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1.
In Brazil, where reefs occur in markedly turbid environments, the relationship between sedimentation/organic matter and corals is poorly known. Thus, the ex situ effects of sediment with and without organic matter over the ΔF/Fm and physical state of Mussismilia braziliensis were analyzed. The ΔF/Fm and coral physical state, evaluated through the susceptibility index to sedimentation (SI), were measured in seven colonies exposed to sedimentation (0–450 mg cm−2 day−1) free of organic matter after 45 days of exposure, and in 12 colonies exposed to sedimentation (0–500 mg cm−2 day−1) with organic matter content (10%), in which case ΔF/Fm was measured after 72 h and SI after 120 h. In both cases there were effects of increasing sedimentation on the SI with no effect on ΔF/Fm. Despite the tolerance to high sedimentation rates shown by this coral, we noted that the presence of organic matter might reduce its tolerance to sedimentation stress.  相似文献   

2.
The major goals of this study were to determine stream bed sediment erosion/deposition rates, sediment age, percent ‘new’ sediment, and suspended sediment origin during two storm events of contrasting magnitudes (11.9 mm over 5 h and 58.9 mm over 39 h) using fallout radionuclides (excess lead 210 – 210Pbxs and beryllium 7 – 7Be) and link the nature and type of sediment source contributions to potential phosphorus (P) off‐site transport. The study was conducted in cropland‐dominated and mixed land use subwatersheds in the non‐glaciated Pleasant Valley watershed (50 km2) in South Central Wisconsin. Fine sediment deposition and erosion rates on stream beds varied from 0.76 to 119.29 mg cm?2 day?1 (at sites near the watershed outlet) and 1.72 to 7.72 mg cm?2 day?1 (at sites in the headwaters), respectively, during the two storm events. The suspended sediment age ranged from 123 ± 12 to 234 ± 33 days during the smaller storm event; however, older sediment was more prevalent (p = 0.037) in the streams during the larger event with suspended sediment age ranging from 226 ± 9 to 322 ± 114 days. During the small and large storm event, percent new sediment in suspended sediment ranged from 5.3 ± 2.1 to 21.0 ± 2.9% and 5.3 ± 2.7 to 6.7 ± 5.7%, respectively. In the cropland‐dominated subwatershed, upland soils were the major source of suspended sediment, whereas in the mixed land use subwatershed, both uplands and stream banks had relatively similar contributions to suspended sediment. In‐stream (suspended and bed) sediment P levels ranged from 703 ± 193 to 963 ± 84 mg kg?1 during the two storm events. The P concentrations in suspended and bed sediment were reflective of the dominant sediment source (upland or stream bank or mixed). Overall, sediment transport dynamics showed significant variability between subwatersheds of different land use characteristics during two contrasting storm events. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
Sediment cores from central Lake Constance were dated with210Pb and137Cs. A sedimentation rate of (0.11±0.02) g·cm−2·y−1 was determined with the210Pb method.137Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm−2·y−1 and (0.08±0.01) g·cm−2·y−1 respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the137Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from7Be measurements.  相似文献   

4.
Measurements of visible and diffuse gas emission were conducted in 2006 at the summit of Sierra Negra volcano, Galapagos, with the aim to better characterize degassing after the 2005 eruption. A total SO2 emission of 11?±?2?t day?1 was derived from miniature differential optical absorption spectrometer (mini-DOAS) ground-based measurements of the plume emanating from the Mini Azufral fumarolic area, the most important site of visible degassing at Sierra Negra volcano. Using a portable multigas system, the H2S/SO2, CO2/SO2, and H2O/SO2 molar ratios in the Mina Azufral plume emissions were found to be 0.41, 52.2, and 867.9, respectively. The corresponding H2O, CO2, and H2S emission rates were 562, 394, and 3?t day?1, respectively. The total output of diffuse CO2 emissions from the summit of Sierra Negra volcano was 990?±?85?t day?1, with 605?t day?1 being released by a deep source. The diffuse-to-plume CO2 emission ratio was about 1.5. Mina Azufral fumaroles released gasses containing 73.6?mol% of H2O; the main noncondensable components amounted to 97.4?mol% CO2, 1.5?mol% SO2, 0.6?mol% H2S, and 0.35?mol%?N2. The higher H2S/SO2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions. 3He/4He ratios measured at Mina Azufral fumarolic discharges showed values of 17.88?±?0.25?R A , indicating a mid-ocean ridge basalts (MORB) and a Galapagos plume contribution of 53 and 47?%, respectively.  相似文献   

