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1.
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   

2.
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   

3.
The first oceanographic research (hydrography, nutrient salts, chlorophyll, primary production and phytoplankton assemblages) in a Middle Galician Ria was carried out in Corme-Laxe during 2001, just a year before the Prestige oil spill, being the only reference to evaluate eventual changes in the phytoplankton community. Due to the small size of this ria (6.5 km2), oceanographic processes were driven by the continental water supplied by Anllons River during the wet season (20–30 m3 s−1 in winter), and the strong oceanic influence from the nearby shelf during the dry season. The annual cycle showed a spring bloom with high levels of chlorophyll (up to 14 μg Chl-a L−1) and primary production (3 g C m−2 d−1) and a summer upwelling bloom (up to 8 μg Chl-a L−1 and 10 g C m−2 d−1) where the proximity of the Galician upwelling core (<13.5 °C at sea surface) favors the input of upwelled seawater (up to 9 μM of nitrate and silicate) to the bottom ria layer, even during summer stratification events (primary production around 2 g C m−2 d−1). Thus, phytoplankton assemblages form a “continuum” from spring to autumn with a predominance of diatoms and overlapping species between consecutive periods; only in autumn dinoflagellates and flagellates characterized the phytoplankton community. In the Middle Rias as Corme-Laxe, the nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were higher than those reported for the Northern (Ria of A Coruña) and Southern Rias (Ria of Arousa) for year 2001; this suggests the importance of the hydrographic events occurring in the zone of maximum upwelling intensity of the Western Iberian Shelf, where a lack of annual cycles studies exists.  相似文献   

4.
Chesapeake Bay is a large and productive estuary that has received close scrutiny in recent years because of indications that its water quality and biota have been damaged by man's activities. Data on primary production for the estuary as a whole, however, are surprisingly sparse. We describe here the distribution of photosynthetic carbon assimilation by phytoplankton in Chesapeake Bay, and relate productivity patterns to hydrographic characteristics of the estuary. Between March 1982 and April 1983, a series of four cruises was conducted on Chesapeake Bay, and two cruises on the urbanized Delaware Bay for comparison. The upper Chesapeake and Delaware were highly turbid with high concentrations of suspended particulate matter and dissolved inorganic nutrients. Low chlorophyll concentrations were usually found in these areas of high turbidity, despite the abundance of nutrients, suggesting light limitation. Application of Wofsy's (1983) model of phytoplanton growth confirmed this suggestion. Chlorophyll and productivity maxima usually occurred seaward of the turbidity maxima where light penetration increased and suffient nutrients were present to support active phytoplankton growth. Further seaward of the chlorophyll maxima in the Chesapeake, the photic zone depth increased, concentrations of nutrients decreased, and phytoplankton biomass decreased, suggesting that nutrient availability, rather than light, controlled phytoplankton growth in the lower portion of the estuary. In contrast to the Chesapeake, Delaware Bay was more turbid, had generally higher nutrient concentrations, and was lower in phytoplankton productivity. The chlorophyll maxima and region of rapid phytoplankton growth occurred further toward the lower estuary and shelf regions in Delaware Bay because the high turbidity extended further seaward. Nutrients were never depleted at the shelf end of the estuary sufficiently to retard phytoplankton growth. Photosynthesis-irradiance (P-I) curves from simulated in situ and constant intensity incubations showed a strong correlation of the light-limited slope (aB) with the light-saturated rate ( ) on each cruise. Spatial variations in corresponded to patterns of phytoplankton abundance, as did integral production (PP) and carbon-based growth rates (μC, μm), and photosynthetic parameters varied significantly with temperature.  相似文献   

