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1.
Michael J. Durako Piotr Kowalczuk Michael A. Mallin William J. Cooper Jason J. Souza David H. Wells 《Estuaries and Coasts》2010,33(6):1430-1441
Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m3s−1) was only 25% of the wet year discharge (429 ± 337 m3s−1). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter
(CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to
PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied
little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher
nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a
CDOM
(412)] ranged from 0.05 to 8.25 m−1 with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater
river inputs, CDOM may exert a major limiting influence over near-shore primary production. 相似文献
2.
Seepage rate and chemical composition of groundwater discharge entering the Neuse River Estuary (NRE) were quantified over
an annual cycle from July 2005 through June 2006. Lee type seepage meters were deployed at eight locations within the NRE
to quantify the amount of submerged groundwater discharge (SGD) entering the system. Sediment porewater nitrate (NO3
−), ammonium (NH4
+), and phosphate (PO4
−3) were also quantified at each of these locations to determine groundwater chemical composition. Seepage rates for the system
ranged from 0.004 to 0.035 m3 m−2 d−1. Both the average and median value for the system-wide SGD were 0.01 m3 m−2d−1. There were no significant differences between upstream and downstream seepage rates or between those at the north and south
side of the estuary. Seepage rates varied greatly in time and space. Discharging groundwater was NO3
− deplete but highly enriched in NH4
+. Porewater PO4
−3 levels varied but were usually present below Redfield values due to NH4
+ enrichment. SGD nutrient loading represented a small part of watershed nitrogen and phosphorus loading, 0.8% and 1.0%, respectively. 相似文献
3.
Flushing of dense water from cavities of the upper reaches of the Swan River estuary in Western Australia was investigated using measured salinity and dissolved oxygen profiles and a two-dimensional, laterally averaged hydrodynamic model (TISAT). Seasonal flushing of dense, hypoxic bottom waters from a relatively deep site took place over ∼3 days at the onset of winter in 1994. Model simulations of the purging of this dense water did not correspond closely with changes in the densimetric Froude number. Purging, expressed as depth of the halocline as a fraction of the total cavity depth, occurred when the simulated mean horizontal velocity at 2 m depth (top of cavity) changed from negative to strongly positive, indicating arrest of upstream flow and continuous downstream flow. This corresponded to freshwater discharge of about 50 m3 s−1. Oxygen depletion of bottom waters was closely related to stratification. Oxygen dynamics at the onset of winter river flow was analysed using an exponential decay model, assuning that there was no net inflow or outflow across the halocline and thus no vertical transport of oxygen during a period of strong stratification. The rate constant for oxygen decay at Ron Courtney Island (RCI) was estimated to be 0.232 d−1 for this period. Bottom waters at RCI declined to less than 1 mg 1−1 prior to complete flushing through increased river flows. This study provided in sights to how freshwater flows may be allocated to maintain suitable oxygen levels in the bottom waters of estuarine cavities. 相似文献
4.
Josette Garnier Pierre Servais Gilles Billen Maïa Akopian Natacha Brion 《Estuaries and Coasts》2001,24(6):964-976
Ecological processes driving the oxygen budget were investigated in the downstream part of the Seine River and its estuary. Phytoplankton and bacterioplankton production were measured along longitudinal profiles (11 to 17 stations) in a range of low discharges from 300 m3 s−1 in 1993 and 1995 to 140 m3 s−1 in 1996. Values representative of the water column were based on investigations carried out during two tidal cycles. Net primary production was invariably greatest in the freshwater estuary, from Poses to Rouen (from 500 to 1,000 μg C l−1 d−1 between PK 202 and 240) and decreased sharply downstream (from 10 to 25 μg c l−1 d−1 between PK 250 and 310). This decrease was mainly due to the deterioration of the light conditions with the increase in depth and suspended matter concentrations. Heterotrophic activity was maximum in the reach where primary production declined. Judging by the production:respiration ratio (P:R), the system appeared clearly heterotrophic in the Seine River immediately downstream of the Paris region due to high allochthonous organic pollution by the incompletely treated Parisian effluents and in the part of the estuary characterized by intense degradation of autochthonous material. Because the effluents are not treated by a nitrification step, the oxygen consumption due to nitrification was much higher than expected from the P:R ratio. Oxidation of ammonium represented an oxygen consumption of between 1 and 14 g O2 m−2 d−1, almost equalling the sum of heterotrophic respirations that were barely balanced by photosynthesis. The reaeration flux at the water-atmosphere interface was deduced from the calculations and a reaeration coefficient was estimated. 相似文献
5.
