Rivers In Southern England Research Articles

Distribution of macroinvertebrate communities across surface and groundwater habitats in response to hydrological variability

Macroinvertebrate communities are strongly influenced by hydrological variability in surface waters. However, the response of these communities in corresponding groundwater-dependent habitats is not well understood. This study characterised the macroinvertebrate fauna and physicochemical characteristics of a chalk aquifer and its rivers in southern England. Over one year, samples were collected from five paired benthic-hyporheic sites located in perennial or temporary rivers, and a further seven phreatic sites in the surrounding aquifer. The study was preceded by a period of below average rainfall, providing an opportunity to assess the response of macro-invertebrate communities to unseasonal declines in river discharge and groundwater levels. Benthic, hyporheic and phreatic habitats each supported a distinct macroinvertebrate community, with the hyporheic habitat support- ing both epigean taxa and stygofauna. As discharge declined, the composition of these communities changed. In particular, the abundance of the epigean amphipod Gammarus pulex was higher in hyporheic than benthic habitats during periods of low river discharge, suggesting potential refuge-seeking behaviour. Similarly, fluctuations in the abundance and distribution of two stygofauna, Crangonyx subterraneus and Niphargus fontanus, coincided with marked changes in groundwater levels, suggesting that the contraction of available habitat and changes in connectivity also influenced the phreatic community. The variable distribution of macroinvertebrates between these habitats, especially in response to hydrological variability, suggests a dynamic connection between the river and its aquifer. This connection is an important consideration for the assessment and conservation management of both surface and groundwater communities and may help underpin integrated, catchment-based management, especially in river systems with temporary reaches.

Bringing methanotrophy in rivers out of the shadows

AbstractMethane oxidation produces biomass that is a potential source of particulate carbon for consumers, and is in addition to photosynthetic production. We assessed methanotrophy and photosynthetic production under differing conditions of light and methane concentration. We measured methane oxidation and photosynthesis in gravel sediments from adjacent shaded and unshaded stretches of 15 chalk rivers in southern England, and also in 30 artificial channels in which we manipulated light and methane experimentally. The capacity for methane oxidation was 78% higher in the shade than unshaded areas, indicating a denser, or more active, methanotrophic assemblage on shaded riverbeds, and the difference was most pronounced when methane concentration was high. Across the 15 rivers, methanotrophic production ranged from 16 to 650 nmol C cm−2 d−1 and net photosynthetic production from 256 to 35,750 nmol C cm−2 d−1. The relative importance of methanotrophy to their total production (i.e., photosynthetic and methanotrophic) increased with methane concentration and ranged from 0.1–2.4% and 0.2–13% in unshaded and shaded areas, respectively. Over an annual cycle in one river, the response of the methanotrophs in the shade to a high summer methane concentration was ∼ five times greater than in the open; in winter, there was no effect of shading on methane oxidation. The response of methanotrophy to shading and methane concentration in the artificial channels resembled that found in the rivers. Methanotrophy makes a non‐negligible (here up to ∼ 13%) contribution to particulate carbon production in these streams, is disproportionately greater in the shade, and constitutes a distinct carbon pathway available for their food webs.

Tetracapsuloides bryosalmonae abundance in river water.

Tetracapsuloides bryosalmonae is a myxozoan parasite of freshwater bryozoans and salmonids, causing proliferative kidney disease in the latter. To date, detection of the parasite has required collection of hosts and subsequent molecular or histological examination. The release of infectious spores from both hosts offers an opportunity to detect the parasite in water samples. We developed a novel SYBR® Green quantitative real-time PCR (qPCR) assay for T. bryosalmonae in water samples which provides an estimation of bryozoan malacospore numbers and tested the assay in 3 rivers in southern England (UK) over a period of 5 wk. The assay proved to be both highly sensitive and specific to the parasite, detecting low levels of spores throughout the study period. Larger-volume samples afforded greater detection likelihood, but did not increase the number of spores detected, possibly as a result of low and patchy spore distributions and lack of within-site replication of large-volume samples. Based on point-measurements, temperature was positively associated with the likelihood of detecting spores, possibly reflecting the temperature dependence of spore shedding from bryozoan hosts. The presence of T. bryosalmonae in water samples was predominantly influenced by spatial (sites within rivers, amongst rivers) and temporal (sampling dates) factors, while the latter also influenced quantification cycle (Cq) values and spore abundance. Environmental monitoring for infectious stages can complement traditional methods, providing faster and easier detection and avoiding potentially prolonged searching, collecting and destructive sampling of invertebrate and vertebrate hosts.

