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1.
Gry Mine Berg Patricia M. Glibert Niels O. G. Jørgensen Maija Balode Ingrida Purina 《Estuaries and Coasts》2001,24(2):204-214
Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1−1 in the northern region (mouth) and 41±5 μg-at N 1−1 in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with15N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1−1 h−1 in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 μg-at N 1−1 h−1 in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells <5 μm, while up to 67% of the community in the northern part was composed of cells >5 μm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf. 相似文献
2.
Isotopic biogeochemistry of dissolved organic nitrogen: A new technique and application 总被引:1,自引:0,他引:1
We present a new technique for isolating and isotopically characterizing dissolved organic nitrogen (DON) for non-marine waters, δ15N values for DON from lacustrine samples and data suggesting that this technique will be applicable to marine samples. Our technique involves preconcentration of DON via rotary evaporation and removal of dissolved inorganic nitrogen (DIN) via dialysis using a membrane that retains material above 100 Da. Results demonstrate quantitative removal of DIN, complete recovery of DON (95% or greater) and retention of isotopic integrity (isotope effect less than 0.4‰) for a solution containing a DON standard (tripeptide) and DIN in deionized water. Reproducibility of carbon and nitrogen isotope values and elemental concentrations is demonstrated for DOM from Chefswet Basin, Lake Superior and Grand Traverse Bay, Lake Michigan. The applicability of this technique to marine samples is suggested by demonstrating 99% removal of DIN from a sample of Gulf Stream water amended with ammonium and nitrate. 相似文献
3.
Characteristics of dissolved organic nitrogen (DON) in the surface water of Beijing Olympic Forest Park 总被引:1,自引:0,他引:1
Shouliang Huo Honglei Yu Beidou Xi Fengyu Zan Chaowei Zhu Jingtian Zhang 《Environmental Earth Sciences》2014,71(9):4021-4028
The characteristics of dissolved organic nitrogen (DON) in surface water from Beijing Olympic Forest Park (BOFP) were investigated in this study. Nanofiltration (NF) pretreatment procedure using two NF membranes (NF90 and NF270) was applied to increase the accuracy and precision of DON measurements in surface water samples with high dissolved inorganic nitrogen/total dissolved nitrogen (DIN/TDN) ratios. Compared to NF90, NF270 showed better performance in lowering the DIN/TDN ratio and retaining DOC in both the synthetic water and raw water samples. DON concentrations ranged from 0.01 to 0.83 mg N L?1 in water samples collected over four different months and showed a seasonal variation. The DON increased in summer due to the higher activity of decomposers on recent litterfall or because of a higher production of biomass in the surface water body. The molecular weight (MW) fractions of <3 kDa accounted for more than 50 % of the total DOC concentration and the fractions of <3 kDa contributed to more than 48 % of the total DON concentration. It could be concluded that most of the DON present in surface water of BOFP was composed of small molecules, which were mainly composed of monomers such as amino acids and urea, readily available for the uptake by phytoplankton and heterotrophic bacteria. 相似文献
4.
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
5.
Jenifer E. Dugan David M. Hubbard Henry M. Page Joshua P. Schimel 《Estuaries and Coasts》2011,34(4):839-850
We investigated the role of sandy beaches in nearshore nutrient cycling by quantifying macrophyte wrack inputs and examining
relationships between wrack accumulation and pore water nutrients during the summer dry season. Macrophyte inputs, primarily
giant kelp Macrocystis pyrifera, exceeded 2.3 kg m−1 day−1. Mean wrack biomass varied 100-fold among beaches (range = 0.41 to 46.43 kg m−1). Mean concentrations of dissolved inorganic nitrogen (DIN), primarily NOx−-N, and dissolved organic nitrogen (DON) in intertidal pore water varied significantly among beaches (ranges = 1 to 6,553 μM
and 7 to 2,006 μM, respectively). Intertidal DIN and DON concentrations were significantly correlated with wrack biomass.
Surf zone concentrations of DIN were also strongly correlated with wrack biomass and with intertidal DIN, suggesting export
of nutrients from re-mineralized wrack. Our results suggest beach ecosystems can process and re-mineralize substantial organic
inputs and accumulate dissolved nutrients, which are subsequently available to nearshore waters and primary producers. 相似文献
6.
