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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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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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Morihisa Hamada Didier Laporte Nicolas Cluzel Kenneth T. Koga Tatsuhiko Kawamoto 《Bulletin of Volcanology》2010,72(6):735-746
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H2O were carried out at a pressure range from 250 MPa to 30–75 MPa in order to characterize effects of magma ascent rate and
temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per
unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10–90 MPa/s) produced huge BNDs
(≈ 2 × 1014 m−3 at 10 MPa/s ; ≈ 2 × 1015 m−3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015–1016 m−3). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×1012 m−3) close to those observed at 800°C and 1 MPa/s (≈ 6 × 1012 m−3), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory
that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge
number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs
just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s). 相似文献
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Detlev Ingendahl Dietrich Borchardt Nicole Saenger Peter Reichert 《Aquatic Sciences - Research Across Boundaries》2009,71(4):399-410
To quantify the contribution of hyporheic community respiration to whole running-water ecosystem respiration in a cultural
landscape setting, we studied the vertical hydraulic exchange in riffle–pool sequences of the River Lahn (Germany). We used
flow through curves from four tracer experiments to estimate flow velocities in the surface and subsurface water. Generally,
vertical exchange velocities were higher in riffle sections and a high temporal variability was observed (range of values
0.11–1.08 m day−1). We then used (1) the exchange velocities and (2) time series of dissolved oxygen concentration in surface and subsurface
water to calculate hyporheic respiration. Hyporheic respiration was estimated in a range of 10–50 mg O2 m−3 day−1 for the upper sediment layer (first 20 cm). It was much lower in the deeper sediment layer (20–40 cm), ranging from 0 to
10 mg O2 m−3 day−1 (volumes are volumes of interstitial water; the average porosity was 20%). We determined primary production and respiration
of the biofilm growing on the sediment by modelling dissolved oxygen concentration time series for a 2,450 m long stream reach
(dissolved oxygen concentrations with diurnal variations from 8 to 16 mg L−1). Modelled respiration rates ranged from 2 to 21 g O2 m2 day−1. All information was integrated in a system analysis with numerical simulations of respiration with and without sediments.
Results indicated that hyporheic respiration accounted for 6 to 14% of whole ecosystem respiration. These values are much
lower than in other whole system respiration studies on more oligotrophic river systems. 相似文献
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Forward-Looking Infrared (FLIR) nighttime thermal images were used to extract the thermal and morphological properties for
the surface of a blocky-to-rubbley lava mass active within the summit crater of the Caliente vent at Santiaguito lava dome
(Guatemala). Thermally the crater was characterized by three concentric regions: a hot outer annulus of loose fine material
at 150–400°C, an inner cold annulus of blocky lava at 40–80°C, and a warm central core at 100–200°C comprising younger, hotter
lava. Intermittent explosions resulted in thermal renewal of some surfaces, mostly across the outer annulus where loose, fine,
fill material was ejected to expose hotter, underlying, material. Surface heat flux densities (radiative + free convection)
were dominated by losses from the outer annulus (0.3–1.5 × 104 s−1m−2), followed by the hot central core (0.1–0.4 × 104 J s−1m−2) and cold annulus (0.04–0.1 × 104 J s−1m−2). Overall surface power output was also dominated by the outer annulus region (31–176 MJ s−1), but the cold annulus contributed equal power (2.41–7.07 MJ s−1) as the hot central core (2.68–6.92 MJ s−1) due to its greater area. Cooled surfaces (i.e. the upper thermal boundary layer separating surface temperatures from underlying
material at magmatic temperatures) across the central core and cold annulus had estimated thicknesses, based on simple conductive
model, of 0.3–2.2 and 1.5–4.3 m. The stability of the thermal structure through time and between explosions indicates that
it is linked to a deeper structural control likely comprising a central massive plug, feeding lava flow from the SW rim of
the crater, surrounded by an arcuate, marginal fracture zone through which heat and mass can preferentially flow. 相似文献
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Naomi Greenwood Rodney M. Forster Veronique Créach Suzanne J. Painting Anna Dennis Stewart J. Cutchey Tiago Silva David B. Sivyer Tim Jickells 《Ocean Dynamics》2012,62(2):307-320
The seasonal and interannual variability in the phytoplankton community in Liverpool Bay between 2003 and 2009 has been examined
using results from high frequency, in situ measurements combined with discrete samples collected at one location in the bay.
