•Estimating recession constant is key to the one-parameter digital filtering.•The Eckhardt method is sensitive to the maximum baseflow index.•Difference among the improved digital filtering methods ...is small.•The improved Lyne–Hollick method with two passes performs overall best.
Baseflow is the portion of streamflow that comes from shallow and deep subsurface flow, and is the key for catchment ecology and water resource management. This paper comprehensively evaluates four widely used non-tracer baseflow separation methods against tracer-based hydrograph separation for five Eastern Australian catchments. The four methods include United Kingdom Institute of Hydrology (UKIH) method and three digital filtering methods: Lyne–Hollick method, Chapman–Maxwell method and Eckhardt method. The first two filtering methods include a parameter of recession constant, and the last one has two parameters: the recession constant and the maximum baseflow index. We used an Automatic Baseflow Identification Technique (ABIT) to estimate the recession constant, which varies from 0.943 to 0.987 for the five catchments that is evidently higher than the default value of 0.925, and used the default Eckhardt and UKIH methods to estimate the maximum baseflow index, respectively. All modelling results are evaluated against the tracer-based hydrograph separation. Using the recession constant estimated from the ABIT method performs noticeably better than using the default parameter, indicated by the absolute bias reduced about 20% in average. For the two-parameter Eckhardt method, estimating the maximum baseflow index has larger effect on baseflow separation than estimating the recession constant. Compared to the different parameterisation schemes, the difference among the improved non-tracer methods is small. Using multiple passes into the Lyne–Hollick method can only slightly improve or deteriorate baseflow index estimates. Our results suggest that it is critical to get appropriate parameter(s) before applying the digital filtering methods.
Nitrate (NO3−) pollution in rivers caused by intensive human activities is becoming a serious problem in irrigated agricultural areas. To identify NO3− sources and reveal the impact of irrigation ...projects on NO3− pollution in rivers, the hydrochemistry and isotopes of irrigation water from the Yellow River (IW) and river water (RW), and potential source samples were analyzed. The mean NO3− concentrations in the IW and RW were 24.4 mg/L and 49.9 mg/L, respectively. Approximately 45.2% of RW samples (n = 31) exceeded the Chinese drinking water standard for NO3− (45 mg/L). The δ15N and δ18O values, combined with the Cl−/Na+, SO42−/Ca2+ ratio distributions, indicate that the NO3− in the RW mainly originated from chemical fertilizers, manure and sewage. A Bayesian model showed that manure and sewage contributed the most to the overall NO3− levels of the IW. In the RW, chemical fertilizers and IW contributed the most to the overall NO3− levels. The mean nitrate contribution to the RW from the combination of chemical fertilizers and IW is estimated to be 51.6%. Nitrogen from manure and sewage, soil N and precipitation also contributed. The NO3− pollution in rivers was largely influenced by the irrigation regime, with a large amount of nitrogen in chemical fertilizer lost because of low utilization efficiency and subsequent transfer, via irrigation runoff, into the rivers. This study suggests that with a detailed assessment of the sources and fate of NO3−, effective reduction strategies and better management practices can be implemented to control NO3− pollution in rivers.
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•NO3− pollution of rivers is more serious than that of the irrigation water.•Manure and sewage were the main NO3− sources of the irrigation water.•NO3− in rivers was derived from fertilizer and irrigation water.•The NO3− transport from fertilizer to rivers was driven by flood irrigation regime.
River confluences are pivotal junctions that have vital influences on hydraulic characteristics and sediment particle distributions as well as on hyporheic water exchange. However, hyporheic water ...exchange is poorly understood because of the complicated river morphology within a river confluence. Therefore, the river confluence between the Juehe River and Haohe River located in arid and semi-arid areas of northwestern China was selected to evaluate the hyporheic water exchange processes, and the temperatures of different depth sediment were measured on July 11th and 12th, 2016 by an instrument equipped with five temperature sensors. The patterns and magnitudes of hyporheic water exchange were estimated using a one-dimensional heat transport model coupled with temperature data. Meanwhile, terrain points elevations and sediment particle distributions in this river confluence were collected to determine the confluence riverbed morphology. Furthermore, the river confluence morphology effects on hyporheic water exchange were investigated in this study. The different riverbed morphology and hydrodynamic zone locations were observed, which were controlled by the planform geometry with low river confluence flux momentum during the test period. Meanwhile, the upwelling flow dominated in the test area, and the downwelling occurred at three of the 23 total test points, which was induced by the complicated riverbed morphology and hydraulic characteristics. Additionally, the magnitudes of the upwelling flow were significantly influenced by the sediment heterogeneity subjected to the erosional and depositional processes. Hyporheic water exchange is a vital hydrological process in arid and semi-arid areas, where it significantly impacts the ecological environment of rivers. This study provides a valuable guideline for water quality and quantity management in arid and semi-arid areas.
