Water policy effectiveness: 30 years of change in the hypernutrified Colne estuary, England.

Wastewater discharges and agricultural run-off have caused nutrient enrichment leading to eutrophication, in receiving waters worldwide. Analysis of a 30 year data set (1981-2010) for the Colne estuary, a hypernutrified estuary in the south-east of England, revealed significant reductions in nutrient concentrations in freshwater inputs and along the estuarine gradient linked to management actions. DIN concentrations decreased, mainly as a result of reduced ammonia outputs from Colchester STW and reduced nitrate loads from the catchment. Declines in phosphate concentrations occurred due to improved STW processes. There were significant declines in phytoplankton chlorophyll a over the period. Long-term trajectories of nutrient decreases were also strongly influenced by interannual patterns of rainfall and climatic signals (winter NAO). Standardised winter DIN concentrations in the Colne estuary significantly exceed the Water Framework Directive good status target, but the estuary shows no symptoms of eutrophication.

Assessing visual fields for driving in patients with paracentral scotomata.

BACKGROUND: The binocular Esterman visual field test (EVFT) is the current visual field test for driving in the UK. Merging of monocular field tests (Integrated Visual Field, IVF) has been proposed as an alternative for glaucoma patients. AIMS: To examine the level of agreement between the EVFT and IVF for patients with binocular paracentral scotomata, caused by either ophthalmological or neurological conditions, and to compare outcomes with useful field of view (UFOV) performance, a test of visual attention thought to be important in driving. METHODS: 60 patients with binocular paracentral scotomata but normal visual acuity (VA) were recruited prospectively. Subjects completed and were classified as "pass" or "fail" for the EVFT, IVF and UFOV. RESULTS: Good agreement occurred between the EVFT and IVF in classifying subjects as "pass" or "fail" (kappa = 0.84). Classifications disagreed for four subjects with paracentral scotomata of neurological origin (three "passed" IVF yet "failed" EVFT). Mean UFOV scores did not differ between those who "passed" and those who "failed" both visual field tests (p = 0.11). Agreement between the visual field tests and UFOV was limited (EVFT kappa = 0.22, IVF kappa 0.32). CONCLUSIONS: Although the IVF and EVFT agree well in classifying visual fields with regard to legal fitness to drive in the UK, the IVF "passes" some individuals currently classed as unfit to drive due to paracentral scotomata of non-glaucomatous origin. The suitability of the UFOV for assessing crash risk in those with visual field loss is questionable.

Effects of vaccine dose, virus challenge dose and interval from vaccination to challenge on protection of broiler chickens against Marek's disease virus challenge.

OBJECTIVES: To examine the effects of varying the doses of turkey herpesvirus (HVT) vaccine and Marek's disease virus (MDV) challenge at two intervals after vaccination on the protection of chickens against challenge with MDV. DESIGN AND PROCEDURE: Experiment 1, a dose response study, consisted of 11 doses of HVT vaccine administered at hatch followed by challenge with 100 plaque forming units (pfu) of MDV 5 days post vaccination. Experiment 2, a 2 x 6 x 2 factorial design, included two HVT vaccine types, six different doses of HVT vaccine and 50 pfu and 200 pfu of MDV challenge 2 days post vaccination. All chickens were reared up to day 56 post challenge when all survivors were killed humanely. Dead and killed chickens were examined for gross MD tumours. RESULTS: Experiment 1 showed a significant positive linear relationship between dose of HVT vaccine and protective index in chickens challenged 5 days post vaccination. However the range of protective index observed was limited. In Experiment 2 neither HVT vaccine provided significant protection at any dose. There was no significant effect of vaccine type or MDV challenge dose on overall protection against challenge. Chickens challenged with 200 pfu of MDV had significantly higher mortality and MD incidence than those with 50 pfu. CONCLUSIONS: HVT vaccine dose had a significant impact on protective index, but vaccination to challenge interval appeared to have greater impact on the protective efficacy of vaccination. A fourfold increase in challenge dose increased mortality rate and incidence of MD.

Monitoring Migration and Measuring Biomass in Benthic Biofilms: The Effects of Dark/far-red Adaptation and Vertical Migration on Fluorescence Measurements.

Pulse modulated fluorescence has increasingly been used as an ecological tool to examine changes in the vertical distribution of microphytobenthic cells within the upper layers of estuarine sediments (most often using the minimum fluorescence yield F(o)) as well as to indicate the health of the community (using the maximum PS II quantum efficiency F(v)/F(m)). However, the practicalities of in situ measurements, often dictates that short dark adaptation periods must be used ( approximately 15 min). The use of far-red light as an alternative to dark adaptation was investigated in natural migratory microphytobenthic biofilms and artificial non-migratory biofilms. Prolonged periods of darkness ( approximately 24 h) were not adequate to achieve 'true' measurements of F(o) and F(v)/F(m), which require complete oxidation of Q(A) and full reversal of non-photochemical quenching (NPQ). In some instances, stable values were only achieved using far-red light. Prolonged exposure to dark/far-red light led to a downwards migration of cells in natural assemblages, as seen by a reduction in both F(o) and the maximum fluorescence yield (F(m)). In non-migratory biofilms, F(m) increased in the dark and far-red treatments, indicating a reversal of NPQ, whereas F(o) decreased in far-red light but increased in the dark. It is suggested that far-red light and darkness differentially affected the balance between NPQ reversal and Q(A) oxidation that lead to the measured F(o) yield. The use of far-red light as an alternative to dark adaptation is discussed and the implications of short (e.g., 15 min) dark adaptation times used in situ are discussed with reference to the vertical migration of cells within sediment biofilms.

The role of herbicides in the erosion of salt marshes in eastern England.

