Typical Watershed Research Articles

Annual soil erosion characteristics of unpaved roads in the Loess Plateau hilly and gully region, China

The problem of unpaved road erosion is prominent in the Loess Plateau hilly and gully region. Unpaved roads contribute substantially to watershed sediment due to their high soil bulk density, low infiltration rates and extensive network. In this study, a field investigation was conducted on typical unpaved roads within a typical watershed in this region, focusing on assessing the damage state, annual soil loss and the factors influencing erosion in a comparatively wet year. The results showed that the soil erosion from unpaved roads was very severe, with an annual erosion intensity of 470 t hm−2, following three heavy rain events and two rainstorm events in the summer of 2022. The main unpaved roads (MUR) suffered the most severe road erosion, with 22.2 % of road segments experiencing severe erosion with classical gullies. The erosion gullies on the road had an average depth of 16.1 cm and an average width of 36.5 cm, with the widest being 146.0 cm and the deepest being 174.0 cm. The road erosion intensity was significantly related to drainage area, road area, road length and coverage. Road erosion reduced significantly when the land use in the drainage areas of the road was covered with shrub or grass, or road surface was covered with grass or gravel. Our findings offer valuable insights for road construction and erosion prevention in similar terrains.

Estimation of the Potential for Soil and Water Conservation Measures in a Typical Basin of the Loess Plateau, China

Abstract: In the context of the large-scale management of the Loess Plateau and efforts to reduce water and sediment in the Yellow River, this study focuses on a typical watershed within the Loess Plateau. The potential for vegetation restoration in the Kuye River Basin is estimated based on the assumption that vegetation cover should be relatively uniform under similar habitat conditions. The potential for terrace restoration is assessed through an analysis of topographic features and soil layer thickness, while the potential for silt dam construction is evaluated by considering various hydrological and geomorphological factors. Based on these assessments, the overall potential for soil erosion control in the watershed is synthesized, providing a comprehensive understanding of target areas for ecological restoration within the Kuye River Basin. The study demonstrates that the areas with the greatest potential for vegetation restoration in the Kuye River Basin are concentrated in the upper and middle reaches of the basin, which are in closer proximity to the river. The total potential for terracing is 1013.85 km2, which is primarily distributed across the river terraces, farmlands, and gentle slopes on both sides of the riverbanks. Additionally, the potential for the construction of check dams is 14,390 units. The target areas for terracing measures in the Kuye River Basin are primarily situated in the middle and lower reaches of the basin, which are in closer proximity to the river. Conversely, the target areas for forest, grass, and check dams, as well as other small watershed integrated management measures, are predominantly located in the hill and gully areas on the eastern and southern sides of the basin. The implementation of the gradual ecological construction of the watershed, based on the aforementioned objectives, will facilitate the protection, improvement, and rational utilization of soil, water, and other natural resources within the watershed.

A local perspective on the links between flora biodiversity and ecosystem services in the Northwest Highlands of Ethiopia

The main concern that this study attempts to address is the reason that the local people sustainably conserve church forests while aggressively exploiting biodiversity in common forests, shrublands, and grasslands. The study assesses the local perspective on the links between flora biodiversity and ecosystem services across a range of management options in the typical watershed of the Northwest highlands of Ethiopia. A mixed study design that included questionnaires, remote sensing, and hermeneutics was used because of the multidisciplinary character of the research. There has been a perceptible decline in flora biodiversity in the open-access shrublands, forests, and grasslands as a result of increased settlement encroachment, unchecked and continuous overgrazing, excessive firewood collection, and the cutting of living and dead tree and shrub biomass. Because of this, it was noticed that the availability of wild edible plants, medicinal plants, trees to produce tools, habitat for wild animals, and lumber production is drastically reduced. Alternatively, the church forests were preserved with responsive caring, which enables the outstanding performance of the majority of ecosystem services (except for collecting firewood and fibers) for the local community with the principles of equality and inclusiveness. Therefore, to restore open-access communal grazing ecosystems and the synergy of many ecosystem services in a given watershed, an effective institutional structure must be developed at the local administration level. To offer a range of ecosystem services and socioeconomic benefits, reforestation and planting of both exotic and native plants with enclosure management established on the values of justice, equality, inclusivity, and well-managed local governance with strict laws, sanctions, and enforcement must be the cornerstones of the management plan.

