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1.
Sulphate,dissolved organic carbon,nutrients and terminal metabolic products in deep pore waters of an intertidal flat 总被引:6,自引:0,他引:6
Melanie Beck Olaf Dellwig Jan M. Holstein Maik Grunwald Gerd Liebezeit Bernhard Schnetger Hans-Jürgen Brumsack 《Biogeochemistry》2008,89(2):221-238
This study addresses deep pore water chemistry in a permeable intertidal sand flat at the NW German coast. Sulphate, dissolved
organic carbon (DOC), nutrients, and several terminal metabolic products were studied down to 5 m sediment depth. By extending
the depth domain to several meters, insights into the functioning of deep sandy tidal flats were gained. Despite the dynamic
sedimentological conditions in the study area, the general depth profiles obtained in the relatively young intertidal flat
sediments of some metres depth are comparable to those determined in deep marine surface sediments. Besides diffusion and
lithology which control pore water profiles in most marine surface sediments, biogeochemical processes are influenced by advection
in the studied permeable intertidal flat sediments. This is supported by the model setup in which advection has to be implemented
to reproduce pore water profiles. Water exchange at the sediment surface and in deeper sediment layers converts these permeable
intertidal sediments into a “bio-reactor” where organic matter is recycled, and nutrients and DOC are released. At tidal flat
margins, a hydraulic gradient is generated, which leads to water flow towards the creekbank. Deep nutrient-rich pore waters
escaping at tidal flat margins during low tide presumably form a source of nutrients for the overlying water column in the
study area. Significant correlations between the inorganic products of terminal metabolism (NH4
+ and PO4
3−) and sulphate depletion suggest sulphate reduction to be the dominant pathway of anaerobic carbon remineralisation. Pore
water concentrations of sulphate, ammonium, and phosphate were used to elucidate the composition of organic matter degraded
in the sediment. Calculated C:N and C:P ratios were supported by model results. 相似文献
2.
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
3.
Mangroves represent a major environment of tropical coasts. They are highly productive, and act both as a source and a sink of organic carbon. Concentrations and characteristics (fluorescence and hydrophobic–hydrophilic fractions) of dissolved organic matter (DOM) were investigated in relation to the organic content of sediments and to the chemistry of pore waters along the coastline of French Guiana. The pore waters studied were extracted (centrifugation, soil moisture sampler) from sediments cored beneath A. germinans mangrove stands representative of development stages: pioneer, mature and senescent. In order to asses the effects of seasonal changes, two cores were performed in each location, just after dry and wet seasons, respectively. Dissolved organic carbon (DOC) concentrations in pore waters of the upper sediment were found to increase, from 0.7 mmol l−1 under the pioneers to 9 under senescent mangroves. The evolution of sedimentary organic carbon (SedOC) in the same sediment paralleled that of DOC, increasing from 0.7 to 28%. On the contrary, in the lower parts of sediment cores SedOC and DOC displayed contrasting vertical trends: SedOC decreased sharply with depth while DOC increased, reaching concentrations up to 30 mmol l−1 at 50 cm in the older, senescent mangroves. In addition, the Fluorescence/DOC ratios and the hydrophobic contents of DOC were higher at greater depths in most cores, expressing changes in the DOC composition. These results suggest that the DOC of the upper layers originated directly from the SedOC of the enclosing sediment, while the hydrophobic and fluorescent DOC accumulated in the anoxic bottom layer. The mechanisms responsible for this accumulation at depth requires additional research to be fully understood. However, the anoxic conditions and high pH values prevailing in the lower sediment, by lessening DOM sorption and enhancing SedOC dissolution, may be partly responsible for the high DOC concentrations and fluorescences at depth. In addition, seasonal variation may be involved. During the rainy season, water sources were mixed resulting in lower DOC concentrations in the upper sediment, whereas during the dry season, increased evapotranspiration concentrate salts and DOC, which are transported vertically with percolating water. 相似文献
4.