Check dams are small engineering structures. They are used worldwide for soil and water conservation, gully rehabilitation, hydrological regulation, and food supply. Eroded materials trapped and ...buried in check dams constitute an important carbon (C) sink. However, as a typical deposition site, systematic information about C cycling processes in check dams is relatively unknown, despite its crucial role in estimating the fate of buried C and elucidating the ongoing C sink/source debate on soil erosion. This study reviewed the stock, source, enrichment, distribution, stability, and underlying mechanisms of sediment C in check dams. Current studies have found a large amount of C stored in check dams (approximately 1–30 Mg C km−2 yr−1), and have demonstrated that C retention ability relied more on factors governing sediment production and trapping at larger scales than on check dam trapping efficiency at smaller scales. Stable isotopes, radiocarbon, geochemical properties, biomarkers, and spectroscopy methods have proven to be practical in identifying the sources of sediment C but can only be used in certain situations because of their intrinsic limitations. Both enrichment and impoverishment of sediment C compared with source soils have been reported, and have depended on soil erosion type, land-use type, sediment connectivity, and the loss of C during transportation. Sediment C generally increases from the back of the check dam to the front along the flow pathway and fluctuates vertically, depending on the clay and sand layers of the deposition couplets. Information about C mineralization and sequestration is relatively limited, and the existing studies have shown reduced C mineralization and promoted C-fixing potential in check dam sediments. Given the specific benefits of deposition couplets in reflecting information about burial period, erosion intensity, and historical land use, further studies should integrate C stability with soil erosion and deposition information for the deposit profiles. The responses of C cycling to climate change and human disturbances, such as warming, dam-break, tillage, and fertilization for check dam sediments require further research.
•Check dams store significant C depending on sediment input and trapping efficiency.•Both enrichment and impoverishment of sediment C occur compared with source soils.•Sediment C raises with flow path horizontally and fluctuates with couplets vertically.•Stable C fractions dominated in the sediments and changed little with depth.•Effects of warming, tillage, fertilization, and dam-break on C stability are needed.
Nitrate pollution in surface water has become an environmental problem of global concern. The effective way for controlling the nitrate pollution of surface water is to identify the pollution source ...and reduce the input of nitrate. In recent decades, nitrogen (δ15N) and oxygen (δ18O) isotopes of nitrate has been used as an effective approach for identifying the source and fate of nitrate pollution in surface water. However, owing to the complexity of nitrate pollution source and the influence of isotopic fractionation, the application of this method has some limitations. In this work, we systematically discussed the fundamental principle of using nitrogen and oxygen isotopes to trace the nitrate source, the fate identification of nitrate, and the major testing techniques. Subsequently, the applications of nitrogen and oxygen isotopes for source identification of surface water were illustrated. However, there are still significant gaps in the application of the source identification and transformation mechanisms to nitrate and many research questions on these topics need to be addressed.
•The driving factors of human appropriation of net primary production (HANPP) were quantitatively assessed.•Eight indicators were introduced to specifically evaluate the impact of human and climate ...factors on HANPP.•The effect of climate change and human activities to the change of HANPP accounted for 73.2% and 26.8%, respectively.
The combined effects of climate change and human activities pose threat to the sustainable development of ecosystems. Human appropriation of net primary production (HANPP) has been extensively used as an important indicator for evaluating the sustainable development of the ecosystem. However, few studies quantitatively assessed the driving factors of HANPP. Based on Moderate-Resolution Imaging Spectroradiometer (MODIS) data, methods of net primary production (NPP) model and regression analysis, the spatial and temporal distribution of HANPP and its driving factors in the Qilian Mountains from 2005 to 2015 were illustrated. The results showed that the HANPP in the Qilian Mountains decreased gradually from both east to west and from south to north, showing a slight upward overall. The regions affected by human activities and climate change accounted for 26.8% and 73.2% respectively. Moreover, there was a significant negative impact between grain yield and HANPP, and a significant positive impact of either the annual sunshine duration, or livestock amount to HANPP.
•The response of vegetation to drought on different time scales was evaluated.•Spatial differences were identified in vegetation response to drought.•The critical period of vegetation response to ...drought were determined.•The timescale of vegetation response to drought were revealed.
A deep understanding of the response characteristics of vegetation to drought is important for ecosystem and water resource management. In this study, we investigate spatiotemporal patterns of vegetation responses to droughts and their causes in the Qinling Mountains (QMs). The study showed that (1) there was a significant positive correlation (p < 0.05) between the Normalized Difference Degetation Index (NDVI) and Standardized Precipitation Evapotranspiration Index (SPEI) in 80.98% of the QMs. The most sensitive period of vegetation growth in response to drought was May-July. The average timescale of the vegetation response to drought changes was 11.88 months, where the vegetation response timescale on the northern slope (10.67 months) was shorter than that on the southern slope (12.02 months). (2) A clear relationship was identified between the vegetation response to drought and vegetation type and elevation, indicating that the overall vegetation sensitivity in the QMs is relatively high, with grasses being the most sensitive to drought conditions. Vegetation drought management should be focused on extremely sensitive and severely sensitive areas in aridified regions in the future.
