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1.
Stream food web function is often assessed using carbon stable isotope assessments of the relative contribution of autochthonous
and allochthonous sources of organic matter to consumer diets. As a result, variability in source signatures can strongly
influence the assessment of carbon flows. To examine the implications of temporal source variability on food web interpretations,
benthic algal δ13C signatures were measured over 8 weeks in five streams in subtropical Queensland, Australia. All food webs were largely driven
by benthic algal carbon; however, substantial week-to-week variation in benthic algal δ13C signatures modified the calculated contributions of algae to consumer diets, with differences in autochthonous contributions
of up to 11% between weeks. In addition, variable algal signatures led to many occasions in which the δ13C signatures of some consumers was beyond the range of available sources, meaning the mixing model analyses did not have a
valid solution. Together, these findings suggest that temporal variability in algal δ13C signatures can strongly influence the interpretation of carbon flows in stream food webs. Future food web studies should
assess the temporal variability of sources prior to sampling consumers, in order to characterise end member signatures and
their relevance to consumers at the time of collection. 相似文献
2.
Stable isotopic structure of aquatic ecosystems 总被引:1,自引:0,他引:1
Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous
function and structure of an ecosystem. Distributions ofδ
13C andδ
15N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope
biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic
framework of the ecosystem was successfully described in aδ
15N–δ
13C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived
organic matter, and marine-derived organic matter.
A trophic-level effect of15N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived
organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin.
The contributions of both land and marine organic matter were comparable for mollusca in the lagoon. 相似文献
3.
Decreased trophic position as a function of increasing body size of a benthic omnivorous fish from the largest freshwater lake in China 总被引:1,自引:0,他引:1
Potential body size-trophic position relationships of the Darkbarbel catfish Pelteobagrus vachelli (Richardson 1846) were examined using stable isotope analysis. Pelteobagrus vachelli is a benthic feeding fish from Lake Poyang, the largest freshwater lake in China. Two-source mixing model with mussel (Corbicula fluminea) and snail (Bellamya aeruginosa) as baseline primary consumers of planktonic and benthic food webs, respectively, was used to estimate contribution of carbon
derived from planktonic vs. benthic food web. Results showed that as an indicator of trophic position, δ15N was negatively correlated with the body length and weight of the fish; on the other hand, as an indicator of the end-member
food sources, δ13C was not correlated with fish size. The mixing model results showed that the averaged trophic position of our sampled 3.3–12.7 cm
Pelteobagrus vachelli was 3.1 ± 0.2 and derived 68 ± 27% of their food from the benthic food web, confirming that the feeding behavior of the catfish
favors benthic food sources. 相似文献
4.
Fish track wastewater pollution to estuaries 总被引:1,自引:0,他引:1
Excess nitrogen is a forceful agent of ecological change in coastal waters, and wastewater is a prominent source of nitrogen.
In catchments where multiple sources of nitrogen pollution co-exist, biological indicators are needed to gauge the degree
to which wastewater-N can propagate through the receiving food webs. The purpose of this study was to test whether estuarine
fish are suitable as indicators of sewage-N pollution. Fish were analysed from three estuaries within a 100-km strip on the
Australian East Coast. The estuaries differ substantially in wastewater loading: (1) the Maroochy Estuary receives a large
fraction of the local shire’s treated sewage, (2) the Mooloolah Estuary has no licensed treated wastewater outfalls but marinas/harbours
and stormwater may contribute nitrogen, and (3) the Noosa Estuary which neither receives licensed discharges nor has suspected
wastewater loads. Sampling for fish included both high rainfall (‘wet’ season) and low rainfall (‘dry’ season) periods. Muscle-δ15N was the variable predicted to respond to treated wastewater loading, reflecting the relative enrichment in 15N resulting from the treatment process and distinguishing it from alternative N sources such as fertiliser and natural nitrogen
inputs (both 15N-depleted). Of the 19 fish species occurring in all three estuaries, those from the Maroochy Estuary had significantly elevated
δ15N values (up to 9.9‰), and inter-estuarine differences in fish-δ15N were consistent across seasons. Furthermore, not only did all fish from the estuary receiving treated wastewater carry a
very distinctive sewage-N tissue signal, but enriched muscle-δ15N was also evident in all species sampled from the one estuary in which sewage contamination was previously only suspected (i.e. the Mooloolah Estuary: 0.2–4.8‰ enrichment over fish from reference system). Thus, fish-δ15N is a suitable indicator of wastewater-N not only in systems that receive large loads, but also for the detection of more
subtle nitrogen inputs. Arguably, fish may be preferred indicators of sewage-N contamination because they: (1) integrate nitrogen
inputs over long time periods, (2) have an element of ‘ecological relevance’ because fish muscle-δ15N reflect movement of sewage-N through the food chain, and (3) pollution assessments can usually be based on evidence from
multiple species. 相似文献
5.
