Is water quality in British rivers "better than at any time since the end of the Industrial Revolution"?

We explore the oft-repeated claim that river water quality in Great Britain is "better now than at any time since the Industrial Revolution". We review available data and ancillary evidence for seven different categories of water pollutants: (i) biochemical oxygen demand (BOD) and ammonia; (ii) heavy metals; (iii) sewage-associated organic pollutants (including hormone-like substances, personal care product and pharmaceutical compounds); (iv) macronutrients (nitrogen and phosphorus); (v) pesticides; (vi) acid deposition and (vii) other variables, including natural organic matter and pathogenic micro-organisms. With a few exceptions, observed data are scarce before 1970. However, we can speculate about some of the major water quality pressures which have existed before that. Point-source pollutants are likely to have increased with population growth, increased connection rates to sewerage and industrialisation, although the increased provision of wastewater treatment during the 20th century will have mitigated this to some extent. From 1940 to the 1990s, pressures from nutrients and pesticides associated with agricultural intensification have increased in many areas. In parallel, there was an increase in synthetic organic compounds with a "down-the-drain" disposal pathway. The 1990s saw general reductions in mean concentrations of metals, BOD and ammonia (driven by the EU Urban Waste Water Treatment Directive), a levelling out of nitrate concentrations (driven by the EU Nitrate Directive), a decrease in phosphate loads from both point-and diffuse-sources and some recovery from catchment acidification. The current picture is mixed: water quality in many rivers downstream of urban centres has improved in sanitary terms but not with respect to emerging contaminants, while river quality in catchments with intensive agriculture is likely to remain worse now than before the 1960s. Water quality is still unacceptably poor in some water bodies. This is often a consequence of multiple stressors which need to be better-identified and prioritised to enable continued recovery.

Modelling soil erosion responses to climate change in three catchments of Great Britain.

Simulations of 21st century climate change for Great Britain predict increased seasonal precipitation that may lead to widespread soil loss by increasing surface runoff. Land use and different vegetation cover can respond differently to this scenario, mitigating or enhancing soil erosion. Here, by means of a sensitivity analysis of the PESERA soil erosion model, we test the potential for climate and vegetation to impact soil loss by surface-runoff to three differentiated British catchments. First, to understand general behaviours, we modelled soil erosion adopting regular increments for rainfall and temperature from the baseline values (1961-1990). Then, we tested future climate scenarios adopting projections from UKCP09 (UK Climate Projections) under the IPCC (Intergovernmental Panel on Climate Change) on a defined medium CO2 emissions scenario, SRES-A1B (Nakicenovic et al., 2000), at the horizons 2010-39, 2040-69 and 2070-99. Our results indicate that the model reacts to the changes of the climatic parameters and the three catchments respond differently depending on their land use arrangement. Increases in rainfall produce a rise in soil erosion while higher temperatures tend to lower the process because of the mitigating action of the vegetation. Even under a significantly wetter climate, warmer air temperatures can limit soil erosion by enhancing primary productivity and in turn improving leaf interception, infiltration-capacity, and reducing soil erodibility. Consequently, for specific land uses, the increase in air temperature associated with climate change can modify the rainfall thresholds to generate soil loss, and soil erosion rates could decline by up to about 33% from 2070 to 2099. We deduce that enhanced primary productivity due to climate change can introduce a negative-feedback mechanism limiting soil loss by surface runoff as vegetation-induced impacts on soil hydrology and erodibility offset the effects of increased precipitation. The expansion of permanent vegetation cover could provide an adaptation strategy to reduce climate-driven soil loss.

The effects of pastoral intensification on the feeding interactions of generalist predators in streams.