The spring phytoplankton bloom (up to 29.4 mg chlorophyll m−3) is an annual feature at the study site and its timing may vary by up to 50 days between years. The variability in the underwater
light climate and turbulent mixing are identified as key factors controlling the timing of phytoplankton blooms. Modelled
average annual gross and net production are estimated to be 223 and 56 g C m−2 year−1, respectively. Light microscope counts showed that the phytoplankton community is dominated by diatoms, with dinoflagellates
appearing annually for short periods of time between July and October. The zooplankton community at the study site is dominated
by copepods and use of a fine mesh (80 μm) resulted in higher abundances of copepods determined (up to 2.5 × 106 ind. m−2) than has previously reported for this location. There is a strong seasonal cycle in copepod biomass and copepods greater
than 270 μm contribute less than 10% of the total biomass. Seasonal trends in copepod biomass lag those in the phytoplankton
community with a delay of 3 to 4 months between the maximum phytoplankton biomass and the maximum copepod biomass. Grazing
by copepods exceeds net primary production at the site and indicates that an additional advective supply of carbon is required
to support the copepod community. 相似文献
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Based on the stem analysis of 59 individuals of Pinus elliottii in combination with tree biomass models, we calculated annual biomass increment of forest plots at Qianyanzhou Ecological
Station, Chinese Academy of Sciences in subtropical China. In addition, canopy layer and community NPP were calculated based
on 12 years’ litter fall data. NPP of the 21-year-old forest was estimated by using the BIOME BGC model; and both measured
NPP and estimated NPP were compared with flux data. Community biomass was 10574 g · m−2; its distribution patterns in tree layer, shrub layer, herbaceous layer, tree root, herbaceous and shrub roots and fine roots
were 7542, 480, 239, 1810, 230, 274 and 239 g · m−2, respectively. From 1999 to 2004, the average annual growth rate and litter fall were 741 g · m−2 · a−1 (381.31 gC · m−2 · a−1) and 849 g · m−2 · a−1 (463 gC · m−2 · a−1), respectively. There was a significant correlation between annual litter fall and annual biomass increment; and the litter
fall was 1.19 times the biomass increment of living trees. From 1985 to 2005, average NPP and GPP values based on BGC modeling
were 630.88 (343.31–906.42 gC · m−2 · a−1) and 1 800 gC · m−2 · a−1 (1351.62–2318.26 gC · m−2 · a−1). Regression analysis showed a linear relationship (R
2=0.48) between the measured and simulated tree layer NPP values. NPP accounted for 30.2% (25.6%–32.9%) of GPP, while NEP accounted
for 57.5% (48.1%–66.5%) of tree-layer NPP and 41.74% (37%–52%) of stand NPP. Soil respiration accounted for 77.0% of measured
tree NPP and 55.9% of the measured stand NPP. NEE based on eddy covariance method was 12.97% higher than the observed NEP.
Supported by the National Key Basic Research Special Foundation of China (Grant No. 2002CB4125), International Joint Research
Project under Ministry of Science and Technology of China (Grant No. 2006DFB91920) 相似文献
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Agnes Mazot Dmitri Rouwet Yuri Taran Salvatore Inguaggiato Nick Varley 《Bulletin of Volcanology》2011,73(4):423-441
During 2007–2008, three CO2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering
the entire crater floor (including the lake). The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m−2 day−1 (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day−1 (April 2008). The mean CO2 flux estimated from the entire crater floor area was 1,102 g m−2 day−1 for April 2008 with a total emission rate of 144 ± 5.9 t day−1. Significant change in CO2 flux was not detected during the period of survey, and the mapping of the CO2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3He/4He ratio (as high as 8.1 R
A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt
and the Central American Volcanic Arc. The CO2/3He ratios for the high 3He/4He gases tend to have the MORB-like values (1.41 × 109), and the CO2/3He ratios for the lower 3He/4He gases fall within the range for the arc-type gases. The high 3He/4He ratios, the MORB-like CO2/3He ratios for the high 3He/4He gases and high proportion of MORB-CO2 (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes. 相似文献
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Corrado Cigolini 《Bulletin of Volcanology》2010,72(6):693-704
Data collected at Somma-Vesuvius during the 1998–1999 radon surveys have been revisited and reinterpreted in light of recent
geophysical and geochemical information. The duration of selected radon anomalies, together with the decay properties of radon,
have been used to estimate the permeability and porosity of rocks of the deep hydrothermal system. The current local cyclic
seismicity is explained by means of a double convective-cell model. Convective cells are separated by a low-permeability horizon
located at about 2–2.5 km below sea level. Fluids convecting within the upper cells show temperatures ranging 300–350°C. Rock
permeabilities in this sector are estimated on the order of 10−12 m2, for porosities (ϕ) of about 10−5 typical of a brittle environment where fluid velocities may reach ∼800 m/day. Fluid temperatures within the lower cells may
be as high as 400–450°C, consistent with supercritical regimes. The hydrodynamic parameters for these cells are lower, with
permeability k ∼ 10−15 m2, and porosity ranging from 10−6 to 10−7. Here, fluid motion toward the surface is controlled by the fracture network within a porous medium approaching brittle–ductile
