River Yare Research Articles

The role of sediments as a source of metals in river catchments

Aquatic sediments are a known source of pollutants, but their impact on the quality of overlying waters is not easily quantified. Sediments are generally considered to behave as a sink for pollutants such as heavy metals in the aquatic environment, frequently acting as a source for their presence in waters, with implications for catchment management. This study aimed to calculate the contribution of sediments to metal levels in overlying waters, helping understand their role as a source of metals in river catchments. An aquivalence mass balance approach was modified to take into account both natural and anthropogenic influences and applied to assess sediment contribution in a reach of the River Yare in the UK. The rates of total metal transport from sediments to overlying waters were estimated to be 29.89gd−1 for cadmium (Cd), 1633.39gd−1 for lead (Pb), 8.29gd−1 for mercury (Hg) and 357.56gd−1 for nickel (Ni). The results from the case study demonstrated that sediments could be a significant source of metal emissions in river catchments. The calculations proposed in the paper could be useful in developing strategies for sediment management, not only to improve and/or maintain quality of sediments but also to inform the selection of measures of pollution control for the catchment.

The unusual mineral vaterite in shells of the freshwater bivalve Corbicula fluminea from the UK

Asian clams (Corbicula fluminea) with abnormally thickened shell valves were found in four rivers in the UK (Rivers Yare, Waveney, Thames and New Bedford River). The material making up these malformations was the rare calcium carbonate polymorph vaterite. Vaterite is seldom found in the natural environment because it is less stable than the other calcium carbonate polymorphs (aragonite and calcite). In the few reported cases of vaterite formation in molluscs, it is usually related to unusual biomineralisation events such as shell regeneration, pearls and initial stages of shell formation. We compared two populations from the Rivers Yare and Waveney in the Norfolk Broads, UK, one (River Waveney) displaying dominantly the normal Corbicula shell form with aragonitic shells. In the River Yare population, all individuals sampled had shell deformations to different extents. These deformations were apparent as bulges on the inside of the ventral shell margin. X-ray diffraction confirmed that the shell material in the bulges of recently collected clams was vaterite. Other parts of the deformed shells were aragonitic. The shell deformations alter the shell morphology, leading to higher and wider shells. The shell microstructure is fibrous in the vateritic parts and crossed-lamellar in the aragonitic parts of deformed or non-deformed shells. The cause for the malformations is probably a disrupted biomineralisation process in the bivalves. Fossil Corbicula specimens from the late Pleistocene had similar deformations, suggesting that this is not a response to anthropogenic causes, such as pollution.

Modelling the Long-Term Fate of Mercury in a Lowland Tidal River. II. Calibration and Comparison of Two Models with Field Data

This study presents results of the application of two-one-dimensional/dynamic-deterministic models developed to evaluate and predict mercury contamination of a lowland river, the River Yare, Norfolk, UK. As a general indication of model performance, MODEL 1 produced a prediction of the overall mass balance of mercury in the River Yare that was 6% lower than an estimate, based on measurements, and 10% lower than the prediction provided by MODEL 2. The mercury surficial sediment concentrations calculated by MODEL 1 varied from 0.46 mg kg(-1) in 1995 (Reach 3) to 3.55 mg kg(-1) in 1986 (Reaches 6 and 7), whereas the minimum mercury concentration calculated by MODEL 2 was 0.42 mg kg(-1) in 1995 (Reach 3) and the maximum was 8.45 mg kg(-1) in 1986 (Reach 5). Average mercury concentrations experimentally measured in surficial sediments ranged from 0.47 mg kg(-1) in 1995 (Reach 3) to 8.10 mg kg(-1) in 1986 (Reach 6). MODEL 2 gave an excellent prediction of mercury in fish flesh compared with the results obtained from the actual analysis of fish flesh. Both models demonstrated good ability to simulate actual values determined for all compartments, water, surficial sediments, bottom sediments, and fish.

