Limnology of Morton dam and upper Karori reservoir,Wellington, New Zealand

Chemical and biological data were collected between 1947 and 1967 from Morton Dam and Upper Karori Reservoir, two artificial lakes which are part of the water supply of Wellington City, New Zealand.

Chemical analyses included the major ions, nutrients, and physical and chemical properties of engineering importance. The emphasis in biological analyses was on the dominant phytoplankters. Bacteriological results are presented as tables of plate counts and “most probable numbers” of confirmed faecal coli‐forms; iron‐fixing bacteria were identified.

Primary productivity has accelerated since 1940–42: annual maxima have increased 30‐fold at Morton Dam, and 10‐fold in Upper Karori Reservoir. In 1942, Morton Dam was believed to be oligotrophic, but the type and quantity of phytoplankton at present indicate a rapid progression to eutrophy.

Despite the extent of biological changes, no dramatic changes in the physical and chemical characteristics of either reservoir can be detected.     

Nitrogen budget of the eelgrass, Zostera marina in a bay system on the south coast of Korea

Above- and below-ground productivities and tissue N content were measured monthly to quantify N incorporation to sustain eelgrass growth in Koje Bay on the south coast of Korea from January to December 2002. N acquisition was also estimated through measurements of N uptake kinetics, tissue biomass, and in situ inorganic N concentrations in water column and sediments. Above- and below-ground productivities were highest in summer and lowest in late fall and winter. Leaf tissue N content was highest in December and lowest in July, while rhizome tissue N content was highest in October and lowest in April. Estimated monthly N incorporation by leaf tissues based on the leaf productivity and N content ranged from 0.4 g N m^?2 month^?1 in November to 2.0 g N m^?2 month^?1 in May. N incorporation by below-ground tissues ranged from 0.1 g N m^?2 month^?1 in February to 0.2 g N m^?2 month^?1 in October. Annual whole plant N incorporation was 14.5 g N m^?2 y^?1, and N incorporation by leaf tissues accounted for about 87 % of total N incorporation. Maximum uptake rate (V _max ) and half saturation constant (K _m ) of leaf NH₄ ⁺ uptake were significantly lower than those of root NH₄ ⁺ uptake. Above- and below-ground biomass ranged from 20.8 g DW m^?2 and 8.6 g DW m^?2 in winter to 350.0 g DW m^?2 and 81.3 g DW m^?2 in spring, respectively. NH₄ ⁺ concentrations varied from 0.2 to 4.3 mM in water column and from 93.0 to 551.7 mM in sediment pore water. Based on these measurements, annual N acquisition by root tissues contributed slightly higher than that by leaf tissues to total plant N acquisition. During winter, monthly leaf N acquisition was lower than monthly leaf N incorporation. This implies that Z. marina has internal nitrogen retention system to offset the shortage and excess of nitrogen.     

Coastal environmental assessment and management by ecological simulation in Yeoja Bay, Korea

An eco-hydrodynamic model was used to estimate the carrying capacity of pollutant loads and response of water quality to environmental change in Yeoja Bay, Korea. An energy-system model also was used to simulate the fluctuation in nutrients and organic matter in the bordering wetland. Most water quality factors showed a pulsed pattern, and the concentrations of nutrients and organic matter of seawater increased when input loads of nutrients increased due to freshwater discharge. The well-developed tidal zones and wetlands in the northern area of the bay were highly sensitive to input loads. Residence times of water, chemical oxygen demand (COD), and dissolved inorganic nitrogen (DIN) within the bay were estimated to be about 16 days, 43.2 days, and 50.2 days, respectively. Water quality reacted more sensitively to the effects of nitrogen and phosphorus input than to COD. A plan to reduce the present levels of COD and dissolved inorganic phosphorus (DIP) by 20–30% and DIN by at least 50% in pollutant loads is needed for satisfying the target water quality criteria. The natural removal rate of nutrients in wetlands by reeds was assessed to be approximately 10%.     

