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1.
Wen‐Cheng Liu 《水文研究》2005,19(20):4039-4054
A vertical (laterally integrated) two‐dimensional numerical model was applied to study the hydrodynamic characteristics, salt‐water intrusion and residual circulation in the Danshuei River estuarine system. The cross‐sectional profiles measured in 2001 and 1990 respectively represent the conditions after and before channel regulation in the Keelung River. The model was re‐verified with the available hydrological data measured in 2001. Detailed model re‐verification has been conducted with water surface elevations, tidal current, and salinity distributions measured. The overall performance of the model is in qualitative agreement with the available field data. The model was then used to investigate the change in tidal ranges, salt‐water intrusion, and residual circulation as a result of channel regulation in the Keelung River. The model simulations indicate that more tidal energy propagates into the estuarine system before channel regulation because of the substantial increase in river cross‐sections. The residual circulations before channel regulation are greater than those after channel regulation and result in the limits of the salt intrusion before channel regulation being extended farther inland than those after channel regulation. This may show that channel regulation for flood control in the Keelung River did not contribute to the expansion of the mangrove areas and the disappearance of freshwater marshes at the Kuan‐Du wetlands. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

2.
Groundwater recharge and discharge in the Akesu alluvial plain were estimated using a water balance method. The Akesu alluvial plain (4842 km2) is an oasis located in the hyperarid Tarim River basin of central Asia. The land along the Akesu River has a long history of agricultural development and the irrigation area is highly dependent on water withdrawals from the river. We present a water balance methodology to describe (a) surface water and groundwater interaction and (b) groundwater interaction between irrigated and non‐irrigated areas. Groundwater is recharged from the irrigation system and discharged in the non‐irrigated area. Uncultivated vegetation and wetlands are supplied from groundwater in the hyperarid environment. Results show that about 90% of groundwater recharge came from canal loss and field infiltration. The groundwater flow from irrigated to non‐irrigated areas was about 70% of non‐irrigated area recharge and acted as subsurface drainage for the irrigation area. This desalinated the irrigation area and supplied water to the non‐irrigated area. Salt moved to the non‐irrigation area following subsurface drainage. We conclude that the flooding of the Akesu River is a supplemental groundwater replenishment mechanism: the river desalinates the alluvial plain by recharging fresh water in summer and draining saline regeneration water in winter. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
Nonpoint source pollution and hydromodification are the leading causes of impairment to our nation's rivers and streams. Roadside ditch networks, ubiquitous in both rural and urban landscapes, intercept and shunt substantial quantities of overland runoff and shallow groundwater to stream systems. By altering natural flowpaths, road ditches contribute not only to hydromodification but also potentially to nonpoint‐source (NPS) pollution by acting as hydrological links between agricultural fields and natural streams. Unfortunately, the impacts of these alterations on watershed hydrology and water quality are not well understood. Through a series of field measurements, including field surveys and discharge monitoring, this study examined the effect of road ditch networks on basin morphometry, field‐ and watershed‐scale hydrology, and pollutant transport in a 38 km2 agricultural watershed in south‐central NY. Salient findings include the following: (i) 94% of road ditches discharged to natural streams, effectively doubling the drainage density; (ii) on average, road ditches increased peak and total event flows in their receiving streams by 78% and 57%, respectively, but displayed significant variation across ditches; and (iii) ditches intercepted large quantities of surface and subsurface runoff from agricultural fields and therefore represent efficient conduits for the transport of agricultural NPS pollutants to sensitive receiving waterbodies. Our results provide useful information for hydrologists who wish to further understand how artificial drainage may be affecting watershed hydrology and for managers and engineers tasked with designing appropriate flood and NPS pollution control measures. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Abiotic variability is known to structure lotic invertebrate communities, yet its influence on lentic invertebrates is not clear. This study tests the hypothesis that variability of nutrients and macro-ions are structuring invertebrate communities in agricultural drainage ditches. This was determined by investigating invertebrate adaptations to disturbance using insect life-history strategies. Many low-lying agricultural areas contain drainage ditches which potentially provide suitable habitat for aquatic invertebrates. In the province of North Holland (The Netherlands) the extensive network of eutrophic ditches are hydrologically managed, creating seasonal variability of water quality arising from agricultural run-off and the inlet of mineral rich, river derived water. This temporal variability was analysed from monitoring data, collected over a 7 month period (February till August) and covering 84 ditches in three soil regions; sand, clay and peat. Invertebrate diversity was determined as local (α diversity), regional (γ diversity) and species-turnover (β diversity). We ran canonical correspondence analysis and linear mixed models to determine correlations between invertebrate diversity, functional community composition and specific abiotic parameters, including variability (expressed as the Median Absolute Deviation). Invertebrate α diversity was positively correlated to variability in water transparency and negatively correlated to average pH, with the two parameters reflecting a water quality gradient in the environment. Insect life-history strategies expressed adaptations to abiotic variability and harsh (eutrophic) conditions. These adaptations were mainly achieved through good dispersal abilities and developmental trade-offs. The results support measures to reduce influxes of excess nutrients to this network of ditches.  相似文献   

