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1.
The reproductive cycle of anchovy, Engraulis encrasicolus (L.), was studied from monthly random samples of purse seine catches. A total of 1477 anchovy specimens were collected from January to December 2003 in the Zrmanja River estuary (Novigrad Sea). The analysis was based on the temporal evolution of gonadosomatic index, mass and stage of gonads. The total length of anchovy ranged from 4.5 to 14.5 cm and mass from 0.56 to 19.80 g. Sex ratio was slightly different from 1:1; the females were insignificantly predominated (♂/♀ = 0.99). The period of reproductive activity was from April to September coinciding with the most developed stages of gonads as well as with the highest gonad weights, and gonadosomatic indices. To estimate the length at maturity, a sub sample of 454 anchovy was taken from May to July (peak of anchovy spawning period). The length at which 50% of anchovy were mature (L50) was calculated to be 8.2 cm. The length–weight relationship of anchovy was described by the expression: W = 3.51 × 10−3 LT3.211 (r2 = 0.998). The relationships between total length–standard length and total length–fork length are LT = 1.1405LS + 0.2420 and LT = 1.0425 LF + 0.3944, respectively.  相似文献   

2.
An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (Kiequ), total ligands concentration (LiT) and association/dissociation rate constants (ki1,ki- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K1equ: 11.2–13.0, log K2equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k11:6.1–20 × 103 (M s)− 1, k21: 1.3–6.3 × 103 (M s)− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µMC, i.e. 1 mgCL− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).  相似文献   

3.
This paper describes the age structure, growth, diet and aspects of gonadal development in the cobbler, Cnidoglanis macrocephalus (Valenciennes), in the large Swan estuary in south-western Australia between August 1982 and June 1984. Analysis of otolith annuli showed that while the 0+ to 3+ age classes were regularly represented in monthly samples, the 4+ and more particularly the 5+ and 6+ were much less abundant. The weighted means for the back calculated lengths at the end of the first to fourth years of life were 181 mm (≡ 26 g), 314 mm (≡ 156 g), 418 mm (≡ 410 g) and 518 mm (≡ 833 g) respectively. The mean length at the end of the second year of life was similar to the minimum legal size for capture by commercial fishermen (320 mm). The von Bertlanffy growth curve calculated from the back calculated lengths was Lt = 917 [1 − e−0·20(t + 0·11)]. The relative weight of mulluscs, crustaceans and polychaetes in the intestine varied markedly between small and large fish, apparently reflecting differences in the size of these prey. The large mean diameter of mature eggs ( ) was correlated with a low mean absolute fecundity (2078). Trends shown by egg size, gonadosomatic index and time of appearance of spent females indicate that spawning takes place between October and December. The attainment of sexual maturity is both age- and size-dependent. Although sexually maturing and occasionally spent fish were found in the lower estuary, meristic values, commercial catch statistics and other data indicate that the cobbler found in the Swan estuary are part of a population which typically spawns at sea.  相似文献   

