was related among all three vegetation types at the 0–20, and 0–70 cm soil layer, but in the 20–40 and 40–70 cm soil layers, significant correlation (p <.01) occurred only between adjacent vegetation types. In the upper soil layer (0–20 cm), soil water relations were mainly affected by surface runoff. In the lower soil layer (20–40 and 40–70 cm), soil water relations among the three vegetation types were highly complex, and probably resulting from a combination of root distribution and activity, interflow, and the impact of deep soil freeze–thaw dynamics. These results suggest that the factors affecting soil water are complex, and further research should address the relative importance of and interactions among different determining factors. [ABSTRACT FROM AUTHOR]

The response of karst groundwater level to rainfall features spatial and temporal variability. There is no consensus regarding the groundwater dynamic system structure of the Zengpiyan cave site in Guilin, Guangxi, China. Based on high-resolution data on rainfall water level, the study area was divided into different aquifers. The characteristics and cause of spatial and temporal variability of karst groundwater level's response to rainfall were explored using water level dynamics, correlation analysis, and sliding window cross-correlation analysis. The results show that in terms of the response to rainfall, the water level of aquifers with a high degree of karst development and diffusion flow for water diversion rises and falls slowly, featuring a strong autocorrelation in water level; the water level of aquifers developed with karst conduits rises and falls rapidly, with a fast decay rate of water-level autocorrelation coefficient, a short lag time in response to rainfall, and a multimodal cross-correlation function graph. The extreme non-uniformity of karst development is the primary cause of differences in spatial response. The response lag of the groundwater level to rainfall in the rainy season is much smaller than during the dry season. This is because, in the rainy season, there is a large amount of cumulative rainfall, the buried depth of groundwater is shallow, and the aerated zone is constantly in a saturated or near-saturated state, causing the groundwater supply to become saturated by vertical rainfall infiltration relatively quickly. Further, the frequent rainstorms in the rainy season can generate to a large hydraulic gradient in a short period of time, accelerating the runoff replenishment speed of aquifers. Taken together, the groundwater system of the Zengpiyan cave site consists of 3 sub-runoff systems, i. e. the NE karst conduit, the NS conduit-fracture, and the NE strong runoff zones. The research results can provide theoretical basis and technical reference for the cave site to formulate plans of preventing and controlling underground water hazards. [ABSTRACT FROM AUTHOR]

The spatial and temporal characteristics of drought are investigated for Luanhe River basin, using monthly precipitation data from 26 stations covering the common period of 1958–2011. The spatial pattern of drought was assessed by applying principal component analysis (PCA) to the Standardized Precipitation Index (SPI) computed on 3- and 12-month time scales. In addition, annual SPI and seasonal SPIs (including spring SPI, summer SPI, autumn SPI, and winter SPI) were also defined and considered in this study to characterize seasonal and annual drought conditions, respectively. For all seven SPI cases, three distinctive sub-regions with different temporal evolutions of droughts are well identified, respectively, representing the southeast, middle, and northwest of the Luanhe River basin. The Mann-Kendall (MK) trend test with a trend-free pre-whitening (TFPW) procedure and Sen’s method were used to determine the temporal trends in the annual and seasonal SPI time series. The continuous wavelet transform (CWT) was employed for further detecting the periodical features of drought condition in each sub-region. Results of MK and Sen’s tests show a general tendency of intensification in summer drought over the entire basin, while a significant mitigating trend in spring drought. On the whole, an aggravating trend of inter-annual drought is discovered across the basin. Based on the CWT, the drought variability in the basin is generally dominated by 16- to 64-month cycles, and the 2- to 6-year cycles appear to be obvious when concerned with annual and seasonal droughts. Furthermore, a cross wavelet analysis was performed to examine the possible links between the drought conditions and large-scale climate patterns. The teleconnections of ENSO, NAO, PDO, and AMO show significant influences on the regional droughts principally concentrated in the 16- to 64-month period, maybe responsible for the physical causes of the cyclical behavior of drought occurrences. PDO and AMO also highlight a noteworthy correlation with drought variability on a decadal scale (around 128-month period). The findings of this study will provide valuable references for regional drought mitigation and water resource management. [ABSTRACT FROM AUTHOR]

