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1.
The composition, productivity, and standing crop of net (>20 μm) and nano-(<20 μm) phytoplankton of Peconic Bay, Long Island, New York was examined from June 1978 through May 1979. Nanoplankton, primarily small solitary flagellates, chlorophytes, and diatoms, dominated from May through September accounting for 88.5% of the productivity and 88.1% of the standing crop (measured as chlorophyll a). An apparent net plankton bloom began in December and continued through March. The dominant organism through most of the winter bloom was the chain-forming diatom Skeletonema costatum (Grev.) Cl. Net plankton at this time represented 66.4% of the standing crop. For both size fractions, productivity/chlorophyll a (g C per g chl a per d, integrated through the euphotic zone) was a function of light energy over the year with the exception of a few sampling dates during the post-winter bloom period. Assimilation numbers (g C per g chl a per h at saturating light intensities) were a function of temperature between 0 and 20°C. Nitrogen deficiency did not appear to be a factor in regulating phytoplankton growth rate through the euphotic zone, as ratios of 14C assimilation for dark bottles enriched with NH3 and with no enrichment exhibited no relationship to environmental dissolved inorganic nitrogen concentrations. Zooplankton grazing pressure appeared to have been an important factor in regulating the upper limit of phytoplankton biomass and in influencing size fraction dominance. Dominance of one phytoplankton size fraction over the other on any given date was not based on physiological differences between the two groups since both fractions were composed of the same species. Apparent net phytoplankton blooms (in terms of productivity and chlorophyll a) were artifacts of increased chain lengths of nanoplankton diatoms such as Skeletonema costatum, and to a lesser extent, Thalassiosira nordenskioldii Cl. and Detonula confervacea (Cl.) Gran, rather than to the dominance of large, solitary cells.  相似文献   

2.
Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 14C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 14C ka, and the onset of biogenic silica occurred at 10 14C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 14C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake.  相似文献   

3.
Particulate organic carbon (POC), dissolved organic carbon (DOC), and plant pigments (chlorophylls and carotenoids) were measured approximately bimonthly from March 1992 to October 1993 in the Sabine-Neches estuary (Sabine Lake region), located on the Texas-Louisiana border. High freshwater inflow into this shallow turbid estuary results in the shortest hydraulic residence time (ca. 7 d) of all Texas estuaries (Baskaran et al. in press). Annual averages of chlorophyll-a (3.0 μg l?1) and particulate organic carbon (1.1 mg l?1) in the water column were extremely low in comparison to other shallow estuaries. The highest chlorophyll-a concentrations were observed in October 1993, in the mid and lower regions of the estuary, during the lowest river discharge. Zeaxanthin and fucoxanthin concentrations suggested that much of the chlorophyll-a during this low flow period was represented by cyanobacteria and diatoms that entered from the Gulf of Mexico. The range of DOC concentrations was generally high (4.4–20.9 mg l?1) and were significantly correlated with POC, but not with chlorophyll-a concentrations. When total suspended particulate (TSP) concentrations were below 20 to 30 mg l?1, there were significant increases in %POC and %PON of the TSP. The unusually high POC: chlorophyll-a ratios (highest value of 1423) suggested that much of the POC contained low concentrations of chlorophyll-a that had degraded during transport from wetlands in the Sabine and Neches rivers. Based on these data, this estuary can be characterized as a predominantly heterotrophic system, with low light penetrance, short particle-residence times, high DOC, and low inputs from autochthonous carbon sources.  相似文献   

4.
Lake Kivu is a gas-charged East African rift lake with currently anoxic bottom water. The extractable compounds and residual organic matter of a short sediment core have δ13C values typical of lacustrine microbial detritus. The total extracts consist primarily of polar compounds such as n-alkanoic acids, hydroxyalkanoic acids, triterpenoids, steroids and monosaccharides, with minor amounts of n-alkanes and n-alkanols. These tracer compounds and δ13C values indicate that the organic matter in the surficial and deeper sedimentary record was dominated by bacterial sources. The sapropelic sediment between these horizons contains organic matter from primarily algal with lesser bacterial input. Terrestrial organic markers are minor in all samples. The major fractions of the compounds in the total extracts were oxidized in the upper water column prior to transit through the anoxic bottom water to sedimentary deposition. The sapropelic horizon may reflect lake water turnover with ventilation or hydrothermal activity and consequently increased algal blooms.  相似文献   

