Dominant Water Source Research Articles

An arid-semiarid climate during the Noachian-Hesperian transition in the Huygens region, Mars: Evidence from morphological studies of valley networks

Fluvial activities play important roles in the geologic evolution of early Mars. As one of the most ancient fluvial features on Mars, the widely distributed valley networks (VNs) provide clues for understanding the early martian climate. Our study focuses on the morphological and hydrological features of VNs around the Huygens basin in the ancient southern highland. A total of 198 VNs are identified in the Huygens region with a total length of 23,991.6 km, among which 83 VNs are firstly identified. VNs possess drainage patterns of dendritic to parallel, and show average stream order of 2.45 with a maximum of 5, suggesting a simple branching morphology. Sinuosity indexes of mainstreams range from 1.02 to 1.98 with an average of 1.15, exhibiting a straight to winding form. Two types of VN channels are observed with distinct elevational distribution, headwater morphology, and longitudinal profile shape, and are considered to be sapping-related and surface runoff-related, respectively. Age estimations from crater size-frequency distribution measurements suggest that VN activities at the basin rim mainly started around the Noachian/Hesperian boundary at ~3.7 Ga, and decayed near the Early/Late Hesperian boundary. VNs at the basin floor show a younger age of ~3.5 Ga, which supports a potential short-lived lake inside the basin during the Noachian-Hesperian transition. A combined effect of rainfall and groundwater is considered as the dominant water sources of VNs in the Huygens region, with the climate condition characterized by transient warm and arid-semiarid periods under a possibly cold and arid environment.

Epikarst shallow fissure soil systems are key to eliminating karst drought limitations in the karst rocky desertification area of SW China

AbstractSurface soil water shortages are among the primary factors limiting revegetation in most degraded regions with shallow soil, especially in karst areas. Finding water sources for plants is an urgent task to ensure maximum vegetation restoration in these areas. We combined soil water content monitoring and isotope tracing to reveal the principal water source supply systems for plants in karst areas. The results showed that the content and storage of water in the shallow fissure soil system (SFSS) of the epikarst zone were consistently higher and more temporally stable than that of the surface soil. Thus, epikarsts with dissolution voids and fissures are important, stable aquifers that provide water to plants. Moreover, the IsoSource results showed that the SFSS was the primary water source for three monitored tree species (Cupressus torulosa D. Don, Pyracantha fortuneana [Maxim.] Li and Rosa cymosa Tratt.), especially C. torulosa and P. fortuneana. The water‐uptake patterns of C. torulosa and P. fortuneana changed from dominant SFSS and surface soil water sources during the rainy period to the dominant SFSS and transfer zone (TZ) of vadose zone water sources during the dry period. In contrast, Rhynchospora cymosa uses water from SFSS and TZ water sources only during drought. These results suggest that the SFSS is key to eliminating vegetation restoration limitations due to surface drought in karst areas. It is proposed that deeply rooted plants with dimorphic root systems are optimal for sustainable vegetation restoration in karst areas.

Predicting long-term hydrological change caused by climate shifting in the 21st century in the headwater area of the Yellow River Basin

The Qinghai-Tibetan Plateau (QTP) is one of the amplifiers of global climate change. The headwater area of the Yellow River Basin (HYRB) on the QTP is the dominant water source region for the whole Yellow River Basin. However, the sensitive responses of hydrological processes to the intensifying climate change are exerting high uncertainties to the water cycle in the HYRB. The aim of this study was to investigate the potential climate change under three Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5) and their hydrological impacts in this region using the ensemble climate data from eight general circulation models (GCMs) and the Soil and Water Assessment Tool (SWAT). Compared to the baseline (1976–2015), the projected climate indicated a rise of 7.3–7.8% in annual precipitation, 1.3–1.9 °C in maximum air temperature, and 1.2–1.8 °C in minimum air temperature during the near future period (2020–2059), and an increment of 9.0–17.9%, 1.5–4.5 °C, and 1.3–4.5 °C in precipitation, maximum and minimum temperature, respectively, during the far future period (2060–2099). The well-simulated SWAT modeling results suggested that due to a wetter and warmer climate, annual average actual evapotranspiration (AET) would increase obviously in the future (31.9–35.3% during the near future and 33.5–54.3% during the far future), which might cause a slight decrease in soil water. Water yield would decrease by 16.5–20.1% during the near future period, implying a worsening water crisis in the future. Till the end of this century, driven by the increased precipitation, water yield would no longer continue to decrease, with a decline by 15–19.5%. Overall, this study can not only provide scientific understanding of the hydrological responses to the future climate in both semi-arid and alpine areas, but also contribute to the decision support for sustainable development of water resources and protection of eco-environment in the HYRB.