5.
N. Alam  Theo N. Olsthoorn 《水文研究》2014,28(20):5288-5296
The key to ‘sustainable conjunctive use of groundwater for additional irrigation’ is the salt balance of groundwater below an irrigated field. This paper aims to develop a mathematical tool to study the accumulation of salt in the groundwater below an irrigated field as caused by irrigation recirculation. This study derives a salt balance of groundwater to ensure that the additional irrigation from groundwater remains possible in the future. The water and salt budgets by themselves do neither provide information concerning farmers' options nor on the limits of the individual terms in the budget equations. It is presumed that farmers will intuitively aim for (1) an optimal value of the actual evapotranspiration, and (2) a return flow as a feasible low fraction of the available water. We, therefore, derive the irrigation from groundwater Q as a consequence of the predefined farmers' aims to achieve a high actual evapotranspiration in combination with a given optimally used irrigation system. Our model concludes that the required amount of drainage is only dependent on the ratio of the salinity in the surface irrigation water and the acceptable salinity of the groundwater. The final salinity in the saturated zone only depends on salt‐carrying inflows and outflows. From the aforesaid model, it is further concluded that sustainable conjunctive use of groundwater for additional irrigation requires long‐term salt management, which should be founded on the essential controlling factors as derived in this paper. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
ABSTRACT

A Mixed-Integer Nonlinear Programming (MINLP) model is formulated and solved in this study to optimize environmental sustainability of flood control, drainage, and irrigation (FCDI) projects in the deltaic regions of Bangladesh. The model optimizes the value of integrated resource benefit, a dimensionless variable defined to measure the environmental sustainability based on the water, agricultural and ecological resources, with a set of project interventions being the major drivers. The resource benefits were evaluated with the help of several indicators, such as flood, navigability, salinity, waterlogging, cropping intensity, land loss and vegetation. The solution of MINLP model provided optimal values of the decision variables, which are the quantities of project interventions (e.g. length and height of dike, number of sluices and drainage inlets, lengths of drainage canals, erosion protection and afforestation works). The approach and the MINLP formulation presented in this study can be used for any real-life FCDI project improvements.  相似文献   

7.
Seawater intrusion into fresh groundwater formations generally results inadvertently from human activities, such as over‐abstraction from coastal aquifers. This article describes the data analysis to quantify drain–aquifer interactions in a low‐lying pump‐drained coastal aquifer, which is subject to saline intrusion due to widespread land drainage, and the resulting development and application of a numerical groundwater model to understand the spatial groundwater system behaviour (including groundwater salinity fluxes). Without measured flow data in this pump‐drained catchment, a novel groundwater head‐dependent approach to hydrograph separation is described. Time‐variant and time‐invariant MODFLOW analyses are utilised to examine the flow processes. A new approach to calculate drain coefficients, which represent the extensive network of drainage ditches in the regional model, using field information, is described; the sum of the drainage coefficients are close to the values independently estimated from the head‐dependent hydrograph separation. Results show that (1) the groundwater flows into the drainage systems are well reproduced using the new drain coefficients, (2) particle tracking of fresh and saline water can explain observed spatial salinity distribution within drainage networks and (3) the modelled flow of seawater across the coast is approximately 25% greater than that discharged by the pumps, demonstrating the need for drainage management to be aware of the slow response of groundwater systems to past drainage system changes. The article demonstrates that numerical groundwater modelling can produce the improved understanding needed to inform management decisions in such complex environments. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
This paper addresses the effect of accurately mapping spatially heterogeneous drainage densities in high‐altitude alpine basins on Rescaled Width Functions (RWFs), used in some applications as a minimalist model of the hydrologic response. The channel network and 373 of its channel heads were mapped in the field in a high mountain catchment in the Swiss Alps. The mapped channel network is characterized by highly uneven drainage density, here described by the distribution of the length to the first channelized site computed along steepest descent from any unchannelled site. Various channel networks were extracted from a 1 m lidar‐derived digital terrain model and compared with the field‐mapped channel network using geomorphologic parameters, hillslope‐to‐channel distance and RWFs. Our results show that the channel network derived by statistical analysis of surface morphology is consistent with the field‐mapped network. Larger discrepancies were observed when the channel network was obtained with classical threshold‐based approaches relying on cumulative drainage area and local slope. The actual arrangement of the drainage densities has a significant impact on the RWFs. The discrepancy was largest between RWFs derived from classical extraction methods and RWFs derived with the field‐mapped network, indicating an inappropriate extraction of the channelled portion of the high‐altitude catchment that is a reflection of the variety of channel initiation processes. Our results suggest that spatial heterogeneity of the drainage density might play an important role in modelling streamflow generation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

