British Rivers Research Articles

River response to rapid Holocene environmental change: evidence and explanation in British catchments

Since the late 1980s our understanding of the relationship between climate, land-use and Holocene river development in Britain has changed radically. Conceptually simplistic and data-poor models of people–river environment interaction, many of which considered human activity alone to be the control of Holocene flooding and alluviation, have been replaced by more data-rich models that explain river behaviour in terms of a continuum of climate and anthropogenic drivers, individually operating over a range of temporal and spatial scales. One of the key factors in this paradigm shift has been the significant increase in the number of 14C-dated fluvial units that has itself recently facilitated the application of meta-analysis techniques to large fluvial data sets. These analyses have produced the first probability-based national and regional reconstructions of Holocene flooding in the British Isles that can be correlated with independent, high-resolution hydro-climate records. This paper critically reviews the major findings of this new research focusing on process-based causality relationships in fluvial systems and quantifying how environmental signals are propagated in river basins and preserved in landform and sedimentary sequences. By using cumulative probability density function (CPDF) plots of fluvial 14C dates that have been classified on the basis of sedimentary environment and evidence for changing depositional regime, 17 multi-centennial length periods of flooding and river instability during the Holocene are identified in the UK. The scale and timing of these episodes vary regionally and correlations can be made with a range of climate proxy records, including the North Atlantic drift-ice index, glacier variations in Europe, and mire surface wetness and water-table reconstructions. A new analysis of overbank floodplain sedimentation rates points to an acceleration after ca 1000 cal. BP, which can be related to the agricultural revolution of the Middle Ages. This is the first time that an unequivocal anthropogenic signal, affecting most British rivers, can be recognised in the Holocene fluvial record of the UK and it appears to have been a broadly synchronous ‘event’ in many catchments.

Statistical Modeling Suggests that Antiandrogens in Effluents from Wastewater Treatment Works Contribute to Widespread Sexual Disruption in Fish Living in English Rivers

BackgroundThe widespread occurrence of feminized male fish downstream of some wastewater treatment works has led to substantial interest from ecologists and public health professionals. This concern stems from the view that the effects observed have a parallel in humans, and that both phenomena are caused by exposure to mixtures of contaminants that interfere with reproductive development. The evidence for a “wildlife–human connection” is, however, weak: Testicular dysgenesis syndrome, seen in human males, is most easily reproduced in rodent models by exposure to mixtures of antiandrogenic chemicals. In contrast, the accepted explanation for feminization of wild male fish is that it results mainly from exposure to steroidal estrogens originating primarily from human excretion.ObjectivesWe sought to further explore the hypothesis that endocrine disruption in fish is multicausal, resulting from exposure to mixtures of chemicals with both estrogenic and antiandrogenic properties.MethodsWe used hierarchical generalized linear and generalized additive statistical modeling to explore the associations between modeled concentrations and activities of estrogenic and antiandrogenic chemicals in 30 U.K. rivers and feminized responses seen in wild fish living in these rivers.ResultsIn addition to the estrogenic substances, antiandrogenic activity was prevalent in almost all treated sewage effluents tested. Further, the results of the modeling demonstrated that feminizing effects in wild fish could be best modeled as a function of their predicted exposure to both antiandrogens and estrogens or to antiandrogens alone.ConclusionThe results provide a strong argument for a multicausal etiology of widespread feminization of wild fish in U.K. rivers involving contributions from both steroidal estrogens and xenoestrogens and from other (as yet unknown) contaminants with antiandrogenic properties. These results may add further credence to the hypothesis that endocrine-disrupting effects seen in wild fish and in humans are caused by similar combinations of endocrine-disrupting chemical cocktails.

