Min River Basin Research Articles

A framework for analyzing the most relevant indicators of ecohydrology in a changing environment

ABSTRACT Human activities and climatic changes have altered the hydrological ecosystem of the Min River Basin and affected in-river biodiversity. In this paper, the year of abrupt hydrological change was identified using multiple tests, and the drivers of ecohydrological change were quantified in conjunction with the Budyko coupled hydrothermal equilibrium theory. Combined with ecological flow indicators (ecological surplus (ES) and ecological deficit (ED)) calculated based on discharge hydrographs and multiple hydrological indicators (ES/ED), the degree of river hydrological alteration in the Min River Basin was comprehensively evaluated, and its impacts on in-river biodiversity analyzed. The results of the study showed that: (1) according to the Budyko theory, the influence of human activities on the runoff changes in the Min River Basin reached 56.80%, which was the main influence factor, followed by climatic factors (41.56% for precipitation and 1.64% for evapotranspiration); (2) dam construction has generally resulted in an increase in seasonal ES and a decrease in seasonal ED; (3) the combination of the ecological flow indexes with the ecologically relevant hydrological indicators not only reduces the redundancy between the parameters, but also reflects the essential hydrological information and ecological connotations, and it is an effective method for evaluating ecohydrological mechanisms.

Investigation of Spatiotemporal Changes and Impact Factors of Trade-Off Intensity in Cultivated Land Multifunctionality in the Min River Basin

Exploring the interrelationships and influencing factors of the multifunctionality of cultivated land is crucial for achieving its multifunctional protection and sustainable use. In this paper, we take the Min River basin as a case study to construct a multifunctional evaluation system based on “agricultural production, social security, ecological service, and cultural landscape” using multi-source data. We analyze the spatial and temporal characteristics of the multifunctionality of cultivated land through kernel density estimation (KDE) and visual mapping. Subsequently, we assess the trade-off strength between the multifunctional aspects of cultivated land using the root mean square error (RMSD). Finally, we identify the drivers of the multifunctional trade-off intensity of cultivated land and analyze their influencing mechanisms using Geographic Detectors. The results show that (1) from 2010 to 2020, the multifunctional structure of cultivated land in the study area underwent significant changes: the levels of agricultural production, social security, and ecological service functions first increased and then decreased, while the levels of cultural landscape function and comprehensive function continued to increase. The spatial distribution is characterized, respectively, by “high in the east and low in the west”, “high in the west and low in the east”, “high in the north and low in the south”, “high in the whole and sporadically low in the northeast”, and “high in the middle and low in the surroundings”. (2) During the study period, the trade-off strengths related to social security functions increased, while the trade-off strengths of the remaining multifunctional pairs of cultivated land showed a weakening trend, with high values of trade-off strengths among functions particularly prominent in the Nanping Municipal District. (3) Both natural and human factors significantly affect the multifunctional trade-off strength of cultivated land. Among the specific factors, elevation, slope, average annual temperature, and per capita GDP are the key factors influencing the strength of the trade-offs between functions. The results of this study provide empirical support for enriching the understanding of the multifunctionality of cultivated land and offer a decision-making basis for promoting the differentiated management of cultivated land resources and the synergistic development of its multifunctionality.

