Recent sediment deposition rates in the oyster ground,North Sea

Recent sediment accumulation rates were calculated from downcore ²¹⁰Pb-excess activity profiles obtained from box cores taken in the Oyster Ground, North Sea. The rates ranged from 0.04 to 0.94 cm·yr⁻¹ with an average of 0.39 cm·yr⁻¹. In the top sediment layer the activities were rather low, the highest being only 1.15 dpm·g⁻¹, and the average value 0.92 dpm·g⁻¹.As shown by X-ray radiographs, downcore variations in texture were small: most samples being homogeneous and lacking primary sedimentary structures. Burrowing was evident in all cores, and most of them had a surface mixed layer of at least 5 cm, below which the ²¹⁰Pb activity rapidly dropped to background value.Downcore deviations from the logarithmic decrease in ²¹⁰Pb with depth could generally be attributed to biological disturbance or physical processes causing reworking of the sediment. Only in one core did the ²¹⁰Pb activity decrease regularly with depth. The activities of ¹³⁷Cs in this core and another demonstrated recent accumulation rates of 0.44 and 0.88 cm·yr⁻¹, respectively, which are in good agreement with the rates obtained from the ²¹⁰Pb method in the same cores (viz. 0.37 and 0.94 cm·yr⁻¹). From these sedimentation rates the total amount of mud yearly deposited in the muddy part of the Oyster Ground is estimated to be in the order of 2×10⁹ kg·yr⁻¹, which is 4 to 5% of the total amount of mud yearly deposited in the North Sea.     

Actual flux of the Huanghe (yellow river) sediment to the Western Pacific ocean

More than 90% of the Huanghe sediment load is deposited in the lower reaches of the river and within the shallow estuarine area. Additional sedimentation occurs in the southern part of Bohai so that the actual flux of sediment to the Yellow Sea (Huanghai) is very limited. We show that this flux takes place via a nepheloid layer across the Bohai Sea strait, transporting ∼ 6·10⁹ kg·y⁻¹, i.e. less than 1% of the Huanghe sediment discharge.     

Measuring the flux of oxygen to a muddy sediment with a cylindrical microcosm

We have examined the effects of changing the flow velocity and the oxygen concentratin in the water overlying a muddy sediment on the flux of oxygen across the sediment-water interface and on the distribution of oxygen within the pore water. The experiment was carried out on an intertidal sediment from the western Wadden Sea, using a cylindrical microcosm with a calibrated flow regime. Steady-state and transient-state models were used to estimate the values of the effective diffusion coefficient for oxygen in the pore water.Increasing the flow velocity caused a significant though small increase in the oxygen concentration in the pore water, but had little effect on the concentration gradient at the sediment-water interface. The concentration gradient in the boundary layer was too small at any of the flow velocities to account for the oxygen flux into the sediment via molecular diffusion. This is ascribed to a pressure gradient which exists in rotating flows, disrupting the diffusive boundary layer and augmenting the flux via advection. Model calculations indicate that about 25% of the flux can be attributed to irrigation by burrowing organisms, but in contrast to previous results with sandy sediments, irrigation of the pore water caused by the radial pressure gradient can be considered to be negligible. The effective diffusion coefficient ranged from 4·10⁻⁹ m²·s⁻¹ at a depth of 1 mm below the sediment-water interface to 1·10⁻⁹ m²·s⁻¹ deeper in the sediment. These estimates are within a factor of 1 to 3 of the modelular diffusion coefficient for oxygen, which is suprisingly close in view of the high numerical densities of meiofauna and macrofauna in this sediment.     

An experiment on the relative importance of denitrification,nitrate reduction and ammonification in coastal marine sediment

Simultaneous determinations of ¹⁵N-nitrogen gas production, ¹⁵N-ammonia formation by nitrate reduction and ammonia production from organic nitrogen were carried out after addition of ¹⁵N-nitrate to anaerobically incubated sediment slurries from a location in the Dutch Wadden Sea. The rate of nitrogen gas production was 1.57 μmol N·cm⁻³ wet sediment·d⁻¹, nitrate reduction to ammonia occurred at a rate of 0.79 μmol N·cm⁻³·d⁻¹ and ammonification at 1.17 μmol N·cm⁻³·d⁻¹. At the end of the incubation experiment (after 30 h) 63% of the originally added ¹⁵N-nitrate was present as nitrogen gas, 32% ended up as ammonia and ∼4% as particulate organic nitrogen. Ammonia production by degradation of organic nitrogen compounds was the most important process in building up the ammonia pool in the anaerobic sediment incubation.     