Using high-frequency water quality data to assess sampling strategies for the EU Water Framework Directive

Abstract. The EU Water Framework Directive (WFD) requires that the ecological and chemical status of water bodies in Europe should be assessed, and action taken where possible to ensure that at least "good" quality is attained in each case by 2015. This paper is concerned with the accuracy and precision with which chemical status in rivers can be measured given certain sampling strategies, and how this can be improved. High-frequency (hourly) chemical data from four rivers in southern England were subsampled to simulate different sampling strategies for four parameters used for WFD classification: dissolved phosphorus, dissolved oxygen, pH and water temperature. These data sub-sets were then used to calculate the WFD classification for each site. Monthly sampling was less precise than weekly sampling, but the effect on WFD classification depended on the closeness of the range of concentrations to the class boundaries. In some cases, monthly sampling for a year could result in the same water body being assigned to three or four of the WFD classes with 95% confidence, due to random sampling effects, whereas with weekly sampling this was one or two classes for the same cases. In the most extreme case, the same water body could have been assigned to any of the five WFD quality classes. Weekly sampling considerably reduces the uncertainties compared to monthly sampling. The width of the weekly sampled confidence intervals was about 33% that of the monthly for P species and pH, about 50% for dissolved oxygen, and about 67% for water temperature. For water temperature, which is assessed as the 98th percentile in the UK, monthly sampling biases the mean downwards by about 1 °C compared to the true value, due to problems of assessing high percentiles with limited data. Low-frequency measurements will generally be unsuitable for assessing standards expressed as high percentiles. Confining sampling to the working week compared to all 7 days made little difference, but a modest improvement in precision could be obtained by sampling at the same time of day within a 3 h time window, and this is recommended. For parameters with a strong diel variation, such as dissolved oxygen, the value obtained, and thus possibly the WFD classification, can depend markedly on when in the cycle the sample was taken. Specifying this in the sampling regime would be a straightforward way to improve precision, but there needs to be agreement about how best to characterise risk in different types of river. These results suggest that in some cases it will be difficult to assign accurate WFD chemical classes or to detect likely trends using current sampling regimes, even for these largely groundwater-fed rivers. A more critical approach to sampling is needed to ensure that management actions are appropriate and supported by data.

The winter storms of 2013/2014 in the UK: hydrological responses and impacts

This paper outlines the hydrological aspects of the 2013/2014 winter flooding in the UK, as well as the impacts. The episode is considered in a long-term historical context and wider issues raised by the flood events are discussed briefly.

Restoration versus recolonisation: The origin of Atlantic salmon ( Salmo salar L.) currently in the River Thames

Since the 1970s, when major improvements to the water quality were made, the River Thames has been subject to a high-profile project aimed at restoring Atlantic salmon to the catchment. Whilst initially successful, with hundreds of salmon returning each year in the late 1980s, the number of adults returning to the river has declined steeply again in recent years, reaching a low in 2005 when no salmon were recorded. Using a baseline of genetic information gathered from 3830 salmon from throughout their southern European range, and incorporating samples from the hatchery fish used to stock the Thames, all 10 tagged hatchery fish captured in 2003 and all 16 returning untagged adult salmon captured between 2005 and 2008 were assigned to their most likely river of origin. The results suggest that untagged salmon currently ascending the river originate not from exogenous fish stocked into the Thames, but predominantly from other rivers in southern England. This highlights the potential for natural processes of recolonisation to operate in rivers where salmon have become locally extirpated. These findings also underscore several important considerations when undertaking species restoration projects: (i) previous causes of declines must be sufficiently ameliorated to allow new/translocated individuals to thrive, (ii) introduced individuals should originate from a stock that is closely related to the extirpated population, according to the principles of contemporary conservation biology, and (iii) dispersal and gene-flow from neighbouring populations may play a significant role in establishing new populations.