5.
Phytoplankton chlorophyll a concentration, biovolume, cell diameter, and species composition differed across the narrow, low salinity zone between 0.6‰ to 4‰ and may influence copepod food availability in the northern San Francisco Bay Estuary. The highest chlorophyll a concentrations (range 3.2–12.3 μg 1?1), widest cell diameters (>5 μm diam), highest diatom densities and highest production rates of >10 μm diam cells occurred at the landward edge of the salinity zone in April during a strong spring tide and May during a strong neap tide. Near optimum predator/prey ratios, large prey estimated spherical diameters, and high chlorophyll a concentrations suggest these phytoplankton communities provided good food quantity and quality for the most abundant copepods, Eurytemora affinis, Sinocalanus doerrii, and Pseudodiaptomus forbesi. At the center of the zone, chlorophyll a concentrations, diatom densities, and production rates of >10 μm diam cells were lower and cell diameters were smaller than upstream. Downstream transport was accompanied by accumulation of phytoplankton with depth and tide; maximum biomass occurred on spring tide. The lowest chlorophyll a concentrations (1.4–3.6 μg 1?) and consistently high densities (3,000–4,000 cells ml?1) of <5 μm diam cells occurred at the seaward edge of the zone, where the green alga Nannochloris spp. and the bluegreen alga Synechococcus spp. were the most abundant phytoplankton. Low chlorophyll a concentrations and production rates of >10 μm diam cells, small prey estimated spherical diameters, and high predator/prey ratios suggested the seaward edge of the zone had poor phytoplankton food for copepodids and adult copepods. The seaward decrease in phytoplankton chlorophyll a concentration and cell diameter and shift in species composition in the low salinity zone were probably a function of an estuary-wide decrease in chlorophyll a concentration, cell diameter, and diatom density since the early 1980s that was enhanced in the low salinity zone by clam herbivory after 1987. *** DIRECT SUPPORT *** A01BY090 00008  相似文献   

6.
Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m−2) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m−2). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.  相似文献   

7.
Measurements of primary production in surf-zone habitats are relatively rare and often utilize simulation approaches, owing to the physical challenges of working in surf. The study reported here examined primary production in situ at two open ocean sandy beaches in southeastern North Carolina during relatively calm summer conditions. In situ bottle incubations using 14C uptake methods were complemented by simultaneous measures of phytoplankton photo-physiology assessed by Fast Repetition Rate Fluorometry (FRRF) in flow-through mode at the two sites across a spring-neap tidal cycle in July, 2010. The surf-zone phytoplankton was dominated by small centric and pennate diatoms as well as cyanobacteria and chlorophytes with biomass concentrations of 3.63?C9.23?mg chl a m?3. Primary productivity was relatively high, ranging from 31.5?C88.0?mg?C?m?3?h?1 by 14C. Biomass-specific productivity averaged ??9.4?mg C (mg chl a)?1?h?1 by 14C, indicating healthy phytoplankton populations. Measurements of the functional absorption cross section of photosystem II, ??PSII, via FRRF were 327?C380, comparable to values reported by other investigators of open ocean phytoplankton. Averaged values of the maximum effective quantum yield, F v/F m, corresponded to proportions of photochemically competent PSII reaction centers of 62.6?% to 72?%, indicating that the phytoplankton were nutrient-replete. These data suggest that the surf zone, although a spatially confined habitat, is a productive one that plays a significant role in coastal ocean ecology. Further investigation is needed to better understand primary productivity of phytoplankton in the surf zone and the effect of the dynamic environment on their physiological responses.  相似文献   