Structure and energy demand of the benthic soft-bottom communities in the Java Sea and around the islands of Madura and Bali,Indonesia

In July 1984 benthic research was carried out in the Java Sea and around the islands of Madura and Bali.The aim was to describe the structure of the benthic communities in terms of numerical density (numbers of dominant macrofaunal groups and meiofauna per square metre) and biomass (g ashfree dry weight (AFDW) per square metre), and in relation to geographical position and main ambient factors, i.e. water depth, bottom temperature and sediment characteristics.In addition attempts were made to estimate the activity of these benthic ecosystems, and to show their relation to the pelagic.Box-core samples, collected along west-east axis in the Java Sea and in the Strait of Madura, showed relatively poor benthic communities. The average densities of macrofaunal organisms (> 1 mm) did not exceed 250 specimens·m⁻²; the total biomass was below 1 g AFDW·m⁻²; small polychaetes and crustaceans were the dominant groups.A number of larger organisms have developed very remarkable adaptations to the muddy environment. Meiofaunal organisms (nematodes being the dominant group) numbered 0.06·10⁶ to 0.46·10⁶ specimens·m⁻². In general there is a trend from west to east towards somewhat richer communities. The actual carbon demand of the benthic ecosystem in the area investigated is tentatively estimated at an average of 38 g C·m⁻²·y⁻¹, which amounts to about 40% of the primary production.Both the very soft fluid-mud bottoms in the central Java Sea and in Strait Madura, and the relatively low amount of energy available for growth, probably prevent the establishment of well developed benthic communities.     

Examination of the connection between the patchiness of benthic nutrient efflux and epiphytobenthos patchiness on intertidal flats

Intertidal epiphytobenthos activity (expressed in mmol oxygen evolution·m⁻²·h⁻¹) and nutrient efflux out of the sediment (computed from pore water nutrient concentration profiles and expressed in μmol·m⁻²·h⁻¹) were studied at the same places. Increased ammonia or phosphate efflux stimulated epiphytobenthos activity, and an optimum of epiphtobethos activity was observed when the molar N:P ratio in the efflux agreed with the N:P ratio in diatom biomass. It is concluded that epiphytobenthos patchiness depends on the spatial distribution of nutrient efflux and on the N:P ratio in the efflux. The conditions of nutrient efflux were further studied by fertilizing the sediment with urea and phosphate. Phosphate could be traced in the pore water over two months; ammonia over more than two months. The formation of a diatom bed at the fertilized are was observed once, but efforts to reproduce it failed, indicating the importance of other growth-determining conditions. Nutrient efflux was prevented by a plastic foil to stimulate a possible efflux inhibition by diatom mats. Concentrations below the foil were examined and compared with results from an untreated area. An increase of nutrient concentrations in the pore water was observed.     

Radon profiles in the Indonesian archipelago

A series of near-bottom excess radon profiles was measured in the Indonesian archipelago during the Snellius-II Expedition. The results show considerable variations in structure, ²²²Rn concentrations and integrated excess ²²²Rn inventory in the water column. Near-bottom vertical eddy diffusion coefficients vary from 46.4 to 63.6 cm²·s⁻¹ in the basins; they are in general much higher on slopes and sills. The standing crop (the integrated amount of excess ²²²Rn) ranges from 0.9 to 49.6 dpm·cm⁻². ²²⁶Radium supported ²²²Rn concentrations range from 9 to 3888·10⁻² dpm·kg⁻¹ Compared to mid-ocean basins the vertical mixing processes of near-bottom water masses in the Indonesian archipelago is fast, especially in the water layer from 50 to 200 m above the bottom, with diffusion coefficients in the order of 10 times higher than in the Pacific Ocean. With the exception of two stations standing crop values were comparable with those found in the Pacific Ocean but higher than those from the Atlantic Ocean. ²¹⁰Pb analyses show high sedimentation rates, up to 75 cm·10⁻³·a⁻¹. This does not agree with related standing crops. One explanation can be that erosion plays an important role on the sills and slopes.     