H. N. McKellar D. L. Tufford M. C. Alford P. Saroprayogi B. J. Kelley J. T. Morris 《Estuaries and Coasts》2007,30(6):989-1006
Tidal freshwater sections of the Cooper River Estuary (South Carolina) include extensive wetlands, which were formerly impounded
for rice culture during the 1,700s and 1,800s. Most of these former rice fields are now open to tidal exchange and have developed
into productive wetlands that vary in bottom topography, tidal hydrography and vegetation dominants. The purpose of this project
was to quantify nitrogen (N) transport via tidal exchange between the main estuarine channel and representative wetland types
and to relate exchange patterns to the succession of vegetation dominants. We examined N concentration and mass exchange at
the main tidal inlets for the three representative wetland types (submerged aquatic vegetation [SAV], floating leaf vegetation,
and intertidal emergent marsh) over 18-21 tidal cycles (July 1998–August 2000). Nitrate + nitrite concentrations were significantly
lower during ebb flow at all study sites, suggesting potential patterns of uptake by all wetland types. The magnitude of nitrate
decline during ebb flow was negatively correlated with oxygen concentration, reflecting the potential importance of denitrification
and nitrate reduction within hypoxic wetland waters and sediments. The net tidal exchange of nitrate + nitrite was particularly
consistent for the intertidal emergent marsh, where flow-weighted ebb concentrations were usually 18–40% lower than during
flood tides. Seasonal patterns for the emergent marsh indicated higher rates of nitrate + nitrite uptake during the spring
and summer (> 400 μmol N m-2 tide-1) with an annual mean uptake of 248 ± 162 μmol m–2 tide–1. The emergent marsh also removed ammonium through most of the year (207 ± 109 μmol m–2 tide–1), and exported dissolved organic nitrogen (DON) in the fall (1,690 ± 793 μmol m–2 tide–1), suggesting an approximate annual balance between the dissolved inorganic N uptake and DON export. The other wetland types
(SAV and floating leaf vegetation) were less consistent in magnitude and direction of N exchange. Since the emergent marsh
site had the highest bottom elevation and the highest relative cover of intertidal habitat, these results suggest that the
nature of N exchange between the estuarine waters and bordering wetlands is affected by wetland morphometry, tidal hydrography,
and corresponding vegetation dominants. With the recent diversion of river discharge, water levels in the upper Cooper estuary
have dropped more than 10 cm, leading to a succession of wetland communities from subtidal habitats toward more intertidal
habitats. Results of this study suggest that current trends of wetland succession in the upper Cooper River may result in
higher rates of system-wide inorganic N removal and DON inputs by the growing distributions of intertidal emergent marshes. 相似文献
7.
Inorganic nitrogen dynamics in intertidal rocky biofilms and sediments of the Douro River estuary (Portugal) 总被引:1,自引:0,他引:1
Catarina M. Magalhäes William J. Wiebe Samantha B. Joye Adriano A. Bordalo 《Estuaries and Coasts》2005,28(4):592-607
In this study rates of oxygen, ammonium (NH4
+), nitrate (NO3
−), nitrite (NO2
−), and nitrous oxide (N2O) fluxes, nitrogen (N) fixation, nitrification, and denitrification were compared between two intertidal sites for which
there is an abundant global literature, muddy and sandy sediments, and two sites representing the rocky intertidal zone where
biogeochemical processes have scarcely been investigated. In almost all sites oxygen production rates greatly exceeded oxygen
consumption rates. During daylight, NH4
+ and NO3
− uptake rates together with ammonification could supply the different N requirements of the primary producer communities at
all four sites; N assimilation by benthic or epilithic primary producers was the major process of dissolved inorganic nitrogen
(DIN) removal; N fixation, nitrification, and denitrification were minor processes in the overall light DIN cycle. At night,
distinct DIN cycling processes took place in the four environments, denitrification rates ranged from 9 ± 2 to 360 ± 30 μmol
N2 m−2 h−1, accounting for 10–48% of the water column NO3
− uptake; nitrification rates varied from 0 to 1712 ± 666 μmol NH4
+ m−2 h−1. A conceptual model of N cycle dynamics showed major differences between intertidal sediment and rocky sites in terms of
the mean rates of DIN net fluxes and the processes involved, with rocky biofilm showing generally higher fluxes. Of particular
significance, the intertidal rocky biofilms released 10 times the amount of N2O produced in intertidal sediments (up to 17 ± 6 μmol N2O m−2 h−1), representing the highest N2O release rates ever recorded for marine systems. The biogeochemical contributions of intertidal rocky substrata to estuarine
and coastal processes warrant future detailed investigation. 相似文献
8.