Peak discharge of a Pleistocene lava-dam outburst flood in Grand Canyon, Arizona, USA 总被引:1,自引:0,他引:1
The failure of a lava dam 165,000 yr ago produced the largest known flood on the Colorado River in Grand Canyon. The Hyaloclastite Dam was up to 366 m high, and geochemical evidence linked this structure to outburst-flood deposits that occurred for 32 km downstream. Using the Hyaloclastite outburst-flood deposits as paleostage indicators, we used dam-failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph. Failure of the Hyaloclastite Dam released a maximum 11 × 109 m3 of water in 31 h. Peak discharges, estimated from uncertainty in channel geometry, dam height, and hydraulic characteristics, ranged from 2.3 to 5.3 × 105 m3 s−1 for the Hyaloclastite outburst flood. This discharge is an order of magnitude greater than the largest known discharge on the Colorado River (1.4 × 104 m3 s−1) and the largest peak discharge resulting from failure of a constructed dam in the USA (6.5 × 104 m3 s−1). Moreover, the Hyaloclastite outburst flood is the oldest documented Quaternary flood and one of the largest to have occurred in the continental USA. The peak discharge for this flood ranks in the top 30 floods (>105 m3 s−1) known worldwide and in the top ten largest floods in North America. 相似文献
6.
Formation and failure of the Tsatichhu landslide dam, Bhutan 总被引:1,自引:1,他引:1
At 00:30 (local time) on the 10th September 2003 a joint and foliation defined wedge of material with an estimated volume of 7–12×106 m3 slid into the narrow Tsatichhu River Valley, in Jarrey Geog, Lhuentse, eastern Bhutan. The Tsatichhu River, a north–easterly flowing tributary of the Kurichuu River, was completely blocked by the landslide. During its movement, the landslide transitioned into a rock avalanche that travelled 580 m across the valley before colliding with the opposite valley wall. The flow then moved down valley, travelling a total distance of some 700 m. The rock avalanche was accompanied by an intense wind blast that caused substantial damage to the heavily forested valley slopes. The resulting geomorphologically-typical rock-avalanche dam deposit created a dam that impounded a water volume of 4–7×106 m3 at lake full level. This lake was released by catastrophic collapse of the landslide, which occurred at 16:20 (local time) on 10th July 2004, after reported smaller failures of the saturated downstream face. The dam failure released a flood wave that had a peak discharge of 5900 m3 s−1 at the Kurichhu Hydropower Plant 35 km downstream. 相似文献
7.