American mink control on inland rivers in southern England: An experimental test of a model strategy

Invasive species are an important driver of global biodiversity loss. Under international legislation, the UK has an obligation to eradicate or to control the alien, invasive American mink. Using a large-scale field experiment, we tested the effectiveness of a specified mink removal strategy, identified through earlier modelling work, in reducing the relative abundance of mink. We found that mink removal could be effective in reducing mink populations with four months or less of trapping per year, over only 2–3 years, but that for small sites (c. 20 km) a flexible, reactive approach, coupled with continual monitoring for mink presence is necessary. Survival of reintroduced water voles at four sub-sites within our mink removal sites suggest that the reactive mink removal strategy adopted in this study was sufficient for water vole protection. We discuss the use of an adaptive management approach in local mink management, and consider the wider implications of our results for invasive species control on mainlands.

Karstic behaviour of groundwater in the English Chalk

Although the Chalk is only weakly karstified, tracer testing from stream sinks has demonstrated groundwater flow velocities comparable to those observed in highly karstic aquifers. Field survey of surface karst features in the catchments of the Pang and Lambourn rivers in southern England demonstrates the importance of overlying and adjacent Palaeogene strata in the development of karst features. Tracer techniques employed within the catchments enable further characterisation of the range and connectivity of solutional voids in this area of the Chalk, and allow assessment of the relative importance of different mechanisms of contaminant attenuation. Quantitative tracer test results suggest that groundwater flow may be through a complex combination of small conduits, typically 10–1000 mm in diameter, and more laterally extensive fissures with apertures of 1–50 mm. Evidence of connectivity between conduits and fissures suggest that in areas of the Chalk with rapid groundwater flow, fissures supplying abstraction boreholes may be connected to karst conduit networks with low potential for contaminant attenuation.

Histopathologic biomarkers in three spined sticklebacks, Gasterosteus aculeatus, from several rivers in Southern England that meet the freshwater fisheries directive.

This study demonstrates the utility and sensitivity of histopathologic biomarkers by recording lesions to the gill, liver and spleen in three spined sticklebacks (Gasterosteus aculeatus) from several rivers in Southern England which broadly comply with the water quality directives to protect fish health. The main study site was the Letcombe Brook system near Wantage, graded 1 (good) to 3 (fair) by the Environment Agency, using the River Ecosystem (RE) Class system. Sites with similar grades on the rivers Erme, Clyst, Exe and Plym were also selected in Devon. A normal condition factor (0.9 +/- 0.02, mean +/- S.E., n = 90), the presence of food in the stomach, and the whole body ionic composition (Na, K, Mg, Ca, Cu, Zn) suggested that fish were generally healthy. All fish showed some minor incidence of gill and liver lesions, even in the best (grade RE1) river water quality. Scoring the percentage of branchial secondary lamellae showing lesions did not reflect water quality because of biotic factors such as parasite load. However, fatness of secondary lamellae (length/width) increased in lower class rivers. Hepatic fatty change and focal necrosis was related to river quality grades with fatty change increasing from 0.8% to 12% of total liver area in grade RE1 and RE2 rivers, respectively. The gross anatomy of the spleen showed normal red and white pulp, and sinusoid space varied between 11% and 34% of the tissue area, but was not correlated with river grade. Overall, we conclude that histopathologic lesions are present in fish even when water quality meets the Freshwater Fisheries Directive. The Directive therefore only partly protects fish health. The incidence of fatty change in the liver, or fatness of secondary lamellae, in adult three spined sticklebacks are suggested as simple but sensitive histopathologic biomarkers which may be used to protect freshwater fishes as a novel alternative approach to water quality based Directives. We propose histopathologic biomarkers of the three spined stickleback for routine monitoring of fish health in EU freshwaters.