Roach, Sex, and Gender-Bending Chemicals: The Feminization of Wild Fish in English Rivers

Feminization of the male roach, Rutilus rutilus, a freshwater, group-spawning fish, is widespread in English rivers; among the causative agents are natural and synthetic steroidal estrogens and chemicals that mimic estrogens. In feminized male roach, concentrations of the egg-yolk protein vitellogenin are elevated, sex steroid hormone dynamics are altered, and gonad development is disrupted (most notably, a female reproductive duct or developing eggs [oocytes] are present in the testis). In some English rivers containing high levels of estrogens, all male roach sampled have been feminized to varying degrees. In the more severely affected males, individuals produce low-quality sperm with a reduced capability for fertilization. Laboratory studies have shown that the environmental estrogens responsible for inducing gonadal feminization in roach can also alter reproductive behavior, disrupting normal breeding dynamics (parentage) in the zebrafish, another group-spawning fish. Together these findings indicate ...

The effect of severe drought on the dissolved organic carbon (DOC) concentration and flux from British rivers

The effect of severe drought on the biogeochemistry of dissolved organic carbon (DOC) production has been proposed as a possible explanation of the widespread observed increase in the flux and concentration of DOC in sub-boreal catchments across the northern hemisphere. It compares the pattern and extent of DOC increases to the pattern and extent of severe droughts. It also considers the effect of the two most severe droughts during the period of the available DOC records and includes DOC records from 97 sites. This study derives five different drought severity indices and compares these to the observed increase in DOC over the 4-year period after each severe drought. The results show no visual correlation between drought indices and trends in either DOC concentration or flux. Decreasing DOC fluxes and concentrations were observed in the areas that had experienced severe droughts, even in peat-covered catchments. Using analysis of variance (ANOVA) and multiple linear regressions, no consistent or significant pattern of DOC increase after severe drought could be distinguished. This study does not exclude a role for drought in causing the observed DOC increases, but it suggests that the role of drought in DOC is limited to some individual catchments or some peat-covered headwaters.

Modelling selected implications of potential future climate change on the archaeological resource of river catchments: an application of geographical information systems

This paper outlines the use of geographical information systems for predicting the possible implications of future climate change (as suggested by General Circulation Models) on the archaeological resource of selected parts of two major British river systems, the Trent and Yorkshire Ouse. The effects of future climatic change on the historic environment are likely to come from both natural 'system' responses, such as increased bank erosion and valley floor sedimentation, as well as the human adaptive responses selected to manage the impacts of climate change. The models described in this paper allow predictions to be made and quantified about how selected natural and anthropogenic responses may impact upon the archaeological resource. Such approaches, which are relatively rapid to implement and low cost, provide an important management tool for guiding policy makers and heritage managers in the face of changing climates.

Dissolved and total organic and inorganic carbon in some British rivers

Rivers transport both organic and inorganic carbon from their sources to the sea. Results of ~800 organic and inorganic analyses from various British rivers of contrasting size and land use are presented here: (1) the headwater River Tern, a rural river of 852 km2 catchment; (2) the Ouseburn, a small urban 55 km2 catchment; (3) the River Tyne, a larger river system of ~3000 km2 catchment; (4) a spatial survey from 205 sample sites on ~60 rivers from SW England. We found that, with the exception of peat‐rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO3 − , with DIC concentrations highest in highly urbanised catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognised anthropogenic inorganic carbon input to urban rivers.

Trends in DOC concentration in Great Britain

Increasing DOC concentrations in rivers of boreal and sub-boreal regions have been a widely observed phenomena. However, individual studies have been limited in time and space and this has limited the ability to test hypotheses of the explanation of the observed increases. This study examines 315 records from across Britain all of which are at least 10 years in length up to 2002, but with some records extending back to 1975 and combines these with results from 198 sites from a previous study. The study covers catchment areas up to 9948 km2. The results show that: Of the 315 records analysed, 216 showed a significant increase but 55 showed a significant decrease. This is the first time that significant long-term decreases in DOC concentration have been documented for British rivers. Trends in DOC concentration ranged from −5.7% to 16% annual percentage change. Although increasing trends are predominantly in catchments with peat covered headwaters, some peat catchment also show significant decreases. Some sites which show significant decreases over 10-year time periods exhibit significant increases over longer term records (23 years). Regional trends in DOC concentration cannot be explained by spatial or temporal trends in atmospheric deposition of acidity, oxides of N, and non-marine S. Further, trends in DOC concentrations do not appear to correlate with the occurrence of droughts.

