共查询到20条相似文献,搜索用时 46 毫秒
1.
Autumn Oczkowski Scott Nixon Kelly Henry Peter DiMilla Michael Pilson Stephen Granger Betty Buckley Carol Thornber Richard McKinney Joaquin Chaves 《Estuaries and Coasts》2008,31(1):53-69
Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one
of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage
treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third
or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary
(macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ15N) and carbon (δ13C). The δ15N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source
loading. There is also evidence of a west to east gradient of heavy to light values of δ15N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett
Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ15N values in macroalgae there reflected preferential uptake of 14N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of
dissolved C species may control the observed δ13C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ15N (13.2 ± 0.54‰ SD) and δ13C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ15N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a
food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate
that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources. 相似文献
2.
Autumn Oczkowski Courtney Schmidt Emily Santos Kenneth Miller Alana Hanson Donald Cobb Jason Krumholz Adam Pimenta Leanna Heffner Sandra Robinson Joaquín Chaves Rick McKinney 《Estuaries and Coasts》2018,41(8):2260-2276
Over the past decade, nitrogen (N) loads to Narragansett Bay have decreased by more than 50%. These reductions were, in large part, the direct result of multiple wastewater treatment facility upgrades to tertiary treatment, a process which employs N removal. Here, we document ecosystem response to the N reductions and assess how the distribution of sewage N in Narragansett Bay has changed from before, during, and shortly after the upgrades. While others have observed clear responses when data were considered annually, our seasonal and regional comparisons of pre- and post-tertiary treatment dissolved inorganic nitrogen (DIN) concentrations and Secchi depth data, from bay-wide surveys conducted periodically from the early 1970s through 2016, resulted in only a few subtle differences. Thus, we sought to use stable isotope data to assess how sewage N is incorporated into the ecology of the Bay and how its distribution may have changed after the upgrades. The nitrogen (δ15N) and carbon (δ13C) stable isotope measurements of particulate matter served as a proxy for phytoplankton, while macroalgae served as short-term integrators of water column bio-available N, and hard clams (Mercenaria mercenaria) as integrators of water column production. In contrast to other estuarine stable isotope studies that have observed an increased influence of isotopically lower marine N when sewage N is reduced, the opposite has occurred in Narragansett Bay. The tertiary treatment upgrades have increased the effluent δ15N values by at least 2‰. The plants and animals throughout Narragansett Bay have similarly increased by 1–2‰, on average. In contrast, the δ13C values measured in particulate matter and hard clams have declined by about the same amount. The δ15N results indicated that, even after the N reductions, sewage N still plays an important role in supporting primary and secondary production throughout the bay. However, the δ13C suggests that overall net production in Narragansett Bay has decreased. In the 5 years after the major wastewater treatment facilities came on-line for nutrient removal, oligotrophication has begun but sewage remains the dominant source of N to Narragansett Bay. 相似文献
3.
L. C. Radke P. W. Ford I. T. Webster I. Atkinson G. Douglas K. Oubelkheir J. Li B. Robson B. Brooke 《Aquatic Geochemistry》2010,16(1):1-29
The Fitzroy River delivers large amounts of nutrients and fine sediments to Keppel Bay (contiguous with the Great Barrier
Reef Lagoon) during intermittent flow events. This study explores sources, forms and transformations of nutrients in Keppel
Bay, and develops a functional process zonation that integrates seabed geochemistry and water column nutrient characteristics
which are controlled by suspended sediment. The water column and seabed properties were investigated over two dry seasons,
with supplementary core incubations taken to measure carbon decomposition rates and nutrient fluxes. Keppel Bay can be divided
into three zones, the: zone of maximum resuspension (ZMR); coastal transitional zone (CTZ); and blue water zone (BWZ). Mineralisation
of predominantly terrestrial organic matter occurs in the ZMR where nutrient uptake by phytoplankton is light limited. The
CTZ and BWZ had higher light penetration and phytoplankton growth was likely limited by N and P, respectively. The identified
zones conform to the bathymetry and hydrodynamic characteristics of the bay, allowing for the development of an integrated
conceptual model accounting for the benthic and pelagic biogeochemical processes. Recognition of these different zones shows
that considerable variation in benthic and water column properties is possible within a small system with the bathymetric
and hydrodynamic characteristics of the fluidized bed reactor. 相似文献
4.
