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1.
Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities
of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth
profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the
redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient
over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change
the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to
be 6 × 10−8 cm2 s−1. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused
by the irrigational activities of the benthic fauna. 相似文献
2.
Methanogenesis in Arizona,USA dryland streams 总被引:1,自引:0,他引:1
Jeremy B. Jones Jr. Robert M. Holmes Stuart G. Fisher Nancy B. Grimm Dena M. Greene 《Biogeochemistry》1995,31(3):155-173
Methanogenesis was studied in five streams of central and southern Arizona by examining the distribution of methane in interstitial
water and evasion of methane in three subsystems (hyporheic, parafluvial and bank sediments). In Sycamore Creek, the primary
study site (studied during summer and early autumn), methane content of interstitial water exhibited a distinct spatial pattern.
In hyporheic (sediments beneath the wetted channel) and parfluvial zones (active channel sediments lateral to the wetted channel),
which were well oxygenated due to high hydrologic exchange with the surface stream and had little particulate organic matter
(POM), interstitial methane concentration averaged only 0.03 mgCH4-C/L. Bank sediments (interface between the active channel and riparian zone), in contrast, which were typically vegetated,
had high POM, low hydrologic exchange and concomitantly low dissolved oxygen levels, had interstitial concentration averaging
1.5 mgCH4-C/L. Methane emission from Sycamore Creek, similar to methane concentration, averaged only 3.7 mgCH4-C·m−2·d−1 from hyporheic and parafluvial zones as opposed to 170 mgCH4-C·m−2·d−1 from anoxic bank sediments. Methane in four additional streams sampled (one sampling date during late winter) was low and
exhibited little spatial variation most likely due to cooler stream temperatures. Interstitial methane in parafluvial and
bank sediments of all four streams ranged from only 0.005 to 0.1 mgCH4-C/L. Similarly methane evasion was also low from these streams varying from 0 to 5.7 mgCH4-C·m−2·d−1. The effects of organic matter and temperature on methanogenesis were further examined by experimentally manipulating POM
and temperature in stoppered flasks filled with hyporheic sediments and stream water. Methane production significantly increased
with all independent variables. Methane production is greatest in bank sediments that are relatively isolated hydrologically
and lowest in hyporheic and parafluvial sediments that are interactive with the surface stream. 相似文献
3.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
4.
This study examined how sediment-sorbed PCBs and several large storms affected sediment nutrient dynamics based on potential
nitrification rates and benthic flux measurements. PCBs were hypothesized to negatively affect potential nitrification rates
due to the sensitivity of nitrifying bacteria. Sediment disturbance caused by the succession of storms, which can enhance
nutrient inputs and phytoplankton production, was hypothesized to enhance both potential nitrification rates and benthic flux
measurements as a result of higher nutrient and organic matter concentrations. Potential nitrification rates, benthic fluxes
(NO3
− + NO2
−, NH4
+, and DIP), sediment PCB content, water content, organic content, salinity, bottom water dissolved oxygen, and sediment chlorophyll
were measured at 13 different sites in Escambia Bay during the summer of 2005. Potential nitrification rates were highest
at deep, organic-rich sites. Total PCB content did not have a direct effect on potential nitrification rates. An analysis
of recent changes in benthic processes in relation to extreme meteorological events was performed by comparing the 2005 results
with data from 2000, 2003, and 2004. Storm effects on sediment biogeochemistry were mixed with sediment nitrogen dynamics
enhanced at some sites but not others. In addition, SOC and NH4
+ fluxes increased in deeper channel sites after Hurricanes Ivan and Dennis, which could be attributed to the deposition of
phytoplankton blooms. Sediment nutrient dynamics in Escambia Bay appear to be resilient to these extreme meteorological events
since there were no significant effects on sediment processes in the Bay as a whole.
Handling editor: P. Viaroli 相似文献
5.