Sediment nutrient characteristics and aquatic macrophytes in lowland English rivers

Aquatic macrophytes play an important role in the nutrient dynamics of streams. As a result, there is much interest in their use as trophic indicators. However, the relationship between aquatic macrophytes and the trophic status of rivers is a complex one, partly because of the effects of a wide range of environmental variables and partly because submerged, rooted macrophytes can absorb nutrients from the river sediments and/or the water column. Experiments which have tried to establish the relative importance of sediments or water as sources of nutrients are inconclusive and further work is needed to establish how sediment nutrient characteristics vary within and among rivers (spatially and temporally) and the inter-relationships between sediment nutrients, water column chemistry and macrophytes. This paper presents the initial findings from a study of 17 lowland rivers in southern England which is exploring the spatial variability of sediment characteristics (total and inorganic phosphorus, total nitrogen, organic carbon, silt–clay fraction and organic matter content) and the relationship with aquatic macrophytes. The preliminary analysis indicates that although sediment characteristics are highly variable within 100-m river reaches, the variability across the 17 rivers is even greater; this is despite the limited geographic and trophic range of the study sites. The results presented in this paper also give some indication of the sediment characteristics associated with five macrophyte species but it is too early to ascribe sediment preferences for particular species.

The distribution of micro-organic contaminants in river bed-sediment cores

There is little information available on the distributions of micro-organic contaminants in river bed-sediments below a depth of 5 cm. The aim of this study is to determine the concentrations and distributions of contaminants in river bed-sediments up to 1 m depth and to make an assessment of the results. The approach taken was to collect five cores from each of two lowland rivers in southern England, the first a rural river and the second a dominantly urban catchment. The cores were analysed for micro-organic compounds and sediment/sediment porewater characteristics. Compounds detected were polyaromatic hydrocarbons (naphthalene, fluoranthene and pyrene), pesticides (carbaryl, linuron, fenpropimorph, the synthetic pyrethroids, and prometryn), and non-ionic surfactant residue (nonylphenol). A particularly important finding was that some micro-organic contaminants penetrated to depths of 1 m, and in one of the rivers they were detected in undisturbed Eocene substrata. The more hydrophobic contaminants showed a clear depth distribution with higher concentrations towards the top of the cores. The less hydrophobic contaminants demonstrated no systematic trend suggesting they had become soluble in porewaters and subsequently travelled within the cores. Partition between the porewater and sediment appeared to be controlling the distribution of the compounds with depth.

Cormorant Phalacrocorax carbo occupancy and impact at stillwater game fisheries in England and Wales

This study provides an assessment of Cormorant occupancy and impact at stillwater game fisheries in England and Wales, during 1988/89 to 1992/93. A total of 167 waterbodies operated as ‘put-and-take’ trout fisheries was included within a questionnaire survey, and this provided the bulk of the data used in the analyses. The results show that Cormorants are widespread at inland stillwater game fisheries in England and Wales throughout the year, with higher densities present during October–March. Peak counts by fishery managers at 45 of the fisheries increased by about 20% per year, regardless of season. Site use by Cormorants is investigated and the results imply that large, low altitude sites that are close to rivers in southern England are more likely to be used by these birds. The survey revealed that Cormorants are widely perceived by fishery managers to be responsible for significant economic losses through consumption and/or injury of stock fish. While this may be justified locally, we found no overall relationship between Cormorant density and anglers' catches of Rainbow Trout, the principal stock fish.