A Modified Xinanjiang Model for Quantifying Streamflow Components in a Typical Watershed in Eastern China

A Modified Xinanjiang Model for Quantifying Streamflow Components in a Typical Watershed in Eastern China

Critical factors in soil organic carbon mineralization induced by drying, wetting and wet-dry cycles in a typical watershed of Loess Plateau

As global climate change progresses, soil will experience prolonged periods of both drought and heavy rainfall, leading to a more frequent drought-re-wetting process that may impact the ecosystem's carbon (C) cycle. However, understanding the extent to which different water conditions and wet-dry cycles alter the process of soil organic carbon (SOC) mineralization remains limited. Therefore, our study focused on the dammed land unique to the Loess Plateau, silted by check dams constructed for erosion control. We implemented three water gradients-drought (30% WHC), water stress (100% WHC), and wet-dry cycling (30–100%)-indoors to observe the SOC mineralization process five times. We identified a transient excitation effect of the wet-dry cycles on SOC mineralization. Soil mineralization decreased gradually with the alternation of wet-dry cycles. The wet-dry cycles not only significantly impacted the contents of SOC and TN but also stimulated the activities of enzymes related to C and N cycles. As the cycle frequency increased, the utilization of C sources by soil microorganisms gradually decreased, and the dominance of carbohydrates, amines, and acids evolved into a single acid, esters, or alcohols. Phosphatase and Chloroflexi were the main factors influencing SOC mineralization under drought stress, while TN and Ascomycota were the primary factors under water stress. SOC and Gemmatimonadetes were the main limiting factors for SOC mineralization under the wet-dry cycles. Additionally, we quantified the direct and interactive contributions of each factor to SOC mineralization. The direct contributions of drought stress, water stress, and the wet-dry cycles to SOC mineralization were 0.961, 0.736, and 0.942, respectively. This study contributes to a more comprehensive understanding of the mechanisms underlying SOC mineralization in the Loess Plateau under changing conditions.

Spatial and Temporal Heterogeneity of Eco-Environmental Quality in Yanhe Watershed (China) Using the Remote-Sensing-Based Ecological Index (RSEI)

The long-term impacts of climate change and human activities have resulted in the Yanhe watershed, a typical watershed in the Loess Plateau region, exhibiting a high degree of vulnerability and significant heterogeneity in ecological environmental quality. This has led to environmental degradation and complex socio-ecological challenges. Consequently, there is an urgent need to carry out research on the spatial and temporal differentiation patterns of ecological environment quality. By utilizing remote sensing data spanning 21 years, this study evaluated the evolutionary trends and consistency of ecological environment quality (EEQ) within the Yanhe watershed based on the remote-sensing-based ecological index (RSEI). Furthermore, it examined global and local spatial autocorrelation of the RSEI by constructing a hexagonal grid, thereby revealing the spatiotemporal characteristics of EEQ at different scales within the Yanhe watershed. The results were as follows: (1) The EEQ has exhibited an overall upward trend in the past two decades, while it has displayed significant fluctuations; (2) the Global Moran’s I values for the years 2000, 2010, and 2020 were 0.18, 0.32, and 0.21, respectively, indicating a presence of spatial autocorrelation within the RSEI; (3) the overall EEQ of the Yanhe watershed will continue to improve, although the ecological quality in certain areas remains unstable due to local natural conditions and human activities. This research not only contributes to the technical framework for analyzing the spatiotemporal heterogeneity of EEQ but also provides actionable insights for ecosystem restoration and sustainability within the Loess Plateau watershed. Our work advances the understanding of ecological dynamics in semi-arid regions and offers a model for assessing ecological quality in similar environmental contexts.

Transition from opportunistic to conservative water use strategy with the growth of Robinia pseudoacacia in a typical watershed in the semiarid Loess Plateau

