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71.
The sediment cores 225514 and 225510 were recovered from 420 and 285 m water depth, respectively. They were investigated for their benthic foraminiferal δ13C during the last 500 years. Both cores were recovered from the southern flank of the Skagerrak. The δ13C values of Uvigerina mediterranea and other shallow infaunal species in both cores indicate that organic matter rain rates to the seafloor varied around a mean value until approximately AD 1950 after which they increased. This increase might result from changes in the North Atlantic Current System and a co-occurring persistently high North Atlantic Oscillation index state in the 1980s to 1990s, rather than from anthropogenic eutrophication. Using δ13C mean values of multiple species, we reconstruct δ13C gradients of dissolved inorganic carbon (DIC) within pore waters for the time periods AD 1500 to 1950 and AD 1950 to 2000. The calculated δ13CDIC ranges, interpreted as indicating total organic matter remineralization due to respiration, are generally bigger in Core 225514 than in Core 225510. Since mean δ13C values of U. mediterranea suggest that organic matter rain rates were similar at both locations, differences in total organic matter remineralization are attributed to differing oxygen availability. However, oxygen concentrations in the overlying bottom water masses are not likely to have differed significantly. Thus, we suggest that organic matter remineralization was controlled by oxygen availability within the sediments, reflecting strong differences in sedimentation rates at the two investigated core sites. Based on the assumptions that tests of benthic foraminiferal species inhabiting the same microhabitat depth should show equal δ13C values unless they are affected by vital effects and that Globobulimina turgida records pore water δ13CDIC, we estimate microhabitat-corrected vital effects for several species with respect to G. turgida: > 0.7‰ for Cassidulina laevigata, > 1.3‰ for Hyalinea balthica, and > 0.7‰ for Melonis barleeanus. Melonis zaandami seems to closely record pore water δ13CDIC. 相似文献
72.
The assemblage composition of cryptic mobile animals inhabiting coral rubble was sampled using mesh traps containing clean
coral rubble, and used as indicators of land-based pollution at 14 sites in three coral lagoons at Ishigaki Island, southern
Japan. Cluster analyses identified three groups of large mobile animal assemblages (molluscs, echinoderms, fishes, decapod
and stomatopod crustaceans). Using a distance-based redundancy analysis (db-RDA) there was a significant relationship between
the assemblage composition and environmental variables. The 1st axis of the db-RDA ordination was regarded as the land-based
pollution gradient because of the strong relationship with silicate sediment, turbidity, and salinity, indicating effects
of terrestrial-sediment runoff. Species response curves were derived from a plot of the number of individuals against the
1st axis of the db-RDA sites sample score. The response curves of Galathea mauritiana, an indicator species for the intermediate sites, were unimodal along the land-based pollution gradient. This study demonstrates
the use of traps containing clean coral rubble for nondestructive quantitative sampling and environmental monitoring in coral
lagoons, and their potential for monitoring changes in the reef environment.
Communicated by Environmental Editor Prof. Rob van Woesik. 相似文献
73.
We studied the response of benthic algae to points of hyporheic-surface water exchange in the main channel of the Middle Fork
Flathead River within the Nyack Flood Plain, Montana. We examined hyporheic exchange at 120 sites using piezometers and measuring
vertical hydraulic gradient (VHG), hydraulic conductivity, and vertical discharge. We removed benthic algae from a single
cobble at each site, and we used VHG to group sampling sites for statistical analysis. Algal cell density and chlorophyll
a concentration were significantly higher at sites with hyporheic discharge (+VHG, upwelling) compared to both sites with hyporheic
recharge (−VHG, downwelling) and sites with no hyporheic-surface water exchange (=VHG, neutral) (ANOVA, P < 0.05). The assemblages of algae at upwelling sites were also significantly different from downwelling and neutral exchange
sites (ANOSIM, P < 0.05). Filamentous green algae Stigeoclonium sp. and Zygnema sp. and a chrysophyte, Hydrurus foetidus (Villars) Trevisan were abundant at upwelling sites, whereas an assemblage of diatoms Achnanthidium minutissimum (Kützing) Czarnecki, Cymbella excisa Kützing, Diatoma moniliformis Kützing, and Gomphonema olivaceoides Hustedt, were the most abundant taxa at downwelling and neutral exchange sites, occurring attached to, or in close association
with the stalks of Didymosphenia geminata (Lyngbye) Schmidt. These data show that benthic algal communities are structured differently depending on the direction of
hyporheic flux in the main channel of a large alluvial river, suggesting that hyporheic-surface exchange may influence the
spatial distribution of main-channel benthic algae in rivers with hyporheic-surface water connectivity.
