Formation of braided river floodplains, Waimakariri River, New Zealand

Floodplains along the braided gravel-bed Waimakariri River are discontinuous although generally extensive landforms composed predominantly of gravel bars capped with vertically accreted fines. In order of importance, three mechanisms lead to floodplain formation. River bed abandonment by lateral migration of the braid-train initiates the formation of the largest floodpiains, which usually occur downstream of tributary fans and valley bedrock spurs. In the headwater reaches, localized river bed aggradation during high magnitude events leads to floodplain formation by producing a surface resistant to erosion by lesser events due to either the coarse nature of the deposit, or by its elevation over the river bed, or both. The least important mechanism initiating floodplain development is localized river or channel incision. A six stage model is proposed for the sequential development of floodplains on the Waimakariri River from: (i) active river bed; (ii) stabilizing bar; (iii) incipient floodplain; (iv) established floodplain; (v) mature floodplain; and to (vi) terrace. Two mechanisms, lateral migration by the braid-train and reactivation of abandoned channels within floodplains, operating separately or in combination, are responsible for floodplain reworking and their relatively young age (<250 years). Clearly, braided rivers can construct substantial areas of well developed floodplain.     

Geological controls and effects of floodplain asymmetry on river–groundwater interactions in the southeastern Coastal Plain, USA

Channel sediment and alluvial aquifer hydraulic properties exert a major control on river–groundwater interactions. Channels and floodplains are often asymmetrical, resulting in differences in sediment hydraulic properties across the river. Floodplain asymmetry is common along Coastal Plain rivers in South Carolina and North Carolina, USA. The Tar River, North Carolina, has an asymmetrical valley. The study objective was to characterize the effects of floodplain asymmetry and geological controls on river–groundwater interactions. Floodplain and river channel sediments adjacent to the river were characterized with split spoon cores and hand auger samples along a 22-km reach. Hydrogeology was characterized with 38 piezometers and water level recorders in and adjacent to the river. Ground penetrating radar was used to define the shallow stratigraphy. Channel sediments were significantly different between the north and south sides of the river. Hydraulic conductivity and groundwater inputs were greater on the side of the river (north) that contained more permeable fluvial deposits. Groundwater chemistry (δ¹⁸O, specific conductance) data also suggested greater exchange between surface water and groundwater on the north side of the river channel. A conceptual hydrogeological model illustrates that groundwater movement and contaminant transport to the river differs across the channel due to asymmetrical geology.     

Upstream control of river anastomosis by sediment overloading,upper Columbia River,British Columbia,Canada

Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well‐known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most‐studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross‐valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long‐term (millennia‐scale) floodplain sedimentation rates and avulsion frequencies are calculated using ¹⁴C‐dated deeply buried organic floodplain material from cross‐valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age (ca 1100 to 1950 ad ). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low‐gradient floodplains, a situation commonly found in intermontane and foreland basins.     

The long term fate and environmental significance of contaminant metals released by the January and March 2000 mining tailings dam failures in Maramureş County,upper Tisa Basin,Romania

In January and March 2000 two tailings dam failures in Maramureş County, northwest Romania, resulted in the release of 200,000 m³ of contaminated water and 40,000 tonnes of tailings into tributaries of the Tisa River, a major tributary of the Danube. The high concentrations of cyanide and contaminant metals released by these dam failures resulted in pollution and fish deaths not only in Romania, but also downstream in the Tisa and Danube rivers within Hungary, Serbia and Bulgaria. Following these accidents, a research programme was initiated in northwest Romania to establish metal levels in rivers affected by the tailings dam failures and to compare these to metal values in river systems contaminated by historic mining and industrial activity. In July 2000, 65 surface water, 65 river sediment and 45 floodplain sediment samples were collected from trunk streams and principal tributaries of the Lapuş/Someş rivers (affected by the January 2000 spill) and the Vişeu/Tisa rivers (affected by the March 2000 Novat spill) down to the Hungarian and Ukrainian borders, respectively. Sample analyses for Pb, Zn Cu and Cd show that metal contamination in surface water and river sediment decreases rapidly downstream away from presently active mines and tailings ponds. Concentrations of heavy metals in water and sediment leaving Romania, and entering Hungary and the Ukraine, generally fall below EC imperative and Dutch intervention values, respectively. However, Zn, Cu and Cd concentrations in river sediments approach or exceed intervention values at the Romanian border. The results of this survey are compared with earlier surveys to ascertain the long-term fate and environmental significance of contaminant metals released by mine tailings dam failures in Maramureş County.     