Understanding water use strategy is essential to evaluate plant adaptability in water-limited regions, but whether this strategy changes with plant growth needs further investigation. Robinia pseudoacacia is an exotic pioneer plantation species widely planted in the semiarid Loess Plateau of China to restore degraded ecosystems. Plant water uptake proportion from different soil layers and the water uptake pattern calculated through soil water uptake niche breadth (B index) were determined for R. pseudoacacia in 11-, 25-, 33–, and 43-yr plantations. Leaf physiological parameters and carbon stable isotopic composition (δ13C) were measured concurrently to calculate short-term and long-time integrated water use efficiency (WUE). Then, the water use strategy for R. pseudoacacia at different plantation ages was assessed through water uptake patterns, stomatal conductance (gs), and WUE variation under varied soil water conditions. Results showed that R. pseudoacacia maintained high gs and low short-term WUE and δ13C through a relative equal water uptake pattern and absorbed water within 0 − 400 cm soil depths in 11- and 25-yr plantations. However, this species exhibited an exclusive water uptake pattern and absorbed water mainly from 50 − 400 cm soil depth, adopted low gs and high short-term WUE and δ13C in 33– and 43-yr plantations. Therefore, R. pseudoacacia transited from an opportunistic to a conservative water use strategy with plant growth. The short-term WUE and δ13C were mainly and significantly influenced by gs and specific leaf area, respectively. Furthermore, the significant influence of B index on gs, δ18OΔ, short-term WUE, and δ13C indicated that R. pseudoacacia coordinated both water uptake pattern and water use behavior to contend with varied soil water conditions. This study suggested that changes in age-related water use strategy were essential for the adaptability of R. pseudoacacia in water-limited conditions.

Predicting water ecosystem services under prospective climate and land-use change scenarios in typical watersheds distributed across China

Water-related ecosystem services (WES) critical to anthropogenic-related water security are being severely degraded, primarily due to climate and land-use change. Clarifying future trends in WES (i.e., water yield and water purification services) will contribute to water resource sustainability. However, most existing studies are single case studies and rarely consider the combined impacts of climate change and land-use change on ecosystem services, resulting in patterns that cannot be adequately summarized. In this study, the “Annual Water Yield” module of the InVEST model was used to estimate water yield and the “Nutrient Delivery Ratio” module was used to analyze water purification services. In order to compare the impacts of different natural conditions and geographic locations on water ecosystem services, 17 typical watersheds throughout China were selected as study areas. Coupled scenarios were also considered when setting climate and land-use scenarios to predict prospective (2020–2100) evolutionary trends in WES. The response of WES under different scenarios was also assessed. Results show that climate change is more likely to affect water yield services than water purification services. The impact of land use on water purification services is more pronounced than its impact on water yield services. Climate change contributed > 90 % to water yields in 15 out of the 17 watersheds, contributed 79.4 % in the Hei River watershed, while only contributing 11.2 % in the Yarkant River watershed. The influence of climate change on total nitrogen (TN) output in eight of the watersheds was greater than that of land-use change, especially in the Min River and Mintuo River watersheds, for which the contribution was > 95 %. Furthermore, water purification services in nine of the watersheds were more affected by land-use change, especially in the Dongting Lake and Hei River watersheds, for which the contribution was > 95 %. The aim of this study is to assist in the planning of sound water resource measures while developing sustainable management strategies to help relevant water resource sectors cope with prospective risks and challenges.

Response of soil nutrients and erodibility to slope aspect in the northern agro-pastoral ecotone, China

Abstract. Soil erosion, considered a major environmental and social problem, leads to the loss of soil nutrients and the degradation of soil structure and impacts plant growth. However, data on the effects of land use changes caused by vegetation restoration on soil nutrients and erodibility for different slope aspects are limited. This study was conducted to detect the response of soil nutrients and erodibility to slope aspect in a typical watershed in the northern agro-pastoral ecotone in China. The following indexes were used to determine the improvement in soil nutrients and erodibility through a weighted summation method: the comprehensive soil nutrient index and the comprehensive soil erodibility index. The results showed that the vegetation types with the highest comprehensive soil quality index (CSQI) values on western, northern, southern, and eastern slopes were Pinus sylvestris and Astragalus melilotoides (1.45), Caragana korshinskii and Capillipedium parviflorum (2.35), Astragalus melilotoides (4.78), and Caragana korshinskii and Lespedeza bicolor (5.00), respectively. Slope aspect had a significant effect on understory vegetation characteristics, soil nutrients, and soil erodibility. Understory vegetation and soil characteristics explained 50.86 %–74.56 % of the total variance in soil nutrients and the erodibility. Mean weight diameter and total phosphorus were the main factors that affected the CSQI for different slope aspects. Our study suggests that the combinations of species, such as C. korshinskii and L. bicolor, were the optimal selection to improve soil nutrients and soil erodibility for any slope aspect.

A framework for assessing the impacts of land-use/cover change and climate change on wheat productivity under 1.5 and 2.0 °C warming at watershed scale.