Thomas C. Malone Daniel J. Conley Thomas R. Fisher Patricia M. Glibert Lawrence W. Harding Kevin G. Sellner 《Estuaries and Coasts》1996,19(2):371-385
The scales on which phytoplankton biomass vary in response to variable nutrient inputs depend on the nutrient status of the plankton community and on the capacity of consumers to respond to increases in phytoplankton productivity. Overenrichment and associated declines in water quality occur when phytoplankton growth rate becomes nutrient-saturated, the production and consumption of phytoplankton biomass become uncoupled in time and space, and phytoplankton biomass becomes high and varies on scales longer than phytoplankton generation times. In Chesapeake Bay, phytoplankton growth rates appear to be limited by dissolved inorganic phosphorus (DIP) during spring when biomass reaches its annual maximum and by dissolved inorganic nitrogen (DIN) during summer when phytoplankton growth rates are highest. However, despite high inputs of DIN and dissolved silicate (DSi) relative to DIP (molar ratios of N∶P and Si∶P>100), seasonal accumulations of phytoplankton biomass within the salt-intruded-reach of the bay appear to be limited by riverine DIN supply while the magnitude of the spring diatom bloom is governed by DSi supply. Seasonal imbalances between biomass production and consumption lead to massive accumulations of phytoplankton biomass (often>1,000 mg Chl-a m?2) during spring, to spring-summer oxygen depletion (summer bottom water <20% saturation), and to exceptionally high levels of annual phytoplankton production (>400 g m?2 yr?1). Nitrogen-dependent seasonal accumulations of phytoplankton biomass and annual production occur as a consequence of differences in the rates and pathways of nitrogen and phosphorus cycling within the bay and underscore the importance of controlling nitrogen inputs to the mesohaline and lower reaches of the bay. 相似文献
9.
Leucine and thymidine incorporation were examined in size-fractionated estuarine communities and in cultures of phytoplankton
known to use dissolved organic nitrogen (DON). Cultured phytoplankton species were used to establish that phytoplankton took
up leucine and thymidine into protein and DNA, respectively. Subsequently, incorporation of leucine and thymidine was measured
in size-fractionated populations collected from the Lafayette River, VA, a eutrophic estuary where resident populations contain
bloom-forming phytoplankton known to take up DON, and the Gulf of Mexico during a bloom of the mixotrophic red tide dinoflagellate,
Karenia brevis. We examined the efficacy of size fractionation for determining phytoplankton versus bacterial incorporation of leucine and
thymidine under conditions employed during bacterial productivity bioassays, and antibiotics were used to distinguish between
bacterial and phytoplankton incorporation in cultured and natural populations. Results suggest that cultures and natural assemblages
of phytoplankton can take up both leucine and thymidine when supplied at low concentrations (10 and 12 nmol L−1, respectively) and during short incubations (15 min to 1 h). In natural populations, up to 95% of the leucine and thymidine
incorporation during short bioassays was recovered in the >5.0-μm size fraction that contained ≤4.2% of the bacterial biomass. 相似文献
10.
Jie Xu Patricia M. Glibert Hongbin Liu Kedong Yin Xiangcheng Yuan Mianrun Chen Paul J. Harrison 《Estuaries and Coasts》2012,35(2):559-571
Phytoplankton uptake rates of ammonium (NH4
+), nitrate (NO3
−), and urea were measured at various depths (light levels) in Hong Kong waters during the summer of 2008 using 15N tracer techniques in order to determine which form of nitrogen (N) supported algal growth. Four regions were sampled, two
differentially impacted by Pearl River discharge, one impacted by Hong Kong sewage discharge, and a site beyond these influences.