Forested lands dominate drinking water supply in the conterminous United States

Forests provide the most stable and highest quality water supplies among all land uses. Quantitatively evaluating the benefits of forest water supply functions is important to effectively mitigate the impacts of land development, climate change, and population growth. Here, by integrating a water balance model and national drinking water data, we determined the amount of surface water yield originating on different forest ownership types at a fine resolution (88,000 watersheds) and tracked that water through the river network to drinking water intakes and the populations they serve. We found that forested lands comprised 36% of the total land area but contributed 50% of the total surface water yield. Of the 23,983 public surface drinking water intakes depending on surface water sources, 89% (serving around 150 million people) received some (>0.01%) surface water from forested lands, and 38% (serving about 60 million people) received more than 50% of their surface drinking water supply from forested lands. Privately-owned forests were the most important water source in the eastern U.S., benefiting 16 million people, followed by federal forests (14.4% of the total water supply). In contrast, federally-owned forested lands were the dominant water source (52% of the total water supply) in the West. Privately-owned forests are the most vulnerable to future land use change and associated water supply impacts. Continuing programs that support private forest landowners with financial and technical assistance through federal and state forest management agencies and potentially developing payment for ecosystem service schemes could maximize benefits for landowners so they may retain their land assets while minimizing forest loss and associated impacts on critical ecosystem services including the provisioning a clean and reliable water supply for the American public.

Using the sun to co-generate electricity and freshwater

Using the sun to co-generate electricity and freshwater

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.

Repeated high flows drive morphological change in rivers in recently deglaciated catchments

AbstractClimate change is decreasing glacier cover and increasing the frequency and magnitude of precipitation‐driven high flows and floods in many regions of the world. Precipitation may become the dominant water source for river systems in recently deglaciated catchments, with major rainfall events driving significant changes in river channel morphology. Few studies, however, have examined river channel response to repeated precipitation‐driven high flows. In this study, we measured the geomorphological condition of four low‐order rivers in recently deglaciated catchments (70–210 years ice free) before and after a series of repeated precipitation‐driven high flows during summer 2014. High flows drove substantial initial morphological change, with up to 75% change in baseflow channel planform position and active channel form change from pre‐ to post‐high flow. Post‐high flow years were associated with increased instream wood and geomorphological complexity at all but the youngest river. Channel changes were part of an active relaxation stage at all rivers, where channels continued to migrate, and complexity varied through time. Overall, these measurements permit us to propose a conceptual model of the role of geomorphologically effective high flows in the context of paraglacial adjustment theory. Specifically, we suggest that older rivers in recently deglaciated catchments can undergo a short‐term (<10 years) increase in the rate of geomorphological development as a result of the recruitment of instream wood and channel migration during and following repeated precipitation‐driven high flows. Enhancing our knowledge of these geomorphological and paraglacial processes in response to high flows is important for the effective management of riverine water and ecosystem resources in rapidly changing environments.

