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1.
N. J. Anderson R. D. Dietz D. R. Engstrom 《Proceedings. Biological sciences / The Royal Society》2013,280(1769)
Lakes are a central component of the carbon cycle, both mineralizing terrestrially derived organic matter and storing substantial amounts of organic carbon (OC) in their sediments. However, the rates and controls on OC burial by lakes remain uncertain, as do the possible effects of future global change processes. To address these issues, we derived OC burial rates in 210Pb-dated sediment cores from 116 small Minnesota lakes that cover major climate and land-use gradients. Rates for individual lakes presently range from 7 to 127 g C m–2 yr–1 and have increased by up to a factor of 8 since Euro-American settlement (mean increase: 2.8×). Mean pre-disturbance OC burial rates were similar (14–22 g C m–2 yr–1) across all land-cover categories (prairie, mixed deciduous and boreal forest), indicating minimal effect of the regional temperature gradient (approx. 4°C) on background carbon burial. The relationship between modern OC burial rates and temperature was also not significant after removal of the effect of total phosphorus. Contemporary burial rates were strongly correlated with lake-water nutrients and the extent of agricultural land cover in the catchment. Increased OC burial, documented even in relatively undisturbed boreal lake ecosystems, indicates a possible role for atmospheric nitrogen deposition. Our results suggest that globally, future land-cover change, intensification of agriculture and associated nutrient loading together with atmospheric N-deposition will enhance OC sequestration by lakes. 相似文献
2.
The sensitivity of surface waters to acidic deposition is governed by the interaction of catchment geology, soils, topography,
land use, climate and atmospheric deposition. Accordingly at the landscape scale, catchment attributes may be used to predict
lake chemistry (for example, acid neutralising capacity (ANC), pH, calcium (Ca2+) and dissolved organic carbon (DOC)). Empirical (multiple linear regression) models based on average measured chemistry (2000–2006)
for 204 lakes in Nova Scotia (NS) Canada, and their catchment attributes, were used to predict chemistry for all lakes in
NS (n = 6104). Damage to aquatic biota, such as loss of species and/or reduced biodiversity has been widely evaluated using critical
chemical thresholds commonly based on pH, ANC and Ca2+. The proportion of sensitive lakes in NS (that is, the stock at risk) was estimated as lakes with ANC less than 20 μeq l−1, pH below 6, and Ca2+ less than 75 μeq l−1 (13, 73 and 74%, respectively). Many lakes in NS are characterized by high DOC (>7 mg l−1); in these lakes organic acids contribute to total acidity, making anthropogenic influences difficult to discern. To account
for the potential contribution of organic acidity, all lakes with pH below 6 (and DOC < 7 mg l−1) and lakes below a threshold for ANC adjusted for organic acids were quantified; 63% of the lakes fell below either of these
thresholds. Despite substantial reductions in sulphur emissions in North America since the 1980s, many lakes in NS remain
at risk to acidic deposition. 相似文献
3.
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
4.
A novel application of a continuous flow incubation system (CFIS) was used to assess four phosphorus (P) inactivation agents—alum,
Phoslock™, a new modified zeolite (Z2G1 or Aqual-P™), and allophone—when used as sediment capping agents to manage internal
P loads in lakes. The CFIS technique allowed combined efficacy and sustainability assessment, including: (1) flux measurements
during simulation of stratified (anoxic) and mixed (aerobic) conditions on the same sediment through multiple cycles to assess
the longevity of a range of product doses; (2) simulation of a summer algal bloom collapse and subsequent burial of the products;
and (3) investigation of non-target effects on nitrification and denitrification processes at the sediment–water interface.
