Effects of salinity on treatment of municipal wastewater by constructed mangrove wetland microcosms

The effects of salinity on the removal of dissolved organic carbon and nutrients from municipal wastewater by constructed mangrove microcosms planted with Aegiceras corniculatum were investigated. During the four-month wastewater treatment, the treatment efficiency was reduced by high salinity, and the removal percentages of dissolved organic carbon, ammonia-N and inorganic N dropped from 91% to 71%, from 98% to 83% and from 78% to 56%, respectively, with salinity increasing from 0 to 30 parts per thousands (ppt). In spite of such inhibition at high salinity, 100% of the effluents discharge from the constructed mangrove microcosms still complied with the discharge standards set by the Hong Kong Government for Coastal Water Control Zones. These results suggested that constructed mangrove wetland treatment systems were promising to effectively treat municipal wastewater, even those with high salinity. In addition, the denitrification potential in soil was found to be retarded by the high salinity while mangrove plants grew best at 15 ppt salinity condition.     

Some Observations on the Changes of Physico-Chemical and Biological Factors in Victoria Harbour and Vicinity, Hong Kong, 1988–1996

This study analysed monthly physico-chemical and biological data collected from 18 marine monitoring stations in Victoria Harbour and its vicinity in Hong Kong, from 1988 to 1996. Cluster analysis based on all water quality parameters measured shows that the 18 monitoring stations can be grouped into four clusters: Cluster I consists of stations located in the Harbour proper; Cluster II consists of stations located west of the Harbour and along the Rambler Channel; Cluster III consists of stations located east of the Harbour near Junk Bay and Cluster IV consists of stations located west of the Harbour and near the Ma Wan, Kap Shui Mun and Western Fairways. Factor analysis shows high positive loadings for nutrients in the first two factors of the four clusters. This suggests that effluents from the 11 outfalls of sewage screening plants influence the water quality of Victoria Harbour and its vicinity. Other factors such as storm water runoff, marine traffic, construction and industrial activities and the Pearl River discharges also appear to play an important role in determining local water quality. Five stations located along an east–west transect across the Harbour were selected for trend analysis. The three stations located in the Harbour exhibit an increasing trend for temperature and levels of total phosphorus (TP), ortho-phosphate phosphorous (PO₄-P) and faecal bacteria and a decreasing trend for pH and levels of total nitrogen (TN), total kjeldahl-nitrogen (TKN), 5-day biochemical oxygen demand (BOD₅) and chlorophyll a. For the station located east of the Harbour, an increasing trend is observed for levels of TP, PO₄-P, but no decreasing trend in TN and TKN is detected. For the station located west of the Harbour, no decreasing trend in TN, TKN and chlorophyll a is observed. Changes in levels of phosphorus and nitrogen in Victoria Harbour and the immediate vicinity have led to significant increases in the ratios of Total Silica (TSi) to TN, as well as a decrease in TN to TP and TSi to TP in most stations. Results of the present study show that Victoria Harbour and its immediate vicinity remain polluted.     

The transition from physical infrastructure to infostructure: infrastructure as a modernising agent in Singapore

This study examines the modernising role played by infrastructure and the transition of emphasis from physical infrastructure to knowledge-based infostructure as a source of economic growth in Singapore, noting the factors behind the change in strategy. Occupying a strategic sea route location and serving a resource-rich hinterland, Singapore inherited from the old British empire a well-established infrastructure when it achieved self-government in 1959. Since 1965, Singapore's development has been led by a pro-business developmentalist government, and strongly linked to technological advances in the West on which it also relies heavily for its exports and multinational corporation investments. From the 1980s, the government has launched a series of pro-IT plans to prepare the city-state's transition to an `intelligent island', and a regional hub for high-technology, and international financial transactions, a full-swing state-initiated strategy to leap from a semi-peripheral economy to be part of the developed core, and enhance its status to that of a world city. Despite barriers, some positive results have been observed. In terms of IT's spatial effect, it is largely overshadowed by the predeterministic long-term plans of the state's powerful planning authority. This revised version was published online in July 2006 with corrections to the Cover Date.     

