Nitrogen uptake,ammonium oxidation and nitrous oxide (N2O) levels in the coastal waters of western Cook Strait,New Zealand

Vertical measurements of $\text{NH}{}_4{}^{\mathrm{+}}$, $\text{NO}{}_3{}^{\mathrm{?}}$ and N₂O concentrations, $\text{NO}{}_3{}^{\mathrm{?}}$ and $\text{NH}{}_4{}^{\mathrm{+}}$ uptake, and $\text{NH}{}_4{}^{\mathrm{+}}$ oxidation rates were measured at 5 sites in western Cook Strait, New Zealand, between 31 March and 3 April 1983. Nitrate increased with depth at all stations reaching a maximum of 10.5 μg-atom $\text{NO}{}_3{}^{\mathrm{?}}\text{N l}{}^{\mathrm{?1}}$ at the most strongly stratified station whereas $\text{NH}{}_4{}^{\mathrm{+}}$ was relatively constant with depth at all stations (～0.1 μg-atom $\text{NH}{}_4{}^{\mathrm{+}}\text{N l}{}^{\mathrm{?1}}$). The highest rates of $\text{NH}{}_4{}^{\mathrm{+}}$ oxidation generally occurred in the near surface waters and decreased with depth. N₂O levels were near saturation with respect to the air above the sea surface and showed no obvious changes during 24 h incubation. $\text{NH}{}_4{}^{\mathrm{+}}$ oxidation by nitrifying bacteria may account for about 30% of the total $\text{NH}{}_4{}^{\mathrm{+}}$ utilization (i.e. bacterial+agal) and, assuming oxidation through to $\text{NO}{}_3{}^{\mathrm{?}}$, may supply about 40% of the algal requirements of $\text{NO}{}_3{}^{\mathrm{?}}$ in the study area. These results suggest that bacterial nitrification is of potential importance to the nitrogen dynamics of the western Cook Strait, particularly with respect to the nitrogen demands of the phytoplankton.     

Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions

The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Niño could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.     

Comparison of precipitation and land runoff as sources of estuarine nitrogen

The seasonal and year-to-year variation of bulk precipitation as a source of total N, nitrate and ammonia is reported for a 7-year period at the Rhode River, a subestuary of Chesapeake Bay, U.S.A. These values are placed in perspective by comparison with analogous nitrogen loading due to watershed discharges.Although year-to-year variations were important, in an average year about the same amount of readily available nitrogen entered the system via precipitation as entered in land runoff and, during the summer and fall, precipitation was the largest source.     

The behaviour of dissolved silica during the mixing of river and sea waters in Tokyo Bay

The behaviour of dissolved silica was studied in Tokyo Bay during six surveys in 1979 and 1980. The data from late spring and mid-summer samples showed concave mixing curves of silica versus salinity, whereas for the winter samples a simple conservative dillution curve was obtained. Plots of particulate silicon to particulate aluminium showed that even for winter samples as well as summer ones there were some processes removing silica from solution. The processes could not be adequately explained by adsorption onto suspended solids. The data are indicative of uptake by diatoms as the principal removal mechanism. Most of the diatom skeletons settled to the bottom where dissolution was rapid. The silica-salinity curves in this study thus demonstrate an apparent removal process for dissolved silica. This is because during summer the displacement rate of biogenic silica from a unit water column to the bottom as fecal pellets or by sinking is greater than the supply rate of dissolved silica by the action of diffusion and mixing of bottom water enriched with dissolved silica whereas in winter these rates are reasonably balanced.     

The principal factors contributing to the flux of salt in a narrow, partially stratified estuary

Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides.The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation.The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt.At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget.On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides.     

The behavior of iron,manganese and silicon in the Peconic River estuary,New York

The behavior of dissolved and particulate iron and manganese and dissolved silicon has been studied as a function of chlorinity in the Peconic River estuary, New York. This study sought to identify important geochemical processes in a relatively pristine estuary facing increasing anthropogenic impact.Dissolved iron behaved in the classical non-conservative manner exhibiting removal of nearly 80% at very low chlorinities, while particulate iron increased by a corresponding amount over the same chlorinity range. Dissolved manganese was enriched by up to 200% over its predicted concentration at low and intermediate chlorinities by desorption from suspended particulates and by a probable benthic flux. Dissolved silicon was enriched by up to 100% at low and intermediate chlorinities also from a probable benthic flux. These fluxes were estimated to be 5 μg cm^?2 day^?1 for dissolved manganese and 70 μg cm^?2 day^?1 for dissolved silicon.The quantity of both particulate iron and manganese increased at high chlorinities due to an influx of suspended inorganic particulates. In the intermediate to high chlorinity region, oxidation of sediment-derived manganese is believed to contribute to the observed increase in particulate manganese.Total iron was essentially conservative throughout most of the estuary, while total manganese was non-conservative presumably due to extensive remobilization of dissolved manganese from the sediments.     

