Site In South-east England Research Articles

Eutrophication of heathland ponds at a site in Southern England: Causes and effects, with particular reference to the Amphibia

Chemical and biological features of bog pools at a heathland site in south-east England were investigated. The heath is one of the largest remaining in Britain, and the only locality where all 12 species of native herpetofauna coexist. The ponds showed considerable variation with respect to water chemistry, and several ion sources causing eutrophication of some of the pools were identified. Species richness and abundance were greater in the eutrophicated ponds, which generally had pHs of 5·0–6·5 and calcium concentrations of 4–10 mg litre −1, than in the purely rain-fed bog pools with pHs of 3·8–4·3 and calcium concentrations of 1–5 mg litre −1. Palmate newts Triturus helveticus occurred in all pond types, but were rarest in the purely rain-fed ones; the other five amphibians were confined to eutrophicated pools, with the rare natterjack Bufo calamita breeding only in ponds enriched by calcium-rich solid debris (limestone or concrete fragments). The significance of these findings with regard to recent natterjack declines on heathland is discussed.

Variation in populations of mine- and gall-forming Diptera and the growth form of their host plant, bracken (Pteridium aquilinum(L.) Kuhn)

Eight species of Diptera belonging to the families Anthomyiidae, Cecidomyiidae and Agromyzidae utilize bracken in different ways and show preferences for different types of bracken habitat. The annual and local variation found in populations of these mining and gall-forming herbivores in different sites in Southeast England over a four-year period are described. Possible reasons for the differences in distribution patterns are discussed, in terms of the growth and phenology of the host plant, resource availability and natural enemies.

The chemistry of bulk precipitation at a site in southeast england—I. Small-scale spatial variation, frequency distributions and variation with time

This paper contains a statistical analysis of bulk precipitation chemistry data from rain falling on the Tillingbourne Catchment, Surrey, SE England, in the years 1978–1981. Measurements of weekly average pH, organic content, sulphate, nitrate, ammonium and chloride were made. There was some evidence for small-scale spatial variation in precipitation chemistry, particularly for the organics. Frequency distributions were mostly log-normal but for ammonium and total sulphate there were more high values and for H + fewer high values, than expected on a log-normal basis. There was a Spring peak in the concentration of most ions, but Cl t- had a Winter peak. These seasonal variations are probably determined by meteorological factors.

Atmospheric measurements of peroxyacetylnitrate (PAN) in rural, south-east England: Seasonal variations winter photochemistry and long-range transport

Peroxyacetylnitrate (PAN) is an important secondary pollutant formed in the ambient atmosphere during photochemical episodes; it constitutes a significant component of the atmospheric NO x cycle. The behaviour of PAN in the atmosphere has been studied at Harwell, a rural site in south-east England, using a sensitive technique with a detection limit of < 30 ppt(v). Even during winter months, daytime levels of PAN above the detection limit were always present, demonstrating the ubiquity of this molecule in the atmosphere. Results for the periods November 1974–October 1975 and January 1980–June 1981 show the existence of a pronounced seasonal variation. Maximum levels were observed during summer months, and minimum values during winter. There is a large difference between these maxima and minima, in contrast to typical patterns for ozone, and it is suggested that PAN is a better indicator of overall chemical reactivity in the lower atmosphere. Simultaneous measurement of CFCl 3, was found to be a good indicator of air mass quality and anthropogenic influence; increased levels of this tracer were always associated with elevated PAN concentrations. Unexpectedly high levels of PAN during two episodes in February 1981 showed the possibility of significant photochemical activity during winter months. Back-trajectory analysis for these periods, indicated the influence of mainland European emissions and subsequent transport of photochemically-aged air masses. Similar observations of high PAN made during February 1975 suggest that the occurrence of late-winter photochemical episodes may not be uncommon.