长江口北支河槽容积变化特征的定量分析

北支河槽容积变化是北支河道演变趋势在定量上的直接表现,河道边界条件和河床泥沙运动是影响河槽容积变化的主要因素。收集1986—2013年长江口北支河道年实测地形资料,利用GIS技术建立不同时期水下数字高程模型,进行北支河槽容积变化和河床冲淤变化特征分析。结果表明,北支岸线圈围和泥沙淤积导致了1986年以来河槽容积萎缩。北支河槽0m线以下容积共减少约7.110亿m3,岸线圈围引起河槽容积减少4.000亿m3,占比56.3%;泥沙淤积引起的河槽容积减少3.110亿m3,占比43.7%。具体而言,北支上段河槽容积萎缩主要是泥沙淤积所致,其航道开发综合利用应遵循上段的泥沙运动规律特点;中段则是边滩圈围和沙洲并岸引起,边界调整后束流作用加强,河床冲刷,断面形态调整后水深条件更加有利于中段的航道利用开发;下段是泥沙淤积和边滩圈围共同影响所致,泥沙淤积影响略大,但下段沿北岸-5m深槽始终存在且稳定,具备航道开发利用的河势基础,且南侧河道边界仍具有可圈围的余地。     

The impact of tailings dam spills and clean-up operations on sediment and water quality in river systems: the Rı́os Agrio–Guadiamar,Aznalcóllar,Spain

The Aznalcóllar tailings dam at Boliden Apirsa's Aznalcóllar/Los Frailes Ag–Cu–Pb–Zn mine 45 km west of Seville, Spain, was breached on 25 April 1998, flooding approximately 4600 hectares of land along the Rı́os Agrio and Guadiamar with approximately 5.5 million m³ of acidic water and 1.3×10⁶ m³ of heavy metal-bearing tailings. Most of the deposited tailings and approximately 4.7×10⁶ m³ of contaminated soils were removed to the Aznalcóllar open pit during clean-up work undertaken immediately after the spill until January 1999. Detailed geomorphological and geochemical surveys of the post-clean-up channel, floodplain and valley floor, and sediment and water sampling, were carried out in January and May 1999 at 6 reaches representative of the types of river channel and floodplain environments in the Rı́o Guadiamar catchment affected by the spill. The collected data show that the clean-up operations removed enough spill-deposited sediment to achieve pre-spill metal (Ag, As, Cd, Cu, Pb, Sb, Tl, Zn) concentrations in surface sediment. These concentrations, however, are still elevated above pre-mining concentrations, and emphasise that mining continues to contaminate the Agrio-Guadiamar river system. Dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and As concentrations occur downstream, presumably as a result of factors such as sewage and agriculture. River water samples collected in May 1999 have significantly greater dissolved concentrations of metals and As than those from January 1999, probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months. These concentrations are reduced downstream, probably by a combination of dilution and removal of metals by mineral precipitation. Single chemical extractions (de-ionised water, CaCl₂ 0.01 mol l⁻¹, CH₃COONH₄ 1 M, CH₃COONa 1 M and ammonium oxalate 0.2 M) on alluvial samples from reaches 1 and 6, the tailings, pre-spill alluvium and marl have shown that the order of sediment-borne contaminant mobility is generally Zn>Cd>Cu>Pb>As. Pb and As are relatively immobile except possibly under reducing conditions. Much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings-related sulphide minerals which are potentially reactive and may continue to release contaminants to the Agrio–Guadiamar river system. Our work emphasises the need for pre-mining geomorphological and geochemical data, and an assessment of potential contributions of contaminants to river systems from other, non-mining sources.     