The application of isotopic and biogeochemical markers to the study of the biochemistry of organic matter in a macrotidal estuary, the Loire, France

The biogeochemistry of organic matter in a macrotidal estuary, the Loire, France, has been studied for two years during different seasons. Both particulate matter and sediment have been sampled in the riverine zone, in the maximum turbidity zone and in the ocean near the river mouth. Two techniques have been used: carbon isotopic ratio determination and analysis of lipid-marker signatures in the n-alkane, n-alkene and fatty acid series. For the period corresponding to the output of the maximum turbidity zone in the ocean, the complete change of organic matter, continental in nature in the inner estuary, pure marine in the outer estuary is well illustrated by the decrease of δ¹³C values and of carbon preference index of n-alkanes. Input sources of organic matter by continental plants, plankton and micro-organisms are discussed from biogeochemical-marker analyses data along with the processes of accumulation of particles and their evolution with the season. Some criteria for evidencing the nature of various organic-matter pools are assessed and compared in different chemical-marker series as follows: high molecular weight n-alkanes and fatty acids, perylene for continental imprints, polyunsaturated 18-, 20- and 22-carbon fatty acids, n-C₁₇, n-alkenes and squalene for algae imprints, branched iso and anteiso fatty acids, Δ11-C_18:1 for microbial imprints.     

Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair⁻¹ vs. 1.40 young fledged pair⁻¹) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation.     

Spatial intertidal distribution of bivalves and polychaetes in relation to environmental conditions in the Natori River estuary,Japan

This paper aims to reveal spatial variation in the abundance of infaunal bivalves and polychaetes at different spatial scales (station: 200–800 m intervals; plot: 5–20 m), and to reveal environmental variables affecting the spatial distribution of animals in the Natori River estuary, Japan. We found six bivalve species and eight polychaete species from 52 plots at 12 stations. Nuttallia olivacea and Heteromastus sp. were found to be the most abundant species of bivalves and polychaetes, respectively. Assemblage patterns of bivalves and polychaetes were classified into five distinct groups. Substrata (silt-clay contents), salinity, and relative elevation were the variables found to affect the infaunal assemblage patterns. Chlorophyll a was not a significant variable, but benthic animals were absent at sites with extremely low chlorophyll a conditions. Macrobenthic assemblage patterns were different not only between stations but often differed between plots at the same station, reflecting the complex assemblage structure of benthic invertebrates. Detailing such animal–environment relationship is essential in understanding the potential food supply for estuarine fishes.     

A finite-element,multi-scale model of the Scheldt tributaries,river, estuary and ROFI

We report on the development and validation of a coupled two- and one-dimensional finite-element model for the Scheldt tributaries, river, estuary and region of fresh water influence (ROFI). The hydrodynamic equations are solved on a single, unstructured, multi-scale mesh stretching from the shelf break to the Scheldt tributaries. The tide is forced on the shelf break and propagates upstream in the riverine network. Upstream boundaries lie on sluices or outside of the region of tidal dominance where daily averaged discharges are imposed. Two-dimensional, depth-averaged shallow water equations are solved by means of the discontinuous Galerkin (DG) method over the marine and estuarine parts of the computational domain. In the rivers, however, one-dimensional equations are dealt with using the DG method with the addition of a technique to cope with confluence points. Model parameters are carefully calibrated, leading to the simulation of wind- and tide-forced flows that are in excellent agreement with available data. The diffusivity in the transport equation is calibrated using time series of salinity at various locations in the estuary. Finally, the Lagrangian residual transport in the estuary and the adjacent coastal zone is investigated. This work is a major step towards an integrated model for studying the dynamics of waterborne contaminants and the water renewal timescales in the Scheldt land-sea continuum.     

