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1.
The eastern Alaska Beaufort Sea coast is characterized by numerous shallow (2–5 m) estuarine lagoons, fed by streams and small
rivers that drain northward from the Brooks Range through the arctic coastal plain, and bounded seaward by barrier islands
and shoals. Millions of birds from six continents nest and forage during the summer period in this region using the river
deltas, lagoons, and shoreline along with several species of anadromous and marine fish. We examined biogeochemical processes
linking the benthic community to the overall food web structure of these poorly studied but pristine estuaries, which are
largely covered by 1.8 m of ice for 10 months annually. In summer, these lagoons are relatively warm with brackish salinities
(5–10°C, S = 10–25) compared to more open coastal waters (0–5°C, S > 27). The stable isotopic composition of organic materials in sediments (i.e., benthic particulate organic matter) and water
column suspended particulate organic matter from both streams and lagoons are largely indistinguishable and reflect strong
terrestrial contributions, based upon δ13C and δ15N values (−25.6‰ to −27.4‰ and 1.4‰ to 3.3‰, respectively). By comparison, shifts toward more heavy isotope-enriched organic
materials reflecting marine influence are observed on the adjacent coastal shelf (−24.8‰ to −25.4‰ and 3.4‰ to 5.3‰, respectively).
The isotopic composition of lagoon fauna is consistent with a food web dominated by omnivorous detritovores strongly dependent
on microbial processing of terrestrial sources of carbon. Biomagnification of 15N in benthic organisms indicate that the benthic food web in lagoons support up to four trophic levels, with carnivorous gastropod
predators and benthic fishes (δ15N values up to 14.4‰) at the apex. 相似文献
2.
Autumn J. Oczkowski F. Graham Lewis Scott W. Nixon H. Lee Edmiston Rebecca S. Robinson Jeffrey P. Chanton 《Estuaries and Coasts》2011,34(5):993-1005
Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds
have long been thought to contribute to the support of an unusually productive and commercially important oyster fishery.
Links between the river and productivity have been shown to lie in salinity-induced reductions in oyster predators and oyster
disease as well as organic supplements from an extensive floodplain. Several studies have also indicated that nitrogen (N)
and phosphorous (P) carried by the river are important in fertilization of bay primary production. While there is concern
that upstream water withdrawals may impact the fishery, the importance of riverine N to oyster diets remains unclear. We measured
N and carbon (C) stable isotopes (δ15N, δ13C) in macroalgae, surface-water nitrate, and surface sediments, which showed a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope values throughout Apalachicola
Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine
inflows. 相似文献
3.
Rachel Marie Wilson Jeffrey Chanton Graham Lewis Douglas Nowacek 《Estuaries and Coasts》2009,32(5):999-1010
Stable isotope ratios of carbon and sulfur were used to assess organic matter utilization of numerically abundant consumers
present in Apalachicola Bay, FL, USA. These results were used to infer nitrogen isotopic enrichment of organic matter sources
in an effort to establish baseline δ
15N enrichment for trophic evaluations. We compared results from concentration-independent and concentration-dependent mixing
models and found that the two methods resulted in widely different conclusions about the importance of organic matter sources
that varied ninefold in sulfur concentrations. Nitrogen isotopic enrichment was used to determine relative trophic positions
of consumer organisms. Source elemental concentrations of nitrogen were also considered in the calculation of relative trophic
levels in a concentration-dependent approach. Concentration-independent and concentration-dependent methods of calculating
trophic results were compared. While relative trophic levels of individual species varied continuously from approximately
1.7 to 3.5, comparisons of trophic level among consumers indicated four possible trophic groupings. Filter feeders (mussels
and oysters) made up the lowest trophic tier while teleost fishes made up the highest trophic tier. Invertebrates sampled
were assigned intermediate nondiscrete trophic levels. Because δ
15N values of important organic matter sources in the system were similar, the concentration-independent and concentration-dependent
methods did not result in significantly different conclusions about trophic level for any of the consumers examined. However,
a comparison of the two methods applied to a hypothetical case found that differences in base δ
15N values ranging approximately 4‰ resulted in significantly different trophic-level assignments when comparing the concentration-dependent
and concentration-independent methods of trophic-level calculations. Our results confirm that consideration of the elemental
concentrations of the base organisms is an important factor in determining source contributions and may affect trophic-level
calculations in systems with a sufficient range of base nitrogen enrichment. However, this result depended on the relative
isotopic signatures of the chosen sources and their elemental concentrations and should be considered individually for each
system. 相似文献
4.