Algal communities and export of organic matter from sea ice were studied in the offshore marginal ice zone (MIZ) of the northern
Barents Sea and Nansen Basin of the Arctic Ocean north of Svalbard by means of ice cores and short-term deployed sediment
traps. The observations cover a total of ten stations within the drifting pack ice, visited over a period of 3 years during
the period of ice melt in May and July. Maximum flux of particulate organic carbon and chlorophyll a from the ice at 1 m depth (1,537 mg C m−2 per day and 20 mg Chl a m−2 per day) exceeded the flux at 30 m by a factor of 2 during spring, a pattern that was reversed later in the season. Although
diatoms dominated the ice-associated algal biomass, flagellates at times revealed similarly high biomass and typically dominated
the exported algal carbon. Importance of flagellates to the vertical flux increased as melting progressed, whereas diatoms
made the highest contribution during the early melting stage. High export of ice-derived organic matter and phytoplankton
took place simultaneously in the offshore MIZ, likely as a consequence of ice drift dynamics and the mosaic structure of ice-covered
and open water characteristic of this region. 相似文献
5.
Sedimentation in Boreal Lakes—The Role of Flocculation of Allochthonous Dissolved Organic Matter in the Water Column 总被引:1,自引:0,他引:1
We quantified sedimentation of organic carbon in 12 Swedish small boreal lakes (<0.48 km2), which ranged in dissolved organic carbon (DOC) from 4.4 to 21.4 mg C l−1. Stable isotope analysis suggests that most of the settling organic matter is of allochthonous origin. Annual sedimentation
of allochthonous matter per m2 lake area was correlated to DOC concentration in the water (R
2 = 0.41), and the relationship was improved when sedimentation data were normalized to water depth (R
2 = 0.58). The net efflux of C as CO2 from the water to the atmosphere was likewise correlated to DOC concentration (R
2 = 0.52). The losses of organic carbon from the water column via mineralization to CO2 and via sedimentation were approximately of equal importance throughout the year. Our results imply that DOC is a precursor
of the settling matter, resulting in an important pathway in the carbon cycle of boreal lakes. Thus, flocculation of DOC of
terrestrial origin and subsequent sedimentation could lead to carbon sequestration by burial in lake sediments. 相似文献
6.
The influence of biogeochemical processes on nitrogen and organic matter transformation and transport was investigated for two urban streams receiving groundwater discharge during the dry summer baseflow period. A multiple lines of evidence approach involving catchment-, and stream reach-scale investigations were undertaken to describe the factors that influence pore water biogeochemical processes. At the catchment-scale gaining stream reaches were identified from water table mapping and groundwater discharge estimated to be between 0.1 and 0.8 m3 m?2 d?1 from baseflow analysis. Sediment temperature profiles also suggested that the high groundwater discharge limited stream water infiltration into the sediments. At the stream reach-scale, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were higher in stream water than in groundwater. However, DOC and DON concentrations were greatest in sediment pore water. This suggests that biodegradation of sediment organic matter contributes dissolved organic matter (DOM) to the streams along with that delivered with groundwater flow. Pore water ammonium (NH4 +) was closely associated with areas of high pore water DOM concentrations and evidence of sulfate (SO4 2?) reduction (low concentration and SO4:Cl ratio). This indicates that anoxic DOM mineralization was occurring associated with SO4 2? reduction. However the distribution of anoxic mineralization was limited to the center of the streambed, and was not constrained by the distribution of sediment organic matter which was higher along the banks. Lower sediment temperatures measured along the banks compared to the center suggests, at least qualitatively, that groundwater discharge is higher along the banks. Based on this evidence anoxic mineralization is influenced by groundwater residence time, and is only measurable along the center of the stream where groundwater flux rates are lower. This study therefore shows that the distribution of biogeochemical processes in stream sediments, such as anoxic mineralization, is strongly influenced by both the biogeochemical conditions and pore water residence time. 相似文献
7.
