Ecological study of chalk and limestone stream. Annual report October 1975 to September 1976

Few detailed studies have been made on the ecology of the chalk streams. A complex community of plants and animals is present and much more information is required to achieve an understanding of the requirements and interactions of all the species. It is important that the rivers affected by this scheme should be studied and kept under continued observation so that any effects produced by the scheme can be detected. The report gives a brief synopsis of work carried out during the third year of a four year ecological study sponsored jointly by the Thames Water Authority and the Central Water Planning Unit. It assumes . It assumes some familiarity with the investigations carried out on the River Lambourn during the preceding three years which was sponsored jointly by the Thames Conservancy and Water Resources Board (immediate predecessors of the present sponsoring organisations). (PDF contains 35 pages)

Ecological study of chalk streams. Lambourn project. Interim report October 1977 to April 1979

Few detailed studies have been made on the ecology of the chalk streams. A complex community of plants and animals is present and much more information is required to achieve an understanding of the requirements and interactions of all the species. It is important that the rivers affected by this scheme should be studied and kept under continued observation so that any effects produced by the scheme can be detected. The report gives a synopsis of work carried out between 1971 and 1979 focusing on the present phase 1978-1979. It assumes some familiarity with the investigations carried out on the River Lambourn during the preceding years. The aims of the present phase of the project may be divided into two broad aspects. The first involves collecting further information in the field and includes three objectives: a continuation of studies on the Lambourn sites at Bagnor; comparative studies on other chalk streams; and a comparative study on a limestone stream. The second involves detailed analyses of data previously collected to document the recovery of the Lambourn from operational pumping and to attempt to develop simple conceptual and predictive models applicable over a wide range of physical and geographical variables. (PDF contains 43 pages)

Ecological study of the River Lambourn. Report for the period October 1973 to September 1977

The investigations described in this report were carried out to fulfill three distinct but interrelated objectives. In 1973 the Thames Conservancy were making plans for a second stage of their groundwater scheme which would take water from the chalk aquifers in the valley of the Kennet and they wanted basic information on the ecological state of this river and its upper tributaries. Little appeared to be known about limestone streams and a preliminary study of one of the streams in this area was desirable as a basis for planning more detailed studies if these were needed later. At a progress meeting held in March 1976 the problems and opportunities presented by the developing drought conditions were considered. It was concluded that the ecological effects of the exceptionally low natural flows should be studied and that it would be important to assess the ecological impact of the groundwater scheme if it was brought into operation that year. This could only be done on the Lambourn and the Winterbourne and it was decided that considerable effort should be diverted there for this purpose and that the field observations should be extended to cover any recovery period after the end of the drought. To make this possible it was agreed that the studies of invertebrates and detritus on the Kennet should be reduced considerably and that the proposed study of the limestone stream should be abandoned. The revised objectives were as follows: A detailed ecological study of several sites on the Kennet and its tributaries above Kintbury, extending over at least two years and involving observations on wate r weeds , invertebrates, fish, detritus and the trophic relationships within the river community. Quantitativ e and qualitative sampling of water weeds and invertebrates during one year at a number of sites on several chalk streams to determine whether the patterns and relationships found in the Lambourn are also found at the other sites. Observations on the Lambourn at Bagnor were to continue for most of the period to look for long-term fluctuations and to enable these sites to act as controls with which the other sites could be compared. Further detailed studies on the Lambourn and the Winterbourne to assess the impact of low flows, trial pumping and the operation of the groundwater scheme.

Ecological effects of trial pumpings in the Upper Lambourn: Stage 1 group pumping test Upper Lambourn group, September - November 1975

This report to the Thames Water Authority and Central Water Planning Unit is on research carried out in conjunction with the Stage 1 Group Pumping Test of five boreholes in the upper Lambourn Group for a period of three months in September, October and November 1975. The aim of the study was to assess the ecological effects of the pumpin g of five bore-holes in the upper Lambourn. That is, to determine how the seasonal sequence of ecological events in the river differed from what would hav e occurred had no pumping taken place. Since this 'experiment' has no control it is not possible to make a direct assessment. Nevertheless, by careful monitoring of ecological events before, during and after the pumping it is possible to document changes in th e river and by reference to the data already available for the Rive r Lambourn, normal seasonal changes in the flora and fauna can be separated from changes which may be attributable to the pumping and subsequent events.