Life cycle and population dynamics of Idotea balthica basteri (Pallas, 1772), Isopoda Valvifera from the Bizerte lagoon (Southern Mediterranean Sea – Tunisia)

The population dynamics and life cycle of Idotea balthica basteri (Pallas, 1772) were studied at the Menzel Jemil (lagoon of Bizerte, Tunisia) based on monthly samples taken from October 2009 to September 2011. The presence of juveniles and gravid females throughout the sampling period showed that this species exhibits continuous reproduction. Sexual differentiation occurs in approximately 43–59 days. Females took 88–160 days (3–5.5 months) to reach sexual maturation, and males took 102 days (3.5 months). The fecundity and fertility values exhibited a great variation in the number of eggs and embryos or mancae inside the marsupium which was correlated with the length of the gravid females. The sex ratio underwent fluctuations throughout the sampling period but was always in favour of females. Size frequency distributions were analysed recognizing 24 cohorts during the sampling period. Six cohorts were identified in October 2009 and 18 cohorts in November 2009–September 2011. Among these latter cohorts, nine were tracked till they disappeared. The minimum average size of new cohorts ranged from 1.92 ± 0.31 to 2.97 ± 0.26 mm and the maximum values ranged from 12.83 ± 0.96 to 19.23 ± 0.56 mm. Life span was estimated at 10–14 months. I. balthica basteri, in the lagoon of Bizerte, is a semi‐annual species with iteroparous females, and a bivoltine life cycle that produces two generations per year.     

Effects of ocean acidification and high temperatures on the bryozoan Myriapora truncata at natural CO2 vents

There are serious concerns that ocean acidification will combine with the effects of global warming to cause major shifts in marine ecosystems, but there is a lack of field data on the combined ecological effects of these changes due to the difficulty of creating large‐scale, long‐term exposures to elevated CO₂ and temperature. Here we report the first coastal transplant experiment designed to investigate the effects of naturally acidified seawater on the rates of net calcification and dissolution of the branched calcitic bryozoan Myriapora truncata (Pallas, 1766). Colonies were transplanted to normal (pH 8.1), high (mean pH 7.66, minimum value 7.33) and extremely high CO₂ conditions (mean pH 7.43, minimum value 6.83) at gas vents off Ischia Island (Tyrrhenian Sea, Italy). The net calcification rates of live colonies and the dissolution rates of dead colonies were estimated by weighing after 45 days (May–June 2008) and after 128 days (July–October) to examine the hypothesis that high CO₂ levels affect bryozoan growth and survival differently during moderate and warm water conditions. In the first observation period, seawater temperatures ranged from 19 to 24 °C; dead M. truncata colonies dissolved at high CO₂ levels (pH 7.66), whereas live specimens maintained the same net calcification rate as those growing at normal pH. In extremely high CO₂ conditions (mean pH 7.43), the live bryozoans calcified significantly less than those at normal pH. Therefore, established colonies of M. truncata seem well able to withstand the levels of ocean acidification predicted in the next 200 years, possibly because the soft tissues protect the skeleton from an external decrease in pH. However, during the second period of observation a prolonged period of high seawater temperatures (25–28 °C) halted calcification both in controls and at high CO₂, and all transplants died when high temperatures were combined with extremely high CO₂ levels. Clearly, attempts to predict the future response of organisms to ocean acidification need to consider the effects of concurrent changes such as the Mediterranean trend for increased summer temperatures in surface waters. Although M. truncata was resilient to short‐term exposure to high levels of ocean acidification at normal temperatures, our field transplants showed that its ability to calcify at higher temperatures was compromised, adding it to the growing list of species now potentially threatened by global warming.     

Seasonal variability of community structure and breeding activity in marine phytal harpacticoid copepods on Ulva pertusa from Pohang,east coast of Korea

Seasonal changes in community structure and reproductive status of phytal harpacticoid copepods in the shallow sublittoral bottom at two sites (Masan-ri and Guryongpo) in Pohang (Korea) are described monthly over a period of 1 year (October 1996 to September 1997). A total of 36 harpacticoid species was identified and the numerically dominant copepods were made up of the families Porcellidiidae and Tisbidae. Although the number of species did not show a seasonal trend, total harpacticoid density revealed a favorable distribution for the warmer season (spring and summer) at both sites. Multiple linear regression analyses showed that univariate indices such as density, evenness and diversity are closely associated with certain environmental parameters. For example, the dominant species fluctuated seasonally in abundance and their maximum densities were found to be temperature- (+ with Porcellidium ofunatense) and nutrient-dependent (+ with Scutellidium longicauda acheloides, + with Zaus unisetosus, and ? with P. wandoensis). In addition, the dominant species appeared to breed year round and their reproductive indices are significantly correlated with some environmental parameters such as temperature (?), pH (+), and phosphate (+). Three species (S. l. acheloides, P. wandoensis, and P. ofunatense) showed maximum density two or three months after their reproductive activity reached a maximum. Overall, the seasonal changes in a phytal harpacticoid community could be explained by combinations of environmental parameters supporting the complexity and biodiversity for this specific group of species in coastal ecosystems.     