Scott W. Nixon 《Estuaries and Coasts》1997,20(2):253-261
Calculations by others of the preindustrial deposition of inorganic nitrogen from the atmosphere in the area of Narragansett Bay compared with recent measurements suggest that this flux has increased almost 15 times over natural background. On the basis of modern studies of the export of nitrogen and phosphorus from temperate forests, the prehistoric watershed also probably contributed very little reactive N or P to the bay. New information from undisturbed old-growth forests suggests that most of the N that was exported from the watershed was probably associated with refractory dissolved organic matter and thus contributed little to the fertility of the bay. The largest source of reactive dissolved inorganic nitrogen (DIN) and phosphorus (DIP) for Narragansett Bay under prehistoric conditions was the coastal ocean water entrained in the bay in estuarine circulation. The total input of DIN to this estuary has increased about five-fold and the input of total DIP has approximately doubled as a result of human activities. Recent ecosystem-level experiments using large (13 m3, 5 m deep) mesocosms designed as living models of Narragansett Bay showed that the primary production of phytoplankton in the bay is limited by the supply of DIN and that annual phytoplankton production is strongly correlated with the rate of input of DIN. The relationship between DIN input and annual phytoplankton production in the mesocosms is consistent with observations published by others working in 10 different natural marine systems, and a functional regression of the field and experimental data provides a tool to calculate the rate of prehistoric phytoplankton production that would have been associated with the prehistoric DIN input estimates. The result of this calculation suggests that phytoplankton production in the bay has approximately doubled (from about 130 g C m?2 yr?1 to 290 g C m?2 yr?1 for a baywide average) since the time of European contact. It also seems likely that seagrasses and macroalgae once made a much larger contribution to total system production than they do today. 相似文献
5.
James B. Cotner Rosa H. Sada Harvey Bootsma Thomas Johengen Joann F. Cavaletto Wayne S. Gardner 《Estuaries and Coasts》2000,23(5):611-620
We examined heterotrophic bacterial nutrient limitation at four sites in Florida Bay, U. S. in summer 1994 and winter 1995. Bacterial growth and biomass production in this system were most limited by inorganic phosphorus (P) in the eastern and southern regions of the bay. Nutrient additions stimulated productivity and biomass accumulation mostly in summer. The magnitude of growth responses (thymidine incorporation) to nutrient additions was nearly an order of magnitude less in winter than summer. Biomass-normalized alkaline phosphatase activity in the northeast and south-central region was 5–20 times greater than in the northwest and north-central regions, suggesting that P is most limiting to planktonic growth in those areas. Chlorophyll levels were higher in the northwest and north-central regions and P-uptake into particles >1 μm, primarily phytoplankton, was also higher in these regions. Consistent with these observations, others have observed that P is advected into the bay primarily in the northwestern region. Abundant seagrasses in Florida Bay may promote heterotrophic bacterial production relative to phytoplankton production by releasing dissolved organic carbon that makes bacteria more competitive for limiting quantities of inorganic phosphate, especially in the eastern bay where turbidity is low, P is most limiting, and light levels reaching the benthic plants are high. 相似文献
6.
7.
Nutrient dynamics in estuaries are temporally variable in response to changing physical–chemical conditions and biogeochemical
processes involving primary producer groups such as phytoplankton, microphytobenthos, seagrass and macroalgae. In order to
reveal intra-annual changes in the biomass of primary producer groups and associated changes in estuarine nutrient dynamics,
we developed a box model, coupling water inflows and outflows and nitrogen dynamics in Wilson Inlet, a large, central-basin-dominated,
intermittently closed estuary exposed to a Mediterranean climate in Western Australia. The model is calibrated and validated
with monitoring data, aquatic plant biomass estimates and biogeochemical rate measurements. Macrophytes and their microalgal
epiphytes appear to rapidly assimilate nutrients from the first flush from the catchment in winter, but this buffer capacity
then ceases, and a phytoplankton ‘bloom’ develops in response to subsequent river runoff events in spring. Significant amounts
of bioavailable nitrogen are exported to the ocean because phytoplankton predominance occurs while the sand bar is breached.
Surface sediments play a key role for nitrogen dynamics: In late spring to autumn, high light availability at the sediment
surface stimulates high primary production by microphytobenthos, leading to reduced benthic ammonium fluxes particularly in
the deep basin. Microphytobenthos contributes about 60% of annual whole-system primary production. Despite high benthic primary
production, nitrogen release from sediments is the biggest nitrogen source to the estuary. 相似文献
8.