Land use changes in the Min River basin and their impact on carbon storage

BackgroundThe changes in land use patterns may provide immediate economic advantages, but they also lead to significant disruptions in ecosystem services. These modifications have the potential to adversely impact water supply, air quality, disaster response, carbon storage, and biodiversity. Therefore, these modifications affect the provision of ecosystem services and have a negative effect on human well-being. Hence, it is crucial to investigate how land use changes affect carbon storage to enhance ecosystem services, lessen the consequences of climate change, advance human welfare, and direct effective land management practices. MethodsMin River Basin (MRB) is a significant water reservoir in China, providing valuable ecosystem services. Currently, the MRB is undergoing significant alterations in the land use due to country’s policy changes. Therefore, this study analyzed alterations in land use, dynamics of the alterations, and transfer matrix in MRB. The alterations in these indices were recorded for three time periods, i.e., 2000, 2010, and 2020. Furthermore, the influence of land use changes on carbon storage was investigated by InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model. ResultsThe main land use classes in the MRB consisted of forest land, grassland, and arable land, and most of the alterations were recorded among these three classes. The arable land was declined by 163–333 km2, while grassland reduced by 23–233 km2 from 2000 to 2020. Likewise, forest land witnessed a decrease of 34–167 km2 from 2000 to 2020. The dominant land use dynamics consisted of construction land and water areas, whereas the entire land use dynamics exhibit a consistent increasing trend. Moreover, carbon storage witnessed a significant decrease during the study period due to the reduction in forest land, grassland, and arable land. ConclusionThe land use patterns in the MRB have witnessed substantial transformations because of recent policy implementations. Land use changes from forest land, arable land and grassland to other types exerted significant influence on carbon storage. Generally, carbon storage decreased from 2000 to 2020. The decline in carbon storage in the MRB is mostly attributed to urban growth, and construction activities. Therefore, these activities should be carefully monitored to improve carbon storage in the basin.

Exploring the spatial and temporal evolution of landscape ecological risks under tourism disturbance: A case study of the Min River Basin, China

Numerous ecological issues will arise from the expansion of tourism-related infrastructure and activities, potentially having a major effect on the ecosystem. However, its impact on landscape ecological risk (LER) is still poorly understood. Taking the Min River Basin as an example, an improved LER evaluation method was adopted in this study, which uses landscape disturbance based on landscape pattern and incorporates ecosystem services (ESs) represent landscape vulnerability. On this basis, the impacts of tourism-related infrastructure and activities on ecology environment were comprehensively considered, and buffer zone analysis, scenario analysis, response index (RI), and the bivariate Moran’s I approaches were applied to identify the spatio-temporal evolution characteristics of LER under tourism interference. The results show that: (1) The Min River Basin’s LER from 2000 to 2020 demonstrates a trend of gradually decreased, primarily in the middle and low risk areas. Most of the areas where scenic spots and roads are located are high risk areas, suggesting that tourism disturbances negatively affect LER. (2) There is a spatial gradient effect associated with the influence of tourism infrastructure on LER, and the impact degree varies throughout different tourism infrastructure. (3) The difference of scenic spots causes diverse degrees of LER. Through comparison, it is found that the LER of high-grade and cultural scenic spots is larger than that of low-grade and natural scenic spots. The quantitative results of the RI show that the values inside the influence zones of scenic spots and roads are 5 times and 9 times more than the values outside, respectively. This suggests that tourism infrastructure increases LER. (4)There is a spatial correlation between LER and tourism activities intensity. In order to offer a scientific reference for balancing local tourism development and ecological environmental conservation, this study develops a more thorough and rigorous research framework of the impact of tourism on LER.

Attribution Analysis of Climate Change and Human Activities on Runoff and Vegetation Changes in the Min River Basin

Hydrological processes and the sustainable use of water resources in a river basin are altered by climate change and changes in human variables. This study examined the significant effects of vegetation and hydrological, climatic, and human activity changes on the basin’s biological environment and usage of water resources. The Min River Basin (MRB) in the upper Yangtze River served as the study location. Mann–Kendall and Pettitt mutation test techniques were used to examine the features of runoff changes in the basin. The effects of meteorological and anthropogenic factors on runoff and vegetation changes in the MRB from 1982 to 2020 were quantitatively evaluated using the expanded Budyko equation. Following this, spatial and temporal variations in land use and the NDVI in the basin were studied. The results of the research demonstrated the following: (1) The MRB yearly runoff trended downward and that an abrupt change in runoff happened in 1994. (2) Precipitation (Pr) showed a decreasing tendency from the base period (S1) to the change period (S2), but potential evapotranspiration (ET0) showed an increasing trend. (3) From 1985 to 2020, the land use area of the MRB changed rapidly, and the construction land and water area increased by 322% and 58.85%, respectively, while the cultivated land area decreased by 11.72%. (4) From S1 to S2, there was a rising trend in both the NDVI and the Budyko parameter n. The contributions of Pr, ET0, NDVI, and n to the runoff change were 32.41%, 9.43%, 27.51%, and 30.65%, respectively.