SeaWiFS ocean color measurements were used to investigate interannual, monthly, and weekly variations in chlorophylla (chla) on the Louisiana shelf and to assess relationships with river discharge, nitrate load, and hypoxia. During the study period
(2000–2003), interannual changes in shelf-wide chla concentrations averaged over January–July ranged from +57% to −33% of the 4-yr average, in accord with freshwater discharge
changes of +20% to −29% and nitrate load changes of +20% to −35% from the Mississippi and Atchafalaya Rivers. Chla variations were largest on the shelf between the Mississippi and Atchafalaya Deltas. Within this region, which corresponds
spatially to the area of most frequent hypoxia, lowest January–July mean chla concentrations (5.5 mg m−3 over 7,000 km2) occurred during 2000, the year of lowest freshwater discharge (16,136 m3 s−1) and nitrate load (55,738 MT N d−1) onto the shelf. Highest January–July mean chla concentrations (13 mg m−3 over 7,000 km2) were measured in 2002, when freshwater discharge (27,440 m3s−1) and nitrate load (101,761 MT N d−1) were highest and second highest, respectively. Positive correlations (R2=0.4–0.5) were found between chla and both fresh water and nitrate loads with 0 to 1 month lags, with the strongest relationships just west of the Mississippi
Delta. In 2001, unusually clear skies allowed the identification of distinct spring and summer chla blooms west of the Mississippi Delta 4–5 wk after peaks in river discharge. East of the delta, the chla concentrations peaked in June and July, following the seasonal reversal in the coastal current. A clear linkage was not detected
between satellite-measured chla and hypoxia during the 4-yr period, based on a time series of bottom oxygen concentrations at one station within the area
of most frequent hypoxia. Clear relationships are confounded by the interaction of physical processes (wind stress effects)
with the seasonal cycle of nutrient-enhanced productivity and are influenced by the prior year's nitrate load and carbon accumulation
at the seabed. 相似文献
8.
A quantitative study on fluvial processes was carried out in an upland stream catchment (9.3 ha) near Agolai in the NE of
Jodhpur district in the Thar Desert in Rajasthan. The catchment of the studied second order ephemeral channel (1.0–1.4 km
long and 1.0–1.5 m deep) has developed on a hill — rocky/gravelly pediment — colluvial plain sequence on rhyolite. Initial
results of measurements of channel parameters during two significant runoff generating events of 42 mm and 52 mm in 2007 showed
peak discharges of 20 m3s−1 (upstream) and 13 m3s−1 (downstream) that moved sediments (bedload) to distances of 43 m − 141 m in the upstream reach, 6–28 m in the middle reach
and 63–95 m in the lower reach. The long profile and cross profile measurements showed a balance between load and discharge
through a sequence of alternate deposition and erosion throughout the channel. Hypsometry curves revealed maximum erosion
(7.7 cm) in the upper reach and aggradation (2.90 cm) in the lower reach. Cross profile measurements showed bank cuts (6 cm)
and vertical incisions (1–2 cm) on the rocky-gravelly V shaped valley in the upper reach, incision (4–30 cm) and localized
higher deposition (10–12 cm) in the narrow (<1m) and deep (>1m) U shaped valleys in middle reach and mainly deposition (13
cm) on the wide ( 1–4 m) and shallow channels (0.1 to 0.2 m) in the lower reach. 相似文献
9.
Xi Bin Ji Wen Zhi Zhao Er Si Kang Zhi Hui Zhang Bo Wen Jin 《Environmental Earth Sciences》2011,64(3):619-629
Fluxes of carbon dioxide, water vapor, and heat were measured above crop canopy using the eddy covariance method during the
2008 maize growing season, over an agricultural field within an oasis located in the middle reaches of Heihe River basin,
northwest China. The values for friction velocity, the Monin–Obukhov stability parameter, and energy balance closure indicated
that the eddy covariance system at this study site provided reliable flux estimates. Results from measurements showed that
the mean sensible heat flux was 70 W m−2 with a maximum value of 164 W m−2 (May) and a minimum value of 45 W m−2 (July) during the maize growing season. In contrast, the mean latent heat was 278 W m−2 with a maximum value of 383 W m−2 (July) and minimum of 101 W m−2 (May). The mean downward soil heat flux was 55 W m−2 with a maximum value of 127 W m−2 (May) and minimum of 49 W m−2 (July). The magnitude of mean daytime net CO2 uptake was −11.50 μmol m−2 s−1 with a maximum value of −28.32 μmol m−2 s−1 (18 and 19 July) and a minimum values of −0.32 μmol m−2 s−1 (18 and 19 May). Correlation was observed between daytime half-hourly carbon dioxide flux and canopy conductance. In addition,
the relationship between carbon dioxide flux and photosynthetically active radiation for selected days during different stages
of maize growing season indicated the carbon dioxide flux uptake by the canopy was controlled by actual photosynthetic activity
related to the variation of green leaf area index for the different growing stages. 相似文献
10.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term
reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance
experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon
flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer
plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term
survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta
m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1. 相似文献
11.