• The weight of fine-grained material decreased with distance from the main channel. • Riverbank sediments with smaller K values had weak heterogeneity. • An experimental framework showing how to quantify sediment properties is proposed. A detailed measurement of floodplain riverbank sediment hydraulic conductivity (K) is the first step in analyzing the hydraulic relationship between streams and aquifers. Poyang Lake is the largest freshwater lake in China and has historically been a flood-prone area. A detailed field experiment was conducted in the Xiushui River, China, before and after the flood season. The grain-size distribution analysis method was used to determine the hydraulic conductivity of the riverbank. A total of 116 sediment samples were collected from the test site. An in situ permeameter test was used to confirm the consistency of the spatial distribution trend of the estimated hydraulic conductivity based on the grain-size distribution analysis. A Kruskal–Wallis test of the riverbank sediment K values obtained before and after the flood season showed that they belong to different populations. The probability distribution illustrated the strong heterogeneity of the riverbank sediments before and after the flood season. Previous studies have confirmed the presence of strong hyporheic exchange and biological processes at this study site. Following the flood season, the K values had a higher mean, median, and coefficient of variation, confirming that the flood process enhanced the heterogeneity of the riverbank sediments. Overall, the hydraulic conductivity of the three areas changed with distance from the river; the closer the area was to the river, the smaller the hydraulic conductivity and weaker the heterogeneity. An experimental framework of spatio-temporal variability in riverbank sediments is proposed, providing recommendations for researchers on conducting an integrated experiment. [ABSTRACT FROM AUTHOR]

Soil moisture variations in space and time are critical in ecological, hydrological, pedological and environmental studies. This study used fractal analysis to detect the spatio-temporal variability of soil moisture on two contrasting land use hillslopes in the hilly area of Taihu Lake Basin of China. Surface (0–20 cm) soil moisture data from January 2013 to September 2015 (a total of 37 sampling days) were analyzed at 39 and 38 sites on the tea garden and forest hillslopes, respectively, with a spatial resolution of about 8 m. Results showed that the forest hillslope was significantly ( P < 0.05) wetter than the tea garden hillslope. The spatial mean soil moisture on both hillslopes had a significant negative linear correlation (R 2 = 0.753 for tea garden ( P < 0.05) and R 2 = 0.459 for forest ( P < 0.05)) with corresponding CV for 37 sampling dates. The fractal dimension (D) was found to be better than the nugget/sill ratio in describing the spatial dependence of soil moisture. The advantage of the D is that it does not require the modelling of the semivariogram since it can be calculated on the basis of the experimental semivariogram. Soil moisture on the forest hillslope showed stronger spatial dependence than that on the tea garden hillslope according to D. However, the soil moisture on both hillslopes showed similar temporal dependence and a low-to-moderate autocorrelation structure. In addition, the temporal variability of soil moisture content was spatially correlated on tea garden hillslope. If a location is temporally autocorrelated, the locations nearby tend also to be temporally autocorrelated. It would be possible to make more accurate moisture trend predictions for temporal autocorrelated locations with small D. These findings had important applications related to sampling design, simulation of soil water flow and agricultural water resources management. [ABSTRACT FROM AUTHOR]

Understanding water temperature variation in regulated rivers and reservoirs becomes increasingly important as the environment and ecosystem are approaching their thermal limits. In this paper, a multi-model approach is used to quantitatively access the spatio-temporal change in thermal structures of the Danjiangkou reservoir and its downstream river. The area is subject to thermal and hydrological alterations due to three large water diversion projects and related auxiliary projects, including a project to heighten the Danjiangkou dam and two small downstream reservoirs. It is found that the Danjiangkou dam heightening project alters water temperature seasonally, increasing it in winter and decreasing it in summer; while the three large water diversion projects and the two small downstream reservoirs mitigate the effect. Water temperature change in the downstream river is also studied from the aspects of release temperature and release discharge of the Danjiangkou reservoir. The former mainly changes the water temperature near the dam, while the latter affects the recovery rate and the recuperation distance. Ecological impact of the water temperature change is discussed based on the spawning of fish, indicating that the spawning periods may lag behind and the optimal spawning locations may move downstream. [ABSTRACT FROM AUTHOR]