Plant invasions can fundamentally alter detrital inputs and the structure of detritus-based food webs. We examined the detrital
pathways in mangrove food webs in native (Puerto Rican) and introduced (Hawaiian) Rhizophora mangle forests using a dual isotope approach and a mixing model. Based on trophic-level fractionation of 0–1‰ for δ
13C and 2–3‰ for δ
15N, among the invertebrates, only nematodes, oligochaetes, and nereid polychaetes from native mangroves exhibited stable isotopes
consistent with a mangrove-derived diet. Certain fauna, in particular tubificid oligochaetes, had δ
13C values consistent with the consumption of mangrove leaves, but they were depleted in 15N, suggesting their primary nitrogen source was low in 15N, and was possibly N2-fixing bacteria. In introduced mangroves, all feeding groups appeared to rely heavily on non-mangrove sources, especially
phytoplankton inputs. Mixing model results and discriminant analysis showed clear separation of introduced and native mangrove
sites based on differential food source utilization within feeding groups, with stronger and more diverse use of benthic foods
observed in native forests. Observed differences between native and invasive mangrove food webs may be due to Hawaiian detritivores
being poorly adapted to utilizing the tannin-rich, nitrogen-poor mangrove detritus. In addition, differential utilization
of mangrove detritus between native and introduced mangroves may be a consequence of forest age. We postulate that increasing
mangrove forest age may promote diversification of bacterial food webs important in N and S cycling. Our results also suggest
a potentially important role for sulfur bacteria in supporting the most abundant infaunal consumers, nematodes, in the most
mature systems.
Electronic supplementary material The online version of this article (doi:) contains supplementary material that is available to authorized users. 相似文献
6.
Ayato Kohzu Ichiro Tayasu Chikage Yoshimizu Atsushi Maruyama Yukihiro Kohmatsu Fujio Hyodo Yukio Onoda Akitake Igeta Kiyoshi Matsui Takanori Nakano Eitaro Wada Toshi Nagata Yasuhiro Takemon 《Ecological Research》2009,24(1):127-136
We examined how nitrogen-stable isotopic signatures of food web components (basal resources, primary and lower consumers,
and omnivores) in rivers change with increasing levels of human population density (HPD) in their watersheds. Samples were
collected from 22 rivers flowing in the Lake Biwa basin, Japan. Among three potential resources at the base of food webs (epilithon,
benthic and suspended particulate organic matter), the mean isotopic values (δ15N) of the epilithon (4.5–7.8%) were consistently higher than those of other items (1.9–4.2%) and displayed the most pronounced
elevation (by 3.3%) with increasing HPD. The mean δ15N values of the individual taxa of lower consumers (bivalve, snail and caddisfly) tended to increase with increasing HPD,
although the pattern and the extent of the elevation were highly variable among the taxa. These results suggest a taxon-specific
feature in the N source (or sources) of lower consumers. Our data suggested that human activities (e.g. nutrient loading)
potentially induce changes in the N baselines of river food webs. The major N source of bivalves appeared to be shifted from
suspended particulate organic matter to other items with increasing HPD. Trophic levels of goby fish (Rhinogobius sp. OR) and shrimp (Palaemon paucidens), being estimated to be at 2.4–3.8 and 2.1–3.4, respectively, did not differ significantly among rivers with different HPD
levels.
An erratum to this article can be found at 相似文献
7.