Responses of plant water uptake to groundwater depth in limestone outcrops

The study of plant water uptake from groundwater is important to garner an improved understanding of ecohydrological processes and groundwater management. However, little is known about how fluctuations in groundwater depth influence plant water absorption in carbonate outcrop regions. This study quantified the plant water uptake patterns and plant responses to different groundwater depths at four distinct sites. The aquifers of the boreholes CF10 (4 to 10 m groundwater level) and CF12 (2 to 9 m groundwater level) basically consisted of porous and fissure media. The aquifer of borehole CF13 (historically sustained 0 to 1 m groundwater level) was dominated by fissure and conduit media, while that of borehole CF18 (2 to 3 m groundwater level) was comprised on rocks with considerable small-sized dissolution pores and seams. Borehole water, referred to as rock water in this study, is defined as a potential water source that plants can absorb. The IsoSource model, based on the dual stable isotopes of δ D and δ18O was employed to estimate soil and rock water contributions to the plant xylem water. The results revealed that the groundwater depth of the CF10, CF12, and CF13 boreholes had significant negative correlations with the total precipitation of the previous ten days. At the CF10 site, Toona sinensis and Caesalpinia decapetala absorbed soil water during the rainy season, and rock water during the dry season. At the CF12 site, Toona sinensis primarily absorbed rock water during rainy season and soil resident moisture during the dry season, while the water utilization proportion of Caesalpinia decapetala fluctuated significantly in different seasons. At the CF13 site, rock water was the dominant water source for both plant species during the rainy and dry seasons, while soil water was the main water source for both plants in the CF18 site. The proportion of rock water absorption by plants did not directly statistically correlate with groundwater depth; however, it did with the total precipitation of the previous two and fifteen days, respectively. Nevertheless, groundwater depth is a comprehensive embodiment of precipitation and the structure of karst water-bearing media. Therefore, the plant absorption of rock water is not only contingent on groundwater depth but also on the karst water-bearing media. For the first time, the isotopic values of borehole water were employed to estimate the contributions of plant water sources to improve calculations. The above results indicated that field surveys of hydrogeological structures and high precision monitoring were equally indispensable toward facilitating the restoration of vegetation and groundwater management in fragile rocky desertified ecosystems.

Changing Source‐Transport Dynamics Drive Differential Browning Trends in a Boreal Stream Network

AbstractDissolved organic carbon (DOC) concentrations are increasing in freshwaters worldwide, with important implications for aquatic ecology, biogeochemistry, and ecosystem services. While multiple environmental changes may be responsible for these trends, predicting the occurrence and magnitude of “browning” and relating such trends to changes in DOC sources versus hydrologic transport remain key challenges. We analyzed long‐term trends in DOC concentration from the two dominant landscape sources (riparian soils and mire peats) and receiving streams in a boreal catchment to evaluate how browning patterns relate to land cover and hydrology. Increases in stream DOC were widespread but not universal. Browning was most pronounced in small, forested streams, where trends corresponded to twofold to threefold increases in DOC production in riparian soils and increases in annual DOC export from a forested headwater. By contrast, DOC did not change in mire peats or streams draining catchments with high lake or mire cover, nor did we observe trends in DOC export from a mire‐dominated headwater. The distinct long‐term trends in DOC sources also altered concentration‐discharge relationships, with a forested headwater shifting from transport‐limited toward chemostasis, and a mire outlet stream shifting from chemostasis to source‐limitated. Modified DOC supply to headwaters, together with altered seasonal hydrology and differences in the dominant water source along the stream network gave rise to predictable browning trends and consistent concentration‐discharge relationships. Overall, our results show that the sources of DOC to boreal aquatic ecosystems are responding to environmental change in fundamentally different ways, with important consequences for browning along boreal stream networks.

Forested Wetland Hydrology in a Large Mississippi River Tributary System

Wetlands in the Mississippi River Valley provide numerous functions supported by prolonged periods of soil saturation or inundation. However, few studies document forested wetland hydropatterns, especially in altered systems. In this study, we evaluated hydrologic drivers of forested wetlands in the Yazoo Basin, a large Mississippi River tributary system exhibiting regional hydrologic alteration. Results from 56 water table monitoring locations indicate that precipitation induced the majority (76%) of wetland saturation events, defined as soil inundation or water tables within ≤30 cm of the surface for ≥14 consecutive days. Flooding triggered 19% of saturation events, and 5% of events occurred in response to precipitation induced high water tables followed by flood inundation. Data suggest that most wetlands examined (87%) would persist in the absence of flooding, and that duration and inundation patterns differed with dominant water source. A multi-year hydropattern analysis highlights the influence of precipitation derived saturation during low evapotranspiration winter periods, spring flood water contributions in some wetlands, and decreasing water tables throughout summer and fall. A discussion of rainfall normality and stream discharge places the dataset in a larger context. Results reflect changes in historic hydropatterns, informing efforts to maximize wetland functions during forested wetland management and restoration.

