Effects of an Artificial Breakwater on the Distributions of Planktonic Microbial Communities

The summer distributions of planktonic microbial communities (heterotrophic and phtosynthetic bacteria, phtosynthetic and heterotrophic nanoflagellates, ciliate plankton, and microphytoplankton) were compared between inner and outer areas of Lake Sihwa, divided by an artificial breakwater, located on the western coast of Korea, in September 2003. The semienclosed, inner area was characterized by hyposaline surface water (<17 psu), and by low concentrations of dissolved oxygen (avg. 0.4 mg L¹) and high concentrations of inorganic nutrients (nitrogenous nutrients >36 μM, phosphate <4 μM) in the bottom layer. Higher densities of heterotrophic bacteria and nanoflagellates also occurred in the inner area than did in the outer area, while microphytoplankton (mainly diatoms) occurred abundantly in the outer area. A tiny tintinnid ciliate, Tintinnopsis nana, bloomed into more than 10⁶ cells L¹ at the surface layer of the inner area, while its abundance was much lower (10³-10⁴ cells L¹) in the outer area of the breakwater. Ciliate abundance was highly correlated with heterotrophic bacteria (r = 0.886, p < 0.001) and heterotrophic flagellates (r = 0.962, p < 0.001), indicating that rich food availability may have led to theT. nana bloom. These results suggest that the breakwater causes the eutrophic environment in artificial lakes with limited flushing of enriched water and develops into abundant bacteria, nanoflagellates, and ciliates.     

Shallow water depth retrieval from space-borne SAR imagery

Based on shallow water bathymetry synthetic aperture radar (SAR) imaging mechanism and the microwave scattering imaging model for oceanic surface features, we developed a new method for shallow water depth retrieval from space-borne SAR images. The first guess of surface currents and winds are estimated from the normalized radar crossing section (NRCS) profile of shallow water bathymetry SAR imagery, according to the linear theory and geophysical model function. The NRCS profile is then simulated by the microwave scattering imaging model. Both the surface currents and winds are adjusted by using the dichotomy method step by step to make the M4S-simulated NRCS profiles approach those observed by SAR. Then, the surface currents and the wind speeds are retrieved when a best fit between simulated signals and the SAR image appears. Finally, water depths are derived using the Navier–Stokes equation and finite difference method with the best estimated currents and the surface winds. The method is tested on two SAR images of the Taiwan Shoal. Results show that the simulated shallow water NRCS profile is in good agreement with those measured by SAR with the correlation coefficient as high as 85%. In addition, when water depths retrieved from the SAR image are compared with in situ measurements, both the root mean square and relative error are less than 3.0 m and 6.5%, respectively, indicating that SAR images are useful for shallow water depth retrieval and suggesting that the proposed method in this paper is convergent and applicable.     

Long-term (1998–2007) trends on the spatial distribution of heterotrophic ciliates in the East China Sea in summer: effect of the Three Gorges Dam construction

The spatial distribution of heterotrophic ciliates, environmental factors and potential food items (bacteria, Synechococcus spp. and nanoflagellates) were measured in the East China Sea to examine which variables contributed importantly to the long-term distribution of ciliates between 1998 and 2007. In July 1998 and June 2003, heterotrophic ciliates were found to be abundant (1,000–2,000 × 10³ cells m⁻³) in regions where surface salinity <32 but extremely low (<500 × 10³ cells m⁻³) in shelf waters of surface salinity >32. After August 2003, shortly after the completion of the Three Gorges Dam, we found no significant areal differences in the abundance of heterotrophic ciliates (HC). However, we found a significantly negative correlation between temperature and HC abundance of surface water after the completion of the dam, suggesting that temperature had a greater influence on HC abundance, once the original saline state had changed. For the long-term trends on the vertical distribution of HC, their abundance was significantly higher in the upper 50 m of the water column than at either 75 or 100 m. Abundance of Synechococcus spp. at these levels varied significantly in regions of surface salinity <32, suggesting that ciliates and picophytoplankton contribute greatly to mediating the transfer of organic matter to higher trophic levels in this marine ecosystem.     

Experimental researches on reflective and transmitting performances of quarter circular breakwater under regular and irregular waves

A series of regular and irregular wave experiments are conducted to study the reflective and transmitting performances of quarter circular breakwater (QCB) in comparison with those of semi-circular breakwater (SCB). Based on regular wave tests, the reflection and transmission characteristics of QCB are analyzed and a few influencing factors are investigated. Then, the wave energy dissipation as wave passing over the breakwater is discussed based on the hydraulic coefficients of QCB and SCB. In irregular wave experiments, the reflection coefficients of QCB and their spectrums are studied. Finally, the comparisons between the experimental results and numerical simulations for QCB under regular and irregular wave conditions are presented.     