Significance of instream autotrophs in trophic dynamics of the Upper Mississippi River 总被引:1,自引:0,他引:1
Trophic dynamics of large river–floodplain ecosystems are still not well understood despite development of several conceptual
models over the last 25 years. To help resolve questions about the relative contribution of algal and detrital organic matter
to food webs in the Upper Mississippi River, we (1) separated living and detrital components of ultrafine and fine transported
organic matter (UTOM and FTOM, respectively) by colloidal silica centrifugation; (2) identified stable isotope signatures
(δ13C and δ15N) for these two portions of transported organic matter and other potential organic matter sources; and (3) employed a multiple
source, dual-isotope mixing model to determine the relative contribution of major energy sources to primary consumers and
the potential contribution of basal sources to the biomass of secondary consumers. The δ13C and δ15N of living and detrital fractions of UTOM and FTOM were distinct, indicating clear differences in isotopic composition of
the algal and detrital fractions of transported organic matter. Living and detrital transported organic matter also differed
from other potential organic matter sources by either δ13C or δ15N. A six-source mixing model using both δ13C and δ15N indicated that algal transported organic matter was the major resource assimilated by primary consumers. The contribution
of detrital transported organic matter was small in most cases, but there were a small number of taxa for which it could potentially
contribute to more than half the assimilated diet. Colloidal dissolved organic matter, which includes heterotrophic bacteria,
accounted for only a small fraction of the organic matter assimilated by most primary consumers, indicating that coupling
between microbial processes and metazoan production is minimal. Terrestrial C3 litter from the floodplain forest floor and aquatic macrophytes were also relatively unimportant to the assimilated diet
of primary consumers. Application of the mixing model to compare basal source isotopic ratios to secondary consumers revealed
that most organic matter moving from primary to secondary consumers originated from algal TOM. Our findings indicate that
autochthonous organic matter is the major energy source supporting metazoan production in the main channel of this large river,
at least during the summer. This study joins a number of other investigations performed globally that indicate organic matter
originating from instream production of sestonic and benthic microalgae is a major driver in the trophic dynamics of large
river ecosystems. 相似文献
8.
Hideyuki Doi Elena I. Zuykova Eisuke Kikuchi Shuichi Shikano Keiichi Kanou Natalia Yurlova Elena Yadrenkina 《Hydrobiologia》2006,571(1):395-400
We investigated spatial changes in the isotope ratios of the plankton food web in Lake Chany, Siberia, Russia, especially
at an estuarine transition zone of the lake. The δ13C values of particulate organic matter (POM) varied among the sampling sites, and increased with increasing pH of the lake
water. This may reflect a shift by phytoplankton from using CO2 to using bicarbonate for photosynthesis with increasing pH. The δ13C values of zooplankton community also changed at each site along with those of the POM. This was indicative of carbon isotope
changes of plankton food webs between the stations along an environmental gradient. 相似文献
9.
Richard J. Pruell Bryan K. Taplin Jonathan D. Karr 《Environmental Biology of Fishes》2012,93(1):61-71
Isotopic ratios of fish otoliths have been used in numerous studies as natural tags or markers to aid in the study of connectivity
among fish populations. We investigated the use of spatial and temporal changes in the stable carbon and oxygen isotope ratios
of otoliths to differentiate juvenile habitats of winter flounder (Pseudopleuronectes americanus). Young-of-the-year (YOY) juvenile winter flounder were collected annually over a three-year period from 18 stations along
the coast of Rhode Island, USA. Sagittal otoliths were removed from fish and analyzed for stable carbon (13C/12C or δ13C) and oxygen (18O/16O or δ18O) isotope ratios using continuous flow isotope ratio mass spectrometry. Differences in isotope ratios were observed among
stations and along salinity gradients in the Narragansett Bay estuary and an estuarine river system (Narrow River). Overall,
the isotope ratio patterns observed among stations were consistent over the three sampling years; however, differences were
noted in isotope ratios and the magnitude of the isotope ratio gradients among years. Significant positive correlations were
noted between salinity and δ13C for two of the three years. For each of the three years sampled there was a highly significant positive correlation (2002,
r = 0.93, P < 0.01; 2003, r = 0.85, P < 0.01; 2004, r = 0.97, P < 0.01) between δ18O and the salinity of the collection site. Also, there was a significant negative correlation between the number of months
of above average river flow and δ18O for the three sampling years (r = 0.99, P < 0.05). These findings suggest that yearly changes in the volume of freshwater inputs to these estuarine habitats may be
related to the differences observed in otolith δ18O isotope ratios. Because of these year-to-year differences, sampling of each cohort may be necessary in order to use this
isotopic technique for winter flounder connectivity studies. 相似文献
10.