A Wet‐Bulb Temperature‐Based Rain‐Snow Partitioning Scheme Improves Snowpack Prediction Over the Drier Western United States

AbstractAccumulation of snowfall during winter and snowmelt in the subsequent spring or earlier summer provides a dominant water source in alpine regions. Most land surface and hydrological models use near‐surface air temperature (Ta) thresholds to partition precipitation into snow and rain, underestimating snowfall over drier regions. We developed a snow‐rain partitioning scheme using the wet‐bulb temperature (Tw), which is closer to the surface temperature of a falling hydrometeor than Ta. Tw becomes more depressed in drier environments as derived from Tw depression equation using Ta and surface air humidity, resulting in a greater fraction of snowfall. We implemented this new Tw scheme in the Noah‐MP land surface model and evaluated the model against a high‐quality ground‐based snow product over the contiguous United States. The results suggest that the new Tw scheme substantially improves the model skill in simulating snow depth and snow water equivalent over most snow‐covered grids, especially the higher and drier continental mountain ranges in the Western United States, while it retains the modeling accuracy over the more humid Eastern United States.

Hydrostratigraphy and Hydraulic Characterisation of Shallow Coastal Aquifers, Niger Delta Basin: A Strategy for Groundwater Resource Management

The groundwater from shallow coastal aquifers in Nigeria has been reported to be under intense stress resulting from both natural and anthropogenic impacts ranging from saltwater intrusion, effluent-related contamination and pollution to oil spillage, gas flaring, municipal, industries and agriculture. Here we characterised the hydrostratigraphy and hydraulic characteristics of the shallow coastal aquifers of the Niger Delta basin and assessed the resilience of groundwater to both natural and anthropogenic impacts. Fifty-two borehole logs were analysed from which lithological sections were used to generate cross-sections along with four profiles. The system was more complex than previously reported: a unit of silty sand was observed in the western part of the basin that thins out leaving the eastern part of the basin as an unconfined aquifer underlain by multiple thin beds of the sand aquifer. A layered sand aquifer occurs in the northern parts of the basin, which holds freshwater in this area, and is interbedded by clay layers which serve as aquitards. The relatively higher hydraulic conductivity of the Benin Formation units compared to those of the Deltaic Formation leave it with weaker climate change resilience and more vulnerable to pollution and contamination. While groundwater remains the dominant source of fresh water in the northern part of the basin, a strategic approach is needed to access potable water from the southern part where contaminated surface water appears to directly interact with groundwater of the uppermost unconfined aquifer. Management of waste and effluent related to oil spillage, municipal, industries and agricultural in this area should be engineered to protect the groundwater resources of this aquifer.

Effect of Drought and Topographic Position on Depth of Soil Water Extraction of Pinus sylvestris L. var. mongolica Litv. Trees in a Semiarid Sandy Region, Northeast China

Drought and topographic position are the most important factors influencing tree growth and survival in semiarid sandy regions of Northeast China. However, little is known about how trees respond to drought in combination with topographic position by modifying the depth of soil water extraction. Therefore, we identified water sources for 33-year-old Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) trees growing at the top and bottom of sand dunes by comparing stable isotopes δ2H and δ18O in twig xylem water, soil water at various depths and groundwater during dry and wet periods. Needle carbon isotope composition (δ13C) was simultaneously measured to assess water use efficiency. Results showed that when soil moisture was low during the dry period, trees at the top used 40–300 cm soil water while trees at the bottom utilized both 40–300 cm soil water and possibly groundwater. Nevertheless, when soil moisture at 0–100 cm depth was higher during the wet period, it was the dominant water sources for trees at both the top and bottom. Moreover, needle δ13C in the dry period were significantly higher than those in the wet period. These findings suggested that trees at both the top and bottom adjust water uptake towards deeper water sources and improve their water use efficiency under drought condition. Additionally, during the dry period, trees at the top used shallower water sources compared with trees at the bottom, in combination with significantly higher needle δ13C, indicating that trees at the bottom applied a relatively more prodigal use of water by taking up deeper water (possibly groundwater) during drought conditions. Therefore, Mongolian pine trees at the top were more susceptible to suffer dieback under extreme dry years because of shallower soil water uptake and increased water restrictions. Nevertheless, a sharp decline in the groundwater level under extreme dry years had a strong negative impact on the growth and survival of Mongolian pine trees at the bottom due to their utilization of deeper water sources (possibly groundwater).