Evolving environmental awareness and shifts in management priorities: a socioeconomic lens on the min river basin, China

Watersheds have experienced economic and demographic development for decades. In China, this development has been associated with environmental degradation, including water quality deterioration, abnormal stream flow, and biotic resource depletion. Effective watershed management incorporates sustainability and public involvement, enabling the long-term security of the human and natural world. Management strategies however need to take into account local conditions, as every watershed is unique. This paper adopts the analytic hierarchy process (AHP) combined with the random forest model to investigate the shift in participants’ environmental awareness across different socioeconomic groups over the past 15 years. Additionally, it scrutinizes the changing public perceptions on the management priorities and areas requiring enhancement. The AHP index highlighted the importance of environmental behavioral intentions (EBI) as a component of environmental awareness (EA). Between 2006 and 2021, significant changes occurred in public environmental awareness (perception, knowledge, behavioral intention) and perceived management priorities, stressing the need for timely adjustment of management policies. Notably, environmental concern (EC) appears to have decreased over time, reflecting effective management and increased governmental attention. Emphasis on the recreational ecosystem services offered by watershed forests has increased. Males, individuals aged over 40-years-old, and individuals located in the upper reaches possessed higher risk perceptions than other groups. These findings may help policymakers to adjust management priorities based on geographic region and may assist them in promoting more effective measures to communicate watershed sustainable management goals and strategies to the public.

Analysis of hydrological regime evolution and ecological response in the Min River, China

Abstract Natural fluctuation of the hydrological regime is the key to maintaining river ecosystem function. Given the shortcomings of previous studies on hydrological regime change and the ecological response of the Min River, this study combined two change degree evaluation methods and Budyko theory to quantify the degree of ecohydrological change and its driving factors. Ecological significance indicators (ecosurplus and ecodeficit) and the Shannon index (SI) were used to identify the characteristics of ecohydrological variation and ecological response mechanisms. The results showed the following: (1) The hydrological regime in the Min River basin had an abrupt change in 1993, with the overall alteration degree reaching 44%, which further led to a decrease in ecological surplus and an increase in the ecological deficit in ecological indicators. (2) Budyko's theoretical results show that climate change and human activities together lead to an 83.83 mm reduction in Min River runoff, with human activities contributing 54.20% of the change in the mean annual runoff, while rainfall and evapotranspiration contribute 43.88 and 1.92%, respectively. (3) The SI index indicates a decreasing trend in Min flow biodiversity. The results of the study can provide a reference for enhancing ecological protection and restoration in the Min River basin.

Ecohydrological response to multi-model land use change at watershed scale

Study regionThe Min River basin, China. Study focusIn order to investigate the ecohydrological response under historical and future land use changes, we simulated daily runoff sequences under different land use scenarios by coupling the PLUS model with the Physical Hydrological Model and quantitatively assessed the ecohydrological impacts of different land use changes in the watershed by combining the IHA method. New hydrological insights for the regionThe Min River Basin is dominated by grassland, woodland and, cultivated land which account for 94 % of the total. During the period 2000–2020, the area of cultivated land decreased by 4.47 % overall, and construction land increased by 78.68 % overall. Compared to the base year of 2010, the multi-year average monthly runoff increased under different land use scenarios. The high flow indicators (1 daymax, 7 daymax, and 30 daymax) had the largest increasing trend under the natural development scenario in 2030, 54 m3/s, 33 m3/s, and 24 m3/s, respectively, whereas their increase decreased under the ecological protection scenario in 2030; the low flow indicators (1 daymin, 7 daymin, and 30 daymin) decreased less in the 2030 eco-protection scenario than in the natural development scenario, where they decreased by − 5 m3/s, − 9 m3/s, and − 11 m3/s, respectively. The results of the study contribute to a deeper understanding of the response of watershed hydrological processes to land-use change.

