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1.
Sediment cores were collected from the Neuse and Pamlico River estuaries, North Carolina, at seven different sites, and the data show strong anthropogenic influence on water quality. The sediments from these cores were dated using210Pb,137Cs,14C, and pollen horizon techniques. Specific parameters investigated include bulk density, sedimentation rates, diatom assemblage changes, nutrient and trace metal flux, and vegetation changes as recorded in the pollen record. The greatest increases in sedimentation, nutrient and metal flux and changes in diatom assemblages have occurred in the past 50–60 yr in the Pamlico and Neuse. Diatom diversity has decreased and small planktonic forms have become dominant over time, most likely due to eutrophication and increased turbidity and sedimentation. Major changes occur before phytoplankton surveys and monitoring were initiated. Overall trends are similar to those found in Chesapeake Bay, although the time frame of major changes is more recent. Dominant small planktonic diatom species differ between Chesapeake Bay and the Neuse and Pamlico. Variance in paleoecological indicators between these mid-Atlantic estuaries may be due to geomorphology and land use history.  相似文献   

2.
Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.  相似文献   

3.
Freshwater inputs often play a more direct role in estuarine phytoplankton biomass (chlorophyll a) accumulation than nitrogen (N) inputs, since discharge simultaneously controls both phytoplankton residence time and N loading. Understanding this link is critical, given potential changes in climate and human activities that may affect discharge and watershed N supply. Chlorophyll a (chla) relationships with hydrologic variability were examined in 3-year time series from two neighboring, shallow (<5?m), microtidal estuaries (New and Neuse River estuaries, NC, USA) influenced by the same climatic conditions and events. Under conditions ranging from drought to floods, N concentration and salinity showed direct positive and negative responses, respectively, to discharge for both estuaries. The response of chla to discharge was more complex, but was elucidated through conversion of discharge to freshwater flushing time, an estimate of transport time scale. Non-linear fits of chla to flushing time revealed non-monotonic, unimodal relationships that reflected the changing balance between intrinsic growth and losses through time and along the axis of each estuary. Maximum biomass occurred at approximately 10-day flushing times for both systems. Residual analysis of the fitted data revealed positive relationships between chla and temperature, suggesting enhanced growth rates at higher temperatures. N loading and system-wide, volume-weighted chla were positively correlated, and biomass yields per N load were greater than other marine systems. When combined with information on loss processes, these results on the hydrologic control of phytoplankton biomass will help formulate mechanistic models necessary to predict ecosystem responses to future climate and anthropogenic changes.  相似文献   

4.
Menhaden are one of the most abundant components of fish communities in Gulf and Atlantic estuaries. Juvenile menhaden have been reported to have zooplankton, phytoplankton, andSpartina-derived detritus in their guts. However, there has been disagreement over the importance of the detritus as a food source. We show, using physiological and stable isotope evidence, that detritus can be used by juvenile Gulf menhaden. Their diet is very roughly 30% detritus- and 70% plankton-based.  相似文献   

5.
Estuarine turbidity maxima (ETM) play an important role in zooplankton and larval fish productivity in many estuaries. Yet in many of these systems, little is known about the food web that supports this secondary production. To see if phytoplankton have the potential to be a component of the ETM food web in the Chesapeake Bay estuary a series of cruises were carried out to determine the biomass distribution and floral composition of phytoplankton in and around the ETM during the winter and spring using fluorometry, high-performance liquid chromatography (HPLC), and microscopy. Two distinct phytoplankton communities were observed along the salinity gradient. In lower salinity waters, biomass was low and the community was composed mostly of diatoms, while in more saline waters biomass was high and the community was composed mostly of mixotrophic dinoflagellates, which were often concentrated in a thin layer below the pycnocline. Phytoplankton biomass was always low in the ETM, but high concentrations of phytoplankton pigment degradation products and cellular remains were often observed suggesting that this was an area of high phytoplankton mortality and/or an area where phytoplankton derived particulate organic matter was being trapped. These results, along with a box model analysis, suggest that under certain hydrodynamic conditions phytoplankton derived organic matter can be trapped in ETM and potentially play a role in fueling secondary production.  相似文献   

