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81.
The cladoceran Daphnia magna was acclimated for seven generations to cadmium concentrations ranging from 0 (control) to 250 microg/l Cd (corresponding to a free ion activity of 4.60 nM Cd2+). Acute and chronic cadmium tolerance as well as cadmium accumulation were monitored as a function of acclimation time. After two to three generations of acclimation to concentrations ranging from 0.23 to 1.11 nM Cd2+ increases in acute tolerance were maximal (factor 7.2) and significant. Acclimation for seven generations to the same acclimation concentrations did result in an increased chronic cadmium tolerance (21 days EC50 values increased). Organisms acclimated to 1.93 nM Cd2+ were equally or more sensitive than non-acclimated daphnids in acute and chronic toxicity tests. Cadmium contents in D. magna increased significantly as a function of the acclimation concentration. Maximum body burdens of 236+/-30 microg Cd/g dry weight were measured in organisms exposed to 4.60 nM Cd2+, but detoxification mechanisms were only successful up to 82+/-20 microg Cd/g dry weight as this concentration did not cause major decreases in survival and reproduction in chronic toxicity tests. As the potential positive effect of acclimation on cadmium tolerance disappeared with successive acclimation generations and increasing acclimation concentrations, it is concluded that multi-generation acclimation studies are important for the evaluation of the long-term effects of environmental toxicants. 相似文献
82.
Root porosity and radial oxygen loss related to arsenic tolerance and uptake in wetland plants 总被引:5,自引:0,他引:5
The rates of radial oxygen loss (ROL), root porosity, concentrations of arsenic (As), iron (Fe) and manganese (Mn) in shoot and root tissues and on root surfaces, As tolerances, and their relationships in different wetland plants were investigated based on a hydroponic experiment (control, 0.8, 1.6 mg As L−1) and a soil pot trail (control, 60 mg As kg−1). The results revealed that wetland plants showed great differences in root porosity (9-64%), rates of ROL (55-1750 mmo1 O2 kg−1 root d.w. d−1), As uptake (e.g., 8.8-151 mg kg−1 in shoots in 0.8 mg As L−1 treatment), translocation factor (2.1-47% in 0.8 mg As L−1) and tolerance (29-106% in 0.8 mg As L−1). Wetland plants with higher rates of ROL and root porosity tended to form more Fe/Mn plaque, possess higher As tolerance, higher concentrations of As on root surfaces and a lower As translocation factor so decreasing As toxicity. 相似文献
83.
The aqueous solubility of hexafluorobenzene has been determined, at 298.15 K, using a shake-flask method with a spectrophotometric quantification technique. Furthermore, the solubility of hexafluorobenzene in saline aqueous solutions, at distinct salt concentrations, has been measured. Both salting-in and salting-out effects were observed and found to be dependent on the nature of the cationic/anionic composition of the salt. COSMO-RS, the Conductor-like Screening Model for Real Solvents, has been used to predict the corresponding aqueous solubilities at conditions similar to those used experimentally. The prediction results showed that the COSMO-RS approach is suitable for the prediction of salting-in/-out effects. The salting-in/-out phenomena have been rationalized with the support of COSMO-RS σ-profiles. The prediction potential of COSMO-RS regarding aqueous solubilities and octanol-water partition coefficients has been compared with typically used QSPR-based methods. Up to now, the absence of accurate solubility data for hexafluorobenzene hampered the calculation of the respective partition coefficients. Combining available accurate vapor pressure data with the experimentally determined water solubility, a novel air-water partition coefficient has been derived. 相似文献
84.
Over the past century, the Venice lagoon has experienced a high rate of wetland loss and a strong net export of sediments;
currently the local Authority is running several projects for beneficial use of dredging materials. From March 1993 until
March 1995 the accretionary response of wetlands in the lagoon to changing water levels was studied. Vertical accretion, short
term sedimentation and surface elevation change were measured at six sites with varying sediment availability and wave energy.
Short term sedimentation averaged 6.85 g m−2 d−1 with a minimum of 0.06 g and a maximum of 72 g during periods of high tides and storms. Over two years accretion ranged from
0.3 to 2.3 cm/yr and surface elevation change ranged from+0.7 to −3.7 cm/yr. The sites with highest accretion were near a
river mouth and a site with strong wave energy and rapid erosion of the marsh edge with a high resuspended sediment availability.
The rate of accretion at three sites was clearly sufficient to offset relative sea level rise, but a saline site with low
sediment availability had the lowest accretion. A sediment fence significantly increased accretion at one site. The results
suggest that reduction of turbulent motion or increasing sediment availability are needed to offset wetland loss in different
areas of the lagoon. 相似文献
85.
Joost H. M. de Ruig 《Journal of Coastal Conservation》1998,4(2):127-134
The boundary between land and sea in The Netherlands changes continuously. Every kilometre of the present position of the
Dutch sandy coastline is the result of the interface between natural dynamics initiated by the sea and man-made action on
land.
Before 1990, each year ca. 20 ha of dunes disappeared through coastal retreat. In 1990 the Dutch government decided to stop
any further long-term coastal recession and chose for ‘dynamic preservation’, which primarily aims, at ensuring safety against
flooding and sustainable preservation of the values and interests attached to the dunes and beaches.
Five years later, a first review of the benefits and bottlenecks of the new coastal defence policy could be presented. The
overall conclusion is that the 1990-choice for dynamic preservation was right. The considerable losses of dunes and beaches
do not occur any longer. Sand nourishment is an effective method of coastline maintenance, which also serves the functions
of the beach and dune area for human society.
However, serious erosion of the deeper part of the shoreface threatens the coastline of the 21st century. Nearly a doubling
of the nourishment volume is necessary to prevent a renewed landward shift of the coastline. An anticipated accelerated sea
level rise (ca. 60 cm/century) will increase the sand losses by another 25%.