Nathaniel B. Weston William P. Porubsky Vladimir A. Samarkin Matthew Erickson Stephen E. Macavoy Samantha B. Joye 《Biogeochemistry》2006,77(3):375-408
Porewater equilibration samplers were used to obtain porewater inventories of inorganic nutrients (NH4+, NOx, PO43−), dissolved organic carbon (DOC) and nitrogen (DON), sulfate (SO42−), dissolved inorganic carbon (DIC), hydrogen sulfide (H2S), chloride (Cl−), methane (CH4) and reduced iron (Fe2+) in intertidal creek-bank sediments at eight sites in three estuarine systems over a range of salinities and seasons. Sulfate
reduction (SR) rates and sediment particulate organic carbon (POC) and nitrogen (PON) were also determined at several of the
sites. Four sites in the Okatee River estuary in South Carolina, two sites on Sapelo Island, Georgia and one site in White
Oak Creek, Georgia appeared to be relatively pristine. The eighth site in Umbrella Creek, Georgia was directly adjacent to
a small residential development employing septic systems to handle household waste. The large data set (>700 porewater profiles)
offers an opportunity to assess system-scale patterns of porewater biogeochemical dynamics with an emphasis on DOC and DON
distributions. SO42− depletion (SO42−)Dep was used as a proxy for SR, and (SO42−)Dep patterns agreed with measured (35S) patterns of SR. There were significant system-scale correlations between the inorganic products of terminal metabolism
(DIC, NH4+ and PO43−) and (SO42−)Dep, and SR appeared to be the dominant terminal carbon oxidation pathway in these sediments. Porewater inventories of DIC and
(SO42−)Dep indicate a 2:1 stoichiometry across sites, and the C:N ratio of the organic matter undergoing mineralization was between
7.5 and 10. The data suggest that septic-derived dissolved organic matter with a C:N ratio below 6 fueled microbial metabolism
and SR at a site with development in the upland. Seasonality was observed in the porewater inventories, but temperature alone
did not adequately describe the patterns of (SO42−)Dep, terminal metabolic products (DIC, NH4+, PO43−), DOC and DON, and SR observed in this study. It appears that production and consumption of labile DOC are tightly coupled
in these sediments, and that bulk DOC is likely a recalcitrant pool. Preferential hydrolysis of PON relative to POC when overall
organic matter mineralization rates were high appears to drive the observed patterns in POC:PON, DOC:DON and DIC:DIN ratios.
These data, along with the weak seasonal patterns of SR and organic and inorganic porewater inventories, suggest that the
rate of hydrolysis limits organic matter mineralization in these intertidal creek-bank sediments. 相似文献
8.
Metal pollution, in combination with other environmental stressors such as acid deposition and climate change, may disturb
metal biogeochemical cycles. To investigate the influence of dissolved organic carbon, acidity and seasonality on metal geochemistry,
this study has described concentrations of 19 metals as they pass through an acidified forested catchment on the Precambrian
Shield in south-central Ontario, Canada. Metal, dissolved organic carbon (DOC) and sulphate (SO4
2−) concentrations fluctuate throughout the catchment compartments as the water passes through and interacts with vegetation,
soils and bedrock. Relationships among metals, DOC and SO4
2− are most pronounced in compartments where DOC and SO4
2− exhibit high variability, namely in the throughfall, organic horizon soil water, and wetland-draining stream. Metal, DOC
and SO4
2− concentrations varied seasonally in the streams, and temporal coherence occurred among metal, DOC and SO4
2− concentrations in the organic horizon soil water and the wetland-draining stream (PC1). In the wetland-draining stream, the
highest DOC, Cr, Cu, Fe, Pb, and V concentrations occur in the summer, whereas concentrations of SO4
2− and most other metals peak in the fall after a period of drought. Despite the rural location, provincial water quality objectives
for surface water were exceeded for many metals when the peak fall values occurred. 相似文献
9.