Land-use change can alter trophic interactions with wide-ranging functional consequences, yet the consequences for aquatic food webs have been little studied. In part, this may reflect the challenges of resolving the diets of aquatic organisms using classical gut contents analysis, especially for soft-bodied prey. We used next-generation sequencing to resolve prey use in nearly 400 individuals of two predatory invertebrates (the Caddisfly, Rhyacophila dorsalis, and the Stonefly Dinocras cephalotes) in streams draining land with increasingly intensive livestock farming. Rhyacophila dorsalis occurred in all streams, whereas D. cephalotes was restricted to low intensities, allowing us to test whether: (i) apparent sensitivity to agriculture in the latter species reflects a more specialized diet and (ii) diet in R. dorsalis varied between sites with and without D. cephalotes. DNA was extracted from dissected gut contents, amplified without blocking probes and sequenced using Ion Torrent technology. Both predators were generalists, consuming 30 prey taxa with a preference for taxa that were abundant in all streams or that increased with intensification. Where both predators were present, their diets were nearly identical, and R. dorsalis's diet was virtually unchanged in the absence of D. cephalotes. The loss of D. cephalotes from more intensive sites was probably due to physicochemical stressors, such as sedimentation, rather than to dietary specialization, although wider biotic factors (e.g., competition with other predatory taxa) could not be excluded. This study provides a uniquely detailed description of predator diets along a land-use intensity gradient, offering new insights into how anthropogenic stressors affect stream communities.

Global versus local change effects on a large European river.

Water temperature and discharge are fundamental to lotic ecosystem function, and both are strongly affected by climate. In large river catchments, however, climatic effects might be difficult to discern from background variability and other cumulative sources of anthropogenic change arising from local land and water management. Here, we use trend analysis and generalised linear modelling on the Loire, the longest river in France to test the hypotheses that i) long-term trends in discharge and river temperature have arisen from climate change and ii) climatic effects on water quality have not been overridden by local effects. Over 32 years (1977-2008), discharge in the Middle Loire fell by about 100 m³/s while water temperature increased by 1.2 °C with greatest effects during the warm period (May-August). Although increasing air temperature explained 80% of variations in water temperature, basin-wide precipitation showed no long-term trend and accounted for only 18% of inter-annual fluctuations in flow. We suggest that trends in abstraction coupled with a potential increase in evapo-transpiration at the catchment scale could be responsible for the majority of the long-term discharge trend. Discharge and water temperature explained only 20% of long-term variations in major water quality variables (conductivity, dissolved oxygen, pH, suspended matter, biochemical oxygen demand, nitrate, phosphate and chlorophyll-a), with phosphate and chlorophyll declining contrary to expectations from global change probably as a consequence of improved wastewater treatment. These data partially support our first hypothesis in revealing how warming in the Loire has been consistent with recent atmospheric warming. However, local management has had larger effects on discharge and water quality in ways that could respectively exacerbate (abstraction) or ameliorate (reduced point-source pollution) warming effects. As one of the first case-studies of its kind, this multi-parametric study illustrates the potential for complex interactions between climate change and other environmental factors in large rivers.

Evidence needed to manage freshwater ecosystems in a changing climate: turning adaptation principles into practice.

It is widely accepted that climate change poses severe threats to freshwater ecosystems. Here we examine the scientific basis for adaptively managing vulnerable habitats and species. Our views are shaped by a literature survey of adaptation in practice, and by expert opinion. We assert that adaptation planning is constrained by uncertainty about evolving climatic and non-climatic pressures, by difficulties in predicting species- and ecosystem-level responses to these forces, and by the plasticity of management goals. This implies that adaptation measures will have greatest acceptance when they deliver multiple benefits, including, but not limited to, the amelioration of climate impacts. We suggest that many principles for biodiversity management under climate change are intuitively correct but hard to apply in practice. This view is tested using two commonly assumed doctrines: "increase shading of vulnerable reaches through tree planting" (to reduce water temperatures); and "set hands off flows" (to halt potentially harmful abstractions during low flow episodes). We show that the value of riparian trees for shading, water cooling and other functions is partially understood, but extension of this knowledge to water temperature management is so far lacking. Likewise, there is a long history of environmental flow assessment for allocating water to competing uses, but more research is needed into the effectiveness of ecological objectives based on target flows. We therefore advocate more multi-disciplinary field and model experimentation to test the cost-effectiveness and efficacy of adaptation measures applied at different scales. In particular, there is a need for a major collaborative programme to: examine natural adaptation to climatic variation in freshwater species; identify where existing environmental practice may be insufficient; review the fitness of monitoring networks to detect change; translate existing knowledge into guidance; and implement best practice within existing regulatory frameworks.

Priority wetland invertebrates as conservation surrogates.