Gravel extraction and planform change in a wandering gravel-bed river: The River Wear, Northern England

Within-channel alluvial gravel extraction is one of the most important forms of anthropogenically induced morphological change in river channels. In British rivers commercial gravel extraction was widespread between the 1930s and 1960s, and limited gravel extraction operations to reduce flood risk or maintain navigation continue to the present day. Despite this, gravel extraction has received little attention in UK river studies. This paper examines the significance of within-channel gravel extraction, during the period 1945–1960, on the planform of the River Wear in northern England. The study focuses on two 3 km piedmont reaches at Wolsingham and Harperley Park, located at the margin of the upland zone. Examination of detailed archival accounts of the gravel extraction operations, supplemented by the analysis of aerial photographs has enabled the impact of gravel extraction on the channel of the River Wear to be determined. Sediment budget calculations suggest large sediment deficits in both study reaches, however, assessing potential impacts simply in terms of a sediment deficit may be misleading as channel adjustments depend on local factors and a detailed consideration of the reach-scale sediment budget. Differences in the nature of channel adjustments of both reaches were found to be primarily a function of the method of gravel extraction employed. Overall patterns of channel change along the extraction reaches, over the past 150 years, were similar to reaches where gravel extraction was not practiced. This highlights the difficulty of trying to establish the significance of different processes where both local (gravel extraction) and catchment-scale factors (climate and land use) are operating.

A long‐term study of population characteristics and downstream migrations of the European eel Anguilla anguilla (L.) and the effects of a migration barrier in the Girnock Burn, north‐east Scotland

Downstream migrations and population characteristics of eels Anguilla anguilla were studied between 1967–1982 and 2002–2005 using a fish trap and electrofishing in the Girnock Burn, a small oligotrophic upland sub‐catchment of the River Dee, north‐east Scotland, 70 km from the tidal limit. In limited mark‐recapture studies, 9% of eels were recaptured up to three times and 97% of all recaptures were made at the same electrofishing site. The recaptured eels had a low mean growth rate of c. 13 mm year−1. Smaller eels appeared to show preferences for shallower habitats with small boulder and gravel–sand substrata. Trap catches exhibited seasonal modes in total length at 140–180 mm in late spring, and 320–340 mm in early autumn, probably relating to water temperatures and discharges. From other studies, it is inferred that the spring mode comprised sexually undifferentiated nomadic eels and the autumn mode differentiated males beginning their spawning migration. Large female eels were rare. The fish trap appears to have formed a major barrier to upstream migration since its construction in 1966. In‐stream density has decreased significantly since then from 16 to three eels 100 m−2, biomass from 260 to 78 g 100 m−2 and emigrants from 700 to 100 individuals year−1. Emigrants have comprised c. 5% of the standing stock year−1 since the 1970s. The proportion of larger differentiated eels in the Girnock Burn has, however, remained relatively constant and escapement has been c. 100–200 (probably male) eels year−1 since the late 1960s. Evidence, including that from other northerly British rivers, is reviewed to assess the possible impacts of Europe‐wide declines in glass eel recruitment since the 1980s. It is recommended that the data series be maintained, plus further sex determination and ageing studies. Installation of an upstream trap to capture immigrants and studies of recolonization are proposed.

