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1.
The collapse of soil pipes due to internal erosion can result in fully mature gullies. Few studies have measured the rates of sediment detachment and transport through soil pipes in situ. The objectives of this work were to determine suspended sediment concentration (SSC) in soil pipes as a function of pipeflow rate to develop sediment rating curves (SRC) and measure the bedload transport as a function of cumulative flow per storm event. H-flumes were installed in seven discontinuous gullies formed by pipe collapse and instrumented for pipe discharge measurements and suspended sediment sampling. The typical response to pipeflow was an initial flush of high concentration of suspended sediment followed by a decrease as pipeflow increased (rising limb of hydrograph). Pipeflows were often so dynamic that it was difficult to consistently capture the initial flush of sediment, resulting in weak to non-existent SRCs. The falling limb of the hydrograph tended to have a relatively low SSC. Thus, soil pipe SRCs tended to be better represented by hysteretic SRCs, although relationships between SSC and flow rate were poorly represented by SRCs. A power law equation given by SSC = aQb was adopted to represent the SRC relationships. Fitting this equation to data showed a correlation between the offset, a, and the slope, b, with the slope decreasing as the offset increases. Both SRC parameters (a and b) were correlated to the contributing area of the individual pipe. Bedload appeared to be an important contributor to sediment transport, with bedload – expressed as an average event sediment concentration (mg l−1) – decreasing as the volume of the event discharge (m3) increased. A significant portion (11–31%) of the bedload material was gravel and aggregates (>2 mm diameter material). While this work was the first to determine SRCs for soil pipes, refined sampling and measurement techniques are needed. © 2020 John Wiley & Sons, Ltd.  相似文献   

2.
Piping is a widespread phenomenon in the world and can significantly contribute to the downward movement of water, sediments, and nutrients. This study examines the hydrological functioning of soil pipes in a loess‐derived soil under pasture using hydrometric and hydrochemical analyses. It aims to investigate the relation between pipeflow, rainfall, and groundwater table fluctuations and to determine the dominant source of the water flowing through the soil pipes using both hydrometric and hydrochemical approaches. A rapid pipeflow response is observed when a threshold rainfall depth is exceeded. This threshold depth is larger in the summer (9 mm) compared with that in the winter (4 mm) which is related to the prestorm wetness of the soil. Hydrochemical analyses indicate that both groundwater and rainfall contribute to the pipeflow with a dominance of groundwater. This study shows that pipeflow can be an important hydrological pathway in loess‐derived soils with a clear seasonal pattern in pipeflow responses to rainfall events.  相似文献   

3.
Many concepts have been proposed to explain hydrologic connectivity of hillslopes with streams. Hydrologic connectivity is most often defined by qualitative assessment of spatial patterns in perched water tables or soil moisture on hillslopes without a direct linkage to water flow from hillslopes to streams. This form of hydrologic connectivity may not explain the hydrologic response of catchments that have network(s) of preferential flow paths, for example, soil pipes, which can provide intrinsic connectivity between hillslopes and streams. Duplex soils are known for developing perched water tables on hillslopes and fostering lateral flows, but the connectivity of localized perched water tables on hillslopes with soil pipes has not been fully established. The objectives of this study were to characterize pipeflow dynamics during storm events, the relationships between perched water tables on hillslopes and pipeflows, and their threshold behaviour. Two well‐characterized catchments in loess soil with a fragipan were selected for study because they contain multiple, laterally extensive (over 100 m) soil pipe networks. Hillslopes were instrumented with shallow wells adjacent to the soil pipes, and the wells and pipe collapse features were equipped with pressure transducers. Perched water tables developed on hillslopes during a wetting up period (October–December) and became well connected spatially across hillslope positions throughout the high flow period (January–March). The water table was not spatially connected on hillslopes during the drying out (April–June) and low flow (July–September) periods. Even when perched water tables were not well‐connected, water flowing through soil pipes provided hydrologic connectivity between upper hillslopes and catchment outlets. Correlations between soil pipeflow and perched water tables depended on the size and location of soil pipes. The threshold relationship between available soil‐moisture index plus storm precipitation and pipeflow was dependent on the season and strongest during dry periods and not high‐flow seasons. This study demonstrated that soil pipes serve as a catchment backbone of preferential flow paths that provide intrinsic connectivity between upper hillslopes and streams.  相似文献   