5.
Production of the marine calanoid copepod Acartia steueri was measured from 2 October 1991 to 8 October 1992 at a station in Ilkwang Bay, on the southeastern coast of Korea. Phytoplankton standing stock ranged over 1.0 to 9.3 mg chl.a m−3, and annual primary productivity (by the C-14 method) at three stations was estimated at 200 gC m−2 yr−1. Acartia steueri (nauplii + copepodids + adults) were present in the plankton throughout the year, with seasonal variation in abundance. Biomass of A. steueri, excluding the NI stage, was 0.01–4.55 mgC m−3 (mean: 0.68 mgC m−3) with peaks in November, February, May and July-early August, and relatively low biomass in September– January. Instantaneous growth rates of the nauplius stages were higher than the copepodid stages. Annual production of A. steueri was 25.1 mgC m−3 yr−1 (or 166 mgC m−2 yr−1), showing peaks in November, May and July–August with a small peak in February, and low production in December–April and September–October. There were no significant relationships between the daily production rate of A. steueri and temperature or chlorophyll a concentration, indicating that unknown other factors might be related to the variation of the production rate.  相似文献   

6.
The seasonal dynamics of inorganic nutrients and phytoplankton biomass (chlorophyll a), and its relation with hydrological features, was studied in the NW Alboran Sea during four cruises conducted in February, April, July and October 2002. In the upper layers, the seasonal pattern of nutrient concentrations and their molar ratios (N:Si:P) was greatly influenced by hydrological conditions. The higher nutrient concentrations were observed during the spring cruise (2.54 μM NO3−, 0.21 μM PO43− and 1.55 μM Si(OH)4, on average), coinciding with the increase of salinity due to upwelling induced by westerlies. The lowest nutrient concentrations were observed during summer (<0.54 μM NO3−, 0.13 μM PO43− and 0.75 μM Si(OH)4, on average), when the lower salinities were detected. Nutrient molar ratios (N:Si:P) followed the same seasonal pattern as nutrient distribution. During all the cruises, the ratio N:P in the top 20 m was lower than 16:1, indicating a NO3− deficiency relative to PO43−. The N:P ratio increased with depth, reaching values higher than 16:1 in the deeper layers (200–300 m). The N:Si ratio in the top 20 m was lower than 1:1, excepting during spring when N:Si ratios higher than 1:1 were observed in some stations due to the upwelling event. The N:Si ratio increased with depth, showing a maximum at 50–100 m (>1.5:1), which indicates a shift towards Si-deficiency in these layers. The Si:P ratio was much lower than 16:1 throughout the water column during the four cruises. In general, the spatial and seasonal variation of phytoplankton biomass showed a strong coupling with hydrological and chemical fields. The higher chlorophyll a concentrations at the depth of the chlorophyll maximum were found in April (2.57 mg m−3 on average), while the lowest phytoplankton biomass corresponded to the winter cruise (0.74 mg m−3 on average). The low nitrate concentrations together with the low N:P ratios found in the upper layers (top 20 m) during the winter, summer and autumn cruises suggest that N-limitation could occur in these layers during great part of the year. However, N-limitation during the spring cruise was temporally overcome by nutrient enrichment caused by an intense wind-driven upwelling event.  相似文献   

7.
Global change models predict effects of climate change on hydrological regimes at the continental scale in Europe. The aim of this study was to gain a better understanding of the possible effect of changing external forcing conditions on the functioning of estuarine ecosystems. In densely populated areas, anthropogenic nutrient enrichment and consequent alteration of nutrient biogeochemical cycles have already had a big impact on these ecosystems. The average yearly discharge of the upper Schelde estuary increased nearly threefold over the period 1996–2000, from 28 m3 s−1 in 1996 to 73 m3 s−1 in 2000. The continuously rising discharge conditions over the five-year period were used as a reference situation for possible future effects of climate on ecological functioning through increase of discharge. At high discharges, nutrient (NH4+, NO3−, dissolved silica and PO43−) concentrations in the tidal fresh- and brackish water showed a decrease of up to 50% while total discharged nutrient loadings increased up to 100%. Opposite effects of increasing discharge on NH4+, NO3− and dissolved silica concentrations in summer and winter, resulted in the flattening out of seasonal cycles for these nutrients. Under high discharge conditions, silica uptake by diatom communities was lowered. Dissolved silica loadings to the coastal area increased concurrently with total silica loadings upstream. Salt intrusion to the marine parts of the estuary decreased. This resulted in a downstream shift of the salinity gradient, with lower salinity observed near the mouth. As a result, TDIN, NO3− and dissolved silica concentrations doubled at the mouth of the estuary.  相似文献   

