Estuarine nitrification: A naturally occurring fluidized bed reaction?

The rates of nitrification in the water column of the Tamar river estuary, southwest England have been measured using the incorporation of H¹⁴CO₃ in samples with and without the inhibitor of nitrification, 2-chloro-6-(trichloromethyl) pyridine (N-Serve). N-Serve proved successful in totally inhibiting NH₄-oxidizing bacteria but the activity of NO₂-oxidizing bacteria was inhibited by only 30%; other organisms were only slightly affected. Measurements of the nitrification rate made over the entire salinity range of the estuary (0–30‰) showed that maximum nitrification always coincided with the turbidity maximum. The field data suggest that the organisms responsible for nitrification were associated with periodically resuspended particulate material and that the turbidity maximum acts in a manner similar to a fluidized bed reactor. A dispersion model has been used to demonstrate that nitrification in the water column can account for 100% of the NO₂ maximum which is apparent down estuary from the turbidity maximum.     

预修正快速傅里叶变换高阶边界元方法在波浪对物体作用问题中的应用

边界元方法被广泛应用于波浪对海上婕筑物作用领域,但由于传统边界元方法的存储量和计算量均为未知量的平方量级,很难满足大范围多未知量问题的计算需要.本文基于高阶边界元方法,应用预修正快速傅里叶变换方法,使计算量与存储量分别降低至O(NlogN)和O(N)量级,并得到一个连续的压强分布以适应结构设计的要求,同时可以通过使用满...     

Annual variation in the nocturnal nekton assemblage of a tropical estuary

A nocturnal demersal nekton assemblage was sampled fortnightly for two years at five sites in the Labu estuary using a 3 m beam trawl with a 3·2 cm mesh net. Forty-eight species were caught, totalling 31 458 individuals with the five most abundant species comprising over 95% of the catch. Using multiple regression techniques with Fourier transformations, the mean number of species, S, the mean abundance, N, and mean weight, W, were found to conform to a regular annual cycle with maxima in April and May. Seven of the 11 most abundant species demonstrated regular annual cycles of abundance. S, N and W were greatest in the wider, middle sites and lowest in a shallow, stagnant side branch of the estuary. Catch weights and abundances were significantly correlated with physical data.Salinity and temperature values in the estuary exhibited an annual cycle with maxima occurring in February/March. The annual thermal variation of surface water outside the estuary followed a similar cycle. The salinity at the mouth of the Markham River is lowest during January/February, which corresponds with the rainy season in the Markham River catchment. Significant annual variation existed between years in estuarine bottom salinity and salinity values in Labu Bay.Several species exhibited a greater variation in abundance and mass between years than within years. This supports the hypothesis that in the tropics between-year variation in coastal marine biotic communities is greater than within-year variation.     

Annual variation in the nocturnal nekton assemblage of a tropical estuary

A nocturnal demersal nekton assemblage was sampled fortnightly for two years at five sites in the Labu estuary using a 3-m beam trawl with a 3·2-cm mesh net. Forty species were caught, totalling 31458 individuals with the five most abundant species comprising over 95% of the catch. Using multiple regression techniques with Fourier transformations, the mean number of species (S), the mean abundance (N), and mean weight (W) were found to conform to a regular annual cycle with maxima in April and May. Seven of the 11 most abundant species demonstrated regular annual cycles of abundance. S, N and W were greatest in the wider, middle sites and lowest in a shallow, stagnant side branch of the estuary. Catch weights and abundances were significantly correlated with physical data.Salinity and temperature values in the estuary exhibited an annual cycle with maxima occurring in February-March. The annual thermal variation of surface water outside the estuary followed a similar cycle. The salinity at the mouth of the Markham River is lowest during January-February, which corresponds with the rainy season in the Markham River catchment. Significant annual variation existed between years in estuarine bottom salinity values in Labu Bay.Several species exhibited a greater variation in abundance and mass between years than within years. This supports the hypothesis that in the tropics between-year variation in coastal marine biotic communities is greater than within-year variation.     