5.
Using sediment traps, we aimed to elucidate the temporal and spatial variations in sediment fluxes in large and shallow Lake Peipsi, over the May to October 2011 period, and analyze the factors behind those variations. The effects of weather factors (mean and maximum wind velocity, water level and water temperature) on sediment resuspension and the concentrations of suspended solids (SS), total phosphorus (TP), soluble reactive phosphorus (SRP), and chlorophyll a (Chl a) were investigated. Moreover, the internal loading of TP due to sediment resuspension was determined. The sediment resuspension rates were significantly higher in the shallower waters than in the deeper parts of the lake. Resuspension was a major factor in sedimentation dynamics of the lake, which is presently subject to eutrophication. The rates of sediment resuspension followed the same pattern as gross sedimentation during the study period, and their respective values differed significantly between sampling dates. The highest resuspension rates were observed in September (mean 55.4 g dw m?2 day?1), when the impacts of wind events were particularly pronounced. Weather factors that were recorded approximately 2 weeks before water and sediment sampling affected the gross sedimentation and sediment resuspension. The water quality variables of SS, TP, SRP, Chl a were similarly affected. During the study, TP concentrations of the water were mainly determined by the resuspension of sediments containing a large pool of organic material. Although internal loading of TP due to resuspension was several times greater than external loading, external loading determines the amount of phosphorus that enters the lake and can be resuspended.  相似文献   

6.
We investigated greenhouse gas emissions (CO2, CH4, and N2O) from reservoirs located across an altitude gradient in Switzerland. These are the first results of greenhouse gas emissions from reservoirs at high elevations in the Alps. Depth profiles were taken in 11 reservoirs located at different altitudes between the years 2003 and 2006. Diffusive trace gas emissions were calculated using surface gas concentrations, wind speeds and transfer velocities. Additionally, methane entering with the inflowing water and methane loss at the turbine was assessed for a subset of the reservoirs. All reservoirs were emitters of carbon dioxide and methane with an average of 970?±?340?mg?m?2?day?1 (results only from four lowland and one subalpine reservoir) and 0.20?±?0.15?mg?m?2?day?1, respectively. One reservoir (Lake Wohlen) emitted methane at a much higher rate (1.8?±?0.9?mg?m?2?day?1) than the other investigated reservoirs. There was no significant difference in methane emissions across the altitude gradient, but average dissolved methane concentrations decreased with increasing elevation. Only lowland reservoirs were sources for N2O (72?±?22???g?m?2?day?1), while the subalpine and alpine reservoirs were in equilibrium with atmospheric concentrations. These results indicate reservoirs from subalpine/alpine regions to be only minor contributors of greenhouse gases to the atmosphere compared to other reservoirs.  相似文献   

7.
Vertical profiles of excess bottom222Rn and potential temperature were measured at 23 stations in the northwestern Pacific Ocean. The Rn profiles were classified into the following three types: quasi-exponential (type E), benthic boundary layer (type B), and horizontally disturbed (type H). The ratio among types E, B and H was approximately 2 : 3 : 1.An apparent vertical eddy diffusivity (K) was calculated by applying a one-dimensional diffusion model to the Rn profiles of types E and B. Type E had K values ranging from 15 to 180 cm2 s?1 (average: 70 cm2 s?1). As to type B, K values for the benthic boundary layer (4.5–260 cm2 s?1, average: 120 cm2 s?1) were always more than an order of magnitude larger than those for the upper layer (0.2–35 cm2 s?1, average: 7 cm2 s?1), indicating more active vertical mixing in the benthic boundary layer than in the upper layer.Rn profiles were measured in regions where the bottom topography is known. It was verified that the occurrence of type H related closely with local bottom topographic features accompanied by lateral transient supply of Rn-rich or Rn-poor water.A couple of Rn profiles at the same location, measured at time intervals of several years, were compared with each other for three locations. The general characteristics of Rn profiles were shown to remain unaltered with time, while the fine structure of Rn profiles may have short-term variations caused by local bottom topography and fluctuations of bottom current as indicated in type H.  相似文献   