behaviour, and fluid velocities may reach ∼1,800 m/day. The low-permeability horizon is a layer where upper and lower convecting
cells converge. In this region, fluids (convecting both at upper and lower levels) percolate through the wallrock and release
their brines. Due to self-sealing processes, permeability within this horizon reaches critical values to keep the fluid pressure
near lithostatic pressure (for k ∼ 10−18 m2). Deep fluid pressure buildups precede the onset of hydrothermally induced earthquakes. Permeability distribution and rock
strength do not exclude that the next eruption at Somma-Vesuvius could be preceded by a seismic crisis, eventually leading
to a precursory phreatic explosion. The coupling of these mechanisms has the potential of inducing pervasive failure within
rocks of the hydrothermal shell, and may be a prelude to a magmatic eruption. It is finally emphasised that the integrated
analysis of seismic and geochemical data, including radon emissions, could be successfully used in testing temperature distributions
and variations of porosity and permeability in active geothermal reservoirs. 相似文献
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Sabine Roedelsperger Michael Kuhn Oleg Makarynskyy Carl Gerstenecker 《Pure and Applied Geophysics》2008,165(6):1131-1151
It is sometimes assumed that steric sea-level variations do not produce a gravity signal as no net mass change, thus no change
of ocean bottom pressure is associated with it. Analyzing the output of two CO2 emission scenarios over a period of 2000 years in terms of steric sea-level changes, we try to quantify the gravitational
effect of steric sea-level variations. The first scenario, computed with version 2.6 of the Earth System Climate Model developed
at the University of Victoria, Canada (UVic ESCM), is implemented with a linear CO2 increase of 1% of the initial concentration of 365 ppm and shows a globally averaged steric effect of 5.2 m after 2000 years.
In the second scenario, computed with UVic ESCM version 2.7, the CO2 concentration increases quasi-exponentially to a level of 3011 ppm and is hold fixed afterwards. The corresponding globally
averaged steric effect in the first 2000 years is 2.3 m. We show, due to the (vertical) redistribution of ocean water masses
(expansion or contraction), the steric effect results also in a small change in the Earth’s gravity field compared to usually
larger changes associated with net mass changes. Maximum effects for computation points located on the initial ocean surface
can be found in scenario 1, with the effect on gravitational attraction and potential ranging from 0.0 to −0.7·10−5 m s−2 and −3·10−3 to 6·10−3 m2 s−2, respectively. As expected, the effect is not zero but negligible for practical applications. 相似文献
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Tao Zhen Shen ChengDe Gao QuanZhou Sun YanMin Yi WeiXi Li YingNian 《中国科学D辑(英文版)》2007,50(7):1103-1114
High-resolution sampling, measurements of organic carbon contents and 14C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application
of 14C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×104 kg C hm−2 to 30.75×104 kg C hm−2 in the alpine meadow ecosystems, with an average of 26.86×104 kg C hm−2. Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of
years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m−2 a−1 to 254.93 gC m−2 a−1, with an average of 191.23 g C m−2 a−1. The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m−2 a−1 to 181 g C m−2 a−1. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow
ecosystem of the Tibetan Plateau will be changed, which needs further research.
Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong
Provincial Natural Science Foundation of China (Grant No. 06300102) 相似文献
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Jennifer S. Le Blond Claire J. Horwell Peter J. Baxter Sabina A. K. Michnowicz Maura Tomatis Bice Fubini Pierre Delmelle Christina Dunster Herman Patia 《Bulletin of Volcanology》2010,72(9):1077-1092
The continuous ash and gas emissions from the Tavurvur cone in Rabaul caldera, Papua New Guinea, during 2007–08, raised concerns
regarding how exposure would affect the respiratory health of nearby populations and impact on the environment. As part of
a formal evaluation of the effects of volcanic emissions on public health, we investigated the potential health hazard of
the ash using a suite of selected mineralogical analyses and in vitro toxicity screening tests. The trachy-andesitic ash comprised 2.1–6.7 vol.% respirable (sub-4 μm diameter) particles. The crystalline silica content was 1.9–5.0 wt.% cristobalite (in the bulk sample) with trace amounts
of quartz and/or tridymite. Scanning electron microscopy showed that the ash particles were angular with sparse, fibre-like particles (∼3–60 μm max. diameter) observed in some samples, which we confirmed to be CaSO4 (gypsum, at <6 wt.% in the bulk samples) and not asbestiform fibres. The ash specific surface area was low (0.1–2.7 m2 g−1). The leached solution from one of the ash samples was slightly acidic (pH 5.6), but did not contain high levels of toxic
metals (such as F, Cu, Zn, Mn, As, Ni and Cd) when compared to previously tested volcanic ash leachates. Ash samples generated
potentially-harmful hydroxyl radicals through an iron-mediated catalytic reaction, in the range of 0.15–2.47 μmol m−2 (after 30 min of reaction). However, measurement of particle oxidative capacity (potential oxidative stress reaction using
ascorbic acid) and silica-like injury to red blood cells (erythrolysis assay, i.e. measurement of cell death) nevertheless revealed low biological reactivity.