Macrofaunal involvement in the sublittoral decay of kelp debris: the polychaete Platynereis dumerilii (Audouin and Milne-Edwards) (Annelida: Polychaeta)

Platynereis dumerilii is found in large numbers in parchment-like tubes attached to sublittoral accumulations of detached maroalgae (principally Laminaria saccharina) in Kames Bay, Isle of Cumbrae and Lochranza, Isle of Arran. Its rôle in weed decomposition has been examined by comparing its responses (behavioural choice, growth rates, absorption efficiencies of both carbon and protein, gut retention times and rate of faecal output) to fresh and rotting weed. Worms grew significantly on either diet, with older individuals gaining more weight than small individuals. Animals of a standard size (derived from measurements of maximum bite size) feeding on fresh weed, however, grew significantly faster than those feeding on rotting weed. The former had a significantly higher protein absorption efficiency which was linearly related to protein content of ingested weed. This was not so on rotting weed. Organic carbon absorption efficiencies did not differ significantly between the two groups, neither did gut retention times nor rates of faecal output. Given a choice, Platynereis chooses to build its tube, and to feed, on fresh kelp—a strategem which ensures both maximum scope for occupancy before fronds decay and a superabundance of preferred food. Platynereis feeds around its tube entrance, recropping small areas for 2–3 days, prior to switching to another area nearby. Ciliate population densities on Platynereis faeces are much lower than on either homogenized or intact weed, associated with their lower, nutritional value (at first). Platynereis bubes act to bind kelp fronds together stabilizing the faecal input to infaunal detritivores. Platynereis is an example of a detritivore which exploits the detrital substratum directly.     

Differential reproductive strategies of two bivalves in the Dutch Wadden Sea

Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria.     

Aliphatic hydrocarbons in particulate matter from the Baltic Sea

During May 1980, particulate matter was collected at an anchor station from different depths by two methods. In the separated hydrocarbon fraction the most abundant component was the highly unsaturated hydrocarbon n-heneicosahexaene (HEH). Also present was a series of mono- and di-unsaturated olefinic hydrocarbons with an uneven number of carbon atoms, starting with n-C₁₇. The alkane pattern was characterized by a maximum in the range between n-pentadecane and n-heptadecane, with a strong uneven to even carbon number predominance. The peculiar composition of the aliphatic hydrocarbons was compared with literature data given for aliphatic hydrocarbons, whether produced by different marine organisms or derived from crude oil of other anthropogenic sources. A suggestion is made for using a set of conditions as indicators for pollution by fossil hydrocarbons.     

Nitrogen and carbon isotopic composition of marine and terrestrial organic matter in Arctic Ocean sediments:: implications for nutrient utilization and organic matter composition

Relationships between organic carbon, total nitrogen and organic nitrogen concentrations and variations in δ¹³C_org and δ¹⁵N_org are examined in surface sediments from the eastern central Arctic Ocean and the Yermak Plateau. Removing the organic matter from samples with KOBr/KOH and determining residual as well as total N shows that there is a significant amount of bound inorganic N in the samples, which causes TOC/N_total ratios to be low (4–10 depending on the organic content). TOC/N_org ratios are significantly higher (8–16). This correction of organic TOC/N ratios for the presence of soil-derived bound ammonium is especially important in samples with high illite concentrations, the clay mineral mainly responsible for ammonium adsorption. The isotopic composition of the organic N fraction was estimated by determining the isotopic composition of the total and inorganic nitrogen fractions and assuming mass-balance. A strong correlation between δ¹⁵N_org values of the sediments and the nitrate concentration of surface waters indicates different relative nitrate utilization rates of the phytoplankton in various regions of the Arctic Ocean. On the Yermak Plateau, low δ¹⁵N_org values correspond to high nitrate concentrations, whereas in the central Arctic Ocean high δ¹⁵N_org values are found beneath low nitrate waters. Sediment δ¹³C_org values are close to −23.0‰ in the Yermak Plateau region and approximately −21.4‰ in the central Arctic Ocean. Particulate organic matter collected from meltwater ponds and ice-cores are relatively enriched in ¹³C (δ¹³C_org=−15.3 to −20.6‰) most likely due to low CO₂(aq) concentrations in these environments. A maximum terrestrial contribution of 30% of the organic matter to sediments in the central Arctic Ocean is derived, based on the carbon isotope data and various assumptions about the isotopic composition of the potential endmembers.     