Invertebrates are important functionally in most ecosystems, but seldom appraised as surrogate indicators of biological diversity. Priority species might be good candidates; thus, here we evaluated whether three freshwater invertebrates listed in the U.K. Biodiversity Action Plan indicated the richness, composition, and conservation importance of associated wetland organisms as defined respectively by their alpha diversity, beta diversity, and threat status. Sites occupied by each of the gastropods Segmentina nitida, Anisus vorticulus, and Valvata macrostoma had greater species richness of gastropods and greater conservation importance than other sites. Each also characterized species assemblages associated with significant variations between locations in alpha or beta diversity among other mollusks and aquatic macrophytes. Because of their distinct resource requirements, conserving the three priority species extended the range of wetland types under management for nature conservation by 18% and the associated gastropod niche-space by around 33%. Although nonpriority species indicated variations in richness, composition, and conservation importance among other organisms as effectively as priority species, none characterized such a wide range of high-quality wetland types. We conclude that priority invertebrates are no more effective than nonpriority species as indicators of alpha and beta diversity or conservation importance among associated organisms. Nevertheless, conserving priority species can extend the array of distinct environments that are protected for their specialized biodiversity and environmental quality. We suggest that this is a key role for priority species and conservation surrogates more generally, and, on our evidence, can best be delivered through multiple species with contrasting habitat requirements.

Molecular systematics and phylogeography of the cryptic species complex Baetis rhodani (Ephemeroptera, Baetidae).

Genetic studies have highlighted cryptic diversity in many well-known taxa including aquatic insects, with the general implication that there are more species than are currently recognised. Baetis rhodani Pictet are among the most widespread, abundant and ecologically important of all European mayflies (Ephemeroptera), and used widely as biological indicators of stream quality. Traditional taxonomy and systematics have never fully resolved differences among suspected cryptic species in the B. rhodani complex because morphological characters alone do not allow reliable distinction. This is particularly true among larvae, the life-stage used most widely in monitoring. Here, we assess the molecular diversity of this complex in one of the largest such studies of cryptic species in the order Ephemeroptera to date. Phylogenies were constructed using data from the mitochondrial cytochrome oxidase subunit I (COI) gene. Two monophyletic groups were recovered consisting of one major haplogroup and a second clade of 6 smaller but distinct haplogroups. Haplogroup divergence ranged from 0.2-3% (within) to 8-19% (among) with the latter values surpassing maxima typically reported for other insects, and provides strong evidence for cryptic species in the B. rhodani complex. The taxonomic status of these seven haplogroups remains undefined. Their distributions across Western Europe reveal no obvious geographic pattern, suggesting widespread diffusion of genetic lineages since the last glacial maximum. The implications of these findings are far-reaching given the ecological and bioindicator significance of what now appears to be several taxa.

Dissolved organic nitrogen regulation in freshwaters.

Dissolved organic nitrogen (DON) has been hypothesized to play a major role in N cycling in a variety of ecosystems. Our aim was to assess the seasonal and concentration relationships between dissolved organic carbon (DOC), DON, and NO3- within 102 streams and 16 lakes within catchments of differing complexity situated in Wales. Further, we aimed to assess whether patterns of land use, soil type, and vegetation gave consistent trends in DON and dissolved inorganic nitrogen (DIN) relationships over a diverse range of catchments. Our results reinforce that DON constitutes a significant component of the total dissolved N pool typically representing 40 to 50% of the total N in streams and lakes but sometimes representing greater than 85% of the total dissolved N. Generally, the levels of DON were inversely correlated with the concentration of DIN. In contrast to DIN concentrations, which showed distinct seasonality, DON showed no consistent seasonal trend. We hypothesize that this reflects differences in the bioavailability of these two N types. The amount of DON, DOC, and DIN was significantly related to soil type with higher DON export from Histosol-dominated catchments in comparison with Spodosol-dominated watersheds. Vegetation cover also had a significant effect on DON concentrations independent of soil type with a nearly twofold decrease in DON export from forested catchments in comparison with nonforested watersheds. Due to the diversity in catchment DON behavior, we speculate that this will limit the adoption of DON as a broad-scale indicator of catchment condition for use in monitoring and assessment programs.

Effects of point-source PCB contamination on breeding performance and post-fledging survival in the dipper Cinclus cinclus.