Laboratory studies and field trials were conducted to investigate the role of herbicides on saltmarsh vegetation, and their possible significance to saltmarsh erosion. Herbicide concentrations within the ranges present in the aquatic environment were found to reduce the photosynthetic efficiency and growth of both epipelic diatoms and higher saltmarsh plants in the laboratory and in situ. The addition of sublethal concentrations of herbicides resulted in decreased growth rates and photosynthetic efficiency of diatoms and photosynthetic efficiency of higher plants. Sediment stability also decreased due to a reduction in diatom EPS production. There was qualitative evidence that diatoms migrated deeper into the sediment when the surface was exposed to simazine, reducing surface sediment stability by the absence of a cohesive biofilm. Sediment loads on leaves severely reduced photosynthesis in Limonium vulgare. This, coupled with reduced carbon assimilation from the effects of herbicides, could have large negative consequences for plant productivity and over winter survival of saltmarsh plants. The data support the hypothesis that sublethal herbicide concentrations could be playing a role in the increased erosion of salt marshes that has occurred over the past 40 years.

Rapid assessment of macro algal cover on intertidal sediments in a nutrified estuary.

Macroalgal blooms have been considered to be an indicator of eutrophication. A new and rapid method is described for the assessment of macroalgal cover in the intertidal zone of estuaries. Macroalgal cover in the intertidal of the nutrient-enriched River Deben estuary was found to reach a maximum of 50% coverage, but this varied seasonally with the highest percentage cover during June and July. Macro-algae mats were particularly associated with areas of hard substrata providing suitable attachment points, rather than with the nutrient concentrations along the estuary. The occurrence of macroalgae may be more related to the substrate than to the nutrient status of the estuary.

The potential for phosphorus release across the sediment-water interface in an eutrophic reservoir dosed with ferric sulphate.

Alton Water, Suffolk, UK is a pumped storage reservoir that has a history of cyanobacterial blooms. Dosing of the input water with ferric sulphate to control external phosphorus loading has occurred since 1983. A detailed study of the sediment chemistry of the site was carried out between May 1995 and July 1997. Sequential phosphorus fraction analysis indicated a decrease along the length of the reservoir in sediment labile phosphorus content from 0.62 to 0.08 mg P g-1 dw and iron-bound phosphorus content from 3.22 to 0.46 mg P g-1 dw. These gradients positively correlated with water column chlorophyll a concentrations reported in a parallel study. Labile and iron-bound sediment phosphorus contents were in a dynamic equilibrium due to diffusional release, contributing to internal loading to the water column. Equilibrium phosphorus concentrations (EPC) determined from phosphorus adsorption capacity (PAC) experiments were lower inside the bunded region (0.01-0.03 mg P-PO4 l-1) where iron content was greatest compared to outside the bund (0.15-0.20 mg P-PO4 l-1) suggesting greater potential for diffusional release of phosphorus at the latter site. PAC experiments indicated that anaerobic and pH-mediated loadings were of less importance than diffusional release, although the latter may have contributed to internal loading in the main reservoir. Sulphate concentrations may act to increase the potential for anaerobic internal loading near to the pumped input in microstratified sediment. Sediment iron content decreased from 250 +/- 13.1 to 51 +/- 4.0 mg Fe g-1 dw across the line of a constructed bund at the north-west end near to the pumped input, which indicated successful control of dispersal of the fine ferric floc. The management implications with regard to phosphorus loadings indicated by these results are discussed.

An experimental investigation of interactions in snail-macrophyte-epiphyte systems.

An experimental investigation under field conditions of enclosures containing freshwater pulmonate snails, the macrophyteCeratophyllum demersum and epiphytes, produced evidence of beneficial interactions.Ceratophyllum growth, measured in terms of stem length, numbers of leaf-nodes and growing tips and leaf survival was significantly enhanced in the presence of snails. This effect was attributed to the increased availability of plant nutrients of snail origin, such as phosphates and ammonia, as well as to the snails' action as "cleaning symbionts" in reducing the density of bacterial and algal epiphyton potentially deleterious to macrophytes. Principal component analysis revealed both seasonal and treatment effects of snail grazing on algal epiphyton. Small adnate algal species (e.g.Cocconeis placentula) survived grazing and benefited from the removal of larger, competitor, species. Snail densities increased in all treatments, despite high (86%) juvenile mortality. It is concluded that freshwater pulmonate snails are strong interactors in lentic habitats, enhancing the growth ofCeratophyllum and producing characterisic epiphyte communities. This benefits not only the snails, but also the plants and epiphytes that are associated with them. Thus the interactions between these component parts of the community can be considered as mutualistic.

Note: Colonization and invasion of leaves of the aquatic macrophyteCeratophyllum demersum L. by epiphytic bacteria.

The colonization of leaves of the aquatic macrophyteCeratophyllum demersum L. by epiphytic bacteria, and the hypothesis that bacterial invasion causes leaf senescence, was studied using transmission and scanning electron microscopy and light microscopy. Population densities of epiphytic bacterial communities onCeratophyllum leaves were positively correlated with leaf age. Initial settlement of bacteria on young leaves appeared to favour the boundaries between epidermal cells. On older leaves, large populations of bacteria were present over the whole surface. One third of senescentCeratophyllum leaves examined by transmission electron microscopy showed signs of bacterial invasion. Of these, up to 54% of the leaf's epidermal cells contained bacteria. Areas of cell wall degradation were associated with invasive bacteria in senescent leaves. In healthy, nonsenescent leaves, no bacterial invasion was observed. These results suggest that epiphytic bacteria did not cause leaf senescence but probably colonized the internal tissues of leaves once senescence had occurred.