Spatial differences in nutrient concentrations, ratios, and phytoplankton biomass were large. Dissolved nutrient ratios suggested
phosphorus (P) limitation throughout the region, largely driven by high N loading from the Pearl River in summer. NH4
+ and urea made up generally ≥50% of the total N taken up and the f ratio averaged 0.26. Even at the river-impacted site where concentrations of NO3
− were >20 μM N, NH4
+ comprised >60% of the total N uptake. Inhibition experiments demonstrated that NO3
− uptake rates were reduced by 40% when NH4
+ was >5 μM N. The relationship between the total specific uptake rates of N (sum of all measured substrates, V, per hour) and the chlorophyll a-specific rates (micromolars of N per microgram of Chl a per hour) varied spatially with phytoplankton biomass. Highest uptake rates and biomass were observed in southern waters,
suggesting that P limitation and other factors (i.e., flushing rate) controlled production inshore and that the unincorporated
N (mainly NO3
−) was transported offshore. These results suggest that, at the beginning of summer, inshore algal blooms are fueled primarily
by NH4
+ and urea, rather than NO3
−, from the Pearl River discharge. When NH4
+ and urea are depleted, then NO3
− is taken up and can increase the magnitude of the bloom. 相似文献
11.
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
12.
Dissolved organic carbon (DOC) flux dynamics were examined in the context of other biogeochemical cycles in intertidal sediments inhabited by benthic microalgae. In August 2003, gross oxygenic photosynthetic (GOP) rates, oxygen penetration depths, and benthic flux rates were quantified at seven sites along the Duplin River, GA, USA. Sediments contained abundant benthic microalgal (BMA) biomass with a maximum chlorophyll a concentration of 201 mg chl a m?2. Oxygen microelectrodes were used to determine GOP rates and O2 penetration depth, which were tightly correlated with light intensity. Baseline and 15N-nitrate amended benthic flux core incubations were employed to quantify benthic fluxes and to investigate the impact of BMA on sediment water exchange under nitrogen (N)-limited and N-replete conditions. Unamended sediments exhibited tight coupling between GOP and respiration and served as a sink for water column dissolved inorganic nitrogen (DIN) and a source of silicate and dissolved inorganic carbon (DIC). The BMA response to the N addition indicated sequential nutrient limitation, with N limitation followed by silicate limitation. In diel (light–dark) incubations, biological assimilation accounted for 83% to 150% of the nitrate uptake, while denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) accounted for <7%; in contrast, under dark conditions, DNF and DNRA accounted for >40% of the NO3 ? uptake. The N addition shifted the metabolic status of the sediments from a balance of autotrophy and heterotrophy to net autotrophy under diel conditions, and the sediments served as a sink for water column DIN, silicate, and DIC but became a source of DOC, suggesting that the increased BMA production was decoupled from sediment bacterial consumption of DOC. 相似文献
13.
Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds
N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for
fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen,
as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different
sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they
were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the
autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB)
activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand
or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment
type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation
by MPB, based on both net primary production (0.7–6.5 mmol N m−2 d−1) and on 80% of gross primary production (1.9–9.4 mmol N m−2 d−1) far exceeded measured rates of denitrification (0.01–0.16 mmol N m−2 d−1). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification
removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal,
shallow-water sediments. 相似文献
14.
