Downstream changes in the transport and storage of sediment-associated contaminants (P, Cr and PCBs) in agricultural and industrialized drainage basins

Samples of suspended, floodplain and channel bed sediment have been used to examine downstream changes in ediment-associated contaminant transport and storage in contrasting rivers in Yorkshire, UK. The concentrations of hosphorus, chromium and selected PCBs associated with sediment in the River Aire and its main tributary, the River Calder, which drain an urbanized and industrialized catchment, are considerably higher than those in the relatively unpolluted River Swale, which drains an agricultural catchment. Concentrations of sediment-associated contaminants in the Aire/Calder system increase downstream, reflecting the location of urban and industrial areas in the middle and lower reaches, and the location of point source inputs, such as sewage treatment works. The ontaminant concentrations associated with floodplain and channel bed sediment in the Rivers Aire and Calder are high, particularly in the lower reaches. This, combined with measurements of sediment storage on the floodplain and channel bed, indicate that significant storage of sediment-associated contaminants occurs in the Rivers Aire and Calder.     

Estimating population served by sewage treatment works from readily available GIS data

Environmental risk assessment of household chemicals at the catchment scale requires an estimate of the load at individual Sewage Treatment Works (STWs). This can be achieved based upon population served and market consumption data. Although the population served is difficult to obtain, this paper shows that reasonable estimates can be made using readily available spatially referenced data. A new method is developed using STW data from the Exe and the Aire and Calder catchments and validated using 193 STWs within the Environment Agency's Anglian region. The estimated populations served were compared with available estimates of Population Equivalents (PEs). The population estimates were broadly similar to PEs for small works but agreement was lower for larger plants. The discrepancy for larger works is consistent with trade influent inclusion in the PE. The method is suitable for application to both rural areas and large urbanised areas, although the interpretation of corroborating data becomes increasingly difficult in very large urban areas serving more than one STW.     

Phosphorus dynamics along a river continuum

Changes in phosphorus concentration and form along 110 km of the River Swale in Northern England were examined over a 2-year period during 1998-2000. This study aimed to use these data to identify the importance of within-channel storage on phosphorus dynamics and to determine the changes in longitudinal transport of phosphorus along a river continuum. The catchment was divided into three contrasting zones: the upland, dominated by sheep farming; a transitional zone, and an intensively-farmed lowland, impacted by sewage inputs. Samples, taken at the downstream extent of each zone at approximately 2-day intervals, were analysed for total phosphorus (TP), total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP), all of which increased in concentration downstream. SRP concentrations were highest in summer and during low flows, although 92% of phosphorus was exported between autumn and spring. The TDP in the upper and transitional zones consisted of both soluble reactive and un-reactive phosphorus, but in marked contrast was almost entirely in soluble reactive form in the lowland. The majority (85%) of phosphorus exported from the catchment was generated within the lowland, due to sewage inputs and losses from intensive agricultural land. It was predominantly particulate-bound, due to interactions of dissolved phosphorus with suspended sediment. The upland contributed less than 5% to the TP annual budget. Intensive river water monitoring highlighted that the lowland dominated phosphorus export during the rising stage of storms (indicating a rapid mobilisation of fine phosphorus-rich sediment), whereas the transitional zone became dominant on the falling stage (due to greater diffuse phosphorus input).     

Restoring Dynamic Fluvial Processes in Urban Rivers: Learning from the Aire and Isar Rivers

In process-based restoration, the objective is not to create a complex river form directly; instead, interventions are intended to “prompt” the natural processes to restore such forms. The improvements in ecological conditions are actually made over time by flowing water during floods (using the stream’s energy), and by the growth of riparian vegetation (using incoming solar energy). On the Aire River in Geneva, ecological function was restored to a formerly canalized river by providing the river with an espace de liberté. A grid of channels cut into the valley bottom allowed the river to freely flood, erode its bed and banks, and deposit bars, creating complex surfaces on which riparian vegetation established to support the food web of the riverine ecosystem. The diamond-shaped bits of land left between these channels (“lozenges”) gradually erode and evolve as the river migrates, creating complex channel forms. The Isar River in Munich restoration involved adding coarse sediment load, creating erodible bed and banks in place of formerly rigid boundaries, expanding process space for river migration, erosion, and deposition, and increased human access to the river over 8 km. Since restoration, natural transport of sediment has resulted in deposition of gravel bars, whose forms evolve during floods, supporting diverse habitats. The Isar and Aire Rivers provide compelling examples of processbased restoration meeting 4 criteria for process-based restoration: space, energy, materials, and time. They demonstrate the possibilities of urban river restoration to achieve both ecological and social goals through restoration of fluvial process.     