Fluvial effects on nutrient and phytoplankton dynamics were evaluated in southern Kaneohe Bay, Oahu, Hawaii. Fluvial inputs occurred as small, steady baseflows interrupted by intense pulses of storm runoff. Baseflow river inputs only affected restricted areas around stream mouths, but the five storm events sampled during this study produced transient runoff plumes of much greater spatial extent. Nutrient loading via runoff generally led to an increase of the phytoplankton biomass and gross primary productivity in southern Kaneohe Bay, but the rapid depletion of nutrients resulted in a decline of the algal populations in the relatively short time of days. Under baseline conditions, water column primary productivity in southern Kaneohe Bay is normally nitrogen limited. Following storm events, the high ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIN:DIP, 25–29) fluxes of runoff nutrients drove bay waters towards phosphorus limitation. A depletion of phosphate relative to DIN in surface waters was observed following all storm events. Due to high flushing rates, recovery times of bay waters from storm perturbations ranged from 3 to 8 d and appeared to be correlated with tidal range. Storm inputs have a significant effect on the water column ecosystem and biogeochemistry in southern Kaneohe Bay. The perturbations were only transient events and the system rapidly recovered to prestorm conditions. 相似文献
9.
J.N Gearing P.J Gearing D.T Rudnick A.G Requejo M.J Hutchins 《Geochimica et cosmochimica acta》1984,48(5):1089-1098
An isotopic survey was made of organic carbon in phytoplankton, sediments, Zooplankton, larval fish, and benthic fauna from Narragansett Bay and the Marine Ecosystems Research Laboratory, Rhode Island; the results quantify the extent of variability in a phytoplankton-based ecosystem and elucidate some of its causes. Carbon from primary producers (phytoplankton) varied with taxon and size, ranging from ?20.3 ± 0.6%. (mean ± 1 s.d.) for diatoms (primarily Skeletonema costatum) to ?22.2 ± 0.6%. for nanoplankton (primarily microflagellates and non-motile ultraplankton). Planktonic isotope ratios varied little with either water temperature (0 to 20°C) or degree of preservation (up to 2-year aerobic diagenesis in sea water). Isotopically, sediments from East and West Passages of the bay were homogeneous with location and depth, with a mean (?21.8 ± 0.6%.) similar to a mixture of carbon from diatoms and nanoplankton. Providence River sediments reflected terrigenous and anthropogenic carbon (sewage) in their isotopic ratios (?24.2 ± 0.7%.). Ratios of macrozooplankton (> 150 μm) were statistically separable from those of concurrently collected phytoplankton, being, on average, 0.5 to 0.6%. more positive. Secondary consumers in the water column (shrimp and larval fish) were 2.4%. heavier than diatoms. Thirty-four taxa of benthic fauna had relatively positive isotope ratios (?18.1 ± 1.5%.) which may indicate preferential use of carbon originally from diatoms rather than nanoplankton. The wide range of benthic ratios (?22.7 to ?14.9%.) resulted from both intraspecific variability (mean range = 3%.) and the variety of trophic positions occupied. Some of the intraspecific variability could be related to size. Among species, the isotope ratios increased from meiofauna (?19.5 ± 0.4%.) to macrofaunal non-carnivores (?18.6 ± 1.3%.) and carnivores (?16.6 ± 0.8%.). 相似文献
10.
Understanding of the role of oceanic input in nutrient loadings is important for understanding nutrient and phytoplankton
dynamics in estuaries adjacent to coastal upwelling regions as well as determining the natural background conditions. We examined
the nitrogen sources to Yaquina Estuary (Oregon, USA) as well as the relationships between physical forcing and gross oceanic
input of nutrients and phytoplankton. The ocean is the dominant source of dissolved inorganic nitrogen (DIN) and phosphate
to the lower portion of Yaquina Bay during the dry season (May through October). During this time interval, high levels of
dissolved inorganic nitrogen (primarily in the form of nitrate) and phosphate entering the estuary lag upwelling favorable
winds by 2 days. The nitrate and phosphate levels entering the bay associated with coastal upwelling are correlated with the
wind stress integrated over times scales of 4–6 days. In addition, there is a significant import of chlorophyll a to the bay from the coastal ocean region, particularly during July and August. Variations in flood-tide chlorophyll a lag upwelling favorable winds by 6 days, suggesting that it takes this amount of time for phytoplankton to utilize the recently
upwelled nitrogen and be transported across the shelf into the estuary. Variations in water properties determined by ocean
conditions propagate approximately 11–13 km into the estuary. Comparison of nitrogen sources to Yaquina Bay shows that the
ocean is the dominant source during the dry season (May to October) and the river is the dominant source during the wet season
with watershed nitrogen inputs primarily associated with nitrogen fixation on forest lands. 相似文献
11.
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
12.
Sbil Seitzinger Scott Nixon Michael E.Q. Pilson Suzanne Burke 《Geochimica et cosmochimica acta》1980,44(11):1853-1860
Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N2 from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N2m?2 hr?1. This nitrogen flux is equal to approximately one-half of the NH+4flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N2 during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N2O, but the amount of nitrogen involved was only about 0.2 μmol m?2 hr?1 at 23°C. 相似文献
13.
