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1.
Long-term patterns in riverine nutrient flux in the lower Mississippi River were examined in relationship to spatial and temporal patterns in surface nutrient concentrations, chlorophyll, and primary productivity in the outflow region in the northern Gulf of Mexico. A retrospective analysis of dissolved inorganic nutrient fluxes based on USGS water quality data and US Army Corps of Engineers discharge data from the 1950s to mid-2004 showed an increase in river-borne dissolved inorganic nitrogen (DIN) flux after 1967. Flux of DIN peaked in the early 1980s and has since fluctuated and shown a general decreasing trend since the early 1990s. Records for total phosphorus (total P) fluxes beginning in mid-1974 exhibited a variable but slight increasing trend up to 2004. The increase in fluxes during the 1970s and into the 1980s can be attributed to increases in both nutrient concentrations and river discharge. DIN concentrations since the 1980s have shown a decreasing trend. Total P concentrations exhibited large fluctuations, with no consistent long-term trend. Dissolved organic nitrogen (DON) concentrations and orthophosphate (Ortho P) peaked in the 1980s, declined relative to DIN and remained relatively low. DIN:Ortho P ratios were consistently well above the Redfield N:P ratio of 16:1. DIN:Total P ratios were variable and lower, fluctuating around the Redfield 16:1 value. Both DIN:Ortho P and DIN:Total P ratios were weakly, but significantly, correlated with river discharge and fluctuations were largely a reflection of higher DIN concentrations during high-discharge events. DIN:Ortho P ratios in surface waters of the outflow region adjacent to the birdfoot delta were higher in spring, consistent with seasonal variation in riverine DIN:Ortho P ratios. The seasonal signal diminished with increasing distance to the west of the delta, indicating a selective removal of DIN or source of Ortho P along the shelf. DIN fluxes and SeaWiFS satellite-derived chlorophyll showed seasonally elevated values during the first half of the year followed by generally lower values in late summer and fall. This seasonal signal diminished from east to west. The observed relationship between DIN flux and chlorophyll was consistent with ship-based observations of a linkage between riverine nutrient inputs and productivity. Long-term trends in river discharge were correlated with the Multivariate ENSO (El Niño Southern Oscillation) Index (MEI) (r=−0.281, p<0.0001), evidence that river discharge was influenced by global climatic trends.  相似文献   

2.
This survey provides baseline information on sediment characteristics, porewater, adsorbed and plant tissue nutrients from intertidal coastal seagrass meadows in the central region of the Great Barrier Reef World Heritage Area. Data collected from 11 locations, representative of intertidal coastal seagrass beds across the region, indicated that the chemical environment was typical of other tropical intertidal areas. Results using two different extraction methods highlight the need for caution when choosing an adsorbed phosphate extraction technique, as sediment type affects the analytical outcome. Comparison with published values indicates that the range of nutrient parameters measured is equivalent to those measured across tropical systems globally. However, the nutrient values in seagrass leaves and their molar ratios for Halophila ovalis and Halodule uninervis were much higher than the values from the literature from this and other regions, obtained using the same techniques, suggesting that these species act as nutrient sponges, in contrast with Zostera capricorni. The limited historical data from this region suggest that the nitrogen and phosphorus content of seagrass leaves has increased since the 1970s concomitant with changing land use practice.  相似文献   

3.
Nutrient enrichment from shrimp aquaculture poses an increasing environmental threat due to the industry's projected rapid growth and unsustainable management practices. Traditional methods to monitor impacts emphasize water quality sampling; however, there are many advantages to bioindicators, especially in developing countries. We investigated the usefulness of three bioindicators -- growth, tissue nitrogen content and nitrogen stable isotope signature (delta(15)N) -- in the tropical red macroalga Acanthophora spicifera. Algae were collected, cultured, and deployed in a spatial array around the outflow from a shrimp farm in Moorea, French Polynesia, to detect nitrogenous wastes. All three parameters were highest adjacent to the shrimp farm indicating nutrient enrichment, and delta(15)N values confirmed the shrimp farm as the dominant nutrient source (5.63-5.96 per thousand). Isotope ratios proved the most sensitive indicator, as delta(15)N signatures were detected at the most distant sites tested, confirming their usefulness in tracing nutrients and mapping the spatial extent of enrichment.  相似文献   