Incidences of gross morphological disorders in barbel (Barbus barbus) in three rivers in southern England

Incidences of gross morphological disorders in barbel (Barbus barbus) were investigated in three rivers in southern England. The water quality at the sites chosen for study on the Rivers Teme, Kennet and Lee were classified (according to the criteria of the National Water Council, 1978) as 1A, IB and 2, respectively. Generally, low levels of gross morphological abnormalities were seen in fish caught in the Teme and Kennet, although there were incidences of ocular disorders and extra barbules in 10 and 7%, respectively, of the Kennet fish. No tumours were found in barbel from the River Teme whereas there was a 2% incidence in the Kennet fish. In contrast barbel from the River Lee showed high levels of all the gross morphological disorders, especially haemorrhagic patches on the ventral surface (36%) and ocular disorders (72%). Tumours were seen in 25% of the barbel caught in the River Lee. The incidences of most of these gross morphological disorders did not appear to be age related. The possibility that these disorders were related to water quality is discussed.

Incidences of gross morphological disorders in barbel (Barbus barbus) in three rivers in southern England

Incidences of gross morphological disorders in barbel (Barbus barbus) were investigated in three rivers in southern England. The water quality at the sites chosen for study on the Rivers Teme, Kennet and Lee were classified (according to the criteria of the National Water Council, 1978) as 1A, IB and 2, respectively. Generally, low levels of gross morphological abnormalities were seen in fish caught in the Teme and Kennet, although there were incidences of ocular disorders and extra barbules in 10 and 7%, respectively, of the Kennet fish. No tumours were found in barbel from the River Teme whereas there was a 2% incidence in the Kennet fish. In contrast barbel from the River Lee showed high levels of all the gross morphological disorders, especially haemorrhagic patches on the ventral surface (36%) and ocular disorders (72%). Tumours were seen in 25% of the barbel caught in the River Lee. The incidences of most of these gross morphological disorders did not appear to be age related. The possibility that these disorders were related to water quality is discussed.

Faunal assembly in chironomids (Diptera): generic association and spread

Faunal assembly in chironomids was analysed using published data in the fauna of three rivers in southern England and of Great Britain as a whole. Two questions, both relating to the generic composition of local faunal assemblages, were asked: (i) to what extent are faunas from different sites within a single geographical area associated in terms of the occurrence of genera (‘generic association’); (u) given the total number of species observed, is the number of different genera represented (‘generic spread’) more than would be expected by chance. The latter question relates to the hypothesis that if interspecific competition is a strong organizing force of local faunal assemblages, species would be more likely to occur as widely spread out among different genera, thus decreasing overlap in resource use and hence the possibility of outright competition. Null models of species occurrence were constructed through Monte Carlo simulation to evaluate quantitatively these two questions. Generic association of faunal assemblages from three localities was statistically significant, though there was some variation among different subfamilies of Chironomidae. No evidence of generic diversification (more genera occurring in the fauna than expected by chance) was found. These results and the original questions were given critical considerations in the discussion.

The growth and reproductive strategy of the gudgeon, Gobio gobio (L.), in two hard‐water rivers in southern England

Scales from 682 gudgeon from the River Frome and 504 from the River Stour were used for age determinations. Growth in length was confined to the period May to October, but some weight increase occurred during the winter because of gonad development. Growth rates in the two rivers were the same, and were higher than most of those reported from other European rivers. Wide fluctuations, up to 12‐fold, occurred in the year‐class strengths of Frome gudgeon, caused by variations in the survival of juvenile gudgeon in their first year of life. Density‐independent factors, particularly water temperature, were major influences. Female gudgeon grew marginally slower than the males, but they matured earlier and at a smaller size. They were fractional spawners but their total reproductive effort each season was high. Both sexes had low survival rates and their reproductive life spans were rarely more than three years. These life history traits support the premise that these gudgeon populations are r‐selected.

