Contemporary changes in sediment yield in an alpine mountain basin due to afforestation (the upper Drôme in France)

The Baurières plain within the upper Drôme River basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment. A considerable body of archival information is available. Furthermore, the plain acts as a natural sediment trap and the reach–basin interaction has not been disrupted by human activity. Based on archival data, channel geometry measurements, dendrogeomorphological and radionuclide analysis (Cs¹³⁷ and unsupported Pb²¹⁰), the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted.Dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s. The ex-Pb²¹⁰ profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment. Bedload yields are estimated to be at least 26 m³ km⁻² year⁻¹ between 1928 and 1996 based on an estimate of storage over a channel length of 11.5 km. Archival data concerning bedload removal from traps yields an estimate of 25.6 m³ km⁻² year⁻¹ between 1993 and 2001. These two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century. If the bedload supply has not strongly decreased in the studied reach during this period, the bedload sources have changed. The volume of sediment stored in the Beaurières area between 1928 and 1996 corresponds to at least 40% of the sediment delivered by channel degradation from an upstream alluvial reach.Both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime. Hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century, and spontaneous hillslope afforestation resulting from grazing decline, mainly in the two decades following World War II. The observed change in suspended sediment supply which occurred around 1960–1965 has a clear synchronicity with spontaneous catchment afforestation following World War II. After this period, a decrease in sediment supply, a change in source, but also a decrease in peak flow, were observed.Changes in run-off are complex and cannot be caused with only land use change. Flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment. In addition flood seasonality has changed, with September and October flood events being much less frequent in the last part of the 20th century.     

三门峡水库对黄河河流地貌的影响

三门峡水库建成后,先后采用了蓄水拦沙、滞洪排沙和蓄清排浑调水调沙三种运用方式,水库在运用过程中也相应的分为三个阶段.第一阶段水库淤积严重,主要在潼关到上游大坝;第二阶段为滞洪排沙,排沙量增加幅度较大,淤积主要在潼关以下;第三阶段为蓄清排浑,使潼关以下淤积得以改善.在分析了三门峡水库运用后库区的冲淤、潼关高程的变化及库区下游河流地貌的变化情况,总结了不同运用方式下下游黄河河流地貌的变化规律.     

Excess River Sedimentation at Bridges in the Raya Graben (Northern Ethiopia)

This study investigates the temporal variability and effects of bio‐climatic factors and bridges on local hydro‐geomorphic conditions that cause excess sedimentation and flood hazard in ephemeral rivers of the Raya graben (northern Ethiopia). Normalized difference vegetation index (NDVI) was analyzed using Landsat imageries of 1972, 1986, 2000, 2005, 2010, and 2014. Daily rainfall data of three meteorological stations were considered to analyze the temporal trends and return time intervals of rainfall intensity in 24 h. Stream‐bed gradient and bed material grain size were measured in 20 river reaches. Results show that the maximum NDVI values were recorded in the time interval from 2000 to 2014. Nevertheless, during this decade, the study bridges experienced the largest excess sedimentation, in some bridges up to 1·6 m. Different factors to account for it are discussed as no evidence of rainfall pattern, accountable for an increase in sediment delivery from the headwaters, is found. The field data show that channel narrowing at bridges is the main cause of thick upstream sedimentation and of increasing frequency of overbank flows during the last 15 years. A simple hydraulic approach is presented to explain the variability of sediment deposition at bridges and change in bed material grain size between the main stem and the reach right upstream of the bridge. Copyright © 2016 John Wiley & Sons, Ltd.     

Use of fallout Cs in investigations of overbank sediment deposition on river floodplains

River floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment. However, information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods. Measurements of the ¹³⁷Cs content of floodplain sediments provide an alternative approach to obtaining; estimates of medium-term rates (ca. 40 years) of overbank sediment deposition. The ¹³⁷Cs approach requires only a single site visit and minimum sample preparation. Furthermore, it is capable of providing information on spatial patterns of sediment deposition on floodplains, which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition. This paper reviews the basis for using ¹³⁷Cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting ¹³⁷Cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total. ¹³⁷Cs inventories of bulk sediment cores. The results obtained from a case study undertaken on the floodplain of the River Stour, Dorset, UK, are presented.     

