Phosphate uptake behavior of natural phytoplankton during exposure to solar ultraviolet radiation in a shallow coastal lagoon

The effect of solar UV radiation (UVR: 290–400 nm) on the ³²P-phosphate uptake rates of natural phytoplankton from a southern Atlantic Ocean coastal lagoon was studied during two consecutive summers at one station located in the marine-influenced area. Due to the shallowness of this lagoon and also to the generally high UV water transparency in this area, phytoplankton are exposed to high UV irradiances. The ³²P-phosphate uptake rates measured at several phosphate concentrations were inhibited up to 59.2% by UVR, although uptake stimulation was also observed in four of nine experiments (up to 28%). The effect of UVR on the apparent maximum velocity of ³²P-phosphate uptake (V _uptake) ranged from an inhibition of 49% to a stimulation of 31%. Although the highest inhibition values were associated with the maximum registered incident UV irradiance, a significant correlation between these two parameters was not observed. Changes in microalgal community structure were not related to the observed UV effect; however, a significant relationship was found between the inhibition of ³²P-phosphate uptake rates and V _uptake used as a proxy for phosphate deficiency. This relationship suggests that the phytoplankton phosphorus nutritional status modulates their sensitivity to UV exposure. Overall, our results suggest that solar UVR has the potential to affect phosphorus cycling.Communicated by O. Kinne, Oldendorf/Luhe     

Integrated biogeochemical modelling of nitrogen load from anthropogenic and natural sources in Japan

This study proposed an integrated biogeochemical modelling of nitrogen loads from anthropogenic and natural sources in Japan. Firstly, the nitrogen load (NL) from different sources such as crop, livestock, industrial plant, urban and rural resident was calculated by using datasets of fertilizer utilization, population distribution, land use map, and social census. Then, the nitrate leaching from soil layers in farmland, grassland and natural conditions was calculated by using a terrestrial nitrogen cycle model (TNCM). The Total Runoff Integrating Pathways (TRIP) was used to transport nitrogen from natural and anthropogenic sources through river channels, as well as collect and route nitrogen to the river mouths. The forcing meteorological and hydrological data is a 30-year (1976–2005) dataset for Japan which were obtained by the land surface model, Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO). For the model validation, we collected total nitrogen (TN) concentration data from 59 rivers in Japan. As a comparison result, calculated TN concentration values were in good agreement with the observed ones, which shows the reliability of the proposed model. Finally, the TN loads from point and nonpoint sources were summarized and evaluated for 59 river basins in Japan. The proposed modelling framework can be used as a tool for quantitative evaluation of nitrogen load in terrestrial ecosystems at a national scale. The connection to land use and climate data provides a possibility to use this model for analysis of climate change and land use change impacts on hydrology and water quality.     

Habitat partitioning among four elasmobranch species in nearshore,shallow waters of a subtropical embayment in Western Australia

There is a need to explore, in an integrated and statistical manner, how the number of species, relative abundance, species composition and life-cycle stages of elasmobranchs in nearshore waters vary among habitat types and during the year. Therefore, four sites in a large marine embayment, each representing a different habitat type, were sampled at regular intervals. These sites were: (1) unvegetated, with no vegetation within at least 200 m; (2) unvegetated, immediately adjacent to sparse mangroves; (3) unvegetated, immediately adjacent to dense mangroves; and (4) vegetated, with seagrass (Posidonia australis) throughout and in the vicinity. Gill netting caught 10 shark species (5 families), 5 ray species (4 families) and 12 teleost species (10 families). Carcharhinus cautus, which contributed approximately 60% to the numbers of elasmobranchs caught, completed its life cycle in nearshore, shallow waters. Negaprion acutidens, Carcharhinus brevipinna, Carcharhinus limbatus and Rhizoprionodon acutus used these waters as a nursery area. C. cautus was caught mainly in the unvegetated sites, particularly in those near mangroves. N. acutidens was caught entirely in unvegetated sites, while R. acutus, C. brevipinna and Chiloscyllium punctatum were caught predominantly or exclusively in seagrass. The mean number of species and mean catch rate of elasmobranchs were greatest for the seagrass site and least for the unvegetated site with no vegetation within at least 200 m and were significantly less for the latter site than for the unvegetated site immediately adjacent to dense mangroves (P<0.05). The numbers of species and catch rates of elasmobranchs were significantly greater in summer and autumn than in winter (P<0.05) and, in the case of number of species, also than in spring (P<0.05). We conclude that the spatial and food resources in the nearshore, shallow waters of Shark Bay are partitioned among elasmobranch species, thus reducing the potential for competition among these species for the resources in those waters.Communicated by G.F. Humphrey, Sydney     