The role of the microzooplankton community in regulating phytoplankton biomass was examined across a gradient from a river-dominated
estuary to an oceanic-influenced coastal zone. Three stations located along a salinity gradient from the central region of
Mobile Bay to 10 km off the coast were sampled from May 1994 to August 1995. Microzooplankton herbivory rates on phytoplankton
and microzooplankton excretion of nitrogen derived from phytoplankton were estimated using the dilution technique. Microzooplankton
grazing rates (range of station means=0.57–1.10 d−1) and phytoplankton growth rates (0.70–1.62 d−1) both increased across the salinity gradient from the bay station to the offshore station. However, the percent of primary
production grazed per day was highest at the bay station (mean=83%) and decreased to a low at the offshore station (mean=64%).
Excretion of phytoplankton-derived nitrogen by the microzooplankton was greatest at the bay and bay mouth stations. Excreted
nitrogen could potentially supply 39%, 29%, and 20% of phytoplankton nitrogen demand at the bay, bay mouth, and offshore stations,
respectively. These results support the idea that herbivorous microzooplankton are important in mediating nitrogen flow to
both lower and higher trophic levels. *** DIRECT SUPPORT *** A01BY085 00012 相似文献
14.
Bottom water hypoxic events were observed in Narragansett Bay, Rhode Island during the summer of 2001 using a towed sensor, vertical casts at fixed stations, and continuous monitoring buoys. This combination of approaches allowed for both extensive spatial and temporal sampling. Oxygen concentrations below the U.S. Environmental Protection Agency (EPA) acute hypoxia criterion of 2.3 mg l?1 were observed in the northern parts of Narragansett Bay, including the Providence River. We estimate 39% of the area of the Providence River was affected by acute hypoxia between July and September 2001. All other regions experienced only small areas of acute hypoxia (<5%), and no acute hypoxia was observed from Quonset Point south. The area encompassing oxygen concentrations below the EPA chronic hypoxia criterion of 4.8 mg l?1 was much more extensive in the upper half of Narragansett Bay, sometimes covering the majority of the region, though it is unclear whether exposure to concentrations below this criterion persisted long enough to significantly affect marine species in these areas. Vertical profiles of dissolved oxygen typically exhibited a mid water oxygen minimum near the pycnocline, followed by a slight increase in oxygen with depth. The surface waters above the pycnocline were typically supersaturated with oxygen. The northern portions of the Bay where the most extensive hypoxia was observed corresponded to the regions with both the greatest thermohaline stratification, the highest nutrient inputs, and the highest primary productivity. 相似文献
15.
An ichthyoplankton survey (18 stations in seven sampling sectors) was conducted in Narragansett Bay in 1990 to provide information on abundance, distribution, and seasonal occurrence of eggs and larvae of estuarine fishes, including seasonal migrants. An additional goal was to examine changes in species composition, abundance, and distribution occurring since the last baywide survey in 1972–73. The taxonomic composition of eggs and larvae in 1990 (41 species in 25 families from 684 plankton samples) and in 1972–73 (43 species in 28 families from 6900 samples) was similar. Maximum abundance of fish eggs occurred in June and larvae in July, minimum abundance in September to February. Species diversity was greatest in May–July and lowest during January in both surveys. However, egg and larval densities in 1990 were considerably lower than in 1972–73. Bay anchovy, tautog, and cunner accounted for 86% of the eggs and 87% of the larvae in the bay in 1990. These three species accounted for only 55% of the eggs and 51% of the larvae in 1972–73, with menhaden accounting for another 18% of the eggs and 34% of the larvae. Searobins, scup, and butterfish eggs were common in 1973 (19%) but rare in 1990 (2%). Ichthyoplankton abundance for several of the most abundant species was significantly lower (p<0.05) in the Providence River, upper bay, and Greenwich Bay in 1990 than in 1972–73. Density of fish eggs and larvae in the lower portions of the bay was lower in 1990 for some species but not others. Distribution data suggested a general down-bay shift in density in 1990. *** DIRECT SUPPORT *** A01BY085 00015 相似文献
16.