Rosa Gómez M. Isabel Arce J. Javier Sánchez M. del Mar Sánchez-Montoya 《Hydrobiologia》2012,679(1):43-59
Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed
to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated
in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments
during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable
sediment NO3
−-N and NH4
+-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments
from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO3
−-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH4
+-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization
and net nitrification from sediments. Afterwards, the extractable NO3
−-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter
are depleted, and to an increase in NO3
−-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore
space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released
as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments
would differ depending on desiccation period duration. 相似文献
6.
Benthic phosphorus regeneration in the Potomac River Estuary 总被引:2,自引:2,他引:0
The flux of dissolved reactive phosphate from Potomac riverine and estuarine sediments is controlled by processes occurring
at the water-sediment interface and within surficial sediment.In situ benthic fluxes (0.1 to 2.0 mmoles m−2 day−1) are generally five to ten times higher than calculated diffusive fluxes (0.020 to 0.30 mmoles m−2 day−1). The discrepancy between the two flux estimates is greatest in the transition zone (river mile 50 to 70) and is attributd
to macrofaunal irrigation.
Bothin situ and diffusive fluxes of dissolved reactive phosphate from Potomac tidal river sediments are low while those from anoxic lower
estuarine sediments are high. The net accumulation rate of phosphorus in benthic sediment exhibits an inverse pattern. Thus
a large fraction of phosphorus is retained by Potomac tidal river sediments, which contain a surficial oxidized layer and
oligochaete worms tolerant of low oxygen conditions, and a large fraction of phosphorus is released from anoxic lower estuary
sediments. Tidal river sediment pore waters are in equilibrium with amorphous Fe (OH)3 while lower estuary pore waters are significantly undersaturated with respect to this phase. Benthic regeneration of dissolved
reactive phosphorus is sufficient to supply all the phosphorus requirements for net primary production in the lower tidal
river and transition-zone waters of the Potomac River Estuary. Benthic regeneration supplies approximately 25% as much phosphorus
as inputs from sewage treatment plants and 10% of all phosphorus inputs to the tidal Potomac River.
When all available point source phosphorus data are put into a steady-state conservation of mass model and reasonable coefficients
for uptake of dissolved phosphorus, remineralization of particulate phosphorus, and sedimentation of particulate phosphorus
are used in the model, a reasonably accurate simulation of dissolved and particulate phosphorus in the water column is obtained
for the summer of 1980. 相似文献
7.
Oxygen uptake rates of undisturbed sediment columns have been used as an integrative measure of the metabolic activities of benthic communities. Since the intensity of metabolic processes of profundal lake is dependent on the production of organic matter in the pelagic zone, oxygen uptake rates reflect the trophic condition of the whole lake. Four small lakes of central Chile, differing strongly in trophic conditions, provided a possibility to compare benthic oxygen uptake rates, under different oxygen conditions (Quiñenco, Grande, Chica and Lleulleu). Our objective was to establish the relationship between the oxygen uptake rates and bottom characteristics of lakes with different trophic conditions. At 8 mg O2 l-1 in the overlying water of the cores studied, the oxygen uptake rates of the sediment were: Quiñenco 51.2–56.0 mg O2 m2 h-1 (eutrophic), Grande 41.2–46.4 mg O2 m2 h-1 (mesotrophic), Chica 23.2–18.1 mg O2 m2 h-1 (mesotrophic) and Lleulleu 11.7–16.0 mg O2 m2 h-1 (oligotrophic). By exposing the sediments to different oxygen levels in the laboratory, it was found that benthic community metabolism decreased with oxygen concentrations. The slope of regression lines, relating oxygen uptake rates to oxygen concentrations, differed for the different sites investigated, closely related with the trophic conditions of the lakes. It was positively correlated with the organic matter content of the sediment of the cores (r
2= 0.78, p<0,05) and the nutrients of the bottom waters (total-P: r
2= 0.73, p<0,05; total-N: r
2= 0.73, p<0,05), and negatively with the redox potential of the sediments (r
2= 0.88, p<0,05). 相似文献
8.