Seasonal cycle of N2O vertical distribution and air-sea fluxes over the continental shelf waters off central Chile (∼36°S)

The continental shelf off central Chile is subject to strong seasonal coastal upwelling and has been recognized as an important outgassing area for, amongst others, N₂O, an important greenhouse gas. Several physical and biogeochemical variables, including N₂O, were measured in the water column from August 2002 to January 2007 at a time series station in order to characterize its temporal variability and elucidate the physical and biogeochemical mechanisms affecting N₂O levels. This 4-year time series of N₂O levels reveals seasonal variability associated basically with hydrographic and oceanographic regimes (i.e., upwelling and non-upwelling). However, a noteworthy temporal evolution of both the vertical distribution and N₂O levels was observed repeatedly throughout the entire study period, allowing us to distinguish three stages: winter/early spring (Stage I), mid-spring/mid-summer (Stage II), and late summer/early autumn (Stage III).Stage I presents low N₂O, the lowest surface saturation ever registered (from 64% saturation) in a period of high O₂, and a homogeneous column driven by strong wind; this distribution is explained by physical and thermodynamic mechanisms. Stage II, with increasing N₂O concentrations, agrees with the appearance of upwelling-favourable wind stress and a strong influence of oxygen-poor, nutrient-rich equatorial subsurface waters (ESSW). The N₂O build-up creates a “hotspot” (up to 2426% N₂O saturation) and enhanced concentrations of (up to 3.97 μM) and (up to 4.6 μM) at the oxycline (4-28 μM) (∼20-40 m depth). Although the dominant N₂O sources could not be determined, denitrification (mainly below the oxycline) appears to be the dominant process in N₂O accumulation. Stage III, with diminishing N₂O concentrations from mid-summer to early autumn, was accompanied by low N/P ratios. During this stage, strong bottom N₂O consumption (from 40% saturation) was suggested to be mainly driven by benthic denitrification.Consistent with the evolution of N₂O in the water column over time, the estimated air-sea N₂O fluxes were low or negative in winter (−9.8 to 20 μmol m⁻² d⁻¹, Stage I) and higher in spring and summer (up to 195 μmol m⁻² d⁻¹, Stage II), after which they declined (Stage III). In spite of the occurrence of ESSW and upwelling events throughout stages II and III, N₂O behaviour should be a response of the biogeochemical evolution associated with biological productivity and concomitant O₂ levels in the water and even in the sediments. The results presented herein confirm that the study area is an important source of N₂O to the atmosphere, with a mean annual N₂O flux of 30.2 μmol m⁻² d⁻¹; however, interannual variability could not yet be properly characterized.     

Robust optimal output tracking control of a midwater trawl system based on T-S fuzzy nonlinear model

A robust optimal output tracking control method for a midwater trawl system is investigated based on T-S fuzzy nonlinear model.A simplified nonlinear mathematical model is first employed to represent a midwater trawl system,and then a T-S fuzzy model is adopted to approximate the nonlinear system.Since the strong nonlinearities and the external disturbance of the trawling system,a mixed H 2 /H ∞ fuzzy output tracking control strategy via T-S fuzzy system is proposed to regulate the trawl depth to follow a desired trajectory.The trawl depth can be regulated by adjusting the winch velocity automatically and the tracking error can be minimized according to the robust optimal criterion.In order to validate the proposed control method,a computer simulation is conducted.The simulation results indicate that the proposed fuzzy robust optimal controller make the trawl net rapidly follow the desired trajectory under the model uncertainties and the external disturbance caused by wave and current.     

Denitrification prevails over anammox in tropical mangrove sediments (Goa,India)

Denitrification, anammox (Anx) and di-nitrogen fixation were examined in two mangrove ecosystems- the anthropogenically influenced Divar and the relatively pristine Tuvem. Stratified sampling at 2 cm increments from 0 to 10 cm depth revealed denitrification as the main process of N₂ production in mangrove sediments. At Divar, denitrification was ∼3 times higher than at Tuvem with maximum activity of 224.51 ± 6.63 nmol N₂ g⁻¹ h⁻¹ at 0–2 cm. Denitrifying genes (nosZ) numbered up to 2 × 10⁷ copies g⁻¹ sediment and belonged to uncultured microorganisms clustering within Proteobacteria. Anammox was more prominent at deeper depths (8–10 cm) mainly in Divar with highest activity of 101.15 ± 87.73 nmol N₂ g⁻¹ h⁻¹ which was 5 times higher than at Tuvem. Di-nitrogen fixation was detected only at Tuvem with a maximum of 12.47 ± 8.36 nmol N₂ g⁻¹ h⁻¹. Thus, in these estuarine habitats prone to high nutrient input, N₂-fixation is minimal and denitrification rather than Anx serves as an important mechanism for counteracting N loading.     