The chemistry of bulk precipitation at a site in southeast england—II. Relationships between ions and comparison with other sites

This paper contains a statistical analysis of bulk precipitation chemistry of rain falling on the Tillingbourne Catchment, Surrey. Over the years 1978–1981, mean volume-weighted concentrations were: pH, 4.15, 70.8 μeq ℓ −1 H +; organic, 2.8 mg ℓ −1; total SO 2− 4, 80.5 μeq ℓ −1; NO − 3, 36.2 μeq ℓ −1; NH + 4, 40.9 μeq ℓ −1; Cl − (2 years) 97.4 μeq ℓ −1, rainfall 1067mm. Compared to other sites in the U.K. and elsewhere receiving acid precipitation in this pH is at the low end of the range, but levels of the other ions are moderate. Similar relations apply to deposition. Ion concentrations are highly correlated, especially total SO 2− 4, NO − 3 and NH + 4. This group is linked more loosely to pH and organic content, while Cl − does not correlate at all with the other ions, implying a totally different source, probably sea salt. H + ions in rain correlate better with NO − 3 than with SO 2− 4 and regression analysis suggests that almost all the NO − 3 is probably associated with nitric acid, whereas only about 57% of the SO 2− 4 is associated with sulphuric acid. Deposition is approximately related to rainfall by a power law relationship in which the exponent of the equation varies between 0.5 and 0.9. However, it is concluded that an adequate estimate of deposition cannot be obtained from rainfall alone.

Plant diversity in four chalk grassland sites with different aspects

Plant diversity and its components was studied on four chalk grassland sites in southeast England over a fourteen-month period. The sites were almost adjacent, and each faced one of the major compass points, N, S, E and W. Aboveground vegetation was recorded at monthly intervals by cover repetition, using a point quadrat technique. Seasonal patterns in the development of leaf area, bare ground, number of species present and diversity were similar on all sites. The N and W facing slopes and the S and E facing slopes resembled each other in several characteristics, while these two pairs of slopes differed markedly from each other. Thus, (i) there were more grasses but fewer forbs on the N and W slopes, (ii) overall diversity and forb diversity were lower on the N and W slopes but grass diversity was higher, (iii) equitability was lower on the N and W slopes, (iv) percentage similarity of begetation present was high when the N slope was compared with the W and when the S slope was compared with the E; other comparisons gave lower percentage similarity. It is proposed that the greater abundance of Carex flacca on the N and W slopes is important in causing these differences, and that it results in lower diversity on these slopes by occupying part of the habitat of the species-rich forb community which occurs on the S and E slopes. Dominance-diversity curves range from lognormal to geometric in form; some interpretation of changes they display can be made by assuming that the community is in a non-equilibrium state caused by seasonal environmental fluctuations each winter.

Morphological variation in relation to habitat in some British grasshoppers

Summary (1) Adult females of Chorthippus brunneus and C. parallelus were collected from twenty-six sites in South-East England over a two year period. (2) Ten exo-skeletal characters were measured, and subjected to canonical variate analyses to compare populations from different habitats and between years. (3) Similar patterns of character correlation were found in changes of shape occurring between years and between heathland and grassland populations. (4) C. parallelus is morphologically more variable between habitat types than C. brunneus, and displayed greater differences between years.

Aminostratigraphy of UK Pleistocene deposits

Ratios of D-alloisoleucine to L-isoleucine have been determined on freshwater molluscs from 13 interglacial sites in South East England and on marine molluscs and foraminifera from 10 Pleistocene and Upper Pliocene Crag sites in East Anglia. We can distinguish the Ipswichian, then either one or two interglacials that may be younger than the classical Hoxnian, then the Pleistocene Crags, then the Pliocene Coralline Crag.

Ozone concentrations in South-East England during the summer of 1976

Surface ozone concentrations at five sites in South-East England were measured during the heat wave of 1976 from 22 June to 12 July. At all sites peak hourly concentrations were the highest ever recorded in the UK and the elevated levels persisted for periods longer than any previously measured. Some discussion of the significance of the results is given together with an analysis of back-track air mass trajectories in the context of oxidant formation in North-West Europe.