Using both the photosynthetically active chlorophylla (chla) content of the organic carbon fraction of suspended particulate matter (chla/POC) and the percentage of photosynthetically, active chla in fluorometrically measured chla plus pheophytina (% chla), we determined that under specified hydrodynamic conditions, neap-spring tidal differentiation in particle dynamics could
be observed in the Columbia River estuary. During summer time neap tides, when river discharge was moderate, bottom chla/POC remained relatively unchanged from riverine chla/POC over the full 0–30 psu salinity range, suggesting a benign trapping environment. During summertime spring tides, bottom
chla/POC decreased at mid range salinities indicating resuspension of chla-poor POC during flood-ebb transitions. Bottom % chla during neap tides tended to average higher than that during spring tides, suggesting that neap particles were more recently
hydrodynamically trapped than those on the spring tides. Such differentiation supported the possibility of operation of a
particle conveyor belt process, a process in which low-amplitude neap tides favor selective particle trapping in estuarine
turbidity maxima (ETM)., while high-amplitude spring tides favor particle resuspension from the ETM. Untrapped river-derived
particles at the surface would continue through the estuary to the coastal ocean on the neap tide; during spring tide some
particles eroded from the ETM would combine with unsettled riverine particles in transit toward the ocean. Because in tensified
biogeochemical activity is associated with ETM, these neap-spring differences may be critical to maintenance and renewal of
populations and processes in the estuary. Very high river discharge (15, 000 m3 s−1) tended to overwhelm neap-spring differences, and significant oceanic input during very low river discharge (5,000 m3 s−1) tended to do the same in the estuarine channel most exposed to ocean input. During heavy springtime phytoplankton blooms,
development of a thick bottom fluff layer rich in chla also appeared to negate neapspring differentiation because spring tides apparently acted to resuspend the same rich bottom
material that was laid down during neap tides. When photosynthetic assimilation numbers [μgC (μgchl,a)−1h−1] were measured across, the full salinity range, no neap-spring differences and no river discharge effects occurred, indicating
that within our suite of measurements the compositional distinction of suspended particulate material was mainly a function
of chla/POC, and to a lesser extent % chla. Even though these measurements suggest the existence of a conveyor belt process, proof of actual operation of this phenomenon
requires scalar flux measurements of chla properties in and out of the ETM on both neap and spring tides. 相似文献
12.
Hurricane Frances is shown to greatly alter the hydrodynamics within Tampa Bay, Florida, and the exchange of water with the
Gulf of Mexico in both observational data and a realistic numerical circulation model of the Tampa Bay estuary. Hurricane
Frances hit Tampa Bay on September 5, 2004 with surface winds peaking twice near 22 m s−1. There were three stages to the hydrodynamic effect of Frances on Tampa Bay. The first stage included the approach of Frances
up to the first wind peak. The winds were to the south and southeast. During this stage sea level was maintained below mean
sea level (MSL) and the residual current (demeaned, detided) was weak. The second stage began as the winds turned to the east
and northeast, as the eye passed near the bay, and ended as the second wind peak appeared. During this stage the residual
currents were strongly positive (into the bay), raising sea level to 1.2 m above MSL at St. Petersburg. The measured residual
circulation peaked at over +0.7 m s−1 near the surface. The model shows this velocity peak yielded a maximum volume flux into the bay of +44,227 m3 s−1, displacing a total volume of 1.5 billion m3 in just a few hours, about 42% of the bay volume. In the third stage a strong negative flow developed as the wind and sea
level relaxed to near normal levels. The ADCP measured a peak outflow of −0.8 m s−1 during this time. Model results indicate a maximum flux of −37,575 m3 s−1, and that it took about 50 h to drain the extra volume driven into the bay by Hurricane Frances. 相似文献
13.