Irrigation is used extensively to enhance grain production and ensure food security. Many studies have used crop models and global climate models to study the variation of irrigated crop yield in the context of climate change. But most considered the influence of direct climate change but neglected the influence of irrigation water availability, which is affected by land-use/cover change (LUCC) and indirect climate change, on irrigated crop yield. This study therefore developed a framework including Patch-generating Land Use Simulation model, Soil and Water Assessment Tool, Agricultural Production Systems sImulator Model, and global climate models for exploring the impacts of LUCC, direct climate change, and indirect climate change on wheat yield in a typical watershed. Both LUCC and climate change caused increased runoff from October to May, and thus increased the irrigation water availability, by 51.6 and 30.7 mm per growing season under 1.5 and 2.0 °C warming, respectively. The combined influence of LUCC, direct, and indirect climate change increased wheat yield by about 18.5% and 15.5% in the context of 1.5 and 2.0 °C warming, respectively. The relative contribution of LUCC, indirect climate change and direct climate change to yield was 4.7%, 41.2%, and 54.1% under 1.5 °C warming, and 13.1%, 28.7%, and 58.2% under 2.0 °C warming, respectively. We suggest that changes in irrigation water availability should be considered from a watershed perspective when simulating the influence of climate change on crop yield, especially regional crop production estimation. © 2023 Society of Chemical Industry.

Hydrochemical and Isotopic Characteristics and the Spatiotemporal Differences of Surface Water and Groundwater in the Qaidam Basin, China

In the context of climate change, precipitation and runoff in the arid inland basins of northwest China have undergone significant changes. The Qaidam Basin (QB) is a typical highland arid inland area. Understanding the spatial and temporal variations in surface water and groundwater chemistry and isotopes, as well as their causes, is crucial for future water resource management and ecological protection. Samples of river, lake, and groundwater, as well as others, were collected and tested in five typical watersheds in the summer and winter. The hydrochemistry and isotopic spatiotemporal differences in various water bodies were studied using the significant difference method, water vapor flux models, hydrochemistry, isotopes, and other methods for cause analyses. The results indicate the following: (1) There are differences in hydrochemistry between the southern and northern basins because the southern basin is more influenced by the dissolution of salt rocks and evaporation, whereas the northern basin is mainly affected by carbonate weathering. (2) The enrichment of δD and δ18O in the northern basin gradually increases from west to east, while in the southern basin, it is the opposite. This is because the southern basin receives a larger contribution of water vapor from the mid-latitude westerlies, while the northern basin primarily relies on local evaporation as its water vapor source. (3) Significant differences are observed in the total dissolved solids (TDS) and hydrochemical types of river water and groundwater between the summer and winter due to higher rates of rock weathering and evaporation in the summer. (4) The more pronounced seasonal differences in hydrogen and oxygen stable isotopes in the southern basin are due to higher rates of internal water vapor circulation in the summer. (5) The similarity in characteristics between river water and groundwater is the result of strong exchanges between river water and groundwater from piedmonts to terminals. The spatiotemporal heterogeneity of terminal lakes is attributed to the accumulation of salts and groundwater replenishment from other sources.

Impact ways and their contributions to vegetation-induced runoff changes in the Loess Plateau

Study regionSixteen typical watersheds with long-term continuous runoff monitoring within the Loess Plateau (100°54′∼114°33′E, 33°43′∼41°16′N), Northwest China. Study focusFocusing on the period before and after implementing China's "Grain-for-Green" Program (GFGP) (started in 1999), this study analyzed runoff and vegetation changes and how the latter affects the former. New hydrological insights for the regionThe results show that the vegetation change effect was the main driver of runoff reduction over the LP from 1982–1999 to 2000–2015 and accounted for 78.94% (59.71–97.25%) of the reduced runoff. Changes in vegetation under multiple anthropogenic and natural influences are mainly characterized by increases in greenness, growing season length, and woodland and grassland area (along with a decrease in cultivated area). These changes have altered the repartition of precipitation in favor of evapotranspiration rather than runoff. The GFGP-led LULC shift, particularly the reduction of cropland, plays a vital role (GRD > 0.80) in vegetation-induced runoff losses, which may exacerbate future water stress in the region. To curb the LP's continuous attenuation of river runoff and promote the Yellow River Basin's ecological protection and high-quality development, we suggest focusing on the vegetation change effects on runoff and optimizing afforestation measures.