Factors Controlling Sediment Denitrification in Midwestern Streams of Varying Land Use 总被引:1,自引:0,他引:1
We investigated controls on stream sediment denitrification in nine headwater streams in the Kalamazoo River Watershed, Michigan,
USA. Factors influencing denitrification were determined by using experimental assays based on the chloramphenicol-amended
acetylene inhibition technique. Using a coring technique, we found that sediment denitrification was highest in the top 5 cm
of the benthos and was positively related to sediment organic content. To determine the effect of overlying water quality
on sediment denitrification, first-order stream sediments were assayed with water from second- and third-order downstream
reaches, and often showed higher denitrification rates relative to assays using site-specific water from the first-order stream
reach. Denitrification was positively related to nitrate (NO3
−) concentration, suggesting that sediments may have been nutrient-limited. Using stream-incubated inorganic substrata of varying
size classes, we found that finer-grained sand showed higher rates of denitrification compared to large pebbles, likely due
to increased surface area per volume of substratum. Denitrification was measurable on both inorganic substrata and fine particulate
organic matter loosely associated with inorganic particles, and denitrification rates were related to organic content. Using
nutrient-amended denitrification assays, we found that sediment denitrification was limited by NO3
− or dissolved organic carbon (DOC, as dextrose) variably throughout the year. The frequency and type of limitation differed
with land use in the watershed: forested streams were NO3
−-limited or co-limited by both NO3
− and DOC 92% of the time, urban streams were more often NO3
−-limited than DOC-limited, whereas agricultural stream sediments were DOC-limited or co-limited but not frequently limited
by NO3
− alone. 相似文献
9.
10.
The influence of land use on potential fates of nitrate (NO3
−) in stream ecosystems, ranging from denitrification to storage in organic matter, has not been documented extensively. Here,
we describe the Pacific Northwest component of Lotic Intersite Nitrogen eXperiment, phase II (LINX II) to examine how land-use
setting influences fates of NO3
− in streams. We used 24 h releases of a stable isotope tracer (15NO3-N) in nine streams flowing through forest, agricultural, and urban land uses to quantify NO3
− uptake processes. NO3
− uptake lengths varied two orders of magnitude (24–4247 m), with uptake rates (6.5–158.1 mg NO3-N m−2 day−1) and uptake velocities (0.1–2.3 mm min−1) falling within the ranges measured in other LINX II regions. Denitrification removed 0–7% of added tracer from our streams.
In forest streams, 60.4 to 77.0% of the isotope tracer was exported downstream as NO3
−, with 8.0 to 14.8% stored in wood biofilms, epilithon, fine benthic organic matter, and bryophytes. Agricultural and urban
streams with streamside forest buffers displayed hydrologic export and organic matter storage of tracer similar to those measured
in forest streams. In agricultural and urban streams with a partial or no riparian buffer, less than 1 to 75% of the tracer
was exported downstream; much of the remainder was taken up and stored in autotrophic organic matter components with short
N turnover times. Our findings suggest restoration and maintenance of riparian forests can help re-establish the natural range
of NO3
− uptake processes in human-altered streams. 相似文献
11.
Organic matter diagenesis at the oxic/anoxic interface in coastal marine sediments,with emphasis on the role of burrowing animals 总被引:18,自引:0,他引:18
The present paper reviews the current knowledge on diagenetic carbon transformations at the oxic/anoxic interface in coastal marine sediments. Oxygen microelectrodes have revealed that most coastal sediments are covered only by a thin oxic surface layer. The penetration depth of oxygen into sediments is controlled by the balance between downward transport and consumption processes. Consumption of oxygen is directly or indirectly caused by respiration of benthic organisms. Aerobic organisms have the enzymatic capacity for complete oxidation of organic carbon. Anaerobic decay occurs stepwise, involving several types of bacteria. Large organic molecules are first fermented into small moieties. These are then oxidized completely by anaerobic respirers using a sequence of electron acceptors: Mn4+, NO3
-, Fe3+, SO4
2- and CO2. The quantitative role of each electron acceptor depends on the sediment type and water depth. Since most of the sediment oxygen uptake is due to reoxidation of reduced metabolites, aerobic respiration is of limited importance. It has been suggested that sediments contain three major organic fractions: (1) fresh material that is oxidized regardless of oxygen conditions; (2) oxygen sensitive material that is only degraded in the presence of oxygen; and (3) totally refractory organic matter. Processes occurring at the oxic/anoxic boundaries are controlled by a number of factors. The most important are: (1) temperature, (2) organic supply, (3) light, (4) water currents, and (5) bioturbation. The role of bioturbation is important because the infauna creates a three-dimensional mosaic of oxic/anoxic interfaces in sediments. The volume of oxic burrow walls may be several times the volume of oxic surface sediment. The infauna increases the capacity, but not the overall organic matter decay in sediments, thus decreasing the pool of reactive organic matter. The increase in decay capacity is partly caused by injection of oxygen into the sediment, and thereby enhancing the decay of old, oxygen sensitive organic matter several fold. Finally, some future research directions to improve our understanding of diagenetic processes at the oxic/anoxic interface are suggested. 相似文献
12.