Minimum P-removal dose rates were found to differ substantially at 80 g m−2 for alum, 190 g m−2 for Z2G1, 220 g m−2 for allophane and 280 g m−2 for Phoslock™, for similar capping layer thickness of about 2 mm, and would be effective for at least 4 years. All products
temporarily suppressed nitrification and denitrification under aerobic conditions, and it may be important to minimise product
application to any permanently aerobic zones, such as the littoral areas of a lake. While the aluminium (Al)-based products
did not enhance Al fluxes in the CFIS, lanthanum (La) was released at a near constant rate of around 2 mg La m−2 day−1 from the Phoslock™ treatments over a period of at least 14 days. Spatial variability of sediment P, bioturbation, and burial
are factors that will affect up-scaling these results to a whole lake. 相似文献
5.
Alchichica is a warm-monomictic, oligotrophic lake whose phytoplanktonic biomass is dominated by large size (average ca. 55 μm) diatoms. The fast sinking phytoplankton leads to silica, and other nutrient exportation out of the productive zone
of the lake. The aim of the present study was to identify and measure the sedimentation fluxes of the diatom species and their
temporal dynamics to better understand the magnitude of silica and carbon fluxes. Sediment-traps were exposed at three different
depths and collected monthly. A total of 13 diatom species were observed in the traps. The maximum diatom flux was in February
(304 × 106 cells m−2 day−1) related to the winter diatom bloom. The diatom silica (DSi) fluxes varied from 2.2 to 2,997 mg m−2 day−1 and the diatom carbon (DC) fluxes from 1.2 to 2,918 mg m−2 d−1. Cyclotella alchichicana was the main contributor (>98%) to the total DSi and DC fluxes. The annual diatom (15 × 109 cells m−2 year−1), DSi (147 g m−2 year−1) and DC (92 g m−2 year−1) fluxes are higher than in other aquatic ecosystems of similar or even higher trophic conditions. Our findings in Alchichica
are indicative of the relevance of the phytoplankton type and size in understanding the role tropical and oligotrophic lakes
play regarding silica and carbon fluxes. In addition, our results support previous findings suggesting that inland aquatic
ecosystems are more important than formerly thought in processing carbon, and can, therefore, affect regional carbon balances. 相似文献
6.
Garrett W. Meigs David P. Turner William D. Ritts Zhiqiang Yang Beverly E. Law 《Ecosystems》2011,14(5):758-775
Fire influences carbon dynamics from local to global scales, but many uncertainties remain regarding the remote detection
and simulation of heterogeneous fire effects. This study integrates Landsat-based remote sensing and Biome-BGC process modeling
to simulate the effects of high-, moderate-, and low-severity fire on pyrogenic emissions, tree mortality, and net ecosystem
production. The simulation area (244,600 ha) encompasses four fires that burned approximately 50,000 ha in 2002–2003 across
the Metolius Watershed, Oregon, USA, as well as in situ measurements of postfire carbon pools and fluxes that we use for model
evaluation. Simulated total pyrogenic emissions were 0.732 Tg C (2.4% of equivalent statewide anthropogenic carbon emissions
over the same 2-year period). The simulated total carbon transfer due to tree mortality was fourfold higher than pyrogenic
carbon emissions, but dead wood decomposition will occur over decades. Immediately postfire, burned areas were a simulated
carbon source (net C exchange: −0.076 Tg C y−1; mean ± SD: −142 ± 121 g C m−2 y−1). As expected, high-severity, stand-replacement fire had disproportionate carbon impacts. The per-unit area effects of moderate-severity
fire were substantial, however, and the extent of low-severity fire merits its inclusion in landscape-scale analyses. These
results demonstrate the potential to reduce uncertainties in landscape to regional carbon budgets by leveraging Landsat-based
fire products that account for both stand-replacement and partial disturbance. 相似文献
7.