4.
Stable nitrogen isotope ratios were used to study the incorporation of anthropogenically-derived nitrogen into the food webs of salt marsh systems along a contamination gradient in Narragansett Bay. Nitrogen isotope ratios (delta(15)N) were measured in six estuarine species collected from three marshes along this gradient, monthly from June to October between 1997 and 1999. A significant decrease in delta(15)N was found with distance along the estuary for four of the six species. Significant differences were found among monthly isotope ratios for some species. Nitrogen isotope ratios in sea lettuce (Ulva lactuca) increased during the summer season with highest delta(15)N values measured during September and October. This trend was most pronounced at the station receiving the highest nutrient inputs. Elevated delta(15)N values at this station appeared to correlate with seawater ammonia/nitrate concentration ratios. The temporal variations in delta(15)N suggest that care should be taken in species selection and the design of sampling schemes of studies using delta(15)N for monitoring anthropogenic nutrients in aquatic systems. Sampling programs designed to determine long-term trends should consider species that do not show rapid fluctuations in isotope ratios. The mud snail, Nassarius obsoletus, responded this way in the present study. Studies designed to measure short-term changes should include species such as U. lactuca, which rapidly respond to isotope changes. The results from this study also help to establish a baseline for nitrogen isotope values in Narragansett Bay. This information can be used to monitor future trends in nitrogen inputs to this estuary.  相似文献   

5.
The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton. Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes) and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton. Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes with high to very high amounts of N deposition.  相似文献   

6.
Inventory of nutrients in the Bohai   总被引：3，自引：0，他引：3  
Biogeochemical observations were carried out to address the influence of major sources on nutrient composition and the ecosystem of the Bohai. Relatively high concentrations of nutrients off the Huanghe mouth and the shallow water areas were observed in the Bohai suggesting the effects of tidal and residual currents and anthropogenic perturbation. Sediment in the Bohai represents a source for ammonium, phosphate and dissolved silicate, while it is a sink for nitrite and nitrate. Benthic nutrient fluxes were 2-3 times higher than the riverine input with the regeneration rate of phosphate being slower relative to DIN and dissolved silicate. The release of dissolved silicate and phosphate from sediments may mitigate the decrease of dissolved silicate and phosphate due to the reduction of freshwater discharge. Compared with submarine groundwater discharge, nutrient regeneration in sediment provides similar DIN flux, 2-5 times phosphate and dissolved silicate fluxes. DIN/P molar ratios in the three mentioned sources were 155-845, indicating that phosphorus limitation for phytoplankton growth could be intensified, which likely results in changes of ecosystems of the Bohai.  相似文献   

7.
The impact of pond aquaculture effluents on the distribution and performance of seagrasses was examined in NE Hainan, tropical China. Samples were taken along transects in three back-reef areas with different extent of aquaculture production in their hinterland. High δ15N in seagrass leaves and epiphytes (6–9‰) similar to values in pond effluents documented aquaculture as dominant nitrogen source in the back-reefs with decreasing impact with distance from shore. Seagrass species abundance, shoot density and biomass were lower and concentrations of nutrients, chlorophyll and suspended matter were higher at nearshore sites with high and moderate pond abundance than at the control site. High epiphyte loads and low δ34S in seagrass leaves suggest temporal shading and sulphide poisoning of the nearshore seagrasses. Observed gradients in environmental parameters and seagrass performance indicate that the distance from the pond outlets and size of the adjacent pond agglomeration are major determinants of seagrass degradation.  相似文献   

8.
Many studies show that seagrass δ15N ratios increase with the amount of urbanization in coastal watersheds. However, there is little information on the relationship between urbanization and seagrass δ15N ratios on a global scale. We performed a meta-analysis on seagrass samples from 79 independent locations to test if seagrass δ15N ratios correlate with patterns of population density and fertilizer use within a radius of 10–200 km around the sample locations. Our results show that seagrass δ15N ratios are more influenced by intergeneric and latitudinal differences than the degree of urbanization or the amount of fertilizer used in nearby watersheds. The positive correlation between seagrass δ15N ratios and latitude hints at an underlying pattern in discrimination or a latitudinal gradient in the 15N isotopic signature of nitrogen assimilated by the plants. The actual mechanisms responsible for the correlation between δ15N and latitude remain unknown.  相似文献   