黄河临河辫状河段心滩变化及其影响因素分析

心滩作为辫状河道最主要的微地貌特征,其变化特征的研究对于理解辫状河道的演变具有重要意义。以黄河临河段213km长的辫状河道为研究对象,基于1988—2013年的遥感图像绘制了相应日期的河道平面形态图,分析了该河段心滩数量和心滩面积变化;利用2013年内6幅河道平面图建立了心滩面积与巴彦高勒站水位之间的线性关系式,利用该关系式求取了其他年份1 050m参考水位下的心滩面积并进行心滩冲淤变化对比。结果表明:黄河临河段心滩总个数、心滩总面积、心滩平均面积、中位数心滩面积和最大心滩面积总体上都具有减小的趋势。在1 050m参考水位下,黄河临河段心滩面积在1988—2013年具有不同的冲淤变化特征,其中在2000年以前的变化幅度大,趋势不明显,2000年以后则分布较为集中,且有减小的趋势,并在1990—2000年大幅减小。在龙羊峡、刘家峡等水库运行影响下汛期黄河临河段水量和输沙量占全年的比例在减小,年内分配趋于均衡化,并且输沙量的减幅要大于水量的减幅,这对于研究区心滩的冲淤有重要影响。同时,上游流域来沙系数的变化也在一定程度上影响着该河段心滩的冲淤变化。     

Relationship between suspended sediment load, channel geometry and land area increment in the Yellow River Delta

The annual river discharges and suspended sediment loads into the Yellow River Delta show a declining tendency with some distinct fluctuations over the last 50 years. The decrease of river discharge and suspended sediment load and the change in the river channel must influence the evolution of the Yellow River Delta. During this period several new river mouths formed via channel switch at the river delta, and the old watercourse was gradually abandoned. Recently, in years with very low annual suspended load, erosion of land area has been recorded for the delta. The aims of this work are (1) to determine what is the critical suspended sediment load needed in order to maintain the land balance of the Yellow River Delta for two periods before and after 1976 (the last time the channel shifted), and (2) to examine the variation in the channel geometry and gradient in response to changes in suspended sediment load and delta area at the river mouth. In order to estimate these critical values, we used statistical method to analyze the relationships between land area increment, and suspended sediment load and channel geometry. In order to examine the variation in the channel geometry, the channel cross-sections of the Q1 and Q6 were compared. The results show that to maintain the land area balance between 1953 and 1973, when the river mouth was the Diaokouhe, the critical annual suspended sediment load entering the delta was 4.21  10⁸ tonnes/a. After the main channel switched to Qingshuigou in 1976, the critical value to maintain the Qingshuigou mouth between 1976 and 1997 was 1.51  10⁸ tonnes/a. To maintain the land area balance for the entire Yellow River Delta between 1976 and 1997 the critical suspended sediment load was 3.18  10⁸ tonnes/a. The annual mean channel thalweg elevation and channel gradient at the river delta increase with increasing land area increment at the Qingshuigou mouth. The critical channel gradient at the channel reach between cross sections Q1 and Q6 is 0.000095. The channel has narrowed during the time period from 1976 to 1997. Also, lateral channel migration has decreased remarkably, resulting in enhanced hydraulic efficiency of the deltaic channel and artificial levees. This channel geometry evolution was influenced by river adjustment and human activities. These results are of importance for the management of the lower Yellow River channel and the delta. Future water diversion or river damming should consider the balance between suspended sediment delivery and delta growth.     

Fluvial development and the sediment regime of the lower Calder,Ribble catchment,northwest England

In the lower reaches of the Calder (Lancashire) tributary of the Ribble catchment (northwest England), five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated. The earliest terrace (T1) reflects sandur-style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds. Incision below T1 spanned the start of the Holocene, driven by a combination of reduced sediment supply under a stabilising landscape and lower base-levels. T2 had aggraded and was being abandoned by 4000 BC; its formation latterly involving a period of comparative stability in terms of channel migration, perhaps a function of extensive forest cover and sea levels reaching above present day levels. The last 3000 years were marked by substantial changes in the sedimentary regime, with increased and varying sediment supply driving cycles of cut-and-fill and greater lateral channel migration. These changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape. Between the aggradation of terraces T3 and T4 there was a substantial increase in sediment supply, which is broadly in keeping with the erosion history in the surrounding uplands. This sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll-style migration. Late Holocene vegetation changes, particularly woodland removal, driven by anthropogenic land-pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion.     