The findings suggest that acute exposure to the ash would have a limited potential to exacerbate pre-existing conditions such as asthma or chronic bronchitis, and the potential for chronic exposure leading to silicosis was
low. 相似文献
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We present an uncertainty analysis of ecological process parameters and CO2 flux components (R
eco, NEE and gross ecosystem exchange (GEE)) derived from 3 years’ continuous eddy covariance measurements of CO2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to
analyze the random error of CO2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters
and CO2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather
than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters.
Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary
least square method (OLS). (3) The differences between simulated Reco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m−2·a−1), 34.33% (79 g C·m−2·a−1) and 5.4% (92 g C·m−2·a−1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from
a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m−2·a−1), 2.1% (5.7 g C·m−2·a−1), and 0.26% (4.3 g C·m−2·a−1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing
uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the
timescale, the smaller the uncertainty. The relative uncertainties of Reco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale.
Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership
Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No.
2002CB412502) 相似文献
19.
Belowground carbon balance and carbon accumulation rate in the successional series of monsoon evergreen broad-leaved forest 总被引:4,自引:0,他引:4
ZHOU Guoyi ZHOU Cunyu LIU Shuguang TANG Xuli OUYANG Xuejun ZHANG Deqiang LIU Shizhong LIU Juxiu YAN Junhua ZHOU Chuanyan LUO Yan GUAN Lili LIU Yan 《中国科学D辑(英文版)》2006,49(3):311-321
The belowground part of terrestrial ecosystem is a huge carbon pool. It is believed that of the total 2500Gt carbon stored in global terrestrial ecosystem, soil carbon storage within the 1 m surface layer ac- counts for 2000Gt, which is 4-fold of vegetation car- bon storage[1,2]. Compared with the carbon in the vegetation, carbon in the deep soil layers is much more stable, and it will stay in soil profile permanentlyunless geological vicissitude occurs. Essentially, forest restoration is the… 相似文献
20.
Paul A. Bukaveckas Amy MacDonald Anthony Aufdenkampe John H. Chick John E. Havel Richard Schultz Ted R. Angradi David W. Bolgrien Terri M. Jicha Debra Taylor 《Aquatic Sciences - Research Across Boundaries》2011,73(3):419-436
Main channel habitats of the Ohio, Missouri, and Upper Mississippi Rivers were surveyed during the summers of 2004, 2005 and
2006 using a probability-based sampling design to characterize inter-annual and inter-river variation in suspended chlorophyll
a (CHLa) and related variables. Large (fivefold) differences in CHLa were observed with highest concentrations in the Upper
Mississippi (32.3 ± 1.8 μg L−1), intermediate values in the Missouri (19.7 ± 1.1 μg L−1) and lowest concentrations in the Ohio (6.8 ± 0.5 μg L−1). Inter-annual variation was small in comparison to inter-river differences suggesting that basin-specific factors exert
greater control over river-wide CHLa than regional-scale processes influencing climate and discharge. The rivers were characterized
by variable but generally low light conditions as indicated by depth-averaged underwater irradiance <4 E m−2 day−1 and high ratios of channel depth to euphotic depth (>3). Despite poor light conditions, regression analyses revealed that
TP was the best single predictor of CHLa (R
2 = 0.40), though models incorporating both light and TP performed better (R
2 = 0.60). Light and nutrient conditions varied widely within rivers and were inversely related, suggesting that riverine phytoplankton
may experience shifts in resource limitation during transport. Inferred grazing and sedimentation losses were large yet CHLa
concentrations did not decline downriver indicating that growth and loss processes were closely coupled. The contribution
by algae to suspended particulate organic matter in these rivers (mean = 41%) was similar to that of lakes (39%) but lower
relative to reservoirs (61%). 相似文献