Unravelling and improving the potential of global discharge reanalysis dataset in streamflow estimation in ungauged basins

Mastery in forecasting the streamflow is of great importance in environmental and sustainability research. Although many global-scale reanalysis products provide a new way to overcome the lack of streamflow records in ungauged basins, streamflow estimation through hydrological models remains a great challenge mostly due to inevitable biases. In this study, we developed a novel bias-correction system equipped with the proposed Piecewise Random Forest (P-RF) model to improve the potential of GloFAS-ERA5 (GloFAS), a global-scale river discharge reanalysis product, as a calibration benchmark for building hydrological models in ungauged basins. Considering three ungauged scenarios, several cases of temporal, spatial, and spatiotemporal bias-corrections were implemented with a total of 13 river gauges located in the Min River Basin in China, and the Fuji River Basin and the Shinano River Basin in Japan. Then, the well-improved GloFAS discharge was applied for the calibration of the Block-wise use of the TOPMODEL (BTOP) model to evaluate its performance in substituting the discharge observations. The results show that: (1) the bias-correction system performs better on the temporal scale, which applies to ungauged basins lacking long-term continuous observations; (2) the integrity and adequacy of the samples used for training the P-RF model have a significant impact on the spatial and spatiotemporal bias-corrections, and they can be reliably estimated by the proposed metric, Ratio of the Valid samples' Proportion; and (3) the statistical metric differences between the simulated discharges obtained by the calibrated BTOP model using observations and GloFAS discharge, are reduced by 25%–50% through the bias-correction.

Spatial-temporal evolution of sediment transport in the upper Yangtze River Basin considering the cumulative impacts of mega reservoirs

The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion.

Characterization of the evolution of runoff‐sediment relationship in Min River based on coupling coordination theory

AbstractGlobal climate change and human activities have profoundly affected the hydrological processes in the basin. The study of the characteristics of runoff and sediment variations in the basin and their driving factors is of great significance in promoting the efficient use of water resources and high‐quality development in the basin. The determination of the abrupt change point of the runoff‐sediment relationship is the key to delineate the base period, and is important to assess the contribution of climate change and human activities to the change of the runoff‐sediment relationship. Therefore, this study constructs a binary coupled coordination model of runoff and sediment load to describe the coupled runoff‐sediment coordination relationship, and uses the Pettitt method and the double cumulative curve method to test for mutations. The effects of climate change and human activities on changes in runoff and sediment load were assessed using the Budyko framework‐based elasticity factor method and the cumulative slope rate of change method. The results show that the annual runoff and annual sediment load in the Min River basin show a decreasing trend between 1970 and 2019, with monthly sediment load changing more significantly than monthly runoff. Annual runoff and annual sediment load were significantly coherent throughout the study period, and there were significant resonant cycles of positive phase on 2‐, 3‐, 5‐ and 6‐year time scales. The coupling coordination degree of runoff and sediment load is generally at a coordinated developmental stage and is moving from low to high levels of coordination. Relative to the base period, changes in runoff and sediment load during the change period are mainly attributed to human activities. The contribution of human activities to the change in runoff ranged from 78.92% to 66.71%, and the contribution to the change in sediment load reached 93.40% to 94.15%. In contrast, precipitation in climate change has a greater impact on changes in runoff and sediment load than potential evapotranspiration. Land use changes and reservoir construction in the Min River basin have both contributed positively to the reduction of runoff and sediment load. The results of the study will help us to gain a deeper understanding of the processes and driving mechanisms of the runoff‐sediment relationship in the Min River basin, and provide a scientific basis for water resources management and sustainable development in the basin.

Comprehensive Evaluation of the Level of Water Ecological Civilization Construction in the Min River Basin, China

Water Ecological Civilization Construction (WECC) is critical for promoting long-term resource, economic, and social development. The Min River is the longest in Fujian Province, China, and is known as the “golden canal” for shipping. In this study, data from cities around the Min River were used to build an evaluation index system for WECC in the Min River, incorporating the Pressure–State–Response model, and the matter element extension model was used to examine the WECC level in the Min River Basin. The results indicate that notable progress has been made for WECC in the Min River Basin, despite evident regional variation. The upper parts of the Min River have seen the most development; however, the downstream regions have been mainly stable and retained a high WECC level. Changes in industrial structure and government actions substantially affect the degree of WECC. This study can act as a reference for river basin WECC.