Observations on the age, growth, reproduction and food of the pike Esox lucius (L.) in two rivers in southern England

Opercular bones of 261 pike from the River Stour and 117 from the River Frome were used for age and back‐calculated growth determinations. The annuli were laid down during late April and early May and most growth occurred between May and September. Pike growth in the two rivers was comparable with the fastest growth in other waters, though Frome pike grew slightly faster than Stour pike. Spawning occurred from the end of March into May. Elaboration of the ovaries commenced in September and was virtually completed by February, whereas the testes reached their maximum weight in October and maintained it until spawning. Immature pike had an annual cycle of condition reaching a maximum in May and a minimum during the winter. The gonad cycle affected the condition of mature females which had their minimum condition in mid‐summer. The fecundity of Stour pike is expressed by the formula: log10 egg number =3.56 log10 fish length (mm) – 5.40. Approximately 75% of all Stour pike were sexually mature by age II and these fish were, on average, larger than immature pike of the same age. The most numerous items in the diet of pike were small cyprinids, 30–80 mm fork length, although pike over 700 mm long ate larger fish. Few salmonids appeared in the diet of either Frome or Stour pike. The percentage of empty stomachs was highest in Stour samples taken during the summer, shorter digestion times and longer feeding periods in this period are suggested as reasons for the apparent anomaly.

Observations on the age, growth, reproduction and food of the dace, Leuciscus leuciscus (L.), in two rivers in southern England

Scales of 497 dace from the river Stour and 573 from the river Frome were used for age determinations. Annuli were laid down in late May to early June at the start of the growth period. Minimal growth occurred from November to April. Male dace grew minimally faster than females; Frome dace faster than those from the Stour. Growth rates in the two rivers were similar to those published for most other European waters. Variation in growth rates in different years was not great, but there were marked differences in recruitment success. Spawning occurred in the second half of March and elaboration of the gonads between September and March. Immature dace have an annual cycle in condition with a maximum in June and a minimum during the winter months. The condition of the mature females is affected by the gonad cycle. The fecundity of Stour dace is represented by the formula: image and for Frome dace by: image Most dace were mature by age IV, but there were more mature II and III group fish in the Frome population. Molluscs and Trichoptera larvae comprised the bulk of the winter diet of Stour dace, and Ephemeroptera nymphs, Simulium and chironomid larvae were the principal constituents during the summer.

Observations on the age, growth, reproduction and food of the roach Rutilus rutilus (L.) in two rivers in southern England

Scales and opercular bones from 632 roach from the River Stour were used for age and back‐calculated growth determinations. The scales had clearer inner annuli but operculars clearer outer annuli in fish more than nine years old. The annuli were laid in late May or early June at the beginning of the growth period. Growth was minimal between November and April. Roach from both rivers grow faster than those in most other European waters. Female roach grow faster than males; River Frome roach faster than those from the Stour. Spawning occurred in May and elaboration of gonads between September and May. Immature roach have an annual cycle in condition with a maximum in June and a minimum in early Spring. The condition of mature females is affected by the gonad cycle. The fecundity of Stour roach is represented by the formula: log egg number=4.43 log length (mm)—1.69. Approximately half of the Stour males attained sexual maturity at age III and most of the rest by age IV. Half of the females were mature at age IV and the remainder by age V. Both brood success and growth rate varied from year to year but independently of one another. Most Stour roach ate aquatic insect larvae and molluscs but algae were more frequent in the diet of larger fish.

THE REACTIVITY OF DISSOLVED SILICON IN SOME NATURAL WATERS

Several samples of natural waters, from the deep North Atlantic Ocean and four rivers in southern England, have been examined for the presence of dissolved silicon unreactive under the conditions generally used for its absorptiometric determination; none was detected. Polymeric silicon added to the samples depolymerized completely within a few days, most rapidly in seawater. When filtered river water was frozen and subsequently thawed, the silicon was largely present in an unreactive form; the unreactive fraction could be removed by membrane filtration. The silicon became entirely reactive on standing at about 25C for several hours. Unreactive forms of dissolved silicon were not formed when natural waters of salinity >27‰ were similarly treated.