Despite widespread information on the incidence and biochemical effects of polychlorinated biphenyls (PCBs) in birds, field studies of effects on population processes are still scarce. This is particularly so in passerines. We therefore assessed breeding performance and post-fledging survival in dippers, Cinclus cinclus, breeding along the Afon Mule, a Welsh river where previous work indicated locally elevated PCB concentrations. We hypothesised that marked toxicological effects, including endocrine disruption, would be detectable as altered clutch-size, hatching success, nest success, brood-size, post-fledging survival or recruitment to the breeding population. Congener-specific analysis of PCBs in failed and deserted dipper eggs during 1990-93 revealed that geometric mean concentrations were four to 20 times higher along the Mule than elsewhere in Wales, UK. PCB signatures also varied highly significantly from other locations, with congeners 138, 153 and 180 dominant at the contaminated site, but 118 or 170 more frequent in eggs elsewhere. Subsequent analysis of surface runoff confirmed a small breaker's yard as a point source. Neither laying dates, clutch-sizes, brood-sizes, nest failure nor hatching failure along the contaminated Mule (n=46 breeding attempts and 218 eggs) differed significantly from dippers along adjacent reference rivers (n=82 breeding attempts and 315 eggs) or Welsh rivers as a whole (n=332 breeding attempts and 1534 eggs). Subsequent recaptures of breeding dippers ringed initially as nestlings were nearly identical between the Mule (7.7% of 182 nestlings), the reference set (7.5% of 323 nestlings) and all other Welsh rivers (7.3% of 2821 nestlings). These data illustrate the value of congener-specific analysis of bird's eggs in indicating local PCB sources. The data show also that PCBs can occur in dipper eggs at total concentrations of 0.49 (geometric mean)-1.29 (upper quartile) microg g(-1) wet mass without effects on breeding performance and survival. These values are below those at which biochemical or reproductive effects on other passerines have been detected, but above current concentrations in any other population of European dippers for which PCB data are available. Population effects by PCBs on European dippers are therefore unlikely. Survivors from locally contaminated sites like that in our study might allow field assessments of second-generation effects on breeding performance in wild birds that have developed under PCB exposure.

Aquatic bryophytes in Himalayan streams: testing a distribution model in a highly heterogeneous environment.

1. Aquatic bryophytes were sampled from 108 streams spanning over 3000 m of altitude in four regions of Nepal. Richness, cover and community composition were related to physicochemistry using multiple regression, DECORANA ordination and TWINSPAN. The performance of a hierarchically scaled descriptive model, developed in New Zealand for predicting bryophyte distribution, was examined in this highly heterogeneous Himalayan region. 2. Community composition and cover varied highly significantly with altitude, streambed stability and alkalinity, with evidence of effects of riparian land use on bryophyte cover. Cover was greatest in streams at low to middle altitudes with steep slopes (> 15°), high stability and low conductivity (< 60 µS cm-1), where communities were dominated by two Isopterygium spp., two Philonotis spp., Mnium punctatum and Lejeuneaceae. 3. Richness, by contrast, increased significantly but weakly at high altitude and moderate stability, where streams were dominated by Eurynchium praelongum, Rhynchostegium spp., Fissidens grandifrons and Hygroamblystegium spp. Richness and cover were lowest in unstable streams at the lowest altitude, where no single taxon was consistently most abundant. 4. Although these results were similar to those in the descriptive model developed for bryophytes in New Zealand, subtle differences were apparent. Substrate size, although influencing the presence of bryophytes in New Zealand streams, appeared to be unimportant in Nepal. By contrast, streambed stability was more important in Nepal than New Zealand, perhaps reflecting pronounced monsoonal floods, and subsequent increased frequency of bed movement in the former. A suggested habitat template indicates that large plant size and vegetative reproduction may be responsible for the widespread distribution of some species, even into unstable Himalayan streams.

The effect of sampling frequency on chemical parameters in acid-sensitive streams.