8.
From 2005 to 2009, the spatial distribution and the seasonal dynamics of chromophoric dissolved organic matter (CDOM) were explored in Lake Taihu in eastern China. The spatial-seasonal dynamics of CDOM absorption and three CDOM composition variables, including spectral slope (S), spectral slope ratio (SR) and the M value, defined as the ratio of absorption at 250 nm/365 nm, were analyzed and discussed. Furthermore, river input processes and degradation of phytoplankton were studied to assess their impact on CDOM composition and the factors involved in the spatial-seasonal variability of CDOM. The CDOM absorption coefficient at a wavelength of 350 nm, a(350), ranged from 1.37-9.55 m−1 with a mean of 3.33 ± 1.32 m−1. Spatially, higher a(350) values, but lower spectral slope, spectral slope ratio and M values, were recorded in the northern algae dominated bays while lower values were recorded in southeastern macrophyte dominated bays. The a(350) was significantly higher in inshore waters than in offshore waters. Values of S, SR and M decreased during the flood and algal bloom season in spring and summer whereas a(350) increased. In the three river profiles, the gradual decrease of a(350) along the trajectory from the river mouth into the lake during the flood season showed the contribution of allochthonous CDOM. A laboratory phytoplankton degradation experiment was conducted to determine the contribution of CDOM production from phytoplankton. The significant increase of a(350) with time in the CDOM production experiment underlines the importance of autochthonous CDOM production during the algal bloom season. In summary, the significant increase of a(350) in spring and summer (algal bloom season) may be due to both the allochthonous CDOM input from the surrounding rivers and the autochthonous production of CDOM from degrading phytoplankton.  相似文献   

9.
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l?1 and a winter minimum of 1.4 μg chl a l?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ?1?h?1 (32–803 mg C m?3?day?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m?3?year?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.  相似文献   

10.
The biogeochemical cycle of iron and associated elements in Lake Kinneret   总被引：2，自引：0，他引：2  
Iron biogeochemical cycling and distribution between particulate, reactive (colloidal + dissolved, oxine-labile, Fe(II)) fractions were studied in the seasonally stratified, mesotrophic Lake Kinneret. This article presents various aspects of the Fe budget in the lake and relates them to the chemical reactivity of various physicochemical forms of Fe.The budget of Fe in Lake Kinneret is dominated by fluvial Fe load, rather than by internal recycling of Fe from the sediment, as shown by the fact that 75 to 94% of the variance in Fe concentrations in the lake can be explained by the fluctuation in the water discharge of the Jordan River. Iron associated with phytoplankton accounts for 9-16% of the bulk particulate Fe in the lake. However, within patches of the dominate algae, the dinoflagellate Peridinium gatunense, algal Fe accounts for more than 70% of the lake’s particulate Fe. The algal Fe is predominantly intracellular, and the Fe: chlorophyll a ratios were within the range of published values for dinoflagellates and cyanobacteria. Iron associated with particles larger than 0.025 μm (20-300 nM) accounts for 80-95% of total Fe in the epilimnion of Lake Kinneret throughout the year. In contrast, this fraction of Fe is dominant in the hypolimnion only during the period of lake mixing. Iron concentration of different size fractions (<0.025 μm, <0.2 μm and >0.025 μm) in the surface water covaried throughout the research period. These covariations suggest dynamic transformations of Fe between different size fractions, either due to partial dissolution/precipitation or desorption/adsorption. Oxine-labile Fe concentrations, the Fe fraction considered chemically labile and available for phytoplankton, ranged from 15 to 75 nM. In wintertime, the oxine-labile Fe accounts for only 10-20% of the total Fe, while in other seasons most of the Fe is oxine-labile. Oxine-labile Fe concentrations always exceed the 0.025 μm-filtered Fe, implying that some of the larger particles contain oxine labile-Fe, and therefore are reactive. The fraction of reactive particles in Lake Kinneret (10-80%) is high relative to that of the marine environments, and can most likely be attributed to its fluvial source, which contains a significant proportion of reactive Fe oxide and hydrous oxide particles.The annual variability in the epilimnetic concentrations of other trace elements and nutrients, such as Al, Mn, Cd, Zn, Pb, and P were studied and grouped according to their resemblance with river water discharge, redox processes, or biological uptake and scavenging. Distribution patterns of Al, Pb and Cd resembled that of Fe, suggesting that similar processes control the concentrations of these metals, namely significant contribution from the watershed, high affinity to particulate matter and little control of biota on their fate in the lake. Other elements such as Zn and P are more affected by biological uptake, while Mn is more affected by redox cycling within the lake.  相似文献   