Hybrid <Emphasis Type="Italic">N</Emphasis>-order Lagrangian interpolation Eulerian-Lagrangian method for salinity calculation

The Eulerian-Lagrangian method (ELM) has been used by many ocean models as the solution of the advection equation, but the numerical error caused by interpolation imposes restriction on its accuracy. In the present study, hybrid N-order Lagrangian interpolation ELM (LiELM) is put forward in which the N-order Lagrangian interpolation is used at first, then the lower order Lagrangian interpolation is applied in the points where the interpolation results are abnormally higher or lower. The calculation results of a step-shaped salinity advection model are analyzed, which show that higher order (N=3-8) LiELM can reduce the mean numerical error of salinity calculation, but the numerical oscillation error is still significant. Even number order LiELM makes larger numerical oscillation error than its adjacent odd number order LiELM. Hybrid N-order LiELM can remove numerical oscillation, and it significantly reduces the mean numerical error when N is even and the current is in fixed direction, while it makes less effect on mean numerical error when N is odd or the current direction changes periodically. Hybrid odd number order LiELM makes less mean numerical error than its adjacent even number order LiELM when the current is in the fixed direction, while the mean numerical error decreases as N increases when the current direction changes periodically, so odd number of N may be better for application. Among various types of Hybrid N-order LiELM, the scheme reducing N-order directly to 1st-order may be the optimal for synthetic selection of accuracy and computational efficiency.     

Variations in mangrove forest productivity in northern Australia and Papua New Guinea

A survey method previously developed for estimating potential net primary production (P_N) of mangrove forests was applied at 19 widely separated sites in tropical northern Australia and six sites in the Gulf of Papua. These estimates are compared with previous results for mangrove forests at Hinchinbrook Island, north Queensland. Surveys of soil properties in these areas indicate that low availability of soil phosphorus is a major contributing factor to the consistently in P_N estimates of Cape York and North-western Australian forests (range in P_N=11–26; mean P_N= 19kg C ha^?1 day^?1) compared with the Hinchin-brook Island and Gulf of Papua forests (range in P_N=3–38; mean P_N=26 kg C ha^?1 day^?1). The regional variation and possible effects of other soil properties, such as redox potential and salinity, are discussed briefly. It is suggested that the generally low salinities and moderate soil redox status may partially offset the effects of low soil P in the Cape York region.     

Interannual variability of Si and N cycles at the time-series station KERFIX between 1990 and 1995 – a 1-D modelling study

Interannual variability of nutrients and plankton cycles were studied at the time-series station KERFIX (50°40′S, 68°25′E) using a 1-D coupled physical-biogeochemical model that is descended from that of Pondaven et al. (1998). At KERFIX, a high half saturation constant for silicic acid uptake (K_Si) and a high Si/N uptake ratio are required to reproduce the Si and N cycles. Although very high in comparison with most data from temperate systems, these values are consistent with K_Si and Si/N uptake ratios measured in the Indian sector of the Southern Ocean. Past and recent finding on the role of light and iron limitation on nutrient consumption ratios might explain these “unusual” silicon uptake kinetic parameters. Comparison of model results with observations show that the model correctly reproduces the observed interannual variability of nutrients and plankton cycles at KERFIX between 1992 and 1995. Characteristic features of this region are a spring phytoplankton bloom of 1.0–1.5 mg Chlorophyll a m⁻³ and a net excess of silicic acid utilisation over that of nitrate. This high silicic acid utilisation leads to low Si concentrations in late summer and subsequent Si limitation of diatom growth. The interannual variability of production of silicon and nitrogen predicted by the model is 1.93±0.04 mol Si m⁻² yr⁻¹ and 1.35±0.07 mol N m⁻² yr⁻¹ (±SD). In parallel, the predicted export is 1.12±0.04 mol Si m⁻² yr⁻¹ and 0.06±0.01 mol N m⁻² yr⁻¹. It is shown that diatoms may contribute significantly to export if diatom sinking is taken into account. An interannual variability of the predicted Si and N cycles is detected. This variability is associated with changes in the mixed layer properties, which have been documented to be linked to the Pacific El Niño Southern Oscillation or displacement of the Polar Front.     