4.
Headcut formation and migration was sometimes mistaken as the result of overland flow, without realizing that the headcut was formed and being influenced by flow through soil pipes into the headcut. To determine the effects of the soil pipe and flow through a soil pipe on headcut migration in loessic soils, laboratory experiments were conducted under free drainage conditions and conditions of a perched water table. Soil beds with a 3-cm deep initial headcut were formed in a flume with a 1.5-cm diameter soil pipe 15 cm below the bed surface. Overland flow and flow into the soil pipe was applied at a constant rate of 68 and 1 l min−1 at the upper end of the flume. The headcut migration rate and sediment concentrations in both surface (channel) and subsurface (soil pipe) flows were measured with time. The typical response was the formation of a headcut that extended in depth until an equilibrium scour hole was established, at which time the headcut migrated upslope. Pipeflow caused erosion inside the soil pipe at the same time that runoff was causing a scour hole to deepen and migrate. When the headcut extended to the depth of the soil pipe, surface runoff entering the scour hole interacted with flow from the soil pipe also entering the scour hole. This interaction dramatically altered the headcut processes and greatly accelerated the headcut migration rates and sediment concentrations. Conditions in which a perched water table provided seepage into the soil pipe, in addition to pipeflow, increased the sediment concentration by 42% and the headcut migration rate by 47% compared with pipeflow under free drainage conditions. The time that overland flow converged with subsurface flow was advanced under seepage conditions by 2.3 and 5.0 min compared with free drainage conditions. This study confirmed that pipeflow dramatically accelerates headcut migration, especially under conditions of shallow perched water tables, and highlights the importance of understanding these processes in headcut migration processes. © 2020 John Wiley & Sons, Ltd.  相似文献   

