Baseflow:Potential Pathway Underlying a High Nitrogen Concentra-tion in a Less-rainy WatershedTaking Chaohe River Basin of China as an Example

Baseflow is one of the major pathways of runoff in hilly areas,and its contributions to surface water resources and pollutant loads cannot be ignored.In this study,based on water quantity and quality data from 1988 to 2019 in hilly and low rainfall watersheds,we focused on the impact of long-term baseflow on nitrogen load using the load allocation based on the baseflow separation method.We also constructed a nitrogen balance model for the Chaohe River Basin of China from 2012 to 2021 to analyze the nitrogen accumulation in the basin.We used the baseflow nitrogen load lag analysis method to study the lag characteristics of the baseflow discharge process and analyzed the response and periodicity of baseflow nitrogen to precipitation and soil accumulation using time delay analysis.The res-ults showed that the contribution rate of baseflow nitrogen reached 69%and showed a slight increasing trend from 1988 to 2019.The ef-fects of changes in precipitation and nitrogen accumulation on the baseflow contribution was observed after 1-2 and 2 yr,respectively.After nitrogen accumulation,it entered the river channel through baseflow,which was already the main and continuous source of nitro-gen in rivers in hilly areas.

Use of Groundwater, Baseflow and SPEI to Evaluate Water Resources in Michigan, USA

Precipitation and evaporation are commonly used to assess and forecast droughts. However, surface and groundwater respond to both land surface processes, land use, and climatic variables, and should be integrated into water management decisions. Water trend analysis near the Great Lakes is limited due to fluctuating cycles and data scarcity. In this study, we examine daily discharge data from 46 surface water gauges with high baseflow contributions and groundwater elevation from 28 observation wells in Michigan. Using established hydrograph separation techniques, we determined baseflow and standardized both annual average baseflow levels (SDBF) and groundwater levels (SDGW) from 1960 to 2022. These results are compared to the widely used Standardized Precipitation-Evapotranspiration Index (SPEI). SPEI is a widely used drought indicator that integrates both precipitation and potential evapotranspiration, offering a more comprehensive measure of water balance. While the SPEI suggests that Michigan is becoming wetter, the SDBF shows a mix of both wet and dry conditions. Interpreting SDGW is more challenging due to incomplete records, but it indicates varying groundwater stability across the state. In some areas, SDGW mirrors the trends seen in SDBF, while in others, it takes 3 to 4 years for groundwater levels to reflect the same changes observed in baseflow. Overall, SDBF provides a better understanding of surface processes and responses to changing climatic variables.

Standardized Baseflow Drought Index Comparison to SPEI in High Baseflow Streams

Increased use of streamflow, most importantly minimum flow/baseflow data should be incorporated into drought indices, especially in regions where streams have a high baseflow component. Standard departure for streamflow (SDSF) and standard departure for baseflow (SDBF) were compared to the standardized precipitation and evapotranspiration index (SPEI) drought index values for 17 baseflow-dominated watersheds in the northern, central, and southern regions of Wisconsin. For each watershed, comparisons of SDSF, SDBF, and SPEI time series (for 1, 3, and 12-month time scales) were evaluated using correlation, run lengths of negative and positive values, sign congruence, and Mann-Kendall trend test. In general, SDBF performed better than SDSF for longer time scales. Trends of wetness appear to be distinguished earlier in SDBF compared to SDSF and SPEI-1, SPEI-3, and SPEI-12. The results of this study are consistent with regional statewide climate studies on precipitation and changes in precipitation intensity. This study highlights how standardized baseflow data are robust and compare to SPEI 12-month time scales.