•Local factors played a critical role on the phytoplankton community.•Phosphorus has a greater impact on the phytoplankton community than nitrogen.•Regional factors affecting the phytoplankton ...community were indirect and less prominent.•Environmental factors affecting the phytoplankton community existed seasonal differences.
Knowledge of the phytoplankton community dynamics is fundamentally important for river ecological management. Disentangling the relative impacts of co-occurring factors is critical to understanding the community responses to environmental heterogeneity, as well as anthropogenic activities. Taking phytoplankton community as the indicative variable, this study aimed at elucidating the impacts of driving forces (local factors: water environments; regional factors: land-use, fertilizers application, and socio-economic factors) on the phytoplankton community dynamics. We found that spatial and seasonal processes played a vital role in structuring the phytoplankton community, with Bacillariophyta and Chlorophyta accounting for>79.0% of taxa composition. Bacillariophyta had the highest cell density (>41%), followed by Cyanophyta (>20%) and Chlorophyta (>11%), which mainly contributed to the spatial and seasonal differences in the composition and abundance of the phytoplankton community. Meanwhile, local factors (such as total phosphorus, permanganate index, flow velocity, transparency, and stream depth) and regional factors (the application of phosphate fertilizers) (p < 0.05) were the dominant factors that influenced the phytoplankton community. Here, the phosphorus related factors interfered with the phytoplankton community on both local and regional scales. On the whole, the local factors (including nutrients and hydrology factors) have a more direct impacts on the phytoplankton community in a temperate river. It is of guiding significance for river ecology monitoring and improvement in north China, while paying attention to terrestrial influences, the eutrophication of the river itself still needs to be focused on accompanied with the hydrology factors.
Persistent Organic Pollutants (POPs) may exert adverse effects on human and ecosystem health. However, as an ecologically fragile zone with strong interaction between river and groundwater, the POPs ...pollution in the riparian zone has received little attention. The goal of this research is to examine the concentrations, spatial distribution, potential ecological risks, and biological effects of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in the riparian groundwater of the Beiluo River, China. The results showed that the pollution level and ecological risk of OCPs in riparian groundwater of the Beiluo River were higher than PCBs. The presence of PCBs (Penta-CBs, Hexa-CBs) and CHLs, respectively, may have reduced the richness of bacteria (Firmicutes) and fungi (Ascomycota). Furthermore, the richness and Shannon’s diversity index of algae (Chrysophyceae and Bacillariophyta) decreased, which could be linked to the presence of OCPs (DDTs, CHLs, DRINs), and PCBs (Penta-CBs, Hepta-CBs), while for metazoans (Arthropoda) the tendency was reversed, presumably as a result of SULPHs pollution. In the network analysis, core species belonging to bacteria (Proteobacteria), fungi (Ascomycota), and algae (Bacillariophyta) played essential roles in maintaining community function. Burkholderiaceae and Bradyrhizobium can be considered biological indicators of PCBs pollution in the Beiluo River. Note that the core species of interaction network, playing a fundamental role in community interactions, are strongly affected by POPs pollutants. This work provides insights into the functions of multitrophic biological communities in maintaining the stability of riparian ecosystems through the response of core species to riparian groundwater POPs contamination.
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●The first investigation of POPs pollution in riparian groundwater of Beiluo River.●OCPs may pose a higher ecological risk compared to PCBs in the Beiluo River.●Burkholderiaceae and Bradyrhizobium can be considered as biological indicators.●Proteobacteria and Bacillariophyta are essential in maintaining community function.
•The natural and man-made land use has exactly opposite effect on ecosystem services.•The lower water yield depth forms, the higher soil retention per unit area occurs.•The effect of land use changes ...on ecosystem services is highest at middle elevation.
Land use changes affect the supply of ecosystem services, which are related to human health and well-being. Demonstration the interaction of land use and ecosystem services play a great role on the social-economic sustainable development. As a typical greatly land use changes and an important ecological function area, Zhangjiakou and Chengde city (Zhangcheng District) exert a profound impact on the sustainable development of the Beijing-Tianjin-Hebei region in northern China. Based on InVEST model, the variations in water yield and soil retention at different elevations in the Zhangcheng District during 2011 and 2015 were illustrated. And the responses of water yield and soil retention to land use changes were revealed as well. The natural and man-made land use have exactly opposite effects on ecosystem services. With the increase of cultivated land, the capacity of water yield increases significantly, while soil retention decreases largely at all elevations (p < 0.05). However, with the increase of arbor land, shrub land, grassland, and water bodies, the capacity of water yield decreases, while soil retention increases at all elevations (p < 0.05). Comparably, the effect of land use changes on water yield depth is greater than that on soil retention; the whole effect of land use changes on ecosystem services is significantly highest at middle elevation. Generally, the lower water yield depth forms, the higher soil retention occurs. This study is helpful for rational regulation of land uses and protection of ecosystem services for both our study area and similar regions.
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