6.
Atlantic menhaden (Brevoortia tyrannus) is well known for its commercial and ecological importance and has been historically declining in the Chesapeake Bay (Maryland), one of its principal nursery habitats along the eastern coast. Using data from the Striped Bass Seine Survey of the Maryland Department of Natural Resources (2003), we evaluated how the distribution of Atlantic menhaden has changed from 1966 to 2004 for 12 river drainages. We observed significant or marginally significant declines in 42% of the drainages, with drainages of the northern Bay showing the majority of those declines. Continued recruitment to several drainages of the Bay may partly explain why the adult spawning population is not declining. We determined if temporal changes in abundance were related to changes in salinity or water quality for five major drainages of the watershed. For one of these drainages, the Patuxent River, differences in productivity across sites largely explained differences in abundance. For the four remaining drainages, differences in recruitment could not be explained by productivity or salinity gradients. While reducing nitrogen loading and enhancing water clarity may improve Atlantic menhaden production, we suggest that the role of offshore processes on large-scale declines has been largely neglected and studies on larval ingression are necessary for further elucidation of spatial and temporal patterns of juvenile distribution in the Chesapeake Bay.  相似文献   

7.
Changes in freshwater inflow and salinity patterns may affect the nursery value of estuarine systems for penaeid shrimp, but the relationship between salinity and shrimp abundance is complex and likely confounded by other environmental variables. Laboratory experiments can provide insights into salinity selection, and we designed an experimental gradient tank to examine salinity preferences of juvenile brown shrimp and white shrimp. Our design uses gently flowing water to eliminate various physical constraints often associated with selection experiments. We conducted experiments with juvenile brown shrimp (12 trials) and white shrimp (seven trials), to examine selection for salinities along a gradient from 1 to 42. Data were analyzed using contingency tables and log-linear modeling to examine relationships with salinity and possible interactions with temperature. Both brown shrimp and white shrimp were present in all salinities examined within the experimental range. In general, brown shrimp showed a preference for salinities from 17 to 35 and demonstrated avoidance for the extreme low salinities along the gradient. Results for white shrimp were not statistically significant, and this species did not appear to avoid low salinities. There was no effect of water temperature on the observed selection patterns for brown or white shrimp. Our results suggest that although salinity preferences likely exist for these species, strong distribution trends associated with salinity gradients in estuaries are likely caused by other environmental factors.  相似文献   

8.
The emigration of juvenile Atlantic menhaden,Brevoortia tyrannus (Latrobe), from the York River Estuary, Virginia, was studied during the years 1981 and 1982. Concurrent observations of menhaden catch, water temperature, and phytoplankton abundance suggested that the migration began in response to environmental events in the estuary. Juvenile menhaden appeared to begin their migration five days after the sustained onset of water temperatures below 24 °C. The temperature change was hypothesized as the proximate factor that initiates the migration. Coincident with the migrations, phytoplankton communities in the estuary bloomed, suggesting that the ultimate factor that initiates the migration may be the occurrence of sufficient food for the emigrating menhaden as they moved down and out of the estuary. Migration timing may have evolved as a mechanism to enhance the survival of migrating juvenile menhaden during a period of physiologic stress.  相似文献   

9.
Hurricane Floyd in September 1999 caused disastrous flooding from South Carolina to Massachusetts in the United States, with particularly severe and prolonged flooding in eastern North Carolina resulting in record flood-flow loadings of freshwater and contaminants to Pamlico Sound, North Carolina. The inland flooding, water quality, and loadings to Pamlico Sound were determined as part of a multi-agency response to the floods and in an effort to understand the effects of the floods on the greater Pamlico Sound Basin. All major river basins draining to Pamlico Sound experienced floods at the 500-yr recurrence level. The volume of flood waters entering Pamlico Sound during September–October 1999 was estimated to be equivalent to about 95% of the volume of Pamlico Sound, meaning that flood waters could have essentially displaced most of the water present in Pamlico Sound. Nitrogen and phosphorus loads to the Pamlico River estuary and Neuse River estuary, the two principal estuaries draining to Pamlico Sound, in a 36-d period during the flooding were between 50–90% of the long term average annual loads. Pesticide concentrations in flood waters were surprisingly high, given the amount of dilution produced by the floodwaters.  相似文献   