Particulate phosphorus transport by sub-surface drainage from agricultural land in the UK. Environmental significance at the catchment and national scale

Phosphorus (P) is the key limiting nutrient in most UK freshwater systems. With increased legislation controlling point source inputs, dissolved (DP) and particulate P (PP) derived from diffuse sources are making a more significant contribution to the total P loading of surface waters. Recent research has focused on pathways linking diffuse sources to the fluvial system and sub-surface field drains have been shown to transport both sediment and P rapidly to watercourses. Preliminary results are presented from an ongoing study using environmental tracers to identify the source of the drain sediment and its potential as a carrier of PP. These results suggest that the majority of sediment in drains is topsoil derived, but the significance of P loss via this pathway in a regional or UK context has yet to be evaluated. A protocol to study the potential problem at a regional/national scale is discussed and initial data presented.     

The strategic significance of wastewater sources to pollutant phosphorus levels in English rivers and to environmental management for rural, agricultural and urban catchments

The relationship between soluble and particulate phosphorus was examined for 9 major UK rivers including 26 major tributaries and 68 monitoring points, covering wide-ranging rural and agricultural/urban impacted systems with catchment areas varying from 1 to 6000 km² scales. Phosphorus concentrations in Soluble Reactive (SRP), Total Dissolved (TDP), Total (TP), Dissolved Hydrolysable (DHP) and Particulate (PP) forms correlated with effluent markers (sodium and boron) and SRP was generally dominant signifying the importance of sewage sources. Low flows were particularly enriched in SRP, TDP and TP for average SRP > 100 μg/l indicating low effluent dilution. At particularly low average concentrations, SRP increased with flow but effluent sources were still implicated as the effluent markers (boron in particular) increased likewise. For rural areas, DHP had proportionately high concentrations and SRP + DHP concentrations could exceed environmental thresholds currently set for SRP. Given DHP has a high bioavailability the environmental implications need further consideration. PP concentrations were generally highest at high flows but PP in the suspended solids was generally at its lowest and in general PP correlated with particulate organic carbon and more so than the suspended sediment in total.Separation of pollutant inputs solely between effluent and diffuse (agriculture) components is misleading, as part of the “diffuse” term comprises effluents flushed from the catchments during high flow. Effluent sources of phosphorus supplied directly or indirectly to the river coupled with within-river interactions between water/sediment/biota largely determine pollutant levels.The study flags the fundamental need of placing direct and indirect effluent sources and contaminated storage with interchange to/from the river at the focus for remediation strategies for UK rivers in relation to eutrophication and the WFD.     

Suspended sediment phosphorus composition in tributaries of the Okanagan lakes,B.C.

The phosphorus composition of suspended sediments transported during snowmelt to the Okanagan lakes averaged 62% apatite P, 16% non-apatite inorganic P (NAIP), and 22% organic P. Based on the average NAIP content, less than 16% of these P inputs were available for algal growth in the lakes. The content of NAIP in some stream suspended sediments was much higher than average, however. Management of the suspended sediment inputs to reduce P loadings will be most effective if applied to those tributaries contributing the most NAIP.     

Titanium in UK rural, agricultural and urban/industrial rivers: geogenic and anthropogenic colloidal/sub-colloidal sources and the significance of within-river retention

Operationally defined dissolved Titanium [Ti] (the < 0.45 μm filtered fraction) in rivers draining rural, agricultural, urban and industrial land-use types in the UK averaged 2.1 μg/l with a range in average of 0.55 to 6.48 μg/l. The lowest averages occurred for the upland areas of mid-Wales the highest just downstream of major sewage treatment works (STWs). [Ti] in rainfall and cloud water in mid-Wales averaged 0.2 and 0.7 μg/l, respectively. Average, baseflow and stormflow [Ti] were compared with two markers of sewage effluent and thus human population: soluble reactive phosphorus (SRP) and boron (B). While B reflects chemically conservative mixing, SRP declined downstream of STW inputs due to in-stream physico-chemical and biological uptake. The results are related to colloidal and sub-colloidal Ti inputs from urban/industrial conurbations coupled with diffuse background (geological) sources and within-river removal/retention under low flows as a result of processes of aggregation and sedimentation. The urban/industrial inputs increased background [Ti] by up to eleven fold, but the total anthropogenic Ti input might well have been underestimated owing to within-river retention. A baseline survey using cross-flow ultrafiltration revealed that up to 79% of the [Ti] was colloidal/nanoparticulate (> 1 kDa i.e. > c. 1-2 nm) for the rural areas, but as low as 28% for the urban/industrial rivers. This raises fundamental issues of the pollutant inputs of Ti, with the possibility of significant complexation of Ti in the sewage effluents and subsequent breakdown within the rivers, as well as the physical dispersion of fine colloids down to the macro-molecular scale. Although not directly measured, the particulate Ti can make an important contribution to the net Ti flux.     