Field testing the AWIC index for detecting acidification in British streams

Using data from 132 acid-sensitive streams in Wales and Scotland from two available data sets, we tested a recently proposed indicator system that uses aquatic invertebrates to detect acidification in British rivers, the Acid Water Indicator Community (AWIC). Although many sites held less than a quarter of AWIC scoring taxa, index values at sites in both data sets correlated significantly with acid-base variables including pH, calcium concentration, alkalinity and dissolved aluminium. Relationships with acid-base status during acid episodes were particularly strong in the more comprehensive test set. Strong correlations between the AWIC index and pH in a subset of sites from Scotland indicated potential for some extrapolation beyond the initial calibration regions of England and Wales. Despite considerable pH variability within AWIC classes, measured base-flow pH was within 0.5 pH units of values expected from invertebrates at over 55-70 % of test sites, and within 1 pH unit at 87-100 %. This compares favourably with direct pH measurement, where samples at fortnightly-monthly intervals are typically required to confidently estimate mean pH within 0.7-1.2 pH units. These data, drawn from a realistic application, illustrate the potential accuracy and integrating value of invertebrate bioassessment in acid-sensitive waters. Further developments should involve more specific identification and targeted calibration to i) improve discrimination between sensitive streams of contrasting acidity; ii) further improve the accuracy of pH determination based on invertebrates; iii) avoid the apparent over-estimation of pH in the lower AWIC classes; iv) clearly differentiate between acid-sensitive and acidified streams.

Are River Bioassessment Methods using Macroinvertebrates Applicable to Wetlands?

A predictive model, incorporating macroinvertebrate and environmental data, similar to that developed for Australian rivers (AUSRIVAS) and British rivers (RIVPACS) was constructed using a dataset collected from 23 reference (least altered) wetlands on the Swan Coastal Plain, Western Australia, sampled in summer and spring, 1989 and spring, 1990. Four main groups of reference wetlands were identified by UPGMA classification (using the Bray–Curtis dissimilarity measure). Distinguishing environmental variables identified by Stepwise Multiple Discriminant Function Analysis were: calcium, colour (gilvin), latitude, longitude, sodium and organic carbon. Observed to expected ratios of taxa with a >50% chance of occurrence (OE50) derived from the model for a suite of 23 test wetlands sampled in spring, 1997, were significantly correlated with pH and the depth of the sampling sites. Greater discrimination between the test wetlands was provided by the OE50 ratios than either raw richness (number of families) or a biotic index (SWAMPS). Results obtained for a subset of 11 test wetlands sampled with both a rapid bioassessment protocol (incorporating field picking of 200 invertebrates collected in 2 min sweeps from selected habitats) and a semi-quantitative protocol (incorporating laboratory picking of all invertebrates collected in sweeps along 10 m transects at randomly allocated sites) were not significantly different, indicating that the former could be used to reduce the time and costs associated with macroinvertebrate-based wetland monitoring programs. In addition to providing an objective method of assessing wetland condition, predictive modelling provides a list of taxa expected to occur under reference conditions, which can be used as a target in wetland restoration programs. The probable impediment to widespread adoption of predictive modelling for wetland bioassessment is the need to produce models tailored to specific geographic regions and specific climatic conditions. This may incur significant costs in countries, such as Australia, which span a wide range of climatic zones.

The development and application of a database of radiocarbon-dated Holocene fluvial deposits in Great Britain

This paper reports on the development of a British database of 14C dated Holocene fluvial units over the last 15 years. Since its inception in 1989, the database has undergone substantial expansion, refinement and improvement together with considerable methodological development, so that today it serves as a powerful research tool for investigating the spatial and temporal dynamics of Holocene river development and flooding in Great Britain. The improved analytical method is here applied to the currently existing database by examining datasets of 14C dated fluvial units from river basins that lie within and beyond the limits of Late Devensian glaciation. This analysis indicates how the contrasted conditions in these two types of river environment have, to an extent, led to divergent records of flooding in response to Holocene climate and land-use change. However, even in the contrasting sedimentary records of upland glaciated, and lowland unglaciated river basins, six corresponding episodes of increased flood frequency are identified at c. 5730, c. 3540, c. 2730, c. 2280, c. 660 and c. 570 cal. BP. These represent widespread common responses from British river systems to large-scale changes in climate. The method of database construction and analysis outlined and demonstrated in this paper could be readily adopted in other parts of the world to improve our understanding of Holocene river behaviour at the continental- and global-scale.