Periodical characteristics of baseflow in the source region of the Yangtze River

Baseflow, which represents the drainage of groundwater aquifers, is an essential component of runoff in hydrological basins. In the source region of the Yangtze River, the change of baseflow typically reflects the in- teractions between groundwater system and climatic factors in cold and arid areas. With modified Kalinen separa- tion method, annual baseflow between 1957 and 2009 in this region was estimated and calculated. In comparison with the inner-annual variations of total streamflow, baseflow showed a weaker fluctuation. Before the 1980s, it was in a steady state; and after then, it demonstrated dramatic variations and large amplitudes. Based on the calculation results of baseflow, the real Morlet wavelet method was applied to reveal the periodical characteristics of baseflow as well as the precipitation and air temperature in the study area. It was found that annual baseflow has a 43-year trend as well as a 21-year period and a 7-year period. The 21-year period is most significant, with its wavelet coef- ficient having the largest fluctuation and amplitude. Summation of wavelet coefficients on these periods exhibits a similar change pattern with respect to that of annual baseflow. The summation curve takes a ＂W＂ shape, which means that the baseflow follows a four-stage sequence of descending-ascending-descending-ascending. As analyzed, the relationship among baseflow, precipitation and temperature is implied in the correlation between their normalized wavelet coefficients at different temporal scales. By the significant positive linear correlations both be- tween precipitation and baseflow （correlation coefficient is 0.98） and between temperature and baseflow （correla- tion coefficient is 0.90） for the 43-year wavelet coefficients, it is suggested that the long-term increasing trends of precipitation and air temperature will lead to an increasing trend of baseflow. For wavelet coefficients of 21-year and 7-year periods, the positive linear correlation between precipitation and baseflow is significant. However, the cor- relation between air temperature and baseflow is not so evident, especially for the 21-year period. As a conclusion, correlation analysis with normalized wavelet coefficients showed that the change of annual baseflow was contrib- uted mostly by the change of precipitation and secondly by the change of temperature.

Baseflow Separation and Its Response to Meteorological Drought in a Temperate Water-limited Basin,North China

Baseflow,a component of the total streamflow,plays a key role in maintaining aquatic habitats,particularly during extreme drought events.This study investigated baseflow response to a prolonged and extreme meteorological drought event in the Baiyangdian Basin(BYD basin),a temperate water-limited basin in North China.Applying a precipitation series,piecewise regression was used to determine this extreme meteorological drought event,while the Automatic Baseflow Identification Technique(ABIT)was used to estimate a recession parameter(α),which was used to isolate baseflow from total streamflow.Results showed that:1)annual precipitation exhibited significant decreasing trends(P<0.05)with an average change of–1.81 mm/yr^(2).The precipitation deficit revealed that the start and end date of the extreme meteorological drought event was from August 1996 to May 2011,respectively,persisting for a total of 178 months(roughly 15 yr);2)hydrological drought(including streamflow and baseflow)lagged behind meteorological drought while predictably persisting longer than extreme meteorological drought(i.e.,precipitation);and 3)baseflow decreased dramatically under meteorological drought at both seasonal and annual scales,resulting in significantly decreasing trends during drought periods.Findings from this study confirmed that hydrological events caused by extreme meteorological drought can alter the magnitude and duration of baseflow and total streamflow,which will have an inevitable influence on aquatic ecosystems.

Baseflow Characteristics in Alpine Rivers-a Multicatchment Analysis in Northwest China

As a component of streamflow, baseflow is critical for regulating seasonal distribution of river fows and stabilizing water supplies. Water resources in the arid area of Northwest China are mainly from multiple catchments in the alpine that could be influenced by varieties of climatic, land cover, soil and geological factors. While numerous studies have been done on streamflow, systematic analysis of baseflow in the alpine river systems is scare. Based on historical daily streamflow data and the automated digital filter method of baseflow separation, this study investigated characteristics of hydrographs of overland flow, streamflow and baseflowof river systems fed by rainfall, snowmelt, glacier melt or mixtures of these. This study also calculated the recession constants and baseflow indices of 65 river systems. While the recession constant was o.oo34- o.o728 with a mean of o.o18, the baseflow index was 0.27-0.79 with a mean of 0.57. Further, Spearman＇s correlation analysis showed that the baseflow index was significantly correlated with catchment climatic factors （e.g., precipitation and temperature）, topographic factors （e.g., elevation and slope） and aquifer properties represented by the recession constant. Multiple regression analysis indicated that the factors explained 65% of the variability of baseflow index in the studv area.

Baseflow variations and its causes in a subtropical watershed of southern China

Baseflow is an essential component of streamflow and plays a crucial role in maintaining the stability of streamflow.However,few quantitative studies have identified the effects of leading factors on baseflow variation at the small watershed scale,especially in subtropical China.In this study,the small watershed(Pengchongjian watershed,2.90 km2),located in Southern China,was considered to explore the quantitative impact of precipitation,evapotranspiration,temperature,and vegetation restoration on baseflow.The digital filter method was used to separate baseflow by daily streamflow records from 1983 to 2014.The stepwise regression models were developed for selecting significant influencing factors of baseflow at seasonal and annual scales.The direct and indirect effects,as well as their quantitative relationships between baseflow and multiple factors,were clarified by the path analysis.The results showed that filtered average annual baseflow significantly decreased(p<0.05),ranging from 72.82 to 305.85 mm,and the average yearly baseflow index was 0.22.In addition,various significant influencing factors of baseflow had different direct and indirect effects on baseflow at seasonal and annual scales.The precipitation was the dominant factor with respect to the direct impact,which directs path coefficient was 0.891 in spring,0.823 in summer,1.599 in autumn,1.332 in winter,and 0.917 in an annual scale,respectively.In terms of the indirect effects,evapotranspiration played a leading role during the spring,autumn,winter,and annual scale,whereas the average temperature was the dominant factor during the summer.Overall,results demonstrated that the baseflow variation was mainly attributed to climate change.The present works are beneficial for revealing the internal mechanism of the baseflow variations in the study area,and it can provide a scientific basis for managing water resources in the watershed.

