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William F. James 《Aquatic Sciences - Research Across Boundaries》2010,72(1):61-69
Backwaters connected to large rivers retain nitrate and may play an important role in reducing downstream loading to coastal
marine environments. A summer nitrogen (N) inflow-outflow budget was examined for a flow-regulated backwater of the upper
Mississippi River in conjunction with laboratory estimates of sediment ammonium and nitrate fluxes, organic N mineralization,
nitrification, and denitrification to provide further insight into N retention processes. External N loading was overwhelmingly
dominated by nitrate and 54% of the input was retained (137 mg m−2 day−1). Ammonium and dissolved organic N were exported from the backwater (14 and 9 mg m−2 day−1, respectively). Nitrate influx to sediment increased as a function of increasing initial nitrate concentration in the overlying
water. Rates were greater under anoxic versus oxic conditions. Ammonium effluxes from sediment were 26.7 and 50.6 mg m−2 day−1 under oxic and anoxic conditions, respectively. Since anoxia inhibited nitrification, the difference between ammonium anoxic–oxic
fluxes approximated a nitrification rate of 29.1 mg m−2 day−1. Organic N mineralization was 64 mg m−2 day−1. Denitrification, estimated from regression relationships between oxic nitrate influx versus initial nitrate concentration
and a summer lakewide mean nitrate concentration of 1.27 mg l−1, was 94 mg m−2 day−1. Denitrification was equivalent to only 57% of the retained nitrate, suggesting that another portion was assimilated by biota.
The high sediment organic N mineralization and ammonium efflux rate coupled with the occurrence of ammonium export from the
system suggested a possible link between biotic assimilation of nitrate, mineralization, and export. 相似文献
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Béatrice Allard Michaël Danger Loïc Ten-Hage Gérard Lacroix 《Aquatic Sciences - Research Across Boundaries》2011,73(1):113-126
The effects of food web structure on the quantity and biochemical composition of seston, zooplankton and recently deposited
sediment in experimental freshwater mesocosms were examined. Food web structure was manipulated by addition of zooplanktivorous
fish. Biochemical characterisations were carried out using lipid biomarkers (sterols, fatty acids, chlorophyll-derived compounds
and long-chain alkanediols). Fish addition decreased zooplankton biomass and increased seston biomass and deposited sediment
through a trophic cascade. Fish presence strongly influenced the biochemical characteristics of seston and sediment. In contrast,
food web structure had a minor impact on the lipid biomarker composition of zooplankton. Although the relative abundance of
sterols in the different compartments did not differ strongly between treatments, sterol profiles in seston and sediment depended
on food web structure. The predominance of Δ7-sterols in seston and sediment in the fish treatment indicated a major contribution of Chlorophyceae. In contrast, the distribution
of sterols in seston and sediment in the fishless treatment, dominated by cholesterol, indicated a major zooplanktonic input.
The distribution of fatty acids and the relative abundance of chlorophyll-derived compounds and long-chain alkanediols agreed
with the predominant contribution of phytoplankton or zooplankton to seston and sediment in the two treatments. The relative
abundance of bacterial biomarkers suggested that the contribution of bacteria was rather low. The high relative abundance
of polyunsaturated fatty acids (PUFAs) and the absence of stanols in sediments suggested low microbial reworking of organic
matter in the recently accumulated sediments. The trophic cascade, generated by the addition of fish, increased the relative
abundance of PUFAs in deposited organic matter, thus enhancing sediment quality and potential degradability. 相似文献
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Paula Sardiña Daniel H. Cataldo Demetrio Boltovskoy 《Aquatic Sciences - Research Across Boundaries》2009,71(4):479-486
We conducted a field experiment to assess the influence of conspecific adults on recruitment success of the golden mussel
Limnoperna fortunei. Tiles, 225 cm2 surface area, were used as artificial substrates in four treatments: control (blank tiles), low (800 mussels m−2), medium (4,000 mussels m−2) and high (12,000 mussels m−2) density treatments. Results indicated that recruitment was strongly affected by the presence and density of conspecifics.