10.
Hydrologic conditions, especially changes in freshwater input, play an important, and at times dominant, role in determining the structure and function of phytoplankton communities and resultant water quality of estuaries. This is particularly true for microtidal, shallow water, lagoonal estuaries, where water flushing and residence times show large variations in response to changes in freshwater inputs. In coastal North Carolina, there has been an increase in frequency and intensity of extreme climatic (hydrologic) events over the past 15 years, including eight hurricanes, six tropical storms, and several record droughts; these events are forecast to continue in the foreseeable future. Each of the past storms exhibited unique hydrologic and nutrient loading scenarios for two representative and proximate coastal plain lagoonal estuaries, the Neuse and New River estuaries. In this synthesis, we used a 13-year (1998–2011) data set from the Neuse River Estuary, and more recent 4-year (2007–2011) data set from the nearby New River Estuary to examine the effects of these hydrologic events on phytoplankton community biomass and composition. We focused on the ability of specific taxonomic groups to optimize growth under hydrologically variable conditions, including seasonal wet/dry periods, episodic storms, and droughts. Changes in phytoplankton community composition and biomass were strongly modulated by the amounts, duration, and seasonality of freshwater discharge. In both estuaries, phytoplankton total and specific taxonomic group biomass exhibited a distinctive unimodal response to varying flushing rates resulting from both event-scale (i.e., major storms, hurricanes) and more chronic seasonal changes in freshwater input. However, unlike the net negative growth seen at long flushing times for nano-/microphytoplankton, the pigments specific to picophytoplankton (zeaxanthin) still showed positive net growth due to their competitive advantage under nutrient-limited conditions. Along with considerations of seasonality (temperature regimes), these relationships can be used to predict relative changes in phytoplankton community composition in response to hydrologic events and changes therein. Freshwater inputs and droughts, while not manageable in the short term, must be incorporated in water quality management strategies for these and other estuarine and coastal ecosystems faced with increasing frequencies and intensities of tropical cyclones, flooding, and droughts.  相似文献   

11.
The lower Neuse River Estuary is a temperate mesohaline system which forms the major southern tributary of Pamlico Sound, North Carolina. The crustacean zooplankton of this well-mixed system were sampled for a 20-month period from May 1988 through December 1989. A submersible pump was used to sample both the entire water column and the sediment surface. Seasonal dominants included the calanoid copepodsAcartia tonsa andParacalanus crassirostris in summer, the cyclopoid copepodOithona colcarva in fall, the cladoceranPodon polyphemoides in winter, and harpacticoid copepods in spring. Non-naupliar biomass over the study period consisted of 38.8%A. tonsa, 7.7%P. crassirostris, 21.2%O. colcarva 23.6% harpacticoid copepods, and 6.0% cladocerans. The remainder of the biomass consisted ofPseudodiaptomus coronatus and barnacle nauplii. Mean total copepod densities ranged from 600 m?3 in May 1988 to 180,000 m?3 in August 1988. Mean copepod densities for 1989 were 25,000 m?3. Maximum densities during both years occurred during summer, with subsequent descreases throughtout the year until early spring. Abundances of total copepods, and ofAcartia tonsa in particular, were significantly correlated with water temperature, but with neither chlorophylla, phytoplankton productivity, nor any of an array of other physical or chemical variables. Regression analyses using data from this investigation, and supported by results from other regional studies, indicate that water temperature is likely the single most important variable predicting zooplankton temporal abundance in North Carolina estuaries.  相似文献   