Modelling the Long-Term Fate of Mercury in a Lowland Tidal River. I. Description of Two Finite Segment Models

Crucial determinants of the potential effects of mercury in aquatic ecosystems are the speciation, partitioning, and cycling of its various species. These processes are affected by site-specific factors, such as water chemistry, sediment transport, and hydrodynamics. This study presents two different approaches to the development of one-dimensional/dynamic-deterministic models for the evaluation and prediction of mercury contamination in a lowland tidal river, the River Yare (Norfolk, UK). The models described here were developed to encompass the entire river system and address the mass balance of mercury in a multicompartment system, including tidal reversal and saline limit. The models were focused on river systems, with the River Yare being used as a case study because previous modelling studies have been centred on lakes and wetlands whilst there is a paucity of information for rivers. Initial comparisons with actual measured water parameters (salinity and suspended solids) indicate that both models exhibit good agreement with the actual values.

Distribution of mercury and methylmercury in the sediments of a lowland river system

Concentrations of total mercury (T-Hg) and methylmercury (MeHg) were determined in surficial sediments from the River Yare, Norfolk, UK over the period 1986–1998, to assess the temporal and spatial trends of contamination arising from a historical point source discharge. The results demonstrate that the spatial distribution pattern follows that of a distinct pollution plume in the sediments with an initial increase 2–3 km downstream from the point source discharge at Whitlingham sewage treatment works (STW) outfall. Temporally, this pollution plume remains evident, although there has been an overall decline in the mean T-Hg concentrations from 5.4 in 1986 to 1.8 mg kg −1 in 1998. The major factor for this improvement has been the reduction in discharge of metals from the STW, together with burial by a fresh overlay of uncontaminated sediments. MeHg concentrations also exhibited a dispersed pollution plume. Mean concentrations of MeHg fluctuated during the study period between 3.3 and 8.5 μg kg −1 . There has been no concomitant decline in MeHg concentrations over this period. MeHg was found to constitute less than 1% of T-Hg concentrations in the sediments. The weak correlations observed between T-Hg and MeHg concentrations indicate external environmental factors have a significant influence on determining MeHg concentrations in the sedimentary compartment.

Spatial distribution of mercury in the sediments and riparian environment of the River Yare, Norfolk, UK

Concentrations of total mercury (T-Hg) were determined in sediments and riparian (bankside) soils from the River Yare, Norfolk, UK to assess the current extent of contamination arising from a historical point source discharge. The results demonstrate that the spatial distribution pattern in surficial sediments and soils follows that of a distinct pollution plume with an initial increase 2–3 km downstream from the point source discharge at Whitlingham Sewage Treatment Works (STW) outfall. Average T-Hg concentrations in the surficial sediments ranged from 0.1 to 8.13 mg kg −1; bankside soil concentrations ranged from 0.1 to 2.63 mg kg −1. There has been a decline in downstream background sediment concentrations of Hg over time. This is likely to be the result of burial by fresh relatively uncontaminated sediments and possibly in the lower reach as a consequence of the influence of the freshwater–saline interface occurring near Cantley. Channel morphology was also shown to be an important factor in determining the large variations of Hg concentrations between sample points within transects. The predominant source of Hg to the soils appears to be due to dredging and the deposition of sediments during flooding.

Comparison of Mercury Bioaccumulation in Eel (Anguilla Anguilla) and Roach (Rutilus Rutilus) from River Systems in East Anglia, UK I. Concentrations in Fish Tissue

Concentrations of total mercury (T-Hg) were measured in eel and roach from five selected rivers in East Anglia, U.K, to determine Hg bioaccumulation in fish throughout the region. Levels of T-Hg in sediment and river water were also analysed to assess their potential as pathways to the fish. Accumulated Hg levels in River Yare eel and roach continue to exhibit a strong positive relationship with surface sediment Hg levels, which are declining with time. Mercury in muscle from all sampled fish were below the limit set by the EU Directive (93/351/EEC). Analysis of muscle:liver (M:L) ratios confirm that eel from all sites are in equilibrium with their environment. Various statistical methods (single factor analysis of variance, Spearman's correlation coefficients) were performed on the experimentally derived data on mercury concentrations in fish flesh. Significant correlations were noted for accumulated Hg in fish flesh with length and weight in eel, and length, weight and age in roach.