Environmental characterization of a Mediterranean protected shallow brackish coastal aquatic system,Klisova Lagoon,Western Greece: a case study

The Klisova lagoon aquatic system belongs to the wetland of Messolonghi - Aetoliko – Klisova Lagoon Complex, located in the western Greece and represents one of the most important Mediterranean lagoon systems, as it is protected by international conventions and is listed in the Natura 2000 European Network. Water physicochemical parameters such as pH, temperature, salinity, dissolved oxygen, nutrients definition, TOC, TN and bacteriological indicators (E.coli and Enterococcus spp.) were analyzed in a time period of 1 year monthly monitoring in five sampling sites along the lagoon. The geographical distribution of these parameters show a clear zonation and partition of the lagoon as the result of: (a) the discharging of poorly treated wastes into the lagoon of Mesolonghi city waste water treatment plant and (b) the interplay between sea water influence via the lagoon inlet and the fresh water inflow via lagoon’s perimeter channels. The lagoon is characterized by seasonal hypoxic conditions, which are responsible for several ecological socks in the past including fish mortalities. The system is threatened by human interference and sedimentological processes such as the longshore drifting and siltation of the lagoon inlet. Measurements should immediately be taken in order to prevent further downgrading of the water quality.     

Isotopic composition (C & N) of the suspended particles and N uptake by phytoplankton in a shallow tropical coastal lagoon

The spatial distribution of the C/N ratios and variations in δ¹³C and δ¹⁵N of suspended particulate matter were used to characterise their source in Asia’s largest brackish water lagoon, Chilika, India. In addition, the significance of re-mineralised nutrients in the primary productivity of the shallow lagoon was also determined through quantification of the subsurface nitrogen uptake conditions at two relatively stable locations in the lagoon. The results indicated that the influence of terrestrial organic matter was the maximum in the northern sector and was relatively limited at the central and southern part of the lagoon. In situ ¹⁵N uptake experiments (daytime) under biogeochemically stable conditions revealed that the N uptake by phytoplankton ranged between 0.24 and 1.01?mM?m^?3?h^?1 during pre-monsoon and post-monsoon seasons. New production and regenerated production in the shallow lagoon was also estimated by calculating f-ratios (ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation, have been estimated), which varied from 0.52 in the post-monsoon to 0.38 in the pre-monsoon. Lowering of the f-ratio from post- to pre-monsoon indicated a dominance of mineralisation over the new production.     

Dissolved nutrient dynamics along the southwest coastal waters of India during northeast monsoon: a case study

Dissolved nutrients, Chl-a and primary productivity were measured from seven transects along the coastal waters of the southeastern Arabian Sea during northeast monsoon. Ten major estuaries were chosen to study the influence of estuarine discharge on the nutrient dynamics in the coastal waters. The mean water discharge of the estuaries in the north (64.8?±?18?×?10⁵?m³?d^?1) was found to be higher than those in the south (30.6?±?21.4?×?10⁵?m³?d^?1), whereas the nutrient concentrations were found to be higher in the estuaries of the south. The results from the offshore waters were discussed in accordance with the depth contour classification, that is, shelf (depth?≤?30?m) and slope waters (depth?≥?30?m). Our results suggest that the estuarine discharge plays a major role in the nutrient distribution in near shore shelf waters, whereas in shelf and slope waters, it was mainly controlled by in situ biological processes. The inorganic form of N to P ratios were found to be higher than Redfield ratio in slope waters when compared with shelf waters, suggesting that PO₄^3? (<0.15?µmol?L^?1) is a limiting nutrient for primary production. The multivariate statistical analysis revealed that the nutrient dynamics in the coastal waters was controlled by both biological and physical processes.     