Landscape Fragmentation and Spatial Autocorrelation of a Typical Watershed in the Wenchuan Earthquake-Affected Area—A Case Study in the Longxi River Basin

The 2008 8.0 Ms Wenchuan earthquake caused serious ecological degradation in the northwest of China’s Sichuan Province. Elucidating landscape fragmentation and spatial pattern of post-earthquake landscape is of great interest in order to improve ecological restoration and predict the spatial distribution of damaged ecosystems in earthquake-affected areas. We used four real-time remote sensing images to analyze the landscape pattern characteristics and spatial autocorrelation of the Longxi River Basin before and after the Wenchuan earthquake during the period from 2005 to 2015. In the study period, the degree of landscape fragmentation increased 1 year after the earthquake in 2009 but decreased in 2011 and 2015. The spatial distribution of forest, farmland, and shrub-grassland had significantly positive spatial correlation and the characteristics of spatial aggregation from 2005 to 2015. Construction land had no significant spatial correlation before the earthquake in 2005, but significantly positive spatial correlation after the earthquake, while traffic land had no significant spatial correlation across the study period. Unlike the other landscape types, geological disasters changed from a significantly negative spatial correlation before the earthquake to a significantly positive spatial correlation after the earthquake. However, the positive autocorrelation of all landscape types decreased with the increase of space distance, but in different distance-decay rates. The High-high spatial aggregation areas of geological disasters and construction land clustered gradually upstream of the basin and distributed in Longchi town, respectively; those of farmland distributed in the southeast of the basin increased in 2009 but then decreased, while those of forests had the opposite pattern as the dominant landscape type after the earthquake. Our results elucidated the spatial structure and distribution features of the Longxi River Basin to give a theoretical foundation for assessing the effects of ecological restoration and reconstruction management in earthquake-affected areas.

Flood Simulation Study of China’s Data-Deficient Mountainous Watersheds Based on CMPA-Hourly

Heavy rainfall and flood disasters are frequent in mountainous watersheds in southwest China, and forecasting runoff floods in some mountainous watersheds is difficult. In this study, a typical watershed in the southwest mountainous region, the Qingyi River (13,000 km2), was selected for the lack of precipitation observation data in the watershed, and the BTOPMC (block-wise use of the topographic-based hydrologic model (TOPMODEL)) was used, using CMPA-Hourly (China Hourly Merged Precipitation Analysis combining observations from automatic weather stations, meteorological satellite, and weather radar at 0.05° × 0.05° grid) to improve the accuracy of flood forecasting. The results show that the Nash–Sutcliffe efficiency (NSE) of the flood forecast for the verification period in the Jiajiang section of the Qingyi River using CMPA-Hourly improved from 0.66 to 0.78, the flood error reduced from 18% to 9%, and the overall accuracy reached grade B or above. The results indicate that CMPA-Hourly, which integrates ground observation–radar–satellite precipitation, effectively combined the advantages of different sources of data to improve the resolution and accuracy of precipitation data, and then CMPA-Hourly can be used to improve the accuracy of runoff and flood forecasting.

Variation of runoff-sediment relationship at flood event scale in three typical watersheds of the Loess Plateau

River runoff and sediment load are characterized by topography, climate patterns, and vegetation in the watershed. The relationship runoff and sediment load has been greatly altered in many rivers throughout the world, as well as rivers in the Chinese Loess Plateau (LP) due to large-scale ecological restoration and soil conservation measures implementation. This study attempts to identify the changes of runoff-sediment relationship in three watersheds: the Gushanchuan River watershed, Jialu River watershed and Xichuan River watershed by using the flood event data during the periods of 1974–1989 and 2007–2019 in the LP. The results indicated that both runoff depth and sediment yield of flood events during 2007–2019 reduced significantly compared with those during 1974–1989 in all the watersheds. The highest decrease was found in the Gushanchuan River watershed, exhibiting reduction of 56.48% and 95.03% in runoff and sediment yield, respectively. The ratios between sediment yield and runoff depth in all three watersheds showed significant decrease during 2007–2019 when comparing to those in 1974–1989. The correlations between runoff and sediment variables became worse in 2007–2019, compared with those during 1974–1989. The implementation of soil and water conservation (SWC) measures (vegetation restoration, terraces and check dams) accounted for the changes in runoff-sediment relationship in all three watersheds. The result of this study could provide valuable information for the influences of SWC implementation and guide soil erosion control in the LP.