The Qinghai Lake Basin acts as a natural barrier, preventing the western desert from spreading eastward. This is an important link in preserving the ecological stability of the northeastern region of the Qinghai-Tibet Plateau (QTP). Therefore, quantitative research into the net primary productivity (NPP) of vegetation and its driving force in the Qinghai Lake Basin is required. The effects of land use/cover change (LUCC) and climate change on NPP in the Qinghai Lake Basin were studied using R-contribution ratio and partial correlation analysis methods using MOD17A3H products, Land Use/Land Cover (LULC) data, and meteorological data. (1) The LULC of the Qinghai Lake Basin showed a trend that "the area of grassland, cultivated land, and unused land continued to decrease, while the area of other LULC types increased" from 2000 to 2020, according to the study's findings. Grassland, water bodies, construction land, and unused land dominated the mutual transformation of LULC types. (2) The NPP of the basin showed a growing trend, with a growth rate of 3.93 gC·m -2 ·a -1 before 2010 and 0.88 gC·m -2 ·a -1 after 2010. Significant regional heterogeneity was found in NPP, with gradients decreasing from southeast to northwest. (3) The impact of LUCC on overall NPP changes had gradually increased. Climate change has been the primary driver of NPP changes in the Qinghai Lake Basin over the last 20 years.

Individual impacts of climate change, land use/coverage change, the regulation of water reservoir and water use to intra-annual distribution of streamflow of the Dongjiang River basin, South China, are quantitatively separated. Data on precipitation, streamflow, regulation of water reservoirs, and water use are used in the analysis. Changes in the concentration degree and non-uniformity coefficient of intra-annual distribution of streamflow over time scales from daily to monthly are evaluated. Trend and change point analyses are applied to determine characteristics of intra-annual distribution of streamflow. By comparison with the difference among region precipitation, naturalized streamflow and observed streamflow, the contribution of main impact factors to the intra-annual distribution of streamflow are quantified. Results demonstrate the non-uniformity coefficient decreases with a negative logarithmic linear function of the time scale. Change points of the concentration degree and non-uniformity coefficient occurred in 1973 exhibited a significant downward trend. In the period posterior to the change point the former and the latter decrease approximately by 15-34 % and by 29-40 %, respectively. The decrease in concentration degree and non-uniformity coefficient is due to the regulation of water reservoirs and land use/cover change; while the increase is the result of water use and climate change. The individual contributions to the impact on the intra-annual distribution of streamflow from regulation of water reservoirs, land use/cover change, water use, and climate change are approximately −33.5, −9.0, 4.5 and 1.0 %. It is observed that the impacts of the regulations of the Xinfengjiang, Fengshuba, and Baipenzhu reservoirs account for −21, −10, and −2 %, respectively. There is an increasing tendency in the impacts of land use/cover change and water use in the past 30 years. [ABSTRACT FROM AUTHOR]

Abstract: The Pearl River Estuary is among the largest estuaries in the subtropical areas of the world. Along the salinity and turbidity gradient between the freshwater reach of the Pearl River and the marine water of the South China Sea, the spatial and temporal composition and abundance of phytoplankton was examined in relation to physic-chemical variables during the dry and wet seasons of 2009. Water samples for phytoplankton and environmental parameters were collected from 18 stations during two seasons along a transect from upper estuary to estuarine and marine sectors. A total of 162 species belonging to 7 phyla were identified, with diatoms dominated in both seasons while dinoflagellates proliferated in autumn. Two main clusters and three sub-clades under each main cluster corresponding to seasons and water sectors were defined with multivariate analysis (cluster and nMDS). Based on the species composition and abundance of phytoplankton, both seasonal and spatial variability were observed at a significant level (ANOSIM: season effect, R=0.896, P<0.01; station effect, R=0.463, P<0.01). The correlation analysis between biotic and abiotic variables indicated that instead of the “proverbial” anthropogenic nutrients loading and salinity gradient, the best 2-variable combination (temperature and turbidity) showed a significant effect on the pattern of phytoplankton assemblages ( ρ w =0.49, BIOENV analysis) between wet and dry seasons in the Pearl River Estuary. This result suggests that physical disturbance either natural or manmade is a more important factor in regulating the phytoplankton community structure within the hydrologically distinct zone of estuaries. [Copyright &y& Elsevier]