5.
Alan R. Hill 《水文研究》2012,26(20):3135-3146
The effect of preferential flow in soil pipes on nitrate retention in riparian zones is poorly understood. The characteristics of soil pipes and their influence on patterns of groundwater transport and nitrate dynamics were studied along four transects in a 1‐ to >3‐m deep layer of peat and marl overlying an oxic sand aquifer in a riparian zone in southern Ontario, Canada. The peat‐marl deposit, which consisted of several horizontal layers with large differences in bulk density, contained soil pipes that were generally 0.1 to 0.2 m in diameter and often extended vertically for 1 to >2 m. Springs that produced overland flow across the riparian area occurred at some sites where pipes extended to the peat surface. Concentrations of NO3?–N (20–30 mg L?1) and dissolved oxygen (DO) (4–6 mg L?1) observed in peat pipe systems and surface springs were similar to values in the underlying sand aquifer, indicating that preferential flow transported groundwater with limited nitrate depletion. Low NO3?–N concentrations of <5 mg L?1 and enriched δ15N values indicated that denitrification was restricted to small areas of the peat where pipes were absent. Groundwater DO concentrations declined rapidly to <2 mg L?1 in the peat matrix adjacent to pipes, whereas high NO3?–N concentrations of >15 mg L?1 extended over a larger zone. Low dissolved organic carbon values at these locations suggest that supplies of organic carbon were not sufficient to support high rates of denitrification, despite low DO conditions. These data indicate that it is important to develop a greater understanding of pipes in peat deposits, which function as sites where the transport of large fluxes of water with low biogeochemical reaction rates can limit the nitrate removal capacity of riparian zones. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
Glenn Wilson 《水文研究》2011,25(15):2354-2364
The role of soil pipeflow in ephemeral gully erosion is not well understood. Experiments were conducted on continuous soil pipes to better understand the role of internal erosion of soil pipes and its relation to ephemeral gully development. Soil beds of 140 cm length, 100 cm width and 20 cm depth had a single soil pipe of different initial sizes (2, 4, 6, 8, and 10 mm diameter) extend from a water reservoir to the outlet. Experiments were run on Providence silt loam and Smithdale loam soils under a constant head of 15 cm established for 30 min. Either the tunnel collapsed or the head could not be maintained. Soil pipes that were initially 2 and 4 mm clogged instantaneously at their mouth and did not exhibit flow, whereas, pipes initially ≥ 6 mm enlarged by 268, 397, and 699% on average for the 6, 8, and 10 mm diameters, respectively. Critical shear stress values were found to be essentially zero, and erodibility values gave erosion indexes that were extremely high. The rapid internal erosion resulted in erratic flow and sediment concentrations with periods of no flow as pipes were temporarily clogged followed by surges of high flow and high sediment concentrations. Tensiometers within 6 cm of the soil pipes did not exhibit pressure increases typically associated with pipe clogging. Flow through 10 mm diameter soil pipes exhibited tunnel collapse for both soils tested. Tunnel collapse typically occurred within minutes of flow establishment suggesting that ephemeral gullies could be misinterpreted as being caused by convergent surface flow if observations were made after the runoff event instead of when flow is first established through soil pipes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
Measurements of saturated hydraulic conductivity (Ks) and diagnostic model simulations show that all types of logging road/trail in the 14·4 ha Bukit Tarek Experimental Catchment 3 (BTEC3) generate substantial Horton overland flow (HOF) during most storms, regardless of design and level of trafficking. Near‐surface Ks(0–0·05 m) on the main logging road, skid trails and newly constructed logging terraces was less than 1, 2 and 34 mm h?1, respectively. Near‐surface Ks on an abandoned skid trail in an adjacent basin was higher (62 mm h?1), owing to the development of a thin organic‐rich layer on the running surface over the past 40 years. Saturated hydraulic conductivity measured at 0·25 m below the surface of all roads was not different (all <6 mm h?1) and corresponded to the Ks of the adjacent hillslope subsoil, as most roads were excavated into the regolith more than 0·5–1 m. After 40 years, only limited recovery in near‐surface Ks occurred on the abandoned skid trail. This road generated HOF after the storage capacity of the upper near‐surface layer was exceeded during events larger than about 20 mm. Thus, excavation into low‐Ks substrate had a greater influence on the persistence of surface runoff production than did surface compaction by machinery during construction and subsequent use during logging operations. Overland flow on BTEC3 roads was also augmented by the interception of shallow subsurface flow traveling along the soil–saprolite/bedrock interface and return flow emerging from the cutbank through shallow biogenic pipes. The most feasible strategy for reducing long‐term road‐related impacts in BTEC3 is limiting the depth of excavation and designing a more efficient road network, including minimizing the length and connectivity of roads and skid trails. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Erosion and the associated loss of carbon is a major environmental concern in many peatlands and remains difficult to accurately quantify beyond the plot scale. Erosion was measured in an upland blanket peatland catchment (0.017 km2) in northern England using structure-from-motion (SfM) photogrammetry, sediment traps and stream sediment sampling at different spatial scales. A net median topographic change of –27 mm yr–1 was recorded by SfM over the 12-month monitoring period for the entire surveyed area (598 m2). Within the entire surveyed area there were six nested catchments where both SfM and sediment traps were used to measure erosion. Substantial amounts of peat were captured in sediment traps during summer storm events after two months of dry weather where desiccation of the peat surface occurred. The magnitude of topographic change for the six nested catchments determined by SfM (mean value: 5.3 mm, standard deviation: 5.2 mm) was very different to the areal average derived from sediment traps (mean value: –0.3 mm, standard deviation: 0.1 mm). Thus, direct interpolation of peat erosion from local net topographic change into sediment yield at the catchment outlet appears problematic. Peat loss measured at the hillslope scale was not representative of that at the catchment scale. Stream sediment sampling at the outlet of the research catchment (0.017 km2) suggested that the yields of suspended sediment and particulate organic carbon were 926.3 t km–2 yr–1 and 340.9 t km–2 yr–1, respectively, with highest losses occurring during the autumn. Both freeze–thaw during winter and desiccation during long periods of dry weather in spring and summer were identified as important peat weathering processes during the study. Such weathering was a key enabler of subsequent fluvial peat loss from the catchment. © 2019 John Wiley & Sons, Ltd.  相似文献   