Riverine Habitat Requirements of the White–Clawed Crayfish, <i>Austropotamobius pallipes</i>

Ireland remains an important refuge for the freshwater crayfish Austropotamobius pallipes. To determine factors that influence their riverine distribution, forty rivers or tributaries of rivers that flow into Upper and Lower Lough Erne were sampled and surveyed. The nineteen sites where crayfish occurred had more bedrock and moss than those without crayfish, indicating the importance of a stable substrate and an indirect source of food. A subset of these sites, for which hydrochemical data were available, showed greater water hardness where crayfish were present, indicating that a high calcium water content is important to these animals. However, neither biological water quality nor invertebrate community structure varied between sites where crayfish were present and sites where they were absent. This indicates that biological factors have little influence on the presence of crayfish in a river and that crayfish influence biological water quality to a limited degree. M.B. Gallagher, J.T.A. Dick and R.W. Elwood (corresponding author; e-mail: r.elwood@qub.ac.uk), School of Biology and Biochemistry, Queen's University Belfast, Belfast BT9 7BL, Northern Ireland. Received 21 April 2004. Read 2 June 2005. Published 28 February 2006. INTRODUCTION The white-clawed crayfish, Austropotamobius pallipes, was previously widespread in mainland Europe, Great Britain and Ireland, but its distribution and abundance has declined in recent years due to habitat destruction, pollution (Holdich 1991) and the introduction of exotic crayfish (Holdich 1998; Holdich and Gherardi 1999). These exotics tend to be larger, and they compete for resources (Capelli and Munjal 1982; Butler and Stein 1985; S?derback 1991). American exotics are also carriers of the crayfish plague, Aphanomyces astaci, which can eliminate native populations (Capelli and Munjal 1982; Holdich 1998; Holdich and Gherardi 1999). Austropotamobius pallipes has been classified as vulnerable in the IUCN Red List (Groombridge 1993). It is also listed under Appendix III of the Bern Convention (EU/82/ 72/EEC) and Annexes II and V of the EU Habitats Directive (EU/92/43/EEC). In Ireland, however, exotic species have not been introduced and legislation bans their importation. Furthermore, although plague has been noted (Matthews and Reynolds 1990), its effect on A. pallipes was geo graphically restricted and plague is not currently a problem (Matthews and Reynolds 1992). Thus, Ireland retains healthy populations of white-clawed crayfish and has an important role to play in the conservation of this species (Reynolds 1997). Apart from legislation, conservation depends on an understanding of habitat requirements, especially if reintroductions are attempted as part of a conservation/management strategy. Within British rivers, high water quality, hard water and plentiful refugia in terms of tree roots and boulders appear to be required (Foster 1995; Smith et al. 1996; Naura and Robinson 1998). However, river studies pose a problem concerning the unit of analysis. Multiple samples taken from each river are not independent, and thus the assumptions of most statistical tests will be invalid. At the extreme, taking twenty samples from each of two rivers, one with and one without crayfish, and treating the data as independent would not be a valid approach. The present study attempts to overcome this potential problem of pseudo-replication by examining the habitat and crayfish status in the numerous rivers of a large catchment that all flow into a single lake system. Whether or not crayfish are present in specific rivers in this continuous system should depend on the habitat within each river and should be independent of their presence in other rivers. Environmental conditions (water chemistry, phys ical characteristics and invertebrate community structure) were measured at each site in order to evaluate the possibility of using these data to predict sites where crayfish should be present.