Nitrous oxide concentration and flux in Min River Basin of southeast China: Effects of land use, stream order and water variables

Estimates of riverine nitrous oxide (N2O) emissions have great uncertainty partly due to the fact that the data is still sparse for stream sizes and land uses. Here we determined water dissolved N2O concentration and water–air interface N2O flux across the land uses and stream orders in Min River Basin of southeast China. N2O concentrations ranged from 11.1 to 27.4 nmol/L, increasing from first- to eighth-order rivers. The first- and second-order streams showed negative N2O flux (−0.33 and −0.05 µg m−2h−1, respectively) compared to third- to eighth-order rivers (from 0.29 to 2.85 µg m−2h−1). Average N2O flux was significantly higher in urban (1.60 µg m−2h−1) and cropland rivers (0.89 µg m−2h−1) than in forest rivers (−0.47 µg m−2h−1), which could be due to the main effect of land use was on the nitrogen load. Indirect N2O emission factor varied between 0.035 and 0.14 % across the rivers, which decreased from the urban to forest rivers and were lower than the IPCC default value (0.26 %). N2O concentration and flux were positively correlated with NO3−, NH4+, depth, velocity and temperature, suggesting the importance of stream surface hydromoprhology to N2O emissions. Land use indirectly affected N2O flux by affecting water NO3−, NH4+, DO, DOC, pH and temperature, which could further explain the land use dependence of N2O emissions on water variables. High DOC:NO3− ratio (>6) was the main factor of N2O sink in the small streams, which may be due to the enhanced N2O consumption and low N2O production. Therefore, riverine N2O emissions are highly variable across stream sizes and land uses, which are not only increased by inorganic nitrogen load and are also dependent on stream hydraulics and morphology.

Comprehensive evaluation of parameter importance and optimization based on the integrated sensitivity analysis system: A case study of the BTOP model in the upper Min River Basin, China

Parameter optimization is mandatory in many numerical modeling studies of hydrology sciences. However, optimizing all parameters (APs) is highly inefficient, including the equifinality phenomenon. This paper proposes an integrated sensitivity analysis system consisting of, multiple Global sensitivity analysis methods, Design of experiment algorithms, Indicators, and Sample size design Combinations (GDISCs), for screening the sensitive parameters (SPs) robustly and reducing parameter optimization burden efficaciously. In this study, four design of experiment (DoE) algorithms are applied to collect samples with varying sizes, and the corresponding three indicator values. We evaluate the effectiveness and efficiency of one qualitative and two quantitative global sensitivity analysis (GSA) methods by identifying the appropriate DoE algorithm and the sufficient sample size. To apply the GDISCs, the Block-wise use of the TOPMODEL (BTOP) model is set up for the hydrological simulation in the upper Min River Basin, China. The results show that the GDISCs system robustly screens out three SPs of the BTOP model, and the DoE algorithms significantly impact the effectiveness and efficiency of the GSA methods. The SA performance with applying the modified Kling–Gupta efficiency (KGE') as the indicator is more robust than the root mean squared error (RMSE) and the Nash-Sutcliffe efficiency (NSE). Compared to the traditional APs optimization, the optimal values are identified quickly through almost 1/2 or even fewer model runs and duration for the SPs optimization, with a very close accuracy (the maximum NSE, KGE' and relative bias (RBias) differences are 0.137, 0.037 and 2.70%, and the minimum are 0.002, 0.001 and 0.20%). Optimizing SPs also has a noticeable improvement for the default parameter values, and the maximum differences of NSE, KGE' and RBias reach 0.764, 0.321, and −20.80%. In summary, the GDISCs system is especially applicable for obtaining the robust SA results to considerably improve model calibration efficiency and reduce model computational burden while ensuring satisfactory model simulation performance.