11.
Investigation of chlorins in the oxic surface sediment of a small eutrophic alpine lake (Motte lake) revealed the presence of a new series of steryl chlorin esters containing the pheophorbide a nucleus, together with their pyropheophorbide a steryl ester counterparts previously observed in the anoxic surface sediment of the same lake. Identification of the pheophorbide a steryl esters was based on comparison of spectroscopic, chromatographic and mass spectrometric characteristics of the compounds with those of a synthetic standard and of pyropheophorbide a steryl esters. Combined liquid chromatography-mass spectrometry analysis confirmed the absence of pheophorbide a steryl esters in the anoxic sediment but allowed their detection in traces in the water column, indicating that pheophorbide a steryl esters are, like their pyropheophorbide a analogs, formed in the water column. The distribution of sterols released by hydrolysis of the pheophorbide a steryl esters shows close similarities to that of the free sterols in the water column and of the sterols of the pyropheophorbide a steryl esters. It appears that, like their pyropheophorbide a counterparts, pheophorbide a steryl esters incorporate mainly sterols of phytoplanktonic origin. Their formation probably involves the same mechanism as for pyropheophorbide a steryl ester formation, i.e. metabolism by zooplankton grazing on phytoplankton. The presence of pheophorbide a steryl esters in the oxic sediment and their absence from the anoxic sediment is probably due to a lower stability of compounds containing a carbomethoxy substituent in the anoxic environment.  相似文献   

12.
An experimental in situ microcosm study was conducted in the tropical lagoon La Mancha (Gulf of Mexico) to determine whether or not nutrient limitation occurs and to examine the direct effect of an inorganic nutrient pulse on the phytoplankton community structure. The phytoplankton community response to the addition of four treatments with different combinations of nitrogen (N), phosphorus (P), and silica (Si) (+N-NH4 +, +P-PO4 ?, +Si-SO3, and N:P16) showed that phytoplankton was N-limited as indicated by an increase in phytoplankton biomass (i.e., chlorophyll a) (range, 8–34 mg m?3) during the dry season in two consecutive years (2006 and 2007). Picophytoplankton abundance significantly increased in the +N treatment (145.46 103 cells L?1), while microphytoplankton reached a maximum abundance (68.38 103 cells L?1) in the N:P16 treatment. Phytoplankton composition changed from a community initially dominated by dinoflagellates (e.g., Prorocentrum spp.) to another dominated by diatoms (Thalassiosira and Nitzschia longissima) in the N:P16 treatment. The +N treatment significantly increased Synechococcus sp. growth rates (1.3 divisions per day) (picocyanobacteria). Biomarker pigments measured in the experimental microcosms confirmed observed changes in phytoplankton groups. Our results reveal that La Mancha lagoon is a N-limited coastal system during the dry season and provides evidence of the temporal species successional patterns and mechanisms regulating the phytoplankton community response to nutrient enrichment pulses in this already eutrophic coastal lagoon.  相似文献   

13.
During 1995 the phytoplankton in the Swan River were intensively sampled to assess biomass and species composition. Continuous measurements of fluorescence, salinity, and temperature were made weekly during 40 km sampling trips along the estuary and used to map the seasonal progression of the algal biomass. Weekly measurements of primary production were made and used to model net primary production from the vertical distribution of biomass, irradiance, and phytoplankton species composition. Potential nutrient limitation was assessed with “all but one” nutrient bioassays. The results indicate a complex mixture of potentially limiting factors, which vary in time and space. Although the data sequence is short, it suggests a annual succession pattern of diatoms, chlorophytes, diatoms, and finally dinoflagellates and cryptophytes in late summer-autumn. Peak seasonal biomass was observed during January to April. Mean annual chlorophylla biomass was greatest in upstream stations (5–9), where estimates of net primary production rates averaged 1.55 g C m?2 d?1 and gross primary production was 800–1000 g C m?2 yr?1. Potential nutrient limitation was most severe from November to May, although not during January 1995. Based on bioassay results, during the period of greatest potential for nutrient limitation, nitrogen was 15 to 30 times more limiting to biomass development than phosphate. Runoff due to consistent rainfall during winter eventually breaks down stratification and flushes the estuary with low-salinity, nutrient-rich water, producing, a light-limited, nutrient-rich aquatic ecosystem. Timing and magnitude of physical forcing events, mainly rainfall, appear critical in determining the susceptibility of this ecosystem to summer and autumn algal blooms.  相似文献   