9.
The complete natural drainage in 2008, 2011, and 2012 of Mountain Lake in Giles County, Virginia, allowed detailed observations of the only natural lake basin in the southern Appalachian Mountains. Here we use these observations to support geomorphic analysis and develop a model of basin evolution, which may advance the understanding of rare flow‐through lakes with subsurface drainage elsewhere. Key features included (a) an angle‐of‐repose slope with a smoothly concave planform across the entire 260 m width of the north end of the basin, (b) an arc of steep‐sided depressions along the deep northern margin of the basin floor, and (c) an abrupt transition between colluvial and finer‐grained sedimentary deposits on the floor. Our geomorphic analysis suggests that subsurface erosion has enabled long‐term northward scarp retreat in the basin by removing water and sediment. Mountain Lake formed on the northern limb of a breached anticline along the Eastern Continental Divide, where strong‐over‐weak stratigraphy and a small watershed have enabled the basin to evolve generally as follows. (1) Pond Drain, a first‐order tributary of the New River, incised north‐dipping sandstones and underlying shales on the northern limb of the anticline. The valley floor subsequently accumulated meters to tens of meters of mostly late Pleistocene colluvial fill. (2) Subsurface drainage developed likely along the contact between the sandstones and shales, facilitated by pre‐existing fractures. (3) Ongoing subsurface erosion has progressively undermined the sandstone, causing scarp retreat along the northern margin of the basin while a surface stream intermittently incised the shallow southern end. Sedimentary deposits indicate that only the deeper northern portion of the basin is usually flooded under Holocene conditions. Our basin evolution model suggests slow development of the basin over hundreds of thousands of years rather than sudden damming by a catastrophic landslide. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

10.
Over the past centuries, the agricultural use of wetlands in Central Europe has required interference with the natural wetland water balance. Often this has consisted of drainage measures alone. In low‐precipitation areas, it has also involved the operation of combined drainage and sub‐irrigation systems. Model studies conducted as part of planning processes, or with a view to finding out the impact of changing climate conditions on the water balance of wetlands, must take these facts into account. For this reason, a water balance model has been devised for wetlands whose water balance is governed by water resources management systems. It is based on the WBalMo model system. Special modules were integrated into WBalMo to calculate the water balance of wetland areas (WABI module) and to regulate inflow partitioning within the wetland (REGINF module). When calculating the water balance, the WABI module takes into account precipitation and potential evapotranspiration, groundwater levels below surface, soil types, land‐use classes, inflows via the running water system, and data for target water levels. It provides actual evapotranspiration, discharge into the running water system, and groundwater levels in the area. The example of the Spreewald, a major wetland area in north‐eastern Germany, was used to design and test the WBalMo Spreewald model. The comparison of measured and calculated water balance parameters of the wetland area confirms the suitability of the model for water balance studies in wetlands with complex water resources management systems. The results reveal the strong influence of water management on the water balance of such areas. The model system has proved to be excellently suited for planning and carrying out water management measures aimed at the sustainable development of wetlands. Furthermore, scenario analyses can be used to assess the impact of global change on the water balance of wetlands. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