4.
The Mussel Watch program conducted along the French coasts for the last 20 years indicates that the highest mercury concentrations in the soft tissue of the blue mussel (Mytilus edulis) occur in animals from the eastern part of Seine Bay on the south coast of the English Channel, the “Pays de Caux”. This region is characterized by the presence of intertidal and submarine groundwater discharges, and no particular mercury effluent has been reported in its vicinity. Two groundwater emergence systems in the karstic coastal zone of the Pays de Caux (Etretat and Yport with slow and fast water percolation pathways respectively) were seasonally sampled to study mercury distribution, partitioning and speciation in water. Samples were also collected in the freshwater–seawater mixing zones in order to compare mercury concentrations and speciation between these “subterranean” or “groundwater” estuaries and the adjacent macrotidal Seine estuary, characterized by a high turbidity zone (HTZ). The mercury concentrations in the soft tissue of mussels from the same areas were monitored at the same time.The means of the “dissolved” (< 0.45 μm) mercury concentrations (HgTD) in the groundwater springs were 0.99 ± 0.15 ng l− 1 (n = 18) and 0.44 ± 0.17 ng l− 1 (n = 17) at Etretat and Yport respectively. High HgTD concentrations were associated with strong runoff over short water pathways during storm periods, while low concentrations were associated with long groundwater pathways. Mean particulate mercury concentrations were 0.22 ± 0.05 ng mg− 1 (n = 16) and 0.16 ± 0.10 ng mg− 1 (n = 17) at Etretat and Yport respectively, and decreased with increasing particle concentration probably as a result of dilution by particles from soil erosion. Groundwater mercury speciation was characterized by high reactive-to-total mercury ratios in the dissolved phase (HgRD/HgTD: 44–95%), and very low total monomethylmercury concentrations (MMHg < 8 pg l− 1). The HgTD distributions in the Yport and Etretat mixing zones were similar (overall mean concentration of 0.73 ± 0.21 ng l− 1, n = 43), but higher than those measured in the adjacent industrialized Seine estuary (mean: 0.31 ± 0.11 ng l− 1, n = 67). In the coastal waters along the Pays de Caux dissolved monomethylmercury (MMHgD) concentrations varied from 9.5 to 13.5 pg l− 1 (2 to 8% of the HgTD). Comparable levels were measured in the Seine estuary (range: 12.2– 21.1 pg l−1; 6–12% of the HgTD). These groundwater karstic estuaries seem to be mostly characterized by the higher HgTD and HgRD concentrations than in the adjacent HTZ Seine estuary. While the HTZ of the Seine estuary acts as a dissolved mercury removal system, the low turbid mixing zone of the Pays de Caux receives the dissolved mercury inputs from the groundwater seepage with an apparent Hg transfer from the particulate phase to the “dissolved” phase (< 0.45 μm). In parallel, the soft tissue of mussels collected near the groundwater discharges, at Etretat and Yport, exhibited significantly higher values than those found in the mussel from the mouth of the Seine estuary. We observe that this difference mimics the differences found in the mercury distribution in the water, and argue that the dissolved phase of the groundwater estuaries and coastal particles are significant sources of bioavailable mercury for mussels.  相似文献   

5.
Uptake of inorganic carbon and ammonium by the plankton community of three North Carolina estuaries was measured using 14C and 15N isotope methods. At 0% light, C appeared to be lost via respiration, and at increasing light levels uptake of inorganic carbon increased linearly, saturated (mean Ik = 358±30 μEin m−2 s−1), and frequently showed inhibition at the highest light intensities. At 0% light NH4+ uptake was significantly greater than zero and was frequently equivalent to uptake in the light (light independent); at increasing light levels NH4+ uptake saturated (mean Ik = 172±44 μEin m−2 s−1) and frequently indicated strong inhibition. Light-saturated uptake rates of inorganic carbon and NH4+ were a function of chlorophyll a (r2 = 0·7−0·9); average assimilation numbers were 625 nmol CO2 (μg chl. a)−1 h−1 and 12·9 nmol NH4+ (μg chl. a)−1 h−1 and were positively correlated with temperature (r2 = 0·3−0·7). The ratio of dark to light-saturated NH4+ uptake tended to be near 1·0 for large algal populations at low NH4+ concentrations, indicating near light independence of uptake; whereas the ratio was lower for the opposite conditions. These data are interpreted as indicative of nitrogen stress, and it is suggested that uptake of NH4+ deep in the euphotic zone and at night are mechanisms for balancing the C:N of cellular pools. A 24-h study using summed short-term incubations confirmed this; the cumulative C:N of CO2 and NH4+ uptake during the daylight period was 10–20, whereas over the 24-h period the ratio was 6 due to dark NH4+ uptake. Annual carbon and nitrogen primary productivity were respectively estimated as 24 and 4·0 mol m−2 year−1 for the South River estuary, 42 and 7·3 mol m−2 year−1 for the Neuse River estuary, and 9·6 and 1·6 mol m−2 year−1 for the Newport River estuary.  相似文献   

6.
Two physicochemical parameters: specific surface area (SSA) and heat-of-wetting (ΔwH) were measured in order to characterize the surface of sediments from river and marine environments. The data for the sediment samples of the Krka River Estuary were compared with polluted river and shelf marine sediment samples. It was found that organic free samples from the polluted river sediments show two to three times larger SSA compared to native samples. At the same time, ΔwH was two to three times higher for native samples. The inverse of this trend was found for marine sediment samples. In the Krka River Estuary a narrow transition zone is evident, where such an inversion occurs. This inversion is attributed to significant compositional changes of organic matter within the estuary.  相似文献   