9.
This paper describes the design, operation and performance of a field‐portable ‘drip‐type’ simulator and erosion measurement system. The system was constructed specifically for soil erosion research in the humid tropics and has been used extensively in Malaysian Borneo. The simulator is capable of producing replicable storms of up to 200 mm h?1 intensity and 20–30 minutes duration with a drop‐size distribution close to that of natural storms of such intensity (D50 of simulated rainfall is 4·15 mm at 200 mm h?1 and 3·65 mm at 160 mm h?1, D50 measured during natural rainfall = 3·25 mm). The simulator is portable and simply constructed and operates without a motor or electronics, thus making it particularly useful in remote, mountainous areas. The erosion measurement system allows assessment of: (1) rainsplash detachment and net downslope transport from the erosion plot; (2) slopewash (erosion transported by overland flow); and (3) infiltration capacity and overland flow. The performance of the simulator–erosion system compared with previous systems is assessed with reference to experiments carried out in primary and regenerating tropical rainforest at Danum Valley (Malaysian Borneo). The system was found to compare favourably with previous field simulators, producing a total storm kinetic energy of 727 J m?2 (over a 20‐minute storm event) and a kinetic energy rate of 0·61 J m?2 s?1, approximately half that experienced on the ground during a natural rainfall event of similar intensity, despite the shorter distance to the ground. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

10.
Piping has been recognized as an important geomorphic, soil erosion and hydrologic process. It seems that it is far more widespread than it has often been supposed. However, our knowledge about piping dynamics and its quantification currently relies on a limited number of data for mainly loess‐derived areas and marl badlands. Therefore, this research aimed to recognize piping dynamics in mid‐altitude mountains under a temperate climate, where piping occurs in Cambisols, not previously considered as piping‐prone soils. It has been expressed by the estimation of erosion rates due to piping and elongation of pipes in the Bere?nica Wy?na catchment in the Bieszczady Mountains, eastern Carpathians (305 ha, 188 collapsed pipes). The research was based on the monitoring of selected piping systems (1971–1974, 2013–2016). Changes in soil loss vary significantly between different years (up to 27.36 t ha?1 yr?1), as well as between the mean short‐term erosion rate (up to 13.10 t ha?1 yr?1), and the long‐term (45 years) mean of 1.34 t ha?1 yr?1. The elongation of pipes also differs, from no changes to 36 m during one year. The mean total soil loss is 48.8 t ha?1 in plots, whereas in the whole studied catchment it is 2.0 t ha?1. Hence, piping is both spatially and temporally dependent. The magnitude of piping in the study area is at least three orders of magnitude higher than surface erosion rates (i.e. sheet and rill erosion) under similar land use (grasslands), and it is comparable to the magnitude of surface soil erosion on arable lands. It means that piping constitutes a significant environmental problem and, wherever it occurs, it is an important, or even the main, sediment source. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

11.
Based on interpolation of thermoluminescence dates and the mean accumulation rate of 0.034 mm yr?1, four cycles of pedogenic CaCO3 accumulation are found within the Loveland Loess: 415–325 ka, 325–250 ka, 250–195 ka and 195–95 ka. The four CaCO3 peaks correspond chronologically to marine oxygen isotope stages 11, 9, 7 and 5, respectively. The early Wisconsin (95–70 ka) was characterized by sand dune activity. The reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation (0·016 mm yr?1). The Gilman Canyon pedocomplex, enriched in organic matter and dated at 35–20 ka, was formed under a strong physical weathering regime and a relatively high rate of silt accumulation (0·15 mm yr?1), indicating a windy, relatively moist, probably cool environment. It developed when the Laurentide ice sheet was advancing and dust content in Greenland ice core was low. The Peoria Loess was accumulated at a rate of 0·3 mm yr?1 in central Kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the Greenland ice core was the highest. Even the warm substage around 13 ka has some corresponding evidence in the central Great Plains. The well-developed Brady Soil, dated at 10·5–8·5 ka, indicates that the early Holocene was the optimal time for soil development since 20 ka. The poorly weathered Bignell Loess might have been deposited during the Altithermal Period from 8·5 to 6 ka.  相似文献   

12.
Sustainable water management in semi-arid agriculture practices requires quantitative knowledge of water fluxes within the soil-vegetation-atmosphere system. Therefore, we used stable-isotope approaches to evaluate evaporation (Ea), transpiration (Ta), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre-monsoon, monsoon, and post-monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying Ea); (ii) water and isotope mass balances (to partition Ea and Ta for groundnut and pasture); and (iii) the piston displacement method (for estimating R). Ea losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02 to 0.09 mm d−1 in the Groundnut basin, versus 0.02–0.11 mm d−1 in Ferlo. At the groundnut site, Ea rates ranged from 0.01 to 0.69 mm d−1; Ta was in the range 0.55–2.29 mm d−1; and the Ta/ETa ratio was 74%–90%. At the pasture site, the ranges were 0.02–0.39 mm d−1 for Ea; 0.9–1.69 mm d−1 for Ta; and 62–90% for Ta/ETa. The ETa value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from the previous validated HYDRUS-1D model. However, the HYDRUS-1D model gave a lower Ta/ETa ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways.  相似文献   

