Decomposition rates of purple loosestrife (Lythrum salicaria) and Lyngbyei’s sedge (Carex lyngbyei) in the Fraser River estuary

Using litter bag experiments in the Fraser River estuary in British Columbia, we tested for differences in the relative decomposition rates between leaves of purple loosestrife (Lythrum salicaria), an introduced exotic and a native sedge (Carex lyngbyei). The difference in the mean decay rate coefficient for the two species was significantly defferent (p<0.01) and the coefficient for purple loosestrife (0.0110 d^?1) was nearly four times higher than for Lyngbyei's sedge (0.0028 d^?1). This is the first estimate of the decay rate coefficient for purple loosestrife from an estuary. The rapid decay rate of loosestrife leaves suggests that they supply detritus to the ecosystem in autumn whereas the much slower decay rate of sedge implies that it supplies detritus throughout the winter and early spring. Consumer organisms important in juvenile salmon food webs appear to be adapted to take advantage of the detritus provided in these seasons. The findings have implications for habitat management because purple loosestrife has recently invaded estuaries of the northeast Pacific and may be outcompeting native sedges important in detrital-based food webs.     

Analytic construction of periodic orbits about the collinear points

A third-order analytical solution for halo-type periodic motion about the collinear points of the circular-restricted problem is presented. The three-dimensional equations of motion are obtained by a Lagrangian formulation. The solution is constructed using the method of successive approximations in conjunction with a technique similar to the Lindstedt-Poincaré method. The theory is applied to the Sun-Earth system.     

The Distribution of Talitrid Amphipods (Crustacea) on a Salt Marsh in Southern Tasmania, in relation to Vegetation and Substratum

Supralittoral and terrestrial talitrid amphipods were collected from a salt marsh in Southern Tasmania by pitfall trapping along transects from the mid-tidal level to above the high-tide mark, and by hand collecting from sites chosen to represent the full range from salt marsh to terrestrial vegetation. At each site, the cover of all major plant species was recorded, and soil samples were collected from which soil moisture, organic content and salinity were measured.Eight talitrid species from four ecological groups were collected; one palustral species, one beachflea, three coastal landhoppers and three eastern forest landhoppers. There was substantial overlap in the distributions of these groups. The undescribed beachflea had the widest distribution, from the wettest, most saline sites to theSchoenus nitenstussock grassland at the extreme high-tide mark. The palustral species,Eorchestia palustris, overlapped substantially with the beachflea, but was found within a narrower band of salinities (though not in the most saline sites) and in more poorly-drained sites than the beachflea. Coastal landhoppers,Austrotroides maritimus,Keratroides rexand an undescribed species ofTasmanorchestia, were found mainly in theS. nitenstussock grassland, where they overlapped with forest landhoppers,Keratroides vulgaris,Mysticotalitrus tasmaniaeandM. cryptus, which were found mainly in non-saltmarsh terrestrial sites, well above the high-tide mark.These distributions are discussed in terms of the likelihood that salt marshes provided the route by which talitrid amphipods colonized land. There is no reason from these data to reject salt marshes as the route to land, and it is suggested that they are a more likely route than via rocky or sandy shores.     

Particle dynamics as controlled by the flow field of the eastern equatorial Pacific

Profiles made during the JGOFS EgPac October 1992 time series cruise to the equator with a Large Aggregate Profiling System (LAPS) recorded the concentration and size distribution of particles in the marine snow size range ( > 0.5 mm diameter). Profiles were made routinely at local midnight during the twenty day occupation of the time series station on the equator. The LAPS data set, when combined with the CTD/transmissometer data set from the EgPac program's intensive profiling operation, reveals a complex dynamic of particle production and aggregation driven by the equatorial flow field.During the cruise, the influence of the passage of a Tropical Instability Wave (TIW) was observed in the transmissometer/aggregate and temperature/salinity data sets. A peak in particle production rate occurred in conjunction with the maximum shoaling of the thermocline and a minimum in the aggregate volume concentration. Subsequently, the particle load in the surface water increased followed by an increase in the aggregate abundance. Quasi -oligotrophic conditions on the equator (subsurface particle and aggregate maxima and decreased particle production rates) toward the end of the time series corresponded to the appearance of stratified low salinity water characteristic of more northerly conditions.The variations in temperature and salinity fields are ascribed to the passage of a TIW; in sequence: the trailing edge, the northwestward-flowing cool cusp water and the convergent front. Current meters at the equator recorded a rotational flow at 80 m, with a shift from southeastward to northeastward flow during this sequence. A simple conceptual model of meridional flow field is presented in which poleward transport of the upwelled water from the equator returns at shallow depths to mix with the EUC. The signature of this return flow is reflected in the decrease in the vertical gradients of nutrients and oxygen at the equator with respect to the poleward gradients, and a subsurface particle maximum below the EUC. The flow field's effect on the distribution of particles is reflected in the meridional pattern of the sediment accumulation rate (Murray and Leinen, 1996). The return flow of particles to the equator is reflected in the maximum in accumulation rate near the equator. The longterm influence of TIW's is reflected in the asymmetry of the accumulation rates across the equator as described by Murray and Leinen (1996), with the maximum accumulation rate found south of the equator, a local minimum in accumulation rate at approximately 2°N, and a local maximum near 4°N.     