Inertial and tidal shear variability above Reykjanes Ridge

Yearlong 75 kHz acoustic Doppler current profiler (ADCP) data were obtained well above Reykjanes Ridge (northern extension of the Mid-Atlantic Ridge (MAR)). The area is characterized by relatively large semidiurnal tidal (‘D₂’) currents that have (at lunar M₂) more than half a decade larger variance than inertial (f) currents. However, despite the relatively weak near-inertial kinetic energy, its vertical current shear shows larger magnitudes than at M₂ in an otherwise flat f−D₂ band limited between frequencies 0.74 and 1.35f, which equals the inertio-gravity wave bounds [σ_min, σ_max](N=f). N represents the buoyancy frequency. The shear in this band dominates all shear computed at 20 m effective vertical scale. As the kinetic energy spectrum peaks at M₂, but not (significantly) at S₂ and N₂, a difference in tidal (and inertial) scales and hence sources is observed. M₂-tides contribute mostly to large-scale coherent motions. The dominant incoherent f−D₂ shear is highly variable in time (∼2-day periodicity). Furthermore, inertial and tidal shear are more or less completely separated in space and time, each occurring in different layers in the vertical. The thin shear layers reflect the rapidly varying short vertical scale N_s profile, to within the ∼20 m limitation of ADCP data, rather than the large-scale smooth N_L. In each of large-N_s layers Ri≈1, probably. The yearlong smoothed shear magnitude follows N_L, but only as stable Ri≈5. The shear polarization is more circular than rectilinear, albeit varying with time, and highly symmetric around f. During transitions, e.g., between stratified and homogeneous layers and between waves from varying sources, near-circular motions can generate near-rectilinear shear in the direction of wave propagation (in the direction of the minor axis of the current ellipse). This contrasts with the possibility of near-rectilinear barotropic oscillatory motions generating near-circular shear under viscosity in shallow seas.     

Determining confidence intervals in analyzing climatic series

In the context of the problem of global warming, the question of how much the observed increase in the mean air temperature over the last decades is likely due only to natural variability is studied. It is assumed that an observed temperature-data series of length N is a segment of a stationary random sequence with a spectrum known on an interval that does not include the lowest frequencies. The variance σ²(N) of the sample mean m* and the standard deviation σ(N), which determines the width of the confidence interval of m*, are calculated for different continuations of the spectrum to the low-frequency region. For a continuation of the spectrum that boundlessly increases, as does ω^−2α (0 < α < 1/2) when the frequency ω tends to zero (red-noise spectrum), it is shown that, the closer the parameter α is to 1/2, the more slowly σ(N) tends to zero at N → ∞. Using an empirical spectrum of a global mean annual temperature series as an example, it is shown that the standard deviation significantly depends on the form of the spectrum in the lowest frequency region. An attempt has been made to assess the measure of standard-deviation uncertainty due to a lack of exact information on the spectrum in the low-frequency region. Important series characteristics—the equivalent number of independent observations N _eq(N) and the time scale of correlation T ₁(N) which are determined through the variance σ²(N) of m*—also depend on the form of the spectrum in the low-frequency region. For the red-noise spectrum, N _eq(N) increases with an increase in N proportionally to N ^1–2α (but not proportionally to N as in the case of bounded spectrum); the correlation scale T ₁(N) is no longer constant (as in the case of bounded spectrum) and increases with an increase in N proportionally to N ^2α.     

Experimental investigation on the flow induced vibration of an equilateral triangle prism in water

A series of flow induced vibration (FIV) experiments for an equilateral triangle prism elastically mounted in a water channel are performed with different system stiffness at constant damping and mass. An amplitude variation coefficient is proposed to describe FIV stationarity in the present study. The FIV of the prism can be divided into three primary regions based on the amplitude and frequency responses, which are the vortex induced vibration (VIV) branch, the transition branch from VIV to galloping, and the galloping branch. The transition branch occurs at the reduced velocity in the range of 7.8 < U_r = U/(f_n,air·D) < 10.4, accompanied with a relatively rapid increase in amplitude and a precipitous drop in frequency and vibration stationarity. In addition, the reduced velocity where the transition region is initiated is independent of the system stiffness. The maximum amplitude reaches 3.17 D in the galloping branch. The ratio of the response frequency to the natural frequency of the prism in air remains locked to approximately 0.65 throughout the fully developed galloping branch. Large amplitude responses in an infinite range of flow velocities, excellent vibration stationarity and steady vibration frequencies, which are characteristics of the galloping of the prism, have a positive impact on improving energy conversion.     

Wave power extraction by an axisymmetric oscillating-water-column converter supported by a coaxial tube-sector-shaped structure

An analytical theory is developed to study the effects of a coaxial tube-sector-shaped supporting structure on the conversion efficiency of a suspended, circular OWC converter. An eigen-function expansion method is employed in a cylindrical coordinate system to study wave interaction with an OWC converter in finite depth of water. Effects of the supporting structure, OWC dimensions, wave direction on energy conversion efficiency, and optimization of power-takeoff devices are discussed. Our results show that the coaxial tube-sector-shaped support with an opening in the range of π/2–5π/4 can significantly increase the conversion efficiency and widen the frequency range over which the conversion efficiency is high.