13.
Peatland restoration practitioners are keen to understand the role of drainage via natural soil pipes, especially where erosion has released large quantities of fluvial carbon in stream waters. However, little is known about pipe-to-stream connectivity and whether blocking methods used to impede flow in open ditch networks and gullies also work on pipe networks. Two streams in a heavily degraded blanket bog (southern Pennines, UK) were used to assess whether impeding drainage from pipe networks alters the streamflow responses to storm events, and how such intervention affects the hydrological functioning of the pipe network and the surrounding peat. Pipeflow was impeded in half of the pipe outlets in one stream, either by inserting a plug-like structure in the pipe-end or by the insertion of a vertical screen at the pipe outlet perpendicular to the direction of the predicted pipe course. Statistical response variable η2 showed the overall effects of pipe outlet blocking on stream responses were small with η2 = 0.022 for total storm runoff, η2 = 0.097 for peak discharge, η2 = 0.014 for peak lag, and η2 = 0.207 for response index. Both trialled blocking methods either led to new pipe outlets appearing or seepage occurring around blocks within 90 days of blocking. Discharge from four individual pipe outlets was monitored for 17 months before blocking and contributed 11.3% of streamflow. Pipe outlets on streambanks with headward retreat produced significantly larger peak flows and storm contributions to streamflow compared to pipe outlets that issued onto straight streambank sections. We found a distinctive distance-decay effect of the water table around pipe outlets, with deeper water tables around pipe outlets that issued onto straight streambanks sections. We suggest that impeding pipeflow at pipe outlets would exacerbate pipe development in the gully edge zone, and propose that future pipe blocking efforts in peatlands prioritize increasing the residence time of pipe water by forming surface storage higher up the pipe network.  相似文献   

14.
Concentrations of in‐situ‐produced cosmogenic nuclides 10Be and 26Al in quartz were measured by accelerator mass spectrometry for bedrock basalts and sandstones located in northwest Tibet. The effective exposure ages range between 23 and 134 ka (10Be) and erosion rates between 4·0 and 24 mm ka?1. The erosion rates are significantly higher than those in similarly arid Antarctica and Australia, ranging between 0·1 and 1 mm ka?1, suggesting that precipitation is not the major control of erosion of landforms. Comparison of erosion rates in arid regions with contrasting tectonic activities suggests that tectonic activity plays a more important role in controlling long‐term erosion rates. The obtained erosion rates are, however, significantly lower than the denudation rate of 3000–6000 mm ka?1 beginning at c. 5‐3 Ma in the nearby Godwin Austen (K2) determined by apatite fission‐track thermochronology. It appears that the difference in erosion rates within different time intervals is indicative of increased tectonic activity at c. 5–3 Ma in northwest Tibet. We explain the low erosion rates determined in this study as reflecting reduced tectonic activity in the last million years. A model of localized thinning of the mantle beneath northwest Tibet may account for the sudden increased tectonic activity at c. 5–3 Ma and the later decrease. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
Runoff from natural soil pipes has been shown to be a significant contributor to stream discharge in parts of upland Wales. Attempts have been made to model pipeflow contributions using both theoretical and empirical approaches, but little progress has yet been made towards producing generally applicable models of complete pipeflow systems. The paper identifies some of the problems of devising general models with reference to data from the Maesnant Experimental Catchment. The data suggest that in-pipe travel times are more important here than inferred elsewhere, and that neither simple hydraulic models nor kinematic wave theory can adequately explain the patterns of response. In particular, stormflow tends to begin first at the network outfall and even peak discharge often occurs at the outfalls before the headward zones.  相似文献   