Benthic biofilms have been identified using stable isotope analysis (SIA) as an important resource supporting many freshwater
food webs. However, biofilm δ13C signatures are highly variable in freshwaters, which may hamper our understanding of energy flow through food webs in these
systems. There has been little consideration of the influence that substratum may have on biofilm δ13C signature variability and energy flows to primary consumers. We investigated the effect of organic and inorganic substrata
on biofilm dynamics by examining: (1) temporal variability of biofilm stable isotope (δ13C, δ15N) signatures on allochthonous leaf-litter (Eucalyptus camaldulensis) and cobble substrata over 12 months in a lowland river in south-eastern Australia; and (2) the effect of substrata on biofilm
energy flows to a grazer snail, Physa acuta (Gastropoda: Physidae), using SIA and ecological stoichiometry in a laboratory experiment. The temporal study indicated that
cobble biofilm varied significantly in δ13C signature during the 12 months (up to 11‰), whereas the δ13C signature of leaf biofilm was less variable (less than 2‰). In contrast, biofilm δ15N signatures varied temporally on both cobble (2.6‰) and leaf (1‰) substrata. This suggests that leaf biofilm was more reliant
on leaf tissue for carbon and therefore less limited by carbon supply than cobble biofilm whereas for nitrogen biofilm on
both substrata was reliant on external sources. In the laboratory experiment, snails fed leaf biofilm reflected more of an
allochthonous δ13C signature than cobble biofilm fed snails, suggesting assimilation of leaf carbon via the heterotrophic microbial community
within the biofilm. Snails grew largest on cobble biofilm, which had lower C:N ratios than leaf biofilm. Our results demonstrate
that the type of substratum can influence the temporal variability of biofilm δ13C signatures and energy flow to primary consumers. 相似文献
11.
Rivers link oceans with the land, creating global hot spots of carbon processing in coastal seas. Coastlines around the world
are dominated by sandy beaches, but beaches are unusual in that they are thought to rely almost exclusively on marine imports
for food. No significant connections to terrestrial production having been demonstrated. By contrast, we isotopically traced
carbon and nitrogen pathways leading to clams (Donax deltoides) on beaches. Clams from areas influenced by river plumes had significantly different isotope signatures (δ13C: −18.5 to −20.2‰; δ15N: 8.3–10.0‰) compared with clams remote from plumes (δ13C: −17.5 to −19.5‰; δ15N: 7.6–8.7‰), showing that terrestrial carbon and sewage, both delivered in river plumes, penetrate beach food webs. This
is a novel mechanism of trophic subsidy in marine intertidal systems, linking the world’s largest shore ecosystem to continental
watersheds. The same clams also carry pollution signatures of sewage discharged into rivers, demonstrating that coastal rivers
connect ecosystems in unexpected ways and transfer contaminants across the land–ocean boundary. The links we demonstrate between
terrigenous matter and the largest of all marine intertidal ecosystems are significant given the immense social, cultural,
and economic values of beaches to humans and the predicted consequences of altered river discharge to coastal seas caused
by global climate change. 相似文献
12.
We provide preliminary carbon (δ13C) and nitrogen (δ15N) stable isotope assessment of the Greenland halibut (Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin (Mallotus villosus) and epibenthic represented by shrimp (Lebbeus polaris). The δ13C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models,
IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ15N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore.
This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding
ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as
a useful tool for the study of diet in cold water fish species. 相似文献
13.
Stable isotope signatures of primary producers display high inter- and intraspecific variation. This is assigned to species-specific
differences in isotope fractionation and variable abiotic conditions, e.g., temperature, and nutrient and light availability.
As consumers reflect the isotopic signature of their food source, such variations have direct impacts on the ecological interpretation
of stable isotope data. To elucidate the variability of isotope fractionation at the primary producer level and the transfer
of the signal through food webs, we used a standardised marine tri-trophic system in which the primary producers were manipulated
while the two consumer levels were kept constant. These manipulations were (1) different algal species grown under identical
conditions to address interspecific variability and (2) a single algal species cultivated under different nutrient regimes
to address nutrient-dependent variability. Our experiments resulted in strong interspecific variation between different algal
species (Thalassiosira weissflogii, Dunaliella salina, and Rhodomonas salina) and nutrient-dependent shifts in stable isotope signatures in response to nutrient limitation of R. salina. The trophic enrichment in 15N and 13C of primary and secondary consumers (nauplii of Acartia tonsa and larval herring) showed strong deviations from the postulated degree of 1.0‰ enrichment in δ13C and 3.4‰ enrichment in δ15N. Surprisingly, nauplii of A. tonsa tended to keep “isotopic homeostasis” in terms of δ15N, a pattern not described in the literature so far. Our results suggest that the diets’ nutritional composition and food
quality as well as the stoichiometric needs of consumers significantly affect the degree of trophic enrichment and that these
mechanisms must be considered in ecological studies, especially when lower trophic levels, where variability is highest, are
concerned. 相似文献
14.