We assessed the effects of different simulated sampling regimes (weekly, fortnightly, monthly and bimonthly) on parameters describing the water chemistry of 72 streams in acid-sensitive areas of Wales. For pH, sulphate, total hardness and aluminium, reduced sampling frequency had no discernible or systematic effect on the apparent annual mean chemistry relative to the values derived from weekly data. Standard deviations and coefficients of variation were either unaffected, or were reduced. However, sampling frequency had a moderate effect on mean pH when the data were separated into seasons: winter mean pH increased on average by 0.13 units and summer means decreased on average by 0.12 units, when using bimonthly data relative to weekly. Extreme values were detected less effectively at lower sampling frequencies, significantly altering the intercept and/or the slope of the strong relationships between the means and minimum pH or maximum Al. These effects almost certainly reflect the exclusion of extreme events (summer drought and winter floods) from low sample frequencies and reveal limitations in the use of mean values from periodic sampling programmes for summarising some aspects of site chemistry. Nevertheless, previously established relationships between mean stream chemistry, land use and stream biology were still strong at all sampling frequencies. Clear recommendations about the needs to fully parameterise episodic fluctuations depend on unanswered questions about: (i) whether biota respond to mean or episodic chemical conditions and (ii) whether baseflow chemistry, episodic fluctuations, or some combination of these, will best reflect trends in acidification.

Spatial patterns concentrations in upland Wales in relation to catchment forest cover and forest age.

Data on nitrate nitrogen were collected weekly during 1984 from 136 sites on streams in upland Wales. Mean nitrate concentrations in summer (0.02 to 1.5 mg litre(-1)) were significantly lower (P<0.001) than in winter (0.02 to 1.26 mg litre(-1)), particularly at sites with mature conifers (>30 years old). Mean concentrations increased significantly with the average age of conifers on each catchment (P<0.001), and with increasing areal cover by trees over 30 years old (P<0.001). Nitrate concentrations increased significantly with stream total hardness (P<0.001), possibly reflecting nitrogen mineralisation in soils of higher base status. Concentrations also increased with stream chloride (P<0.001), which is predominantly atmospherically derived, implying that increased nitrate occurred where general atmospheric inputs of solutes were increased. After accounting for variation in hardness, residual nitrate concentrations still increased with the average age of the conifers (P<0.001), and with catchment cover by mature trees (P<0.001). We infer that some additional nitrate under older conifers is thus independent of catchment sources associated with increasing hardness. Two possibilities are increased inputs and decreased retention of nitrogen within the ecosystem of maturing conifer forest. Residual nitrate after accounting for variations in chloride also increased significantly with conifer age (P<0.01) and cover (P<0.01), a pattern implying that some sources of nitrate may also be independent of increased sea-salt deposition. We allude to the possibility that additional nitrogen deposition adds to nitrogen throughputs from maturing forests, and we discuss the potential ecological role of additional nitrogen in runoff.

A review of the likely causal pathways relating the reduced density of breeding dippers Cinclus cinclus to the acidification of upland streams.

Previous work has shown that the breeding density of a bird characteristic of upland streams, the dipper Cinclus cinclus, is markedly reduced at low pH in both Wales and Scotland. Populations also declined when streams became more acidic. Evidence of causal explanation for these relationships is that: (1) Food quantity is reduced in acidic streams, and important prey, including those rich in calcium, are scarce; (2) Blood chemistry in pre-breeding birds differs between acid and circumneutral streams, with plasma calcium reduced in those breeding at low pH. Skeletal sources of calcium are probably limited; (3) The time spent foraging by pre-breeding birds on acidic streams is markedly increased, even though overall energy costs on acidic and circumneutral streams are similar. Body condition is inferior to birds on circumneutral streams; (4) Egg laying is significantly delayed on acidic streams irrespective of an effect on laying of altitude, and clutch and brood sizes are significantly reduced; (5) Eggs are lighter and shells thinner at low pH; (6) Chick growth is reduced at low pH; (7) Contamination by heavy metals and persistent organochlorines is low in the populations on acidic streams and cannot explain the impaired breeding performance. None of these features can exclude the possibilities that acidic streams either hold populations of poor quality birds, which show the above features, or that acidity affects the breeding ecology of all dippers that attempt to breed at low pH. The qualitative outcome of these two alternatives is identical.

Patterns of contamination by organochlorines and mercury in the eggs of two river passerines in Britain and Ireland with reference to individual PCB congeners.