16.
The nature and rates of fluvial and slope processes change over time and space as urbanized areas replace forested land in Singapore. Storm-based and time-based data, from undisturbed rainforests, heavily disturbed construction sites, urban grass-covered slopes and an experimental plot, are collected to observe the impact of rainwater on the soil moisture conditions, surface microtopography, runoff generation, sediment movement, and ground lowering in the three different categories of land use. The undisturbed forested environment is characterized by high throughfall (58% of total rainfall) and frequent negative soil moisture suctions. The slow and unconcentrated overland flow during heavy storms is restricted by the forest floor microtopography. No rills develop. Ground lowering is recorded as 3·2–3·4 mm a?1. But sediment movement is episodic and suspended sediment concentrations in overland flow are 172–222 mg l?1. During urban construction, gully development is rapid on the bare slopes, runoff generation, voluminous, and sediment-laden discharges (5200–75498 mg l?1) lead to sediment plumes at channel mouths. Ground lowering rates are measured at 132·4 mm a?1. Once grass-covered, runoff carries less suspended sediment (800 mg l?1) and ground lowering rates are reduced, but depend on the condition of the cover, ranging from 0·2 to 8·2 mm a?1. As urban development continues, environments are altered both in time as well as spatially.  相似文献   

17.
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18.
A physically based snow-evolution modelling system (SnowModel) that includes four sub-models: MicroMet, EnBal, SnowPack, and SnowTran-3D, was used to simulate eight full-year evolutions of snow accumulation, distribution, sublimation, and surface melt from glaciers in the Zackenberg river drainage basin, in north-east Greenland. Meteorological observations from two meteorological stations were used as model inputs, and spatial snow depth observations, snow melt depletion curves from photographic time lapse, and a satellite image were used for model testing of snow and melt simulations, which differ from previous SnowModel tests methods used on Greenland glaciers. Modelled test-period-average end-of-winter snow water equivalent (SWE) depth for the depletion area differs by a maximum of 14 mm w.eq., or ∼6%, more than the observed, and modelled test-period-average snow cover extent differs by a maximum of 5%, or 0·8 km2, less than the observed. Furthermore, comparison with a satellite image indicated a 7% discrepancy between observed and modelled snow cover extent for the entire drainage basin. About 18% (31 mm w.eq.) of the solid precipitation was returned to the atmosphere by sublimation. Modelled mean annual snow melt and glacier ice melt for the glaciers in the Zackenberg river drainage basin from 1997 through 2005 (September–August) averaged 207 mm w.eq. year−1 and 1198 mm w.eq. year−1, respectively, yielding a total averaging 1405 mm w.eq. year−1. Total modelled mean annual surface melt varied from 960 mm w.eq. year−1 to 1989 mm w.eq. year−1. The surface-melt period started between mid-May and the beginning of June and lasted until mid-September. Annual calculated runoff averaged 1487 mm w.eq. year−1 (∼150 × 106 m3) (1997–2005) with variations from 1031 mm w.eq. year−1 to 2051 mm w.eq. year−1. The model simulated a total glacier recession averaging − 1347 mm w.eq. year−1 (∼136 × 106 m3) (1997–2005), which was almost equal to previous basin average hydrological water balance storage studies − 244 mm w.eq. year−1 (∼125 × 106 m3) (1997–2003). Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

19.
A rapid reduction in run-off has been observed in the middle reaches of the Yellow River basin in recent decades. Understanding the contributions of climate change and human activities, such as vegetation restoration and water consumption, to surface water resource reduction has become urgent and very important for future regional planning. Here, we use attribution approaches to explore the effects of climate change and human activities on run-off over the past six decades. The results showed that the observed annual run-off at Tongguan station, which is located within the mainstream of the Yellow River, exhibited a significant decreasing trend of −0.69 mm year−1 (p < .01) and varied from −0.28 to −1.46 mm year−1 (p < .01) in the eight selected tributaries from 1960 to 2015. Two relatively abrupt changes in the double mass curves occurred around 1979 and 1999; compared with Period 1 (P1; 1960–1979), the average catchment run-off decreased 32% during Period 2 (P2; 1980–1999) and up to 49% during Period 3 (P3; 2000–2015). We calculated that approximately 29% of the reduction in the run-off during P2 and 18% during P3 were attributed to climate change. Increased surface water consumption resulted in effective run-off reduction, with relative contributions of approximately 27% and 28% during P2 and P3, respectively. With the implementation of the “Grain-for-Green” project, the vegetation coverage rapidly increased from 36% in P1 to 52% in P3 and reduced run-off by 35% during P3. These findings explain the run-off reduction and benefit water resource management in the middle reaches of the Yellow River basin.  相似文献   

20.
Abstract

Water quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month-1), discharge (7000–28 000 m3 s-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m-2 d-1; total solid load: <1000 to 100 000 t d-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus.  相似文献   

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