Tom Moens Sandra Vanhove Ilse De Mesel Bea Kelemen Thierry Janssens Ann Dewicke Ann Vanreusel 《Polar Biology》2007,31(1):1-13
δ13C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions,
and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ13C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ13C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up
to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of
some meiofauna for specific components of the sedimenting plankton. However, 13C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in
which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate
(11–20 mg C m−2 day−1) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization;
uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization. 相似文献
13.
Sulfate reduction rates and biogeochemical parameters of fish farm sediments across the Mediterranean were investigated in
the order to evaluate the potential effects of organic matter inputs on habitat quality for the common seagrass Posidonia oceanica. Four study sites were selected in Spain, Italy, Greece and Cyprus to represent the Mediterranean basin. P. oceanica was found in immediate vicinity of all the farms, which were located at physically exposed sites about 1 km from the shore
lines. Organic matter accumulation, sulfate reduction rates and sulfur pools were measured in depth profiles along transects
from the farms in both bare and vegetated sediments. Results show that although the organic matter accumulation was minor
at the sites (POC < 2.8% DW), the sulfate reduction rates were high, in particular at the largest farm in Italy (up to 212 mmol m−2 d−1), similar to rates found at shallower, temperate fish farm sites, where higher sedimentation rates can be expected. Sulfate
reducing bacteria in these low-organic, carbonate-rich Mediterranean sediments respond strongly to organic matter loadings
and cause habitat degradation. Sulfate reduction rates measured in the P. oceanica sediments were among the highest recorded (7.8–42.0 mmol m−2 d−1) similar to rates found in degrading meadows impacted by organic matter loadings. As sulfate reduction rates were correlated
with the sedimentation rates along the transects rather than organic matter pools this suggests mineralization processes were
controlled by organic matter loading in fish farm sediments. The vegetated sediments near the net cages were more reduced
due to accumulation of sulfides compared to control sites, which is a possible contributing factor to the observed seagrass
decline in the farm surroundings. It is recommended that Mediterranean fish farms are placed in areas with rapid dispersal
of particulate waste products to minimize organic matter loading of the sediments and thereby preserve habitat quality for
benthic fauna and flora. 相似文献
14.
Investigation of physicochemical form of uranium in sediment of brackish Lake Obuchi using sequential extraction procedure 总被引:1,自引:0,他引:1
The physicochemical form of uranium (238U) in the sediment of brackish Lake Obuchi was investigated using the standard procedures of sequential extraction. Approximately
60% to 70% of 238U was composed of the form bound to carbonates and iron (Fe)-manganese (Mn) oxides in silty sediments, whereas more than 50%
of 238U existed in the minerals of sandy sediments. The proportions of 238U bound to carbonates in the sediments of brackish Lake Obuchi were larger than those in fresh-water lake sediments. Most
of the uranium in the brackish lake sediment was considered to be mainly influenced by UO2(CO3)3
4− in seawater, judging from the fact that the 234U/ 238U activity ratios (1.13 to 1.16) of silty sediments were very close to that of seawater (1.14). The high correlation found
between the 238U concentration in the sediment and the amount of organic matter demonstrated that organic matter acts as a scavenger for
238U accumulation on the lake bottom.
Received: July 2, 1999 / Accepted: May 25, 2000 相似文献
15.