The biogeochemistry of organic matter (OM) in a macrotidal estuary, the Yalujiang River, was studied during two cruises: the
flood season in August 1994 and the dry season in April 1996. Surface sediments were collected in the riverine zone (RZ),
the turbidity maximum zone (TMZ), and the marine zone (MZ). The molecular distribution of the n-alkanes and fatty acid series
and bulk sediment characteristics, such as C:N and δ13C, were used to assess differences in OM source and transport from the river upstream to the marine end member. Higher C:N
values typical for terrestrial sources were observed at the upper reach for both seasons. The δ13C of OM in surface sediments varied from −27.3‰ to −21.6‰ in the flood season and from −26.8‰ to −31‰ in the dry season. The
concentrations of n-alkanes varied between 0.3–21.4 μg g−1 and the variation of fatty acids was 4.8–32.9 μg g−1. The data showed mixing of terrestrial and autochthonous OM in the middle and lower reaches. The distribution of lipids (n-alkanes
and Carbon Preference Index) encountered in this study confirmed the importance of terrestrial OM in the sediment samples
from degraded soil material. The distribution of fatty acids suggested important phytoplankton, zooplankton, and microbial
signals (short-chain and unsaturated acids; ≤C20). Branched fatty acids, such as the iso- and anteiso-C15 and C17 compounds, relfect bacterial contributions. All samples were characterized by a high proportion of mixture inputs in both
seasons. A slight decreasing trend was observed with increasing salinity except for the highest percentage of mixed fatty
acids in the TMZ of the flood season. Terrestrial fatty acids were approximately 20% in the flood season and 27–46% in the
dry season. Differences in hydrological conditions and primary production between the TMZ, RZ, and MZ resulted in different
OM distributions, which are reflected in the sources and degree of diagenesis of the sedimentary OM. Seasonal variation may
be strongly influenced by hydrological characteristics rather than primary productivity and anthropogenic activities in the
Yalujiang region. 相似文献
5.
Paulo Cesar Abreu César S. B. Costa Carlos Bemvenuti Clarisse Odebrecht Wilhelm Graneli Alexandre M. Anesio 《Estuaries and Coasts》2006,29(2):277-285
Stable isotopes ratios (δ13C and δ15N) were measured in primary producers and consumers of two bays with contrasting eutrophic conditions in the Patos Lagoon
estuary, southern Brazil: the Justino bay, a more pristine ecosystem, and the Mangueira bay, a heavily polluted region that
receives the Rio Grande city sewage and effluencts of several industries. δ13C values of organisms collected in both subsystems were not different, but δ15N values had significant statistical differences, ca. 3.5‰ higher in the Mangueira bay. It is likely that primary producers
and consumers in this subsystem are greatly influenced by higher nitrogen input due to domestic and industrial sewages. The
stable isotope analysis also corroborated several trophic interactions previously established by gut content analysis, and
due to its higher sensitivity, it was possible to better determine the contributions of different primary producers and detrital
fractions to the consumers' diets. It was confirmed that plant detritus represents the main food source for most organisms.
The stable isotope analysis also demonstrated that detritivorous benthic organisms in the same habitat have distinct diet
compositions, with differential consumption of C3 and C4 plants. This technique showed that some consumers that eat detritus
do not have in their stable isotopic signature any relationship with that of plants. It is likely that these consumers assimilate
their carbon and nitrogen from other sources like microalgae or microorganisms that colonize decaying plants. 相似文献
6.