Comparison of Mercury Bioaccumulation in Eel (Anguilla Anguilla) and Roach (Rutilus Rutilus) from River Systems in East Anglia, UK II. Sources of Mercury to Fish and the Role of Atmospheric Deposition

Bulk deposition and soils were analysed for total mercury (T-Hg) from five sites in East Anglia, U.K., in order to evaluate atmospheric deposition as a source of Hg to the region, and to determine whether Hg in soils constitutes a source of Hg to fish. Levels of Cr, Cu, Ni, Pb and Zn were also measured in soils to determine the strength of association with Hg. Average mercury concentrations in soils were 0.135 mg kg−1 and were above the previously reported UK average of 0.098 mg kg−1. All sites revealed an increasing north to south gradient of anthropogenic heavy metal loading to surface soils with enhanced loading for Hg, Cu, Pb, and Zn at the River Yare location. Levels of T-Hg in bulk deposition displayed a similar gradient, averaging 89 ng l−1 for the region, suggesting atmospheric deposition as a likely source of Hg to soils and biota (fish) in East Anglia.

Mercury Contamination of the EEL (Anguilla Anguilla) and Roach (Rutilus Rutilus) in East Anglia, UK

The muscle tissue total mercury (THg) and organomercury (OrHg) concentrations of eel (Anguilla anguilla) and roach (Rutilus rutilis) from the Hg-contaminated River Yare and the uncontaminated Ormesby Broad were compared to their respective bed sediment THg and OrHg concentrations in order to determine if fish in the River Yare had begun to approach 'background' levels. While eel from the Yare had higher flesh concentrations (260 μg kg-1) than those from Ormesby Broad (102 μg kg- 1), roach were found to have similar concentrations regardless of location (55 and 54 μg kg-1 for Yare and Ormesby respectively). However, roach in the Yare had significantly higher body burdens of Hg and organomercury, which when analysed over time (1985–95) showed a decreasing trend approaching the levels observed in fish from Ormesby Broad, suggesting that roach are an overall better biomonitor of contamination then eel. This said, the elevated levels of Hg found in fish from Ormesby Broad indicate the existence of a diffuse source such as atmospheric deposition to the surface waters of East Anglia.

Factors controlling the accumulation of metals within fluvial systems

The magnitude and distribution of European Community (EC) regulated List I and List II metals and metalloids have been investigated in two lowland river systems in East Anglia, U.K. A combination of sediment and water quality data identified municipal sewage treatment work discharges as the main metal input sources to the river systems and identified two main areas of metal contamination: the Pix Brook, downstream of Letchworth STW on the River Ivel, and a 14 km enrichment zone adjacent to Whitlingham STW on the River Yare. The basement geology, flow dynamics, distance from point sources and sediment type were identified as important controls upon the magnitude and spatial distribution of metal contaminants.

Spatial distribution and seasonal changes in methylmercury concentrations in shallow lakes

The environmental factors governing the distribution and behaviour of total and methylmercury within mercury contaminated shallow lakes, associated with the River Yare, Norfolk, UK, have been assessed in situ through the use of sediment cores. These were analysed for microbial and chemical changes on both a temporal and spatial scale. The distribution of total mercury proved to be site dependent and related to the hydrology, sediment transport dynamics, the degree of sediment disturbance and distance from the contamination source. The core profiles revealed a subsurface peak in total mercury with maximum concentrations residing at depths of 12 and 36 cm, depending upon location, with enrichment extending down to depths in excess of 88 cm. This vertical distribution was deemed to reflect historical emission in the late 1960s and early 1970s rather than post depositional migration effects. The distribution of methylmercury was distinct from that of its inorganic counterpart since it also displayed temporal variability with highest concentrations occurring in the spring and summer. Maximum concentrations also prevailed in the uppermost 12 cm of sediment, with peak loadings at or just below the sediment/water interface and detectable levels being restricted to the upper 36 cm. The temporal and spatial behaviour of methylmercury appeared to reflect variations in redox potential, the availability of the Hg2+ ion and the nature of microbial populations.

The use of Landsat imagery to map fluvial sediment discharge into coastal waters

The sediment discharge of the river Yare, via Breydon Water estuary, into the North Sea has been studied. Sixty samples were taken, the average of each sample in the band TM1 was used to estimate the concentrations of suspended solids. Sixty samples were used to extract information from the reflective bands TM1–TM4. The spatial distribution of suspended solids as well as the spatial and vertical extent of different turbidity levels were then detected, estimated and mapped. Based on this information the water circulation pattern at the mouth of river Yare was identified and mapped. The influence of wind velocity and direction, as well as the tidal current conditions prior to and during the image time, on turbidity and water circulation patterns were examined. The tidal influence was found to be the most significant factor in shaping and guiding water circulation near the mouth of river Yare.