Akiko Sasaki Yu Hagimori Ichiro Yuasa Takayuki Nakatsubo 《Landscape and Ecological Engineering》2012,8(1):107-114
To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using
an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment
respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO2-C m−2 h−1 in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r
2 = 0.70, p < 0.05), although we did not detect any significant correlations between the rates and sediment characteristics. We prepared
a model for estimating the annual sediment respiration based on the in situ sediment respiration rates and their temperature
coefficient (Q
10 = 1.8). The annual sediment respiration was estimated to be 92 g CO2-C m−2 year−1. The total amount of organic carbon mineralization for the entire estuarine intertidal flats through sediment respiration
(43 t C year−1) is equivalent to approximately 25% of the annual organic carbon load supplied from the river basin of the estuary. 相似文献
16.
Benthic nutrient fluxes in a eutrophic,polymictic lake 总被引:2,自引:0,他引:2
Sediment release rates of soluble reactive phosphorus (SRP) and ammonium (NH4) were determined seasonally at three sites (water depth 7, 14 and 20 m) in Lake Rotorua using in situ benthic chamber incubations.
Rates of release of SRP ranged from 2.2 to 85.6 mg P m−2 d−1 and were largely independent of dissolved oxygen (DO) concentration. Two phases of NH4 release were observed in the chamber incubations; high initial rates of up to 2,200 mg N m−2 d−1 in the first 12 h of deployment followed by lower rates of up to 270 mg N m−2 d−1 in the remaining 36 h of deployment. Releases of SRP and NH4 were highest in summer and at the deepest of the three sites. High organic matter supply rates to the sediments may be important
for sustaining high rates of sediment nutrient release. A nutrient budget of Lake Rotorua indicates that internal nutrient
sources derived from benthic fluxes are more important than external nutrient sources to the lake. 相似文献
17.
Cappenberg Thom E. Hordijk Kees A. Jonkheer Gert J. Lauwen Jos P. M. 《Hydrobiologia》1982,91(1):161-168
The turnover and exchange rates, as well as the diffusion processes, concerning the input and output of carbon compounds at
the mud-water interface, were studied. The carbon input rates were derived from the annual sedimentation rates of particulate
organic matter (about 1 100 kg C · yr−1). The nature of the sedimented POC, and its breakdown pathways and turnover rates towards important metabolic intermediates
in methanogenesis, were examined. The breakdown kinetics ofChlorella cell walls, a dominant green alga in Lake Vechten, was studied using U-14C-labelled cell walls. The breakdown of the cell walls appears to the rate-limiting step in anaerobic mineralization.
Using first order kinetic equations, and HPLC and GLC and radio-chemical methods, turnover rate constants (k-values) of between
0.18 and 0.32 day−1 and pool sizes of algal cell walls of 37 to 80 μg · g−1 wet mud were found, giving turnover rates of 7.7 to 25.6 μg · g−1 · day−1 of cell wall material. The turnover rates (k-values between 0.07 and 0.31 h−1) of acetate, the most important breakdown product, and its concentration gradients (between 5 and 30 μmol) and diffusion
coefficient (Ds = 2.2 × 10−6 cm2 · s−1) just in and above mud-water interface, was quantified. The diffusion of acetate, within the sediments, could not account
for the turnover rates observed.
Finally, from acetate flux data and from those on the rates of formation of carbon dioxide and methane, the output of carbon
and its cycling in Lake Vechten are discussed. 相似文献
18.
Reed JZ Chambers C Hunter CJ Lockyer C Kastelein R Fedak MA Boutilier RG 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(1):1-10
The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were
measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory
(12 ± 0.3 s, mean ± SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The
mean percentage time spent submerged was 89 ± 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency
was low (4.9 ± 0.19 breaths · min−1) but with high tidal volumes (1.1 ± 0.01 l), enabling a comparatively high minute rate of gas exchange. Oxygen consumption
under these experimental conditions (247 ± 13.8 ml O2 · min−1) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen
stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O2 values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for
the longer dives. Blood oxygen capacity was 23.5 ± 1.0 ml · 100 ml−1, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation.
