A historical assessment of coastal contamination in Birch Harbor, Maine based on the analysis of mussels collected in the 1940s and the Mussel Watch Program

Coastal contamination in the 1940s was assessed based on analysis of canned blue mussels presumably collected from Birch Harbor, Maine, USA. Analytical results on legacy organic contaminants were compared to long-term National Oceanic and Atmospheric Administration (NOAA) Mussel Watch (MW) monitoring data to estimate the degree of coastal contamination before World War II (WWII) when many synthetic organic compounds were first introduced into the environment. While dieldrin and chlordane were not detected in the canned mussels, dichloro-diphenyl-trichloroethane (DDT) and hexachlorocyclohexanes (HCHs) were present at lower concentrations relative to the more recent MW data. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were detected, and the later were significantly higher in canned mussels relative to the MW data (p < 0.05). Furthermore, moving average analysis applied to the MW data depicted three-phased temporal trend patterns (increase-decrease-steady state) for virtually all contaminants indicating an overall increased coastal contamination in post WWII era.     

Experimental and theoretical study of stability of dense hydrous magnesium silicates in the deep upper mantle

Fluid-undersaturated experiments were conducted to determine the phase relations in the simplified peridotite system MgO-SiO₂-H₂O (MSH) at 11.0-14.5 GPa and 800-1400 °C. Stability relations of dense hydrous magnesium silicates (DHMSs) under fluid-undersaturated conditions were experimentally examined. From the fluid-absent experimental results, we retrieved thermodynamic data for clinohumite, phase A, phase E, and hydrous wadsleyite, consistent with the published data set for dry mantle minerals. With this new data set, we have calculated phase equilibria in the MSH system including dehydration reactions. The dehydration reactions calculated with lower water activities of 0.68-0.60 match the fluid-present experiments of this study above 11.0 GPa and 1000 °C, indicating that considerable amounts of silicate component were dissolved into the fluid phase. The calculated phase equilibria illustrate the stability of the post-antigorite phase A-bearing assemblages. In the cold subducting slab peridotite, phase A + enstatite assemblage survives into the transition zone, whereas phase A + forsterite + enstatite assemblage forms hydrous wadsleyite at a much shallower depth of about 360-km. The slab is subducted with no dehydration reactions occurring when entering the transition zone. The phase equilibria also show the high temperature stability of phase E. Phase E is stable up to 1200 °C at 13.5 GPa, a plausible condition in the mantle of relatively low temperature, i.e., beneath subduction zones. Phase E is a possible water reservoir in the mantle as well as wadsleyite and ringwoodite.     

The seasonal variability of the northern Benguela undercurrent and its relation to the oxygen budget on the shelf

The seasonal variations in the advection and mixing of water masses in the northern Benguela were studied in relation to the oxygen minimum zone over the Namibian shelf. The used data set consists of hydrographic and current measurements from an oceanographic mooring 20 nm off Walvis Bay, monthly CTD transects from the Namibian 23°S monitoring line and recent large-scale hydrographic surveys. The current time series showed an intermittent southward continuation of the Angola Current (AC) through the Angola–Benguela frontal zone (ABFZ) into the northern Benguela, commonly known as poleward undercurrent. In austral summer hypoxic, nutrient rich South Atlantic central water (SACW) from the Angola Gyre is transported into the northern Benguela, whereas during the winter season the oxygen rich Eastern SACW (ESACW) spreads northward. The water mass analysis reveals a mixing between both water masses in the northern Benguela between the ABFZ and the Lüderitz upwelling cell (27°S). The oxygen balance over the Namibian shelf depends to a high extent on the water mass composition of the upper central water layer, controlled by the large scale and local circulation. The deviation of the measured oxygen concentration from its mixing concentration, calculated with the source water mass properties, was used to quantify the oxygen consumption. A new local definition SACW was derived to exclude biogeochemical processes, taking place in the Angola Gyre. The oxygen deficit in the northern Benguela central water amounted to about 60–80 μmol l⁻¹ at the shelf edge and increased up to 150 μmol l⁻¹ on the shelf, due to local oxygen consumption. In the austral summer anoxic bottom waters are observed at the central Namibian shelf, which correlate to an SACW fraction >55%. Periods with high SACW fraction in the water mass composition were congruent with hydrogen sulphide events detected by remote sensing.     