River flow,zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary
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N. Mbandzi R. J. Wasserman S. H. P. Deyzel N. G. Vine A. K. Whitfield 《Journal of fish biology》2018,92(6):1747-1767
The possible links between river flow, zooplankton abundance and the responses of zooplanktivorous fishes to physico‐chemical and food resource changes are assessed. To this end, the seasonal abundance, distribution and diet of the estuarine round‐herring Gilchristella aestuaria and Cape silverside Atherina breviceps were studied in the Kariega Estuary. Spatio‐temporal differences were determined for selected physico‐chemical variables, zooplankton abundance and zooplanktivorous fish abundance and distribution. Results indicated that, following a river flood event in winter (>30 m3 s?1), altered physico‐chemical conditions occurred throughout the estuary and depressed zooplankton stocks. Abundance of G. aestuaria was highest in spring, with this species dominant in the upper and middle zones of the estuary, while A. breviceps was dominant in summer and preferred the middle and lower zones. The catch per unit of effort of both zooplanktivores also declined significantly following the flooding, thus suggesting that these fishes are reliant on zooplankton as a primary food source for healthy populations. Copepods dominated the stomach contents of both fish species, indicating a potential for strong interspecific competition for food, particularly in the middle reaches. Temporal differences were evident in dietary overlap between the two zooplanktivorous fish species and were correlated with river flow, zooplankton availability and fish distribution. The findings of this study emphasize the close trophic linkages between zooplankton and zooplanktivorous fishes under changing estuarine environmental conditions, particularly river flow and provide important baseline information for similar studies elsewhere in South Africa and the rest of the world. 相似文献
15.
Particulate organic matter transported from rivers to estuaries (POMR) varies quantitatively and qualitatively across estuaries; however, a lack of comparative studies poses a challenge in general
understanding of responses of estuarine food webs to POMR input. We studied 20 estuarine tidal flats of the Pacific Northwest coast of North America, with watershed areas ranging
from 7 to 8000 km2. We used carbon-stable isotope (δ13C) to test the hypothesis that the nutritional contribution of POMR to macrobenthos is proportional to relative abundances of POMR in tidal flat sediments. The predominant origin of total POM (TPOM) in tidal flat sediments generally shifted from marine-origin
POM (POMM) to POMR as watershed area increased; however, terrestrial-origin POMR with high C/N predominated sediment TPOM even in estuaries with small watershed areas. Some macrobenthos species assimilated
POM sources in proportion to sediment TPOM composition, and incorporated POMR in POMR-predominant sediments. These species were considered to have low food selectivity; however, the relative nutritional contribution
of POMR to these macrobenthos was still lower than the fraction of POMR in sediment TPOM. Other species disproportionately utilized POMM and/or benthic microalgae regardless of the relative abundance of POMR, indicating their high food selectivity. The species-specific, low- or high-food selectivity was likely linked with deposit-feeding
and filter-feeding, respectively. Hence, our hypothesis was supported conditionally. Our findings indicate that watershed
area, relative abundance of POMR in an estuary, and food selectivity of estuarine species are key factors controlling the tightness of linkage between watersheds
and estuarine food webs. 相似文献
16.
Jianzhu Wang Binhe Gu Jianhui Huang Xingguo Han Guanghui Lin Fawen Zheng Yuncong Li 《PloS one》2014,9(7)
Understanding the carbon sources supporting aquatic consumers in large rivers is essential for the protection of ecological integrity and for wildlife management. The relative importance of terrestrial and algal carbon to the aquatic food webs is still under intensive debate. The Yangtze River is the largest river in China and the third longest river in the world. The completion of the Three Gorges Dam (TGD) in 2003 has significantly altered the hydrological regime of the middle Yangtze River, but its immediate impact on carbon sources supporting the river food web is unknown. In this study, potential production sources from riparian and the main river channel, and selected aquatic consumers (invertebrates and fish) at an upstream constricted-channel site (Luoqi), a midstream estuarine site (Huanghua) and a near dam limnetic site (Maoping) of the TGD were collected for stable isotope (δ13C and δ15N) and IsoSource analyses. Model estimates indicated that terrestrial plants were the dominant carbon sources supporting the consumer taxa at the three study sites. Algal production appeared to play a supplemental role in supporting consumer production. The contribution from C4 plants was more important than that of C3 plants at the upstream site while C3 plants were the more important carbon source to the consumers at the two impacted sites (Huanghua and Maoping), particularly at the midstream site. There was no trend of increase in the contribution of autochthonous production from the upstream to the downstream sites as the flow rate decreased dramatically along the main river channel due to the construction of TGD. Our findings, along with recent studies in rivers and lakes, are contradictory to studies that demonstrate the importance of algal carbon in the aquatic food web. Differences in system geomorphology, hydrology, habitat heterogeneity, and land use may account for these contradictory findings reported in various studies. 相似文献
17.