Sophie L. Norris Martin Margold Daniel J. Utting Duane G. Froese 《Boreas: An International Journal of Quaternary Research》2019,48(4):1006-1018
Glacial lake outburst floods occurred frequently during the last deglaciation of the Laurentide Ice Sheet. Within the Interior Plains, these floods carved large spillway systems; however, due to a lack of abundant sediment, deposits within prairie spillways are rarely preserved. Here, we present geomorphic and sedimentary evidence and hydraulic modelling of the eastern Beaver River Spillway, formed by the catastrophic drainage of the ice‐dammed glacial Lake Algar, in north central Alberta. During this flood, coarse‐grained sediment eroded from local till formed large pendant bars. Within the first ~50 km of the spillway (Reach 1), pendant bars contain downstream orientated foresets overlain by horizontally bedded coarser gravels. The remaining pendant bars (Reach 2), present downflow of a moraine barrier, differ, comprising massive, matrix‐supported, inversely graded gravels capped by a boulder layer. We use a HEC‐GeoRAS/HEC‐RAS system in conjunction with palaeostage indicators to estimate the steady‐state water surface elevation. Modelling results show that peak discharge within Reach 1 of the eastern Beaver River Spillway was approximately 14 000–21 000 m3 s?1. For Reach 2, 30 km downstream, the peak discharge was estimated at 23 000–40 000 m3 s?1 (nbulked 18 000–26 000 m3 s?1). The downstream discharge increase, consistent with the sedimentary change in pendant bar deposits, is attributed to sediment bulking of the flood flow. This provides the opportunity to observe a range of flow conditions, and associated sedimentology, from a single flood event. The reconstructed flow conditions, coupled with lake volume estimates from the ponding above the moraine barrier suggest a minimum flow duration of 3–5 days. 相似文献
14.
Maik Pertermann Alan G. Whittington Anne M. Hofmeister Frank J. Spera John Zayak 《Contributions to Mineralogy and Petrology》2008,155(6):689-702
Thermal diffusivity (D) was measured using laser-flash analysis from oriented single-crystal low-sanidine (K0.92Na0.08Al0.99Fe3+
0.005Si2.95O8), and three glasses near KAlSi3O8. Viscosity measurements of the three supercooled liquids, in the range 106.8 to 1012.3 Pa s, confirm near-Arrhenian behavior, varying subtly with composition. For crystal and glass, D decreases with T, approaching a constant near 1,000 K: D
sat ∼ 0.65 ± 0.3 mm2 s−1 for bulk crystal and ∼0.53 ± 0.03 mm2 s−1 for the glass. A rapid decrease near 1,400 K is consistent with crossing the glass transition. Melt behavior is approximated
by D = 0.475 ± 0.01 mm2 s−1. Thermal conductivity (k
lat) of glass, calculated using previous heat capacity (C
P) and new density data, increases with T because C
P strongly increases with T. For melt, k
lat reaches a plateau near 1.45 W m−1 K−1, and is always below k
lat of the crystal. Melting of potassium feldspars impedes heat transport, providing positive thermal feedback that may promote
further melting in continental crust. 相似文献
15.
Phytoplankton Biomass and Production in Subtropical Hong Kong Waters: Influence of the Pearl River Outflow 总被引:1,自引:0,他引:1
Alvin Y. T. Ho Jie Xu Kedong Yin Yuelu Jiang Xiangcheng Yuan Lei He Donald M. Anderson Joseph H. W. Lee Paul J. Harrison 《Estuaries and Coasts》2010,33(1):170-181
The size-fractionated phytoplankton biomass and primary production were investigated in four contrasting areas of Hong Kong
waters in 2006. Phytoplankton biomass and production varied seasonally in response to the influence of the Pearl River discharge.