Numerical studies of methane production from Class 1 gas hydrate accumulations enhanced with carbon dioxide injection

Class 1 gas hydrate accumulations are characterized by a permeable hydrate-bearing interval overlying a permeable interval with mobile gas, sandwiched between two impermeable intervals. Depressurization-induced dissociation is currently the favored technology for producing gas from Class 1 gas hydrate accumulations. The depressurization production technology requires heat transfer from the surrounding environment to sustain dissociation as the temperature drops toward the hydrate equilibrium point and leaves the reservoir void of gas hydrate. Production of gas hydrate accumulations by exchanging carbon dioxide with methane in the clathrate structure has been demonstrated in laboratory experiments and proposed as a field-scale technology. The carbon dioxide exchange technology has the potential for yielding higher production rates and mechanically stabilizing the reservoir by maintaining hydrate saturations. We used numerical simulation to investigate the advantages and disadvantages of using carbon dioxide injection to enhance the production of methane from Class 1 gas hydrate accumulations. Numerical simulations in this study were primarily concerned with the mechanisms and approaches of carbon dioxide injection to investigate whether methane production could be enhanced through this approach. To avoid excessive simulation execution times, a five-spot well pattern with a 500-m well spacing was approximated using a two-dimensional domain having well boundaries on the vertical sides and impermeable boundaries on the horizontal sides. Impermeable over- and under burden were included to account for heat transfer into the production interval. Simulation results indicate that low injection pressures can be used to reduce secondary hydrate formation and that direct contact of injected carbon dioxide with the methane hydrate present in the formation is limited due to bypass through the higher permeability gas zone.     

Depositional architecture and sequence stratigraphy of the Karoo basin floor to shelf edge succession, Laingsburg depocentre, South Africa

The Laingsburg depocentre of the SW Karoo Basin, South Africa preserves a well-exposed 1200 m thick succession of upper Permian strata that record the early filling of a basin during an icehouse climate. Uniformly fine-grained sandstones were derived from far-field granitic sources, possibly in Patagonia, although the coeval staging and delivery systems are not preserved. Early condensed shallow marine deposits are overlain by distal basin plain siltstone-prone turbidites and volcanic ashes. An order of magnitude increase in siliciclastic input to the basin plain is represented by up to 270 m of siltstone with thin sandstone turbidites (Vischkuil Formation). The upper Vischkuil Formation comprises three depositional sequences, each bounded by a regionally developed zone of soft sediment deformation and associated 20-45 m thick debrite that represent the initiation of a major sand delivery system. The overlying 300 m thick sandy basin-floor fan system (Unit A) is divisible into three composite sequences arranged in a progradational-aggradational-retrogradational stacking pattern, followed by up to 40 m of basin-wide hemipelagic claystone. This claystone contains Interfan A/B, a distributive lobe system that lies 10 m beneath Unit B, a sandstone-dominated succession that averages 150 m thickness and is interpreted to represent a toe of slope channelized lobe system. Unit B and the A/B interfan together comprise 4 depositional sequences in a composite sequence with an overall basinward-stepping stacking pattern, overlain by 30 m of hemipelagic claystone. The overlying 400 m thick submarine slope succession (Fort Brown Formation) is characterized by 10-120 m thick sand-prone to heterolithic packages separated by 30-70 m thick claystone units. On the largest scale the slope stratigraphy is defined by two major cycles interpreted as composite sequence sets. The lower cycle comprises lithostratigraphic Units B/C, C and D while the upper cycle includes lithostratigraphic Units D/E, E and F. In each case a sandy basal composite sequence is represented by an intraslope lobe (Units B/C and D/E respectively). The second composite sequence in each cycle (Units C and E respectively) is characterized by slope channel-levee systems with distributive lobes 20-30 km down dip. The uppermost composite sequence in each cycle (Units D and F respectively) are characterised by deeply entrenched slope valley systems. Most composite sequences comprise three sequences separated by thin (<5 m thick) claystones. Architectural style is similar at individual sequence scale for comparable positions within each composite sequence set and each composite sequence. The main control on stratigraphic development is interpreted as late icehouse glacio-eustasy but along-strike changes associated with changing shelf edge delivery systems and variable bathymetry due to differential substrate compaction complicate the resultant stratigraphy.     

Defining the concept of stratigraphic grade and applying it to stratal (reservoir) architecture and evolution of the slope-to-basin profile: An outcrop perspective