We investigated the impact of foraging location (nearshore vs offshore) and foraging latitude (high vs middle) on the carbon
(δ13C) and nitrogen (δ15N) isotope compositions of bone collagen of northern fur seals (Callorhinus ursinus), harbor seals (Phoca vitulina), California sea lions (Zalophus californianus), and northern elephant seals (Mirounga angustirostris). Nearshore-foraging harbor seals from California had δ13C values 2.0‰ higher than female northern elephant seals foraging offshore at similar latitudes. Likewise, nearshore-foraging
harbor seals from Alaska had values 1.7‰ higher than male northern fur seals, which forage offshore at high latitudes. Middle-latitude
pinnipeds foraging in either the nearshore or offshore were 13C enriched by ∼1.0‰ over similar populations from high latitudes. Male northern elephant seals migrate between middle and
high latitudes, but they had δ13C values similar to high-latitude, nearshore foragers. Female northern fur seal δ13C values were intermediate between those of high- and middle-latitude offshore foragers, reflecting their migration between
high- and middle-latitude waters. The δ13C values of California sea lions were intermediate between nearshore- and offshore-foraging pinnipeds at middle latitudes,
yet there was no observational support for the suggestion that they use offshore food webs. We suggest that their “intermediate”
values reflect migration between highly productive and less-productive, nearshore ecosystems on the Pacific coasts of California
and Mexico. The relative uniformity among all of these pinnipeds in δ15N values, which are strongly sensitive to trophic level, reveals that the carbon isotope patterns result from differences
in the δ13C of organic carbon at the base of the food web, rather than differences in trophic structure, among these regions. Finally,
the magnitude and direction of the observed nearshore-offshore and high-to middle-latitude differences in δ13C values suggest that these gradients may chiefly reflect differences in rates and magnitudes of phytoplankton production
as well as the δ13C value of inorganic carbon available for photosynthesis, rather than the input of 13C-enriched macroalgal carbon to nearshore food webs.
Received: 8 September 1998 / Accepted: 24 February 1999 相似文献
18.
Eriocheir sinensis H. Milne Edwards, 1853 is on the list of top 100 invaders compiled by the International Union for Conservation of Nature
and Natural Resources. The recent establishment of a large Chinese mitten crab population in San Francisco Bay and the potential
for introductions from California, Asia and Europe pose a significant invasion potential for estuaries and rivers from California
to Alaska. This alien species would place at risk the catchment areas of the Pacific Northwest including the economic and
social activities that depend upon intact aquatic systems. An analysis of ecological conditions that define the mitten crab’s
native and introduced range suggests that large stable estuaries with long flushing times are necessary to sustain significant
populations. Most Pacific Northwest estuaries have limited salinity intrusion, estuarine habitat and short flushing times
and face a reduced risk of population establishment. Large, stable estuaries, such as the Puget Sound, may support significant
populations. River-dominated estuaries, such as the Columbia River, have flushing times less than the duration of larval development
and wouldn’t support populations. An application of a temperature based larval development rate to near-shore and estuary
sea surface temperatures suggests that estuaries in Oregon and Washington have sufficient thermal regimes to support larval
development. Most estuary systems in Alaska have limited periods where water temperatures are above the mortality threshold
for the larval stages and are at a low risk for the establishment of populations. A potential sea temperature rise of two
degrees Celsius would permit larval development in Alaskan estuaries, where sufficient estuarine and freshwater habitats exist. 相似文献
19.
