Elevated land runoff after European settlement perturbs persistent foraminiferal assemblages on the Great Barrier Reef.

Coral reefs are under pressure from a variety of human-induced disturbances, but demonstration of ecosystem changes and identification of stressors are often difficult. We tested whether global change or increased agricultural runoff after European settlement of Northeast Australia (ca. 1860) has affected inshore reefs of the Great Barrier Reef. Eleven sediment cores were retrieved from inner reefs, intermediate reefs, and outer-island reefs, and benthic foraminiferal assemblages were analyzed in dated (14C, 210Pb, 137Cs) core sections (N = 82 samples). Data were grouped into six age bands (< 55, 55-150, 150-500, 500-1000, 1000-1500, and > 1500 yr). Principal component analysis and two-factor (Zone and Age) permutational analysis of variance (PERMANOVA) suggested that assemblages from the three zones were significantly different from each other over several millennia, with symbiont-bearing (mixotrophic) species dominating the outer reefs. A significant interaction term indicated that within-zone patterns varied. Assemblages in outer reefs unaffected from increased land runoff were persistent until present times. In both other zones, assemblages were also persistent until 150 yr ago, suggesting that benthic foraminiferal assemblages are naturally highly persistent over long (> 2000 yr) timescales. Assemblages in core sections < 55 yr old from inner reefs were significantly (post hoc t test) different from those older than 150 yr. Similarly, assemblages < 55 yr old from intermediate reefs were significantly different compared to older assemblages. A multivariate regression tree (environmental variables: Zone and Age) explained 56.8% of the variance in foraminiferal assemblages and confirmed patterns identified by PERMANOVA. With some exceptions, changes on the inner and intermediate reefs were consistent with a model predicting that increased nutrients and higher turbidity enhance relative abundance of heterotrophic species. Given that assemblages did not change in outer-island reefs (not impacted by runoff) we argue that changes in assemblages due to global change can be rejected as an explanation. Thus, the findings are more consistent with the hypothesis that agricultural runoff since European settlement altered foraminiferal assemblages than with the hypothesis that global forcing caused changes.

A preliminary study on the use of (10)Be in forensic radioecology of nuclear explosion sites.

Cosmogenic (10)Be, known for use in dating studies, unexpectedly is also produced in nuclear explosions with an atom yield almost comparable to (e.g.) (137)Cs. There are major production routes via (13)C(n, alpha)(10)Be, from carbon dioxide in the air and the organic explosives, possibly from other bomb components and to a minor extent from the direct fission reaction. Although the detailed bomb components are speculative, carbon was certainly present in the explosives and an order of magnitude calculation is possible. The (n, alpha) cross-section was determined by irradiating graphite in a nuclear reactor, and the resulting (10)Be estimated by Accelerator Mass Spectrometry (AMS) giving a cross-section of 34.5+/-0.7mb (6-9.3MeV), within error of previous work. (10)Be should have applications in forensic radioecology. Historical environmental samples from Hiroshima, and Semipalatinsk (Kazakhstan) showed two to threefold (10)Be excesses compared with the background cosmogenic levels. A sample from Lake Chagan (a Soviet nuclear cratering experiment) contained more (10)Be than previously reported soils. (10)Be may be useful for measuring the fast neutron dose near the Hiroshima bomb hypocenter at neutron energies double those previously available.

Systematics of radon at the Wairakei geothermal region, New Zealand.

222Rn and 220Rn in geothermal steam at Wairakei, NZ, range from 11 to 19, 500 Bq kg-1, and 25 to 16, 700 Bq kg-1, respectively, but do not cause toxic concentrations in air. The wide ranges are mainly due to differences in different physical conditions underground (e.g. thin silica diffusion barriers), not geochemical differences. Groundwater Rn from outside the area probably plays only a minor role. 210Po was found present in non-toxic levels in the steam. Historical records showed little change in Rn concentration over several decades, therefore potentially hazardous concentrations might be predicted from early exploration. 220Rn concentrations at Wairakei should decrease as the field becomes steam-dominated. Rock surfaces were variably leached or enriched with U, Th, Ra and 210Pb, providing a possible model for deposition in cooler regions near the field. Estimates of 222Rn permeability ranged from 2 to 77% of the maximum possible, with a median of 13%.

A study of microscopical and chemical tests for the rapid diagnosis of urinary tract infections in general practice.

Aids to the rapid diagnosis of urinary tract infection were assessed by the examination of 325 consecutive urine samples taken in the normal course of work in a general practice. Of these samples 103 produced a pure growth of at least 10(5) organisms per ml. The appearance and smell of each sample was noted and it was then tested by simple low-power microscopy of a drop of urine and by a dipstick which measured leucocyte esterase and nitrite, together with protein, blood and pH. In addition, pus cell counts per mm3 were performed on 272 of the samples using a cytometer chamber. This method is too time-consuming for routine use in the surgery. Neither a cloudy appearance nor haematuria were sufficiently specific to be of much use in the diagnosis of urinary tract infection. In the prediction of a 'positive' culture the sensitivity and specificity of the other tests were as follows: drop method microscopy 95% and 76%, respectively; cytometer count 95% and 81%; leucocyte-esterase estimation 89% and 68%; and nitrite 57% and 96%. These figures may underestimate the true values of the tests in the diagnosis of urinary tract infection because infection may be present in some cases producing growths of less than 10(5) organisms per ml. It is concluded that the most useful aid to the diagnosis of urinary tract infection is low-power microscopy of a drop of urine.