Doubled CO2 impact on subarctic marine carbon cycle: a case study at Ocean Station P

Along with meteorological observations, complementary and systematic oceanographic observations of various physical, biological and chemical parameters have been made at Ocean Station P (OSP) (50°N, 145°W) since the early 1950s. These decadal time scale data have contributed to a better understanding of the physical, biological and chemical processes in the surface layer of the northeastern subarctic region of the Pacific Ocean. These data have demonstrated the importance of the North Pacific in the global carbon cycle and, in particular, the role of biological/chemical processes in the net exchange of CO₂ across the air–sea interface. Although we do not fully comprehend how climatic variations influence marine communities or marine biogeochemistry, previous studies have provided some basic understanding of the mechanisms controlling the seasonal and inter-annual variations of biological and chemical parameters (such as phytoplankton, bacteria, nitrate/ammonium concentration) at OSP, and how they affect the carbon cycling in the subarctic North Pacific. In this study, we investigate how these mechanisms might alter the seasonal variations of these parameters at OSP under a 2XCO₂ condition. We examine these influences using a new biological model calibrated by the climatological data from OSP. For the 2XCO₂ simulation, the biological model is driven off line (i.e., no feedback to the ocean/atmospheric model components) by the climatology plus 2XCO₂−1XCO₂ outputs from a global surface ocean model and the Canadian GCM. Under the 2XCO₂ condition, the upper layer ocean shows an increase in the entrainment rate at the bottom of the mixed layer for OSP during the late autumn and winter seasons, resulting in an increase in the f-ratio. Although there is an overall increase in the primary production (PP) by 3–18%, a decrease in the biomass of small phytoplankton and microzooplankton (due to mesozooplankton grazing) lowers the concentration of dissolved organic matter (DOM) by 4–25%. The model also predicts a significant increase in the concentrations of nitrate and ammonium, and in bacterial production during July and August. Doubling of the atmospheric CO₂ from 330 to 660 ppm forces the marine pCO₂ to increase by about 63%, much of which is driven by an increased flux of CO₂ from the atmosphere to the oceans.     

河口污染沉积物中重金属释放与迁移的围隔生态系研究

利用围隔式生态实验装置研究了加拿大False河口污染沉积物中重金属Pb、Zn、Cd、Cu在海水环境中的行为。实验模拟了 4种环境条件 :( 1)高生产力 ;( 2 )低生产力 ;( 3 )高悬浮物含量 ;( 4 )还原环境。结果表明 ,污染沉积物中重金属在海水环境中的行为既取决于元素自身性质 ,亦受外界环境条件制约。还原环境能抑制重金属的释放 ,有助于体系中原有的重金属清除出水柱。低生产力条件下 ,Pb、Zn表现出释放行为 ,而高生产力和高悬浮物含量条件下 ,Pb、Zn表现出先释放后迁移 ,而Cd、Cu则呈现出相反的图象。研究了实验期间 4种重金属释放与迁移的净通量 ,表明氧化条件下Cu、Zn净释放通量比Cd、Pb高 1～ 2个量级。研究表明 ,添加粘土及向还原环境倾倒均有助于减轻污染沉积物倾倒后重金属的二次污染     

Temporal and spatial variability of sea level and volume flux in the Murderkill Estuary

The instantaneous sea level determined at two sites in the Murderkill Estuary, a tributary of Delaware Bay, results from the superposition of temporal variability operating over different time and spatial scales. Over the relatively short tidal time scales, the semidiurnal tides that represent the dominant tidal constituents in lower Delaware Bay show a modest increase in tidal amplitudes from the bay mouth (Lewes, Delaware), up to Bowers Beach (the mouth of the Murderkill Estuary). However, as the tides propagate into the Murderkill Estuary, the semidiurnal constituents undergo heavy attenuation, resulting in a 48% reduction in tidal amplitude from Bowers to Frederica (approximately the extent of saline intrusion). The diurnal tide, on the other hand, experiences only a 25% reduction in amplitude. The limited tidal asymmetry that is observed may be a result of interaction between flows in the tidal channel and the adjacent salt marsh. At longer time scales, the subtidal sea level experiences no attenuation. The Murderkill Estuary thus behaves like a low pass filter to preferentially damp out high frequency sea level forcing from lower Delaware Bay. The subtidal volume flux in the Murderkill is highly coherent with the time rate of change of sea level, indicating that the Murderkill basically co-oscillates with Delaware Bay in a standing wave fashion over the subtidal time scale. This remote coupling controls more than 90% of the variance in subtidal sea level in the estuary. The surface slopes in the lower bay and the Murderkill Estuary are closely correlated with winds along the orientation of the two waterways, consistent with the effect of local wind on subtidal sea level.     

Effects of side keels on patrol vessel safety in astern waves

Planing hull vessel is well-known to have the problem of low damping and susceptible to large roll angles when encountering beam seas especially when stopped or operated at low speed. One approach to reduce this problem is to incorporate a pair of side keels. The effects of the side keels on both roll damping and resistance of a planing hull patrol vessel were experimentally evaluated by varying length, breadth and the position of the side keels. Tests data of the side keels have been presented on the roll damping coefficients and the resistance forces of the vessel. Next, the roll damping coefficients were utilised in time domain simulation program based on a six-degree-of-freedom mathematical model to predict the roll response and assess the vessel safety in astern waves for the case with and without the side keels. The results from the time domain simulation program have indicated that the effects of a pair of side keels can improve the vessel safety.     