The pulsing of river discharge affects biodiversity and productivity of whole river–floodplain ecosystems, triggering the transport, storage and processing of carbon. In this study we investigate the short-term changes in water chemistry and net pelagic metabolism (NEP) in two floodplain lakes in response to a flood pulse. The two oxbow lakes investigated in the floodplain of the Mediterranean Ebro River (NE Spain) showed a clear temporal shift in their metabolic balance, controlled by the river discharge and associated changes in water physical and chemical characteristics. Water chemistry (turbidity, water organic matter, chlorophyll a and nutrients concentration) returned to pre-flood values after 4 days, highlighting the resilience of the ecosystem to flood pulses. Lake NEP was depressed before and during floods to a minimum of −34 mg O2 m−3 h−1, and increased after the flood pulse to a maximum of +463 mg O2 m−3 h−1. The phytoplankton assemblage showed before and after floods a replacement of autotrophic species (e.g. Chlorophyceans) by mixotrophic organisms (e.g. Cryptophyceans, Euglenoids). A linear mixed effects model identified abiotic factors, particularly temperature and river discharge, as significant predictors of the net aquatic metabolism and community respiration during flood conditions. Our results suggest that the role of the Ebro floodplain lakes as sources or sinks of C is complex and relative to the time scale investigated, depending strongly on the river discharge dynamics and the transport of limiting nutrients (phosphorus). 相似文献
8.
Large amounts (36.4 Mg ha−1 or 179 m3 ha−1) of buried dead wood were found in overmature (146–204-year-old) black spruce (Picea mariana (Mill.) B.S.P.) forests in the high boreal region of eastern Canada. Amounts of this size indicate that burial reduces rates
of wood decay producing an important component of long-term carbon (C) storage. Radiocarbon-derived ages of black spruce stems
buried near the bottom of the organic soil horizon at three old-growth sites were up to 515 years old. Together with information
on current stand age, this suggests that the stems have been dead for more than 250 years. Most aboveground dead wood decays
or becomes fragmented within about 70 years of tree death in these forests. The presence of old yet well-preserved buried
wood suggests that decay rates are greatly reduced when downed dead wood is quickly overgrown by moss. Thus, the nature and
type of ground-layer vegetation influences the accumulation of organic matter in these forests. This process of dead wood
burial and the resultant addition to a large and long-enduring belowground C pool should be considered when estimating dead
wood abundance for habitat or forest C accounting and cycling. 相似文献
9.
We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary
production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m < < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and
deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values.
Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO3
−–N + NH4
+–N) were consistently below the detection limit (0.05 μmol l−1) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l−1), total-P (0.29 μmol l−1), and total-N (33 μmol l−1), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos,
GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l−1 and 0.7–3.8 μmol C l−1 day−1. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m−2 and 3.2–5.8 mmol C m−2 day−1. Average values of epipelic chl a ranged from 131 to 549 mg m−2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average
epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m−2 day−1) than in intermediate and deep lakes (3.4 and 2.4 mmol C m−2 day−1). Total primary production (6.7–15.4 mmol C m−2 day−1) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables
were significantly higher in shallow lakes than in intermediate or deep lakes.
Handling editor: L. Naselli-Flores 相似文献
10.
K. P. Krishnan Rupesh Kumar Sinha Kiran Krishna Shanta Nair S. M. Singh 《Polar Biology》2009,32(12):1765-1778
The significance of freshwater systems in global manganese cycles is well appreciated. Yet, the polar systems, which encompass
the largest freshwater repository in the world, have been least studied for their role in manganese cycling. Here, we present
results from a study that was conducted in the brackish water lakes in the Larsemann Hills region (east Antarctica). The rate
of in situ manganese oxidation ranged from 0.04 to 3.96 ppb day−1. These lakes harbor numerous manganese-oxidizing bacteria (105 to 106 CFU l−1), predominantly belonging to genera Shewanella, Pseudomonas and an unclassified genus in the family Oxalobacteriaceae. Experiments were conducted with representatives of predominant
genera to understand their contribution to Mn cycling and also to assess their metabolic capabilities in the presence of this
metal. In general, the total and respiring cell counts were stimulated to a maximum when the growth medium was amended with
10 mM manganese. The addition of manganese promoted the use of d-mannitol, maltose, etc., but inhibited the use of maltotriose, l-serine and glycyl l-glutamic acid. The bacterial isolates were able to catalyze both the redox reactions in manganese cycling. In vitro manganese
oxidation rates ranged from 3 to 147 ppb day−1, while manganese reduction rates ranged from 35 to 213 ppb day−1. It was also observed that the maximum stimulation of manganese oxidation occurred in the presence of cobalt (81 ± 57 ppb day−1), rather than iron (37 ± 16 ppb day−1) and nickel (40 ± 47 ppb day−1). Our studies suggest that cobalt could have a more profound role in manganese oxidation, while nickel promoted manganese
reduction in polar aquatic systems. 相似文献
11.