7.
Transparent exopolymer particles (TEP) are formed by the assembly of dissolved precursors, mainly mono and polysaccharides (DMCHO and DPCHO) that are released by microorganisms. Although TEP formation plays a significant role in carbon export to deep waters and can affect gas exchange at the sea surface, simultaneous measurements of TEP and their precursors in natural waters have been scantly reported. In this study, we described the spatial (vertical and regional) distribution of TEP, DMCHO and DPCHO in a region located around the Antarctic Peninsula, assessed their contribution to the total organic carbon pool, and explored their relationships with phytoplankton (with chlorophyll a (chl a) as a proxy) and bacteria. TEP concentration ranged from undetectable values to 48.9 µg XG eq L− 1 with a mean value of 15.4 µg XG eq L− 1 (11.6 µg TEP-C L− 1). DMCHO and DPCHO showed average values of 4.3 µmol C L− 1 and 8.6 µmol C L− 1, respectively. We did not find simple relationships between the concentrations of TEP and dissolved carbohydrates, but a negative correlation between DMCHO and DPCHO was observed. Chl a was the best regressor of TEP concentration in waters within the upper mixed layer, while bacterial production was the best regressor of TEP concentration below the mixed layer, underlining the direct link between these particles and bacterial activity in deep waters.  相似文献   

8.
Quantity, timing, duration, and fluctuation of freshwater inflow are important factors affecting the development and health of aquatic and adjacent wetland ecosystems in coastal estuaries. This study assessed six decades of freshwater inflow from the Amite River, Tickfaw River, and Tangipahoa River watersheds to Lake Pontchartrain, a large oligohaline estuary in the Northern Gulf of Mexico, whose flood waters caused recent damage to the city of New Orleans in the aftermath of Hurricane Katrina. By utilizing the long-term (1940–2002) river discharge and climatic data from the three major tributary watersheds, monthly and annual freshwater inflows have been quantified and their spatial and temporal variations have been analyzed. On average, the three rivers discharged (±standard error) 0.27 ± 0.04 km3 freshwater monthly and 3.29 ± 0.15 km3 freshwater annually into the lake estuarine system, with the highest inflow from the Amite River (0.16 ± 0.03 m3 mon−1, and 1.91 ± 0.09 km3 yr−1) and the lowest inflow from the Tickfaw River (0.03 ± 0.00 km3 mon−1, and 0.34 ± 0.02 km3 yr−1). A distinct seasonality was evident with over 69% of the total annual inflow occurring during December and May (wet months) and with a low flow period from August to November (dry months). The monthly inflow during the wet months was positively correlated with the monthly precipitation (r2 = 0.64), while the monthly inflow during the dry months was subject to evapotranspiration. Furthermore, the study found a 20-year low flow period from 1954–1973 (2.76 ± 0.24 km3 yr−1) and a 24-year high flow period from 1975–1998 (3.84 ± 0.24 km3 yr−1), coinciding with both the climate variation and population growth in the watersheds.  相似文献   

9.
The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m−3) and biomass (up to 168 mg dry weight m−3) of H. longirostris were considered to be comparable with those of copepods in the estuary.  相似文献   

10.
Caging and a mark–recapture design were used to estimate the growth rate of the brittle, infaunal bivalve Soletellina alba in the Hopkins River estuary. The growth of both caged and uncaged individuals was monitored at three sites near the mouth of the estuary over 180 days. Growth rates did not differ for caged and uncaged bivalves, or for bivalves subject to different amounts of handling, or between sites. Growth did differ between consecutive time intervals, which was attributable to negligible growth occurring during the colder months of autumn/winter. Comparisons of the condition (as indicated by total mass for length3) of S. alba were inconsistent between sites for caged and uncaged bivalves and for those subject to different amounts of handling. Soletellina alba is a rapidly growing bivalve with mean growth rates for the three time intervals being 0.04±0.002 mm day−1 in summer, 0.02±0.001 mm day−1 in autumn and 0.03±0.001 mm day−1 from summer to winter. Using existing literature, it was shown that a significant relationship exists between maximum shell length and onset of sexual maturity in bivalve molluscs. This relationship predicts that S. alba should reach the onset of sexual maturity at 15.8 mm length. Therefore, it appears that it may be possible for juvenile S. alba (<1 mm) to grow, reach sexual maturity and reproduce in between annual mass-mortality events caused by winter flooding.  相似文献   

11.
Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m−2, mean chlorophyll a was 11·8 mg m−3, and mean phytoplankton density was 1·56 × 103 cells ml−1. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m−2.  相似文献   