Marine benthic communities are effective indicators of environmental change. Yet in the Arctic, there are few empirical tests of how sustained climatic change may influence community structure. Northern Svalbard is influenced by both warm Atlantic and cold Arctic water masses, providing an opportunity to assess potential effects of long-term environmental changes by examining spatial variation in community structure. We examined benthic macroinfaunal communities and sediment pigments under Atlantic and Arctic water masses on the northern shelf and fjords of Svalbard. We report on infaunal biomass, abundance, species composition, and diversity at 10 stations spanning 79°–81°N and ranging in depth from 200 to 500?m. Benthic biomass averaged 128?g?WW?m?2 (48–253?g?WW?m?2), mean density was 3,635?ind.?m?2 (780–7,660?ind.?m?2), and species richness varied from 45 to 136?taxa?stn.?1. Abundance-based community structure clustered stations in groups related to water mass characteristics, with Atlantic and Arctic shelf stations being well distinguished from each other. Dominant taxa were different in Atlantic- and Arctic-influenced locations. Faunal biomass was highest in the Atlantic-influenced fjords, followed by Arctic fjords and Arctic shelf stations, with Atlantic shelf stations having the lowest biomass. Species richness and diversity were inversely related to biomass. Patterns in faunal biomass were strongly correlated with sedimentary pigments (R 2?=?0.74 for chl a and R 2?=?0.77 for phaeopigments), with large differences in sedimentary pigment concentration among stations. These relationships suggest that benthic fauna on the northern Svalbard shelf are food limited and dependent on predictable, albeit episodic, delivery of organic matter from the water column. 相似文献
10.
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
11.
J.-P. Torréton 《Coral reefs (Online)》1999,18(1):43-53
Biomass, production and heterotrophic activity of bacterioplankton were determined for two weeks in the Great Astrolabe Reef
lagoon, Fiji. Bacterial and Bacterial activities were distributed homogeneously throughout the water column (20 to 40 m deep)
and varied little from site to site inside the lagoon. Bacterioplankton biomass and production also varied little over a diel
period with coefficients of variation of 9 and 22%, respectively. On average, over the whole study, bacterial abundance was
0.77×109 cells l-1 and bacterial production averaged 0.36 μg-at. C l-1 d-1. Bacterial abundance and production were greater in the lagoon than in oceanic waters. Attachment to particles seems to provide
an advantage for bacterioplankton growth because specific growth rates for attached bacterioplankton were, on average, significantly
greater than that of the free community. Growth efficiency, determined by correlating the net increase of bacterial biomass
and the net decrease of dissolved organic carbon (DOC) in dilution cultures, was very low (average 6.6%). Using carbon growth
efficiency and bacterial production rates, heterotrophic activity was estimated to average 5.4 μg-at. C l-1 d-1. The turn-over rate of DOC (average 114 μg-at. C l-1) due to bacterial consumption was estimated to be 0.048 d-1 during the period of study.
Accepted: 25 July 1998 相似文献
12.
Are arctic soft-sediment macrobenthic communities impoverished? 总被引:2,自引:2,他引:0
M. A. Kendall 《Polar Biology》1996,16(6):393-399
Samples of the macrobenthic fauna of soft sediments were collected from around Svalbard during the 1991 Arctic EPOS cruise
of RVPolarstern. Although faunal variability could be related to sediment granulometry and depth, all stations to the south and east of the
Archipelago lay within the broadly defined central Barents Sea community. In this community, α-diversity was variable and
sampled between 77 and 337 m showed no clear relationship to depth. Diversity in the area close to the polar front was notably
high, rarefaction predicting that 43±5.5 species might occur in a sample of 201 individuals. k-Dominance plots suggested that muddy sand communities around Svalbard were no less diverse than similar assemblages in the
North Sea.
Received: 27 March 1995/Accepted: 30 July 1995 相似文献
13.
María Fernanda Adame Ruth Reef Jorge A. Herrera-Silveira Catherine E. Lovelock 《Hydrobiologia》2012,691(1):239-253
Poor water quality affects the biogeochemistry functions and the biological community structure of coastal ecosystems. In this study we investigated the effect of water quality on: (a) The exchange of dissolved organic carbon (DOC) between floodwater and mangrove forests, (b) the abundance of sediment bacteria, (c) the microbial community composition, and (d) the microbial catabolic activity. We selected six mangrove forests that were flooded by creeks with differing water qualities to test for thresholds of nutrient concentrations associated with changes in DOC dynamics and the microbial community. Our results show that in sites flooded by water high in soluble reactive phosphorus (SRP) (>20 μg l−1) and NH4 + (>30 μg l−1) the DOC concentrations in the floodwater were higher than in ebb water, suggesting DOC import by the mangroves. In contrast, in sites flooded by water low in SRP (<20 μg l−1) and NH4 + (<30 μg l−1), DOC concentrations in the floodwater were lower than in the ebb water, suggesting DOC export by the mangroves. Bacterial abundance was higher in sediments with low bulk density, high organic carbon and when flooded by water with low N:P (1–2), but the microbial composition and total catabolic activity assessed using Biolog Ecoplates™ did not differ among sites. The relationship between water quality, microbial communities and DOC exchange suggests that, at least during some periods of the year, poor water quality increases bacterial abundance and modifies DOC exchange of mangrove forests with floodwater and thus, their role in supporting near-shore productivity. 相似文献
14.