Determination of the maximum run‐off sediment transport capacity during a rainstorm flood in a small watershed on the Loess Plateau

AbstractThe channel sediment transport capacity is an important parameter in soil erosion models, and it determines the proportion of soil erosion that is sent outside the watershed. However, the calculation and judgment methods for the sediment transport capacity of channel are still incomplete, and further research is needed. Therefore, this paper takes Chabagou, a typical watershed in the hilly and gully region of the Loess Plateau, as an example and, based on the measured hydrological and sediment data collected during rainstorm floods in 1961–1969 at three hydrological stations, Caoping, Shejiagou, and Tuanshangou, studies the sediment transport capacity of channels in a small watershed from the perspective of energy dissipation. Clearly, the sediment transport capacity is better determined by using a single flood and sediment concentration peak process. The discriminant conditions are determined for the sediment concentration to reach sediment transport capacity during the flood rising and falling sections of the sediment process of the small watershed storm flood. When determining sediment transport capacity based on the characteristics of the flood and sediment concentration peak, we find that sediment transport capacity is reached in the flood discharge peak when the flood discharge peak occurs earlier than the sediment concentration peak. When determining sediment transport capacity based on the flow discharge and sediment concentration characteristics of the sediment fall section, we find that when the flood event exhibits a counterclockwise hysteresis curve and a time‐lagged effect occurs, the sediment concentration at that time reaches sediment transport capacity. In this study, the sediment concentration as a function of run‐off amount is logarithmic at different subbasin scales when run‐off reaches its maximum capacity to transport sediment. The R2 is high, ranging from 0.78 to 0.92. The results of this research provide a reference for the study of sediment transport capacity.

Fingerprinting sediment sources in two typical watersheds in the dry-hot valleys of Southwest China: The role of gully and orchard land

Identifying the contributions of sediment sources is important for effectively understanding soil erosion processes, adopting appropriate management measures, and optimizing soil conservation strategies. Currently, the sediment fingerprinting technique has gained significant attention worldwide to assess the contributions of sediment sources; however, such studies in the dry-hot valleys of Southwest China, one of the most important sediment sources for several major rivers (e.g., the Yangtze, Mekong, Salween and Yuanjiang River), are largely lacking. In this study, two typical, small watersheds in the dry-hot valley in the Yuanjiang river, which were representative of the landscape, were selected to quantify the relative contributions of potential sediment sources based on the sediment fingerprinting technique. In the orchard-forest watershed, four potential sediment sources, including the slope and level of orchard land, forest, and gully, were identified, while two sources (gully and slope) were identified for the shrub-grass watershed, and the relative contributions of these sources were estimated based on the Bayesian model. The results indicate the following:1) The gully contributed to 55.43% of the total sediment in the shrub-grass watershed, indicating that gully erosion is still significant in the dry-hot valleys, which is in accordance with several previous studies; 2) the ecological restoration in the gully in the orchard-forest watershed has greatly improved the vegetation cover from 2014 to 2021 and substantially reduced the sediment contribution of the gully, indicating that vegetation restoration is an effective ways to reduce sediment yield at the watershed scale; and 3) the orchard land, with an area proportion of<40%, in the orchard-forest watershed contributed to more than 90% of the sediment; this highlights the dominant role of orchard land in sediment yield in the watershed of the dry-hot valley, implying that suitable conservation strategies are necessary to protect soil in the orchard-related watersheds. This study quantitatively evaluated the relative contributions of the main sediment sources in dry-hot valleys, a natural gully, a gully with vegetation restoration, and orchard land, through combined studies. The results of this study could be helpful for deploying appropriate measures to reduce soil erosion and sediment yield in dry-hot valleys.

Spatial Distribution of Al, Zn, Fe, As, Pb, Mn, Cr, and Cu in Surface Waters of the Urumqi River Basin, China, and Assessment of Risks to Ecosystems and Human Health