On Redefining the Onset of Baseflow Recession on Storm Hydrographs

Two methods that define the point of baseflow recession onset were compared using storm hydrograph data for 27 storm events that occurred between 1982-1995 in the Upeo watershed located in the Andes mountain range in central Chile (Figure 1). Three well-known baseflow recession equations were used to determine whether the method we are proposing here, that defines baseflow recession onset as the third inflection point on the logarithmic graph of the falling limb of the storm hydrograph, more accurately models observed data than the most widely used method that defines baseflow onset as the second inflection point on the same graph. Five time intervals were used to modify the recession coefficient in search of a more accurate fit. Results from the coefficient of determination, standard error, Mann-Whitney U test, and Bland-Altman test suggest that redefining baseflow recession onset via the proposed approach more accurately models baseflow recession behavior.

基流分割法在黄河流域地下水研究中的应用

为研究黄河流域地下水可再生能力变化规律和制定黄河流域水资源管理方案,应用基流指数法（BFI）和直线平割法的原理与方法,计算了黄河流域干流13个水文断面与20条主要支流31个水文断面的基流量,并分析了基流量的形成机理、地下水对黄河水的贡献、基流变化过程、流域地下水资源的构成及地下水资源总量。研究结果表明：花园口断面的基流量占多年平均径流量的44%,流域内河水与地下水存在极其密切的转化关系,地下水对黄河水的贡献很大。黄河的径流量与基流量主要来自兰州以上的源区,兰州断面的年径流量与基流量分别占花园口断面径流量的59%和60%;而兰州以下到花园口之间的上、中游地区,地下水对黄河水的贡献很小。1990年前后,黄河干流与支流河段的基流量发生了很大变化。除玛多以上的源头段基流量衰减率较大外（衰减率为0.38）,兰州以上的干流河段基流量衰减率较小（0.08～0.20）,而兰州以下的黄河干流基流量衰减率都很大（0.22～0.31）。基流量的剧烈衰减是天然和人类活动（如地下水开采）共同作用下地下水资源量减少的结果。从流域水循环的观点考虑,黄河流域的区域地下水资源由参与黄河水循环的地下水资源、未参与黄河水循环的地下水资源和流域地下水的开采等3大部分构成。1990年6月—2000年6月近10年黄河流域地下水天然资源量平均值为353.9亿m3/a,比多年地下水资源量平均值减少了15%。

Hydrological and water cycle processes of inland river basins in the arid region of Northwest China

The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China(ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources(including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that:(1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains;(2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains;(3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and(4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.

Estimation of groundwater residence time and recession rate in watershed of the Loess Plateau

Groundwater residence time is an important indicator of hydrological cycle and essential for water resources development and utilization. In this paper, groundwater residence time in non-flood season, flood season and water year has been determined from daily streamflow hydrograph of ten hydrological stations in Wudinghe River Basin located in the middle reaches of the Yellow River Basin. Results have showed that： baseflow recession constant in Wudinghe River Basin ranges from 0.72 to 0.94 with a larger recession rate in flood season than that in non-flood season. Spatially, the recession rate of baseflow in loess area is the biggest, but is the smallest in the sandy area. The half-residence time of groundwater varies from 1.8 to 45.5 days while overall residence time of groundwater is between 34 and 342 days in different sub-basins of the Wudinghe River Basin. The annual average overall residence time of groundwater decreases from 117 days in the upper reaches to 73 days in the lower reaches.