River flow and associated transport of sediments and solutes through a highly urbanised catchment, Bradford, West Yorkshire

The hydrological characteristics of catchments become drastically modified in response to urbanisation. The total contributions and dynamics of runoff, suspended sediment and solutes may change significantly and have important implications downstream where they may affect flooding, instream ecological habitat, water quality and siltation of river channels and lakes. Although an appreciation of the likely hydrological changes is crucial for effective catchment management they are still poorly understood. In this paper we present data from a network of river monitoring stations throughout the heavily urbanised Bradford catchment, West Yorkshire. Sites are upstream, within and downstream of the highly urbanised central part of the catchment. Flow, turbidity (calibrated to suspended sediment concentration) and specific conductance (surrogate for solute concentration), logged at 15-min intervals, are presented for a 12-month period (June 2000 to June 2001). The total amounts and dynamics of flow, solute and suspended sediment transport were investigated. Estimated total flow and suspended sediment transport for the monitoring period were found to be high in response to the high total rainfall. Flow and sediment transport regimes were extremely 'flashy' throughout the catchment and became increasingly flashy in a downstream direction. Suspended sediment discharged from the Bradford subcatchment makes an important contribution to downstream sediment transport on the river Aire at Beal. Data suggest that the urbanised part of the Bradford catchment is extremely important in contributing solutes to the Beck (river). Although flow and sediment are also contributed to the Bradford Beck in the urbanised part of the catchment the data suggest that significant amounts may enter the combined sewer system and bypass the river. Understanding the spatial and temporal variations of flow and the transport of suspended sediment and solutes in rivers in urbanized subcatchments is crucial to their effective management and monitoring. Furthermore, this knowledge may be extremely important to the management and monitoring of downstream rivers in large scale mixed catchments.     

Total phosphorus content of river sediments in relationship to calcium,iron and organic matter concentrations

Data on the total concentrations of phosphorus, calcium, iron and organic matter in surface bed-sediments taken from rivers in the Thames catchment (Wey, Blackwater, Thame and Kennet), the River Swale in Yorkshire (data excludes the organic matter content) as well as the headwaters of the Great Ouse, are collated and compared. Total concentrations of phosphorus, iron and calcium range from 1.7–649, 12–8333 and 9–4605 μmol g⁻¹ (dry weight), respectively, with organic matter in the range of 0.6–19% by dry weight. For the Wey, Blackwater and Great Ouse, sewage inflows had no detectable effect on the sediment concentrations of total calcium, iron and organic matter whereas for the Blackwater and Great Ouse, the total phosphorus contents of the sediment were higher downstream of the effluent input in comparison with a less impacted upstream location. Relationships between the total phosphorus content of the sediments and contents of iron, calcium and organic matter indicated marked differences between the rivers. Although the organic matter content of the sediments was found to be a significant predictor for the total phosphorus concentration for the Blackwater and Great Ouse, the total iron content was also useful for the Blackwater and total calcium for the Great Ouse. It is postulated that this difference is a result of the sediment processes that are known to occur in these two systems, i.e. co-precipitation of phosphate with calcite in the Great Ouse and the formation of vivianite in anoxic sediments of the Blackwater.     

Modelling of phosphorus inputs to rivers from diffuse and point sources

The difference in timing of point and diffuse phosphorus (P) delivery to a river produces clear differences in the P concentration-flow relationship. Point inputs decrease in concentration with increasing river flow, due to dilution of a relatively constant input, whereas diffuse (non-point) load usually increases with river flow. This study developed a simple model, based on this fundamental difference, which allowed point and diffuse inputs to be quantified by modelling their contribution to river P concentration as a power-law function of flow. The relationships between total phosphorus (TP) concentration and river flow were investigated for three contrasting UK river catchments; the Swale (Yorkshire), the Frome (Dorset) and the Avon (Warwickshire). A load apportionment model was fitted to this empirical data to give estimates of point and diffuse load inputs at each monitoring site, at high temporal resolution. The model produced TP source apportionments that were similar to those derived from an export coefficient approach. For many diffuse-dominated sites within this study (with up to 75% of the annual TP load derived from diffuse sources), the model showed that reductions of point inputs would be most effective in order to reduce eutrophication risk, due to point source dominance during the plant and algae growing period. This modelling approach should provide simple, robust and rapid TP source apportionment from most concentration-flow datasets. It does not require GIS, information on land use, catchment size, population or livestock density, and could provide a valuable and versatile tool to catchment managers for determining suitable river mitigation options.     