9.
The distribution and nutritional profiles of sub-tidal seagrasses from the Torres Strait were surveyed and mapped across an area of 31,000 km2. Benthic sediment composition, water depth, seagrass species type and nutrients were sampled at 168 points selected in a stratified representative pattern. Eleven species of seagrass were present at 56 (33.3%) of the sample points. Halophila spinulosa, Halophila ovalis, Cymodocea serrulata and Syringodium isoetifolium were the most common species and these were nutrient profiled. Sub-tidal seagrass distribution (and associated seagrass nutrient concentrations) was generally confined to northern-central and south-western regions of the survey area (<longitude 142.60), where mean water depth was relatively shallow (approximately 13 m below MSL) and where sediments were comprised primarily muddy sand to gravelly sand. Seagrass nitrogen and starch content, the most important nutrients for marine herbivores, were significantly correlated with species and with the plant component (above or below ground). For all seagrass species, the above-ground component (shoots and leaves) possessed greater nitrogen concentrations than the below-ground component (roots and rhizomes), which possessed greater starch concentrations. S. isoetifolium had the highest total nitrogen concentrations (1.40±0.05% DW). However, it also had higher fibre concentrations (38.2±0.68% DW) relative to the other four species. H. ovalis possessed the highest starch concentrations (2.76±0.12% DW) and highest digestibility (83.24±0.66% DW) as well as the lowest fibre (27.2±0.66% DW). The high relative abundance (found at 55% of the sites that had seagrass) and nutrient quality characteristics of H. ovalis make it an important source of energy to marine herbivores that forage sub-tidally in the Torres Strait. There were two regions in Torres Strait (north-central and south-western) where sub-tidal seagrass meadows were prevalent and of relatively higher nutritional value. This spatial and nutritional information can be used by local agencies to manage and to protect the ecological, economic and cultural values of the sub-tidal seagrass ecosystems and associated fisheries of the Torres Strait.  相似文献   

10.
In remote, tropical areas human influences increase, potentially threatening pristine seagrass systems. We aim (i) to provide a bench-mark for a near-pristine seagrass system in an archipelago in East Kalimantan, by quantifying a large spectrum of abiotic and biotic properties in seagrass meadows and (ii) to identify early warning indicators for river sediment and nutrient loading, by comparing the seagrass meadow properties over a gradient with varying river influence. Abiotic properties of water column, pore water and sediment were less suitable indicators for increased sediment and nutrient loading than seagrass properties. Seagrass meadows strongly responded to higher sediment and nutrient loads and proximity to the coast by decreasing seagrass cover, standing stock, number of seagrass species, changing species composition and shifts in tissue contents. Our study confirms that nutrient loads are more important than water nutrient concentrations. We identify seagrass system variables that are suitable indicators for sediment and nutrient loading, also in rapid survey scenarios with once-only measurements.  相似文献   

11.
Chemical compositions of Coscinodiscus wailesii were determined for four samples of natural cells. Results revealed that the cellular Si:N ratio of C. wailesii cell was 2.4:1.0-5.2:1.0. The impacts of C. wailesii on surrounding coastal water were evaluated from hydrographic observations, in which C. wailesii cell density, nutrients concentrations and temperature were monitored from November 2001 to February 2005 in Harima-Nada, the Seto Inland Sea, Japan. In low temperature periods, from October to December, two peaks of C. wailesii cell density were observed and nutrient concentrations were depleted. The draw-down ratio of Si(OH)(4) and DIN (Si(OH)(4):DIN ratio) in the water column were similar to the cellular Si:N ratio of C. wailesii cells, which have high Si contents. In addition the effects of different Si(OH)(4):DIN ratio were determined for in situ bottle incubation experiments. In the culture experiments, picoplankton (0.2-2.0 microm) which consisted of small flagellates became dominant under low Si(OH)(4):DIN ratios. These results suggested that the sizes distribution shifted to small size and the phytoplankton community was changed to small flagellates after the C. wailesii bloom. These changes would influence predators at higher trophic levels in its coastal ecosystem.  相似文献   