Meltwater is the dominant water source controlling α-cellulose δ18O in a vascular-plant-dominated alpine peatland in the Altai Mountains, Central Asia

Few studies have fully considered how hydrological inputs and climate influence the linkage between the oxygen isotopic composition of α-cellulose (δ18Ocell) and their source waters in vascular-plant-dominated alpine peatlands. In this study, in order to test whether δ18Ocell can be used as a hydroclimatic indicator, we investigated the relationship between the δ18O values of cellulose extracted from the dominant plant species (Carex pamirensis) and those of potential source waters during two growing seasons (from May to September) in the Sahara sand peatland in the southern Altai Mountains. Concurrently, the Roden–Lin–Ehleringer (RLE) mechanistic model was applied to better understand oxygen isotopic fractionation during cellulose synthesis. We found that the meltwater from snow/ice cover and seasonally-frozen soil played a critical role in controlling the hydrological processes in this alpine peatland. The δ18O values of both swale water and soil water responded more sensitively to variations in inflow meltwater than did summer precipitation. IsoSource modelling demonstrated that the mean 76–24% split between meltwater and summer precipitation inputs determined the overall isotopic composition of the peatland water. The slopes of the peatland water line (6.38) and meltwater line (6.87) were slightly lower than that of the local meteoric water line (LMWL) (7.72), suggesting limited evaporation from these external water sources due to the relatively high humidity (73–80%) in the studied fen. However, the slopes of the stem water line (4.53) and leaf water line (3.57) were generally lower than that of the LMWL, indicating that the internal plant waters have experienced isotopic enrichment during transpiration. Interestingly, the variations of δ18Ocell (of shoots, stems and leaves) fall within a relatively narrow range (<±3‰), which is mainly attributed to a nearly constant monthly net 18O enrichment factor (11.13 ± 1.07‰ for ΔModelled), together with a smoothing effect. Furthermore, empirical correlation and RLE modeling both showed the co-variation of external source water and cellulose synthesis, demonstrating that the cellulose oxygen isotope composition of C. pamirensis can faithfully reflect variations in soil/swale water. These findings strongly suggest that inflow meltwater is the dominant water source in determining δ18Ocell, implying that the δ18Op signals of precipitation in the winter half-year (October–April) may be inherited by the δ18Ocell values of C. pamirensis at the study site. Therefore, our results provide important insights for the hydroclimatic interpretation of past variations in δ18Ocell values in vascular plants in alpine peatlands.

Response of plants water uptake patterns to tunnels excavation based on stable isotopes in a karst trough valley

Karstic aquifers are very sensitive and fragile to environmental changes. With more tunnels excavated in karst areas, groundwater levels are increasingly lowered and resulted in changed natural hydrogeological flow system and groundwater-dependent vegetation, soil and hydrology of surface water systems. Water, especially groundwater, is a limited and key factor and significant driving force for karst ecosystem processes. However, the effects of tunnels excavation on the ecosystems in karst areas remain largely unknown. This study aimed at investigating whether there were variations in soil water contents and shifts of plants water uptake patterns between rainy and dry seasons in a karst trough valley affected by tunnels excavation, and comparing their differences with those in a tunnel-free karst trough valley in southwest China. Monthly soil water contents at two soil layers of the upper 20 cm and lower 20–40 cm were measured, and soil water at two soil layers, subcutaneous water and plant (arbor and shrub) xylem water were sampled in February (mid dry season) and September (late rainy season) 2017, respectively, and the δ2H and δ18O of those waters were analyzed. The IsoSource model based on dual stable isotopes of δ2H and δ18O was used to estimate the contributions of different sources to the plant xylem water. Although the soil water contents at both valleys showed similar vertical and temporal variations resulted primarily from the evaporation and precipitation, the soil water contents of two soil layers in the tunneling affected valley were significantly lower than that of the tunnel-free valley at both seasons. Plants uptake water pattern changed from a dominant soil water source during the rainy season to a dominant subcutaneous water source during the dry season at both valleys. However, plants extracted more water from the subcutaneous zone in the tunneling affected karst trough valley than that of the tunnel-free karst trough valley at both seasons, of which the proportion of plants water uptake from the subcutaneous zone was 33% in rainy season and 76% in dry season, respectively, in the tunneling affected karst trough valley, while the proportion of plants water uptake from the subcutaneous zone was 24% in rainy season and 59% in dry season, respectively, in the tunnel-free karst trough valley. The above results indicated that tunnels excavation decreased the soil water contents and then changed plants water uptake patterns in karst areas.