Handling editor: J. Padisak 相似文献
74.
Until the E.U. Water Framework Directive listed benthic invertebrates as a biotic element to be used for ecological classification of lakes, techniques for the assessment of the response of littoral invertebrates to anthropogenic pressures were extremely limited compared with those of rivers and lake profundal zones. We describe here the development of an ecological classification model based on changes of littoral invertebrate assemblages across a gradient of eutrophication, which is the most widespread anthropogenic pressure on lakes across Europe. The model comprises three derived parameters, two of which were developed from taxon-specific optima along a total phosphorus gradient calculated using canonical correspondence analysis, and the third based on invertebrate abundance. Combining the parameter metrics, we can estimate the ecological quality ratio (EQR), relative to those from paleolimnologically-confirmed reference lakes. The model was tested using independent samples collected from both hard and soft substrata and across two seasons from 45 lakes, comprising three alkalinity groups (n = 15 in each), and across gradients in water column total phosphorus concentrations. For hard substrata, EQRs were related consistently and highly significantly to water column concentrations of total phosphorus, accounting for the majority of the variance in every alkalinity group. For samples taken from soft substrata, a significant relationship was found only for high alkalinity lakes, accounting for a moderate proportion of the variability in water column total phosphorus concentrations. Our results compare highly favourably with those from other aquatic ecological assessment methods, irrespective of the faunal or floral group upon which they are based, demonstrating that littoral invertebrate assemblages can provide a statistically robust prediction of nutrient status when samples are collected from hard substrata. While the method was developed specifically to assess nutrient pressures on littoral invertebrates, many lakes are subject to multiple pressures. The development of classification models that incorporate multiple pressures presents a particularly significant challenge for the implementation of the Water Framework Directive, requiring both reliable identification of minimally-impacted reference states and incorporation of pressures that are unlikely to interact in predictable ways. 相似文献
75.
The environment of Lake Carey, a large salt lake in the goldfields of Western Australia, has been subjected to mining for
the past 100 years. The effect of discharge of hypersaline water to the playa as a result of pit dewatering has been a grave
concern. The aim of this paper was to investigate the influences of seasonal parameters and mining activity on the physico-chemical
and biological attributes of Lake Carey. Assessment of water and sediment chemistry and benthic microbial communities (BMCs)
has been carried out opportunistically since 1999, with particular emphasis on the differences between sites receiving dewatering
discharge currently or in the past (Impacted Sites), and those which have never received dewatering discharge (Control Sites).
Results of water and sediment analyses indicated that the impacts of dewatering discharge on Lake Carey were localised and
evident in the vicinity of the discharge sites. However, large rainfall events, such as the cyclonic rainfall in 2004, could
result in flushing and amelioration of sediments. This was also reflected in the sites which were historically impacted by
dewatering discharge. The sites directly impacted by dewatering discharge displayed poor abundance and species richness of
diatoms compared to the sites unaffected by dewatering discharge. However, recovery of these sites in terms of species richness
and abundance is also initiated by large rainfall events, as shown by data collected from the historical dewatering discharge
sites.
Guest Editors: J. John & B. Timms
Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for
Salt Lake Research 相似文献
76.
Tadeu Siqueira Luis Mauricio Bini Marcus Vinicius Cianciaruso Fabio Oliveira Roque Susana Trivinho-Strixino 《Hydrobiologia》2009,620(1):163-172
In situ measurements of both community metabolism (primary production and respiration) and PAM fluorometry were conducted
during emersion on intertidal sediments in the Mont Saint-Michel Bay, in areas where oysters and mussels were cultivated.
Results highlighted a low benthic metabolism compared to other intertidal areas previously investigated with the same methods.
Comparisons between gross community primary production and relative electron transport rates confirmed this statement. More
specifically, primary productivity remained very low all over the year, whereas the associated microalgal biomass was estimated
to be high. We suggest that the microphytobenthic community studied was characterized by a self-limitation of its primary
productivity by its own biomass, as previously shown in Marennes-Oléron Bay for example. The almost permanent high biomass
would represent a limiting factor for micromigration processes within the first millimetres of the sediment. This could be
explained by very low resuspension processes occurring in the western part of the bay, enhanced by the occurrence of numerous
aquaculture structures that could decrease tidal currents in the benthic boundary layer.
Handling editor: N. Desroy 相似文献
77.
78.