Effect of forest thinning on hydrologic nitrate exports from a Nsaturated plantation

Although several studies have assessed the effects of thinning on water quality,including nitrogen(N)exports,few have examined N-saturated plantations.This study assessed the short-term effect of thinning on N exports from a N-saturated plantation forest in northern Kyushu,western Japan,that was thinned(43%of basal area)during January-March 2012.Water levels at the gauging station were continually measured,and streamwater baseflow and stormflow samples were collected before(2011)and after(2013)forest thinning.Annual precipitation before(2469 mm)and after(2418 mm)forest thinning differed little,and annual water discharge after thinning(1641 mm)was similar to that before thinning(1609 mm).However,direct flow during stormflow periods was higher after thinning(260 mm)than before(153 mm).The concentrations of major ions in stream water did not differ before and after thinning.As a result,the high annual dissolved inorganic N(DIN)exports differed little before(35.8 kg N ha^-1 a^-1)and after(36.5 kg N ha^-1 a^-1)forest thinning.DIN exports during stormflow periods were slightly higher after(12.2 kg N ha^-1 a^-1)than before thinning(10.5 kg N ha^-1 a^-1)and were proportional to the increased direct flow after thinning(561 mm after vs.470 mm before thinning).We concluded that thinning does not affect annual N exports from the N-saturated plantation forest,but it can increase the proportion of N exported during stormflow periods in proportion to increased water volume of direct flow after thinning.

Hydrological functioning of forested catchments,Central Himalayan Region,India

Background:Central Himalayan forested catchments provide fresh water supply and innumerable ecosystem services to millions of people.Hence,the understanding of linkages between forests and water is very crucial for availability and quality of water at catchment scale.Therefore,the present study aims to understand the hydrological response of two forested catchments(namely,Arnigad and Bansigad)in the Central Himalayan Region.Methods:Threeyears’data(March,2008 to February,2011)were collected from meteorological and hydrological stations in Arnigad and Bansigad catchments.The present paper describes the mean hydrological response of these forested catchments investigated through detailed field investigation.Results:The annual hyetograph analysis revealed that the rainfall at both the catchments was highly seasonal,and wetperiod(June–September)plays a key role in catchment functioning.Exceedance of rainfall threshold of^200 mm(~10%of annual rainfall)significantly increased streamflow generation in both catchments.In Arnigad,the stream was perennial with a mean baseflow of^83mm per month(~6%of annual baseflow)whereas,Bansigad had greater seasonality due to lack of streamflow during the prewetperiod(March–May).Separation of hydrographs in Arnigad and Bansigad catchments i.e.stormflow(6%and 31%,respectively)and baseflow(50%and 32%,respectively)helped to understand the probability of flooding during wetperiod and drought during dryperiod.The forest ecosystem in Arnigad displayed healthier hydrological functioning in terms of reduced stormflow(82%),and enhanced baseflow(52%),soil moisture(13%),steady infiltration rate(22%)and lag time(~15 min)relative to Bansigad.These enhanced values indicated soil capability to store water in the forested catchment(Arnigad)and helped to understand the volume of water(discharge)that was available during dryperiod.The lower denudation rate at Arnigad by 41%resulted in decreased suspended sediment(18%)and bed load(75%)compared to Bansigad.Further,the enhanced dissolved solids in the Arnigad stream resulted from the higher organic matter generated in the forest floor.Conclusion:This study shows that rainfall during the wetperiod was the main driver of hydrological functioning,whereas,forests provided substantial services by regulating water balance,soil moisture and sediment budget through different mechanisms of forest components at catchmentscale in the Central Himalayan Region.

Quantity and Trends in Streamflows of the Malewa River Basin,Kenya

Freshwater availability in sufficient quantity and quality is necessary for both people and nature.Environmental flow data is useful in the management and allocation of water resources.This study aimed at quantifying stream flows and their trends in the Malewa Basin rivers in central rift valley,Kenya.Daily stream flow data(1960-2013)in four gauges(2GB01,2GB05,2GB0708 and 2GC04)were subjected to exploratory data analysis,fixed interval method of baseflow separation and Mann Kendall trend test.The results shows that on average,the Malewa river at Gauge 2GB01 discharge(excluding abstractions)about 191.2 million cubic metres of water annually,equivalent to a discharge of 6.06 m3/s.While discharges had not experienced a step change,huge annual fluctuations were noted suggesting periodicity with changes in climatic conditions.No trend was noted in annual stream data for the four gauges assessed.However,extreme low and high flows,median flows and baseflows for daily data showed either positive or negative trends.The baseflow index for daily flows showed trends:2GB01(Z=4.519),2GB05(Z=-6.861),2GB0708(Z=-16.326)and 2GC04(Z=5.593).The findings suggest that Malewa rivers are likely experiencing effects of extreme climatic conditions and land cover changes.Land cover degradation seems to create conditions of increased flow,although the intensity varies from sub-catchment to another.The data also seems to suggest that stream discharge is much dependent on baseflows.There is need to regulate water use,improve soil cover and manage or adapt to the adverse effects of climate change.Key words:Streamflow,baseflow,trend,discharge.1.Introduction?Freshwater availability in sufficient quantity and quality is necessary for both people and nature.The concept of environmental flows has been the subject of study and consideration[1-5].Environmental flow information guides on how water is managed and allocated to different competing uses.The need for improved water efficiency in the allocation has led to increasing focus on environmental flows or environmental water allocations[6],although national and international policies have not yet accounted for them[7].Streamflow volumes and trends are important for decision making on water allocation.As reported by Kundzewicz,W.Z.,et al.[8],changes in?