12.
Salinities occupied by different life stages of bay anchovy (Anchoa mitchilli) were compared over annual cycles at 128 stations in 12 Florida estuaries. The comparison included eight stations in an oligotrophic, groundwater-based estuary in which all life stages were rare or absent. At other stations, adults, eggs, and early larvae occurred in intermediate to high salinities (10-30 psu) with no apparent central salinity tendency. The larva-juvenile transition was marked by an upstream shift to lower salinities (0-15 psu), also with no central salinity tendency. Mean salinities of the juvenile catch were strongly dependent on the salinities of the sampling effort. This dependence was strongest in estuaries that had weak horizontal salinity gradients. Weak salinity gradients were either natural or resulted from estuarine dams. After using nonlinear regression to account for the interaction between effort salinity and catch salinity, catch salinities were found to be similar from year to year within estuaries, but widely different among estuaries, with interestuarine differences ranging as high as 10–13 psu. Lower salinities were occupied by juveniles in estuaries that had long freshwater turnover times. Inherent geomorphic and inflow-related effects on the distribution of prey resources, coupled with an ontogenetic diet shift, are proposed as the explanation for both the habitat shift and the strong interestuarine variability in salinity at capture.  相似文献   

13.
Examination of small-scale spatial variation in essential to understanding the relationships between environmental factors and benthic community structure in estuaries. A sampling experiment was performed in October 1993 to measure infauna association with sediment composition and salinity gradients in Nueces Bay, Texas, USA. The bay was partitioned into four salinity zones and three sediment types. Higher densities of macrofaua, were found in sediments with greater sand content and in areas with higher salinity. High diversity was also associated with high homogeneous salinity (31–33‰) and greater sand content. Macrofauna biomass and diversity were positively correlated with bottom salinity, porewater salinity, and bottom dissolved inorganic nitrogen (DIN). Furthermore, species dominance shifted along the estuarine gradient.Streblospio benedicti dominated at lower salinity, but,Mediomatsus ambiseta andMulinia lateralis were the dominant species at higher salinity. Statistical analyses revealed significant correlations for sediment characteristics (i.e., increased fine sediments, water content, and total organic carbon) with decreased total abundance and diversity. Increased salinity and DIN were correlated with increased total biomass, diversity, and macrofauma community structure. These physico-chemical variables are regulated by freshwater inflow, so inflow is an important factor influencing macrofauna community structure by indirectly influencing the physico-chemical environment.  相似文献   

14.
The seasonal pattern of phytoplankton biomass (chlorophyll and particulate organic carbon) and the salinity-related pattern of phytoplankton biomass and size composition were determined in Apalachicola Bay, Florida, throughout 2004. Phytoplankton biomass was highest during summer and lowest during winter. During summer, phytoplankton biomass was highest in waters with salinity between about 5 and 23. In waters between 5 and 23, phytoplankton biomass was primarily (> 50%) composed of < 5 μm cells. The results from this study support the idea that a microbial food web characterizes mass and energy flow through the planktonic food web in Apalachicola Bay and other estuaries. During winter, the carbonxhlorophylla ratio averaged 56 ± 60 (standard deviation). During summer, the ratio ranged from 23 to 345, with highest values occurring in waters with salinity between about 8 and 22. The carbonxhlorophylla ratio was positively related to the percent of chlorophyll < 5 μm in size during summer.  相似文献   