Kjell Nordberg Helena L. Filipsson Pernilla Linn Mikael Gustafsson 《Marine Micropaleontology》2009,73(1-2):117-128
Significant faunal changes reported from recent, coastal environments, which are not directly influenced by urban and industrial impact, are rarely seen. In Gullmar Fjord on the Swedish west coast, a significant foraminiferal fauna change occurred in connection with severe low-oxygen conditions that evolved in the winter of 1979/1980. A foraminiferal fauna marked by common Skagerrak–Kattegat species, which had previously characterised the deep fjord basin, was replaced by the opportunistic, low-oxygen tolerant species Stainforthia fusiformis (Williamsson).To study this phenomenon further we performed stable oxygen and carbon isotope analyses on the indicator species itself, S. fusiformis, both on specimens from sediment cores representing approximately the last 85 years and on living (stained) individuals taken from a transect across the deep fjord basin. Our purpose was to detail how and why S. fusiformis, came to dominate the fauna.The oxygen isotope results suggest that salinities and temperatures in the deep basin have been relatively constant over the last c. 85 years, while the carbon isotopes show a significant change towards more negative values in association with the faunal shift of 1979/1980. The combined results from both the cores and the surface sediments suggest that S. fusiformis did not inhabit the deep basin until 1980. Before then, almost all specimens of S. fusiformis were small sized and their carbon isotope values suggest they were re-deposited shallow-water specimens that had been transported down to the central, deep basin as part of a suspension load. After a major faunal extinction in 1979–1980, S. fusiformis of all sizes suddenly appeared in large numbers and their carbon isotopic values were similar to the signal from registered in the recent, living fauna within the deep basin. This suggests that the opportunistic S. fusiformis established itself in the deep basin as a consequence of the severe low-oxygen event and the faunal crash of the previously dominating Skagerrak–Kattegat fauna. 相似文献
79.
Éric Armynot du Châtelet Viviane Bout-Roumazeilles Armelle Riboulleau Alain Trentesaux 《Revue de Micropaléontologie》2009,52(1):75
The paleoecological interpretation of fossil foraminiferal assemblages depends on an understanding of the ecological processes operating at the present. This study investigates both the quality of organic matter (OM) by elemental analysis as well as the sediment grain size and clay mineralogy to understand their relative influence on distribution and abundance of benthic foraminifera. This study is carried out on 15 samples regularly spaced from the mudflat to the tidal marsh. The results indicate that grain size is the most limiting parameter. Living (stained) benthic foraminiferal density and species richness are both very low within coarser sediments. OM is the second limiting factor. The density of foraminifera is the lowest and the species richness is the highest with the lowest organic carbon (Corg) contents and C/N < 12. Conversely, when the Corg is very high and C/N > 12, the density is high and the species richness medium. A high smectite proportion within the clay-size fraction seems to favor the development of Miliammina fusca. Trochammina inflata and Jadammina macrescens are both favored by an increase of organic carbon proportion but Trochammina inflata preferentially feeds on algal-derived OM when compared with Jadammina macrescens. 相似文献
80.
L.L. Loseto G.A. Stern T.L. Connelly B. Gemmill L. Fortier 《Journal of experimental marine biology and ecology》2009,374(1):12-18
Beluga whales (Delphinapterus leucas) are the most abundant odontocetes in Arctic waters and are thus thought to influence food web structure and function. The diet of the Beaufort Sea beluga population is not well known, partly due to the inherent difficulty of observing feeding behaviour in Arctic marine cetaceans. To determine which prey items are critical to the Beaufort Sea beluga diet we first examine and describe the Mackenzie Delta and Beaufort Sea food web using fatty acid analyses. Fatty acid profiles effectively partitioned prey items into groups associated with their habitat and feeding ecology. Next, the relative contribution of various prey items to beluga diet was investigated using fatty acids. Finally, beluga diet variability was examined as a function of body size, a known correlate of habitat use. Beluga appeared to feed predominantly on Arctic cod (Boreogadus saida) collected from near shore and offshore regions. Size related dietary differences suggested larger sized beluga preferred offshore Arctic cod given the shared high levels of long chain monounsaturates, whereas smaller sized beluga appeared to feed on prey in their near shore habitats that included near shore Arctic cod. The presence of Arctic cod groups in shallow near shore and deep offshore habitats may facilitate the behavioural segregation of beluga habitat use as it relates to their size and resource requirements. Given Arctic cod are a sea ice associated fish combined with the accelerated sea ice loss in this region, beluga whales may need to adapt to new dietary regimes. 相似文献