黄河下游漫滩洪水冲淤规律

滩地的淤积层分布记录着以往漫滩洪水的特征,即反映漫滩洪水的量级、频率和持续时间等,同时河漫滩也是预估河流泥沙、洪水灾害防治和湿地生态系统保护等的重要组成部分。根据黄河下游水文年鉴资料,分析滩地的淤积与漫滩洪水的定量关系,为未来河流泥沙预估提供依据。经分析得到大漫滩洪水在来沙系数S/Q<0.030 kg·s/m6时,主槽冲刷而滩地淤积,反之则滩槽同淤。当S/Q<0.030 kg·s/m6时,大漫滩洪水滩地的淤积量主要与漫滩系数Q_max/Q_p、上滩水量W₀和含沙量S有关;大漫滩洪水的主槽冲刷量则除了与洪水期水量W和沙量W_s有关外,还与滩地的淤积量有关。一般漫滩洪水,当来沙系数S/Q<0.023 kg·s/m6时,主槽冲刷而滩地淤积,反之则滩槽同淤。一般漫滩洪水主槽冲刷量与来沙系数S/Q和洪水期水量W有关,而滩地淤积量仅与含沙量S有关。黄河下游漫滩洪水滩地的淤积和主槽的冲刷主要发生在孙口以上河段,而孙口以下河段主槽冲刷和滩地淤积量均较少。     

Spatial distribution of trace elements in floodplain alluvium of the upper Blackfoot River,Montana

The Mike Horse Mine tailings dam in western Montana was partially breached in 1975 due to heavy rainfall and a failed drainage bypass. Approximately 90,000 tons of metal and arsenic-enriched tailings flowed into Beartrap Creek and the Blackfoot River. The spatial distribution of trace elements As, Cd, Cu, Mn, Pb, and Zn in floodplain alluvium of the upper Blackfoot River were examined along 20 transects in the upper 105 river kilometers downstream from the tailings dam. Trace element concentrations decrease with distance from the failed dam, with As reaching background concentrations 15 km from the Mike Horse dam, Cd and Pb at 21 km, Cu at 31 km, and Mn and Zn at 37 km. Distance from the Mike Horse tailings dam and mine area is the dominating factor in explaining trace element levels, with R ² values ranging from 0.67 to 0.89. Maximum floodplain trace element concentrations in the upper basin exceed US. EPA ecological screening levels for plants, birds and other mammals, and reflect adverse hazard quotients for exposure to As and Mn for ATV/motorcycle use. Trace element concentrations in channel bank and bed alluvium are similar to concentrations in floodplain alluvium, indicating active transport of trace elements through the river and deposition on the floodplain. The fine fraction (<2 mm) of floodplain alluvium is dominated by sand-sized particles (2.0–0.05 mm), with Cu and Mn significantly correlated with silt-sized (0.05–0.002 mm) alluvium. Ongoing remediation in the headwaters area will not address metal contamination stored downstream in the channel banks and on the floodplain. Additionally, some trace elements (Cu, Mn and Zn) were conveyed farther downstream than were others (As, Cd, Pb).     

黄河下游漫滩高含沙洪水滩槽界定及泥沙时空沉积特性

黄河下游漫滩高含沙洪水河床调整剧烈,多数断面洪水后形成"相对窄深河槽",洪水前后河槽宽度发生明显变化。分别以观测断面洪水前后的河槽宽度为基准,计算漫滩高含沙洪水期泥沙时空沉积分布,结果表明,漫滩高含沙洪水与非漫滩高含沙洪水相比,能将主河槽内淤积泥沙量的59.3%搬运至嫩滩或滩地,减缓主河槽淤积。在分析研究基础上,建立了洪水后漫滩河段河槽相对缩窄率与洪水前期河槽宽度的量化关系,洪水后主槽宽度缩窄率为15.5%~44.0%;分析遴选了漫滩高含沙洪水滩地淤积量与主要水力因子间关联度及物理含义,给出了漫滩高含沙洪水滩地淤积量与相应水力因子间的响应函数;初步提出漫滩洪水河道塑槽淤滩的临界水沙配置指标,临界水沙系数取值为0.025~0.040。成果对高含沙洪水调控具有一定的指导意义。     

Floodplain sedimentology of the Squamish River, British Columbia: relevance of element analysis