14.
An unusual phytoplankton bloom dominated by unidentified green coloured spherical algal cells (∼5μm diameter) and dinoflagellates (Heterocapsa, Scripsiella and Gymnodinium) was encountered along the coast of Goa, India during 27 and 29 January, 2005. Pigment analysis was carried out using both fluorometric and HPLC methods. Seawater samples collected from various depths within the intense bloom area showed high concentrations of Chl a (up to 106 mg m − 3) associated with low bacterial production (0.31 to 0.52 mg C m − 3 h − 1) and mesozooplankton biomass (0.03 ml m − 3). Pigment analyses of the seawater samples were done using HPLC detected marker pigments corresponding to prasinophytes, dinoflagellates and diatoms. Chlorophyll b (36–56%) followed by peridinin (15–30%), prasinoxanthin (11–17%) and fucoxanthin (7–15%) were the major diagnostic pigments while pigments of cryptophytes and cyanobacteria including alloxanthin and zeaxanthin formed <10%. Although microscopic analysis indicated a decline in the bloom, pheaophytin concentrations in the water column measured by both techniques were very low, presumably due to fast recycling and/or settling rate. The unique composition of the bloom and its probable causes are discussed in this paper.  相似文献   

15.
Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996–2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer–early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future.  相似文献   

16.
In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m3s?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m3 s?1, but sustained discharges greater than 1,100 m3 s?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.  相似文献   

17.
In coastal ecosystems with long flushing times (weeks to months) relative to phytoplankton growth rates (hours to days), chlorophyll a (chl-a) integrates nutrient loading, making it a pivotal indicator with broad implications for ecosystem function and water-quality management. However, numerical chl-a criteria that capture the linkage between chl-a and ecosystem impairments associated with eutrophication (e.g., hypoxia, water clarity and loss of submerged aquatic vegetation, toxic algal blooms) have seldom been developed despite the vulnerability of these ecosystems to anthropogenic nutrient loading. Increases in fertilizer use, animal wastes, and population growth in the Chesapeake Bay watershed since World War II have led to increases in nutrient loading and chl-a. We describe the development of numerical chl-a criteria based on long-term research and monitoring of the bay. Baseline chl-a concentrations were derived using statistical models for historical data from the 1960s and 1970s, including terms to account for the effects of climate variability. This approach produced numerical chl-a criteria presented as geometric means and 90th percentile thresholds to be used as goals and compliance limits, respectively. We present scientific bases for these criteria that consider specific ecosystem impairments linked to increased chl-a, including low dissolved oxygen (DO), reduced water clarity, and toxic algal blooms. These multiple lines of evidence support numerical chl-a criteria consisting of seasonal mean chl-a across salinity zones ranging from 1.4 to 15 mg m?3 as restoration goals and corresponding thresholds ranging from 4.3 to 45 mg m?3 as compliance limits. Attainment of these goals and limits for chl-a is a precondition for attaining desired levels of DO, water clarity, and toxic phytoplankton prior to rapid human expansion in the watershed and associated increases of nutrient loading.  相似文献   

18.
Seasonal phosphate (Pi) uptake kinetics were determined using chambers encompassing the water column, sediment and the entire system (water column + sediment + seagrass/epiphyte) in Florida Bay (FB) during 2003–2006 and on the Little Bahama Bank (LBB) during a cruise June, 2004. Pi uptake was a linear function of concentration at low Pi levels (< 2 μmo11-1). Applying the Pi system rate constant (Sp) from western (177 ±50 x 10-6 m s-1) and eastern (272 ±66 x 10-6 m s-1) bay sites, and using Pi measured during the study (0.02 to 0.177 μmol Pi 1-1), we calculated a Pi uptake rate of 0.30 to 2.62 mmol Pi m-2 d-1 for western and 0.47 to 4.16 mmol Pi m-2 d-1 for eastern bay sites which includes phytoplankton uptake (0.455 m height). During non-bloom conditions, phytoplankton dominated Pi uptake in the east (46%) and both phytoplankton and the seagrass-epiphyte consortium in the west (32 and 52%, respectively), with a smaller contribution by the sediment (15–20%). On LBB interior sites, the water column always dominated (≽94%) Pi uptake with a higher Sp (573-881 x 10-6 m s-1) than FB. During cyanobacterial blooms in FB (chla 17 μg 1-1), the water column dominated Pi uptake (100%) and Sp was the highest (>2,800 x 10-6 m s-1) measured. Phytoplankton accounted for 88% of this sequestered Pi with only 12% in the acid extractable fraction, likely as calcium bound and/or adsorbed P, and only 1% attributable to small heterotrophs. When chl α levels declined (2 μg I-1) Pi uptake was still dominated by phytoplankton (77%), the acid extractable pool increased (18%) and the heterotrophic community became more important (22%). In carbonate-dominated seagrass systems, Pi is primarily taken up by the water column biota and is subsequently remineralized/hydrolyzed in the water column or settles to the benthos where it becomes available to benthic primary producers.  相似文献   