The uptake and distribution of copper in the lugworm,Arenicola marina (annelida,polychaeta)

The uptake and distribution of copper in the polychaetous worm Arenicola marina (L.) have been studied both under experimental conditions and in a natural environmental situation, by analyzing the whole body and three body-compartments; body-wall, intestine and blood.No relationship between the copper concentrations in various fractions of the sediment and any of the body-compartments could be found.Under experimental conditions, the copper concentrations in the blood were higher than in the intestine and the body-wall. Uptake of dissolved copper occurred directly from the water. Copper uptake also occurs via sediment at high copper concentrations of the silt fraction of the habitat sediment.The data obtained from the field showed small differences in copper concentrations between blood, intestine and body-wall. The copper concentrations in the blood varied from 1 to 4 μ·cm⁻³, in the inetestine from 2 to 6μg·g⁻¹, and in the body-wall from 1 to 3 μg·g⁻¹ wet weight.A significant correlation existed between blood cooper concentration and body weight: small (young) individuals had higher copper concentrations in their blood than larger (older) ones. This means that young animals will encounter more stress at similar environmental copper levels than older animals.The concentration in the different body-compartments appears to be dependent on the season the samples were taken. The copper concentration in the intestine and the body decreased from April to November, whereas the blood copper concentration increased.     

Abundance and salt tolerance of obligately aerobic,phototrophic bacteria in a marine microbial mat

Data have been collected on the abundance of obligately aerobic, bacteriochlorophyll-a-containing bacteria in a marine microbial mat on the West Frisian Island of Texel, The Netherlands. Plate counts on media rich in organic matter revealed average numbers of 3¹10⁵·cm⁻³ sediment in the top 10 mm of the mat; the number of purple non-sulphur bacteria was of the same magnitude. Due to the relatively small dimensions of obligately aerobic anoxygenic phototrophic bacteria and purple non-sulphur bacteria, compared to those of purple sulphur bacteria, the contributions of either of the two former groups to the biomass of Bchl-a-containing organisms was approximately 3%. The specific Bchl-a-content of the isolated obligately aerobic phototrophs was very low (0.8 to 1.0 μg·mg⁻¹ protein) compared to that of purple non-sulphur bacteria (16 to 20 μg·mg⁻¹ protein), and purple sulphur bacteria (27 to 30 μg·mg⁻¹). As a consequence, the relative contribution to the total Bchl a concentration of the two former groups (0.1% and 2.1%, respectively) was negligible, compared to that of the purple sulphur bacteria (97.8%).Salinities <50 had little effect on growth rate and yield of isolates; at salinities between 50 and 100 the doubling time increased progressively with a concomitant decrease in yield; no growth occurred at salinities > 140.     

Recycling of poultry droppings through tilapia fish culture. Effect of monosex and mixed-sex culture on production

Tilapia fish production in tanks manured with poultry droppings and stocked either with tilapia males and females separately or together is compared and discussed.The mixed-sex group gave the highest production rate of 34·2 kg ha⁻¹ day⁻¹ with a manure coefficient of 2·2. The ‘all female’ group ranked last with a production rate of 22·9 kg ha⁻¹ day⁻¹ and a manure coefficient of 3·3. Sixty per cent of the tilapia biomass produced in the ‘mixed-sex’ tanks was contributed by reproduction. While monosex culture is better for the production of large fish for human consumption, where small fish do not matter, as in the case of the preparation of fishmeal for animal feeding, mixed-sex culture may be adopted without curtailing production.     