8.
Measurement of excess 234Th (t1/2 = 24.1 days) in surface sediment from 12 stations throughout Long Island Sound, U.S.A., demonstrates: (1) a mean (summer) sediment inventory of 3.6 dpm/cm2 consistent with complete, nearly instantaneous removal of 234Th from the overlying water and capture within the estuary, and (2) preferential association of excess 234Th with small particles and inventory build-ups in muddy bottom areas. There may also be a tendency for higher inventories in areas of high physical or biogenic reworking of surface sediments. A range of particle reworking rates (0–5 cm) from <0.01 × 10?6 to 1.6 × 10?6 cm2/s is found in the Sound with most values ～0.2?0.5 × 10?6 cm2/s. The inventory and reworking patterns demonstrate the high mobility, both horizontal and vertical, of particles in the estuary on 234Th decay time scales and are unequivocal evidence for control of reactive element distribution in the water column by the muddy regions of the basin.  相似文献   

9.
The near-bottom sedimentation rates were measured by placing cylindrical sediment traps 10 m above the sea floor on each of six moorings deployed between 4100 and 5100 m along a transect across an energetic deep-sea current in the HEBBLE area centered at 40°N, 63°W on the Nova Scotian Rise. Sedimentation rates above the sea floor were monitored with additional traps at 23, 54, 100, 200 and 500 m above the bottom (mab) on the mooring at 4950 m. The total flux at 500 mab for the two-week period, consisting mostly of primary particles from surface water, was 166 mg/m2 day and increased exponentially towards the bottom. The total flux at 10 mab increased down slope from 1160 mg/m2 day at 4158 m where the mean current speed was 8 cm/s to a maximum of 77,300 mg/m2 day at 5022 m where the mean current speed was 32 cm/s, then decreased to 59,400 mg/m2 day at the mooring at 5076 m. The size frequency distributions of large, discrete particles such as foraminifera, diatoms, radiolarians and fecal pellets were quantified in all trap samples to examine whether the large variation in fluxes was due to artifacts such as current velocity or trap tilt. Based on the source, persistence and distribution of these particles, we conclude that the large variations in fluxes across the rise and with distance from the sea floor are due primarily to resuspension and resettling of bottom sediments, with tilt and current effects on trapping having only a secondary effect. The vertical gradients of large-particle fluxes suggest effective vertical eddy diffusivities of 102–104 cm2/s using a two-dimensional model. Horizontal advection and secondary circulation probably play a large role in moving large, rapidly falling (up to 1 cm/s) particles to a height of 50–100 m above the sea floor.  相似文献   

10.
Vertical profiles of the activities of 137Cs and 210Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm?2 yr?1 and were in good agreement with sedimentation rates calculated from the inventories of 137Cs and 210Pb. Sedimentation rates calculated from the position of the 137Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of 137Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the 137Cs and 210Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
Relaxation experiments on vitreous SiO2, densified at 900°C, 20 kbar to a permanent density of 2.36 g cm?3 yield an activation energy of69 ± 5kcal mol?1 in the temperature range 700–800°C. The data can be used to estimate minimum cooling rates, maximum depositional temperatures or maximum thicknesses of shock-metamorphosed rocks containing diaplectic glasses, if relaxation of a glass densified under dynamic conditions is assumed to be similar to that of statically densified glass.  相似文献   

12.
210Pb- and137Cs-measurements, and varve counting have been used to date sediment cores from Lake Zurich (Switzerland). Two cores from different water depths were dated with210Pb/210Po and revealed sediment accumulation rates of (0.055±0.015) g·cm?2·y?1 and (0.09±0.03) g·cm?2·y?1, respectively. A comparable rate of (0.07±0.01) g·cm?2·y?1 has been obtained from137Cs measurements. These rates were confirmed by annual layer (varve)-counts which lead to rates of 0.07 g·cm?2·y?1. Constant210Pb activities were observed in the top 6 cm of the sediment cores. This constancy is generally explained in the literature by mixing processes caused by bioturbation and by distortion during coring operations of the uppermost water-rich fluffy sediments. However the distinct137Cs-maxima and the regular and undisturbed varve lamination of the top sediment observed in the cores of Lake Zurich contradict this assumption. In addition, measurements of7Be at the water/sediment interaces proved complete sediment core recovery and mechanically undisturbed sediments. Remobilization processes are assumed to cause the observed constant210Pb activities. Remobilization may also be the reason for an incomplete210Pb inventory in the sediments which contain only about 50% of the fallout from atmosphere. The results of the210Pb dating should therefore be considered with some care. If existent, varve counting represents the easiest and most reliable means for dating lake sediments.  相似文献   