Relative importance of benthic microalgae,phytoplankton, and mangroves as sources of nutrition for penaeid prawns and other coastal invertebrates from Malaysia

Carbon, sulfur, and nitrogen stable isotope ratio techniques were used in 1989 and 1990 to evaluate the relative importance of algae and of mangrove detritus in the nutrition of two penaeid prawn species on the west coast of Peninsular Malaysia. Mangrove detritus was found to contribute to the nutrition of juvenile Penaeus merguiensis de Man living within tidal creeks, but not to adult P. merguiensis and juvenile and adult Parapenaeopsis sculptilis (Heller) captured offshore. Results from radiotracer feeding studies, with refractory ¹⁴C mangrove lignocellulose as the food source, indicated that juvenile P. merguiensis from tidal creeks assimilated mangrove carbon with an efficiency of 13.4%. This did not differ significantly (P=0.05) from the assimilation efficiencies of juvenile and adult P. sculptilis living offshore (10.0 and 10.9%, respectively); these values were significantly higher (P<0.001) than for adult P. merguiensis (2.1%). Thus, the differential contribution of mangrove material to the nutrition of prawns in the tidal creeks and offshore was not related to differences in the prawn's ability to utilize detritus. Instead, our analysis of C stable isotopes in sediments indicated that mangrove detritus was generally more abundant within the tidal creeks than offshore. Juvenile prawns in the tidal creeks may also utilize mangrove material indirectly by feeding on small detritivorous invertebrates. Stable isotope analyses suggest that benthic microalgae constitute the other major dietary component for prawns living in tidal creeks. Prawns offshore were utilizing mainly phytoplankton-based material.     

Simultaneous nitrogen and silicate deficiency of a phytoplankton community in a coastal jet-front

The nutritional status of a phytoplankton community was investigated in a coastal jet-front located in the Gulf of St. Lawrence, Canada, in 1987. During the sampling period, the frontal community was mainly composed of the diatomsChaetoceros debilis, Skeletonema costatum, Thalassiosira gravida andC. pelagicus. As previously reported for the St. Lawrence, some frontal stations were depleted both in nitrate and silicate. At stations impoverished in nitrate, internal nitrate pool concentrations were low or undetectable, suggesting that cells had not, recently, been exposed to a nitrate flux which exceeded the nitrate assimilation rate. At these impoverished stations, however, ambient and intracellular concentrations of ammonium and urea were high, suggesting that the community was not nitrogen-deficient. The comparison between the ambient silicate concentrations and the silicate requirement (K _s ) of the dominant diatoms suggests thatC. debilis andS. costatum were Si-deficient. This is further supported by the low silicate uptake rates and intracellular concentrations measured at the silicate impoverished stations. The silicate deficiency also resulted in a decrease in the seston and phytoplankton N:C ratios.Please address all correspondence and requests for reprints to Dr Levasseur at his new address: Maurice Lamontagne Institute, 850 Route de la Mer, Mont-Joli, Québec G5H 3Z4, Canada     

Bacterioplankton in the coastal euphotic zone: Distribution,activity and possible relationships with phytoplankton

Bacterioplankton were studied in the euphotic zone of the Southern California Bight, USA, with special attention to biological factors affecting bacterial distribution and activity. Measurements were made of bacterial abundance, thymidine incorporation into acid insoluble material, primary production (particulate and dissolved), chlorophyll, phaeopigments, total microbial ATP, particulate organic carbon and nitrogen, dissolved organic carbon, dissolved primary amines, and glucose and thymidine turnover rates. The data were analyzed by pairwise rank correlations with significance tested at the P<.005 level. Bacterial abundance and thymidine incorporation both declined progressively with increasing distance from shore (to 100 km); similar trends occurred for the phytoplankton, with several stations having subsurface maxima. Bacterial abundance, thymidine incorporation, and thymidine and glucose turnover rates were all significantly correlated to each other, suggesting they are comparable as relative measures of bacterial activity. Thymidine incorporation per cell, an indicator of specific growth rate, was not correlated to bacterial abundance, suggesting density independent specific growth rates. Bacterioplankton growth rate was evidently influenced more by the standing stock of phytoplankton than by the primary production of the phytoplankton. Thus, bacterial growth may possibly be stimulated by leakage of dissolved organic matter not so much from healthy photosynthesizing cells as from phytoplankton being disrupted and incompletely digested during predation by the zooplankton and nekton.     