Yoshioka T. Ueda S. Miyajima T. Wada E. Yoshida N. Sugimoto A. Vijarnsorn P. Boonprakub S. 《Limnology》2002,3(1):51-59
The distributions of organic matter in the tropical swamps in southern Thailand are reported. The concentrations of particulate
and dissolved organic carbon (POC and DOC) in the Bang Nara River, which drains swamp forests and nearby paddy fields, were
2.9 ± 2.0 and 6.2 ± 1.3 mg C l−1, respectively. Although the variation was large, DOC concentration in the Bang Nara River seemed to be higher than POC in
November 1992 (DOC/POC ratio, 2.8 ± 2.2). River waters from the upland areas were characterized by low POC and DOC concentrations
as compared with Bang Nara River water. The δ13C values of POC and river sediments were useful to distinguish between organic matter originating in upland and swamp areas.
It is suggested that the distributions of organic matter and its isotopic composition reflect the difference in drainage characteristics
between lowland swamp and upland areas. Isotopic analyses of plant leaves and soils revealed that the swamp forest ecosystems
were characterized by low δ13C and low δ15N values, which suggested low efficiency of water use by plants and large contributions of atmospheric deposition of nitrogen,
respectively. Although CO2 recycling in the forest might be an important factor determining the δ13C values of understory plants, the main process in carbon metabolism of tropical swamp forests would be CO2 exchange between the atmosphere and forest canopy.
Received: May 1, 2001 / Accepted: September 28, 2001 相似文献
15.
Luitgard Schwendenmann Rainer Riecke Rubén J. Lara 《Wetlands Ecology and Management》2006,14(5):463-475
Although water in mangrove sediments influences nutrient cycling in both, mangrove forest and estuary, little information
exists on seasonal and vertical distribution of dissolved organic and inorganic compounds in the sediment column. We studied
the influence of sediment texture and chemistry, permeability (K), tides, and rainfall on dissolved organic carbon (DOC) and nitrogen (DON), dissolved inorganic phosphate (DIP) and salinity
in creek and sediment waters of a mangrove in Pará, Brazil. Water samples were taken from boreholes and piezometers in the
mangrove forest and from an adjacent tidal creek at neap and spring tides, during the dry and rainy season. Forest sediment
was analysed for carbon (C), nitrogen (N), salinity and permeability. Clay, C and N decreased with depth. Sediment permeability
(K) was lowest (<0.1 m day−1) in the upper, clay-rich and crab-burrow-free mud layer. In the deeper, fine sand strata, K ranged from 0.7 to 1.8 m day−1. Tidal range in the creek was 3.5 and 5.5 m for neap and spring tides, respectively. Salinity, DOC, DON and DIP in creek
water were inversely related to tidal height. Piezometer data revealed significant water level changes in deeper, sandy sediment
layer, which followed, time-lagged, the tidal fluctuations. In contrast, tide did not affect the water level in the upper
sediment due to low permeability. Compared with creek water, sediment water was enriched in DOC, DON and DIP because of organic
matter input and mineralization. In deeper layers, solute concentration was most likely affected by sorption processes (DOC
and DIP) and reduction reactions (DIP). During the rainy season, DOC and DON in creek and sediment water were higher than
in the dry season. DIP appeared invariant to seasonal changes. In the rainy season, salt flushing from surface sediments resulted
in higher salinities at intermediate sediment depths, while in the deeper layers salinity was lower due to exchange with water
from the tidal creek. 相似文献
16.
Seasonal dynamics of suspended minerals, organic matter, particulate, and dissolved organic carbon (DOC), chlorophyll, and
their vertical fluxes were studied in a small Arctic fjord (Adventfjorden, Spitsbergen) from November 2006 to October 2007.