The bacteriology of a rural general practice: a retrospective six-year study.

The organisms cultured and their antibiotic sensitivities, together with clinical details, were obtained from all the available bacteriology requestlresult forms from a rural practice over a six-year period. The 3022 bacteriology specimens analysed yielded 997 potential pathogens. The main infections studied were those of the urinary tract, the upper respiratory tract and the skin and soft tissue. In spite of the fact that trimethoprim alone had never been used in the practice, 29% of urinary tract pathogens were resistant to this drug. Ninety-six per cent of isolates of Haemophilus influenzae were sensitive to ampicillin. The overall results suggest that most infectious disease in rural general practice can be managed with a limited and inexpensive antibiotic regimen. Such a regimen is described.

What is psychophysically perfect image stabilization? Do perfectly stabilized images always disappear?: comment.

This Communication calls attention to an earlier paper [L. E. Arend and G. T. Timberlake, J. Opt. Soc. Am. A 3, 235 (1986)] in which direct measurements have shown that retinal-image movements less than 1 arc min are required for perfect stabilization. It also cites papers that show that stabilized images of targets that contain no sharp structure in the foveal region disappear completely and permanently. Other targets disappear and reappear as a whole or as fragments intermittently.

Effect of imposed retinal image movements on colour vision at a heterochromatic boundary in a stabilized retinal image.

A stabilized image, including a straight-line boundary between two areas of different colour was displayed. Movements normal to itself were imposed on this boundary while other boundaries remained stabilized. Broad band filters giving red, yellow, green and blue were used in various pairs. Step movements, pulse movements and oscillatory movements (including sinusoidal, triangular and square wave forms) were applied in turn. Threshold movements to give perception of hue were measured for steps and pulses and signal/photon-noise ratios were calculated for a red/blue boundary. The ratio was found to be constant at a value of about 20 when the retinal illuminance (ER) varied between 5 td and 60 td. When ER was increased (up to 2000 td) the ratio increased rapidly. None of the colour appearances produced by moving the boundary exactly matched the corresponding appearances in an unstabilized image, though the nearest matches were obtained with oscillatory movements of frequency 2 Hz and displacement greater than 5'.

Effect of imposed step-movements and pulse-movements of the retinal image on perception of hue with coloured targets.

There is strong experimental evidence that colour discrimination depends upon signals originating at colour boundaries. Controlled movements were imposed on a boundary between an illuminated coloured area and a dark area in a previously stabilized image. Red, yellow, green and blue fields were used. Step-movements of amplitude M min arc and pulse-movements of amplitude M min arc and pulse width tau s were studied. The movement M50 to produce 50% positive responses for perception of hue was measured as a function of retinal illuminance, boundary length and speed for step-movements and pulse-width (tau) for pulse movements. Signal/photon-noise ratios were calculated.

Effect on perception of hue of imposed oscillatory movements of a stabilized retinal image.

A stabilized image of a coloured square seen against a black background was produced. After the image had faded, oscillatory movements were applied in a direction parallel to a diagonal so that all boundaries had an equal component of motion normal to themselves. Movements of different frequency, amplitude and wave-form were studied. Most of the experiments were carried out at fairly high retinal illuminance (80-500 td). The objective was to find the amplitude and frequency required for perception of hue and saturation. It was found that these movements had (i) a minimum amplitude of about 5' (10' peak-to-peak), (ii) a minimum velocity of 15'(-1) and (iii) a frequency range from about 1 Hz to about 4 Hz. The movements required are larger than those required for perception of the shape of the target and also larger than the normal movements which remain when a subject fixates a well-defined mark. Also the movements associated with the perception of hue and saturation are restricted to a narrower frequency range. These features probably imply that it is necessary to excite numbers of cones covering a minimum area to give perception of hue and saturation.

Information concerning colour derived from a single boundary.

Two experiments are described in which visual information is derived from a single moving boundary in the retinal image, all other boundaries being stabilized so that they contribute no visual information. In this situation the subject perceives the same colours on the two sides of the boundary as would be perceived in normal vision when, owing to eye-movements, all boundaries in the retinal image are moving relative to the retina. Thus complete information leading to perception of hue and saturation as well as brightness, and not merely differences of hue etc. on the two sides, can be derived from a single boundary.

Whooping cough after stopping pertussis immunisation.

An epidemic of whooping cough occurred in a rural practice in Shetland, containing 144 children under 16. Before July 1974 all children were immunised against pertussis, but after that date immunisation was stopped. Of the 134 children studied, 93 had been immunised. Sixty-five of the children developed whooping cough. The incidence of infection was similar in those who had and had not been immunised. The incidence was also similar in those born before and after July 1974. There was no evidence to support the routine use of pertussis immunisation in rural Shetland.