Depositional environment and luminescence chronology of the Hoarusib River Clay Castles sediments,northern Namib Desert,Namibia

The Clay Castles in the Hoarusib River valley are fine-grained deposits in a tributary immediately upstream of a narrow gorge. Sedimentological analysis reveals three lithofacies associations: (1) Channel Facies Association near the mouth of the tributary, (2) Back-Flow Facies Association in the middle section, and (3) Silt and Massive Sand Facies Association in the head of the tributary. Overall sedimentary architecture shows that aggradation of the main Hoarusib channel led to back flooding into the tributary and the deposition of massive fine-grained deposits. Decreased discharge competency, increased sediment load and the presence of narrow gorges within the main valley are suggested as reasons for the aggradation. Inter-fingering of desert-derived sediments channeled down the tributary and backflow sediments from the main river indicate an increase in both upland and desert rainfall during the course of sedimentation. Optically Stimulated Luminescence (OSL) dating of these deposits indicates formation between 44 and 20 ka, with the possibility that deposition occurred during two phases of rapid sedimentation at ca. 42 and 25 ka.     

Sedimentation-induced eutrophication in large river floodplains – An obstacle to restoration?

Conservation and restoration of floodplain ecosystems and their specific functions often suffer from a deficient knowledge on basic processes and dynamics such as sedimentation and related nutrient inputs. In this study, we present the results of a joint analysis of site conditions and vegetation of alluvial meadows along a gradient of increasing distance to the main channel of the river Rhine. In particular we scrutinized whether the flooding frequency mediated by the ground elevation or the distance to the river channel determines the degree of eutrophication by river water and sediments.We found a remarkably strong transversal gradient in the functional floodplain. Extremely high concentrations of CAL-soluble phosphorous (more than 150 mg kg⁻¹) were measured in close proximity to the main channel. These sites were characterized by low vascular plant species richness and a significantly higher proportion of species with high nutrient demands. At a distance of 300 m from the main channel P concentrations in the soil dropped to a quarter of this figure, whereas the average species richness per plot strongly increased. Contrary to our expectations, the influence of the flooding duration was of minor importance for the nutrient status. We can specify that strong eutrophication effects induced by sediment deposits are confined to the close proximity to the main channel within a distance of 200–300 m. At more distant sites, target vegetation of flood meadows was obviously not affected by recent nutrient input in the course of flooding. Concerns by conservationists that the restoration of active floodplains by the removal of dykes will generally lead to unwanted eutrophication by river water and sediments require revision and thorough specification.     

The Impact of Bioturbation by Small Mammals on Heavy Metal Redistribution in an Embanked Floodplain of the River Rhine

Floodplains along large European rivers are diffusely polluted with heavy metals due to emissions in the past. Because of low mobility of heavy metals in floodplain soils and improvements of water quality, these pollutants will remain in place, and can gradually become covered with less contaminated sediments. Bioturbators, especially earthworms, can play an important role in the mixing and surfacing of contaminated substrate. Surfaced substrate can be redistributed by recurrent flooding events, even to areas outside the floodplain. The question remained to what extent bioturbation by small mammals contributes to the redistribution of heavy metals from river sediments in floodplains. Extensive fieldwork on bioturbators such as voles, moles and earthworms and their distribution patterns, as well as on sediment deposition and bioturbation, was conducted at the ‘Afferdensche en Deestsche Waarden’ floodplain over the years 2001–2003. Field data were combined with data of experiments in field enclosures and substrate columns to calculate the amounts of sediment and heavy metals (Zn, Cu, Pb and Cd) redistributed during the floods as well as on an annual basis. Moles and voles surfaced considerable amounts of substrate and heavy metals, but not as much as earthworms which contribute a substantial proportion of the total deposition and redistribution during floods. Although the impact of moles and voles on the redistribution during floods was only locally important, on an annual basis the bioturbation activity of especially moles in floodplains cannot be neglected. The annual amounts of substrate and heavy metals surfaced by all investigated bioturbators were even larger than the total amounts of substrate and heavy metals deposited during floods.     