Phytoplankton dynamics and species diversity in a shallow eutrophic,natural mid-altitude lake in Himachal Pradesh (India): role of physicochemical factors

Rewalsar Lake, a mid-altitude, shallow and recreational water body located in the north-western Himalayas, Himachal Pradesh (India) was studied through monthly surveys in two consecutive years (March 2008 to February 2010). Forty-seven species belonging to seven groups of phytoplankton were identified from the lake. Microcystis aeruginosa and Synedra ulna exhibited a perennial habit. Ankistrodesmus falcatus, Chlorella vulgaris, Scenedesmus bijugatus, Chlamydomonas reinhardi, Eudorina elegans, Navicula cuspidate, Synedra ulna, Euglena acus, Euglena oxyuris, Spirulina gomontii, Oscillatoria princeps and Arthrospira khannae were abundant, and Oscillatoria limosa and Microcystis aeruginosa were highly abundant. Twenty-one important criteria were studied, for example, temperature, free carbon dioxide, biochemical oxygen demand, total alkalinity, nitrate, silicate and phosphate, which provide an idea of the portability of water for irrigation and drinking purposes as per the permissible limits given in World Health Organization, Indian Council of Medical Research and Indian Standards Institute standards. Pearson's correlation revealed a significant relationship between physicochemical parameters and different algal groups. Both plankton and chlorophyll a showed a bimodal pattern of fluctuation. High annual mean concentrations of chlorophyll a (mg L^?1) were recorded as 11.44 in 2008–09, and 11.04 in 2009–10. As per the Palmer pollution index, 13 pollution-tolerant algal species with a pollution score of 37 were observed. The Central Pollution Control Board categorised the water at Rewalsar Lake as ‘D–E’.     

The effects of intensive aquaculture on nutrient residence time and transport in a coastal embayment

Aquaculture in many countries around the world has become the biggest source of seafood for human consumption. While it alleviates the pressure on wild capture fisheries, the long-term impacts of large-scale, intensive aquaculture on natural coastal systems need to be better understood. In particular, aquaculture may alter habitat and exceed the carrying capacity of coastal marine ecosystems. In this paper, we develop a high-resolution numerical model for Sanggou Bay, one of the largest kelp and shellfish aquaculture sites in Northern China, to investigate the effects of aquaculture on nutrient transport and residence time in the bay. Drag from aquaculture is parameterized for surface infrastructure, kelp canopies, and bivalve cages. A model for dissolved inorganic nitrogen (DIN) includes transport, vertical turbulent mixing, sediment and bivalve sources, and a sink due to kelp uptake. Test cases show that, due to drag from the dense aquaculture and thus a reduction of horizontal transport, kelp production is limited because DIN from the Yellow Sea is consumed before reaching the interior of the kelp farms. Aquaculture drag also causes an increase in the nutrient residence time from an average of 5 to 10 days in the middle of Sanggou Bay, and from 25 to 40 days in the shallow inner bay. Low exchange rates and a lack of DIN uptake by kelp make these regions more susceptible to phytoplankton blooms due to high nutrient retention. The risk is further increased when DIN concentrations rise due to river inflows.     

Development and application of GIS datasets for assessing and managing coastal impacts and future change on the central coast of Western Australia

The coastal zone between Guilderton and Kalbarri, north of Perth, Western Australia, is a highly dynamic area of high landscape and conservation values under increasing development pressures. Intensification of terrestrial and coastal impacts has highlighted the need to develop a georeferenced data base for land management. The Coastal Assessment and Restoration project aimed to document the natural resources and coastal developments to the region and to identify & assess threats to the coastal strip through the creation of GIS datasets. GIS datasets provide a key source of reference information which can be accessed by a number of stakeholders for future coastal planning and management and provide a basis for developing a risk management assessment of the coastal zone and a strategy for coastal managers in our climate change future.     