Long-Term and Seasonal Changes in Nutrients,Phytoplankton Biomass,and Dissolved Oxygen in Deep Bay,Hong Kong 总被引:1,自引:0,他引:1
Jie Xu Kedong Yin Joseph H. W. Lee Hongbin Liu Alvin Y. T. Ho Xiangcheng Yuan Paul J. Harrison 《Estuaries and Coasts》2010,33(2):399-416
Deep Bay is a semienclosed bay that receives sewage from Shenzhen, a fast-growing city in China. NH4 is the main N component of the sewage (>50% of total N) in the inner bay, and a twofold increase in NH4 and PO4 concentrations is attributed to increased sewage loading over the 21-year period (1986–2006). During this time series, the
maximum annual average NH4 and PO4 concentrations exceeded 500 and 39 μM, respectively. The inner bay (Stns DM1 and DM2) has a long residence time and very
high nutrient loads and yet much lower phytoplankton biomass (chlorophyll (Chl) <10 μg L−1 except for Jan, July, and Aug) and few severe long-term hypoxic events (dissolved oxygen (DO) generally >2 mg L−1) than expected. Because it is shallow (~2 m), phytoplankton growth is likely limited by light due to mixing and suspended
sediments, as well as by ammonium toxicity, and biomass accumulation is reduced by grazing, which may reduce the occurrence
of hypoxia. Since nutrients were not limiting in the inner bay, the significant long-term increase in Chl a (0.52–0.57 μg L−1 year−1) was attributed to climatic effects in which the significant increase in rainfall (11 mm year−1) decreased salinity, increased stratification, and improved water stability. The outer bay (DM3 to DM5) has a high flushing
rate (0.2 day−1), is deeper (3 to 5 m), and has summer stratification, yet there are few large algal blooms and hypoxic events since dilution
by the Pearl River discharge in summer, and the invasion of coastal water in winter is likely greater than the phytoplankton
growth rate. A significant long-term increase in NO3 (0.45–0.94 μM year−1) occurred in the outer bay, but no increasing trend was observed for SiO4 or PO4, and these long-term trends in NO3, PO4, and SiO4 in the outer bay agreed with those long-term trends in the Pearl River discharge. Dissolved inorganic nitrogen (DIN) has
approximately doubled from 35–62 to 68–107 μM in the outer bay during the last two decades, and consequently DIN to PO4 molar ratios have also increased over twofold since there was no change in PO4. The rapid increase in salinity and DO and the decrease in nutrients and suspended solids from the inner to the outer bay
suggest that the sewage effluent from the inner bay is rapidly diluted and appears to have a limited effect on the phytoplankton
of the adjacent waters beyond Deep Bay. Therefore, physical processes play a key role in reducing the risk of algal blooms
and hypoxic events in Deep Bay. 相似文献
15.
A study of nutrient limitation of phytoplankton biomass production with emphasis on nitrate-nitrogen (NO3 ?) and ortho-phosphate-phosphorus (PO4 3?) was conducted in Perdido Bay, Alabama-Florida. The experimental design employed 18-1 outdoor microcosms operated in a static renewal mode. Phytoplankton growth responses (i.e., growth stimulation) measured as chlorophyll a (chl a) fell into three principal categories: primary P stimulation occurred mostly during the cooler months at the upper bay (tidal brackish) and mid bay (lower mesohaline) stations; a total of 12 out of 36 experiments; primary N stimulation occurred mostly during the warmer months primarily at the mid-bay station and infrequently at the upper and lower bay stations (upper mesohaline); a total of 7 out of 36 experiments; and N+P costimulation occurred primarily during the warmer months in the upper bay and mid bay and during both warmer and cooler months of the lower bay; a total of 17 out of 36 experiments. Primary P stimulation was generally associated with high ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) (ratio range: 18 to 288). Conversely, primary N stimulation was associated with decreasing DIN:DIP ratios (range 8–46). Redfield ratios of particulate organic N (PON) to particulate organic P (POP) often indicated N limitation (i.e., values often less than 10). PON:chl a ratios often indicated N sufficiency, but three occasions were noted where PON:POP and PON:chl a ratios were not congruent. It is difficult to reconcile the inorganic and organic N and P ratios with the relatively low DIP and DIN concentrations. The phytoplankton assemblage appeared not to be strongly nutrient-limited but, given a nutrient increase, responded differentially to N and P, both seasonally and along the longitudinal salinity gradient. Grazing pressure in concert with nutrient limitation was advanced as an hypothesis to explain N+P co-limitation. 相似文献
16.