11.
Residential areas in Kuwait City have witnessed a dramatic rise in subsurface water tables over the last three decades. This water rise phenomenon is attributed mainly to over irrigation practices of private gardens along with leakage from domestic and sewage networks. This paper presents a comprehensive study for urban drainage in two selected areas representing the two hydrogeological settings encountered in Kuwait City. In the first area, a vertical drainage scheme was applied successfully over an area of 1 km2. The system has been under continuous operation and monitoring for more than 4 years without problems, providing a permanent solution for the water rise problem in this area. The hydrogeological system has approached steady state conditions and the water levels have dropped to about 3·5 m below the ground surface. In the second area a dual drainage scheme, composing of horizontal and vertical elements, is proposed. Horizontal elements are suggested in the areas where the deep groundwater contains hazardous gases that may pose environmental problems. The proposed drainage scheme in the second area has not yet been implemented. Field tests were conducted to assess the aquifer parameters in both areas and a numerical model has been developed to predict the long‐term response of the hydrogeological system in the two areas under consideration. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

12.
The semiarid Chaco plains present one of the highest rates of forest clearing and agricultural expansion of the world. In other semiarid plains, such massive vegetation replacements initiated a groundwater recharge and salt mobilization process that, after decades, raised regional water tables and salts to the surface, degrading agricultural and natural ecosystems. Indirect evidence suggests that this process (known as dryland salinity) began in the Chaco plains. Multiple approaches (deep soil profiles, geoelectric surveys and monitoring of groundwater salinity, level and isotopic composition) were combined to assess the dryland salinity status in one of the oldest and most active agricultural hotspots of the region, where isolated forest remnants occupy an extremely flat cultivated matrix. Full vadose moisture and chloride profiles from paired agriculture‐forest stands (17 profiles, six sites) revealed the following: a generalized onset of deep drainage with cultivation (32 to >87 mm year?1), full leaching of native chloride pools (13.7 ± 2.5 kg m?2) down to the water table after >40 years following clearing and differential groundwater table rises (0.7 to 2 m shallower water tables under agriculture than under neighbouring forests). Continuous level monitoring showed abrupt water table rises under annual crops (up to 2.6 m in 15 days) not seen under forests or pastures. Varying deep drainage rates and groundwater isotopic composition under agricultural plots suggest that these pulses are strongly modulated by crop choices and sequences. In contrast to other dryland salinity‐affected areas of the world, forest remnants in the study area (10–20% of the area) are not only surviving the observed hydrological shifts but also sustaining active salty groundwater transpirative discharge, as evidenced by continuous water table records. The overall impact of these forest remnants on lowering neighbouring water tables would be limited by the low hydraulic conductivity of the sediments. As highly cultivated areas of the Chaco evolve to new hydrological conditions of shallower saline water tables, innovative crop rotations that minimize recharge, enhance transpirative discharge and tolerate salinity will be needed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