After one and 3 months of exposure, numbers of recruits were significantly higher on tiles with conspecific adults than on
blank tiles, and there was a positive and significant relationship between the number of recruits and the number of adults
in the three treatments assayed. Also, after 3 months of exposure, recruits in all treatments with adults present were larger
than recruits in the control treatment. Our results suggest that conspecific adults have a positive effect on recruitment
success and growth of newly settled juveniles through factors that enhance larval settling or that contribute to the survival
of settlers in areas colonized by adult conspecifics. 相似文献
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《Continental Shelf Research》2006,26(17-18):2260-2280
On October 3, 2002 Hurricane Lili made landfall on a previously studied region of the inner Louisiana shelf as a Category 2 storm with winds over 160 km/h. A week after the hurricane, major impacts of the storm were not evident in the water column except for the lower than expected inshore salinities (∼12 psu) for this time of year, which was characterized by low river discharge. Turbidity profiles were typical of those measured during previous investigations with suspended sediment concentrations >75 mg/L at inshore stations and <50 mg/L in surface waters and offshore. The implication is that the sediments resuspended during the hurricane settled soon after the storm passage. Water column particulate organic carbon (POC) concentrations ranged from 0.1 to over 2.0 mg/L, with the highest concentrations measured near the seabed and in the inshore portions of the study area. Suspended particles were characterized by low organic matter content (%POC of 0.5–2 wt%), low chlorophyll:POC ratios (Chl:POC<4 mg/g) and moderately elevated POC:particulate nitrogen ratios (POC:PN of 10–14 mol/mol), all suggesting their source was locally resuspended seabed sediment rather than from algal biomass or land-derived vascular plant detritus.Post hurricane sediment deposition throughout the study area resulted in a storm layer that ranged from <0.5 to 20 cm in thickness. In most locations sediment accumulation ranged from 3 to 10 cm. The storm deposits were generally composed of silty clays with a coarser, somewhat sandy 1–2 cm basal layer. Surface sediments from the storm layer were characterized by relatively high mineral surface areas (SA of 30–50 m2/g) and elevated OC contents (%OC of 1.0–2.0%). The dispersal of fine sediments following the hurricane resulted in marked changes in the SA and %OC values of surface sediments from offshore locations, which prior to the storm contained coarser, organic-poor particles (SA of 5–15 m2/g and %OC of 0.2–0.6%). The OC:SA and OC:N ratios of storm layer sediments ranged from 0.4 to 0.6 mg OC/m2 and from 10 to 12 mol/mol, respectively, and were comparable to those measured in surface sediments prior to the hurricane. Such similarities in the composition of the organic matter reinforce the idea that the source of the storm deposits was the finer fraction of resuspended seabed sediments, with little evidence for inputs from local land-derived sources or autochthonous algal production. Overall, the magnitude of sediment and organic matter deposition on the seabed after the storm greatly exceeded the annual inputs from the Atchafalaya River and coastal primary production. The combined effects of hurricane-driven erosion and post-storm deposition represent a major perturbation to the benthic community of the region, which is already subject to these types of disturbances due to the combined effects of peaks in river discharge and the passage of storm fronts. 相似文献
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Organic biomarkers for tracing carbon cycling in the Gulf of Papua (Papua New Guinea) 总被引：1，自引：0，他引：1
K.A. Burns P. Greenwood R. Benner D. Brinkman G. Brunskill S. Codi I. Zagorskis 《Continental Shelf Research》2004,24(19):2373-2394
Sediment traps were deployed in the Gulf of Papua in June–July 1997, to determine fluxes of organic matter and inorganic elements from the photic zone to deeper waters at the base of the continental slope and in the northern Coral Sea. Three stations, ranging from 900 to 1500 m depth, had “shallow” traps at 300 m below the water surface and “deep” traps set 100 m above the bottom. Infiltrex II water samplers collected particulate and dissolved organic matter from the Fly, Purari and Kikori rivers, and near-surface water from the shelf of the Gulf of Papua. Samples were analysed for molecular organic biomarkers to estimate the sources of organic carbon and its cycling processes.Dry weight fluxes from the shallow traps ranged from 115 to 181 mg m−2 day−1 and particulate organic carbon (POC) fluxes ranged from 1.2 to 1.9 mM OC m−2 d−1 with molar organic carbon to particulate nitrogen ratios (C/N) ranging from 6.0 to 6.5. Fluxes in deep traps were likely influenced by both early diagenesis and entrapment of resuspended shelf sediments. Dry weight fluxes in deep traps ranged from 106 to 574 mg m−2 day−1 and POC fluxes ranged from 0.6 to 1.5 mM OC m−2 d−1, with C/N ratios ranging from 8.5 to 10.8. 