泾河泾阳段高河漫滩沉积元素与化合物指示的洪水事件

根据泾阳泾河高漫滩沉积剖面中128个样品的元素、化合物含量与粒度分析,研究了泾阳泾河高漫滩剖面沉积特征与洪水变化.结果表明,元素Ma,Ni,Cu,Zn,Ga,Pb,Ba,Rb,V和化合物Al2O3,Fe2O3,K2O含量在剖面各层中变化明显,分辨率高,能够清晰地指示洪水以及降水量的变化.JYa剖面分为18个沉积层,指示了18次大小不同的洪水和18个降水较多的年份.沉积物粒度细,元素Mn,Ni,Cu,Zn,Ga,Pb,Rb,V和化合物Al2O3Fe2O2,K2O含量高,元素Ba含量低,指示沉积时洪水强度小,洪水水位低,降雨量少.沉积物粒度粗,元素Mn,Ni,Cu,Zn,Ga,Pb,Rb,V和化合物Al2O3,Fe2O3,K2O含量低;元素Ba含量高,指示沉积时洪水强度大,洪水水位高,降雨量多.在这18次洪水事件中,在同一次洪水沉积层内形成了两个以上薄层的元素和化合物含量、粒度成分的微小变化,指示多数期次的洪水发生时期常有两个以上洪峰出现.泾阳泾河高漫滩第14,12,13,8,5,1层洪水沉积反映了泾河泾阳段全流域性的年降水量增加,且年降水量至少达到约800 mm.     

特大暴雨条件下小流域沟道的泥沙连通性及其影响因素——以陕西省子洲县为例

[目的]研究特大暴雨条件下小流域沟道泥沙输移路径、泥沙连通程度及其影响因素,旨在探讨水库溃坝的原因,为沟道防洪措施的布设提供依据。[方法]以陕西省子洲县"7·26"暴雨条件下小流域沟道泥沙连通情况为例,选取面积相近、形状相异的清水沟和蛇家沟小流域,对沟道泥沙淤积情况进行现场调查,同时将沟道分为坝地沟段和自然沟段,选取流域面积与形状系数、沟道比降,以及淤地坝的类型与分布进行对比分析两个小流域沟道泥沙连通性的差异。[结果]在此次特大暴雨条件下,清水沟和蛇家沟的淤地坝大都呈现打开状态,由上游到下游清水沟泥沙连通性呈现较强的增长趋势,蛇家沟泥沙连通性则呈现先增长后减弱的趋势。整体上清水沟的泥沙连通性比蛇家沟的强,且清水沟流域的土壤侵蚀也较为严重。串联和混联坝系以及修建有卧管、竖井和排水渠的淤地坝防洪能力更强。[结论]流域面积、流域形状和沟道比降均影响着沟道泥沙的连通性,而淤地坝类型及分布是影响沟道泥沙连通性的主导因子。     

Rapid shrinkage of Kushiro Mire,the largest mire in Japan,due to increased sedimentation associated with land-use development in the catchment

The suspended sediment discharge in the Kuchoro River, a tributary of the Kushiro River, showed that wash load was about 90% of the yearly total suspended load carried into the wetland from the entire watershed. Seasonal floods associated with typhoons and snowmelt carried a large volume of wash load, 44% and 37%, respectively, of the yearly total wash load. The deposition of suspended sediment in the channelized section has aggraded the riverbed by 2 m in the past two decades, which has reduced the cross-sectional area of the channel, so that turbid water spills over and carries wash load and suspended sediment deep into the wetlands. Flooding of turbid water, in association with aggradation of the riverbed, was detected by using a Water Turbidity Index. The flooding and turbidity have significantly increased between 1984 and 1994. Similarly, a Normalized Difference Vegetation Index map showed that forest establishment has continued from the wetland margins and in areas adjacent to the river channel. The suspended sediment carried and deposited by floods and sediment-associated nutrients should alter the edaphic environment from wet nutrient-poor soil to dry nutrient-rich soil providing regeneration habitats for tree species. The vegetation in turn adds resistance and friction against flows and contributes to additional sedimentation. However, flooding and the associated high water table causes stress for trees and may lead to premature decay. Environmental variables, such as water level, water content, organic content and grain size, varied significantly along cross-sectional distance, and are likely regulated by deposition of fine sediments transported by floods. Electrical conductivity and total nitrogen in groundwater varied significantly along the longitudinal distance. Basal areas of willow and alder stands correlated with variables related to spread of turbid water, which indicates that eutrophication of groundwater indirectly affects marsh forest expansion.     