Exposure,vegetation and sediment as primary factors for mobile epibenthic faunal community structure and production in shallow marine soft bottom areas

Mobile epibenthic fauna was quantitatively assessed in 22 shallow-water (0–1.5 m), soft-bottom areas on the Swedish west coast. Relationships between faunal structure, density, biomass and annual production on the one hand, and physical factors such as exposure, vegetation cover and sediment structure on the other, were investigated. The areas were grouped according to their physical characteristics into 4 categories: exposed, semi-exposed and sheltered with little or no vegetation and vegetated.Species number, density, biomass and annual production were shown to be significantly higher in vegetated areas (Zostera marina L.) than in mainly unvegetated ones. The epibenthic production in Z. marina meadows was 6 g (AFDW)-m⁻²·y⁻¹. Species composition was also different and Carcinus maenas L. was the only dominant species occurring in both vegetated and unvegetated areas. In all unvegetated areas the number and composition of species were about the same, regardless of exposure, whereas biomass and production varied with the degree of exposure. Highest production (3 to 5.5 g (AFDW)-m⁻²·y⁻¹) in these areas was found in semi-exposed areas. In exposed and sheltered areas production was 1.1 to 3.3 g and 0.6 to 1.7 g (AFDW)-m⁻²·y⁻¹, respectively.Degree of exposure, vegetation cover and sediment structure are suggested as the primary factors affecting the composition and quantity of mobile epibenthic fauna in the investigated areas. Biotic factors e.g. predation and competition are generally considered to be subordinate to these physical factors.     

Accumulation rates of estuarine sediment in the dollard area: comparison of 210Pb and pollen influx methods

Profiles of excess ²¹⁰Pb activity in sediment cores collected on the muddy tidal flats of the Dollard indicate deposition rates ranging from 0.14 to 0.27 cm·y⁻¹. One profile was also analysed for pollen: the pollen profile in the core provided a record of the sedimentation rate because two independent historical events were found recorded in the profile. The first, a sudden abundance of an Aster-type pollen, reflected, at a depth of 33 cm in the sediment, the large land reclamation of 1862 A.D. The second, the appearance of Zea mays (corn) at a depth of 6 cm, reflected the increase of the area in which corn was cultivated: from 44 ha in 1970 up to 552 ha in 1973. The pollen data gave an estimated sedimentation rate of 0.25 cm·y⁻¹. Excess ²¹⁰Pb analysis of the same core yielded a sedimentation rate of 0.27 cm·y⁻¹.     

Biomass and activity of benthic fauna on the fladen ground (northern North Sea)

During May 1983 the abundance and biomass of macrobenthos and meiobenthos populations, as well as the metabolic activity (shipboard incubated and in situ measured respiration, and potential respiration activity by ETS) were studied in the Fladen Ground area.Macrofauna showed an abundance of 4500 specimens per m²; the corresponding biomass was 10.7 g ash-free dry weight per m². The bivalve Arctica islandica, with 12 specimens per m² contributed 7.2 g to this biomass. Average meiofauna numbers, 0.9·10⁶ per m² were low; a meiofaunal biomass of only 0.3 g was estimated. Depending on the method applied, large variations in metabolic activity were found. Results from shipboard incubation experiments probably present a large underestimate. The in situ bell-jar experiments showed an average oxygen uptake of 1010 μmol O₂·m⁻²·h⁻¹, equalling a carbon demand of 7.3 gC·m⁻²·month⁻¹ in May. ETS measurements gave a 3 times higher estimate. Taking into account that macrofaunal and meiofaunal abundance and biomass, as well as bottom temperatures, show minimum values in spring, an annual carbon mineralization by the benthic system of 50 to 70 gC·m⁻² is suggested. This would mean that about one third of the total primary produced organic matter is channelled into the benthic system.     

Distribution of chroococcoid cyanobacteria and size-fractionated chlorophyll a biomass in the central and southern north sea waters during June/July 1989

The spatial and vertical distribution of phycoerythrin(PE)-containing chroococcoid cyanobacteria and the contribution of the <3 μm size fraction to overall phytoplankton chlorophyll a biomass were investigated in the central and southern North Sea during June and July 1989. PE-containing chroococcoid cyanobacteria cell numbers ranged between 6×10⁵ and 4.4×10⁷ cells·dm⁻³ and was typically between 0.5×10⁷ and 3×10⁷ cells·dm⁻³, lowest numbers being recorded near the British coast in central North Sea waters. The vertical distribution of these cyanobacteria showed no evidence to suggest a preferential accumulation deep in the euphotic zone. The <3 μm size fraction accounted for 6.6 to 57.5% of the total phytoplankton chlorophyll a biomass (mean 19.7%). In general, the relative significance of the <3 μm size fraction decreased with increasing total chlorophyll a biomass.     