Ciliate and bacterial densities and their link with eutrophication were studied in fourteen shallow lakes in northwest Spain.
Total phosphorus (TP) in these lakes varied between 30 μg l−1 and 925 μg l−1 and chlorophyll a concentration (chla) between 0.5 μg l−1 and 107 μg l−1. Bacterial abundance ranged from 1 × 106 to 14 × 106 cells ml−1, while ciliate abundance ranged from 0.6 cells ml−1 to 229 cells ml−1. Lakes were classified into three trophic types from their TP and chla concentrations. Bacterial abundance was significantly
correlated with trophic type, as well as with TP and with chla separately, whereas ciliate abundance was only correlated with
chla. No significant relationship could be established between bacterial and ciliate abundance across the trophic gradient.
A general pattern was observed in the ratios of bacterial abundance to TP and chla concentrations, of decreasing ratios with
increases in the nutrient loading. This pattern was not found for ciliates. The dominant zooplankton group in 13 of the 14
lakes studied was Rotifera, which accounted for a mean of 71% of total zooplankton abundance (41% of zooplankton biomass).
The positive correlation between bacteria and ciliates with this group, and the absence of any relationship with Cladocera
suggest that top down control by cladocerans was weaker in our lakes than previously shown in northern European shallow lakes.
Rotifers could be important predators of bacteria in the high-nutrient lakes of our study. Higher slopes of regressions on
bacterial abundance towards the hypertrophic range indicate that top-down control was weaker in our lakes than in northern
European shallow lakes. 相似文献
12.
Changes in soil carbon flux and carbon stock over a rotation of poplar plantations in northwest China 总被引:2,自引:0,他引:2
Forest soil is a major component of terrestrial ecosystems for carbon sequestration and plays an important role in the global
carbon cycle. Soil carbon flux and soil carbon pools were investigated in a poplar plantation chronosequence over a rotation
in northwest China. Based on continuous field observation in 2007, the results showed that mean soil CO2 efflux rate was 5.54, 4.81, and 3.93 μmol CO2 m−2 s−1 for stands of 2-, 8-, and 15-year-old, respectively, during the growing season. Significant differences in soil respiration
of three age classes were mainly because soil temperature, carbon allocation, and fine root growth changed greatly with stand
age. Multiple regression analysis suggested that soil temperature and fine root biomass in the upper layer could explain 78–85%
of the variation in soil respiration. Mineral soil C stock at 0–40 cm depth was 55.77, 55.09, and 58.14 t ha−1 in the 2-, 8-, and 15-year-old stands, respectively. The average rate of soil C sequestration was 0.13 t ha−1 year−1 following afforestation on former crop lands. Although the plantations had similar management practices and soil types since
their establishment, many biotic and abiotic factors such as root biomass and turnover rate, soil condition of the plantations
had undergone marked changes at different development stages, which could result in the remarkable differences in soil carbon
flux and storage over a rotation. Our results highlight the importance of the development stage within a rotation of poplar
plantation in assessment of soil carbon budget. 相似文献
13.