Element analysis of modern-day floodplains provides a framework for characterizing associations amongst depositional forms, the processes responsible for them and their local depositional environment. From interpretation of the spatial association of elements, mechanisms of floodplain evolution can be analysed. The Squamish River, in southwestern British Columbia, is a high-energy, gravel-based river, which exhibits a distinct downstream gradation in channel planform type. The floodplain sedimentology of this river is evaluated using an element approach. Five elements, defined on the basis of their morphological outline, position within sediment sequences and sedimentological character, describe the floodplain sedimentology: (i) top-stratum, (ii) chute channel; (iii) ridge; (iv) bar platform; (v) basal channel gravels. The sedimentological composition of each element is described. Each of these units relates directly to morphostratigraphic units which make up contemporary bars of the Squamish River. Associations among facies defined at the bedform scale, morphostratigraphic units on bar surfaces and elemental floodplain features are described and explained. The vertical stacking arrangement of elements is analysed in trenches (dug perpendicular to the main channel) and in bank exposures. Two elemental sedimentology models are proposed. In the first model, bar platform sands are discontinuous above basal channel gravels. Chute channel, ridge and proximal topstratum elements form thick sequences above. The second model is characterized by sequences in which distal top-stratum deposits are observed. In these instances, bar platform sands are better preserved beneath the distal top-stratum element, with proximal top-stratum elements above. The applicability of these models is determined primarily by position on the floodplain. Chute channel reworking of floodplain sediments and replacement by top-stratum elements is the dominant process marginal to contemporary bars. Sites in which channel avulsion has resulted in preservation of distal top-stratum deposits in the midsequence of the present-day channel banks determine the occurrence of the second model. Although channel planform style changes down-valley in the study reach from braided to meandering, these two models apply in each reach. It is concluded that processes operative at the element scale, rather than the channel planform scale, determine floodplain sedimentology.     

Lead, zinc, and antimony contamination of the Rio Chilco-Rio Tupiza drainage system, Southern Bolivia

An intense, but localized rainfall event in February 2003, led to the severe erosion and failure of a tailings disposal impoundment at the Abarόa Antimony Mine in southern Bolivia. The failure released approximately 5,500 m³ of contaminated tailings into the Rio Chilco-Rio Tupiza drainage system. The impacts of the event on sediment quality are examined and compared to contamination resulting from historic mining operations in the headwaters of the basin. Of primary concern are contaminated floodplain soils located along downstream reaches of the Rio Tupiza which were found to contain lead (Pb), zinc (Zn), and antimony (Sb) concentrations that locally exceed Canadian, German, and Dutch guidelines for agricultural use. Spatial patterns in sediment-borne trace metal concentrations, combined with Pb isotopic data, indicate that Pb, Zn, and Sb are derived from three tributary basins draining the Abarόa, Chilcobija, and Tatasi-Portugalete mining districts. Downstream of each tributary, geographical patterns in trace metal concentrations reflect local geomorphic changes throughout the drainage system. Trace metal concentrations within the Rio Chilco decrease rapidly downstream as a result of dilution by uncontaminated sediments and storage of metal enriched particles (e.g., sulfide minerals) in the channel bed as a result of ongoing aggradation. Storage in the floodplains is limited. These processes significantly reduced the dispersal and, thus, the relative environmental affects of tailings eroded from the Abarόa Mine during the 2003 flood. In contrast, storage of Pb, Zn, and Sb in floodplains along the Rio Tupiza is significant, the majority of which is derived from historic mining operations, particularly mining within the Tatasi-Portugalete district.     

Incorporation of metalliferous sediments from historic mining into river floodplains

Rivers and their floodplains are dynamic systems, sediments are continually added to floodplain surfaces, while erosion and scour may remove sediments to be added to floodplains further downstream. When mining sediments were introduced into some catchments in Britain as ore deposits were exploited, river channels and floodplains were grossly polluted with metals. The legacy of this uncontrolled release of contaminants is apparent still, and contemporary channel deposits are enriched in metals. While the floodplains acted as a buffer to the dispersal of metals straight through the catchment, metals are still being released hundreds of years later as the floodplains are eroded and this secondary pollution of the river is a long-term problem.By studying a range of mining catchments, the effects of key variables on heavy metal dispersal in the fluvial environment can be assessed. As no single catchment displays the whole array of possible situations, a mosaic of case studies from several areas provides a good representation of potential conditions.     

Sediment distribution and depositional processes along the fluvial to marine transition zone of the Mekong River delta,Vietnam