Settlement,abundance, growth and mortality of juvenile flatfish in a subtropical tidal estuary (Georgia,U.S.A.)

The population dynamics of juveniles of some flatfish species were studied in the Duplin River, a tidal creek in a subtropical salt-marsh area in Georgia, U.S.A. from April until September 1990. Seven species were found. Paralichthys dentatus, Paralichthys lethostigma, Paralichthys oblongus and Trinectus maculatus were relatively rare. Etropus crossotus, Citharichthys spilopterus and Symphurus plagiusa were abundant and settled during the period studied. E. crossotus was the most abundant species with a mean abundance of 18 ind·10⁻² m⁻² (max. 287). Demersal settlement of E. crossotus took place in shallow areas and over sandy bottoms from mid-May to August. Prolonged settlement hampered the calculation of growth rate and instantaneous mortality rate. However, laboratory growth experiments indicated a mean growth of about 0.50 mm·d⁻¹ at 24–28°C. Juveniles of C. spilopterus were already present in the Duplin River in March. Settling continued until the end of April with a mean abundance of 3.5 ind·10⁻² m⁻² (max. 183). With increasing size the juveniles of this species tended to migrate to deeper waters and to the mouth of the river, possibly as a reaction to increasing water temperatures. Maximum growth rate was 1.4 mm·d⁻¹ at about 26°C. The mean instantaneous mortality rate (z) was estimated at 0.03·d⁻¹. Settling of S. plagiusa occurred from mid-May onwards. The mean abundance was 10.3 ind·10⁻² m⁻² (max. 98.3). Newly settled juveniles were most abundant on muddy sediments in the shallow river areas. The maximum growth rate was 1.3 mm·d⁻¹ at about 28°C. The mean instantaneous mortality rate (Z) decreased from 0.04·d⁻¹ in April to 0.01·d⁻¹ in August. At all sites the abundance of juveniles of this species decreased with increasing water depth. Predation experiments indicated that blue crabs (Callinectes similis and C. sapidus) and sea robins (Prionotus sp.) are potential predators on juvenile flatfish. The high abundances of juvenile flatfish indicate that the tidal creeks are an important nursery area. The correspondence between growth rates estimated from field data and those observed in the laboratory suggests that growth in the nursery is mainly related to water temperature and not food limited.     

Temporal and lateral fluctuations in production and biomass of bacterioplankton in the western Dutch Wadden Sea

To contribute to the validation of a recently developed ecosystem model of the western Wadden Sea (EON, 1988), data on bacterial biomass and production were acquired. Seven field stations, spread over the two main basins of the estuarine system, were sampled monthly in 1986. Between these basins significant differences were found in counts, biovolume, biomass and production of bacteria (measured by the ³H-thymidine method) with consistently higher mean values of bacterial variables in the Vlie basin. Bacterial production rates of 2 to 175 mg C· m⁻³· d⁻¹ were obtained for the Vlie basin, with an annual production of 10 to 11 g C· m⁻³, while the production in the Marsdiep basin did not exceed 45 mg C·m⁻³ ·d⁻¹, with an annual production of g C·m⁻³. Bacterial biomass varied over the year from 2 to 140 mg C·m⁻³ in the study area, with a mean biomass of 39 mg C·m⁻³ in the Vlie basin and 23 mg C·m⁻³ in the Marsdiep basin. Blooms of bacteria occurred in May and July–August. Spatial and temporal fluctuations in bacterial variables are discussed, taking into account different environmental factors and the availability of food for bacteria in relation to transport and exchange of water masses between the two basins and the North Sea. Results are compared with the results as simulated by the ecosystem model.     