In the dry season, the phytoplankton biomass and production were low (<42 mg chl m−2 and <1.8 g C m−2 day−1) in all four areas, due to low temperatures and dilution and reduced light availability due to strong vertical mixing. In
contrast, in the wet season, in the river-impacted western areas, the phytoplankton biomass and production increased greater
than five-fold compared to the dry season, especially in summer. In summer, algal biomass was 15-fold higher than in winter,
and the mean integrated primary productivity (IPP) was 9 g C m−2 day−1 in southern waters due to strong stratification, high temperatures, light availability, and nutrient input from the Pearl
River estuary. However, in the highly flushed western waters, chl a and IPP were lower (<30 mg m−2 and 4 g C m−2 day−1, respectively) due to dilution. The maximal algal biomass and primary production occurred in southern waters with strong
stratification and less flushing. Spring blooms (>10 μg chl a L−1) rarely occurred despite the high chl-specific photosynthetic rate (mostly >10 μg C μg chl a
−1 day−1) as the accumulation of algal biomass was restricted by active physical processes (e.g., strong vertical mixing and freshwater
dilution). Phytoplankton biomass and production were mostly dominated by the >5-μm size fraction all year except in eastern
waters during spring and mostly composed of fast-growing chain-forming diatoms. In the stratified southern waters in summer,
the largest algal blooms occurred in part due to high nutrient inputs from the Pearl River estuary. 相似文献
16.
Huan-Xin Weng Ya-Chao Qin Xiang-Wei Sun Xun-Hong Chen Jing-Feng Chen 《Environmental Geology》2009,57(1):9-15
Laboratory culture experiments have been conducted to evaluate the effects of light intensity on the growth of Cryptomonas sp. (Cryptophyceae) and the discrepancy in absorption of iron and phosphorus under different light conditions. Results show
that there is an exponential correlation between algal growth rate and light intensity. The saturating and semi-saturating
light values for Cryptomonas sp. cells are 150 and 47 μmol photons m−2 s−1, respectively. More uptake of Fe, P, and other trace elements such as Zn, Mn, Co, and Mo is observed in the low light cultures,
although the algal growth rates are slow. The growth rate at 10 μmol photons m−2 s−1 is only 10% of that at 150 μmol photons m−2 s−1, whereas Fe and P uptake increases by 150 and 100%, respectively. These results suggest potential implications of differentiation
in absorption of iron and phosphorus at different light intensities for the occurrence of harmful algal blooms (HABs). The
mechanisms of light intensity regulating nutrient uptake as well as the occurrence of HABs are also discussed. 相似文献
17.
Tetsutaro Takikawa Goh Onitsuka Ken-ichi Fukudome Jong-Hwan Yoon Akihiko Morimoto Masatoshi Moku Atsushi Watanabe 《Estuaries and Coasts》2011,34(4):775-784
Horizontal, vertical and temporal distribution of a cyclonic (counterclockwise) eddy, where biological productivity is high,
downstream of the Tsushima Islands in the eastern channel of the Tsushima Straits in November 2007 was revealed using conductivity–temperature–depth
and acoustic Doppler current profiler data. The eddy had a horizontal scale of approximately 40–60 km, and the accompanying
baroclinic current was more than 15 cm s−1 at the edge of the eddy. The island-induced cyclonic eddy moved east-northeastward at about 10 km day−1 (∼10 cm s−1) along the Tsushima Warm Current and was intensified by the barotropic instability in the current shear. The cyclonic eddy
with high surface chlorophyll a concentrations intensified in the vicinity of the Tsushima Islands and was advected by the Tsushima Warm Current towards
the southwestern Japan Sea. 相似文献
18.