Unhatched eggs were collected in 1988 and 1990 from nests of the Eurasian Dipper Cinclus cinclus and the Grey Wagtail Motacilla cinerea in Wales, eastern Scotland and south-western Ireland. Mercury concentrations in Dipper eggs (geometric means 0.45-0.91 ppm (microg g(-1)) dry mass) were significantly lower in eastern Scotland than in either south-western Ireland or Wales, where the incidence of detectable residues increased markedly between 1988 (2% of eggs) and 1990 (69%). By contrast, DDE (geometric means 0.63-3.54 ppm in lipid), TDE (<0.01-1.80 ppm), DDT (<0.01-0.65 ppm), total PCBs (3.99-10.47 ppm), HEOD (0.39-0.61 ppm) and HCB (0.02-0.13 ppm) were all significantly higher in Scottish eggs than others. Around 33-46% of the total PCB burden in Dipper and Grey Wagtail eggs could be accounted for by six congeners (IUPAC numbers 118, 180, 101, 153, 138 and 170). Amongst these attributable PCBs, Dipper eggs from eastern Scotland were dominated by congener 153 (2,2',4,4',5,5'-hexachlorobiphenyl), whilst Welsh and Irish eggs were dominated by congener 118 (2,3',4,4',5-pentachlorobiphenyl). With the latter exception, all the individual congeners were found at significantly higher concentrations in Scottish eggs than others. Grey Wagtail eggs were dominated by congeners 118 and 101 (2,2,4,5,5'-pentachlorobiphenyl). In general, these congeners are common, widespread, and dominant components in the eggs of other wild birds for which data are available. Consistent with the low to medium levels of contaminants found in Dipper eggs, there was only slight evidence of any toxic effects. These included moderate shell thinning in relation to increasing DDE, and some evidence that contaminants had contributed to egg failure.

Restoring acidified streams in upland Wales: a modelling comparison of the chemical and biological effects of liming and reduced sulphate deposition.

Increasing emphasis is being placed on the restoration of surface waters which have been affected by acidification. Amongst the possible strategies are management of the causes, by reducing acidic deposition, and management of the symptoms, by treating affected areas with basic material such as limestone. In few cases have there been comparisons of the likely effect of these two strategies on surface water chemistry and ecology, although there is widespread belief that the two are similar in outcome. At present, only a modelling approach permits such a comparison. This paper describes chemical and biological responses of three Welsh streams whose catchments were limed experimentally in 1987-1988 as part of the Llyn Brianne project. Actual changes are compared with simulated changes which occur following reduced acid deposition according to the hydrochemical model, MAGIC (Model of Acidification of Groundwaters in Catchments). The results indicate that liming and 90% reduction in sulphate deposition reduce concentrations of toxic aluminium to similar levels. However, calcium concentrations and pH were increased by liming to values which were high by comparison with conditions simulated at low acid deposition, either in the past or future. Trout density increased in two of the streams following liming to levels similar to those simulated under low acid deposition. By contrast, the aquatic invertebrate fauna changed after liming so that streams acquired species typical of higher calcium concentrations than those simulated under low acid deposition. Species characteristic of 'soft water' communities were apparently lost, although more data are required to separate treatment effects from random change in the longer term. The 'soft water' community also declined in the model as a result of acidification, indicating that both liming and acid deposition resulted in a different faunal community from that prior to acidification. The results support those who conclude that liming is suitable for the restoration or protection of a fishery, but indicate that there may be other ramifications, for example to conservation, which must be considered when liming is implemented. However, the simulation of biological conditions under low acid deposition involves extrapolation from the initial data base. Further data are now required to assess empirically the likely biological character of British streams which have low base cation concentrations unaffected by acid deposition.

The ecology of dippers Cinclus cinclus (L.) in relation to stream acidity in upland Wales: time-activity budgets and energy expenditure.

The time-activity budget and energy expenditure of a riverine bird, the dipper Cinclus cinclus, was studied from March 1988 to July 1989, across a range of streams of contrasting acidity in upland Wales. Differences in time-activity budgets of birds on acidic and circumneutral streams were consistent with documented differences in prey availability and diet. Birds spent a significantly greater proportion of their active day foraging, swimming and flying, and less time resting, on acidic streams. Activity measurements varied significantly through the year, through the day, and with river flow. Despite differences in time budgets, mean Daily Energy Expenditure (DEE) on acidic streams was only 4.5-7.0% greater than on circumneutral streams. However, rates of energy gain were greater for dippers on circumneutral streams for every month of the year, a pattern confirmed by differences in body condition. By spending more time feeding, dippers on acidic streams will have less time for other activities such as self-maintenance and predator surveillance; they may also be less able to meet the additional demands accompanying the initiation of breeding. These findings are discussed in relation to the feeding ecology and breeding performance of dippers on streams of contrasting water quality in upland Wales.