13.
Chemical speciation of vanadium is important to understand the true nature of this element in the environment as well as its biochemical pathways. Sample pretreatment, preparation, and chemical speciation methods were applied for vanadium in coal bottom ash here. Two‐stage microwave acid digestion was used to preparation of samples. Determination of vanadium was performed using inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Speciation of vanadium was carried out using a seven‐step sequential extraction procedure of the coal bottom ash each releasing species of vanadium: Water soluble, exchangeable, carbonate, reducible, oxidizable, sulfide, and residual fractions. Total vanadium concentration in the coal bottom ash is 701 mg kg?1 d.w. The most abundant form of vanadium in coal bottom ash is residual fraction of vanadium (196 mg kg?1 d.w.). Relative abundances of the remaining vanadium fractions in coal bottom ash are as follows: Reducible (176 mg kg?1 d.w.) > sulfide (176 mg kg?1 d.w.) > carbonate (85 mg kg?1 d.w.) > oxidizable (50 mg kg?1 d.w.) > water soluble (10.6 mg kg?1 d.w.) > exchangeable (9.0 mg kg?1 d.w.).  相似文献   

14.
In laboratory experiments, the cold-water coral Lophelia pertusa was exposed to settling particles. The effects of reef sediment, petroleum drill cuttings and a mix of both, on the development of anoxia at the coral surface were studied using O2, pH and H2S microsensors and by assessing coral polyp mortality. Due to the branching morphology of L. pertusa and the release of coral mucus, accumulation rates of settling material on coral branches were low. Microsensors detected H2S production in only a few samples, and sulfate reduction rates of natural reef sediment slurries were low (<0.3 nmol S cm−3 d−1). While the exposure to sediment clearly reduced the coral’s accessibility to oxygen, L. pertusa tolerated both partial low-oxygen and anoxic conditions without any visible detrimental short-term effect, such as tissue damage or death. However, complete burial of coral branches for >24 h in reef sediment resulted in suffocation.  相似文献   

15.
Excess delivery of land‐based sediments is an important control on the overall condition of nearshore coral reef ecosystems. Unpaved roads have been identified as a dominant sediment source on St John in the US Virgin Islands. An improved understanding of road sediment production rates is needed to guide future development and erosion control efforts. The main objectives of this study were to: (1) measure sediment production rates at the road segment scale; (2) evaluate the importance of precipitation, slope, contributing area, traffic, and grading on road sediment production; (3) develop an empirical road erosion predictive model; and (4) compare our measured erosion rates to other published data. Sediment production from 21 road segments was monitored with sediment traps from July 1998 to November 2001. The selected road segments had varying slopes, contributing areas, and traffic loads. Precipitation was measured by four recording rain gauges. Sediment production was related to total precipitation and road segment slope. After normalizing by precipitation and slope, the mean sediment production rate for roads that had been graded within the last two years was 0·96 kg m?2 cm?1 m m?1 or approximately 11 kg m?2 a?1 for a typical road with a 10 per cent slope and an annual rainfall of 115 cm a?1. The mean erosion rate for ungraded roads was 42 per cent lower, or 0·56 kg m?2 cm?1 m m?1. The normalized mean sediment production rate for road segments that had been abandoned for over fifteen years was only about 10 per cent of the mean value for ungraded roads. Sediment production was not related to traffic loads. Multiple regression analysis led to the development of an empirical model based on precipitation, slope to the 1·5 power, and a categorical grading variable. The measured and predicted erosion rates indicate that roads are capable of increasing hillslope‐scale sediment production rates by up to four orders of magnitude relative to undisturbed conditions. The values from St John are at the high end of reported road erosion rates, a finding that is consistent with the high rainfall erosivities and steep slopes of many of the unpaved roads on St John. Other than paving, the most practical methods to reduce current erosion rates are to minimize the frequency of grading and improve road drainage. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
Production rates of22Na (T1/2 = 2.6years) from aluminium by the action of cosmic rays are measured at the Mont Blanc (altitude 4600 m), the Aiguille du Midi (3840 m), and the Col du Lautaret (2070 m). They are2.3 ± 0.5,1.8 ± 0.3,and0.77 ± 0.18 atoms min?1 kg?1, respectively, in good agreement with the calculated production rates, 2.4, 1.7 and 0.6 atoms min?1 kg?1, respectively, at the three stations.Production rates of24Na (T1/2 = 15hours) from aluminium and magnesium are also measured at the Aiguille du Midi; the observed rates of3.4 ± 0.4and6.0 ± 1.7 atoms min?1 kg?1, respectively, agree well with the theoretically expected rates of 3.7 and 5.6 atoms min?1 kg?1.The production rates of3H,7Be,10Be,14C,22Na,26Al,36Cl,37Ar,39Ar,53Mn,54Mn, and55Fe in terrestrial rocks by the action of cosmic rays are calculated in order to show the possibility of applying the measurements of these cosmogenic radionuclides to the earth science.  相似文献   