柳河流域沙量平衡分析

柳河是东北地区泥沙问题最为严重的河流之一，该文分析了流域水沙运移特征，在此基础上建立起流域16年的沙量平衡关系，分析了流域产沙、沉积特征及沉积的分布格局。研究表明，53.5％的悬移质泥沙沉积在河道中，其中，87.9％沉积在闹德海至彰武之间；对流域上游产水、产沙与流域内泥沙沉积及流域产沙之间的关系进行了耦合分析，丰富了沙量平衡计算的内容，并可对深入认识流域泥沙发展趋势及泥沙治理提供参考。     

柳河流域沙量平衡分析

柳河是东北地区泥沙问题最为严重的河流之一,该文分析了流域水沙运移特征,在此基础上建立起流域16年的沙量平衡关系,分析了流域产沙、沉积特征及沉积的分布格局.研究表明,53.5%的悬移质泥沙沉积在河道中,其中,87.9%沉积在闹德海至彰武之间;对流域上游产水、产沙与流域内泥沙沉积及流域产沙之间的关系进行了耦合分析,丰富了沙量平衡计算的内容,并可对深入认识流域泥沙发展趋势及泥沙治理提供参考.     

Toward generalizable sediment fingerprinting with tracers that are conservative and nonconservative over sediment routing timescales

Purpose

The science of sediment fingerprinting has been evolving rapidly over the past decade and is well poised to improve our understanding, not only of sediment sources, but also the routing of sediment through watersheds. Here, we discuss channel–floodplain processes that may convolute or modify the sediment fingerprinting signature of alluvial bank/floodplain sources and explore the use of nonconservative tracers for differentiating sediment derived from surface soil erosion from that of near-channel fluvial erosion.

Materials and methods

We use a mathematical model to demonstrate the theoretical effects of channel–floodplain exchange on conservative and nonconservative tracers. Then, we present flow, sediment gauging data, and geochemical measurements of long- (meteoric beryllium-10, ¹⁰Be) and short-lived (excess lead-210 and cesium-137, ²¹⁰Pb_ex and ¹³⁷Cs, respectively) radionuclide tracers from two study locations: one above, and the other below, a rapidly incising knick zone within the Maple River watershed, southern Minnesota.

Results and discussion

We demonstrate that measurements of ¹⁰Be, ²¹⁰Pb_ex, and ¹³⁷Cs associated with suspended sediment can be used to distinguish between the three primary sediment sources (agricultural uplands, bluffs, and banks) and estimate channel–floodplain exchange. We observe how the sediment sources systematically vary by location and change over the course of a single storm hydrograph. While sediment dynamics for any given event are not necessarily indicative of longer-term trends, the results are consistent with our geomorphic understanding of the system and longer-term observations of sediment dynamics. We advocate for future sediment fingerprinting studies to develop a geomorphic rationale to explain the distribution of the fingerprinting properties for any given study area, with the intent of developing a more generalizable, process-based fingerprinting approach.

Conclusions

We show that measurements of conservative and nonconservative tracers (e.g., long- and short-lived radionuclides) can provide spatially integrated, yet temporally discrete, insights to constrain sediment sources and channel–floodplain exchange at the river network-scale. Fingerprinting that utilizes nonconservative tracers requires that the nonconservative behavior is predictable and verifiable.     