SWAT Model Prediction of Phosphorus Loading in a South Carolina Karst Watershed with a Downstream Embayment

The SWAT model was used to predict total phosphorus (TP) loadings for a 1555-ha karst watershed—Chapel Branch Creek (CBC)—which drains to a lake via a reservoir-like embayment (R-E). The model was first tested for monthly streamflow predictions from tributaries draining three potential source areas as well as the downstream R-E, followed by TP loadings using data collected March 2007-October 2009. Source areas included 1) a golf course that received applied wastewater, 2) urban areas, highway, and some agricultural lands, and 3) a cave spring draining a second golf course along with agricultural and forested areas, including a substantial contribution of subsurface water via karst connectivity. SWAT predictions of mean monthly TP loadings at the first two source outlets were deemed reasonable. However, the predictions at the cave spring outlet were somewhat poorer, likely due to diffuse variable groundwater flow from an unknown drainage area larger than the actual surface watershed, for which monthly subsurface flow was represented as a point source during simulations. Further testing of the SWAT model to predict monthly TP loadings at the R-E, modeled as a completely mixed system, resulted in their over-predictions most of the months, except when high lake water levels occurred. The mean monthly and annual flows were calibrated to acceptable limits with the exception of flow over-prediction when lake levels were low and surface water from tributaries disappeared into karst connections. The discrepancy in TP load predictions was attributed primarily to the use of limited monthly TP data collected during baseflow in the embayment. However, for the 22-month period, over-prediction of mean monthly TP load (34.6 kg/mo) by 13% compared to measured load (30.6 kg/mo) in the embayment was deemed acceptable. Simulated results showed a 42% reduction in TP load due to settling in the embayment.

Linking basin-scale hydrology with climatic parameters in western Himalaya:Application of satellite data,temperature index modelling and in-situ observations

Due to limited spatial and temporal in-situ runoff data availability,Himalaya-Karakoram(HK)glaciohydrology has a significant knowledge gap between large-scale and small-scale runoff modelling studies.This study reconstructs longest basin-wide runoff series in Chandra-Bhaga Basin by applying a high-resolution glaciohydrological model SPHY(Spatial Processes in Hydrology)over 1950–2022.Two-tier model calibration is done using in-situ basin-wide runoff(1973–2006)and MODIS snow cover(2003–2018).Model validation is done against in-situ Chhota Shigri Glacier catchment-wide runoff(2010–2015).The modelled mean annual basin-wide runoff is 60.21±6.17 m^(3)/s over 1950–2022,with maximum runoff in summer-monsoon months,peaking in July(182.69 m^(3)/s).Glacier runoff(ice melt+snowmelt over glacier)contributes maximum(39%)followed by equal contributions from snowmelt runoff from non-glacierized basin area and baseflow(25%),while rainfall-runoff contributes minimum(11%)to total runoff.There is a significant volumetric increase by∼7%from pre-(59.17 m^(3)/s)to post-2000(63.47 m^(3)/s)mainly because of early onset of snowmelt post-2000 that resulted in a hydrograph shift by∼25 days earlier in spring.The glacier runoff is overestimated by 3%from RGI 7.0 inventory compared to different manually delineated inventories over 1950–2022,because of higher glacierized area from RGI 7.0.The precipitation shows a negative trend,but total runoff shows a positive trend due to positive trend of temperature that resulted in more glacier runoff and rainfall-runoff for basin over last 72 years.Basin-wide runoff is mainly governed by summer temperature which directly controls the amount of glacier and snowmelt runoffs and is supported by summer rainfall.This study highlights importance of basin-scale model calibration with in-situ data in large scale studies and stresses the need for in-situ observations in high-altitude Himalayan region.Basin-scale calibrated model parameters are transferable to glacier catchment scale within Chandra-Bhaga Basin,showing the model robustness at a small catchment scale.