Depth limit of littoral vegetation in a storage reservoir: A case study of Lipno Reservoir (Czech Republic)

Controlling factors for the occurrence of littoral macrophyte species were investigated in Lipno Reservoir (area: 46.5 km²; z_mean: 6.6 m; z_max: 22 m; water residence time: 0.6 yr), a dam impoundment with moderately fluctuating water level (amplitude up to 4 m) which is used for hydropower and downstream flow augmentation. The options of supporting littoral macrophyte growth for improving the reservoir's ecological potential were evaluated according to the European Water Framework Directive's definitions. Macrophytes were examined at 115 sites, each 50 m long, along the whole reservoir perimeter at regular 1 km intervals. Sites were surveyed for their phytocoenology, shore morphometry, pedological characteristics of substrate, transparency of water, and anthropogenic impacts. Most of the sites were characterised by a wide eulittoral zone with a tenuous cover of terrestrial hydrophilic, amphibious, and/or emergent macrophytes and a low proportion of silt, clay, and organic fractions in the substrate. Infralittoral submerged and floating-leaved macrophytes were restricted to a few sites within the mouths of the main and side tributaries where transparency was maintained by clear inflow water independent of reservoir pool fluctuations. Water transparency was low (1-2 m) compared to annual changes of water level (2 to >3 m). Multivariate statistical analysis (DCA, CCA) confirmed relationships between the occurrence of macrophyte species and morphological and substrate characteristics of the shore. Improvement of macrophyte cover and establishment of vital infralittoral zones requires improvements in water transparency and changes in reservoir operation, i.e., limiting the range of water level fluctuation to less than ca. 1 m.     

Bacterial accumulation by the Demospongiae Hymeniacidon perlevis: A tool for the bioremediation of polluted seawater

Sponges can filter large amounts of water, which exerts an important grazing impact on free bacteria, an important component of the diet of sponges. We examined the accumulation of bacteria in the Demospongiae (Hymeniacidon perlevis). Analyses were performed on homogenates from unstarved and starved sponges in seawater from their sampling site (the Ionian Sea). Culturable heterotrophic bacteria (22 °C), total culturable bacteria (37 °C) and vibrios densities were measured on marine agar 2216, plate count agar and TCBS agar, respectively. Total and fecal coliforms, as well as fecal streptococci, were determined by the most probable number method (MPN). H. perlevis was able to accumulate all of the six microbiological groups. Bacterial groups differed in their resistance to digestion by H. perlevis. Our data suggest that H. perlevis may accumulate, remediate and metabolize bacteria and that they may be employed as a useful bioindicator and bioremediator.     

Estimation of water clarity in Taihu Lake and surrounding rivers using Landsat imagery

In China, the increase in exogenous-source pollutants from rivers is one of the most important causes of lake eutrophication. The application of remote sensing technology to water quality monitoring of rivers connected to these lakes has special significance for lake management at regional scales. Many research studies have estimated water clarity using Landsat imagery. However, most of this work focused on lakes or reservoirs, for which abundant water-only pixels (i.e., pure pixels of water, PPW) were available. Few of these studies have addressed rivers, especially rivers with an average width less than 100 m. In our study, we sought to determine whether water clarity in the rivers connected to Taihu Lake could be estimated using Landsat imagery. We obtained 18 Enhanced Thematic Mapper Plus (ETM+) images from 2009 for 13 rivers ranging from an average of 37.3 to 173.6 m wide. Three field campaigns conducted in May 2009, September 2009, and January 2010 were used to obtain field measurements of Secchi disk depth (SDD). Our results suggested that the widely used model, a(TM1/TM3) + b(TM1) + c, was suitable for the estimation of SDD for Taihu Lake. The brightness of the panchromatic band of ETM+ showed significant correlations with TM1, TM3 and TM1/TM3 (p < 0.001). As a result, SDD in the lake could also be estimated using the Landsat panchromatic band. The multispectral image of ETM+ did not provide adequate PPW for estimation of water clarity in rivers. However, PPW derived from the panchromatic image captured about 93% of the variation in SDD, on average, for the every worst-case scenario in the 13 rivers. Using the PPW in rivers, a significant correlation was found between the brightness of the panchromatic image and SDD (R² = 0.64, p < 0.001). Our results demonstrate that the panchromatic image of Landsat, but not the multispectral image, can be used to estimate water clarity in rivers with an average width greater than 40 m in the Taihu basin.     