The area of coastal rivers with a combination of fluvial, tidal and wave processes is defined as the fluvial to marine transition zone and can extend up to several hundreds of kilometres upstream of the river mouth. The aim of this study is to improve the understanding of sediment distribution and depositional processes along the fluvial to marine transition zone using a comprehensive dataset of channel bed sediment samples collected from the Mekong River delta. Six sediment types were identified and were interpreted to reflect the combined action of fluvial and marine processes. Based on sediment‐type associations, the Mekong fluvial to marine transition zone could be subdivided into an upstream tract and a downstream tract; the boundary between these two tracts is identified 80 to 100 km upstream of the river mouth. The upstream tract is characterized by gravelly sand and sand and occasional heterolithic rhythmites, suggesting bed‐load supply and deposition mainly controlled by fluvial processes with subordinate tidal influence. The downstream tract is characterized by heterolithic rhythmites with subordinate sand and mud, suggesting suspended‐load supply and deposition mainly controlled by tidal processes with subordinate fluvial influence. Sediment distributions during wet and dry seasons suggest significant seasonal changes in sediment dynamic and depositional processes along the fluvial to marine transition zone. The upstream tract shows strong fluvial depositional processes with subordinate tidal influence during the wet season and no deposition with weak fluvial and tidal processes during the dry season. The downstream tract shows strong coexisting fluvial and tidal depositional processes during the wet season and strong tidal depositional processes with negligible fluvial influence during the dry season. Turbidity maxima are present along the downstream tract of the fluvial to marine transition zone during both wet and dry seasons and are driven by a combination of fluvial, tidal and wave processes.     

长江中游曲流河段河道的近代演化过程研究

曲流河是冲积平原河流中的重要河型之一,曲流河的河道演变对冲积平原的建设与演化起着非常重要的作用。地处江汉平原的长江中游藕池口至城陵矶段河道是最典型的曲流河段,其曲流河道的几何形态和变化过程较为复杂,对该段河道演化过程的研究在河流的开发利用及水利工程建设中具有很好的理论指导意义。本研究通过对历史资料和多期卫星遥感影像的解译与分析,表明长江中游藕池口至城陵矶河段的曲流河道演化在受自然和人类活动双重影响的情况下,该河段河道的演化仍然维持曲流河特征。受大洪水的切滩作用及松滋口、太平口和藕池口3个分流口对洞庭湖的分水分沙的影响,该段河道的演化过程较为复杂。自然裁弯取直和人工裁弯取直在一定程度上改变着河道演化的进程,但由裁弯取直及上游水利工程引起的纵坡降增加产生的冲淤变化将会维持河道的稳定,同时在该河段实施的护岸工程也会抑制河流的横向侵蚀,曲流河段河道演化进入自调整和自组织过程。     

黄河河口段一维水流泥沙数学模型

针对黄河河口段河道来水来沙特性和河道冲淤演变特点,综合考虑了断面上水沙分布和冲淤分布不均匀,阻力变化、河口三角洲淤积延伸等问题,建立了黄河利津以下河口段一维水流泥沙数学模型。用该模型对多年汛期和冬季河口段内水沙进行验证计算表明:计算结果与实测结果基本吻合。本模型可用来预测河口段内沿程不同时刻水位、含沙量及河床冲淤的变化过程。     

Controls on the alluviation of oxbow lakes by bed‐material load along the Sacramento River,California

Differences in the nature and quantity of sediment filling oxbow lakes have significant implications for the evolution of meandering rivers and the development of floodplains, influencing rates of meander migration and the valley width over which migration takes place. In an effort to identify the controls on the alluviation of oxbow lakes by coarse bed material, this study examined the sedimentary records stored within oxbow lakes of the Sacramento River of California, USA, and found that the volume of gravel in storage correlated negatively with the diversion angle separating flow between the river channel and the entrance into each lake. A method was devised for estimating the original channel bathymetry of the studied lakes and for modelling the hydraulic and sediment‐transport effects of the diversion angle within channels recently abandoned by meander cut‐off. The diversion angle determines the width of a flow separation within the abandoned‐channel entrance, reducing the discharge diverted from the river channel and thus limiting the ability of the abandoned channel to transport bed material. Aggradation rates are faster within entrances to abandoned channels with high diversion angles, resulting in the rapid isolation of lakes that store only a small volume of coarse‐grained sediment. Aggradation rates are slower within channel entrances where diversion angles are low, resulting in the slow transitioning of such channels into oxbow lakes with a larger and more extensive accumulation of coarse‐grained sediment. These findings compare well with observations in other natural settings and the mechanism which is described for the control of the diversion may explain why some oxbow lakes remain as open‐water environments for centuries, whereas others are filled completely within decades of cut‐off.     