To characterize the isotopic composition of organisms at the base of the food web and the controls on their variability, the concentration and δ13C isotopic composition of dissolved inorganic carbon (DIC) and plankton δ13C, δ15N, and δ34S were measured. The measurements were made during periods of high and low river flow in Apalachicola Bay, Florida, United States, over 3 yr. DIC concentration and δ13C values were related to salinity, indicating that conservative mixing of riverine and marine waters was responsible for the overall distributions. The usefulness of DIC δ13C data for characterizing the trophic processes within the estuary was dependent upon the residence time of water within the season. Plankton δ13C values varied from −22‰ to −30‰ and were directly related to estuarine DIC δ13C, offset by a factor of roughly −20‰. This offset factor varied with salinity. Values of δ34S in estuarine plankton (station means ranged from 11.4‰ to 13.1‰) were depleted relative to marine plankton (17.7±0.4‰) possibly due to the admixture of34S-depleted sedimentary sulfide with estuarine samples. Values of δ34S in plankton were not related to δ13C values of plankton and were only weakly correlated to the salinity of the water from which the plankton were collected, indicating that marine sulfate was the primary source of planktonic sulfur. Values of δ15N in plankton varied from 5.5‰ to 10.7‰ and appeared related to dominance of the sample by phytoplankton or zooplankton. Estuarine plankton was15N enriched relative to offshore plankton and estuarine sediment. 相似文献
7.
Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta 总被引:1,自引:0,他引:1
William V. Sobczak James E. Cloern Alan D. Jassby Brian E. Cole Tara S. Schraga Andrew Arnsberg 《Estuaries and Coasts》2005,28(1):124-137
Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the
role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity
in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The
Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that de tritus is the primary energy
source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic
matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years
to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic
matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus
was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production
was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a
small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic
matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton
production. 相似文献
8.
Analysis of 3-m sediment cores revealed that profiles of carbon (C), sulfur (S), and iron (Fe) varied with relative distance from marine and terrestrial sediment sources in Tomales Bay California. Despite relatively high sedimentation rates throughout the bay (historically 3–30 mm yr−1), sulfate reduction of deposited organic matter led to free-sulfide accumulation in sediments only at the location farthest from terrestrial runoff, the source of reactive iron. Acid-volatile sulfide concentrations in all sediments (<10 μmol g−1) were low relative to concentrations of chromiumreducible sulfide (up to 400 μmol g−1 farthest from the reactive iron source). A calculated index of iron availability, used to describe sediment resistance to build-up of free sulfide, was lowest at this location. Recent, upward shifts in reactive Fe concentration and in the relative contribution of terrestrial orgnic carbon (measured as a shift in δ13C of bulk sediment organic matter) in all cores indicated that erosion and transport of sediments from the watershed surrounding Tomales Bay increased after European settlement in the 1850s. 相似文献
9.
Identification of important primary producers in a Chesapeake Bay tidal creek system using stable isotopes of carbon and sulfur 总被引:1,自引:0,他引:1
The use of multiple stable isotopes in the study of trophic relationships in temperate estuaries has usually been limited to euhaline systems, in which phytoplankton, benthic microalgae, andSpartina alterniflora are major sources of organic matter for consumers. Within large estuaries such as Chesapeake Bay, however, many species of consumers are found in the upper mesohaline to oligohaline portions. These lower salinity wetlands have a greater abundance of macrophytes that use C3 photosynthesis to fix carbon, in addition toS. alterniflora, which fixes carbon via the C4 photosynthetic pathway. In a broad survey of the biota and sediments of a brackish tidal creek tributary to Chesapeake Bay, combined δ13C and δ34S measurements disclosed a balanced contribution to secondary production from phytoplankton, C3 macrophytes,Spartina sp., and benthic microalgae. Surface sediment δ13C suggested that the organic matter from C3 plants was derived both from allochthonous sources (terrestrial runoff) and from autochthonous production (marsh macrophytes). Unlike most estuarine systems studied to date, which are dominated by algae (phytoplankton and benthic microalgae) and C4 macrophytes, C3 plants are of greater importance in the diets of consumers in this low-salinity creek system. 相似文献
10.