15.
In shallow estuaries with strong river influence, the short residence time and pronounced gradients generate an environment for plankton that differs substantially in its dynamics from that of the open ocean, and the question arises “How is phytoplankton biomass affected?” This study assesses the small-scale spatial and temporal distribution of phytoplankton in Apalachicola Bay, a shallow bar-built estuary in the Florida Panhandle. Phytoplankton peaks were characterized to gain insights into the processes affecting spatial heterogeneity in biomass. Chlorophyll a (Chl a) distribution at 50-m spatial resolution was mapped using a flow-through sensor array, Dataflow©, operated from a boat that sampled four transects across the bay every 2 weeks for 16 months. Chl a peaks exceeding background concentrations had an average width of 1.3?±?0.7 km delineated by an average gradient of 3.0?±?6.0 μg Chl a L?1 km?1. Magnitude of E-W wind, velocity of N-S wind, tidal stage, and temperature affected peak characteristics. Phytoplankton contained in the peaks contributed 7.7?±?2.7% of the total integrated biomass observed along the transects during the study period. The river plume front was frequently a location of elevated Chl a, which shifted in response to river discharge. The results demonstrate that despite the shallow water column, river flushing, and strong wind and tidal mixing, distinct patchiness develops that should be taken into consideration in ecological studies and when assessing productivity of such ecosystems.  相似文献   

16.
The Atlantic menhaden,Brevoortia tyrannus, is an abundant plankton-feeding fish that undertakes extensive seasonal migrations, moving from overwintering locations offshore south of Cape Hatteras to the mid-Atlantic Bight and New England inshore waters during spring and summer. A bioenergetic model, based on field and laboratory studies, shows that when large numbers of menhaden enter Narragansett Bay, Rhode Island, during spring and early summer, they significantly influence plankton populations through size-selective grazing and nutrient regeneration. A population biomass of 9.1×106 kg of menhaden feeding for 12 h each day in the upper bay would result, in a substantial reduction of the instantaneous growth rate of the >20-μm phytoplankton. Instantaneous growth rates of zooplankton would be negative if the same population of menhaden was present, resulting in a reduction in the biomass of zooplankton. Given the ambient phytoplankton and zooplankton populations, menhaden could achieve the seasonal growth measured in Narragansett Bay during 1976 by feeding on average about 5 h d?1. Daily nitrogen excretion rates of the 9.1×106 kg menhaden population were 56.4% of the mean standing stock of ammonia-N in the upper bay. Because menhaden travel in schools their effects are likely to be intense but strongly localized, increasing spatial heterogeneity in the ecosystem. When the fish migrate southward in the fall they transfer between 3.3% and 6.2% of the nitrogen exported annually from the bay.  相似文献   

17.
The ichthyofauna of the Sundays Estuary was investigated by monthly seine netting over a period of a year. Forty-seven species were captured though 23 of these were represented by a total catch of less than 25 specimens each. The small clupeidGilchristella aestuarius was numerically dominant and constituted 80%, of the catch. The study confirms that in addition to this species, two species of goby,Caffrogobius multifasciatus andPsammogobius knysnaensis and the soleSolea bleekeri complete their life cycles in the estuary. Many other species such as mullet, utilize the estuary as a juvenile nursery area. First year juveniles ofRhabdosargus holubi, Lithognathus lithognathus, Pomadasys commersonni andMonodactylus falciformis, by virtue of their abundance in the Sundays Estuary and other South African estuaries, and their absence from other coastal environments, appear to be dependent on estuaries as juvenile nursery areas.  相似文献   

18.
The brown shrimp,Farfantepenaeus aztecus, is the major component of the Gulf of Mexico shrimp fishery, and it is critical that we understand its environmental requirements. Brown shrimp spend a large portion of their post-larval (PL) and juvenile life within estuaries distributed along salinity gradients and yet our understanding of the salinity tolerance of various age groups is limited. A series of 48-hr bioassays were conducted in which various ages ofF. aztecus (PL-10, PL-13, PL-15, PL-17, PL-20, and PL-23) were acclimated from a salinity of 26‰ to 1‰, 2‰, 4‰, 8‰, 12‰, and 26‰ in order to determine their tolerance to these salinities. Finally, PL-80.F. aztecus were transferred directly from 25‰ to 2‰, 4‰, and 8‰ waters to study the effects of rapid salinity reductions on juvenile survival. Survival of 10-and 13-day-old PLs was significantly, different from the control (26‰) for all salinities tested. Survival of PL-15 shrimp and older was significantly lower than survival of the controls at 1‰ and 2‰ but similar to the control at all other salinities tested. A 4-wk growth trial was conducted with juvenile shrimp at 2‰, 4‰, 8‰, and 12‰. There was no significant difference in survival among treatments, although shrimp maintained at 8‰ and 12‰ grew significantlymore than shrimp maintained at 2‰ and 4‰. There was no growth difference between shrimp at the two low salinities or between shrimp at the two high salinities. Survival of juveniles transferred directly from 25‰ to various salinities were 100% at 25‰, 94.2% at 8‰, 67.3% at 4‰, and 63.5% at 2‰. These results suggest that PL-13 and younger brown shrimp would have a better chance of survival by delaying entry into estuaries susceptible to rapid salinity declines. The brown shrimp juveniles would, be more densely distributed in areas with salinities greater than 4‰ than in salinities less than 4‰. Although food availability, and bottom type also affect shrimp distribution survival and growth, salinity may also greatly affect the shrimp and its fishery.  相似文献   