Modeling linkages between sediment resuspension and water quality in a shallow,eutrophic, wind-exposed lake

The interactions between bed sediments and the water column in shallow, eutrophic lakes have tremendous implications for the fate and transport of nutrients in those water bodies. This has resulted in the development of water quality models for lakes incorporating the processes of sediment resuspension. Reliable resuspension models are thus needed to accurately represent this phenomenon. In this paper, three different sediment-resuspension models are combined with a hydrodynamic and water quality model, dynamic lake model-water quality (DLM-WQ), and the resulting models are used to simulate nutrient distributions in the highly eutrophic Salton Sea, California, USA. One of the resuspension formulas is based upon sediment characteristics as well as the bed shear stress exerted by wind-induced waves and currents, while the other two are standard, power-law-type formulas for cohesive sediments with two different exponents. The outputs for water quality variables, such as temperature, chlorophyll a, dissolved oxygen and nutrients, obtained from the three resulting models and from an earlier DLM-WQ run with a simple empirical sediment-resuspension model are compared with measured data. The level of agreement between the simulations and the measured data is assessed by using both statistical and graphical model evaluation methods, including measures of residual errors, sample autocorrelations, t-tests, and box plots. Based on these assessments, DLM-WQ with an extended version of the García and Parker [García, M.H., Parker, G., 1993. Experiments on the entrainment of sediment into suspension by a dense bottom current. J. Geophys. Res.-Oceans 98, 4793–4807] relationship gave the best results for water quality in the Salton Sea, confirming that the use of formulas with more information on the sediment characteristics yields more accurate results. To the best of our knowledge, this is the first effort to combine water quality models for lakes and reservoirs with a sediment-resuspension model which was originally intended for open-channel flows. The simulations confirm that sediment resuspension is the most dominant process in the Salton Sea's nutrient cycling. The effect of proposed physical changes to the Salton Sea on water quality characteristics is also addressed.     

Effects of different mobilities of leaf and woody litters on litter carbon dynamics in arid ecosystems in Western Australia

Afforestation of arid land is a promising countermeasure against global warming. We had previously found, through modeling and mass balance analyses of an arid land afforestation experimental project in Western Australia, that a significant amount of litter could have been physically removed from the floors of natural forests. In order to analyze litter carbon dynamics in depth, we investigated the actual mobility of litter in several natural forests in Sturt Meadows in an arid region of Western Australia, and estimated the difference between the removal rate of leaf and woody (twigs and branches) litter on the forest floor. Then we redeveloped a litter carbon dynamics model by incorporating physical removal of litter to show the different mobilities of leaf and woody litters. We also analyzed carbon balances and the effect of differential litter mobility on litter carbon dynamics. Except for twigs in one plot in a high density forest, 29–100% of leaf litter and 10–100% of woody litter was removed annually, demonstrating the physical removal of litter in these natural forests. The main cause of litter removal was wind, not flooding. Decreases in leaf and woody litters could be approximated as first order decay functions in most plots; first order decay or disappearance rate constants were then determined. Estimated disappearance rate constants of leaf and woody litter ranged from 0.19 to 11 and 0.11–12 year⁻¹, respectively; most of the constants ranged from 0.19 to 2.0 and 0.11–0.74 year⁻¹, respectively. Based on the disappearance rate constant, the mobility of woody litter was estimated to be roughly 20% that of leaf litter, confirming that climatic factors move leaves more easily than twigs. The improved model, which took into account the different mobilities of leaf and woody litters, showed that annual physical removal of litter reached 70–82% of the annual litter fall in Acacia aneura forests, and that roughly 40–60% of the existing litter was removed annually from all sites. Incorporating into the model the difference in mobilities of leaf and woody litters showed that the ratio of annual litter removal to annual litter fall increased about 10% points compared with the assumption of that both litter types had equal mobility.     

Natural attenuation of MTBE and BTEX compounds in a petroleum contaminated shallow coastal aquifer

Natural attenuation of MTBE and BTEX compounds in a petroleum contaminated coastal aquifer in the Tel-Aviv area was investigated. Significant decrease in MTBE concentration and complete disappearance of BTEX compounds occur within 100 m groundwater flow. Highly anaerobic conditions were determined in the close vicinity to the spill source. In order to examine the contribution of microbial degradation to the attenuation process at anaerobic conditions, compound-specific carbon isotope ratio analysis was employed. Carbon isotope enrichment of toluene up to 2.4% along with the drop in its concentration up to 80% was observed within 20 cm below the water table. The lack of isotope fractionation despite the significant concentration decrease for other studied compounds indicates significant contribution of abiotic processes to the natural attenuation.     