Abstract: Initiated during the late 1970s in China, the Household Responsibility System (HRS) has brought a profound change to the rural economy. The shift from a collective farming system to individually-owned family farms has changed land management practices, affecting both soil quality and agro-environmental sustainability. The purpose of this study was to investigate spatio-temporal variability of soil nutrients influenced by the altered land tenure system, and to evaluate the potential for site-specific management. Using geostatistics and GIS, we characterized the spatial variability of soil nutrients in paddy rice fields in the Hangzhou–Jiaxing–Huzhou watershed, China, following 20 years of altered land management policy. Soil samples, collected in 1982 and 2001, were analyzed for soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK). The spatial variability of each of these soil properties decreased from 1982 to 2001, verifying that the extrinsic factors of the altered land management practices had a weakening effect on the intrinsic factors of soil formation properties. Spatial correlation ranges for SOM, TN, and AP in 2001 all decreased from 1982 with the exception of AK. Temporal geographic maps revealed significant changes in soil nutrient concentrations in the form of increases in SOM, TN, and AP and a sharp decline of AK during the period 1982–2001. This result gave an indication of the imbalance among N, P, and K fertilizers applied in the study area. The results of the comprehensive assessment for current soil nutrients could also, inversely, present challenges for future site-specific management policy on agriculture. [Copyright &y& Elsevier]

Abstract: The objective of this study was to explore the spatio-temporal variability of soil organic matter (SOM) in the urban–rural transition zone of Beijing. SOM content in agricultural soils were measured in 1980, 1990 and 2000 in Daxing County of Beijing in-situ and data of 1980 and 1990 were obtained from the National Soil Survey (NSS). Descriptive statistics and geostatistics were used to analyze the data and the kriging method was applied to map the spatial patterns of SOM. The results showed that mean SOM was 9.95g kg−1 in 1980, 12.76g kg−1 in 1990 and 12.89g kg−1 in 2000. SOM was spatially correlated at a larger distance of 32.0km in the E–W direction for the three years, and at a shorter distance of 24.6, 23.3 and 19.0km in the N–S direction in 1980, 1990 and 2000, respectively, which showed that there was more variability in SOM in the N–S areas across the period of 20years. The mapping showed a decreasing trend of SOM from north to south across the county. SOM levels were classified into six levels (<6, 6–10, 10–12, 12–15, 15–20 and >20g kg−1) based on the standards set by the NSS. The SOM slightly increased from low to high levels from 1980 to 2000. The main factors affecting SOM levels were the soil texture, land use and farming practices. The increasing trend might be attributed to the widespread practices of mulching and organic manure applications. [Copyright &y& Elsevier]

In recent decades, the severe drought across agricultural regions of China has had significant impact on agriculture. The standardized precipitation evapotranspiration index (SPEI) has been widely used for drought analyses; however, SPEI is prone to be affected by potential evapotranspiration (PET). We thus examined the correlations between soil moisture anomalies and the SPEI calculated by the Thornthwaite, Hargreaves, and Penman–Monteith (PM) equations to select the most suitable for drought research. Additionally, the Mann–Kendall and wavelet analysis were used to investigate drought trends and to analyze and the impact of atmospheric circulation on drought in China from 1961 to 2018. The results showed that (1) PET obtained from the PM equation is the most suitable for SPEI calculation; (2) there were significant wetting trends in Northern China and the whole Chinese mainland and most of the wetting mutation points occurred in the 1970s and 1980s and the significant inter-annual oscillations period in the Chinese mainland was 2–4 years; (3) the Chinese mainland and Northern China are strongly influenced by West Pacific Trade Wind, while Western Pacific Subtropical High Intensity and Pacific Subtropical High Area have primary impact on Southern China. [ABSTRACT FROM AUTHOR]