The study of pollution and risk assessment of surface water in watersheds is important for the use and management of surface water, as well as for the stability of ecosystems and human health. This study focused on a typical watershed in an arid zone, the Urumqi River basin; divided the basin into upper, middle, and lower reaches according to the main uses of the surface water in the region; and collected surface water samples from the basin. We collected 41 surface water samples from the upper, middle, and lower reaches of the Urumqi River Basin, a typical arid zone watershed. The characteristics and spatial distribution of metal elements in the surface waters of the basin were analysed, the pollution status was evaluated, and risk assessments of the effects of these metal elements on natural ecosystems and human health were carried out. The results showed that (1) the average concentration of the metal element Al in the surface water of the Urumqi River Basin was 663.73 µg·L−1, which was 3.3 times that of the standard limit value (200 µg·L−1), with an exceedance rate of 100%, and the standard deviation value was 136.05 µg·L−1, with a large difference in spatial distribution. Spatial distributions for Al, Cu, Cr, Fe, Mn, and Zn were higher upriver and midstream than downriver, and for Pb and As, they were higher upriver, midstream, and downriver than downriver. (2) The values of the single-factor pollution index of the metal elements Zn, As, Pb, Mn, Cr, and Cu in the upper, middle, and lower reaches of the watershed were all less than 1, which is within the safe range. The integrated pollution indexes of 0.03~0.27 were all less than 0.7, which is within the safe range, and the integrated pollution of the upper reaches was significantly greater than that of the middle and lower reaches. (3) The total ecological risk of the basin ranged from 0.09 to 13.72, which is much lower than the low-risk indicator value of 150, and the ecological risk of the upper reaches was higher than that of the middle and lower reaches. (4) The health risk assessment showed that the total health risks of the eight metal elements to adults and children showed an upstream &gt; downstream &gt; midstream pattern, all of which exceeded the ICRP recommended value (10−5). The average annual total health risks of the carcinogenic metal elements chromium and arsenic to adults and children were 10−6 and 10−5 a−1, respectively, with arsenic concentrations exceeding the ICRP recommended value (10−5). Arsenic and lead in the surface waters of the Urumqi River Basin are important indicators of health risk and need to be prioritised as indicators for environmental risk management.

Hydrological characteristics and available water storage of typical karst soil in SW China under different soil–rock structures

Soil hydrological characteristics are influenced by factors such as parent rock weathering, human activities, and soil texture. However, the influence of the complex soil–rock structures and heterogeneous soil types on soil hydrological characteristics resulting from the weathering of carbonate rocks into soils on slopes in the karst region of SW China is not fully understood. The relationships between zonal and nonzonal soil hydrological characteristic differences, land uses, and soil–rock structures were analyzed using a typical watershed in the SW China karst region. In this study, (1) the difference between zonal and nonzonal soil hydrological characteristics is significant. For infiltration capacity (Ks), yellow soil (19.50 ∼ 1058.00 cm·d-1) < limestone soil (34.50 ∼ 2364.00 cm·d-1), while for soil available water storage, limestone soil on the dolomitic slope (43.26 mm) > yellow soil (20.16 ∼ 35.25 mm) > limestone soil on the limestone slope (17.73 ∼ 34.72 mm). (2) Land-use practices and soil–rock structures have long affected the hydrological characteristics of soil in karst. (3) The bare bedrock on carbonate slopes leads to a reduction in the total amount of soil per unit area on the slope, which compresses the space for vegetation growth and reduces the total amount of water provided by the soil for vegetation growth per unit area, which confirms one of the reasons for the low plant biomass in karst. These results suggest that the utilization of soil water in karst areas should consider the weights of soil type, lithology, and soil–rock structures.

Increasing flood risk under climate change and social development in the Second Songhua River basin in Northeast China

Study regionSecond Songhua River basin (SSRB), Northeast China. Study focusAccurately assessing future flood risks is the premise and foundation of flood control and water resources management. At present, studies are still lacking in assessing future watershed flood risks that consider climate change and social development in Northeast China and the relative flood risk assessment framework. This study proposed an integrated flood assessment framework containing the AHP, entropy weight, and GCM downscaling methods, which was implemented in the SSRB, a typical watershed in Northeast China, to estimate future basin flood risks under climate change and social development. New hydrological insights for the regionThe flood risk in the SSRB will increase significantly in the mid-term (2051–2075) and long-term (2076–2100) future. The areas under the four scenarios with greater than high-risk levels will expand by 28.9 %, 105.6 %, 165.6 %, and 156.7 %, respectively, compared to the historical scenario. The newly added areas mainly located in the lower reaches. Precipitation changes are the primary reason for the future flood risks. The increased GDP under a higher forcing degree will also significantly increase the flood risk in the long-term future in the lower reaches. Based on these above findings, extreme precipitation forecasting and flood management in downstream areas in the basin need to be enhanced. Energy-saving and emission-reduction measures should be simultaneously implemented.