Response of Acartia populations to environmental variability and effects of invasive congenerics in the estuary of Bilbao, Bay of Biscay

The effect of environmental factors (river discharge, water temperature and dissolved oxygen saturation) on the abundance and distribution of Acartia populations and the interactions between their congenerics was evaluated by means of transfer function (TF) models in the estuary of Bilbao during the period 1998–2005. The recorded species were Acartia clausi, Acartia tonsa, Acartia margalefi and Acartia discaudata. Acartia clausi dominated in the entire euhaline region of this estuary until 2003 when it was displaced from the inner part by A. tonsa. This invasive species (A. tonsa) was found for the first time in 2001 and colonized successfully the inner (salinity 30) and intermediate (salinity 33) waters of this estuary since 2003. The TF models revealed an immediate and negative effect of A. tonsa on A. clausi in the intermediate salinity (33) waters, where these species showed the highest spatial overlap. The results indicate that environmental changes from 2003 influenced the abundance of Acartia species, being unfavourable for A. clausi. The decrease of A. clausi abundance in low salinity waters was related to a significant decrease of dissolved oxygen saturation levels, whereas the increase of temperature was linked to a significant increase of A. tonsa. Acartia margalefi and A. discaudata were scarce over the entire period, but they were found to be valuable indicators of hydrological changes, which were associated to climate factors. These two latter species increased in abundance and expanded their seasonal distribution, and in the case of A. margalefi also its spatial distribution, in 2002, coinciding with the period in the time-series when autumn–winter rainfall and summer temperatures were lowest, and dissolved oxygen saturation levels were highest.     

A comparative study of mercury contamination in the Tagus estuary (Portugal) and major French estuaries (Gironde,Loire, Rhône)

Concentrations of mercury were determined for the waters, suspended matter and sediments of the Tagus and of major French estuaries.The Tagus estuary is one of the most contaminated by mercury derived from the outfalls of a chloralkali plant and from other industrial sources. In deposited sediments the median level, 1·0 μg Hg g^?1, is twenty times higher than the natural background and Hg contents depend on the sediment grain-size, age and the distance from waste-outfalls. Suspended matter is more regularly and highly contaminated (median value: 4·5 μg Hg g^?1). In the French estuaries Hg levels in the suspended material decrease with salinity due to dilution and/or remobilization processes. In June 1982, in the Loire estuary, high values of Hg are observed in the middle estuary and attributed to urban and industrial sources.In the Tagus estuary, the general distribution of total dissolved Hg confirms the contamination: it increases seaward from 10 ng 1^?1 in the river to 80 ng 1^?1 in the estuary outlet. The dissolved Hg is almost totally organic in the river, inorganic in the middle estuary due to inorganic Hg effluents and again organic in the lower estuary. This variation is related to the dissolved organic carbon values. The dissolved Hg levels in the Loire Estuary (5–300 ng 1^?1) are much higher than in the Gironde estuary (3–6 ng 1^?1) and of the same order as those observed in the Tagus estuary.     

Response of Nereis diversicolor (Polychaeta, Nereidae) populations to reduced wastewater discharge in the polluted estuary of Oued Souss, Bay of Agadir, Morocco

Field investigations on the population dynamics of Nereis diversicolor were carried out from January 2002 to December 2003 in the estuary of Oued Souss (southwestern Morocco) to determine the changes caused by setting up of a domestic and industrial wastewater purification plant (M'zar) before and after by the end of wastewater discharges in November 2002 on the structure of the ecosystem. Samples of N. diversicolor were collected monthly in the intertidal zone at low tide before (during 2002) and after (during 2003) the end of wastewater discharges.Separation of cohorts using the Algorithm EM method (McLachlan, G.J., Krishnan, T., 1997. The EM algorithm and extensions. Wiley Series in Probability and Statistics. Wiley, New York, 274 pp.) allowed determination of the growth rate (mm day⁻¹) by cohort and the annual production. The data showed significant differences between populations of Nereis diversicolor before and after the end of wastewater discharges. During the wastewater discharge period (2002), the population had a mean annual density of 1992 ind m⁻², a mean annual biomass of 75.52 g DW m⁻² and an annual secondary production of 141.3 g DW m⁻² with a P/B ratio of 1.87. After the end of discharges (2003), density, biomass and secondary production decreased significantly. The annual averages for these parameters were 740 ind m⁻², 14.16 g DW m⁻² and 23.83 g DW m⁻², respectively, with a P/B ratio of 1.68.The important decrease observed in density, biomass and secondary production of Nereis diversicolor may be attributed (a) to the environmental changes observed after the end of wastewater discharges in the estuary of Oued Souss, namely the increase of salinity and the decrease of organic matter content, and (b) to the migration of this species towards other areas.     