8.
A steady state, mass balance, trophic network has been constructed to illustrate the flow of energy in the Seine Estuary by using Network Analysis and Ecopath methods. This ecosystem shows 15 compartments from primary producers to the top consumers (fish and birds). This study has been compared with other ecosystems of comparable nature located in North America (Narragansett, Chesapeake, Delaware Bays), Europe (Ems Estuary, Dublin Bay and Bay of Somme), and South Africa (Swartkops Estuary) in which analysis of trophic network has been applied with similar methods.The Seine Estuary shows values of some global parameters and indices either close to large North American bays and a South African estuary characterised by the complexity of their trophic network, or values near European bays and estuaries, or else remain typical of the Seine estuary. All of this reflects specific functioning of the Seine Estuary which can be explained by the analysis of the dominant food web. In the upstream sector an important pelagic food web was found correlated with highest primary production, especially planktonic, which is rapidly consumed by an abundant zooplankton and suprabenthos (Mysidacae and Decapoda Crustacea). This reveals the dominant consumer role of this sector. The external fluvial inputs (277.80 gC m−2 y−1) are transferred to the downstream sector which produces the major export (548.43 gC m−2 y−1), in parallel with the low consumption and efficiency of dominant benthos component from its bentho-pelagic food web. This reflects the dominant exporter role of this sector.In the Seine Estuary low values of detritivory index D/H (2.52), recycling index FCI (16.1%) and connectance (0.24) were found associated with high values of P/B ratio (38.2%), sum of exports (548.43 gC m−2 y−1) and the great difference between ratio of ascendency to capacity development A/C and internal ratio Ai/Ci. This shows the lack of a dominant resource as in Delaware Bay, that the state of development is different from a mature ecosystem, and the dependance on external connections similar to the Bay of Somme, another ecosystem of Eastern Channel, France.  相似文献   

9.
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   

10.
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   

11.
Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m−2 day−1, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m−2 day−1) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre−1 for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre−1 for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g−1 for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m−3 as Chl. a, sharply increased up to 100 mg m−3 only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).  相似文献   

12.
Factors controlling the timing of major (>10 mg chlorophyll a m−3) spring bloom events in the estuarine waters of the Solent, on the south coast of the UK, have been investigated. Winter to summer variations in chlorophyll a concentration together with relevant meteorological and hydrographical data have been analysed for 5 years (1988, 1992, 2001, 2002 and 2003). Mean water column irradiance is demonstrated to be the main factor controlling the timing of the first major spring bloom event, usually dominated by large chain-forming diatoms. When chlorophyll a concentration first exceeds 10 mg m−3 in spring (usually in May) the mean water column photosynthetic active radiation (PAR) averaged for one week prior to the sampling date was always >380 W h m−2 d−1. Prior to the main spring bloom event surface incident radiation and water turbidity combine to limit chlorophyll a concentration to levels <10 mg m−3. Chlorophyll a concentrations >10 mg m−3 do not occur in the Solent until almost the entire 10 m water column is within the euphotic zone (i.e. above 1% light level) and light extinction coefficient (k) is ca. ≤0.5 m−1. Statistically, river flow explains the largest percentage of the variations in k and the delayed bloom in June 2002 is due to increased cloud cover and high levels of rainfall in May, which caused a reduction in surface incident irradiance and increased turbidity. Chlorophyll a peaks during these major bloom events generally occur on spring tides when increased mixing rates favour net growth of diatoms.  相似文献   

13.
A total of 1125 specimens of sardine, Sardina pilchardus, ranging in total length from 4.9 to 12.5 cm (mean 8.31 ± 1.41 cm) and in weights between 1.02 g and 11.18 g (mean 4.40 ± 1.87 g) were randomly sampled using a beach seine from the Krka River estuary. Samples were collected monthly according to their occurrence in this area from October to February during 2002/03, 2003/04 and 2004/05, which is during the spawning period of this species. Monthly fluctuations in the length frequency distributions of sardine were observed during that time. The length–weight relationship of all sardine specimens was described by the equation: W=0.007L2.9587(r2 = 0.9626); and the isometric nature of relative growth was established (t = −5.1495; p < 0.05). According to the allometric condition factor Ka, sardine specimens were in better somatic condition at the beginning of their appearance (spawning period) in the Krka River estuary. The length at which 50% of sardines were mature (L50) was calculated to be 7.9 cm.  相似文献   