Accepted: 11 August 1999 相似文献
19.
Using porewater profiles to assess nutrient availability in seagrass-vegetated carbonate sediments 总被引:6,自引:0,他引:6
We measured porewater profiles of inorganic (NH4
+, NO3
–(+NO2
–), PO4
3– (hereafter referred to as DIP)) and organic (DON, DOP) nutrients in seagrass-vegetated sediments at two sites in a shallow bay in Bermuda within close proximity (200 m) but subject to different nutrient loading. At both sites, total dissolved and inorganic nutrient concentrations were usually 1–2 orders of magnitude higher in the sediments than in the water column, with the exception of NO3
–. Organic N and P were significant components of the total dissolved nutrient pools both in the sediment porewater and in the overlying water column (up to 75% for DON and 40% for DOP), and may be important in meeting plant nutrient demands. We used two approaches to examine how well porewater nutrient concentrations reflected the relative availabilities of N and P for seagrasses: (1) a simple stoichiometric nutrient regeneration model based on the N:P ratio of decomposing organic matter and porewater NH4
+ concentrations to predict porewater DIP, and (2) fitting of the porewater profiles to estimate rates of net nutrient production (or consumption), which reflects the balance between nutrient sources and sinks in the rhizosphere. The stoichiometric model indicated that sediment porewaters were depleted in P relative to N in the low-nutrient outer bay site, and enriched in P relative to N in the higher-nutrient inner bay site. These results are consistent with the mechanism of carbonate sediments in oligotrophic tropical environments being a strong sink for dissolved inorganic P and our previous work suggesting that nutrient enrichment causes P to become disproportionately more available than N. Net nutrient production rates of porewater P at both sites and N at the inner bay site were low (typically < 2%) relative to the nutrient demands of the seagrasses. The implications of the profile interpretation are two-fold: (1) the low rates of net nutrient production indicate diffusive losses from the root zone were insignificant and that nutrient turnover rates were high, except in the P-limited outer bay where N accumulated in sediment porewaters; and (2) because standing stock nutrient concentrations often represent a small fraction of the total nutrients cycled in the sediments, they are in many cases a poor indicator of nutrient availability. Based on our estimates of losses from the root zone, decomposition, and plant uptake we have constructed a rough budget for the cycling of P and N at our two sites. 相似文献
20.
The aim of this study was to determine the effect of sediment grazing and burrowing activities of natural populations of Mictyris longicarpus on benthic metabolism, nitrogen flux and irrigation rates by comparing sediments taken from minimum disturbance exclusion cages and adjacent sediments subject to M. longicarpus activities. M. longicarpus reduced sediment surface chlorophyll a (approximately 77%), organic carbon (approximately 95%) and total nitrogen concentrations (approximately 99%) in comparison to ungrazed sediments. Consequently, they significantly reduced gross benthic O2 production (about 71%) and sediment O2 consumption (approximately 46%). Mean N2 fluxes showed net effluxes (276-430 μmol m−2 day−1) in the presences of M. longicarpus and net uptakes (194.09-449.21 μmol m−2 day−1) where they were excluded. The net uptake of N2 was most likely due to cyanobacteria fixing of N2, as dense microbial mats became established over the sediment surface in the absence of M. longicarpus grazing activity. Sediment irrigation/transport rates calculated from CsCl tracer dilution indicated greater irrigation rates in the exclusions (12.12-16.22 l m−2 h−1) compared to inhabited sediments (6.33-11.73 l m−2 h−1) and this was again was most likely due to the lack of grazing pressure which allowed large populations of small burrowing polychaetes to inhabit the organic matter rich exclusion sediments. As such, the main influence of M. longicarpus was the interception and consumption of transported organic material, benthic microalgae and other small infaunal organisms resulting in the removal of approximately 0.06 g m−2 day−1 of nitrogen and 12.12 g m−2 day−1 of organic carbon. This “cleansing” of the sediments reduced sediment metabolism and the flux of solutes across the sediment water interface and ultimately the heavy predation of M. longicarpus by transient species such as stingrays, results in a net loss of carbon and nitrogen from the system. 相似文献