Long-term change in the suitability of welsh streams for dippers Cinclus cinclus as a result of acidification and recovery: a modelling study.

Using a recognized and widely used hydrochemical model, MAGIC, long-term changes in acidity were simulated at 104 sites in the acid sensitive region of upland Wales. Conditions were modelled in the future (2010) under different reductions in sulphate deposition from 0 to 90% of 1984 values. Chemical output from the model was used to simulate change in the chemical suitability of streams for a species of river bird, the Dipper Cinclus cinclus, known to be affected by acidification According to simulations, only reductions in sulphate deposition by over 50% of 1984 levels prevented decline in the number of streams chemically suitable for Dippers. Greater reductions in deposition in the model permitted some recovery except where conifer forestry occupied acid sensitive catchments. There are several uncertainties with the models in their present form.

The influence of plantation forestry on the pH and aluminium concentration of upland welsh streams: a re-examination.

Previous studies relating forest presence to stream acidity and aluminium concentration were based on small numbers of catchments, often precluding the elimination of confounding influences on stream chemistry, such as geology or soil type. Spatial patterns in aluminium and pH data from 113 Welsh catchments of contrasting land use were therefore analysed in three different ranges of acid sensitivity (< 10, 10-15, 15-25 mg CaCO(3) litre(-1) total hardness). In each range, pH declined and aluminium increased significantly with increasing percentage forest cover. There was no evidence that the relationships reflected a spurious effect of forest location. Where aluminium concentrations were elevated under forest in a sub-set of 13 streams, aluminium was present predominantly in the labile form, most toxic to fish. Regressions of pH and aluminium on percentage forest cover provide a useful method of assessing the amount of forest in Welsh catchments which might give rise to given chemical conditions (e.g. pH <6, Al > 80 microg litre(-1)), though some difficulties are likely in accurately specifying the conditions desirable for fish or other biota.

Chemical and biological effects of acid, aluminium and lime additions to a Welsh Hill-stream.

Chemical and biological responses to simultaneous additions of acid, aluminium and lime were investigated in contiguous 250m-reaches of a chronically acidic stream in Wales. Treatments were applied for 24 h, and from the upstream end were as follows: zone A-untreated, pH 5.0, 0.37 mg litre(-1) filterable Al; zone B-acidified to pH 4.5, 0.40 mg Al litre(-1) (47% of Al attributed to release from the stream bed due to acid additions); zone C-acidified to pH 4.5 and Al dosed to 0.67 mg litre(-1); zone D-dosed with limestone slurry, resulting in pH 7.2, 0.13 mg Al litre(-1). In all reaches, the chemistry of the interstitial water at depths of 0.15 and 0.3 m never fell below pH 5.5, with corresponding decreases in Al and increases in base cation concentrations. Brown trout, Salmo trutta, and crayfish, Austropotamobius pallipes, held in the stream showed decreases in plasma [Na(+)] and haemolymph [Na(+)], respectively, in all acidic zones (A, B, C): these responses were mitigated by liming (zone D). Thus both chronic and simulated episodic levels of pH and dissolved Al were sub-lethally toxic to test species of aquatic fauna. This experiment also demonstrates a stream bed source/sink of Al, and the availability of a possible refuge from acidic surface waters within the substratum.

Egg mass and shell thickness in dippers Cinclus cinclus in relation to stream acidity in Wales and Scotland.

The shell thickness and mass of eggs of the dipper (Cinclus cinclus) collected on streams of different pH in Wales and Scotland were measured. The aluminium, phosphorus and calcium content of their invertebrate prey were also measured. In a regression analysis, significant at p<0.05, stream pH accounted for up to 7% of the variance in shell thickness, with shells decreasing by 2.5% of the overall mean with each unit of pH decline. In the Welsh sample, differences in shell thickness due to pH were small compared with differences between years across all sites. In data pooled between Scotland and Wales, pH accounted for 17% of the variance in egg mass, but a greater proportion (25%) in Scottish eggs alone. Aluminium concentrations in invertebrates showed no relationship with stream pH, but calcium levels in two insect orders increased significantly with pH. Calcium rich prey, such as Gammarus, were found only in circumneutral streams. The importance of calcium in the diet of dippers before and during egg formation is discussed. No evidence that aluminium in prey adversely affected dipper eggs was found.