Duncan P. Gray Jon S. Harding Bo Elberling Travis Horton Tim J. Clough Mike J. Winterbourn 《Ecosystems》2011,14(4):583-597
Natural braided river floodplains typically possess high groundwater–surface water exchange, which is vital to the overall
function and structure of these complex ecosystems. Spring-fed streams on the floodplain are also hotspots of benthic invertebrate
diversity and productivity. The sources of carbon that drive these productive spring-fed systems are not well-known. We conducted
field assessments and a manipulation, modeling, and a laboratory experiment to address this issue. Initially δ13C values of both dissolved inorganic carbon (DIC) and food-web components of five springs were used to assess the sources
of carbon to spring food webs. Partial pressures of CO2 in upwelling water ranged from 2 to 7 times atmospheric pressure, but rapidly approached equilibrium with the atmosphere
downstream commensurate with 13C enrichment of DIC. Speciation modeling and a laboratory out-gassing experiment suggested that downstream changes in pH could
be explained solely by CO2 out-gassing. However, field results indicated that both out-gassing and photosynthetic drawdown by aquatic plants controlled
the net flux of CO2. A whole stream manipulation indicated out-gassing was the primary effect at the spring source, which was confirmed by invariant
diel pH. At 1296 m downstream from the spring source a large diel shift in pH indicated a plant effect on CO2 concentration which would contribute to the overall downstream gradient in δ13C DIC. Within the first 1296 m the gradient in δ13 DIC was transmitted through three trophic levels of the spring food web. These findings indicate dependency on groundwater
inorganic carbon by spring stream food webs and strong hydrologically mediated linkages connecting terrestrial, subsurface,
and aquatic components of the floodplain. 相似文献
20.
Isotopic analysis of three food web theories in constricted and floodplain regions of a large river 总被引:10,自引:0,他引:10
Analyses of stable isotope (δ13C and δ15N) and C:N ratios of food webs within a floodplain and a constricted-channel region of the Ohio River during October 1993
and July 1994 indicate that the increasingly influential flood pulse concept (FPC) does not, for either location, adequately
address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity
model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river.
These␣conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C3 trees, riparian C4 grasses and agricultural crops, submerged macrophytes, benthic filamentous algae, benthic particulate organic matter, and
transported organic matter containing detritus and phytoplankton) and various functional feeding groups of invertebrate and
fish consumers. The FPC, which stresses the key contribution of organic matter, particularly terrestrial organic matter, originating
from the floodplain to riverine food webs, was judged inappropriate for the floodplain region of the Ohio River for hydrodynamic
and biotic reasons. The rising limb and peak period of discharge typically occur in November through March when temperatures
are low (generally much less than 10°C) and greater than bank-full conditions are relatively unpredictable and short-lived.
The major food potentially available to riverine organisms migrating into the floodplain would be decaying vegetation because
autotrophic production is temperature and light limited and terrestrial insect production is minimal at that time. It is clear
from our data that terrestrial C4 plants contribute little, if anything, to the consumer food web (based on δ13C values), and δ15N values for C3 plants, coarse benthic organic matter, and fine benthic organic matter were too depleted (∼7–12‰ lower than most invertebrate
consumer values) for this organic matter to be supporting the food web. The RPM, which emphasizes the primary role of autotrophic
production in large rivers, is the most viable of the remaining two ecosystem models for the constricted-channel region of
the Ohio based on stable isotope linkage between sources and consumers of organic matter in the food web. The most important
form of food web organic matter is apparently transported (suspended) fine (FTOM) and ultra-fine particulate organic matter.
We propose that phytoplankton and detritus of an autochthonous origin in the seston would represent a more usable energy source
for benthic (bivalve molluscs, hydropsychid caddisflies) and planktonic (microcrustaceans) suspension feeders than the more
refractory allochthonous materials derived from upstream processing of terrestrial organic matter. Benthic grazers depend
heavily on nonfilamentous benthic algae (based on gut analysis from a separate study), but filamentous benthic algae have
no apparent connection to invertebrate consumers (based on δ13C values). Amphipod and crayfish show a strong relationship to aquatic macrophytes (possibly through detrital organic matter
rather than living plant tissue). These observations contrast with the prediction of the RCC that food webs in large rivers
are based principally on refractory FTOM and dissolved organic matter from upstream inefficiencies in organic-matter processing
and the bacteria growing upon these suspended or dissolved detrital compounds. The conclusions drawn here for the Ohio River
cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable
data are available on relatively pristine and moderately regulated rivers.
Received: 3 January 1997 / Accepted: 28 August 1998 相似文献