14.
Dissolved iodate and total iodine were studied in St Helena Bay, South Africa, during a period of acute hypoxia, following upwelling off Cape Columbine. Despite the generally high concentrations of chlorophyll α (10–30 mg m−3) total iodine concentration was essentially constant in the main part of the Bay, and similar to that found elsewhere in the oceans. Occasional, lower concentrations of total iodine (0·28 to 0·42 μM) were found with exceptionally high chlorophyll α concentrations (500 mg m−3) in shallow waters. In contrast, iodate was found to be reduced to iodide at both the surface and the bottom of the Bay. The implications of these changes are discussed, given that the surface waters reflect sustained eutrophication while the bottom waters are hypoxic as a result of the organic-rich sediment from the waters above.  相似文献   

15.
Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m−3), low surface primary production (2.55 mg C m−3 day−1) and low zooplankton biovolume (0.14 ml m−3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO3–N > 8.2 μM, PO4–P > 0.8 μM, SiO4–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m−3, PP – 9.23 mg C m−3 day−1), and mesozooplankton biovolume (1.12 ml m−3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.  相似文献   

16.
Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m−2 and <50 mg m−2, respectively). One notable exception is an area of relatively high biomass (50–100 g m−2) and chlorophyll (80 mg m−2) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves.  相似文献   

17.
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   

18.
Elkhorn Slough is a small estuary in Central California, where nutrient inputs are dominated by runoff from agricultural row crops, a golf course, and residential development. We examined the variability in nutrient concentrations from decadal to hourly time scales in Elkhorn Slough to compare forcing by physical and biological factors. Hourly data were collected using in situ nitrate analyzers and water quality data sondes, and two decades of monthly monitoring data were analyzed. Nutrient concentrations increased from the mid 1970s to 1990s as pastures and woodlands were converted to row crops and population increased in the watershed. Climatic variability was also a significant factor controlling interannual nutrient variability, with higher nutrient concentrations during wet than drought years. Elkhorn Slough has a Mediterranean climate with dry and rainy seasons. Dissolved inorganic nitrogen (DIN) concentrations were relatively low (10–70 μmol L−1) during the dry season and high (20–160 μmol L−1) during the rainy season. Dissolved inorganic phosphorus (DIP) concentrations showed the inverse pattern, with higher concentrations during the dry season. Pulsed runoff events were a consistent feature controlling nitrate concentrations during the rainy season. Peak nitrate concentrations lagged runoff events by 1 to 6 days. Tidal exchange with Monterey Bay was also an important process controlling nutrient concentrations, particularly near the mouth of the Slough. Biological processes had the greatest effect on nitrate concentrations during the dry season and were less important during the rainy season. While primary production was enhanced by nutrient pulses, chlorophyll a concentrations were not. We believe that the generally weak biological response compared to the strong physical forcing in Elkhorn Slough occurred because the short residence time and tidal mixing rapidly diluted nutrient pulses.  相似文献   

19.
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.  相似文献   

20.
The magnitude of the exchange flux at the water–sediment interface was determined on the basis of the ammonia concentration gradient at the near-bottom water–interstitial interface and Fick's first law. It was established that in Puck Bay, ammonia almost always passes from the sediment to water. Ammonia flux varied from 5 to 1434 μmol NH4-N m−2 day−1. In total,c. 138·2 tonneammonia year−1pass from sediments of Internal Puck Bay to near-bottom water, the equivalent value for External Puck Bay being 686·9 tonne year−1. In total, about 825 tonne ammonia year−1passes from the sediment to near-bottom water of Puck Bay. In interstitial waters, ammonia occurred in concentrations varying over a wide range (3–1084 μmol NH4-N dm−3).The basic factors affecting the magnitude of ammonia concentration in interstitial waters included: oxidation of organic matter, type of sediment, and inflow of fresh underground waters to the region examined.This paper involves preliminary studies only and constitutes a continuation of the studies on ionic macrocomponents and phosphorus in interstitial waters of Puck Bay undertaken previously.  相似文献   

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