A large mid-channel sand bar in the macrotidal seaway of outer Asan Bay, Korea: 30 years of morphologic response to anthropogenic impacts

Over the past three decades, dike constructions along the shores and dredging activities for navigation purposes have caused significant sedimentologic/morphologic modifications of a mid-channel bar situated in the tidal seaway of outer Asan Bay, Korea, as shown by a comparison of two sediment datasets collected in the channel and over the bar in 1977 and 2008. In addition, three hydrographic charts published in 1976, 1989, and 2006 were analyzed using GIS to estimate sand volume budgets and any bar migration. The bar is currently about 15 km long and 2–5 km wide, with a relief of 15 m. It is elongated in the tidal flow direction, but asymmetric in cross section. Chart analyses reveal a dramatic reduction in size and volume over the study period. An approximate 19% net loss in total sediment volume was calculated between 1976 and 1989. Since then, a net gain of about 7% has been estimated. The surface areas between selected depth contours reveal a similar pattern, i.e., substantial shrinking until 1989, followed by slight expansion up to 2006. Comparing selected textural parameters (mean grain size, sorting) of a 2008 sediment sampling campaign with those of a 1977 survey, it was found that mean grain sizes have decreased by as much as 1-phi interval, and that the sediments have become more poorly sorted in the vicinity of the bar over the 30-year study period, probably due to a sudden decrease in tidal energy flux after completion of the adjacent dikes. A particular feature is the temporary response of the bar to man-made impacts, characterized by substantial shrinking along its southwestern flank, and slight expansion along its northeastern flank. The observed changes in bar morphology can plausibly be explained by a sudden decrease in sediment supply resulting from a reduction in tidal prism in the wake of diking. The bar initially shrunk, but since 1989 has begun to gradually recover. To compensate the deficit, the bar has lowered its base level by scouring troughs along both flanks.     

Instrumentation and Numerical Analysis of Cylindrical Diaphragm Wall Movement During Deep Excavation at Coastal Area

The lateral deflection of a cylindrical diaphragm wall and the associated ground movement induced by deep excavation are analyzed by performing site instrumentations and numerical analyses in the coastal area of Korea. Wall lateral deflection, rebar stress, and pore water pressure were measured and analyzed in eight directions. Variations of soil properties with the decrease of confining pressure are compared by performing various in situ tests before ad after excavation. To calculate the wall lateral deflection accurately, the effects of small strain nonlinearity, confining pressure, and the hysteresis loading/unloading loop developed during excavation are considered in the proposed numerical analysis. By comparing numerical results with measured ones, the importances of considering small strain nonlinearity and confining pressure reduction in the nonlinear (FEM) are emphasized. Also, the effects of wall stiffness on the performance of cylindrical diaphragm walls are studied for future similar excavation in the coastal area.     

Geomorphology of unique reefs on the western Canadian shelf: sponge reefs mapped by multibeam bathymetry

Multibeam imagery of siliceous sponge reefs (Hexactinellida, Hexactinosida) reveals the setting, form, and organization of five reef complexes on the western Canadian continental shelf. The reefs are built by framework skeleton sponges which trap clay-rich sediments resulting in a distinctive pattern of low intensity backscatter from the reefs that colonize more reflective glacial sediments of higher backscatter intensity. Bathymetry and backscatter maps show the distribution and form of reefs in two large complexes in the Queen Charlotte Basin (QCB) covering hundreds of km², and three smaller reef complexes in the Georgia Basin (GB). Ridges up to 7 km long and 21 m in height, together with diversely shaped, coalescing bioherms and biostromes form the principal reef shape in the QCB whereas chains of wave-form, streamlined mounds up to 14 m in height have developed in the GB. Reef initiation is dependent on the distribution of high backscatter-intensity relict glacial surfaces, and the variation in reef complex morphology is probably the result of tidally driven, near seabed currents.     

Numerical and experimental study on hydrodynamic interaction of side-by-side moored multiple vessels

This paper aims to investigate the basic interaction characteristics of side-by-side moored vessels both numerically and experimentally. A higher-order boundary element method (HOBEM) combined with generalized mode approach is applied to analysis of motion and drift force of side-by-side moored multiple vessels (LNG FPSO, LNGC and shuttle tankers). Model tests were carried out for the same floating bodies investigated in the numerical study in regular and irregular waves. Global and local motion responses and drift forces of three vessels are compared with those of calculations. Discussions is highlighted on applicability of numerical method to prediction of sophisticated multi-body interaction problem of which motion behavior is very important to analysis of mooring dynamics of deep sea floating bodies.