Stratigraphic grade is the similarity of the morphology of successive slope-to-basin profiles in a genetically related depositional system. In this article we use data collected from regional cross-sections of six depositional systems, stratal architecture derived from outcrops of the Lewis Shale (Wyoming, USA), and the Ross Sandstone (Ireland), and supplementary outcrop and subsurface data from other depositional systems to determine how stratigraphic grade relates to stratal (reservoir) architecture in deepwater systems.Four methods are developed that collectively define stratigraphic grade: (1) regional stacking patterns of fourth-order stratigraphic surfaces, (2) the relationship between the trajectory of the shelf edge (T_se) and the trajectory of the depocenter (T_d) for fourth-order stratigraphic units, (3) morphology of the slope-to-basin profiles of fourth-order stratigraphic surfaces, and (4) the similarity of the morphologies of slope-to-basin profiles of fourth-order surfaces in a system (σ_s, σ_r). Several characteristics of stratigraphic (reservoir) architecture of fourth-order stratigraphic cycles are related to stratigraphic grade: (1) longitudinal distribution of sandstone in fourth-order cycles, (2) location of maximum sandstone relative to the depocenter of fourth-order cycles, (3) lengths of fourth-order submarine fans, and (4) longitudinal and vertical distribution of architectural elements. Stratigraphic grade is thus a predictor of reservoir architecture and can thereby be used to reduce the uncertainty in the interpretation of subsurface data.The concept of stratigraphic grade is useful in understanding the stratigraphic evolution of deepwater systems. Most deepwater systems analyzed in this study initiated as out-of-grade and temporally evolved to graded systems over a time span of millions of years. Systems rarely evolve from graded to out-of-grade. First-order controls on stratigraphic grade are determined to be angle of slope, tectonically forced changes in angle of slope during deposition, and sediment supply.     

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats in the US Pacific Northwest

This study shows that spatially and temporally recurring benthic macrofauna-habitat patterns validate the ecological relevance of habitat types to benthic macrofauna and suggest they can serve as elements in ecological periodic tables of benthic macrofaunal usage. We discovered patterns across nine habitat types (intertidal eelgrass [Zostera marina], dwarf eelgrass [Zostera japonica], oyster [Crassostrea gigas] ground culture, burrowing mud shrimp [Upogebia pugettensis], burrowing ghost shrimp [Neotrypaea californiensis], shell, sand, mud, and subtidal) on a variety of benthic macrofaunal community state variables in Grays Harbor, Washington, USA and compared them to those in Willapa Bay, Washington, USA. There were nominal differences in benthic macrofaunal Bray-Curtis similarity between all the habitats investigated except eelgrass and oyster in both estuaries. Across-habitat patterns on mean benthic macrofaunal species richness, abundance, biomass, abundance of deposit, suspension and facultative feeders, a dominance and a diversity index for the five habitats common to both studies were the same on a rank measurement scale: eelgrass ≈ oyster > mud shrimp > ghost shrimp ≈ subtidal. The patterns for most of the habitats and benthic macrofaunal measures were the same on a ratio measurement scale.     

Rare earth elements in suspended and bottom sediments of the Mandovi estuary, central west coast of India: Influence of mining

Rare earth elements (REEs) in the suspended particulate matter (SPM) of the Mandovi estuary indicated that the mean total-REEs (∑REE) and light REE to heavy REE ratios are lower than that of the average suspended sediment in World Rivers and Post-Archean average Australian shale. High ∑REE were associated with high SPM/low salinity and also with high SPM/high salinity. Although the ∑REE broadly agree with SPM levels at each station, their seasonal distributions along transect are different. SPM increased seaward in the estuary both during the monsoon and pre-monsoon, but consistently low at all stations during the post-monsoon. The mean ∑REE decreased marginally seaward and was <25% at sea-end station than at river-end station. Spatial variations in ∑REE are maximum (64%) during the pre-monsoon. Strong to moderate correlation of ∑REE with Al, Fe and Mn in all seasons indicates adsorption and co-precipitation of REEs with aluminosilicate phases and Fe, Mn-oxyhydroxides. The ratio of mean ∑REE in sediment/SPM is low during the monsoon (1.27), followed by pre-monsoon (1.5) and post-monsoon (1.62). The middle REE- and heavy REE-enriched patterns with positive Ce and Eu anomalies are characteristic at every station and season, both in SPM and sediment. They also exhibit tetrad effect with distinct third and fourth tetrads. Fe-Mn ore dust is the most dominant source for REEs. However, the seasonal changes in the supply of detrital silicates, Fe-Mn ore dust and particulates resuspended from bottom sediments diluted the overall effect of salinity on fractionation and distribution of REEs in the estuary.     

Marine renewable energy: The ecological implications of altering the hydrodynamics of the marine environment

Many countries now recognise the need for mitigation of climate change induced by human activities and have incorporated renewable energy resources within their energy policy. There are extensive resources of renewable energy within the marine environment and increasing interest in extracting energy from locations with either large tidal range, rapid flow with and without wave interaction, or large wave resources. However, the ecological implications of altering the hydrodynamics of the marine environment are poorly understood. Ecological data for areas targeted for marine renewable developments are often limited, not least because of the considerable challenges to sampling in high energy environments. In order to predict the scale and nature of ecological implications there is a need for greater understanding of the distribution and extent of the renewable energy resource and in turn, of how marine renewable energy installations (MREIs) may alter energy in the environment. Regional ecological implications of a MREI need to be considered against the greater and global ecological threat of climate change. Finally, it is recommended that the identification of species and biotopes susceptible to the removal of hydrokinetic energy could be a suitable strategy for understanding how a MREI may alter flow conditions.