Distribution of heavy metals in the river yare and its associated broads III. Lead and zinc

The magnitude and spatial distribution of lead and zinc within the bottom sediments of the River Yare, Norfolk, have been investigated, together with effects imposed by grain size, sediment organic content and channel morphological controls. Metal concentrations varied widely, ranging between 10.7 and 728 mg Pb kg −1 and between 23 and 1190 mg Zn kg −1, producing maximum enrichments of 22 and 27 times the Yare's natural background levels of lead and zinc, respectively. Non-point source metal inputs appeared to be the dominant mode of entry into the system. Sediment texture, particularly its organic content, appeared to be the principal factor controlling metal accumulation. Mean lead and zinc concentrations increased by a factor of four as the proportion of volatile solids increased from 0.5 to 25%. The influence of grain size appeared to be limited to its effects upon sediment transport and sediment organic content rather than to the adsorptive capacity of different particle sizes. Lead and zinc concentrations did not increase with decreasing particle size, but showed elevated loadings in the 1000-250 and 250-64 μm particle size ranges. A shift in dominant metal/particulate associations was observed towards the finer size fractions with increased distance downstream. This probably reflected disaggregation effects during sediment transport and the contrasting nature of metallic inputs, from the coarser runoff derivatives in the upper urban stretch to the finer, highly organic particles released in STW final effluent further downstream.

Distribution of heavy metals in the River Yare and its associated broads I. Mercury and methylmercury

A detailed sediment sampling program of the River Yare, Norfolk, and adjoining Broad systems was undertaken to evaluate the magnitude, spatial distribution and vertical extent of mercury contamination arising from a point source discharge. Particle size fractionation, total organic loadings and textural properties of the sediments were determined to provide an insight into the potential factors dictating mercury accumulation. Total mercury concentrations ranged between 0.05 and 32.9 mg kg −1 with mean transect loadings of 0.81–11.9 mg kg −1, which corresponded to 2–30-fold increases in sediment mercury concentrations over published background levels. Mercury contamination displayed the characteristic profile of a pollution plume derived from a point source, despite spatial variability which reflected the controls imposed by channel morphology, underlying geology, sediment type and catchment hydrology. Mercury occurred predominantly in surface deposits in upstream areas, principally in association with the 2000–1000 μm size fraction, but shifted towards subsurface enrichment in the downstream reach. Mercury association with smaller grain size fractions occurred with increased distance from the point source, at depth within core profiles and within the shallower Broad systems. Methyl mercury concentrations ranged between <0.7 and 13.2 μg kg −1 in surficial sediments, which represented between 0.01 and 0.2% of the total mercury burden. A crude mercury mass balance indicated that, since industrial mercury discharge began in 1964, 50% of the total released could be accounted for in the sedimentary compartment.

Distribution of heavy metals in the River Yare and its associated broads II. Copper and cadmium

The magnitude and spatial distribution of copper and cadmium in the fluvial sediments of the River Yare, Norfolk, have been investigated and related to the controls imposed by channel morphology, particle size and sediment organic content. Copper loadings ranged between 5 and 375 mg kg −1 and displayed the characteristic profile of a pollution plume of point source origin, with a peak located 1–2 km downstream from a major sewage treatment works outlet. The distribution of cadmium appeared to reflect smaller non-point source inputs, with sediment concentrations ranging between 0.16 and 7.28 mg kg −1, producing an average study reach concentration of 3.35 mg Cdkkg −1. Spatial variability in metal loadings reflected the heterogeneous nature of the bottom deposits as dictated by the flow regime, channel morphology and baserock geology. Sediment texture, particularly in terms of organic content, appeared to be the prime factor controlling metal accumulation, especially in coarser calcareous sediments, where reduced organic loadings [<10% volatile solids (VS)] may have limited the metal-binding capacity of the sediment. Copper and cadmium appeared to be concentrated in the 1000–250 and 250–64 μm fractions, with little evidence of metal enrichment with decreasing particle size. This has been linked to the abundance of organic material in the medium to fine sand size fractions. Subsurface metal enrichment occurred within a central contaminated zone and may have reflected differential dilution of top sediment layers by uncontaminated bank material, or conversely metal depletion at the sediment-water interface coupled with metal complexation at depth.