Carbonates as evidence for groundwater discharge to the Nile River during the Late Pleistocene and Holocene

The African Humid Period (AHP, ~15–5 ka) is the latest in a series of Saharan pluvials studied using carbonates. Evidence from desert paleolakes indicate that water tables rose across the region caused by increased precipitation during these wet periods and that this higher groundwater discharged at the surface creating a wetter environment beyond what increased seasonal precipitation could support alone. Carbonate cemented material and sediments have been noted at key archaeological sites such as Khartoum Hospital, and al-Khiday and at site distributions along Wadi Howar. In the deserts west of the Nile, extensive surface discharge of groundwater is the accepted generator of paleolakes and contributed to wadi flow. In contrast, studies in the Nile Valley have focused on the river itself as the source for any moisture to explain documented effects of a higher water table. Carbonate morphology and oxygen isotope composition of carbonate samples are used to develop a conceptual model demonstrating their accumulation in areas near the Nile River as a result of a regional rise in groundwater driven by greater precipitation. Morphological evidence shows a variety of formative environments at key topographic locations, indicating water availability above modeled contemporary Nile River flood levels. New results presented here from oxygen isotopes show locations dominated by evaporative enrichment at higher elevations, a transition to stable isotopic conditions at lower elevations, and ultimately a return to more enriched values at the lowest elevations that would have undergone intermixing of discharging groundwater and floodwater from the Nile. For areas beyond the river's flood extent or an associated river-fed alluvial aquifer, the only perennial moisture source capable of maintaining an isotopic equilibrium in a monsoonal climate would be groundwater. Results coincide with isotopic patterns and values observed in carbonates from studied paleolakes in the desert. This model provides an explanation for the carbonate accumulation at archaeological sites — while offering greater understanding of contemporary water availability for vegetation, animals, and human populations — and whether the Nile River functioned as the dominant water source for cultural groups in the valley during the early to mid-Holocene, as it did for the later agricultural populations.

Numerical simulation of water age and its potential effects on the water quality in Xiangxi Bay of Three Gorges Reservoir

After the impoundment of Three Gorges Reservoir, algal blooms frequently occurred in the tributaries of the reservoir, which has posed a great challenge for the local aquatic environment and ecology. To investigate the main causes and key factors of the algal blooms, the Environmental Fluid Dynamics Code (EFDC) model is applied to the simulation of the three-dimensional hydrodynamics and water quality in the Yangtze River and Xiangxi Bay, and the concept of water age is adopted to quantitatively analyze the effects of hydrodynamics on the water quality by linking water age and phytoplankton levels, which has seldom been explored in previous studies. The model results show good agreement with the field data, and the simulation reproduces the thermal stratification and density current in Xiangxi Bay. The results show that Xiangxi Bay exhibits quite complicated hydrodynamic characteristics, and could be divided into different zones according to the transport process. In the upper reach, the water quality is mainly affected by the upstream inflows, while it is mainly affected by the intrusion flow from the mainstream near the river mouth. Water age and water temperature are found to be the key factors influencing the algal blooms in Xiangxi Bay. Besides, a significant positive correlation has been found between the chlorophyll a (chl-a) concentration in the surface layer and the water age of the dominant water source. This conclusion can be adopted to interpret the longitudinal distribution of chl-a concentration and to explain why Xiangxi Bay is susceptible to algal blooms. The correlation between water age and chl-a concentration is further used to evaluate the effectiveness of water level fluctuation in preventing algal blooms. The analyses and findings in this study could help to better understand the complicated hydrodynamic and water quality processes in Xiangxi Bay following the impoundment, and provide insights into ecological and environmental management of Three Gorges Reservoir.

Generation of High Mountain Precipitation and Temperature Data for a Quantitative Assessment of Flow Regime in the Upper Yarkant Basin in the Karakoram