Contribution of baseflow nitrate export to non-point source pollution

As a common pollutant of nitrogen in groundwater, nitrate contamination has become a major concern worldwide. Baseflow, one of the dominant hydrological pathways for nitrate migration to streamflow, has been confirmed as a leading nitrate source for stream water where groundwater or subsurface flow contaminated heavily by nitrate. That is, sufficient improvements of water quality may not be attained without proper management for baseflow, even if non-point sources(NPS) pollutants discharged through surface runoff are being well managed. This article reviews the primary nitrate sources, the main factors affecting its transport, and the methodologies for baseflow nitrate estimation, to give some recommendations for future works, including:(1) giving sufficient consideration for the effects of climatological, morphological, and geological factors on baseflow recessions to obtain more reliable and accurate baseflow separation;(2) trying to solve calibration and validation problems for baseflow loads determining in storm flow period;(3) developing a simple and convenient algorithm with certain physics that can be used to separate baseflow NPS pollution from the total directly in different regions, for a reliable estimation of baseflow NPS pollution at larger scale(e.g., national scale);(4) improving groundwater quality simulation module of existing NPS pollution models to have a better simulation for biogeochemical processes in shallow aquifers;(5) taking integrated measures of "source control", "process interception" and "end remediation" to prevent and control NPS nitrate pollution effectively, not just only the strict control of nutrients loss from surface runoff.

An optimized baseflow separation method for assessment of seasonal and spatial variability of baseflow and the driving factors

Baseflow is an important component of river or streamflow.It plays a vital role in water utilization and management.An improved Eckhardt recursive digital filter(IERDF)is proposed in this study.The key filter parameter and maximum baseflow index(BFImax)were estimated using the minimum smoothing method to improve baseflow estimation accuracy.The generally considered BFImax of 0.80,0.50 and 0.25 according to the drainage basin’s predominant geological characteristics often leads to significant errors in the regions that have complex subsurface and hydrologic conditions.The IERDF improved baseflow estimation accuracy by avoiding arbitrary parameter values.The proposed method was applied for baseflow separation in the upstream of Yitong River,a tributary of the Second Songhua River,and its performance was evaluated by comparing the results obtained using isotope-tracer data.The performance of IERDF was also compared with nine baseflow separation techniques belonging to filter,BFI and HYSEP methods.The IERDF was also applied for baseflow separation and calculation of rainfall infiltration recharge coefficient at different locations along the Second Songhua River’s mainstream for the period 2000–2016.The results showed that the minimum smoothing method significantly improved BFImax estimation accuracy.The baseflow process line obtained using IEDRF method was consistent with that obtained using isotope 18 O.The IERDF estimated baseflow also showed stability and reliability when applied in the mainstream of the Second Songhua River.The BFI alone in the river showed an increase from the upstream to the downstream.The proportion of baseflow to total flow showed a decrease with time.The intra-annual variability of BFI was different at different locations of the river due to varying climatic conditions and subsurface characteristics.The highest BFI was observed at the middle reaches of the river in summer due to a water surplus from power generation.The research provided valuable information on baseflow characteristics and runoff mode determination,which can be used for water resources assessment and optimization of economic activity distribution in the region.

Quantitative assessment on basin-scale hydrological services of wetlands

Despite recognizing the importance of hydrological function of wetlands, basin-scale wetlands services have rarely been investigated. The PHYSITEL/HYDROTEL modelling platform was used to quantitatively assess the impact of wetlands on quickflow and baseflow with paired simulation scenarios in Duobukuli River Basin, namely with wetlands and without wetlands.Simulation results showed that wetlands exert significant impact on basin hydrological processes by decreasing streamflow and altering streamflow regime(magnitude, frequency, duration and time of flow events). The intensity(significant or not) of wetlands influences on quickflow had daily, monthly and annual variation. Wetlands significantly attenuated quickflow during flood season while slightly support daily, monthly and annual baseflow. The average quickflow attenuation and baseflow support of wetlands were 5.89% and 0.83%, respectively. Although the intensity and effect(mitigation or augment) of wetlands on streamflow temporally varied at daily, monthly, seasonal and annual scales, wetland overall mitigated quickflow and augment baseflow in Duobukuli River Basin. Our results could provide insights for future decision-making for rehabilitation and conservation of wetlands as well as integrated basin water resources management.