17.
We have studied bacterial abundance and production in samples from sediment traps deployed for 1 and 100 days in several areas of the shelf and slope regions of the Middle Atlantic Bight, U.S.A. By making a series of assumptions about bacterial growth at the expense of POC in traps, we have estimated that the turnover time of organic particles collected in traps during long deployments is slow (mean 1500 ± 300 days), if only bacterial activity is considered. However the abundance and biomass of bacteria in traps is very high, ranging from 3 to 30 × 1011 cells gC?1, i.e., 0.3 to 3% of the POC is bacterial carbon. Fifteen to 88% of the particles in traps were colonized by bacteria, but usually about half the particles had only 0 to 1 cell attached. Growth of bacteria was observed at all scales relevant to these trap deployments; over periods ranging from hours to weeks, at rates of 0.01 to 0.3 d?1. In spite of slow growth, bacteria appeared to be physiologically active in that [3H]adenine and [3H]thymidine were incorporated more rapidly into RNA and protein than into DNA. Total incorporation rates were high. We conclude that even relatively old (ca. 1 y) POC in sediment traps supports high levels of active bacterial biomass, but that POC decomposition is slow, so that bacteria may not be the principal agents of POC turnover following collection.  相似文献   

18.
Bulk hydrocarbon deposition rates have been measured over a 15 month period at four stations in south-eastern Virginia surrounding the lower Chesapeake Bay. A nearly linear trend of atmospheric particulate deposition was recorded. Deposition rates at the urban station (195 μg m?2 day?1) were aproximately three times greater than those recorded for nonurban and coastal locations (mean value 69 μg m?2 day?1). The increased levels at the urban location were attributed to localized source inputs. Anthropogenic hydrocarbons accounted for approximately 50% of the total deposition at all stations. Significant biogenic inputs were indicated by the odd/even n-alkane distribution. A minimum flux to the water surface, based on mean nonurban deposition rates (24 mg yr?1), indicated an annual particulate hydrocarbon flux of +275 metric tons. Little information is available for the comparison of additional source inputs; however, the data reported here indicate that the aerial deposition of hydrocarbons is of the same order of magnitude as the input from municipal wastewater facilities and accidental discharge and is a potentially significant source of hydrocarbon pollution to the Chesapeake Bay Estuary.  相似文献   

19.
The electrical conductivity of Tibetan eclogite was investigated at pressures of 1.5–3.5 GPa and temperatures of 500–803 K using impedance spectroscopy within a frequency range of 10-1–106 Hz. The electrical conductivity of eclogite increases with increasing temperature(which can be approximated by the Arrhenius equation), and is weakly affected by pressure. At each tested pressure, the electrical conductivity is weakly temperature dependent below ~650 K and more strongly temperature dependent above ~650 K. The calculated activation energies and volumes are 44±1 kJ/mol and-0.6±0.1 cm3/mol for low temperatures and 97±3 kJ/mol and-1.2±0.2 cm3/mol for high temperatures, respectively. When applied to the depth range of 45–100 km in Tibet, the laboratory data give conductivities on the order of 10-1.5–10-4.5 S/m, within the range of geophysical conductivity profiles.  相似文献   

20.
The role of microbial sulfate reduction on organic matter oxidation was studied quantitatively in temperate intertidal surface sediments of the German Wadden Sea (southern North Sea) on a seasonal base in the years 1998–2007. The sampling sites represent the range of sediments found in the back-barrier tidal area of Spiekeroog Island: sands, mixed and muddy flats. The correspondingly different contents in organic matter, metals, and porosities lead to significant differences in the activity of sulfate-reducing bacteria with volumetric sulfate reduction rates (SRR) in the top 15 cm of up to 1.4 μmol cm?3 day?1. Depth-integrated areal SRR ranged between 0.9 and 106 mmol m?2 day?1, with the highest values found in the mudflat sediments and lower rates measured in sands at the same time, demonstrating the impact of both temperature and organic matter load. According to a modeling approach for a 154-km2 large tidal area, about 39, 122, and 285 tons of sulfate are reduced per day, during winter, spring/autumn, and summer, respectively. Hence, the importance of areal benthic organic matter mineralization by microbial sulfate reduction increases during spring/autumn and summer by factors of about 2 and 7, respectively, when compared to winter time. The combined results correspond to an estimated benthic organic carbon mineralization rate via sulfate reduction of 78 g C m?2 year?1.  相似文献   

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