12.
The distributions of dissolved organic carbon (DOC), Ba, U, and a suite of naturally occurring radionuclides in the U/Th decay series (222Rn, 223,224,226,228Ra) were studied during high- and low-discharge conditions in the Loxahatchee River estuary, Florida to examine the role of submarine groundwater discharge in estuarine transport. The fresh water endmember of this still relatively pristine estuary may reflect not only river-borne constituents, but also those advected during active groundwater/surface water (hyporheic) exchange. During both discharge conditions, Ba concentrations indicated slight non-conservative mixing. Such Ba excesses could be attributed either to submarine groundwater discharge or particle desorption processes. Estuarine dissolved organic carbon concentrations were highest at salinities closest to zero. Uranium distributions were lowest in the fresh water sites and mixed mostly conservatively with an increase in salinity. Suspended particulate matter (SPM) concentrations were generally lowest (< 5 mg L− 1) close to zero salinity and increased several-fold ( 18 mg L− 1; low discharge) toward the seaward endmember, which may be attributed to dynamic resuspension of bottom sediments within Jupiter Inlet.Surface water-column 222Rn activities were most elevated (> 28 dpm L− 1) at the freshwater endmember of the estuary and appear to identify regions of the river most influenced by the discharge of fresh groundwater. Activities of four naturally occurring isotopes of Ra (223,224,226,228Ra) in this estuary and select adjacent shallow groundwater wells yield mean estuarine water-mass transit times of less than 1 day; these values are in close agreement to those calculated by tidal prism and tidal frequency. Submarine groundwater discharge rates to the Loxahatchee River estuary were calculated using a tidal prism approach, an excess 226Ra mass balance, and an electromagnetic seepage meter. Average SGD rates ranged from 1.0 to 3.8 × 105 m3 d− 1 (20–74 L m− 2 d− 1), depending on river-discharge stage. Such calculated SGD estimates, which must include both a recirculated as well as fresh water component, are in close agreement with results obtained from a first-order watershed mass balance. Average submarine groundwater discharge rates yield NH4+ and PO4− 3 flux estimates to the Loxahatchee River estuary that range from 62.7 to 1063.1 and 69.2 to 378.5 μmol m− 2 d− 1, respectively, depending on river stage. SGD-derived nutrient flux rates are compared to yearly computed riverine total N and total P load estimates.  相似文献   

13.
Nutrients, chlorophyll a, primary production (14C), and standard oceanographic parameters were measured seasonally from 1983 to 1988 along the axis of a karstic estuary of the central Adriatic Sea (the Krka River estuary). Because of anthropogenic phosphorus discharges, the surface-layer orthophosphate concentrations (up to 1.7 mmol m−3), phytoplankton biomass (chlorophyll a up to 23 mg m−3) and primary production (up to 108 mg C m−3 h−1) were significantly higher in ibenik Bay (lower estuary) than in the other estuarine subregions, and the coastal sea in particular. In contrast, nitrate and orthosilicate (up to 59 and 65 mmol m−3, respectively) distributions during autumn and winter were ascribed to dilution of Krka River nutrients along the estuary. As a consequence, the surface-layer inorganic N/P ratio was extremely high in the upper estuary (averages up to 180), but this ratio was reduced up to three times in ibenik Bay and the coastal sea. In spring and summer, nitrate and orthosilicate, but not orthophosphate, were almost exhausted from the water because of biological utilization. In the saline layer below the halocline (depth 2–5 m) oxygen saturation varied over a large range, particularly in the upper estuary (16–176%), and nutrient concentration ratios differed from those in the surface layer. A nutrient regeneration stoichiometric model was derived, based on a linear regression analysis: AOU:Si:N:P = 276:16:6:0.4. Anthropogenic nutrient inputs should be urgently reduced to re-establish a natural nutrient environment.  相似文献   