Xiangcheng Yuan Patricia M. Glibert Jie Xu Hao Liu Mianrun Chen Hongbin Liu Kedong Yin Paul J. Harrison 《Estuaries and Coasts》2012,35(1):325-334
Measurements of uptake rates of inorganic (NO3− and NH4+) and organic (urea, glycine, and glutamic acid) N, and indirect estimates of total N uptake by bacteria, were made in four
contrasting environments in sub-tropical Hong Kong waters in summer of 2008. In addition, the effects of several days of rain
on N uptake rates were studied in eastern waters. Although ambient NO3− was the dominant form of N in Hong Kong waters, the dominant N form taken up by phytoplankton was usually NH4+ and organic N, including urea and amino acids, rather than NO3−. Hence, because of the low NO3− uptake, there was a long turnover time for NO3− (100 days), and most of the NO3− was apparently transported offshore into deeper shelf waters. In eastern waters where NH4+ was undetectable, NO3− uptake rates were positively correlated with phytoplankton cell size. In contrast, potential rates of glutamic acid uptake
were negatively correlated with phytoplankton size. N uptake rates in the smaller size fraction (0.7–2.8 μm) were less affected
by the rain event, and smaller phytoplankton appeared to outcompete larger cells after several days of rain. The surface (PN)-specific
N uptake rates in the >8-μm fraction decreased from 0.02 to 0.0001 h−1, while the smaller fraction only exhibited a one- to threefold decrease after the rainfall. In contrast, bacterial production
and N uptake were not affected by the rain event, and bacteria N uptake accounted for 10–60% of the total N uptake by phytoplankton. 相似文献
17.
Michael J. Durako Piotr Kowalczuk Michael A. Mallin William J. Cooper Jason J. Souza David H. Wells 《Estuaries and Coasts》2010,33(6):1430-1441
Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m3s−1) was only 25% of the wet year discharge (429 ± 337 m3s−1). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter
(CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to
PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied
little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher
nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a
CDOM
(412)] ranged from 0.05 to 8.25 m−1 with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater
river inputs, CDOM may exert a major limiting influence over near-shore primary production. 相似文献
18.
We investigated if the success of the invasive common reed Phragmites australis could be attributed to a competitive ability to use dissolved organic nitrogen (DON) when compared to the dominant macrophyte
Spartina alterniflora in tidal wetlands. Short-term nutrient uptake experiments were performed in the laboratory on two genetic lineages of Phragmites (native and introduced to North America) and S. alterniflora. Our results provide the first evidence for direct assimilation of DON by temperate marsh plants and indicate that amino
acids are assimilated intact by all plant types at similar rates. Both Phragmites lineages had significantly greater urea–N assimilation rates than S. alterniflora, and the affinity for dissolved inorganic nitrogen (DIN) species was the greatest in native Phragmites > introduced Phragmites > S. alterniflora. Field studies demonstrated uptake of both DON and DIN in similar proportion as those determined in the laboratory experiments.
Based on these uptake rates, we estimate that DON has the potential to account for up to 47% of N demand for Phragmites plants, and up to 24% for S. alterniflora plants. Additionally, we suggest that differences in N uptake between native and introduced Phragmites lineages explain one mechanism for the success of the introduced type under increasingly eutrophic conditions. 相似文献
19.
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
20.
To gain insight into the importance of the benthos in carbon and nutrient budgets of Boston Harbor and surrounding bays, we measured sediment-water exchanges of oxygen, total carbon dioxide (DIC), nitrogen (ammonium, nitrate+nitrite, urea, N2O), silicate, and phosphorus at several stations in different sedimentary environments just prior to and subsequent to cessation of sewage sludge disposal in the harbor. The ratio of the average annual DIC release to O2 uptake at three primary stations ranged from 0.84 to 1.99. Annual average DIC:DIN flux ratios were consistently greater than predicted from the Redfield ratio, suggesting substantial losses of mineralized N. The pattern was less clear for P: some stations showed evidence that the sediments were a sink for P while others appeared to be a net source to the water column over the study period. In general, temporal and spatial patterns of respiration, nutrient fluxes, and flux ratios were not consistently related to measures of sediment oxidation-reduction status such as Eh or dissolved sulfide. Sediments from Boston Harbor metabolize a relatively high percentage (46%) of the organic matter inputs from phytoplankton production and allochthonous inputs when compared to most estuarine systems. Nutrient regeneration from the benthos is equivalent to 40% of the N, 29% of the P, and more than 60% of the Si demand of the phytoplankton. However, the role of the benthos in supporting primary production at the present time may be minor as nutrient inputs from sewage and other sources exceed benthic fluxes of N and P by 10-fold and Si by 4-fold. Our estimates of denitrification from DIC:DIN fluxes suggests that about 45% of the N mineralized in the sediments is denitrified, which accounts for about 17% of the N inputs from land. 相似文献