Anthropogenic influence on the degradation of an urban lake - The Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil

The artificial reservoir Lagoa da Pampulha in central Brazil has been increasingly affected by sediment deposition and pollution from urban and industrial sources. This study investigates water chemistry and heavy metal concentrations and their fractionation in the lake sediment using ICP-OES, ICP-MS, and XRD analyses. Fractionation analysis was done by sequential extraction under inert gas as well as after oxidation. The lake exhibits a permanent stratification with an oxygen-free hypolimnion below 2 m depth. Nutrient concentrations are enriched for phosphorous components (SRP, PO₄). In the sediment it was not possible to detect oxygen. Carbon, sulfur, and most of the analyzed heavy metals are enriched in the top sediment layer with a pronounced downward decrease, indicating the presence of an anthropogenic influence. Statistical analysis, including correlations and a Principal Component Analysis (PCA) of depth-related total concentration data, helps to distinguish presumably anthropogenic heavy metals from geogenic components. Some samples with high element concentrations in the sediment also show elevated concentrations in their pore water. Analyses of element distribution between sediment and pore water suggest a strong bonding of heavy metals to the anoxic sediment. The trend towards elevated solubility in the pore water of oxidized samples is clear for most of the analyzed elements. Fractionation analysis reveals characteristic associations of selected elements to specific mineral bonding forms. In addition, it indicates that the behavior of heavy metals in the sediment is strongly influenced by organic substances. These substances provide buffering against oxidation, acidification, and metal release. The high nutrient loading causes reducing conditions in the lake sediment. These conditions trigger the accumulation of sediments rich in S²⁻, which stabilizes the fixation of heavy elements. In the future, care must be taken to reduce the supply of contaminants and to prevent the release of heavy metals from sediments dredged for remediation purposes.     

Temporal variability of the physical and chemical water characteristics at a coastal monitoring observatory: Station ENSENADA

The temporal variability of the physical and chemical conditions of coastal waters off Ensenada, Baja California (Mexico) was characterized. A historical analysis was made based on 11 years (1998–2008) of temperature and salinity data records measured quarterly by IMECOCAL, along a transect perpendicular to the coast (CalCOFI line 100). Moreover, the physical and chemical conditions at a coastal monitoring observatory called station ENSENADA were described using a 2-year data series (October 2006–November 2008) obtained with improved temporal resolution. The historical analysis of line 100 showed marked seasonal variability in the thermohaline conditions associated with fluctuations in the flow of the equatorward California Current and the poleward California Undercurrent, as well as with coastal upwelling events whose magnitude and frequency increase towards spring–summer. Interannual variability was also observed, related to warm and/or cold ENSO phases that modify the characteristics of the water column in this coastal region. The most striking characteristics of the interannual variability at station ENSENADA were La Niña conditions recorded from summer 2007 to mid 2008. During this cold ENSO phase, temperature, salinity, dissolved oxygen, density, and dissolved inorganic carbon data revealed the anomalous presence of subsurface water at the surface layers in spring 2008. Results suggest that the coastal observatory is sensitive to the temporal variability of hydrographic conditions on shelf coastal waters (<50 km) off Ensenada in the northern BC region. Consequently, station ENSENADA would be a good location to high-frequency monitors the oceanographic conditions of the transitional region between tropical/subtropical and subarctic systems of the California Current System.     