19.
In order to examine the variations in concentrations of dimethylsulfide (DMS) and its fluxes to the atmosphere, 25 major and medium estuaries from Indian subcontinent were sampled during wet and dry periods. River discharge brought substantial amount of nutrients and suspended particulate matter (SPM) to the Indian estuaries; however, the concentration of phytoplankton biomass was severely limited by latter due to shallowing of photic depth. Bacillariophyceae was the dominant phytoplankton group in the Indian estuaries followed by green algae, Cyanophyceae, and Dinophyceae. Relatively higher concentrations of DMS were observed in the estuaries located along the east (3.6 ± 5.7 nM) than the west coast of India (0.8 ± 0.3 nM) during wet period whereas no significant differences were observed during dry period. The concentrations of DMS were significantly lower during wet than dry period and it was consistent with the phytoplankton biomass. The slope of the relation between DMS and phytoplankton biomass displayed a significant spatial variation due to contribution of different groups of phytoplankton in the Indian estuaries. The concentrations of DMS in the Indian estuaries were higher than other estuaries in the world except some Chinese estuaries. The annual mean flux (1.95 ± 2.5 μmol m?2 day?1) from the Indian estuaries is lower than that of other estuaries in the world, except Pearl River estuary due to inhibition of phytoplankton growth by suspended load and low flushing rates.  相似文献   

20.
The toxicPfiesteria complex are a group of dinoflagellates that have received considerable attention in recent years as causative factors in fish kill or lesion events in North Carolina estuaries and in the Pocomoke River of Chesapeake Bay. In response to the potentialPfiesteria threat, the South Carolina Task Group on Harmful Algae was formed in late 1997 and implemented programs to monitor harmful algal blooms and respond to fish kills or lesion events with particular emphasis on the Bushy Park (Cooper River, Charleston) region, a site of annually recurrent menhaden lesion events.Pfiesteria piscicida, Pfiesteria shumwayae, andCryptoperidiniopsis spp. were documented in South Carolina estuaries. Routine monitoring and fish kill or lesion event sampling consistently indicated low abundances compared to estimates from similar programs in North Carolina and Maryland that sampled areas with a history ofPfiesteria toxic activity. The finding thatPfiesteria-like organism (PLO) abundances were always low in samples collected during menhaden lesion events in Bushy Park suggested other causes for lesion progression, althoughPfiesteria spp. could not be ruled out as a factor in lesion initiation. Based on the previously demonstrated positive relationship between PLO abundance, chlorophylla, and inorganic nutrient concentrations (in laboratory experiments and North Carolina field observations), we hypothesized that the relatively low abundance ofPfiesteria spp. and other PLO (e.g.,Cryptoperidiniopsis) in South Carolina estuaries is related to the relatively low supply of phytoplankton prey, as supported by interstate comparisons in chlorophylla concentrations. Nitrate concentrations were generally much lower in South Carolina estuaries. Estuarine eutrophication may be an important consideration in explaining interstate differences in susceptibility toPfiesteria-related toxic events.  相似文献   

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