The fjord was usually covered with fast ice in winter, but remained open throughout the year since 2005. The open-water winter
period caused increased wave action and resuspension of organic and mineral particles. The lack of sea-ice in spring accelerated
the onset of the productive season. The earlier light signal also caused an earlier appearance of mesozooplanktonic organisms,
accompanied by a significant increase of the DOC pool in the water. In the cold period (winter and spring) 47% of the annual
organic matter settled on the sampling site, a lot coming from the spring diatom bloom in April. Summer melt (July, August)
resulted in turbid and brackish fjord surface water with stratification and increase of both suspended particles and sedimentation,
causing 60% of the annual minerals and 53% of the annual organic matter to settle at the sampling site. Increased dissolved
organic carbon (DOC) through sloppy feeding on the mixo- and heterotrophic protista by the abundant mesozooplankton indicated
intensive secondary production, resulting in a maximum fecal pellets flux of >5 mg C m−2 day−1. A warmer climate with reduced sea-ice cover in fjords will advance the onset of the spring bloom and will also result in
a larger input of turbid melt water in summer, restricting the light availability and enhancing flocculation and thereby sedimentation. 相似文献
17.
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
18.
To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River,
the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO4 oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along
the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over
the range 0.28–1.21 mg C l−1 and in the Yasu over the range 1.01–2.68 mg C l−1. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought
primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert
or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l−1 in the Ado, which was lower than that (0.35 ± 0.05 mg C l−1) in Lake Biwa. The act-DOC in river waters was reactive to KMnO4 oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD).
In river waters, the relation can be approximated by a straight line expressed as COD (mg O2 l−1) = 0.64 × act-DOC (mg C l−1) − 0.02. In contrast, in the lake water the relation was COD (mg O2 l−1) = 0.97 × act-DOC (mg C l−1) − 0.50.
Received: March 3, 1999 / Accepted: December 2, 1999 相似文献
19.
Picophytoplankton biomass, community structure and productivity in the Great Astrolabe Lagoon, Fiji 总被引:4,自引:0,他引:4
Phytoplankton biomass, community structure and productivity of the Great Astrolabe lagoon and surrounding ocean were studied
using measurements of chlorophyll concentration and carbon uptake. The contribution of picophytoplankton to biomass, productivity
and community structure was estimated by size fractionation, 14C-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll <3 μm.
Consequently, the percentage contribution to chl a<3 μm from each picoplankton group could be calculated using regression estimated values of ψ
i
(fg chl a per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m-3 with 45% of phytoplankton <3 μm. Primary production reached 1.3 g C m-2 day-1 with 53% due to phytoplankton <3 μm. Synechococcus was the most abundant group at all stations, followed by Prochlorococcus and picoeukaryotes. At all stations, Prochlorococcus represented less than 4% of the chl a <3 μm, Synechococcus between 85 and 95%, and Picoeukaryotes between 5 and 10%. In the upper 40 m of surrounding oceanic waters, phytoplankton
biomass was dominated by the >3 μm size fraction. In deeper water, the <1 μm size fraction dominated. Prochlorococcus was the most abundant picoplankton group and their contributions to the chlorophyll a<3 μm were close to that of the picoeukaryotes (50% each).
Accepted: 27 May 1999 相似文献
20.
Jana Woelfel Rhena Schumann Florian Peine Anita Flohr Aleksandra Kruss Jaroslaw Tegowski Philippe Blondel Christian Wiencke Ulf Karsten 《Polar Biology》2010,33(9):1239-1253
During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline
of Kongsfjorden (Svalbard, Norway) at ≤5 m water depth and at two stations at five different water depths (5, 10, 15, 20,
30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment
cores under controlled light (ca. 100 μmol photons m−2 s−1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down
to 30 m showed high biomass of up to 317 mg chl a m−2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ≤5 to
30 m water depth exhibited variable rates of net production from −19 to +40 mg O2 m−2 h−1 (−168 to +360 mg C m−2 day−1) and gross production of about 2–62 mg O2 m−2 h−1 (17–554 mg C m−2 day−1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net
production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to
pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos. 相似文献