Perfluorinated compounds in estuarine and coastal areas of north Bohai Sea, China

Perfluorinated compounds (PFCs) in water, sediment, soil, and biota collected from estuarine and coastal areas of the north Bohai Sea, China, were determined by use of HPLC-MS/MS. Significant concentrations of PFCs were found in water (mean: 18.4 ng/l) and biologic samples (fish: 265 ng/g dw), while concentrations of PFCs in soils and sediments were less. The predominately detected compound was perfluorooctanesulfonate (PFOS), with a maximum concentration of 30.9 ng/l in water and 791 ng/g dw in fish. Concentrations of PFCs were significantly greater in the Liaohe River system than other locations, which suggests point sources in this urbanized and industrialized region. PFOS concentrations in water and biota were both less than the reported threshold concentrations. Detection of PFCs at relatively great concentrations in various environmental matrices from this region suggested that further studies characterizing concentrations of PFCs, their sources and potential risk to both humans and wildlife are needed.     

Distributions of polycyclic aromatic hydrocarbons in the Daliao River Estuary of Liaodong Bay, Bohai Sea (China)

The distributions of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the aqueous phase, suspended particulate matter (SPM), sediment, and pore water of the Daliao River Estuary in Liaodong Bay, Bohai Sea (China). Total PAH concentrations ranged from 139.16 to 1717.87 ng L⁻¹ in surface water, from 226.57 to 1404.85 ng L⁻¹ dry weight in SPM, from 276.26 to 1606.89 ng g⁻¹ dry weight in sediments, and from 10.20 to 47.27 μg L⁻¹ in pore water. PAH concentrations were at relatively moderate levels in water, SPM, sediment and pore water in comparison with those reported for other estuary and marine systems around the world. Sedimentary PAH concentrations decreased offshore owing to active deposition of laterally-transported river-borne particles. PCA analysis of the possible PAH source suggested petrogenic and pyrolytic PAH inputs in the studied region.     

High accuracy measurements of water storage change in Mining Lake 111, Germany

Several pressure sensors were deployed in a small lake to determine its storage change. It could be shown that a deep enough deployment and an averaging over a time interval of 1 hour and 5 measuring points allowed for a measurement of 1 or 2 kg/m² (i.e. 2 mm of water column) of changes in the storage on the scale of the lake size. This accuracy for the lake storage could not be achieved by other methods, especially if conditions were difficult, e.g. snowfall, or in cases when precipitation was small. Finally, the pressure measurement - originally intended to roughly determine the water level - turned out to be a direct measurement of water mass in the lake, which was the proper magnitude for exchanges between atmosphere and lake. Hence the measurement of lake storage could become an interesting approach even for meteorological measurements, such as precipitation and evaporation on a water surface.     

A test of the influence of tidal stream polarity on the structure of turbulent dissipation

Vertical mixing by the tides plays a key role in controlling water column structure over the seasonal cycle in shelf seas. The influence of tidal stirring is generally well represented as a competition between surface buoyancy input and the production of turbulent kinetic energy (TKE) by frictional stresses, a competition which is encapsulated in the Qh/u³ criterion. An alternative control mechanism arises from the limitation of the thickness of the bottom boundary layer due to the effects of rotation and the oscillation of the flow. Model studies indicate that, for conditions typical of the European shelf seas, the energy constraint exerts the dominant control but that for tidal streams with large positive polarisation (i.e. anti-clockwise rotation of velocity vector), some influence of rotation in limiting mixing should be detectable. We report here measurements of flow structure (with ADCPs) and turbulent dissipation (FLY Profiler) made at two similar locations in the Celtic Sea which differ principally in that the tidal currents rotate in opposite senses with approximately equal magnitude (polarity P=±0.6). A clear contrast was observed between the two sites in the vertical structure of the currents, the density profile and the rate of dissipation of TKE. At the positive polarity (PP) site (P≈+0.6), the bottom boundary layer in the tidal flow was limited to ∼20 mab (metre above the bed) and significant dissipation from bottom boundary friction was constrained within this layer. At the negative polarity (NP) site (P≈−0.6), the dominant clockwise rotary current component exhibited a velocity defect (i.e. reduction relative to the free stream) extending into the upper half of the water column while significant dissipation was observed to penetrate much further up the water column with dissipation levels ∼10^−4.5 W m⁻³ reaching to the base of the pycnocline at 70–80 mab. These contrasting features of the vertical distribution of dissipation are well reproduced by a 1-D model when run with windstress and tidal forcing and using the observed density profile. Model runs with reversed polarity at the two sites, support the conclusion that the observed contrast in the structure of tidal velocity, dissipation and stratification is due to the influence of tidal stream polarity. Increased positive polarity reduces the upward penetration of mixing which allows the development of stronger seasonal stratification, which, in turn, further inhibits vertical mixing.     