14.
Midsummer (1 August) population estimates of about 2 million O-group plaice (Pleuronectes platessa L.) were derived for sandy bays around the Firth of Forth in 1979–1980. This is an order of magnitude less than similar estimates made for the Clyde Sea Area in 1973–1974. Autumn population estimates of 0·4–1·0 million fish were comparable to estimates by the Ministry of Agriculture, Fisheries and Food for the area between the Scottish border and Flamborough Head (2·3 million for 1970 and 1973) which represented 4·8% (1973) to 5·3% (1970) of the total number of O-group fish on the English east coast.Largo Bay was the most important nursery area holding 25% of the total population. It is particularly well situated to receive newly metamorphosed plaice carried in water currents along the north side of the Forth from the spawning ground off Fife Ness. Plaice in the Forth are mainly distributed on fine to medium sandy beaches (186–480 μm), the mean number per haul in midsummer (D) being correlated with the median diameter (m.d. in μm) of the low water sediments by the equation: D=−45·7666+0·2327 m.d. (n=11,r=0·68,P<0·02 but>0·01).The shallow inshore water in sandy bays in the outer Firth was well mixed and more marine than estuarine (27·7–35·0‰). The correlation coefficient between fish density and water temperature was low, while that with salinity (S‰) was: D=6·1618+0·2238S (n=23,r=0·62,P<0·005).Regression analysis demonstrated that the relationship between the instantaneous mortality rate (Z) and the initial population density (Dp) was: Z×100=0·7480+0·0546dp (n=12,r=0·87,P<0·001).The mean mortality rate for the O-group plaice in the Forth nursery areas was 53% month−1.  相似文献   

15.
We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH4+, NO3−, PO43−) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O2 m−2 d−1, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O2 m−2 d−1 (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O2 m−2 d−1, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O2 m−2 d−1, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m−2 d−1 for NH4+, 0.58 ± 1.08 mmol m−2 d−1 for NO3−, 0.01 ± 0.09 mmol m−2 d−1 for PO43−. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems.  相似文献   

16.
The composition, density and community structure of the benthic macrofauna were investigated in sediments of the Campeche Canyon in the SW Gulf of Mexico. Total macrofaunal density ranged from 9466±2736 ind m−2 at the continental shelf station to 1550±195 ind m−2 in the canyon. Density values significantly diminished with distance from the coast and depth; only a few stations in the center of the canyon displayed larger density values (E-37 with 4666±1530 ind m−2, E-36 with 5791±642 ind m−2 and E-26 with 6925±2258 ind m−2). Densities were positively correlated to organic nitrogen in the sediment (r=0.82) and coarse silt (r=0.43), and negatively with depth (r=−0.74) and distance from the coast (r=−0.68). At all stations, the polychaete worms contributed most to the multi-species community structure. The nematodes and Foraminifera displayed their highest densities in the center of the canyon. The biomass values declined significantly with depth. We conclude that the macrofauna density and biomass changed in response to organic matter contents in the sediment, both with distance from the coast and with depth.  相似文献   

17.
Suspended particle dynamics were investigated in the Ogeechee River Estuary during neap tide in July 1996. Samples were operationally separated into ‘ truly suspended ’ (settling velocity <0·006 cm s−1) and ‘ settleable ’ (settling velocity >0·006 cm s−1) fractions over the course of a tidal cycle to determine whether these two fractions were comprised of particles with differing biological and chemical characteristics. Total suspended sediment, organic carbon and nitrogen, chlorophyll a and phaeopigment concentrations were measured in each fraction, as well as rates of bacterial hydrolytic enzyme activity [β-1,4-glucosidase (βGase) and β-xylosidase (βXase)]. The majority of the suspended sediment (by weight) was in the truly suspended fraction; all measured parameters were largely associated with this fraction as well. When compared to the settleable material, the truly suspended material was significantly higher in % POC (5·7±0·6 vs. 3·9±1·8), % chlorophyll (0·07±0·02 vs. 0·03±0·01), % phaeopigment (0·030±0·006 vs. 0·018±0·012), and weight-specific maximal uptake rates (Vmaxper mg suspended sediment) of both enzymes (1·8±0·4 vs. 0·7± 0·2 nmol mg−1 h−1βGase and 1·1±0·3vs . 0·3±0·2 nmol mg−1 h−1βXase), providing clear evidence for a qualitative distinction between the two fractions. These results are interpreted to mean that the more organic-rich, biologically active material associated with the suspended fraction is likely to have a different fate in this Estuary, as ‘ truly suspended ’ sediments will be readily transported whereas ‘ settleable ’ sediments will settle and be resuspended with each tide. These types of qualitative differences should be incorporated into models of particle dynamics in estuaries.  相似文献   