19.
In April 2000, we collected box cores from five stations along a cross-shelf transect on the Louisiana (LA) continental shelf. Novel esters of carotenols and chlorins (carotenoid chlorin esters, CCEs), which are highly specific grazing markers, were identified in surface and deep sediments (>10 cm) from the LA shelf. Chlorophyll-a inventory indicated that CCEs are one of the major decay products of chlorophyll-a in shelf sediments. Abundances of total CCEs (9-18%) in surface sediments along the cross-shelf transect were comparable to the abundance of pheophytin-a, pyropheophytin-a, and total steryl chlorin esters (SCEs). Prior work has identified four CCEs which have dehydrated fucoxanthin/fucoxanthinol as a substitute alcohol of phytol. We report on four newly identified CCEs associated with nondehydrated fuxocanthin/fucoxanthinol esterified to (pyro)pheophorbide-a. These nondehydrated CCEs were generally present in lower concentrations than their dehydrated counterparts, but were detectable by atmospheric pressure chemical ionization (APCI) mass spectrometry coupled with high-performance liquid chromatography (HPLC). We attributed differences between this study and previous work to the time allowed for predepositional decay and grazing processes to occur. The rapid sedimentation of CCEs in the shallow water column (ca. 10 m) on the LA shelf allowed for effective burial of all CCEs compared to the deeper water column regions sampled by previous work. This speculation is supported by the fact that the concentrations of CCEs with nondehydrated fucoxanthin/fucoxanthinol were extremely low in sediments from the site on the outer LA shelf with a deeper (253 m) water column. We also tentatively identified an additional CCE and its isomer as fucoxanthinol didehydrate pyropheophorbide-a ester. We suggest that the formation and transformation of CCEs are primarily controlled by the following three biologically mediated reactions: demethoxycarbonylation, dehydration, and deacetylation. Our laboratory copepod grazing experiment also confirmed that CCEs can be excellent class-specific biomarkers of zooplankton grazing on phytoplankton.  相似文献   

20.
Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytoplankton biomass and composition were examined in Apalachicola Bay, Florida during two summers of contrasting river discharge. The <20 μm autotrophs were the main component (92?±?3 %; n?=?14) of phytoplankton biomass in lower (<25 psu) salinity waters. In these lower salinity waters containing higher dissolved inorganic nutrients, phycocyanin containing cyanobacteria made the greatest contribution to phytoplankton biomass (69?±?3 %; n?=?14) followed by <20 μm eukaryotes (19?±?1 %; n?=?14), and phycoerythrin containing cyanobacteria (4?±?1 %; n?=?14). In waters with salinity from 25 to 35 psu that were located within or in close proximity to the estuary, >20 μm diatoms were an increasingly (20 to 70 %) larger component of phytoplankton biomass. Lower summer river discharges that lead to an areal contraction of lower (5–25 psu) salinity waters composed of higher phytoplankton biomass dominated by small (<20 μm) autotrophs will lead to a concomitant areal expansion of higher (>25 psu) salinity waters composed of relatively lower phytoplankton biomass and a higher percent contribution by >20 μm diatoms. A reduction in summer river discharge that leads to such a change in quantity and quality of estuarine phytoplankton available will result in a reduction in estuarine zooplankton productivity and possibly the productivity of higher trophic levels.  相似文献   

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