Denitrification Potential in Lake Sediment Increases Across a Gradient of Catchment Agriculture 总被引:1,自引:0,他引:1
Intensification of catchment agriculture has increased nutrient loads and accelerated eutrophication in some lakes, often
resulting in episodic harmful algal blooms or prolonged periods of anoxia. The influence of catchment agriculture on lake
sediment denitrification capacity as a nitrogen (N) removal mechanism in lakes is largely unknown, particularly in contrast
to research on denitrification in agricultural streams and rivers. We measured denitrification enzyme activity (DEA) to assess
sediment denitrification potential in seven monomictic and three polymictic lakes that range in the proportion of agriculture
in the catchment from 3 to 96% to determine if there is a link between agricultural land use in the lake catchment and sediment
denitrification potential. We collected sediment cores for DEA measurements over 3 weeks in austral spring 2008 (October–November).
Lake Okaro, with 96% catchment agriculture, had approximately 15 times higher DEA than Lake Tikitapu, with 3% catchment agriculture
(232.2 ± 55.9 vs. 15.9 ± 4.5 μg N gAFDM−1 h−1, respectively). Additionally, sediment denitrification potential increased with the proportion of catchment in agriculture
(R
2 = 0.85, P < 0.001). Our data suggest that lakes retain a high capacity to remove excess N via denitrification under increasing N loads
from higher proportions of catchment agriculture. However, evidence from the literature suggests that despite a high capacity
for denitrification and longer water residence times, lakes with high N loads will still remove a smaller proportion of their
N load. Lakes have a denitrification potential that reflects the condition of the lake catchment, but more measurements of
in situ denitrification rates across lake catchments is necessary to determine if this capacity translates to high N removal
rates. 相似文献
14.
Xiuyun Cao Chunlei Song Yiyong Zhou Alena Štrojsová Petr Znachor Eliška Zapomělová Jaroslav Vrba 《Limnology》2009,10(2):95-104
Extracellular phosphatases are an important part of the phosphorus cycle in aquatic environments. Phosphatase activity (PA)
in plankton was studied in seven subtropical shallow lakes of different exploitation management and trophic status in the
urban area of Wuhan City. Bulk PA was rather high (range 1.1–11 μmol l−1 h−1), although concentrations of soluble reactive phosphorus (SRP) were also high (range 27 μg P l−1 to ~1.5 mg P l−1) in all lakes. Cell-associated extracellular PA in phytoplankton was detected using the fluorescence-labelled enzyme activity
technique. Phytoplankton species partly contributed to the bulk PA. We found explicit differences in the presence of cell-associated
phosphatase within the main phytoplankton groups; species belonging to Chlorophyta and Dinophyta were regularly phosphatase-positive,
while Cyanophyta and Bacillariophyceae were phosphatase-negative in all but one case. Furthermore, there is a certain potential
of extracellular phosphatases produced by heterotrophic nanoflagellates in most of the lakes. This new finding compromises
the ‘traditional’ interpretation of bulk phosphatase data as being due to overall phytoplankton or bacterial P regeneration. 相似文献
15.
Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence 总被引:1,自引:0,他引:1
Koh Maki Chulgoo Kim Chikage Yoshimizu Ichiro Tayasu Toshihiro Miyajima Toshi Nagata 《Limnology》2010,11(2):143-153
Semi-labile dissolved organic carbon (DOC) plays an important role in the transport and hypolimnetic remineralization of carbon
in large freshwater lakes. However, sources of semi-labile DOC in lakes remain unclear. This study used a carbon stable isotope
approach to examine relative contributions of autochthonous and allochthonous sources to semi-labile DOC. Vertical and seasonal
variations in the concentration and carbon stable isotope ratio (δ13C) of DOC were determined in large (surface area 674 km2; maximum depth 104 m), monomictic Lake Biwa. A sharp vertical gradient of δ13C of DOC (δ13C-DOC) during the stratification period [mean ± standard error (SE) −25.5 ± 0.1 and −26.0 ± 0.0‰ in the epi- and hypolimnion,
respectively] indicated the accumulation of 13C-rich DOC in the epilimnion. Vertical mixing explained the intermediate values of δ13C-DOC (−25.7 ± 0.0‰) measured throughout the water column during the overturn period. Both DOC concentration and δ13C-DOC decreased in the hypolimnion during stratification, indicating selective remineralization of 13C-rich DOC. Using a two-component mixing model, we estimated the δ13C value of semi-labile DOC to be −22.2 ± 0.3‰, which was close to the δ13C of particulate organic carbon collected in the epilimnion during productive seasons (−22.7 ± 0.7‰) but much higher than
the δ13C-DOC in river waters (−26.5 ± 0.1‰). Semi-labile DOC appeared to be mainly autochthonous in origin, produced by planktonic
communities during productive seasons. The spatiotemporal uncoupling between production and remineralization of semi-labile
DOC implies that hypolimnetic oxygen consumption may be affected by pelagic primary production during productive seasons of
the preceding year. 相似文献
16.