Pathogenic fungi: an unacknowledged risk at coastal resorts? New insights on microbiological sand quality in Portugal

Whilst the potential impact on beach users from microorganisms in water has received considerable attention, there has been relatively little investigation into microbial contaminants in sand. Thirty three beaches across Portugal were analyzed during a five year period (2006-2010) to determine the presence of yeasts, pathogenic fungi, dermatophytes, total coliforms, Escherichia coli and intestinal enterococci in sand.Our results showed that 60.4% of the samples were positive for fungi and that 25.2% were positive for the bacterial parameters. The most frequent fungal species found were Candida sp. and Aspergillus sp., whereas intestinal enterococci were the most frequently isolated bacteria. Positive associations were detected among analyzed parameters and country-regions but none among those parameters and sampling period.Regarding threshold values, we propose 15 cfu/g for yeasts, 17 cfu/g for potential pathogenic fungi, 8 cfu/g for dermatophytes. Eighty four cfu/g for coliforms, 250 cfu/g for E. coli, and 100 cfu/g for intestinal enterococci.     

Rapidly installed temporary gauging for hurricane waves and surge,and application to Hurricane Gustav

Hurricanes can produce extreme nearshore waves and surge, but permanent gauging stations are often much sparser than is desired. This paper describes the rationale behind and outline for rapidly installed temporary coastal gauges, and presents results during Hurricane Gustav (2008). Within 48 h prior to landfall, twenty self-recording pressure gauges were deployed in depths of 1.4–23 m over more than 700 km of coastline, using helicopters to cover the large distances. Results showed a complex picture that was strongly dependent on location. East of the Mississippi Delta, open coast waves were large, and surge reached 3.8 m NAVD88 in marshes. West of the delta but near landfall, waves and surge were generally smaller as the river levees blocked flow from East to West. West of landfall, both waves and surge were very small and the most prominent feature was a water level drawdown that reached 1.5 m. Wave spectra varied strongly depending both on location and time from landfall.     

Maintenance of estuarine water quality by mangroves occurs during flood periods: A case study of a subtropical mangrove wetland

Seasonal changes in water quality were measured in samples taken at various distances from shallow water across mudflat to mangroves during flood period and from mangroves across mudflat to shallow water during ebb period in a subtropical mangrove estuary (Zhangjiang Estuary, Fujian, China). The TN (total dissolved nitrogen), TP (total dissolved phosphorus), COD (chemical oxygen demand), and DOC (dissolved organic carbon) contents during the flood period were significantly higher than those during the ebb period. In contrast, the opposite was true for the POC (particulate organic carbon) content and transparency. The mangroves at Zhangjiang Estuary may trap nutrients at rates of 90.5 g N/m²/yr, 2.2 g TP/m²/yr, and 13.7 g C/m²/yr in the form of DOC, and export POC at a rate of 81.8 g/m²/yr. Our results support the hypothesis that the maintenance of estuarine water quality by mangroves occurs during flood periods.     

Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil

Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L⁻¹ for ∑16PAH and 5-10 μg L⁻¹ for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g⁻¹for ∑16PAH and 0.01-5.0 μg g⁻¹ for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin.     

Persistent organochlorine pollutants in Korean offshore waters: Squid (Todarodes pacificus) as a biomonitor

Persistent organochlorine pollutants (POPs) such as polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane and its metabolites (DDTs), chlordane compounds (CHLs), and hexachlorocyclohexanes (HCHs) were determined in Japanese common squid collected from the offshore waters of Korea. Liver accumulated higher levels of contaminants than mantle. The sums of DDTs, PCBs, CHLs and HCHs in liver were in the ranges of 164-4430 ng g⁻¹, 95-1030 ng g⁻¹, 15-121 ng g⁻¹, and 13-98 ng g⁻¹ on a lipid weight basis, respectively. Among the POPs, DDTs showed distinct regional difference in concentration levels and composition between the western and eastern offshore of Korea. One of the highest concentrations of DDTs so far recorded in the western offshore of Korea, that is Yellow Sea. This implies ongoing fresh input of technical DDT to this regional sea. HCHs were relatively high in the Yellow Sea as well, with an enhanced signal of γ-HCH indicating recent input of lindane. In contrast, CHLs showed higher level in the eastern offshore of Korea, that is East Sea, but PCBs showed an even distribution in both regions. Squid could be a useful bio-indicator for monitoring offshore water contamination by POPs.     