镀镍多壁碳纳米管对序批式反应器性能及其微生物群落的影响

本文研究了长期暴露条件下镀镍多壁碳纳米管(MWCNTs-Ni)对序批式反应器(SBR)性能、微生物酶活性和微生物群落的影响。研究结果表明,10mg/LMWCNTs-Ni的长期暴露未对SBR去除有机物产生影响,而NH+4-N的去除率由(99.10±0.60)%明显降至(39.04±1.61)%。与进水中未加入MWCNTs-Ni时的第32天相比,活性污泥比耗氧速率(SOUR)和脱氢酶(DHA)活性在第148天时分别降低了17.43%和24.32%;而脱氮速率和与脱氮相关的微生物酶活性均降低了60%以上,从而导致SBR对氮的去除效果明显降低。MWCNTs-Ni的长期暴露导致活性污泥活性氧(ROS)产生量和乳酸脱氢酶(LDH)释放量在第148天时分别增加了67.23%和65.33%,表明MWCNTs-Ni的长期暴露能够诱导活性污泥中微生物产生氧化应激和细胞膜损伤。高通量测序结果表明,长期暴露于10mg/L的MWCNTs-Ni条件下,活性污泥中与硝化过程相关菌属(Nitrosomonas、Nitrosospir、Nitrospira)和与反硝化过程相关菌属(Dokdonella、Dechloromonas、Steroidobacter、Devosia、Thermomonas)的相对丰度明显降低,进而影响到SBR对氮的去除。该研究结果可为评价MWCNTsNi对污水生物处理系统的潜在影响提供一定的理论基础和技术依据。     

Spring distribution of dissolved organic matter in a system encompassing the Northeast Water Polynya: Implications for early-season sources and sinks

This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature–salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113±14 μM, n=68) than surface water (SW) outside the polynya area (96±18 μM, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that 80% of early-season DOC and 90–100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area.     

Transportation of water,particulate and dissolved organic and inorganic matter between a salt marsh and the Ems-Dollard estuary,The Netherlands

Transport processes were studied in a gully between a salt marsh and an estuary. After storm tides, ebb currents in the gully reached high values. It is concluded that particulate matter (both organic and inorganic) are imported into the marsh. Coarse organic debris is exported during storm tides, but this amount is low when compared with the primary production on the marsh. Exports are shown for dissolved organic carbon, ammonia, phosphate and silica, while nitrate and possibly nitrite are imported. Organic matter derived from in situ production and net import is buried and partly mineralized in the marsh.     

Nitrogen sources in the South China Sea, as discerned from stable nitrogen isotopic ratios in rivers, sinking particles, and sediments

Stable nitrogen isotopic ratios were measured in sinking particles and surface sediments from the South China Sea (SCS) in order to study recent nitrogen sources and degradation. Average δ¹⁵N values of 16 sediment traps deployed at seven locations in the northern, central and southern SCS were uniformly low, ranging between 2.7 and 4.5‰ with a winter minimum in the northern and central SCS. Enhanced nitrogen contents and δ¹⁵N values were noted in samples affected by swimmers, comprising between 5 and 20% of total nitrogen fluxes. Nitrate sources were subsurface waters from the western Pacific, which were isotopically depleted due to the remineralization of nitrogen from nitrogen fixation in surface waters. Nitrogen fixation in the SCS contributed up to 20% to the settling particles. In the southern SCS, resuspended matter close to the shelf added to the sinking particulates. The long-term trap record from the central SCS revealed decreasing δ¹⁵N values during the 1990s, which correspond with findings from the North Pacific Subtropical Gyre and may be attributable to increased nitrogen fixation due to global warming-related stratification. This trend may be restricted to the 1990s but could also persist due to the projection of more frequent occurrence of El Niño conditions.The δ¹⁵N increase from swimmer-free trap averages of 2.7–3.6‰ to values of 5–6‰ in underlying deep-sea sediments was in the same range as in other deep ocean areas. Similar to results from the northern Indian Ocean, this increase could be related to isotopic enrichment during amino acid degradation. The lowest sedimentary δ¹⁵N values characterize the Pinatubo ash layer deposited off Luzon in an event of mass sedimentation in 1991. The fast deposition of organic matter drawn from the surface waters with the ash in the form of vertical density currents evidently preserved the planktonic δ¹⁵N signal.