13C/12C ratios were −20.2‰ to −21.7‰ in all trap samples, indicating that most of the settling POC was “marine-derived”. Shallow traps had δ15N values of 6.3‰ to 7.2‰ while the values in deep traps were 4.9–5.0‰, indicating the N-rich near-surface OC was less degraded than that in the deep traps. The biogenic lipids consisted of hydrocarbon, sterol and fatty acid biomarkers indicative of marine zooplankton, phytoplankton and bacteria. Sterol markers for diatoms and dinoflagellates were abundant in the water samples. Highly branched isoprenoid alkenes, usually attributable to diatoms, were also detected in both water and shallow traps. Traces of C26–C34 n-alcohols indicative of land–plant biomarkers, were found in river water samples and in the shallow sediment traps. A large unresolved complex mixture (UCM) of hydrocarbons, and a uniform distribution of n-alkanes, indicative of petroleum hydrocarbons, were also detected in the traps. Hopane and sterane biomarkers detected in the trap oil were characteristic of a marine carbonate source, and the aromatic hydrocarbon composition distinguished at least two different oil signatures.We concluded that mass and POC fluxes were similar to those reported for other continental shelves and marginal oceans in tropical and subtropical regions. There was a dramatic decrease in POC as particles sank, due to zooplankton repackaging and photochemical and bacterial decomposition. Carbon isotopic and biomarker patterns showed most of the POC in the sediment traps was marine-sourced with only traces of terrestrial input. There was a significant flux of petroleum, which may signal the existence of natural petroleum seeps in this region. 相似文献
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Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes
Monica Pinardi Marco Bartoli Daniele Longhi Pierluigi Viaroli 《Aquatic Sciences - Research Across Boundaries》2011,73(3):389-403
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine
the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of
dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously,
benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle
Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4
+ (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4
+ m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3
− m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads.
This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic
primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks,
although they simultaneously release CO2 to the atmosphere. 相似文献
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Young-Joo Lee 《中国科学D辑(英文版)》2006,49(8):872-880
Serious interest has been directed toward natural gas hydrate as a potential energy resource; factor in global climate change, and submarine geohazard since naturally occurring gas-hydrate deposits were found in the 1960s. Hydrate Ridge, Cascadia convergent mar- gin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities, and some of the highest methane oxidation rates ever found in the ma-rine environment. All of… 相似文献
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In the region southeast of Okinawa, during May to July 2001, a cyclonic and an anticyclonic eddy were observed from combined measurements of hydrocasts, an upward-looking moored acoustic Doppler current profiler (MADCP), pressure-recording inverted echo sounders (PIESs), satellite altimetry, and a coastal tide gauge. The hydrographic data showed that the lowest/highest temperature (T) and salinity (S) anomalies from a 13-year mean for the same season were respectively -3.0/ 2.5℃ and -0.20/ 0.15 psu at 380/500 dbar for the cyclonic/anticyclonic eddies. From the PIES data, using a gravest empirical mode method, we estimated time-varying surface dynamic height (D) anomaly referred to 2000 dbar changing from -20 to 30 cm, and time-varying T and S anomalies at 500 dbar ranging through about ±2 ℃ and ±0.2 psu, respectively. The passage of the eddies caused variations of both satellite-measured sea surface height anomaly (SSHA) and tide-gauge-measured sea level anomaly to change from about –20 to 30 cm, consistent with the D anomaly from the PIESs. Bottom pressure sensors measured no variation related to these eddy activities, which indicated that the two eddies were dominated by baro-clinicity. Time series of SSHA map confirmed that the two eddies, originating from the North Pacific Subtropical Countercurrent region near 20°―30°N and 150°―160°E, traveled about 3000 km for about 18 months with mean westward propagation speed of about 6 cm/s, before arriving at the region southeast of Okinawa Island. 相似文献
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Chu-Chih Chen Kuen-Yuh Wu Guo-Ping Chang-Chien 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):929-937
A point source for environmental pollution may be identified by the spatial association of samples collected in the vicinity
of the emission source. In this study, we used a simple permutation test to explore the spatial correlations between the ambient
air and soil polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/F) congener profile concentrations and their distances to a municipal solid waste incinerator (MSWI)
in northern Taiwan. Kendall’s τ was applied for the correlation between the PCDD/F concentrations of a total of 9 airborne
and 12 soil sampling sites and their distances to the incinerator. The results showed that the correlation was highly negatively
associated for soil PCDD/Fs (τ = −0.515, p-value = 0.011) and was marginal for airborne PCDD/Fs (τ = −0.667, p-value = 0.055), conditional on the seasonal wind attributions. For the 17 individual congener profiles, most of the air and
soil samples had a negative association, with 7 and 10 reaching statistical significance (p-value < 0.05) or borderline significance (p-value < 0.10), respectively. The permutation test provides a simple and robust statistical method for the identification
of a potential pollution source from a limited sample size. Our analytical results show that dioxin emissions from the investigated
MSWI had a definite environmental impact on the surrounding area. 相似文献
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Giuseppe Crosa Elena Castelli Gaetano Gentili Paolo Espa 《Aquatic Sciences - Research Across Boundaries》2010,72(1):85-95