Distribution of butyltins in the waters and sediments along the coast of India

Water and surface sediment samples were analyzed for butyltins (TBT, DBT, MBT) from various ports along the east and west coast of India. The total butyltin (TB) in water samples varied between ∼1.7 and 342 ng Sn l⁻¹, whereas for sediments it varied between below detection limit to 14861 ng Sn g⁻¹ dry weight of sediment. On an average Chennai port recorded the highest level of butyltins in the sediments while Paradip recorded the highest level of butylins in the waters. A fairly good relationship between the TB in the sediment and overlying water samples, as well as between organic carbon and TB, implicates the importance of adsorption/desorption process in controlling the levels of TBT in these port areas. In India the data on organotin pollution is very sparse; most of the port areas have been surveyed for butyltins for the first time during this study.     

Stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry: An effective tool for determining persistent organic pollutants and nonylphenol in coastal waters in compliance with existing Directives

A multi-residual method based on stir bar sorptive extraction coupled with thermal desorption-gas chromatography-mass spectrometry (SBSE-TD-GC-MS) has been developed to measure 49 organic pollutants (organochlorine pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polybrominated diphenyl ethers and nonylphenol) in seawater. Using 100 ml of water, the method exhibited good linearity, with recoveries between 86% and 118% and relative standard deviation between 2% and 24% for almost all compounds. The method was applied to determine target contaminants in Catalonian seawater, including coastal areas, ports and desalination plant feed water. Overall individual compound levels oscillated between 0.16 and 597 ng l⁻¹; PAHs and nonylpenol were the compounds found at the highest concentrations. The method provided LODs between 0.011 and 2.5 ng l⁻¹, lower than the Environmental Quality Standards (EQS) fixed by Directive 2008/105/EC. In compliance with the directive, this method can be used as a tool to survey target compounds and is aimed at protecting coastal ecosystems from chemical pollution.     

Environmental response to sewage treatment strategies: Hong Kong's experience in long term water quality monitoring

In many coastal cities around the world, marine outfalls are used for disposal of partially treated wastewater effluent. The combined use of land-based treatment and marine discharge can be a cost-effective and environmentally acceptable sewage strategy. Before 2001, screened sewage was discharged into Victoria Harbour through many small outfalls. After 2001, the Hong Kong Harbour Area Treatment Scheme (HATS) was implemented to improve the water quality in Victoria Harbour and surrounding waters. Stage I of HATS involved the construction of a 24 km long deep tunnel sewerage system to collect sewage from the densely populated urban areas of Hong Kong to a centralized sewage treatment plant at Stonecutters Island. A sewage flow of 1.4 million m³ d⁻¹ receives Chemically Enhanced Primary Treatment (CEPT) followed by discharge via a 1.2 km long outfall 2 km west of the harbor. The ecosystem recovery in Victoria Harbour and the environmental response to sewage abatement after the implementation of HATS was studied using a 21-year data set from long term monthly water quality monitoring. Overall, the pollution control scheme has achieved the intended objectives. The sewage abatement has resulted in improved water quality in terms of a significant reduction in nutrients and an increase in bottom DO levels. Furthermore, due to the efficient tidal mixing and flushing, the impact of the HATS discharge on water quality in the vicinity of the outfall location is relatively limited. However, Chl a concentrations have not been reduced in Victoria Harbour where algal growth is limited by hydrodynamic mixing and water clarity rather than nutrient concentrations. Phosphorus removal in the summer is suggested to reduce the risk of algal blooms in the more weakly-flushed and stratified southern waters, while nutrient removal is less important in other seasons due to the pronounced role played by hydrodynamic mixing. The need for disinfection of the effluent to reduce bacterial (E. coli) concentrations to acceptable levels is also confirmed and has recently been implemented.