Variability in in situ shear strength of gassy muds

Torque measurements are made by divers with a vane apparatus to a sediment depth of 136 cm in the high-porosity, gassy sediments of Eckernförde Bay. Corrected shear strength values calculated from torque measurements are quite variable in the Eckernförde Bay sediments, varying from less than 0.5 kPa in the top 10 cm of sediment to 4–5 kPa at 136 cm sediment depth. Variability increases markedly below 60 cm sediment depth, probably because of the presence of methane gas bubbles within the sediment fabric.     

Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

The sulphur content of coal is an important consideration when developing reserves for exploitation, driven by emission limits from power stations becoming more stringent. Variations in the sulphur content of Westphalian A and B coals from the predominantly freshwater Northumberland Coalfield, Northeast England, were studied according to their regional, stratigraphic and in-seam location. The observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas, with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine-influenced. A model of basinal surface water and groundwater flow driven by post-depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal. However, the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the North Pennine Orefield along the southern margin of the coalfield, suggesting an additional potential source of secondary sulphur, as sulphur-rich fluids were expelled northwards through the coal measures during early Permian Variscan transpression from the south. The Westphalian A and B are interpreted as third-order depositional sequences, defined by third-order maximum flooding surfaces. Each sequence is made up of several coal-bearing fourth-order parasequences, which tend to be more brackish to marine in character, on either side of the third-order maximum flooding surfaces when base level was relatively high. The lowest sulphur coals are confined to the lower to middle, relative low stand part of the Westphalian A third-order base level curve and the lowest part of the Westphalian B third-order base level curve. This difference is attributed to a more rapid rise of base level in the Westphalian B. The stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations.     

The use of ultra-sound in the preparation of carbonate and clay sediments for chironomid analysis

Initial investigations of Holocene carbonate sediment from Hawes Water, Northwest England, yielded lower numbers of chironomid head capsules than anticipated. Standard techniques used to prepare sediment for chironomid analysis were ineffective in breaking up the coarse crystalline sediment structure sufficiently. This led to large amounts of sediment being retained and increased sample processing times. The low yield of head capsules also meant that more sediment was needed to produce adequate numbers of head capsules for analysis. The use of ultra-sound as part of the sediment processing was investigated. This technique reduced the amount of sediment left for sorting and yielded significantly more head capsules which were of equivalent structural condition and cleaner than those produced by conventional methods. The technique was extended to clay samples where similar results were obtained although shorter treatment times are recommended. The proportion of Tanytarsini and Tanypodinae heads increased significantly in carbonate and clay samples, respectively; both sediment types showed a significant decline in the proportion of Chironomini. The results indicate that ultra-sonic preparation of samples will yield a more accurate representation of chironomid assemblages in sediments leading to greater sensitivity and reliability in analysing past environmental conditions.     

Metamorphic consequences of crustal eclogite production in overthrust orogenic zones

Continental collision can produce crust of much greater than normal thickness in whose lower part eclogite facies conditions may pertain. The resulting density increase of ca. 0.3 Mg m^?3 greatly decreases the buoyancy forces normally regarded as inhibiting the subduction of continental material. The high-density phase may persist for tens of millions of years giving anomalously low surface elevation of the thickened continent and inhibiting erosion.Temperature relaxation in the overthrust pile produces regional metamorphism. The conditions of metamorphism are analysed in terms of varying initial thermal gradient, erosion rate constant and the presence or absence of the eclogite transition. The suite of recorded metamorphic P-T conditions, called the piezothermic array has a slope which is insensitive to the variable conditions. High-temperature metamorphic rocks can be produced either by high initial thermal gradient or by relatively slow erosion of eclogite-weighted crust: to distinguish these causes, details of the chronology of metamorphic recrystallization are required.     

Textural evidence bearing on the origin of isolated olivine crystals in C2 carbonaceous chondrites

In some cases the mechanical competence of chondrules in carbonaceous chondrites has been reduced by alteration of their mesostasis glass to friable phyllosilicate, providing a mechanism by which euhedral olivines can be separated from chondrules. Morphological features of isolated olivine grains found in carbonaceous chondrites are similar to those of olivine phenocrysts in chondrules. These observations suggest that the isolated olivine grains formed in chondrules, by crystallization from a liquid, rather than by condensation from a vapor.