Community Structure of In-Stream Bryophytes in English and Welsh Rivers

Information on the distribution of bryophytes in mainland British rivers was collected as part of the Joint Nature Conservancy Council (JNCC) survey of in-stream macrophyte distribution between 1978 and 1997. A sub-set of sites (1604) containing the 50 most common bryophytes was analysed. The commonest of these 50 species were Fontinalis antipyretica and Rhynchostegium riparioides. The majority of species encountered are not considered to be truly aquatic. Detrended Correspondence Analysis of community structure revealed a continuum of variation in assemblages across sites rather than distinct groupings of bryophytes. Canonical Correspondence Analysis was used to analyse a sub-set of sites (625) for which water chemistry were available to test the influence of environmental variables on the distribution of bryophytes. The analysis suggested the strongest environmental gradient was the transition from lowland systems on chalk geology to steeply sloping, high altitude systems with resistant geology. Mapping CCA axis 1 scores on to a map of England and Wales suggested a geographic trend in bryophyte species distribution with community structure undergoing a transition from the upland regions and the western seaboard to the south east of England. Stepwise regression analysis confirmed the importance of the upland lowland trend, showing that substrate size, altitude of source, distance to source and altitude were important predictors of species richness (p < 0.0001, adjusted R2 = 0.30).

Valuing river characteristics using combined site choice and participation travel cost models

This paper presents new welfare measures for marginal changes in river quality in selected English rivers. The river quality indicators used include chemical, biological and habitat-level attributes. Economic values for recreational use of three types of river—upland, lowland and chalk—are presented. A survey of anglers was carried out and using these data, two travel cost models were estimated, one to predict the numbers of trips and the other to predict angling site choice. These models were then linked to estimate the welfare associated with marginal changes in river quality using the participation levels as estimated in the trip prediction model. The model results showed that higher flow rates, biological quality and nutrient pollution levels affect site choice and influence the likelihood of a fishing trip. Consumer surplus values per trip for a 10% change in river attributes range from £0.04 to £3.93 (£2001) depending on the attribute.

The geomorphological setting of some of Scotland's east coast freshwater mills: a comment on Downward and Skinner (2005) ‘Working rivers: the geomorphological legacy . . .’

Many of the water mills on Scotland's east coast streams, unlike those discussed recently by Downward and Skinner (2005 Area 37 138–47), are found in predominantly bedrock reaches immediately downstream of knickpoints (i.e. bedrock steps). Bedrock knickpoints in the lower reaches of Scottish rivers are a widespread fluvial response to the glacio‐isostatic rebound of northern Britain. These steps in the river profile propagate headward over time, but for intervals of a few centuries or so they are sufficiently stable to be exploited for the elevational fall necessary to power the mill wheel. Many of these mills were apparently powered by ‘run‐of‐the‐river’, as are some today that formerly had mill dams. The typical lack of sediment storage along the erosional lower reaches of many Scottish rivers means that failure of mill structures in Scotland will probably have less dramatic geomorphological and management implications than those suggested by Downward and Skinner for southern English rivers.

Predicted exposures to steroid estrogens in U.K. rivers correlate with widespread sexual disruption in wild fish populations.