The downstream ecological consequences of two controlled “free flow” flushing operations designed to remove sediments accumulated
in an alpine reservoir are described. The main objectives of the study were (a) to verify to what extent the suspended solid
concentration (SSC) in the receiving water course can be controlled by flushing operations, (b) to determine the biological
consequences of flushing operations, and (c) to produce technical guidelines for the future planning and monitoring of these
activities. We found that the flushing of large volumes of accumulated sediment had clear effects on the stream ecosystem
due to the unpredictability of short duration SSC peaks (70–80 g L−1) and the high average SSC (4–5 g L−1) within flushing periods. The main impacts were decreased fish densities (up to 73%) and biomass (up to 66%). A greater mortality
recorded for juveniles will likely result in long-term impairment of the age-structures of future fish populations. The zoobenthic
assemblages, despite exhibiting a drastic reduction in abundance following the first floods, showed substantial recovery within
3 months of the beginning of flushing operations. Regular sediment removal by yearly flushing is recommended in order to avoid
SSC peaks and to facilitate the control of scouring effects caused by the water used to wash out sediments. We also recommend
maximum allowable SSCs of 10 g L−1 (daily average) and 5 g L−1 (overall average) for flushing operations carried out in similar environmental contexts. 相似文献
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Sediment characteristics and wind-induced sediment dynamics in shallow Lake Markermeer, the Netherlands 总被引：2，自引：1，他引：1
P. Kelderman R. O. Ang’weya P. De Rozari T. Vijverberg 《Aquatic Sciences - Research Across Boundaries》2012,74(2):301-313
In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment
characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed
a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations
were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey
at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly
correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake
Markermeer were high, viz. on average ca. 1,000 g m−2 day−1. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with
its large surface area (dynamic ratio = [√(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most
of the lake’s sediment bed. Indeed, near-bed currents can easily reach values >10 cm/s. Measurements of the thickness of the
settled “mud” layer, as well as 137Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics
were investigated in preliminary laboratory experiments in a small “micro-flume”, applying increasing water currents onto
five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour
with respect to these currents. 相似文献
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Chu-Chih Chen Kuen-Yuh Wu Guo-Ping Chang-Chien 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(2):225-233
A point source for environmental pollution may be identified by the spatial association of samples collected in the vicinity
of the emission source. In this study, we used a simple permutation test to explore the spatial correlations between the ambient
air and soil polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/F) congener profile concentrations and their distances to a municipal solid waste incinerator (MSWI)
in northern Taiwan. Kendall’s τ was applied for the correlation between the PCDD/F concentrations of a total of 9 airborne and 12 soil sampling sites and
their distances to the incinerator. The results showed that the correlation was highly negatively associated for soil PCDD/Fs
(τ = −0.515, p-value = 0.011) and was marginal for airborne PCDD/Fs (τ = −0.667, p-value = 0.055), conditional on the seasonal wind attributions. For the 17 individual congener profiles, most of the air and
soil samples had a negative association, with 7 and 10 reaching statistical significance (p-value < 0.05) or borderline significance (0.05 < p-value < 0.10), respectively. The permutation test provides a simple and robust statistical method for the identification
of a potential pollution source from a limited sample size. Our analytical results show that dioxin emissions from the investigated
MSWI had a definite environmental impact on the surrounding area. 相似文献
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Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland, USA 总被引：2，自引：0，他引：2
Carolyn A. Klocker Sujay S. Kaushal Peter M. Groffman Paul M. Mayer Raymond P. Morgan 《Aquatic Sciences - Research Across Boundaries》2009,71(4):411-424
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects
of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in
Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of
stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to
its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some
stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable
across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was
low in the restored streams during summer baseflow conditions. Uptake length of NO3
−–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3
−–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m
in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank
Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may
be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with
hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary,
however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in
response to the “flashy” hydrologic flow conditions during storms common in urban streams. 相似文献