Six synoptic samplings of nutrient concentrations of the water column and point-source inputs (rivers, sewage treatment plants) were conducted in the Seekonk-Providence River region of Narragansett Bay. Concentrations of nutrients (NH4 +, NO2 ?+NO3 ?, PO4 ?3, dissolved silicon, particulate N, particulate C) were predicted using a conservative, two-layer box model in order to assess the relative influence of external inputs and internal processes on observed concentrations. Although most nutrients were clearly affected by processes internal to the system, external input and mixing explained most of the variability in and absolute magnitude of observed concentrations, especially for dissolved constituents. In the bay as a whole, two functionally distinct regions can now be identified: the Seekonk-Providence River, where dissolved nutrient concentrations are externally controlled and lower Narragansett Bay where internal processes regulate the behavior of nutrients. A preliminary nitrogen budget suggests that the Seekonk-Providence River exports some 95% of the nitrogen entering the system via point sources and bottom water from upper Narragansett Bay. 相似文献
17.
Macronutrients and micronutrients were measured during the phytoplankton bloom period and then seasonally monitored after
the bloom in the polluted Izmir Bay. Iron and the macronutrients (phosphate, ammonium, nitrate, nitrite, and silicate) were
abundant in the waters of the inner and middle sections of Izmir Bay. The iron concentration decreased exponentially from
the eutrophic inner bay to the oligotrophic outer bay. Suboxic–anoxic processes and the resuspension dynamics in the sediment
were the most important factor in the control of iron, ammonium, and phosphate enrichment in the bay beside the anthropogenic
activities. The biological removal of Fe in the inner and middle bay and nonbiological removal in the outer bay were effective
in controlling iron concentration in Izmir Bay. The nitrate, nitrite, and ammonium nitrogen (N) and Si decreased to critical
levels in the middle and outer bay at the end of the summer as long as the concentration of phosphate was high. The N/P ratios
in the bay suggested that N might be the controlling nutrient for phytoplankton growth particularly in the middle and outer
bay throughout summer. Furthermore, Si was also able to have controlling impact probably on diatom growth during autumn and
winter in the inner and middle bay and in the early spring in the outer bay. The N/Si/Chelex labile Fe ratios implied that
the iron could be a critical controlling nutrient for phytoplankton growth during early April in the outer bay unless the
other macronutrients were low. 相似文献
18.
Baseflow and storm runoff fluxes of water, suspended particulate matter (SPM), and nutrients (N and P) were assessed in conservation,
urban, and agricultural streams discharging to coastal waters around the tropical island of Oahu, Hawai‘i. Despite unusually
low storm frequency and intensity during the study, storms accounted for 8–77% (median 30%) of discharge, 57–99% (median 93%)
of SPM fluxes, 11–79% (median 36%) of dissolved nutrient fluxes and 52–99% (median 85%) of particulate nutrient fluxes to
coastal waters. Fluvial nutrient concentrations varied with hydrologic conditions and land use; land use also affected water
and particulate fluxes at some sites. Reactive dissolved N:P ratios typically were ≥16 (the ‘Redfield ratio’ for marine phytoplankton),
indicating that inputs could support new production by coastal phytoplankton, but uptake of dissolved nutrients is probably
inefficient due to rapid dilution and export of fluvial dissolved inputs. Particulate N and P fluxes were similar to or larger
than dissolved fluxes at all sites (median 49% of total nitrogen, range 22–82%; median 69% of total phosphorus, range 49–93%).
Impacts of particulate nutrients on coastal ecosystems will depend on how efficiently SPM is retained in nearshore areas,
and on the timing and degree of transformation to reactive dissolved forms. Nevertheless, the magnitude of particulate nutrient
fluxes suggests that they represent a significant nutrient source for many coastal ecosystems over relatively long time scales
(weeks–years), and that reductions in particulate nutrient loading actually may have negative impacts on some coastal ecosystems. 相似文献
19.
Spatial and temporal characteristics of nutrient and phytoplankton dynamics in the York River Estuary, Virginia: Analyses of long-term data 总被引:1,自引:0,他引:1
Ten years (1985–1994) of data were analyzed to investigate general patterns of phytoplankton and nutrient dynamics, and to identify major factors controlling those dynamics in the York River Estuary, Virginia. Algal blooms were observed during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas peak phytoplankton biomass during the summer bloom occurred in the tidal fresh-mesohaline transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential N and P limitation. Phytoplankton biomass in tidal fresh water regions was limited by high flushing rates. Water residence time was less than cell doubling time during high flow seasons. Positive correlations between PAR at 1 m depth and chlorophylla suggested light limitation of phytoplankton in the tidal fresh-mesohaline transition zone. Relationships of salinity difference between surface and bottom water with chlorophylla distribution suggested the importance of tidal mixing for phytoplankton dynamics in the mesohaline zone. Accumulation of phytoplankton biomass in the mesohaline zone was generally controlled by N with the nutrient supply provided by benthic or bottom water remineralization. 相似文献
20.
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