The Mattaponi River is part of the York River estuary in Chesapeake Bay. Our objective was to identify the organic matter (OM) sources fueling the lower food web in the tidal freshwater and oligohaline portions of the Mattaponi using the stable isotopes of carbon (C) and nitrogen (N). Over 3 years (2002–2004), we measured zooplankton densities and C and N stable isotope ratios during the spring zooplankton bloom. The river was characterized by a May–June zooplankton bloom numerically dominated by the calanoid copepod Eurytemora affinis and cladocera Bosmina freyi. Cluster analysis of the stable isotope data identified four distinct signatures within the lower food web: freshwater riverine, brackish water, benthic, and terrestrial. The stable isotope signatures of pelagic zooplankton, including E. affinis and B. freyi, were consistent with reliance on a mix of autochthonous and allochthonous OM, including OM derived from vascular plants and humic-rich sediments, whereas macroinvertebrates consistently utilized allochthonous OM. Based on a dual-isotope mixing model, reliance on autochthonous OM by pelagic zooplankton ranged from 20% to 95% of production, declining exponentially with increasing river discharge. The results imply that discharge plays an important role in regulating the energy sources utilized by pelagic zooplankton in the upper estuary. We hypothesize that this is so because during high discharge, particulate organic C loading to the upper estuary increased and phytoplankton biomass decreased, thereby decreasing phytoplankton availability to the food web. 相似文献
11.
Investigation of biogeochemistry and amino acids on a 30-m-long core from Mansar Lake has thrown light on palaeoclimate variability
during the Holocene period. The C/N ratio between 6 and 10 with some deviations and δ13C mostly between −20 and −22‰ in the
shallow core, as well as a C/N ratio greater than 13 reaching from 19 to 20 and correspondingly lower δ13C of –28‰ in the
deeper core suggest an aquatic source of carbon in the former and a cellulose-rich land plant source in the latter. This is
supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core, which indicates
a hot and wet climatic regime during the early Holocene and dry and cold during the late Holocene period. The amino acid data
AA-C/C% and AA-N/N% are higher in shallow sediments compared to deeper sediments, indicating an aquatic plant source in the
shallow core and greater supply of land plant sources in the deeper core. The lower percentage of the non-protein amino acids
β-alanine (ALA) and γ-amino-butyric acid in the shallow core compared to the deeper core indicates different sources of organic
matter in the lake basin. The higher amino acid ratio Asp/β-Ala (16.99 av.) and Glu/γ-Aba (18.18 av.) in the shallow core
and lower ratios (10.32 and 12.41 av.) in the deeper core, and Asp/Glu (1.52 av.) and β-Ala/γ-Aba (1.61 av.) ratios in the
former, which are potential indicators of the nature of the organic matter, are higher in the shallow core relative to the
deeper core (1.33 and 1.23 av.), indicating relative biodegradation of organic matter in deeper sediments. It has been observed
that the organic matter associated with the dry season is relatively less biodegraded, as evidenced from their higher ratios,
and is more biodegraded in the wet season as their ratios are lower in the river sediments. In the absence of a bacterial
contribution of organic matter from the soil source in this lake, since Mansar Lake is a non-drainage type, it is envisaged
that the climatic variation may be responsible for biodegradation in the deeper core sediments. Therefore, the C/N ratio and
δ13C values supported by amino acid data, the latter being significant in revealing primary productivity and a terrestrial
source of organic matter, suggest a hot and wet climatic regime during the early Holocene (ca. 7580 bp) and a dry and cold in the late Holocene period (ca. 4050 bp). 相似文献
12.
The stable isotope signatures of marine transient and resident nekton were used to investigate trophic linkages between primary
producers, marsh macrophytes, phytoplankton, benthic microalgae, and consumers within the Delaware Bay. A whole estuary approach
was used to compare the flux of nutrients from primary producers to juvenile weakfish (Cynoscion regalis), bay anchovy (Anchoa mitchilli), and white perch (Morone americana) in open waters of the lower and upper Bay and adjacent salt marshes dominated by eitherSpartina alterniflora orPhragmites australis. Our results suggest that trophic linkages vary significantly along the salinity gradient, reflecting the transition fromSpartina toPhragmites-dominated marshes, and secondarily, in a marsh to open water (offshore) direction at a given salinity. Superimposed on this
pattern was a gradient in the proximate use of organic matter that depended on life history traits of each species ranging
from pelagic to benthic in the order bay anchovy > weakfish > white perch. 相似文献
13.