Characteristics of phytoplankton community structure during and after a bloom of the dinoflagellate Scrippsiella trochoidea by HPLC pigment analysis

A bloom of the dinoflagellate Scrippsiella trochoidea was detected for the first time in inner Tolo Harbor, Hong Kong in 2 000. Water samples were collected at eight stations along a transect passing through a red tide patch for microscopic analysis of phytoplankton composition and high-performance liquid chromatography (HPLC) analysis of phytoplankton pigments. During the bloom, the density of dinoflagellates was 1.1×10⁶ cells L⁻¹ within the patch and 8.6×10⁵ cells L⁻¹ outside the patch where the phytoplankton community was dominated by diatoms. After the bloom the S. trochoidea began to decrease in density and was replaced by diatoms as the dominating bloom-causing organisms at all stations, and the density of dinoflagellates at most stations was less than 1.0 × 10⁶ cells L⁻¹. The status of S. trochoidea as the causative species of the bloom was indicated by the presence of peridinin, the marker pigment for dinoflagellates. The shift from dinoflagellates to diatoms was marked by the decline of peridinin and the prevalence of fucoxanthin. Phytoplankton pigment markers also revealed the presence of other minor phytoplankton assemblages such as cryptomonads and blue-green algal.     

Dissolved inorganic and organic iodine in the Chesapeake Bay and adjacent Atlantic waters: Speciation changes through an estuarine system

The distributions of iodate, iodide and dissolved organic iodine (DOI) were determined in two deep sub-basins in the Chesapeake Bay, the shallow waters at the mouth of the Bay and the adjacent North Atlantic between the late spring and the early fall along the net flow-path of the water entering and exiting the Chesapeake Bay by using an improved analytical scheme designed for the quantitative recovery of DOI. The concentration of R-DOI found in the surface mixed layer in the upper Bay was about twice of those found at the same location in previous studies. (R-X was the concentration of a dissolved iodine species X that had been normalized to a constant salinity of 35.) Thus, DOI in estuarine waters might have been underestimated significantly in the earlier studies. Following the water along its net flow-path, iodate initially constituted more than 60% of total iodine (TI) in the source water in the Middle Atlantic Bight off the Delmarva Peninsula. As this water entered the Chesapeake Bay through the northern part of its mouth, the concentration of R-iodate decreased while that of R-iodide increased progressively until the former became undetectable in the surface mixed layer while the latter reached a maximum of 0.42 μM in the deep water in the upper Bay. Then, the concentration of R-iodate rebounded while that of R-iodide decreased in the outflowing water that exited through the southern part of the mouth of the Bay and was later entrained by the Gulf Stream. The concentration of R-DOI in the surface waters followed the same pattern as R-iodide and reached a maximum of 0.20 μM in the upper Bay. However, R-DOI was depleted in the deep water in the sub-basins. Its concentration dropped to around the detection limit in the suboxic waters in the upper Bay. R-TI in the Bay far exceeded that in the incoming Middle Atlantic Bight water and reached 0.55 μM in the upper Bay. These distributions of the iodine species suggest that, as water from the Middle Atlantic Bight intruded into the Chesapeake Bay, in the well oxygenated surface mixed layer, iodate was reduced to iodide, and the inorganic iodine species could also be converted to DOI. In the deep water, iodate and DOI were converted to iodide. Superimposed on these inter-conversions among the iodine species, dissolved iodine, possibly in the form of iodide, was also added to the water column from the underlying sediments and the process was especially significant in the suboxic deep water in the upper Bay. Mixing between the surface mixed layer and the deep water could also have increased the concentrations of iodide and total iodine in the former.     

Nursery function of mangrove: A comparison with mudflat in terms of fish species composition and fish diet

Shallow soft-bottom habitats including mangroves and mudflats provide important nursery functions for juvenile fishes, but little information exists concerning the relative nursery value of these habitats for juvenile fishes. We compared the potential of a mangrove and a mudflat in a semi-enclosed bay in Hong Kong to serve as fish nurseries by measuring species composition, dietary composition, gut fullness and diet breadth of juvenile fishes. Fish abundance was higher in mangrove than mudflat, but species richness was almost similar between the two habitats. After excluding Ambassis gymnocephalus, which was found mainly in the mangrove, difference in fish abundance between the two habitats was small. The gut fullness and diet breath of most species did not differ between mangrove and mudflat, suggesting that the two habitats were very similar in terms of providing feeding opportunity for juvenile fishes. While the importance of mangrove as nursery of fishes has been repeatedly emphasized, our data suggest that other soft-bottom habitats, such as mudflats, are also important and need to be protected.