Sewage effluent clean-up reduces phosphorus but not phytoplankton in lowland chalk stream (River Kennet, UK) impacted by water mixing from adjacent canal

Information is provided on phosphorus in the River Kennet and the adjacent Kennet and Avon Canal in southern England to assess their interactions and the changes following phosphorus reductions in sewage treatment work (STW) effluent inputs.A step reduction in soluble reactive phosphorus (SRP) concentration within the effluent (5 to 13 fold) was observed from several STWs discharging to the river in the mid-2000s. This translated to over halving of SRP concentrations within the lower Kennet. Lower Kennet SRP concentrations change from being highest under base-flow to highest under storm-flow conditions. This represented a major shift from direct effluent inputs to a within-catchment source dominated system characteristic of the upper part to the catchment. Average SRP concentrations in the lower Kennet reduced over time towards the target for good water quality. Critically, there was no corresponding reduction in chlorophyll-a concentration, the waters remaining eutrophic when set against standards for lakes.Following the up gradient input of the main water and SRP source (Wilton Water), SRP concentrations in the canal reduced down gradient to below detection limits at times near its junction with the Kennet downstream. However, chlorophyll concentrations in the canal were in an order of magnitude higher than in the river. This probably resulted from long water residence times and higher temperatures promoting progressive algal and suspended sediment generations that consumed SRP. The canal acted as a point source for sediment, algae and total phosphorus to the river especially during the summer months when boat traffic disturbed the canal's bottom sediments and the locks were being regularly opened. The short-term dynamics of this transfer was complex. For the canal and the supply source at Wilton Water, conditions remained hypertrophic when set against standards for lakes even when SRP concentrations were extremely low.     

Geochemical signals and source contributions to heavy metal (Cd, Zn, Pb, Cu) fluxes into the Gironde Estuary via its major tributaries

Daily measurements of water discharges and suspended particulate matter (SPM) concentrations and monthly sampling for trace element analyses (Cd, Zn, Pb and Cu) were conducted from 1999 to 2002 on the Garonne, Dordogne and Isle Rivers, the three main tributaries of the Gironde Estuary, France. Dissolved and particulate Cd, Zn, Pb and Cu concentrations in the Isle River were generally higher than those in the Garonne River, despite the known historical polymetallic pollution affecting the Lot-Garonne River system. Even if the relatively high dissolved metal concentrations in the Isle River may be of importance for the local ecosystem, metal inputs into the estuarine and coastal zones are mainly controlled by fluvial transport via the Garonne River. Characteristic element concentration ratios (e.g., Zn/Pb) in SPM and stream sediments from the Dordogne and Isle Rivers suggest two different metal source areas with distinct geochemical signals. Low Zn/Pb ratios (<8) and low Cu/Pb ratios (<0.8) have been attributed to upstream source zones in the Massif Central, featuring various ore deposits and mining areas. High Zn/Pb ratios were assigned to downstream sources (e.g., vineyards), partly explaining high Zn and Cu concentrations and high Cu/Pb ratios (>0.8) in SPM. Although SPM derived from the upstream parts of the studied watersheds may greatly contribute to the observed fluvial metal transport (up to approximately 80% for Pb), the results suggest that intensive agriculture also considerably influences gross metal (e.g., Zn, Cu) fluxes into the Gironde Estuary. Relative contributions of upstream and downstream source zones may vary from one year to another reflecting hydrological variations and/or reservoir management. Monitoring fluxes and identifying distinct geochemical signals from source areas in heterogeneous watersheds may greatly improve understanding of contaminant transport to the coast.     

Sewage-effluent phosphorus: a greater risk to river eutrophication than agricultural phosphorus?