Analysis of Alterations of the Hydrological Situation and Causes of River Runoff in the Min River, China

Construction of water conservancy projects has changed the hydrological situation of rivers and has an essential impact on river ecosystems. The influence modes of different factors on runoff alterations are discussed to improve the development and utilization of water resources and promote ecological benefits. The ecological hydrological indicator change range method (IHA–RVA) and the hydrological alteration degree method were integrated to evaluate the hydrological situation of the Min River in China. Based on six Budyko hypothesis formulas, the rates of contribution of climate change and human activities to runoff change are quantitatively analyzed. The results show that (1) the runoff of the Min River basin showed a significant decreasing trend from 1960 to 2019 and a sudden alteration around 1993; (2) the overall alteration in runoff conditions was 45% moderate and the overall alteration in precipitation was 37% moderate; (3) precipitation and potential evapotranspiration also showed a decreasing trend within the same period but the overall trend was not significant; (4) the contribution of climate variability to runoff alterations is 30.2% and the contribution of human activities to runoff alterations is 69.8%; human activities are the dominant factor affecting the alteration of the runoff situation in the Min River basin.

Coupling Coordination Analysis and Prediction of Landscape Ecological Risks and Ecosystem Services in the Min River Basin

Watershed landscape ecological security and ecosystem service functions are the material basis and environmental guarantee for promoting socioeconomic development. Analyzing the spatiotemporal characteristics of landscape ecological risks (LERs) and ecosystem services (ESs) and exploring the coupling coordination relationship between the two are of great significance for promoting the construction of ecological civilization and achieving sustainable development in the watershed. With the Min River Basin as the study area, the landscape ecological risk assessment, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST), and Carnegie Ames–Stanford Approach (CASA) models were used to evaluate the LERs and ESs based on the shared socioeconomic pathways (SSPs), and the patch-generating land use simulation (PLUS) model was used to predict the land use distribution of the Min River Basin in 2030. On this basis, the coupling coordination degree model was used to explore the coupling coordination relationship between the LERs and ESs. The results show that, from 2000 to 2020, the LER of the Min River Basin gradually decreased, and the overall spatial distribution pattern was “high in the north and low in the south”. The ES of the Min River Basin initially decreased and then increased, showing a spatial distribution pattern of “low in the south and high in the north”. Among the SSPs in 2030, the LER is the largest under the SSP3 scenario and the smallest under the SSP4 scenario. The ES improvement is the most significant under the SSP1 scenario and the lowest under the SSP3 scenario. From 2000 to 2030, the coupling coordination degree of the Min River Basin first decreased and then increased, showing a spatial distribution pattern of “high in the south and low in the north”. Among the five SSPs, the coupling coordination degree was the highest under SSP1. The spatial distribution of urban area is the main driving factor affecting the coupling coordination relationship between the LER and ES, and the development of social and economy is the beginning of landscape pattern optimization.

Distribution of hydrogen and oxygen stable isotopes and pollution indicators in water during a monsoon transitional period in Min River Basin

Based on 197 monthly river water and groundwater samples and 30 event-scale precipitation samples, our study reports the distribution of hydrogen and oxygen isotopes and pollution indicators in Min River Basin. The variation of δ18O and d-excess indicate that the water source in the upper main course water is more variable and that in the middle-lower part is relatively stable. Comparison between plots of δ2H versus δ18O in the river water and precipitation reflect the dominant water source is different between river water in the upper and middle-lower parts. The electrical conductivity (EC) shows a similar spatial variation trend for main course water collected in four campaigns. The pollutant concentration change at the confluences of main tributaries shows that the inflow of Heishui River and Dadu River leads to decreased NO3− and Cl−, while that of Xi River, Pu River and Fuhe River leads to a leap in NO3− and Cl−. A significant positive correlation is observed between EC and δ18O, indicating the consistent control of water sources on isotope distribution and water quality. The relationship between elevation and δ18O in the main course river water suggests that the factors affecting isotope distribution vary spatially. “Altitude effect” can only be observed in October and November for the upper steepest plateau zone due to the spatial variation in the precipitation stored during the wet season. The “inverse altitude effect” is observed for the upper part during the wet season and for the middle-lower part during the whole study period, which can be explained by the contribution of tributaries with different discharge regimes. Our findings show that water source with different discharge regimes can serve as the leading factor controlling the stream component in multi-tributary river basins with large spatial span and may mask the influence of spatial distribution of precipitation.

Water quality assessment and pollution source apportionment using multi-statistic and APCS-MLR modeling techniques in Min River Basin, China.