12.
Mangroves are of great ecological and socio‐economic importance, yet they are under threat from urban development on the southern Pacific coast of Costa Rica. To test for possible nutrient‐related impacts, we compared water‐column nutrient concentrations, C and N stable isotope values and other environmental variables between mangroves with known sewage loading (three “nutrient loaded” locations) and those without such loading (three “reference” locations). Instantaneous nutrient concentrations were low at all locations, Secchi depth was greater at reference locations, and chlorophyll concentrations were higher at nutrient loaded mangroves. Suspended matter did not vary between reference and nutrient loaded mangroves, and nor did bivalve and algal δ13C and δ15N values. Enrichment of δ15N and δ13C of red mangrove leaves at the nutrient loaded locations is attributed to pulsed inputs of materials that were not detected in the instantaneous nutrient data. We provide evidence of isotopic enrichment at nutrient loaded locations from mangrove material and recommend that adequate waste water treatment be carried out on all anthropogenic discharges into this vulnerable marine system.  相似文献   

13.
Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285 kg-H2O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.  相似文献   

14.
Cages and fertilizers were used at Glover's Atoll, Belize to test the relative importance of nitrogen (N) and phosphorus (P) to microbial euendolithic communities (bacteria, algae and fungi) and their bioerosion rates of Strombus gigas shells after 56-days of exposure. By the end of the experiment, the abundance of green algae was higher than cyanobacteria and fungi in N and N+P treatments, although green algae did not increase proportionally with increasing N concentrations, suggesting that green algae were co-limited by P and N. In contrast, cyanobacteria abundance increased with increasing P concentration, suggesting that cyanobacteria were P-limited. Fungi were not significantly affected by the addition of nutrients. Microbioerosion rates in the N and N+P treatments were 2-times greater than rates in the P treatment and 15-times greater than the control treatment. Results demonstrate that increased nutrient concentrations on coral reefs may increase microbioerosion rates, and variations in nutrient ratios can modify microborers community composition.  相似文献   

15.
One of the key environmental concerns about shrimp farming is the discharge of waters with high levels of nutrients and suspended solids into adjacent waterways. In this paper we synthesize the results of our multidisciplinary research linking ecological processes in intensive shrimp ponds with their downstream impacts in tidal, mangrove-lined creeks. The incorporation of process measurements and bioindicators, in addition to water quality measurements, improved our understanding of the effect of shrimp farm discharges on the ecological health of the receiving water bodies. Changes in water quality parameters were an oversimplification of the ecological effects of water discharges, and use of key measures including primary production rates, phytoplankton responses to nutrients, community shifts in zooplankton and delta15N ratios in marine plants have the potential to provide more integrated and robust measures. Ultimately, reduction in nutrient discharges is most likely to ensure the future sustainability of the industry.  相似文献   

16.
《Continental Shelf Research》1999,19(9):1113-1141
Relationships among primary production, chlorophyll, nutrients, irradiance and mixing processes were examined along the salinity gradient in the Mississippi River outflow region. A series of six cruises were conducted during 1988–1992 at various times of year and stages of river discharge. Maximum values of biomass and primary production were typically observed at intermediate salinities and coincided with non-conservative decreases in nutrients along the salinity gradient. Highest values of productivity (>10 gC m−2 d−1) and biomass (>30 mg chlorophyll a m−3) were observed in April 1988, July–August 1990 and April–May 1992; values were lower in March and September 1991. Rates of primary production were apparently constrained by low irradiance and mixing in the more turbid, low salinity regions of the plume, and by nutrient limitation outside the plume. Highest values of primary production occurred at stations where surface nutrient concentrations exhibited large deviations from conservative mixing relationships, indicating that depletion of nutrients was related to phytoplankton uptake. Mixing and advection were important in determining the location and magnitude of primary production maxima and nutrient depletion. In addition to growth within plume surface waters, enhanced growth and/or retention of biomass may have occurred in longer residence time waters at the plume edge and/or beneath the surface plume. Vertical structure of some plume stations revealed the presence of subsurface biomass maxima in intermediate salinity water that was depleted in nutrients presumably by uptake processes. Exchange between subsurface water and the surface plume apparently contributed to the reduction in nutrients at intermediate salinities in the surface layer. DIN (=nitrate+nitrite+ammonium) : PO4 (=phosphate) ratios in river water varied seasonally, with high values in winter and spring and low values in late summer and fall. Periods of high DIN : PO4 ratios in river nutrients coincided with cruises when surface nutrient concentrations and their ratios indicated a high probability for P limitation. N limitation was more likely to occur at high salinities and during late summer and fall. Evidence for Si limitation was also found, particularly in spring.  相似文献   

17.
Kojima  T.  Tanaka  Y.  Katoh  S.  Tahara  K.  Takahashi  N.  Yamada  K. 《中国科学:地球科学(英文版)》2002,45(1):142-147

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.

Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.

In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285 kg-H2O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.

  相似文献   

18.
We examined the relevance of dissolved inorganic nitrogen (DIN) forms (nitrate and ammonium) in stream water as N sources for different macrophyte species. To do this, we investigated the variability and relationships between 15N natural abundance of DIN forms and of four different macrophyte species in five different streams influenced by inputs from wastewater treatment plants and over time within one of these streams. Results showed that 15N signatures were similar in species of submersed and amphibious macrophytes and in stream water DIN, whereas 15N signatures of the riparian species were not. 15N signatures of macrophytes were generally closer to 15N signatures of nitrate, regardless of the species considered. Our results showed significant relationships between 15N signatures of DIN and those of submersed Callitriche stagnalis and amphibious Veronica beccabunga and Apium nodiflorum, suggesting stream water DIN as a relevant N source for these two functional groups. Moreover, results from a mixing model suggested that stream water DIN taken up by the submersed and amphibious species was mostly in the form of nitrate. Together, these results suggest different contribution to in-stream N uptake among the spatially-segregated species of macrophytes. While submersed and amphibious species can contribute to in-stream N uptake by assimilation of DIN, macrophyte species located at stream channel edges do not seem to rely on stream water DIN as an N source. Ultimately, these results add a functional dimension to the current use of macrophytes for the restoration of stream channel morphology, indicating that they can also contribute to reduce excess DIN in streams.  相似文献   

19.
Tobago’s fringing coral reefs (FR) and Buccoo Reef Complex (BRC) can be affected locally by wastewater and stormwater, and regionally by the Orinoco River. In 2001, seasonal effects of these inputs on water-column nutrients and phytoplankton (Chl a), macroalgal C:N:P and δ15N values, and biocover at FR and BRC sites were examined. Dissolved inorganic nitrogen (DIN, particularly ammonium) increased and soluble reactive phosphorus (SRP) decreased from the dry to wet season. Wet season satellite and Chl a data showed that Orinoco runoff reaching Tobago contained chromophoric dissolved organic matter (CDOM) but little Chl a, suggesting minimal riverine nutrient transport to Tobago. C:N ratios were lower (16 vs. 21) and macroalgal δ15N values higher (6.6‰ vs. 5.5‰) in the BRC vs. FR, indicating relatively more wastewater N in the BRC. High macroalgae and low coral cover in the BRC further indicated that better wastewater treatment could improve the health of Tobago’s coral reefs.  相似文献   

20.
The availability and partition of nitrogen (N) and phosphorus (P) in inorganic and organic compartments, as well as their stoichiometric ratio, are influenced by both physical and biological forcing factors. On this basis, the temporal and spatial dynamics in N:P atomic ratios in different compartments may provide information on the functioning of marine ecosystems. Here we explore the relative importance of water temperature, river inputs, wind mixing, stratification, ingression of nutrient-depleted Eastern Adriatic Current and phytoplankton biomass on concentrations and ratios between nitrogen and phosphorus in a semi-enclosed bay (the Gulf of Trieste), using data from monitoring programs carried out during 8 years. Water samples are first classified in 6 water types based on N:P ratios in different components, and then relationships between water type space-time distribution and a set of forcing factors is sought. Results show that the gulf is characterised by relatively stable N:P ratios in all compartments (about 23-26), always exceeding the classical Redfield ratio. In the surface layer, however, nitrogen and phosphorus dynamics are decoupled because of river input and plankton productivity, and a significant spatial and temporal variability is observed in terms of stoichiometric balance, nutrient concentrations and partition among the different pools. Deviations from stable N:P ratios follow a seasonal evolution. In spring, continental inputs alter inorganic nutrient compartments (N:P up to 115); later on, during the seasonal succession of biological processes (e.g. late spring phytoplankton blooms, summer increase in microbial activities and autumn phytoplankton blooms), a change is also seen in the organic dissolved and particulate pools. Multivariate statistical analysis suggests that, among the considered forcing factors, the most relevant in modulating the N:P stoichiometry in the Gulf of Trieste are river inputs and ingression of the Eastern Adriatic Current (acting in opposite directions) along with phytoplankton dynamics. During the whole period, besides variations in N:P stoichiometry, in the Gulf of Trieste dissolved organic matter represents the largest pool of N and P, which can provide a source of nutrients for the planktonic community alternative to inorganic nutrient.  相似文献   

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