Application of Fertilizers for Increased Saffron Yield

Research was undertaken to determine the response of newly planted saffron to the application of different levels of nitrogen (0, 50 and 100 kg N · ha^?1 · year^?1), phosphorus (0, 25, and 50 kg P₂O₅ · ha^?1 · year^?1), and composted cow manure (0, 20, and 40 tons · ha^?1 · year^?1) in terms of fresh flower weight (FFW), saffron yield (SY) and leaf biomass. The experiments were conducted in Birjand, and Ghaen, Khorasan province, Iran, from 1991 to 1993. Significant differences were found between the two locations and among the years within each location for FFW and SY. Averaged over all treatments and years, mean values for FFW and SY were 644.3 and 9.1 kg · ha^?1, respectively, at Birjand, and 296.0 and 3.7 kg · ha^?1, respectively, at Ghaen. At Birjand, mean FFW in the three consecutive years was 229.0, 796.2, and 907.8 kg · ha^?1 and mean SY was 3.4, 10.6, and 13.4 kg · ha^?1. The corresponding means at Ghaen were 87.5, 225.9, and 574.7 kg · ha^?1 for FFW and 1.3, 3.2, and 6.7 kg · ha^?1 for SY. Simple correlation coefficients between FFW and SY were positive and highly significant. At both locations, FFW and SY increased significantly from year to year. The rate of increase, however, decreased with the age of the saffron field because of overcrowding of new corms. Different combinations of fertilizers had either a negative or nonsignificant effect on FFW and SY. The application of phosphorus fertilizer did not result in increased FFW and SY. The application of 40 tons · ha^?1 of cow manure in the first year followed by no fertilizer in the second year and by 20 tons · ha^?1 in the third year increased FFW and SY at Birjand. The use of 100 kg · ha^?1 nitrogen only in the third year also increased FFW and SY at Birjand. At Ghaen, only the application of 50 kg · ha^?1 nitrogen in the third year resulted in increased FFW and SY.     

Chattonella and Fibrocapsa (Raphidophyceae): First observation of,potentially harmful,red tide organisms in Dutch coastal waters

Species of the potentially toxic and red-tide-forming marine-phytoplankton genera Chattonella and Fibrocapsa (Raphidophyceae) were observed for the first time in 1991 in samples taken in Dutch coastal waters; they were again recorded and enumerated in the following years. Chattonella spp. cell numbers varied with the season, with a maximum in May or June in the Dutch Wadden Sea. Cell numbers of Chattonella and F. japonica Toriumi et Takano were up to 6.0·10³ cells·dm⁻³ in the Dutch Wadden Sea, except at one station in June 1993 when over 10⁴ cells·dm⁻³ Chattonella were counted. In May 1993, a minor bloom (over 2.0·10⁵ cells·dm⁻³) was observed at a station in the southern central North Sea, 100 km northwest of the island of Terschelling. The potentially neurotoxic species Chattonella marina (Subrahmanyan) Hara et Chihara was identified and discriminated from morphologically related species within the class of Raphidophyceae by immunofluorescence. F. japonica could only be clearly identified in live samples; in fixed samples cell morphology was severely affected. The identification of this species was supported by the presence of mucocysts, structures that can be observed readily by optical and electron microscopy.     

Denitrification and nitrous oxide in the North Sea

In situ sediment denitrification rates were determined in the major areas of deposition of the North Sea, using the acetylene block technique. In addition, nitrous oxide profiles of the water column were determined. Nitrous oxide production generally occurred in the photic zone possibly due to nitrification; and throughout the water column in the German Bight region. Consumption at depth was possibly due to reduction in the anoxic microzones of faecal pellets, concentrated at the thermocline. Saturation of surface waters was 102.2% compared to 130.3% in the German Bight region. Calculated flux of nitrous oxide to the atmosphere was 9.5 × 10⁶ kg yr⁻¹, over half of which was produced in the German Bight.Sediment denitrification rates varied through three orders of magnitude; the highest value of 150 μmol m⁻² d⁻¹ was recorded in the Norwegian Trench. Nitrous oxide production by the sediments was low (1.1 μmol m⁻² d⁻¹ max.), and was undetectable at half of the sites. Sediment nutrient profiles exhibited porewater nitrate concentrations exceeding that of the overlying water suggesting that denitrification was fuelled by nitrification, which, in turn was related to other environmental variables. A significant positive relationship existed between in situ denitrification rate and the nitrate content of the upper sediment. Extrapolation of the rate to the total area of deposition in the North Sea suggests that denitrification is responsible for a minimum loss of 7.5–12% of the total annual nitrogen contaminant input.