Anthropogenic activities pose challenges on security of water quality. Identifying potential sources of pollution and quantifying their corresponding contributions are essential for water management and pollution control. In our study, 2-year (2017-2018) water quality dataset of 15 parameters from eight sampling sites in tributaries and mainstream of the Min River was analyzed with multivariate statistical analysis methods and absolute principal component score-multiple linear regression (APCS-MLR) receptor modeling technique to reveal potential sources of pollution and apportion their contributions. Temporal and spatial cluster analysis (CA) classified 12months into three periods exactly consistent with dry, wet, and normal seasons, and eight monitoring sites into two regions, lightly polluted (LP) and highly polluted (HP) regions, based on different levels of pollution caused by physicochemical properties and anthropogenic activities. The principal component analysis (PCA) identified five latent factors accounting for 75.84% and 73.46% of the total variance in the LP and HP regions, respectively. The main pollution sources in the two regions included agricultural activities, domestic sewage, and industrial wastewater discharge. APCS-MLR results showed that in the LP region, contribution of five potential pollution sources was ranked as agricultural non-point source pollution (22.13%) > seasonal effect and phytoplankton growth (19.86%) > leakage of septic tanks (15.73%) > physicochemical effect (12.86%) > industrial effluents and domestic sewage (11.59%), while in the HP region ranked as point source pollution from domestic and industrial discharges (20.81%) > municipal sewage (16.66%) > agricultural non-point source pollution (15.23%) > phytoplankton growth (14.82%) > natural and seasonal effects (12.67%). Based on the quantitative assessment of main pollution sources, the study can help policymakers to formulate strategies to improve water quality in different regions.

Surface Mass Variations from GPS and GRACE/GFO: A Case Study in Southwest China

Surface mass variations inferred from the Global Positioning System (GPS), and observed by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) complement each other in terms of spatial and temporal coverage. This paper presents an analysis of regional surface mass variations inverted from GPS vertical displacements under different density distributions of GPS stations, and compares the GPS-derived mass variations with GRACE/GFO inversion results in spatial and temporal domains. To this end, GPS vertical displacement data from a total of 85 permanent GPS stations of the Crustal Movement Observation Network of China (CMONOC), the latest GRACE/GFO RL06 spherical harmonic (SH) solutions and GRACE RL06 mascon solutions are used to investigate surface mass variations in four regions or basins, including the Yunnan Province (YNP), Min River Basin (MRB), Jialing River Basin (JLRB), and Wu River Basin (WRB) in Southwest China. Our results showed that the spatial distributions and seasonal characteristics of GPS-derived mass change time series agree well with those from GRACE/GFO observations, especially in regions with relatively dense distributions of GPS stations (e.g., in the YNP and MRB), but there are still obvious discrepancies between the GPS and GRACE/GFO results. Scale factor methods (both basin-scaled and pixel-scaled) were employed to reduce the amplitude discrepancies between GPS and GRACE/GFO results. The results also showed that the one-year gap between the GRACE and GFO missions can be bridged by scaled GPS-derived mass change time series in the four studied regions, especially in the YNP and MRB regions (with relatively dense distributions of GPS stations).

Water Quality Assessment and Variation Trends Analysis of the Min River Sea-Entry Section, China

In order to further understand the status of the water quality of Min River’s sea-entry section, the index systems for water environmental quality assessment was built based on twenty evaluation parameters including dissolved oxygen (DO), permanganate index (CODMn), chemical oxygen demand (CODCr), biochemical oxygen demand (BOD5), ammonia (NH3-N), total phosphorus (TP), and total nitrogen (TN). Water environmental quality of Min River’s sea-entry section in 2015–2017 was evaluated by utilizing the entire-array-polygon synthesis illustration method, accompanied by the time-dependent trend analysis. The results demonstrated that the water environmental quality of Min River’s sea-entry section was between the levels I and II of the Environmental Quality Standards for Surface Water (EQSSW, GB3838-2002) in 2015–2017, indicating a generally good water quality. The water quality was affected by both natural factors (such as temperature, rainfall, and runoff) and human factors and had a tendency to deteriorate at the duration of 2015–2017. The research results are of great significance for further understanding of the discharge of pollutants from the Min River basin and will be a strong support for the scientific decision-making of marine management in Fujian Province.