Examining the potential impacts of sea level rise on coastal wetlands in north-eastern NSW,Australia

The coastal wetlands of north-eastern New South Wales (NSW) Australia are increasingly being affected by anthropogenic factors such as urbanisation, residential development and agricultural development. However, little is known about their vulnerability to sea level rise as a result of climate change. The aim of this research is to predict the potential impact of sea level rise (SLR) on the coastal wetland communities. Sea Level Affecting Marshes Model (SLAMM) was used to predict the potential impacts of sea level rise. Geographic Information System (GIS) was used for mapping and analysis. It was found that a meter rise in sea level could decrease coastal wetlands such as Inland fresh marshes from about 225.67 km² in February 2009 to about 168.04 km² by the end of the century in north-eastern NSW, Australia. The outcomes from this research can contribute to enhancing wetland conservation and management in NSW.     

Modeling the role of macroalgae in a shallow sub-estuary of Narragansett Bay, RI (USA)

Proliferation of macroalgal mats is a frequent consequence of nutrient-driven eutrophication in shallow, photic coastal marine ecosystems. These macroalgae have the potential to significantly modify water quality, plankton productivity, nutrient cycling, and dissolved oxygen dynamics. We developed a model for Ulva lactuca and Gracilaria tikvahiae in Greenwich Bay, RI (USA), a shallow sub-estuary of Narragansett Bay, as part of a larger estuarine ecosystem model. The model predicts the biomass of both species in units of carbon, nitrogen, and phosphorus as a function of primary production, respiration, grazing, decay, and physical exchange, with particular attention to the effects of biomass layering on light attenuation and suppression of metabolic rates. The model successfully reproduced the magnitude and seasonal cycle of area-weighted and peak biomass in Greenwich Bay along with tissue C:N ratios, and highlighted the importance of grazing and inclusion of self-limitation primarily in the form of self-shading to overcome an order of magnitude difference in rates of production and respiration. Inclusion of luxury nutrient uptake demonstrated the importance of internal nutrient storage in fueling production when nutrients are limiting. Macroalgae were predicted to contribute a small fraction of total system primary production and their removal had little effect on predicted water quality. Despite a lack of data for calibration and a fair amount of sensitivity to individual parameter values, which highlights the need for further autecological studies to constrain formulations, the model successfully predicted macroalgal biomass dynamics and their role in ecosystem functioning. Our formulations should be exportable to other temperate systems where macroalgae occur in abundance.     

Naked Dictyocha speculum — a new type of phytoplankton bloom in the Western Baltic

Chlamydomonas pulsatilla Wollenweber, a euryhaline, marine flagellate (isolated from rockpool at St. Andrew's, New Brunswick, Canada in 1980 by J. A. Hellebust), shows decreasing rates of activity of its four contractile vacuoles in the salinity range of 0 to 15% artificial seawater (ASW). Electron microscopy shows that the contractile vacuole complex persists as a spongiome (collection of small vesicles or tubules) in cells grown at salinities above the range for operation of contractile vacuoles. From calculations of rates of water expulsion, based on size and frequency of contraction of individual vacuoles determined by light microscopy, the time necessary to empty one cell volume increased from ca 20 min at 1% ASW to ca 600 min at 15% ASW. Analysis of inorganic and organic solute contents of cells grown at 1 and 5% ASW allowed the calculation of internal osmotic pressures. Estimates of hydraulic conductivities based on rates of water expulsion via contractile vacuoles and differences in internal and external osmotic pressures resulted in values ranging from 1.1 to 1.4×10^-14 m s^-1 Pa^-1 for individual cells. Growth experiments at low photon flux densities over a salinity range of 1 to 15% ASW, over which contractile vacuole activity varied by a factor of 30, showed little difference in growth rates. This indicates that the cost for operation of contractile vacuoles must be very low. The secretion of large molecular weight organic substances does not appear to be associated with the functioning of contractile vacuoles.