Analysis of dispersion compensation by chirped fiber grating in directly and externally modulated CATV systems

The dispersion compensation effect of the chirped fiber grating (CFG) is analyzed theoretically, and analytic expressions are derived for composite second-order (CSO) distortion in analog modulated sub-carrier multiplexed (AM-SCM) cable television (CATV) systems with externally and directly modulated transmitters. Simulations are given for the two kinds of modulations and for standard single mode fiber and non-zero dispersion shift fiber (NZDSF) systems. The results show that CFG could be used as a dispersion compensator in directly modulated systems, but its dispersion coefficient should be adjusted much more precisely than the externally modulated system. The requirements for the NZDSF system could be loosened much. It is proposed that directly modulated source may be used as a transmitter in CATV systems combined with tunable CFG dispersion compensator being adjusted precisely, which may be more cost-effective than externally modulation technology. (c) 2006 Elsevier GmbH. All rights reserved.

Ecological indicators of water quality in small rivers

At the present time hydrobiological indicators are widely used for the control of surface water quality. Results of the applying of methods suggested at the 1st Soviet-American seminar (1975), development of improved methods and estimation of their usefulness for various conditions are presented in this report. Among the criteria permitting an estimation of the degree and character of changes in water quality and their connection with the functioning of river ecosystems in general, the biological tests of natural waters appears to be the most universal one and is being carried out in two main directions — ecological and physiological. This study summarises approaches in both directions.

The ecological impact of different mechanisms of chronic sub-lethal toxicity on feeding and respiratory physiology

Sub-lethal toxicity tests, such as the scope-for-growth test, reveal simple relationships between measures of contaminant concentration and effect on respiratory and feeding physiology. Simple models are presented to investigate the potential impact of different mechanisms of chronic sub-lethal toxicity on these physiological processes. Since environmental quality is variable, even in unimpacted environments, toxicants may have differentially greater impacts in poor compared to higher quality environments. The models illustrate the implications of different degrees and mechanisms of toxicity in response to variability in the quality of the feeding environment, and variability in standard metabolic rate. The models suggest that the relationships between measured degrees of toxic stress, and the maintenance ration required to maintain zero scope-for-growth, may be highly nonlinear. In addition it may be possible to define critical levels of sub-lethal toxic effect above which no environment is of sufficient quality to permit prolonged survival.

The kingdom of the shore: achievement of good ecological potential in reservoirs

The European Water Framework Directive requires member states to restore aquatic habitats to good ecological status (quality) by 2015. Good ecological status is defined as slightly different from high status, which, according to the Directive, means negligible human influence. This poses problems enough for restoration of natural habitats but artificial reservoirs are not excluded from the Directive. They must be restored to good ecological potential. The meaning of good ecological status is linked to that of 'high' ecological status, the pristine reference condition for aquatic habitats under the Directive. From the point of view of an ecologist, this is taken to mean the presence of four fundamental characteristics: nutrient parsimony, characteristic biological and physical structure, connectivity within a wider system and adequate size to give resilience of the biological communities to environmental change. These characteristics are strongly interrelated. Ecological potential must bear some relationship to ecological status but since the reference state for ecological quality is near absence of human impact, it is difficult to see how the criteria for ecological status can be applied to a completely man-made entity where the purpose of the dam is deliberately to interfere with the natural characteristics of a river or former natural lake. Rservoirs are disabled lakes, ususally lakcing the diversity and function provided by a littoral zone. Nonetheless, pragmatic approaches to increasing the biodiversity of reservours are reviewed and conclusions drawn as to the likely effectivemess of the legislation.

The diversity and ecological role of protozoa in fresh waters

Protozoa feed on and regulate the abundance of most types of aquatic microorganisms, and they are an integral part of all aquatic microbial food webs. Being so small, aerobic protozoa thrive at low oxygen tensions, where they feed (largely unaffected by metazoan grazing) on the abundance of other microorganisms. In anaerobic environments, they are the only phagotrophic organisms, and they live in unique symbiotic consortia with methanogens, sulphate reducers and non-sulphur purple bacteria. The number of extant species of protozoa may be quite modest (the global number of ciliate species is estimated at 3000), and most of them probably have cosmopolitan distributions. This will undoubtedly make it easier to carry out further tasks, e.g. understanding the role of protozoan species diversity in the natural environment.

Digital holographic aberration compensation in electron holography

This paper proposes a new digital method to compensate for the aberration of an electron objective lens in electron holography. In this method, the object wavefront in the exit pupil plane is numerically reconstructed from a digitized electron hologram, and is corrected by multiplying it with the conjugated phase-error function. Then, an aberration-free image can be obtained by calculating the Fresnel integral of this corrected wavefront. In comparison with traditional methods, this method is much more convenient and accurate. Some verifying experiments are also presented in this paper. (C) 2003 Society of Photo-optical Instrumentation Engineers.

Compensation for self-focusing by use of cascade quadratic nonlinearity

We demonstrate theoretically and experimentally compensation for positive Kerr phase shifts with negative phases generated by cascade quadratic processes. Experiments show correction of small-scale self-focusing and whole-beam self-focusing in the spatial domain and self-phase modulation in the temporal domain. (C) 2001 Optical Society of America.