The isotopic composition of dissolved boron, in combination with the elemental concentrations of B, Cl and salinities in freshwater-seawater mixed samples taken from the estuary of the Changjiang River, the largest one in China, was investigated in detail in this study. Brackish water and seawater samples from the estuary of the Changjiang River were collected during low water season in November, 1998. Boron isotopic compositions were determined by the Cs2BO^+2-graphite technique with a analytical uncertainty of 0.2‰ for NIST SRM 951 and an average analytical uncertainty of 0.8‰ for the samples. The isotopic compositions of boron, expressed in δ^11B, and boron concentrations in the Changjiang River at Nanjing and seawater from the open marine East Sea, China, are characterized by δ^11B values of -5.4‰ and 40.0‰, as well as 0.0272 and 4.43 mg B/L, respectively. Well-defined correlations between δ^11B values, B concentrations and Cl concentrations are interpreted in terms of binary mixing between fiver input water and East Sea seawater by a process of straightforward dilution. The offsets of δ^11B values are not related to the contents of clastic sediment and to the addition of boron. These relationships favor a conservative behavior of boron at the estuarine of the Changjiang River. 相似文献
14.
Stable carbon isotope (δ13C) analysis was used in the Peridido Estuary, Florida U.S. to determine the predominant carbon source that supports the bacterial assemblage. Stable carbon isotope values were measured in the suspended particulate matter (SPM), dissolved organic and inorganic matter, and bacteria. Stable nitrogen isotope (δ15N) ratios were measured in SPM and nitrate to assist in understanding carbon cycling through the estuary. Analyses were conducted on samples from riverine, coastal, and anthropogenic sources and compared with samples from the bay. Stable isotope ratio analysis was coupled with estimates of mixing of riverine and coastal waters into the bay. Preliminary observation of the °13C data indicates that terrestrial organic matter is the primary carbon source that is assimilated by bacteria in the ecosystem. Stable isotope data from carbon and nitrogen pools in combination with analysis of estuarine current velocities indicates that primary production is an important factor in the carbon cycle. This study demonstrates the importance of stable isotope analysis of multiple carbon and nitrogen pols to assess sources and cycling of organic matter. 相似文献
15.
Frédéric Gazeau Jean-Pierre Gattuso Jack J. Middelburg Natacha Brion Laure-Sophie Schiettecatte Michel Frankignoulle Alberto Vieira Borges 《Estuaries and Coasts》2005,28(6):868-883
Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the
Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the
1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m−2 d−1) decreasing seaward (22–37 mmol C m−2 d−1). A significant decrease of NIT was observed with regard to previous investigations although this process still represents
up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed
to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time
in the estuary with values ranging from −300 to 165 mmol C m−2 d−1. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published
benthic metabolic rates. A NEP of −39±8 mmol C m−2 d−1 was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from
June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure
applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the
inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much
lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m−2 d−1) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear. 相似文献
16.
The nitrogen and carbon stable isotope ratios (δ15N and δ13C) of the pygmy mussel,Xenostrobus securis, were determined for three estuaries with varying levels of catchment disturbance in northern New South Wales, Australia.
The lower Manning River catchment supported the highest human population densities with 3% residential development and some
livestock agriculture (41%); the Wallamba River catchment was mostly livestock agriculture (56%) while the Wallingat River
catchment was mostly vegetated (79%). Mussels, estuarine particulate organic matter (POM), and livestock and human-derived
waste were collected in two stages during the austral summers of 2001–2002 and 2002–2003 for dual carbon-nitrogen stable isotope
analysis. The disturbed Manning and Wallamba River catchment mussels were enriched in15N by an average of 3.2‰ and 1.5‰, respectively, compared to the vegetated Wallingat River mussels. Mussel δ13C values ranged from −24.8‰ to −30.3‰ and showed an estuarine gradient becoming enriched with distance downstream within estuaries,
but were unable to distinguish patterns in catchment disturbance between estuaries. The δ15N and δ13C values of POM showed a similar pattern to mussels, indicating a direct link between them within each estuary. A multiple
regression model of mussel δ15N using the fractions of land used for livestock agriculture and residential development within 5 km zones from river networks
to a distance equivalent to a tidal ellipse from sites explained 67% of the variation in mussel δ15N with 95% of the differences lying within 1.6‰ of observed values. Increasing fractions of land used for livestock agriculture
depleted mussel δ15N values estimated by the regression equation, indicating the use of cow manure as a nutrient source with a value of 2.0‰.