13.
The dry wadis ‘ephemeral channel’ constituting the main tributaries to the Nile River in Kom Ombo are structurally and tectonically controlled and exhibit complex drainage pattern. This complicated drainage pattern is inherited from the morpho‐tectonic evolution of the ancestral Nile River (‘Protonile’), which drained the Eastern Desert during the Middle Pleistocene. A digital elevation model derived from Shuttle Radar Topography Mission data is used to delineate the contemporary drainage networks and their catchments. Satellite images acquired during a flash flood event were used to validate the delineated watershed divides and flow pathways, particularly where the courses of dry wadis are interlocked. Currently, the westward flow of Wadi Abu‐Suberah is derived from a small area in the Eastern Desert, as the palaeo‐upper reaches of this wadi were captured due to tectonic movements along NW/SE and N/S faults by wadis in the Kharit and Elewa areas. The influence of these tectonic movements on groundwater distribution is also shown where the deep Nubian aquifer discharges its water into the Quaternary aquifer through fault planes. The northward flowing ‘Protonile’ main course has tectonically shifted from the Gallaba plain in the Western Desert, eastward to the current Nile River course. This shift has produced several cut‐off segments of the palaeo‐tributary drainage that was originally flowing westward towards the old ‘Protonile’ main course in the Gallaba plain. However, these segments have reversed their surface run‐off flow directions eastward towards the current Nile course; they could include potential groundwater resources, as their alluvium may be still recharged by the Nile River. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
In the Aral Sea Basin, where the Central Asian countries compete for limited water resources, reliable information on the actual water use for eight million ha of irrigated land are rare. In this study, spatially distributed land use data, seasonal actual evapotranspiration, and reference evapotranspiration derived from multitemporal MODIS data were combined with in situ water flow measurements for irrigation performance assessments in the upper Amu Darya Delta. The functioning of the major irrigation and drainage which supplies an agricultural area of 270,000 ha in the Uzbek province Khorezm was analysed using water balancing and adequacy indicators of irrigation water use.An average relative evapotranspiration of 95% indicated fulfilled water demands and partly over-irrigation, whereas values below 75% disclosed inadequate water supply in distant parts of the irrigation system. On the other hand, immense water withdrawals of approximately 24,000 m3 ha−1 recorded at the system boundaries between April and September 2005 clearly exceeded the field water demands for cotton cultivation. Only 46% of the total irrigation amounts were consumed for crop production at field level. Throughout the vegetation period, approximately 58% of the total available water left the region as drainage water. Monthly observations of the depleted fraction and the drainage ratio highlighted drainage problems and rising groundwater levels at regional scale. In the most distant downstream subsystem, a high risk of groundwater and soil salinity during the main irrigation phase was found.A combination of high conveyance losses, hydraulic problems, direct linkages between irrigation and drainage, and low field application efficiencies were identified as major reasons for underperforming irrigation. The findings underlined the necessity of water saving and of reconsidering water distribution in Khorezm. The remote sensing approach was concluded as a reliable data basis for regular performance assessments for all irrigation systems in Central Asia.  相似文献   

15.
Pollutant delivery through artificial subsurface drainage networks to streams is an important transport mechanism, yet the impact of drainage tiles on groundwater hydrology at the watershed scale has not been well documented. In this study, we developed a two‐dimensional, steady‐state groundwater flow model for a representative Iowa agricultural watershed to simulate the impact of tile drainage density and incision depth on groundwater travel times and proportion of baseflow contributed by tile drains. Varying tile drainage density from 0 to 0.0038 m?1, while maintaining a constant tile incision depth at 1.2 m, resulted in the mean groundwater travel time to decrease exponentially from 40 years to 19 years and increased the tile contribution to baseflow from 0% to an upper bound of 37%. In contrast, varying tile depths from 0.3 to 2.7 m, while maintaining a constant tile drainage density of 0.0038 m?1, caused mean travel times to decrease linearly from 22 to 18 years and increased the tile contribution to baseflow from 30% to 54% in a near‐linear manner. The decrease in the mean travel time was attributed to decrease in the saturated thickness of the aquifer with increasing drainage density and incision depth. Study results indicate that tile drainage affects fundamental watershed characteristics and should be taken into consideration when evaluating water and nitrate export from agricultural regions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
Since 1986, with a sharp decrease in water dis-charges, the Yellow River has entered a period charac-terized by low discharges and seasonally occurring dry-ups[1,2]. Since 1999, more strict management of water diversion has been imposed, and therefore the dry-ups have been well under control. However, the lower reaches of the Yellow River is still predominated by low-discharges, and has become a man-induced shrinking river. In the past 40 years, significant effect of soil and water conservat…  相似文献   

17.
Water and land are the two natural resources restraining crop production in South Africa. With the increasing demand for food, emphasis has shifted from the sole reliance on rain fed crop production, to irrigation. The deterioration in irrigation water quality from surface water sources is, however, posing a big challenge to the sustainability of irrigated crop production. This is because more water is required for leaching, resulting in shallow water tables in agricultural lands. The installation of well designed subsurface drainage systems alone is not enough; the provision of timely maintenance is also necessary. In this study, the extent and severity of problems as a consequence of shallow water tables and their possible causes were investigated at three sugarcane fields in Pongola, South Africa, having low hydraulic conductivity soils. Also investigated were soil salinity levels and the temporal variation in the salinity of the irrigation water. A water table map of a 32 ha sugarcane field was generated, using observed water table depth (WTD) data from 36 piezometers monitored from September 2011 to February 2012. Out of the total 32 ha under cultivation, 12% was found to be affected by shallow WTDs of less than the 1.0 m design WTD. The inability of natural drainage to cope with subsurface drainage needs and the poor maintenance of subsurface drainage systems contributed to the shallow water tables in the area. Furthermore, the currently adopted drainage design criteria also proved unsatisfactory with mean observed water table depth and drainage discharge (DD) of 20% and 50%, respectively, less than their respective design levels. The salinity of the irrigation water was, on average, 32% higher than threshold tolerance level of sugarcane. The root zone soil salinity levels at the three study sites were greater than the 1.7 dS m−1 threshold for sugar cane. The subsurface drainage design criteria adopted at the site needs to be revisited by ensuring that the slope of the land is taken into consideration in the drainage design in addition to adhering to a recommended maintenance schedule.  相似文献   