Steroidal estrogens, originating principally from human excretion, are likely to play a major role in causing widespread endocrine disruption in wild populations of the roach (Rutilus rutilus), a common cyprinid fish, in rivers contaminated by treated sewage effluents. Given the extent of this problem, risk assessment models are needed to predict the location and severity of endocrine disruption in river catchments and to identify areas where regulation of sewage discharges to remove these contaminants is necessary. In this study we attempted to correlate the extent of endocrine disruption in roach in British rivers, with their predicted exposure to steroid estrogens derived from the human population. The predictions of steroid estrogen exposure at each river site were determined by combining the modeled concentrations of the individual steroid estrogens [17β -estradiol (E2), estrone (E1), and 17α -ethinylestradiol (EE2)] in each sewage effluent with their predicted dilution in the immediate receiving water. This model was applied to 45 sites on 39 rivers throughout the United Kingdom. Each site studied was then categorized as either high, medium, or low “risk” on the basis of the assumed additive potency of the three steroid estrogens calculated from data derived from published studies in various cyprinid fish species. We sampled 1,438 wild roach from the predicted high-, medium-, and low-risk river sites and examined them for evidence and severity of endocrine disruption. Both the incidence and the severity of intersex in wild roach were significantly correlated with the predicted concentrations of the natural estrogens (E1 and E2) and the synthetic contraceptive pill estrogen (EE2) present. Predicted steroid estrogen exposure was, however, less well correlated with the plasma vitellogenin concentration measured in the same fish. Moreover, we found no correlation between any of the end points measured in the roach and the proportion of industrial effluents entering the rivers we studied. Overall, our results provide further and substantive evidence to support the hypothesis that steroidal estrogens play a major role in causing intersex in wild freshwater fish in rivers in the United Kingdom and clearly show that the location and severity of these endocrine-disrupting effects can be predicted.

Assessment of Feminization of Male Fish in English Rivers by the Environment Agency of England and Wales

In recent years there has been considerable concern over the ability of substances discharged into the environment to disrupt the normal endocrine function of wildlife. In particular, the apparent widespread feminization of male fish in rivers has received significant attention from regulators in the United Kingdom, the United States, Europe, and Japan. The U.K. and European epidemiological data sets have demonstrated that the occurrence of feminized fish is associated with effluent discharges and that the incidence and severity is positively correlated with the proportion of treated sewage effluent in receiving waters. Although weakly estrogenic substances may contribute to the overall effect, studies have concluded that steroid estrogens are the principal and most potent estrogenic components of domestic sewage. Extensive laboratory data sets confirm that steroid estrogens are capable of eliciting the effects observed in wild fish at concentrations that have been measured in effluents and in the environment. Based on evaluation of the available information, the Environment Agency (England and Wales) has concluded that the weight of evidence for endocrine disruption in fish is sufficient to develop a risk management strategy for estrogenically active effluents that discharge to the aquatic environment.

Working rivers: the geomorphological legacy of English freshwater mills

Freshwater mills historically were found throughout England serving a wide variety of uses. The decline in the need for water power over the last 100 years saw a reduction in the number of operational mills. Despite this decline, the associated river structures were rarely removed and many of these have exceeded their design life and have failed or are now starting to fail, with important geomorphological implications for the river. This paper investigates the geomorphological impacts of mills and their structures on English rivers, and considers their legacy for the contemporary management of these systems.

Endocrine (sexual) disruption is not a prominent feature in the pike (Esox lucius), a top predator, living in english waters

The high incidence of intersex roach (Rutilus rutilus) in some United Kingdom rivers that has been associated with exposure to sewage treatment works (STWs) effluent led us to hypothesize that top predator fish also may be affected by estrogenic chemicals, because they are likely to bioaccumulate lipophilic compounds through a predator-prey relationship. To investigate this possibility, pike (Esox lucius) were sampled both upstream and downstream of STWs and then examined for total estrogenic activity of their bile, as measured using a yeast-based estrogen assay to determine the degree of recent exposure of the pike to estrogens and vitellogenin induction, and for possible disruption of sexual development, as measured using histological analysis of the gonads. No evidence of severe disruption was found in the sampled fish, which came from 16 sampling sites that were representative of English rivers. However, 14% of pike were intersex, of which 15 of 16 showed patches of male germ cells among predominantly female gonadal tissue. The incidence of masculinization was independent of whether the pike had been sampled upstream or downstream of STWs. Although pike are gonochoristic, it is not known if this masculinization of presumptive female pike is normal or, instead, indicative of endocrine disruption. Vitellogenin concentrations were not elevated in male pike at sites either upstream or downstream of STWs. The results suggest that sexual disruption is not common in pike, a fish at the top of the food chain in the freshwaters of England.