The determination of the net fluxes from a mangrove estuary system

Determining the net exchange of constituents between a mangrove estuary system and the adjacent ocean has been re-examined using an extensive dataset from the Sungai Merbok a short, tidally energetic estuary in Malaysia. Previous analysis of the data had indicated that the time-mean sectionally averaged flow was not consistent with mass balance, apparently preventing meaningful estimation of net nutrient fluxes from the mangrove system. In this case the problem was aggravated by the lack of river gauge data and uncertainties introduced by the use of deflected-vane current meters to make the flow measurements. In an alternative approach to the analysis, we have sought to put bounds on the net discharge and hence obtain limits for the nutrient output from the estuary. Tide gauge measurements have been used in conjunction with the section flow data to determine the hypsometry of the mangrove system and hence yield an unbiased estimate of tidal transport Q_t. A salt balance condition, appropriate to a mixed estuary is then applied to permit an estimate of Q_f, the freshwater discharge. Q_f determined this way is found to be close to zero and certainly less than estimates for the period (mean ≈7 m³ s^?1) based on rainfall records and catchment area. The implication is that the combined effects of evaporation and transpiration are removing a large proportion of the fresh water entering the mangrove system from the rivers. The very low net discharge indicates total nitrogen exchange is dominated by the covariance of Q_t with the sectionally averaged concentration N_t. The considerable variation in this latter term combined with the large amplitude of Q_t results in a high variability of the nitrate flux so that the estimate of the mean (0.5 g s^?1) is subject to substantial sampling uncertainty (SE=12 g s^?1). The application of the salt balance condition to flux studies in other estuarine systems is considered. Particular attention is drawn to the requirements of this approach to flux determination and especially the need for good timing control to allow the proper determination of the tidal diffusion flux of salt and other components.     

Effects of natural organic matter from sediments on the growth of marine gas hydrates

Sediments recovered from 0 to 27 + meters below the seafloor (mbsf) of a gas-hydrate and gas-venting active area in the Gulf of Mexico were added to a hydrate growth test cell to determine the influence of the organic and inorganic sedimentary components on hydrate induction times and formation rates. Induction times were sixteen times shorter in the presence of sediment from approximately 18 mbsf (relative to sediment from 1 mbsf), and remained stable in the presence of sediment from 18 to 27 mbsf. Formation rates increased by a factor of 2.5 in the presence of sediments from approximately 18 mbsf and decreased somewhat in the presence of sediment from 18 to 27 mbsf. Selected samples (surface, 18 and 27 mbsf) were density fractionated and subjected to bulk elemental and X-ray photoelectron spectroscopy (XPS) analysis. XPS revealed the presence of iron in various chemical environments at depths of 18 and 27 mbsf. High Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) was used to characterize the organic component of sediments from selected depths. The discovery of intact proteinaceous material in the surface sediment was surprising due to the labile nature of these biopolymers, and potentially reflects microbial activity in these surface layers. This material was less abundant in sediment from increasing depths, where more lipid-like compounds were prominent. The results suggest that hydrate growth is inhibited by the presence of proteinaceous material but enhanced by lipid-like compounds associated with iron-bearing mineral surfaces.     

Displacement and strain patterns from naturally occurring shear zone terminations

Strain distribution patterns are described from several naturally occurring ductile shear zone terminations and a two-fold classification is suggested. Type I termination patterns show a symmetrical decrease in strain area and intensity, and are associated with very low shear strain (ψ) values in the main shear zone. The more common Type II termination patterns show a symmetrical increase in strain area with decrease in strain intensity. Some brittle-ductile examples of Type II terminations contain secondary shears that resemble splay faults. All the available evidence suggests that the deformation near the terminations of these shear zones is not plane strain, nor do the observed strain patterns readily fit the existing theoretical models.     

The formation of deep topsoils in Orkney

The Soil Survey for Scotland, in their mapping of the soils in Orkney, identified a deep top phase of the Bilbster Series. This soil is distinguished by having a topsoil usually in excess of 75 cm and it occurs almost exclusively on the Mainland of Orkney, especially in the west round Marwick and Skaill Bays. An anthropogenic origin to this soil is proposed and the present study is designed to investigate the particular processes of formation which have led to the increase in soil depth. Results from transect and grid surveys indicate how the soil is thickest adjacent to old farms. The historical literature suggests a wide range of possible inputs from seaweed and calcareous sand to turves after they had been used as bedding for cattle. Analytical results support the last process as the dominant one and an accumulation rate of c.1 mm/yr is proposed.     

Uptake and loss of zinc and lead by mussels (Mytilus edulis) and relationships with body weight and reproductive cycle

The uptake and loss of zinc and lead from the whole soft parts of the mussel Mytilus edulis were investigated under natural conditions in north-east England. Mussels in which high concentrations of these metals were found were transferred to an area where low concentrations were found, and vice versa. Mussels from both areas were also kept in tanks and periodic measurements of metal contents were made. Indications of uptake and loss were greatly affected by changing body weights and the work suggests that phase of reproductive cycle (for animals in the environment) and condition (for animals in tanks) have to be closely considered when reporting on levels of metals in mussels, especially in terms of concentration.