Interaction of freshly precipitated silica gel with aqueous solutions was studied at laboratory batch experiments under ambient
and near neutral pH-conditions. The overall process showed excellent reversibility: gel growth could be considered as an opposite
process to dissolution and a linear rate law could be applied to experimental data. Depending on the used rate law form, the
resulting rate constants were sensitive to errors in parameters/variables such as gel surface area, equilibrium constants,
Si-fluxes, and reaction quotients. The application of an Integrated Exponential Model appeared to be the best approach for
dissolution data evaluation. It yielded the rate constants k
dissol ∼ (4.50 ± 0.68) × 10−12 and k
growth ∼ (2.58 ± 0.39) × 10−9 mol m−2 s−1 for zero ionic strength. In contrast, a Differential Model gave best results for growth data modeling. It yielded the rate
constants k
dissol ∼ (1.14 ± 0.44) × 10−11 and k
growth ∼ (6.08 ± 2.37) × 10−9 mol m−2 s−1 for higher ionic strength (I ∼ 0.04 to 0.11 mol L−1). The found silica gel solubility at zero ionic strength was somewhat lower than the generally accepted value. Based on the
and standard Gibbs free energy of silica gel formation was calculated as and −850,318 ± 20 J mol−1, respectively. Activation energies for silica gel dissolution and growth were determined as and respectively. An universal value for growth of any silica polymorph, is not consistent with the value for silica gel growth, which questions the hypothesis about one unique activated complex
controlling the silica polymorph growth. 相似文献
19.
Paul J. Schmieder David T. Ho Peter Schlosser Jordan F. Clark S. Geoffrey Schladow 《Estuaries and Coasts》2008,31(6):1038-1051
A sulfur hexafluoride (SF6) tracer release experiment was conducted in the Stockton Deep Water Ship Channel (DWSC) to quantify mixing and transport
rates. SF6 was injected in the San Joaquin River upstream of the DWSC and mapped for 8 days. From the temporal change in SF6 distributions, the longitudinal dispersion coefficient (K
x
) was determined to be 32.7 ± 3.6 m2 s−1 and the net velocity was 1.75 ± 0.03 km day−1. Based on the decrease in SF6 inventory during the experiment, the pulsed residence time for waters in the DWSC was estimated at ∼17 days. Within the DWSC
from Stockton downstream to Turner Cut, dissolved oxygen concentrations maintained a steady state value of 4 mg l−1. These values are below water quality objectives for the time of year. The low flow rates observed in the DWSC and the inability
of oxygen-rich waters from downstream to mix into the DWSC upstream of Turner Cut contribute to the low dissolved oxygen concentration. 相似文献
20.
Anne E. Giblin Nathaniel B. Weston Gary T. Banta Jane Tucker Charles S. Hopkinson 《Estuaries and Coasts》2010,33(5):1054-1068
Benthic respiration, sediment–water nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium (DNRA)
were measured in the upper section of the Parker River Estuary from 1993 to 2006. This site experiences large changes in salinity
over both short and long time scales. Sediment respiration ranged from 6 to 52 mmol m−2 day−1 and was largely controlled by temperature. Nutrient fluxes were dominated by ammonium fluxes, which ranged from a small uptake
of −0.3 to an efflux of over 8.2 mmol N m−2 day−1. Ammonium fluxes were most highly correlated with salinity and laboratory experiments demonstrated that ammonium fluxes increased
when salinity increased. The seasonal pattern of DNRA closely followed salinity. DNRA rates were extremely low in March, less
than 0.1 mmol m−2 day−1, but increased to 2.0 mmol m−2 day−1 in August. In contrast, denitrification rates were inversely related to salinity, ranging from 1 mmol m−2 day−1 during the spring and fall to less than 0.2 mmol m−2 day−1 in late summer. Salinity appears to exert a major control on the nitrogen cycle at this site, and partially decouples sediment
ammonium fluxes from organic matter decomposition. 相似文献