A comparison of mud- and sand-dominated meanders in a downstream coarsening reach of the mixed bedrock-alluvial Klip River, eastern Free State, South Africa

Along a 28 km reach of the Klip River, eastern Free State, South Africa, mud- and sand-dominated meanders have developed in close proximity within a floodplain wetland up to 1.5 km wide, providing an unusual opportunity to compare their characteristics under similar hydrological conditions. Throughout the reach, the channel bed is grounded on sandstone/shale bedrock although the banks are alluvial, and most river activity occurs during summer high flows. The reach can be divided into three geomorphological zones: Zone 1 (0–11 km), a muddy proximal part with a single meandering channel (w/d < 10) and near-permanent standing water in oxbows and backswamps; Zone 2 (11–17.5 km), a transitional mud-to-sand part with one main channel (w/d  20–30), a number of sinuous palaeochannels and oxbows, and only limited standing water; and Zone 3 (17.5–28 km), a sandy distal part with a single meandering channel (w/d  15–30), scroll bars and oxbows, and little standing water. Each zone also has a distinctive sedimentology: Zone 1 is characterised by an  3–4 m thick succession of basal sand and minor granules overlain by dominantly muddy sediment deposited primarily by oblique accretion in meander bends; Zone 2 is characterised by < 4 m of interbedded sand and mud deposited primarily by lateral point-bar accretion, although a history of avulsions also attests to the importance of abandoned-channel accretion; and Zone 3 is characterised by < 3 m of dominantly sand deposited primarily by lateral point-bar accretion. This unusual downstream sediment coarsening trend, and the associated changes in channel and floodplain character, are independent of sediment inputs from tributaries, and result from a downstream increase in bankfull unit stream power from < 3.5 W m^− 2 (Zone 1) to  4–10 W m^− 2 (Zone 3). Mud is deposited primarily in low-energy Zone 1 but is conveyed in suspension more effectively through higher energy Zones 2 and 3, only forming drapes over sandy lateral accretion deposits during waning flood stages. The downstream increase in unit stream power is controlled in part by a slight downstream increase in floodplain gradient that may be related to a subtle variation in the erosional resistance of the bedrock underlying the channel bed. These findings add to previous work on meandering rivers by demonstrating that mud-dominated meanders can occur in long-term erosional settings where the channel bed is grounded on bedrock, and that downstream fining trends may be reversed locally.     

Pb isotope evidence for contaminant-metal dispersal in an international river system: The lower Danube catchment,Eastern Europe

Lead isotope signatures (²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb), determined by magnetic sector ICP-MS in river channel sediment, metal ores and mine waste, have been used as geochemical tracers to quantify the delivery and dispersal of sediment-associated metals in the lower Danube River catchment. Due to a diverse geology and range of ore-body ages, Pb isotope signatures in ore-bodies within the lower Danube River catchment show considerable variation, even within individual metallogenic zones. It is also possible to discriminate between the Pb isotopic signatures in mine waste and river sediment within river systems draining individual ore bodies. Lead isotopic data, along with multi-element data; were used to establish the provenance of river sediments and quantify sedimentary contributions to mining-affected tributaries and to the Danube River. Data indicate that mining-affected tributaries in Serbia and Bulgaria contribute up to 30% of the river channel sediment load of the lower Danube River. Quantifying relative sediment contributions from mining-affected tributaries enables spatial patterns in sediment-associated metal and As concentrations to be interpreted in terms of key contaminant sources. Combining geochemical survey data with that regarding the provenance of contaminated sediments can therefore be used to identify foci for remediation and environmental management strategies.     

Investigating the origin of Pb pollution in a terrestrial soil–plant–snail food chain by means of Pb isotope ratios

Lead isotope ratios were used to trace the origin of Pb in a soil–plant (Urtica dioica)–snail (Cepaea nemoralis) food chain in two polluted locations in the floodplains of the rivers Meuse and Rhine (Biesbosch National Park) and one reference location in the Netherlands. Lead isotope ratios and concentrations were determined in soil, litter, plant leaves, snails, rainwater and airborne particulate matter. Anthropogenic Pb in the soils of all locations was found to be derived from deposition of Pb polluted river sediments. Discharging rivers influenced the reference location before being reclaimed from the sea. The river sediment contains anthropogenic Pb from various sources related to industrial activities in the hinterland of the rivers Meuse and Rhine. Lead in the atmosphere contributed substantially to Pb pollution and Pb transfer in plant leaves and snails in all locations. Lead pollution in plant leaves and snails can be explained from a mixture of river sediment-Pb and atmospheric Pb from various transfer routes that involve low concentrations.