Plans are being finalized for large-scale land reclamation in front of the coastline as an answer to growing spatial problems
on land. In other plans polders, now safely protected by sea dikes, will be returned to the sea in order to restore ecologically
valuable salt marshes and mud flats.
The position of the coastline will continue to change in the coming decades. Besides natural dynamics, human use of the coastal
zone will certainly affect this process: measures to maintain the coastline at its 1990 position need to be seen in perspective:
the coastline as a part of the coastalzone. 相似文献
86.
Marsh surface sediment deposition and the role of tidal creeks: Implications for created and managed coastal marshes 总被引:3,自引:0,他引:3
Denise J. Reed Thomas Spencer Anne L. Murray Jonathan R. French Lynn Leonard 《Journal of Coastal Conservation》1999,5(1):81-90
The need to understand the processes contributing to marsh sedimentation has become more urgent with the recent recognition
of the role of tidal marshes as sea defences, as well as the many restoration efforts currently under way. This study was
designed to build upon previous sedimentation work at Scolt Head Island by Combining techniques for measuring short-term sedimentation,
with detailed assessment of hydroperiod, previously used only in comparison with longer-term accretion measurements or in
micro-tidal systems. Measurements of water level, sediment deposition (at various distances from the creek margin) and suspended
sediment concentration (SSC) (creek margin and an interior site) were made at Hut Marsh over three sequential over-marsh tides
during May 1994. Sediment trap data show a significant trend of declining sediment deposition away from the creek when data
from all three tides are combined. All tides show higher SSC on the flood tide than on the ebb tide at the creek margin location.
There is little difference in flood and ebb SSCs at the interior site. An order of magnitude decrease in sediment deposition
within 20 m on the creek shows the rapidity with which sediment is deposited on these marshes. Higher tides influence both
the magnitude and pattern of marsh surface sediment deposition. Increased creek velocities on higher tides provide more potential
for resuspension within the creek and increase the supply of sediment to the marsh surface. This study suggests that the design
of tidal creeks may be essential for the development of sustainable coastal marshes in restoration projects. 相似文献
87.
Cadmium accumulation in and tolerance of rice (Oryza sativa L.) varieties with different rates of radial oxygen loss 总被引:1,自引:0,他引:1
Wang MY Chen AK Wong MH Qiu RL Cheng H Ye ZH 《Environmental pollution (Barking, Essex : 1987)》2011,159(6):1730-1736
Cadmium (Cd) uptake and tolerance were investigated among 20 rice cultivars based on a field experiment (1.2 mg Cd kg−1 in soil) and a soil pot trial (control, 100 mg Cd kg−1), and rates of radial oxygen loss (ROL) were measured under a deoxygenated solution. Significant differences were found among the cultivars in: (1) brown rice Cd concentrations (0.11-0.29 mg kg−1) in a field soil, (2) grain Cd tolerance (34-113%) and concentrations (2.1-6.5 mg kg−1) in a pot trial, and (3) rates of ROL (15-31 mmol O2 kg−1 root d.w. h−1). Target hazard quotients were calculated for the field experiment to assess potential Cd risk. Significant negative relationships were found between rates of ROL and concentrations of Cd in brown rice or straw under field and greenhouse conditions, indicating that rice cultivars with higher rates of ROL had higher capacities for limiting the transfer of Cd to rice and straw. 相似文献
88.
Marques B Lillebø AI Pereira E Duarte AC 《Environmental pollution (Barking, Essex : 1987)》2011,159(7):1869-1876
In this study two time scales were looked at: a yearlong study was completed, and a 180-day decay experiment was done. Juncus maritimus and Scirpus maritimus have different life cycles, and this seems to have implications in the Hg-contaminated salt marsh sediment chemical environment, namely Eh and pH. In addition, the belowground biomass decomposition rates were faster for J. maritimus, as well as the biomass turnover rates. Results show that all these species-specific factors have implications in the mercury dynamics and sequestration. Meaning that J. maritimus belowground biomass has a sequestration capacity for mercury per square metre approximately 4-5 times higher than S. maritimus, i.e., in S. maritimus colonized areas Hg is more extensively exchange between belowground biomass and the rhizosediment. In conclusion, J. maritimus seems to provide a comparatively higher ecosystem service through phytostabilization (Hg complexation in the rhizosediment) and through phytoaccumulation (Hg sequestration in the belowground biomass). 相似文献
89.
A field survey was conducted to identify potential Zn accumulators from an artisanal Zn smelting area in southwest China’s Guizhou Province. Hydroponic and soil culture experiments were performed to investigate the accumulation ability of Zn in Corydalis davidii. Zn concentrations in roots, stems and leaves of C. davidii in the smelting site were 1.1-3.5, 1.2-11.2, and 3.3-14 mg g−1, respectively, whereas Zn concentrations in roots, stems and leaves of C. davidii in the contaminated site impacted by the Zn smelting were 1.0-2.4, 1.9-6.5, and 3.0-1.1 mg g−1, respectively. Zn concentrations in leaves and stems of C. davidii were observed at above 10 mg g−1 that refers to the threshold of Zn hyperaccumulator. The concentration distribution of Zn in C. davidii was leaf > stem > root, and the Zn bioaccumulation factors of C. davidii were above 1. It is concluded that C. davidii has high tolerance to concentrate Zn stress, and that C. davidii is a newly discovered Zn-hyperaccumulator with high biomass in the aboveground parts. Based on the cultivation experiments, C. davidii could reduce Zn concentration by 26.6, 21.2, and 10.2 mg kg−1yr−1 by phytoextraction from the smelting slag, Zn-contaminated soil, and background soil, respectively. 相似文献
90.