AbstractImproved daily precipitation and temperature data at 5 × 5‐km grids for 1960–2015 were developed for the Upper Yarkant basin (UYB) based on observations of precipitation gradients and temperature lapse rates. The developed climate data are then used to drive the VIC‐Glacier hydrological model to simulate the runoff process for the UYB. A large altitudinal dependence is observed in both precipitation and temperature, with three altitudinal patterns of precipitation gradient for the elevation bands of &lt;2,000 m, 2,000–3,000 m, and &gt;3,000 m, respectively, and a strong seasonal variation in temperature lapse rate ranging from 0.4 to 0.8 °C/100 m. Basin precipitation and temperature data are greatly improved in both amount and spatial variations after the orographic adjustments. Glacier melt runoff is the dominant water source of the UYB accounting for about 52% of annual total flows, followed by snowmelt (about 26%), and rainfall runoff (about 22%). About 60% of basin runoff originates from the high altitudes (&gt;5,000 m), and about 32% and 8% of runoff originate from middle (4,000–5,000 m) and low (&lt;4,000 m) altitudes, respectively. The variations in annual runoff in the UYB were mainly controlled by glacier melt runoff, middle and high altitudes, and temperature in warm seasons during 1965–2015. However, rainfall and snowmelt runoff, and low altitudes, were playing an increasingly important role in total flow variations of the UYB due to the increase of warm season temperatures in 1994–2015 and precipitation in the entire simulation period.

Water utilization characteristics of typical vegetation in the rocky mountain area of Beijing, China

Seasonal drought are expected to occur more frequent and intense in the some regions due to global climate change, which may significantly influence in the competitive interactions of water uptake depth for vegetation communities. We investigated the impacts of seasonal drought on water utilization for vegetation communities using hydrogen-2 and oxygen-18 stable isotope techniques in Beijing rocky mountainous area. Our results indicate that the water sources of the four plant species varied by season. Platycladus orientalis largely absorbed water from middle (31.5% in May and 35.9% in November) and deep (32.8% in May and 38.4% in November) soil layers during the dry season and switched its main water source to surface layers (50.3% in July and 37.2% in September) during the wet season. Contrary to P. orientalis, Quercus variabilis mainly absorbed water from surface and middle soil layers during the dry season and changed its dominant water sources to the deep soil layer throughout the wet season; at same time, this species utilized water from natural springs in July and the middle soil layer in September. V. negundo var. heterophylla mostly utilized water from deep soil layers (38.7%) in May and transferred its main water source to surface (43.5%) and middle (33.1%) layers in July. This species primarily utilized water from surface (29.2%) and middle (30.8%) soil layers in September, and from middle (35.4%) and deep (27.8%) layers in November, similar to the findings of P. orientalis in this season. In contrast the above three plant species, C. heterophylla Fisch mainly absorbed water from surface and middle soil layers throughout the year, having very little reliance on water from deep soil layers. P. orientalis and Q. variabilis showed the opposite characteristics of water utilization, which suggests that these two species are suitable for a mixed forest vegetation when selecting plant species for afforestation. However, since the water sources of P. orientalis and V. negundo var. heterophylla were from similar soil depths, there may be potential competition for moisture between these two species. Our findings provide an indication as to which vegetation species are suitable to grow together when undertaking restoration in drought prone environments.

Assessment of water sources and their contributions to streamflow by end-member mixing analysis in a subtropical mixed agricultural catchment

Knowledge of the dominant water sources and their relative contributions to streams in time is important for understanding the underlying hydrological processes as well as managing the quantity and quality of water resources. In many subtropical regions, the complexity of mixed agricultural land and water use in combination with lack of data further inhibits such understanding of the dominant catchment scale runoff generation processes. This study provides new insights into the time-variable interactions of natural and anthropogenic influences on the catchment response through integrated hydrometric and multi-tracer (stable water isotopes, Mg2+, Na+, Si4+, Cl−, and Electricity Conductivity) analyses. The combined diagnostic tools of mixing models (DTMM) and end-member mixing analysis (EMMA) were successfully used to evaluate the spatiotemporal variability in key water sources of a subtropical catchment in China. This study site is characterized by rain-fed uplands and irrigated water paddy fields. The EMMA results for one year of data showed that irrigation water, rainwater and ground water were the three main sources, which contributed to 64%, 19% and 17% of the streamflow on average, respectively. However, temporal patterns in rainfall and irrigation practices did cause significant variability in these relative contributions. Overall, we found that routine agricultural practices to optimize crop growth (especially during paddy growth periods) was a more important factor than hydro-meteorological conditions in controlling the regime and properties of water sources. The relatively simple but successful application of EMMA and DTMM in a complex environment demonstrates that it is a valuable approach for understanding water sources and hydrologic processes concerning agricultural or mixed-land use catchments.