Carbon dioxide supersaturation in Florida lakes 总被引:1,自引:0,他引:1
Jenney K. Lazzarino Roger W. Bachmann Mark V. Hoyer Daniel E. CanfieldJr 《Hydrobiologia》2009,627(1):169-180
We examined data on CO2 and related limnological and geographic information from a sample of 948 Florida freshwater lakes. The objectives for this
study were (1) to determine the partial pressures of carbon dioxide (ρCO2) in the surface waters of a large sample of Florida lakes, (2) to determine if several limnological or geographic factors
are related to levels of ρCO2 in Florida lakes, and (3) to estimate the net annual rate of loss of CO2 to the atmosphere from the freshwater lakes of Florida. The calculated ρCO2 for the lakes in our sample range from 0 to 81,000 μatm, with a mean of 3,550 μatm, a median of 1,030 μatm, and a geometric
mean of 1,270 μatm. About 87% of the Florida lakes were supersaturated with CO2. There were statistically significant correlations between values for ρCO2 and several water chemistry variables; however, the R
2 values were small and accounted for only a small portion of the variance. In general the ρCO2 values were higher in the lakes with low alkalinities and low contents of dissolved salts. The best predictor of ρCO2 is pH, with an R
2 of 0.82 for a polynomial relationship. The ρCO2 values tend to decrease from northwest to southeast across the state of Florida, which corresponds to the gradients we found
for pH, alkalinity, and specific conductance. The average areal rate of carbon emission from the Florida lakes was 328 g C m−2 y−1, and the total carbon loss for the lakes and ponds of Florida was 2.0 Tg y−1. This amounts to about 2% of the total carbon emissions from all the lakes of the world as estimated by previous studies.
Handling editors: Darren Bade 相似文献
17.
Das A Sujith PP Mourya BS Biche SU LokaBharathi PA 《Extremophiles : life under extreme conditions》2011,15(2):177-189
It is hypothesized that in the deep-sea, under psychrophilic, barophilic and oligotrophic conditions, microbial community
of Central Indian Basin (CIB) sediments could be chemosynthetic. In the dark, at near ambient temperature, 4 ± 2°C, 500 atm
pressure, pelagic red clay could fix carbon at rates ranging from 100 to 500 nmol C g−1 dry wt day−1. These clays accumulate in the deepest and the most remote areas of the ocean and contain <30% biogenic material. These clays
with volcanic signatures fixed 230–9,401 nmol C g−1 dry wt day−1 while siliceous radiolarian oozes of the basin fixed only 5–45 nmol C g−1 dry wt day−1. These rates are comparable to those of white smoker waters and are 1–4 orders of magnitude less than those of bacterial
mats and active vents recorded at other localities worldwide. The experimental ratios of carbon fixation to metal oxidation
in the sediments were 0–1 order of magnitude higher than the corresponding average theoretical ratio of 0.0215 (0.0218, 0.0222,
0.0207 and 0.0211 for Fe, Mn, Co and Ni, respectively) in the siliceous ooze. In case of pelagic red clay it was 0–2 orders
higher than theoretical ratio. Thus, chemosynthetic activity could be more widespread, albeit at low rates, than previously
considered for abyssal basins. These environments may be dependent partially or even wholly on in situ microbial primary production
for their carbon requirements rather than on photosynthetically derived detritus from surface waters. 相似文献
18.