Phosphorus (P) concentrations from water quality monitoring at 54 UK river sites across seven major lowland catchment systems are examined in relation to eutrophication risk and to the relative importance of point and diffuse sources. The over-riding evidence indicates that point (effluent) rather than diffuse (agricultural) sources of phosphorus provide the most significant risk for river eutrophication, even in rural areas with high agricultural phosphorus losses. Traditionally, the relative importance of point and diffuse sources has been assessed from annual P flux budgets, which are often dominated by diffuse inputs in storm runoff from intensively managed agricultural land. However, the ecological risk associated with nuisance algal growth in rivers is largely linked to soluble reactive phosphorus (SRP) concentrations during times of ecological sensitivity (spring/summer low-flow periods), when biological activity is at its highest. The relationships between SRP and total phosphorus (TP; total dissolved P+suspended particulate P) concentrations within UK rivers are evaluated in relation to flow and boron (B; a tracer of sewage effluent). SRP is the dominant P fraction (average 67% of TP) in all of the rivers monitored, with higher percentages at low flows. In most of the rivers the highest SRP concentrations occur under low-flow conditions and SRP concentrations are diluted as flows increase, which is indicative of point, rather than diffuse, sources. Strong positive correlations between SRP and B (also TP and B) across all the 54 river monitoring sites also confirm the primary importance of point source controls of phosphorus concentrations in these rivers, particularly during spring and summer low flows, which are times of greatest eutrophication risk. Particulate phosphorus (PP) may form a significant proportion of the phosphorus load to rivers, particularly during winter storm events, but this is of questionable relevance for river eutrophication. Although some of the agriculturally derived PP is retained as sediment on the river bed, in most cases this bed sediment showed potential for removal of SRP from the overlying river water during spring and summer low flows. Thus, bed sediments may well be helping to reduce SRP concentrations within the river at times of eutrophication risk. These findings have important implications for targeting environmental management controls for phosphorus more efficiently, in relation to the European Union Water Framework Directive requirements to maintain/improve the ecological quality of impacted lowland rivers. For the UK rivers examined here, our results demonstrate that an important starting point for reducing phosphorus concentrations to the levels approaching those required for ecological improvement, is to obtain better control over point source inputs, particularly small point sources discharging to ecologically sensitive rural/agricultural tributaries.     

High temporal resolution in situ measurement of the effective particle size characteristics of fluvial suspended sediment

This paper reports the use of a LISST-100 device to monitor the effective particle size characteristics of suspended sediment in situ, and at a quasi-continuous temporal resolution. The study site was located on the River Exe at Thorverton, Devon, UK. This device has not previously been utilized in studies of fluvial suspended sediment at the storm event scale, and existing studies of suspended sediment dynamics have not involved such a high temporal resolution for extended periods. An evaluation of the field performance of the instrument is presented, with respect to innovative data collection and analysis techniques. It was found that trends in the effective particle size distribution (EPSD) and degree of flocculation of suspended sediment at the study site were highly complex, and showed significant short-term variability that has not previously been documented in the fluvial environment. The collection of detailed records of EPSD facilitated interpretation of the dynamic evolution of the size characteristics of suspended sediment, in relation to its likely source and delivery and flocculation mechanisms. The influence of measurement frequency is considered in terms of its implications for future studies of the particle size of fluvial suspended sediment employing in situ data acquisition.     

Water Quality Management in the River Calder Catchment

T he PAPER DESCRIBES the many and complex water and sewage treatment problems in the River Calder valley, followed by summaries of the progress made to date and the plans that have been developed to eliminate these problems in the future. The final section describes how a sludge treatment and disposal strategy was evolved for the whole West Yorkshire conurbation, in effect the Calder valley plus the populous section of the Aire valley including the cities of Bradford and Leeds. The first phase of this strategy, the construction of a new dewatering and incineration facility at Esholt (Bradford) was in progress and plans for a second, larger installation in the Calder valley were being examined.     

Chlorophyll-a in the rivers of eastern England

Chlorophyll-a concentration variations are described for two major river basins in England, the Humber and the Thames and related to catchment characteristics and nutrient concentrations across a range of rural, agricultural and urban/industrial settings. For all the rivers there are strong seasonal variations, with concentrations peaking in the spring and summer time when biological activity is at its highest. However, there are large variations in the magnitude of the seasonal effects across the rivers. For the spring-summer low-flow periods, average concentrations of chlorophyll-a correlate with soluble reactive phosphorus (SRP). Chlorophyll-a is also correlated with particulate nitrogen (PN), organic carbon (POC) and suspended sediments. However, the strongest relationships are with catchment area and flow, where two straight line relationships are observed. The results indicate the importance of residence times for determining planktonic growth within the rivers. This is also indicated by the lack of chlorophyll-a response to lowering of SRP concentrations in several of the rivers in the area due to phosphorus stripping of effluents at major sewage treatment works. A key control on chlorophyll-a concentration may be the input of canal and reservoir waters during the growing period: this too relates to issues of residence times. However, there may well be a complex series of factors influencing residence time across the catchments due to features such as inhomogeneous flow within the catchments, a fractal distribution of stream channels that leads to a distribution of residence times and differences in planktonic inoculation sources. Industrial pollution on the Aire and Calder seems to have affected the relationship of chlorophyll-a with PN and POC. The results are discussed in relation to the Water Framework Directive.     

