Water Quality Improvements in Liverpool Docks: The Role of Filter Feeders in Algal and Nutrient Dynamics

Abstract. The redevelopment of disused docks around Liverpool into areas suitable for shops, offices, housing and recreational watersports has necessitated the maintenance of good water quality in these areas. The main source of water to the docks is the River Mersey, which contains high concentrations of nutrients, encouraging algal blooms - including potentially nuisance species - in the enclosed dock basins. Since 1988 an extensive monitoring programme has been run sampling the hydrography, plankton and benthos of the docks. During this period there has been an improvement in water quality, including a reduction in summer phytoplankton biomass and anoxic bottom water. There are strong indications that phytoplankton biomass has been severely reduced by the filter feeding of Mytifus edulis . Changes in the composition of the benthic community since 1988 suggest that the large population of M. edulis is now suffering from limited recruitment. The long-term development and stability of the system is discussed with reference to community succession and its link to ecosystem functioning.     

A carbon and nitrogen flux model of mussel digestive gland epithelial cells and their simulated response to pollutants

The mussel digestive gland epithelial cells provide a key interface between the organism and pollutants such as aromatic hydrocarbons. The simulation of their uptake and export mechanisms as well as an internal protein degradation pathway, and any subsequent disruption to any of them, has been undertaken. A computational model is described, which simulates the flow of carbon and nitrogen through a mussel's digestive cell. The model uses a compartmentalised view of the cell with inviolate 'pipelines' connecting each of the volume-variable partitions. Only the major physiological pathways relevant to the flow of either carbon or nitrogen or volume are modelled. Simulated response to hydrocarbon exposure is examined.     

A numerical method for the solution of a line source under a free surface

A modified source-and-dipole type singularity panel method is proposed to calculate the flow properties for an oscillating arbitrary body in the presence of a free surface. The technique is based on Green's identity whereby the boundary value problem is expressed as a boundary integral equation which is solved numerically. The free-space Green function is used in the integral equation. To demonstrate the feasibility of the method, the problem of a pulsating submerged line source under a free surface is treated and results are compared with the exact solution.An excellent agreement with the theory is obtained for panel density of about ten panels per wavelength and paneled water surface length of two wavelengths with very low computing times, indicating the feasibility of the method for unsteady water wave problems.     

Fossil spreading center and faults within the Panama Fracture Zone

The north/south-trending Panama Fracture Zone forms the present eastern boundary of the Cocos Plate, with the interplate motion being right-lateral strike-slip. This fracture zone is composed of at least four linear troughs some hundreds of kilometers in length. Separate active or historic faults undoubtedly coincide with each trough. The greatest sediment fill is found in the easternmost trough. Surface and basement depths of the western trough are generally greater than those of the other three; the western trough contains the least sediment, and is most continually linear. Morphology and sediments suggest that the principal locus of strike-slip movement within the fracture zone probably migrated incrementally westward from one fault-trough to another. From north to south, the fracture zone apparently narrows from the continental intersection to approximately 5°30N, and again widens from about 5°N to at least 3°N. Residual E/W-trending magnetic anomalies are centered between two of the four troughs; sea floor spreading in a north-south direction is interpreted to have occurred between 5°30N and 7°N from 4.5 m.y. ago to 2 m.y. ago, with the symmetric center roughly coinciding with a rift valley at 6°10N, 82°30W.     

Distribution of lifetimes for coronal soft X-ray bright points

We have measured the lifetimes of all compact emission features visible on three sets of high time resolution soft X-ray images. The spectrum of lifetimes is found to be heavily weighted toward short lifetimes. The number of features present on the disk which live 2–48 hours is at least ten times as great as the number living more than 48 hours. The distribution of lifetimes can be fit in all three cases by a four-parameter function N(t) = N _s exp(-t/ _s ) + N _L exp(-t/ _L ), with _s = 8.7±0.2, _L = 35±4 and N _s 10N _L . Features living two days or less have a very broad latitude distribution (Golub et al., 1974, 1975) whereas nearly all longer-lived features are found within 30° of the equator. The growth rates of long-lived vs short-lived points are the same to within 20%, the major difference being that long-lived points continue to grow and generally reach larger sizes.Harvard College Observatory/Smithsonian Astrophysical Observatory.     

Investigation of Uranus,its satellites,and distant interplanetary phenomena by spacecraft techniques

A brief digest is given of the principal scientific objectives that can be addressed effectively, and perhaps uniquely, by spacecraft missions to Uranus. Practical considerations favor the launching of such missions in late 1979, with subsequent swing-bys of Jupiter and arrival at Uranus in late 1986.     

Supergranular line profile variation of Mg i λ2852

The chromospheric network is barely visible in the Mg i 2852 line. Unlike in plages, where it shows well-defined self-reversed emission structure in the core, the line is an unreversed absorption feature in the network boundaries, exhibiting only a small blue asymmetry. In the network cell interiors, the line is unreversed and symmetrical.     

The decay of coronal loops brightened by flares and transients

The sizes and shapes of X-ray emitting loops brightened by flares and other coronal transients have been derived from the Skylab S-054 photographs. This information has been combined with estimates of temperature and emission measure derived from the photographs and from Solrad data to compute brightness decay times attributable to various coronal energy loss mechanisms. The computed decay times are compared to those actually observed. Examples are presented of the brightness decay of soft X-ray flare kernels, post-flare loops, and the coronal X-ray enhancement asssociated with an H filament disappearance.The computed decay time due to conductive losses is always found to be much more rapid than that due to radiative losses in the corona. However, the observed soft X-ray brightness decay times are always much longer than those computed from conductive cooling.The role of geometrical inhibition of conduction as discussed by Antiochos and Sturrock (1976a) is examined for these events. It is shown that this mechanism might be adequate to account for the observed results in two of the five cases examined, but it is inadequate in the other three. The possible breakdown of classical collisional thermal conductivity (Forslund, 1970) is examined and it is shown that this mechanism is not applicable to the cases presented here. Confirmation of the existence of the very high conductive fluxes predicted by the coronal flare conductive cooling models is sought from EUV and H observations. No evidence is found which unequivocally demonstrates the presence, at lower levels in the atmosphere, of very high conductive fluxes. The soft X-ray results are consistent with the continuation of evaporation driven by thermal conduction (Antiochos and Sturrock, 1976b) late into the decay phase of the event. In this case, no source of continued magnetic energy dissipation after the initial stages of the flare is required to explain the lifetime of the X-ray emitting loops.