18.
Hydrological threshold behaviour has been observed across hillslopes and catchments with varying characteristics. Few studies, however, have evaluated rainfall–run‐off response in areas dominated by agricultural land use and artificial subsurface drainage. Hydrograph analysis was used to identify distinct hydrological events over a 9‐year period and examine rainfall characteristics, dynamic water storage, and surface and subsurface run‐off generation in a drained and farmed closed depression in north‐eastern Indiana, USA. Results showed that both surface flow and subsurface tile flow displayed a threshold relationship with the sum of rainfall amount and soil moisture deficit (SMD). Neither surface flow nor subsurface tile flow was observed unless rainfall amount exceeded the SMD. Timing of subsurface tile flow relative to soil moisture response on the shoulder slope of the depression indicated that the formation and drainage of perched water tables on depression hillslopes were likely the main mechanism that produced subsurface connectivity. Surface flow generation was delayed compared with subsurface tile flow during rainfall events due to differences in soil water storage along depression hillslopes and run‐off generation mechanisms. These findings highlight the substantial impact of subsurface tile drainage on the hydrology of closed depressions; the bottom of the depression, the wettest area prior to drainage installation, becomes the driest part of the depression after installation of subsurface drainage. Rapid connectivity of localized subsurface saturation zones during rainfall events is also greatly enhanced because of subsurface drainage. Thus, less fill is required to generate substantial spill. Understanding hydrologic processes in drained and farmed closed depressions is a critical first step in developing improved water and nutrient management strategies in this landscape.  相似文献   

19.
Wastewater effluents from irrigation and the domestic and industrial sectors have serious impacts in deteriorating water quality in many rivers, particularly in areas under tidal influence. There is a need to develop an approach that considers the impact of human and natural causes of salinization. This study uses a multi-objective optimization–simulation model to investigate and describe the interactions of such impacts in the Shatt al-Arab River, Iraq. The developed model is able to reproduce the salinity distribution in the river given varying conditions. The salinity regime in the river varies according to different hydrological conditions and anthropogenic activities. Due to tidal effects, salinity caused by drainage water is seen to intrude further upstream into the river. The applied approach provides a way to obtain optimal solutions where both river salinity and deficit in water supply can be minimized. The approach is used for exploring the trade-off between these two objectives.  相似文献   

20.
The purpose of this study was to examine the historical change in sedimentation rates in lakes that have been impacted by river regulation and agricultural activities in the Ishikari River floodplain. We dated sediment cores using caesium‐137 (137Cs) dating and tephrochronology, and we estimated sediment sources from 137Cs concentrations in the topsoil of representative land covers. We found that, between 1739 and 1963, the distance between the lake and the main river channel and whether or not the lake was connected to the river affected the sedimentation rates. After 1963, agricultural drainage systems were established in the Ishikari River floodplain. The average sedimentation rate before and after the construction of drainage ditches varied between 1–66 and 87–301 mg cm–2 a–1, respectively. The increase in the sedimentation rate after 1963 was caused by the construction of a number of drainage networks, as well as extensive cultivation activity and/or fragmentation of the swamp buffers surrounding the lakes. The 137Cs activities at the surfaces of the lake as well as the catchment‐derived 137Cs contributions and 137Cs inventory in the lake profiles were used to examine the sediment influx from the various drainage areas after the establishment of the drainage system. Our results indicate that the majority of the lake sediments were derived from cultivated areas, and therefore the catchment‐derived 137Cs contribution in the lakes was strongly correlated with the sedimentation rate. The 137Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the 137Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low 137Cs concentrations, which diluted the overall concentration of 137Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

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