Luz Allende Guillermo Tell Horacio Zagarese Ana Torremorell Gonzalo Pérez José Bustingorry Roberto Escaray Irina Izaguirre 《Hydrobiologia》2009,624(1):45-60
Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated
by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material,
and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic
properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The
underwater light climate was characterized. Clear-vegetated lakes were more transparent (K
d 4.5–7.7 m−1), had high DOC concentrations (>45 mg l−1), low phytoplankton Chl a (1.6–2.7 μg l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla
−1 h−1 W−1 m2) were relatively low. Inorganic-turbid lakes showed highest K
d values (59.8–61.4 m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l−1. Phytoplankton-turbid lakes showed, in general, high K
d (4.9–58.5 m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l−1), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla
−1 h−1 W−1 m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently
of their type (0.086 × 105–41.7 × 105 cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production
of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.
Handling editor: J. Padisak 相似文献
19.
Macrophyte presence is an indicator of enhanced denitrification and nitrification in sediments of a temperate restored agricultural stream 总被引:1,自引:0,他引:1
Stream macrophytes are often removed with their sediments to deepen stream channels, stabilize channel banks, or provide habitat
for target species. These sediments may support enhanced nitrogen processing. To evaluate sediment nitrogen processing, identify
seasonal patterns, and assess sediment processes relative to stream load, we measured denitrification and nitrification rates
in a restored third- to fourth-order agricultural stream, Black Earth Creek, Wisconsin, and estimated processing over a 10 km
reach. Our results show that sediments with submerged and emergent macrophytes (e.g., Potomageton spp. and Phalaris arudinacea) support greater denitrification rates than bare sediments (1.12 μmol N g−1 h−1 vs. 0.29). Sediments with macrophytes were not carbon limited and organic matter fraction was weakly correlated to denitrification.
The highest denitrification potential occurred in macrophyte beds (5.19 μmol N g−1 h−1). Nitrification rates were greater in emergent beds than bare sediments (1.07 μg N ml−1day−1 vs. 0.35) with the greatest nitrification rates during the summer. Total denitrification removal in sediments with macrophytes
was equivalent to 43% of the nitrate stream load (463.7 kg N day−1) during spring and nitrification in sediments with macrophytes was equivalent to 247% of summer ammonium load (3.5 kg N day−1). Although the in-channel connectivity to nitrogen rich water was limited, actual stream nitrogen loads could increase with
removal of macrophytes. Macrophyte beds and supporting fringing wetted areas are important if nitrogen management is a concern
for riparian stream restoration efforts. 相似文献
20.
A regional data set on water chemistry from 1995 was used to set critical values for the survival of brown trout in Norwegian
lakes (n = 790) in relation to pH, inorganic Al and acid neutralizing capacity (ANC). ANC was estimated both traditionally (ANCtrad) and modified by treating one-third of the dissolved organic matter as part of the strong acid anions (ANCmod). The threshold value to avoid fish damage (ANClimit) was compared with that found in a similar study from 1986. Brown trout populations were categorized as unaffected, damaged
or extinct on the basis of questionnaires. In 1995, threshold values to avoid fish damage on the basis of ANCtrad and ANCmod were 67 and 48 μeq l−1, respectively, compared with 20 and 8 μeq l−1, respectively, in 1986. The higher ANClimit found for the data from 1995 is probably caused by a lower pH and a higher inorganic Al concentration at a given ANC value
in 1995 than in the 1980s. ANClimit was highly related to organic carbon concentrations in the study lakes, being estimated at 33, 73 and >100 μeq l−1 for three different TOC categories (<2 mg C l−1, 2–5 mg C l−1 and >5 mg C l−1). These differences in ANClimit are due to lower pH and higher concentrations of inorganic Al in humic lakes than in clear water lakes at the same level
of ANC. It is suggested that the change in ANClimit for fish in acidified lakes is linked to increased concentrations of TOC in recent years. 相似文献