British Sugar Corporation at Cantley, on the River Yare

British Sugar Corporation at Cantley, on the River Yare

An Attempt to Remove Coypus (Myocastor coypus) from a Wetland Habitat in East Anglia

(1) Coypus, Myocastor coypus Molina, are introduced semi-aquatic rodents. They cause serious damage to crops, drainage systems (through burrowing) and native plant communities in the East Anglian wetlands. (2) A trial was carried out to test whether it was possible to eradicate coypus from an area of wetland in Norfolk using cage trapping. The area was a 30-km stretch of the flood plain of the River Yare between Norwich and Reedham. Three trappers worked full-time for 6 years in 1975-81. Trapping intensity was 59% higher than in control trapping elsewhere in East Anglia. (3) Coypus were completely removed from the western part of the study area, none being caught for the last 2-5 years. Some coypus continued to be caught in the east and particularly near the eastern perimeter. A number of lines of evidence, including the movements of tagged animals, showed that the animals in the east were immigrants from extensive marshland outside the area, where trapping was carried out at a lower intensity by the Coypu Control organization. The absence of field evidence of coypus, especially their faeces, in areas that seemed to have been cleared, suggested that there were no 'trap shy' animals. (4) Non-target species were released when the traps were inspected each day and included moorhens, mallards, water rails, water voles, and common rats. Capture rates during and after the trapping exercise showed that trapping had no significant effect on any non-target populations; most species increased over the first 4 years of intense trapping. Cold winters may sometimes have reduced numbers, particularly those of water rails. Some non-target populations also declined in 1979 and 1980 for unknown reasons. (5) The results obtained were part of the evidence considered by the Coypu Strategy Group, which recommended an attempt to eradicate coypus from Britain. This recommendation was accepted and a 10-year campaign was started in 1981. Coypus are not endangered in South America although their numbers and range have been reduced.

METHODS

Crown protection for new Yarmouth bridge. Crown has been chosen by the Tighe Group, Europe's leading industrial painting contractors, to provide the all‐important paint systems covering the huge new Breydon Bridge which is to carry a by‐pass road over the River Yare in Great Yarmouth.

Investigation into wind effects on Breydon bascule bridge

Breyton bridge is a nine-span viaduct across the River Yare which will form part of the Great Yarmouth western bypass now under construction. The span over the navigation channel is a single leaf bascule bridge linked to an overhead counterweight. During the design process the overhead counterweight arms were investigated to ascertain their vulnerability to wind-induced excitation. Consultation with the National Maritime Institute revealed that within the range of depth contained in the tapered arms there was a risk of vortex excitation in the fundamental vertical mode, although because the arms were tapered it was difficult to predict this response on the basis of any previous tests. Because of this doubt a 1:20 scale model test was carried out in a wind tunnel at NMI. It revealed only weak excitation in the range of design wind speeds. It was concluded that no special precautions need to be taken on the full-scale structure. Calculations predicted stable conditions for the road deck structure when closed to shipping, but there was less certainty of its performance under wind excitation when raised to permit shipping to pass: this was tested in two different ways.

Beach profiles at Gorleston and Great Yarmouth

The method of empirical eigenfunction analysis described by Winant et al. (1975) is applied to beach profile data from Gorleston and Great Yarmouth, Norfolk. The eigenfunction corresponding to the largest eigenvalue is the principle beach function which is closely related to the mean beach profile. The second eigenfunction is associated with significant beach changes at Gorleston and the third with small changes at Yarmouth. The profile data run from 1966 to 1976 at irregular time intervals. The analysis suggests a rather stable beach at Yarmouth, whereas the beach at Gorleston appears to have experienced a significant change during this decade. Fluctuations in the wind data for Gorleston for this period are compared with the variations in the beach profile. Some of the differences between the Yarmouth and Gorleston beaches are due to the littoral drift barrier provided by the breakwaters at the entrance to the River Yare.