18.
Summer porewater and spring and summer surficial sediment samples were collected from 26 locations in the intertidal region of the Fraser River estuary. Porewaters were analysed for dissolved iron and manganese (as defined by species <0·2μm in diameter) to assess the contribution of diagenesis to concentrations of iron and manganese oxides at the sediment–water interface. Surficial sediment samples were geochemically characterized as: % organic matter (% LOI); reducible iron (RED Fe, iron oxides) and easily reducible manganese (ER Mn, manganese oxides). Grain size at each site was also determined. The sediment geochemical matrix, as defined by the above four parameters, was highly heterogeneous throughout the intertidal region (three-way ANOVA;P<0·0001). For RED Fe and ER Mn, this heterogeneity could be explained by either diagenetic processes (RED Fe) or by a combination of the proximity of the sample sites to the mouth of the Fraser River estuary plus diagenetic processes (ER Mn). Correlation (Spearman Rank Correlation Test (rs), of dissolved iron within the subsurface sediments with amounts of RED Fe recovered from the associated surface sediments was highly significant (rs=0·80, P<0·0001); high concentrations of RED Fe at the sediment–water interface co-occurred with high concentrations of dissolved iron, regardless of the proximity of the sample locations to riverine input. Compared with iron, the relationship between dissolved manganese and ER Mn from surface sediments was lower (rs=0·58;P<0·0008). Locations most strongly influenced by the Fraser River contained greater concentrations of ER Mn at the sediment–water interface than that which would be expected based on the contribution from diagenesis alone. Sediment grain size and organic matter were also influenced by the proximity to riverine input. Surficial sediment of sites close to the river mouth were comprised primarily of percent silt (2·0μm–50μm) whereas sites not influenced by riverine input were primarily percent sand (grain size >50μm). Concentrations of organic matter declined from the mouth to the foreslope of the estuary. With the exception of RED Fe, temporal variation (May vs July) was insignificant (P>0·05, three-way ANOVA). Concentrations of RED Fe recovered from the surficial sediments were in general greater in the summer vs spring months, although spring and summer values were highly correlated (Pearson Product Moment Correlation Coefficient; PPCC; R=0·89;P<0·0001). As the bioavailability of metals is dependent on sediment geochemistry, availability throughout the intertidal region will also be spatially dependent. This heterogeneity needs to be taken into account in studies addressing the impact of metals on estuarine systems.  相似文献   

19.
The detailed distribution of algal chlorophyll and carotenoid pigments was determined around the halocline (freshwater-seawater interface) in the Krka Estuary on the east coast of the Adriatic Sea; in May 1988. After collection of water along the estuary, particulate matter was extracted and analyzed for pigments by high-performance liquid chromatography coupled with absorbance and fluorescence detection. Bottom marine waters were characterized by lower chlorophyll a (chl a) concentrations than encountered in surface waters, decreasing downstream from 0.50 μg l−1 to 0.16 μg l−1 at the marine end-member. The highest concentrations of chl α (up to 26.34 μg l−1) were found in the interfacial layer, an particularly at one station located off the city of ibenik, where high inputs of nutrients supported the accumulation of living algae at the halocline. Fucoxanthin was the most abundant carotenoid, which indicates a euryhaline dominance of diatoms in the estuary, whereas the dinoflagellate-derived carotenoid peridinin was confined to the interfacial and bottom saline waters of the inner estuary. High concentrations of alloxanthin and chl b were found in the interfacial layer, which also suggests an accumulation of Cryptophyceae and green algae in the inner estuary. Phaeophorbides showed higher concentrations in bottom waters than in surface waters, whereas the highest concentrations occurred in the interfacial layer. These high levels could reflect a density trapping of dead cells in an early degradation state, as suggested by the importance of allomerized chl a and chlorophyllide a vs. total chl a, or of faecal pellets originating from zooplankton grazing in the interfacial layer.  相似文献   

20.
Upogebia deltaura was collected quantitatively and qualitatively between June 1980 and August 1982 from a level, sandy bottom at a 12 m depth in the archipelago of Lysekil (on Gullmarsfjorden) about 70 km north of Göteborg, in western Sweden. A total of 347 individuals were obtained. The deepest burrows reached a depth of more than 65 cm into the substrate. During the cold season, U. deltaura was situated much deeper in the substrate than it was during the summer, probably as a result of ‘hibernation’. The average density was 5·0 individuals 0·1 m−2, and the maximum of 10 specimens was found in one 0·1 m2 sample. Out of the 341 individuals identifiable as to sex, 186 (54·6%) were females and 155 (45·4%) were males. Berried females were found between May and August, and the average number of eggs carried was 4757. Ecdysis took place between May and August; most females moulted in the middle of June and most males about one month later, in mid July. The chelipeds of large males were proportionally bigger than were those of large females. Maximum total body length of the females was 65·7 mm, and that of the males was 65·3 mm.  相似文献   

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