Increasing fractions of land used for residential development enriched estimated mussel δ15N, indicating the use of human-derived waste with a value of 20.8‰. Pygmy mussels are a useful long-term bio-indicator for
the effects of anthropogenic catchment disturbance and nutrient enrichment in estuaries. 相似文献
17.
Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records 总被引:2,自引:0,他引:2
Jianfang Hu Xuesong Sun Ping'an Peng Gan Zhang Allan R. Chivas 《Quaternary International》2009,206(1-2):46
Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ13Corg) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ13Corg for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ13Corg values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs. 相似文献
18.
Isotopic Determination of Food Web Origins in Restoring and Ancient Estuarine Wetlands of the San Francisco Bay and Delta 总被引:1,自引:0,他引:1
We compared the extent to which ancient and restoring wetlands in three estuary regions of San Francisco Bay support estuarine
ecosystems through food web contributions. In comparison to mature marshes, we hypothesized that food webs of increasingly
younger restoration sites would display increased dependency upon allochthonous subsidies due to nominal internal production.
Using multiple stable isotopes (δ13C, δ15N, δ34S) in a mixing model, we traced links among primary producers and estuarine consumers. Results indicate that food webs of
estuarine marshes are heavily dependent upon autochthonous marsh materials (76 ± 17%), even within the youngest restoration
marshes (11 years). Nearly all sampled organisms relied upon autochthonous marsh materials, with the exception of Neomysis kadiakensis, a mysid shrimp, which derived the majority of its support from freshwater-produced phytoplankton. Marsh-derived organic
matter (OM) support was consistent both temporally throughout the year and spatially along the three estuary regions, but
evidence suggests that the specific type of OM supporting estuarine consumers depends on position along the estuarine gradient
and on seasonal shifts in freshwater flow. These results indicate that wetland restoration rapidly provides important contributions
to marsh consumers and potentially bolsters food web linkages in shallow-water ecosystems. 相似文献
19.
Tillamook Bay, Oregon, is a drowned river estuary that receives freshwater input from 5 rivers and exchanges ocean water through
a single channel. Similar to other western United States estuaries, the bay exhibits a strong seasonal change in river discharge
in which there is a pronounced winter maximum and summer minimum in precipitation and runoff. The behavior of major inorganic
nutrients (phosphorus, nitrogen, and silica) within the watershed is examined over seasonal cycles and under a range of river
discharge conditions for October 1997–December 1999. Monthly and seasonal sampling stations include transects extending from
the mouth of each river to the mouth of the estuary as well as 6–10 sites upstream along each of the 5 major rivers. Few studies
have examined nutrient cycling in Pacific Northwest estuaries. This study evaluates the distributions of inorganic nutrients
to understand the net processes occurring within this estuary. Based upon this approach, we hypothesize that nutrient behavior
in the Tillamook Bay estuary can be explained by two dominant factors: freshwater flushing time and biological uptake and
regeneration. Superimposed on these two processes is seasonal variability in nutrient concentrations of coastal waters via
upwelling. Freshwater flushing time determines the amount of time for the uptake of nutrients by phytoplankton, for exchange
with suspended particles, and for interaction with the sediments. Seasonal coastal upwelling controls the timing and extent
of oceanic delivery of nutrients to the estuary. We suggest that benthic regeneration of nutrients is also an important process
within the estuary occurring seasonally according to the flushing characteristics of the estuary. Silicic acid, nitrate, and
NH4
+ supply to the bay appears to be dominated by riverine input. PO4
−3 supply is dominated by river input during periods of high river flow (winter months) with oceanic input via upwelling and
tidal exchange important during other times (spring, summer, and fall months). Departures from conservative mixing indicate
that internal estuarine sources of dissolved inorganic phosphorus and nitrogen are also significant over an annual cycle. 相似文献
20.
Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater
discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and
bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and
Sr2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude
and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ
18O = −2.66‰, δD −7.60‰) similar to rainfall (δ
18O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ
18O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water
from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input
ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of
±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the
total fresh and saline water input. 相似文献