Dispersal of Contaminant Metals in the Mining-Affected Danube and Maritsa Drainage Basins, Bulgaria, Eastern Europe

Metal dispersal in the Danube and Maritsa drainage basins resulting from metal mining activities in Bulgaria has been assessed through the collection of 611 samples of river water, river channel and floodplain sediment, and mine waste from over 218 sites. Concentrations of Cd, Cu, Pb, and Zn in river water were found to be highest in close proximity to locations of Cu and Pb–Zn mining regions in the Maritsa catchment. Downstream dispersal of solute metals in these catchments, and into the River Danube, was found to be limited by physical dilution and a well-buffered pH environment. Dispersal of contaminant metals in channel and floodplain sediment was found to be extensive. Contamination was particularly severe in the Rivers Timok and Iskar (Danube catchment) and the Topolnitsa, Chepelarska, and Arda Rivers (Maritsa catchment) and creates the potential of transboundary dispersal of contaminant metals.     

Slope Basis Deposits Linked to Long-Term Land Use in NE-Germany

In the absence of long-term records of soil erosion by land use change in the moraine landscape, NE-Germany, slope basis deposits offer considerable potential for reconstructing the changing soil erosion rates at a catena scale in response to the environmental change. A pit with a length of 61m and an average depth of 1.5 to 3m was opened along the catena, located 60km east of Berlin, NE Germany. The 137 Cs and 210 Pb ex dating in conjunction with soil profile analysis methods were used to define a chronology for the accumulated soil materials at slope basis of the catena. The temporal patterns of sediment accumulation rates at study catena were subdivided into five time periods. The deposited depth of sediments in the slope basis has increased eight to ten - fold during the periods between 1954 and 1986 compared to the deposit depth over the past 600 years. Over the last 100 years, deposited depth at the slope basis of the catena increased from 0.49 cm/yr to 1.04 cm/yr and then decreased to 0.45 cm/yr. Increase in sedimentation rate in the time period from 1897 to 1986 corresponded to intensive agricultural tillage operations whereas a decrease in sedimentation after 1986 corresponded to a land use change from arable land to grassland of the study catena.     

The impact of environmental changes on the sediment loads of Norwegian rivers

The impact of unusual events on the sediment dynamics in rivers is discussed in this paper. The increase in the number of extreme precipitation events and other unusual weather events in Norway strongly suggests that weather conditions are changing. It is difficult to monitor sediment transport during large magnitude floods. It is however well known that they may deliver substantial amounts of sediment. The suspended sediment load in the upper Atna river during the springflood in 1995 was 44 times the mean load measured during the preceding years. The recurrence interval of this flood was estimated to be 100–200 years. The conditions during the occurrence of a particular flood event may also be of considerable importance and measurements during rainfall on frozen ground have indicated unusually high runoff and erosion rates.The seasonal distribution of runoff in several parts of Norway has changed in recent years and higher winter temperatures have produced an increase in the frequency of flood events. A very long lasting flood caused by a prolonged period of rain occurred in the Vikka stream during September to December 2000. The availability of sediment increased with the increasing soil moisture content in the area. As the ground became saturated, more active slope processes caused erosion rates to increase markedly. The combined effects of climate change and human impact on sediment transport in rivers appear to enhance downstream sediment delivery. Flood protection works along river channels prevent sediment from being deposited on the floodplain. River channels that have been lowered in order to reduce groundwater levels in agricultural floodplain areas will experience the same effect. During the last decade extensive ecological changes have taken place in the coastal areas of southern Norway as 90% of the sugar kelp forest has been lost. This change has been attributed to an apparent increase in sediment delivery to the sea along with a rise in sea temperatures.     

英国Culm河河漫滩沉积物中磷素时空变化研究

河漫滩上沉积物的沉积伴随着与沉积物相结合的营养和污染物质的沉积。已有研究表明,河漫滩是与沉积物相结合的磷的沉积地。采用137Cs技术,并结合河漫滩沉积物中全磷(TP)含量的剖面信息,可以调查近年河漫滩沉积物中的TP含量,计算TP储量。本文根据英国Devon郡Culm河8个河漫滩采样环沉积物中的数据,重建了在过去40～50年内TP储量和含量的变化。结果表明,在Culm河河漫滩沉积物中,在1963～2000年间TP平均含量为0.60～1.96gkg-1,该值自河流上游向下游和自过去到现在有逐渐增加的趋势;在相同的河漫滩沉积物中,在相同的时期内TP储量为18.62～435.48gm-2,即0.49～11.46gm-2a-1,最大值出现在河流的中游。