Seasonal variations and annual fluxes of arsenic in the Garonne, Dordogne and Isle Rivers, France

Daily measurements of water discharges and suspended particulate matter (SPM) concentrations and monthly analyses for arsenic were conducted from 1999 to 2005 on the Garonne, Dordogne and Isle Rivers, the three main tributaries of the Gironde Estuary, France. Despite the known historical polymetallic pollution affecting the Lot-Garonne River system, the highest As concentration level was observed in the Isle River. This was explained by the geological context and various Au/As deposits in this watershed. In the three studied rivers, dissolved As concentrations showed important seasonal variations with maximum values in summer. The dissolved As concentrations were closely related to water temperature and their increase in spring/summer appeared to be induced by water temperatures above approximately 15 degrees C, independently from discharge. The reduction of As(V) to more soluble As(III) and/or destruction of solid As carrier phases by micro-organisms could explain this observation, suggesting that temperature-dependent biogeochemical processes play an important role in controlling As partition and speciation in fluvial systems. Water and SPM fluxes in the Garonne River mainly control arsenic inputs into the Gironde Estuary and the downstream coastal zones. Based on the present data, we propose an empirical model to roughly estimate the annual dissolved and particulate As fluxes in the Garonne, Dordogne and Isle Rivers from annual water and SPM fluxes. The comparison of observed As fluxes and those estimated from the empirical model suggests that resuspension of historical, polluted reservoir sediments during a major flood accounted for approximately 50% of the annual As fluxes in 2003.     

The phosphorus budget of the Thame catchment,Oxfordshire: 2. Modelling

The phosphorus budget of the River Thame was modelled at a daily time scale, using estimates of diffuse and point source contributions of discharge. The model simulated suspended sediment (SS), soluble unreactive phosphorus (SUP), soluble reactive phosphorus (SRP) and particulate phosphorus (PP) concentrations within the main river and major tributaries. Diffuse source estimates of phosphorus loads were based on characteristic losses from identified main landscape classes, with hydrology described by a simple conceptual storage model. In-stream flow was modelled using a kinematic wave equation. Transfer of suspended sediment and phosphorus components was approximated by advection. In-stream sources and sinks included uptake and release of soluble reactive phosphorus by bed sediment, instant equilibration between SRP and the PP concentration on suspended sediment, and flow-related entrainment and deposition of suspended sediment. Simulations at sites within the catchment were compared with measurements made in 1998–1999. Results showed the P budget is dominated by mixing of diffuse and point source water, but some within-river processes have been shown to be capable of significantly influencing SRP concentrations. The development of a sediment entrainment and deposition component of the model has proved particularly valuable in emulating the hysteretic relationship between discharge and suspended sediment concentration in the river. It also provides a measure of available bed sediment.     

The spatial and temporal trends of Cd, Cu, Hg, Pb and Zn in Seine River floodplain deposits (1994-2000)

Fresh floodplain deposits (FD), from 11 key stations, covering the Seine mainstem and its major tributaries (Yonne, Marne and Oise Rivers), were sampled from 1994 to 2000. Background levels for Cd, Cu, Hg, Pb, and Zn were established using prehistoric FD and actual bed sediments collected in small forested sub-basins in the most upstream part of the basin. Throughout the Seine River Basin, FD contain elevated concentrations of Cd, Cu, Hg, Pb and Zn compared to local background values (by factors>twofold). In the Seine River Basin, trace element concentrations display substantial downstream increases as a result of increasing population densities, particularly from Greater Paris (10 million inhabitants), and reach their maxima at the river mouth (Poses). These elevated levels make the Seine one of the most heavily impacted rivers in the world. On the other hand, floodplain-associated trace element levels have declined over the past 7 years. This mirrors results from contemporaneous suspended sediment surveys at the river mouth for the 1984-1999 period. Most of these temporal declines appear to reflect reductions in industrial and domestic solid wastes discharged from the main Parisian sewage plant (Seine Aval).