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241.
Margaret R. Mulholland George E. Boneillo Peter W. Bernhardt Elizabeth C. Minor 《Estuaries and Coasts》2009,32(6):1176-1194
To determine the roles of dissolved organic matter in the onset, duration, and decline of blooms of the “brown tide” pelagophyte,
Aureococcus anophagefferens, nutrient and microbial dynamics, heterotrophic and autotrophic carbon (C) and nitrogen (N) uptake, and peptide hydrolysis
were compared in natural populations: (1) seasonally, among physically similar sites in a mid-Atlantic coastal lagoon, Chincoteague
Bay, (2) at an individual site as a bloom initiated, developed, and declined, and (3) in whole versus size-fractionated water.
Throughout the year, urea was the dominant form of N taken up at both bloom and nonbloom sites. C acquisition in the A. anophagefferens (1.2–5.0 μm) size fraction was dominated by bicarbonate uptake during bloom initiation but organic C compounds were taken
up later during and after the bloom. Bacterial productivity was enhanced during and just after the bloom and bacterial abundance
was four times higher at the bloom versus nonbloom site. 相似文献
242.
da Silva DA Buzitis J Krahn MM Bícego MC Pires-Vanin AM 《Marine pollution bulletin》2006,52(2):175-183
This study reports the analysis of polycyclic aromatic compound (PAC) metabolites, as biomarkers of exposure to PACs in marine environment. PAC metabolites were measured in bile samples from 14 species of demersal fish caught in the São Sebastião Channel (SSC), SE Brazilian coastline. Naphthalene (NPH) equivalents, phenanthrene (PHN) equivalents, and benzo[a]pyrene (BaP) equivalents were quantified using a reverse-phase high-performance liquid chromatography coupled with fluorescence detection method. For all samples, the means (±standard deviation, n = 37) of concentrations obtained for NPH, PHN, and BaP equivalents were, respectively, 290,000 ± 200,000 ng/g, 18,000 ± 14,000 ng/g, and 970 ± 1900 ng/g. These results indicate recent exposure of these fish to PACs in their environment. In addition, two species (Cyclichthys spinosus and Prionotus nudigula) of fish were analyzed in order to investigate local sources of PAC contamination in the SSC and the influence of the petroleum terminal in fish caught in remote areas. The results showed that these fish species potentially migrate along the channel, especially P. nudigula. Correlations among groups of PAC metabolites indicate the same petrogenic source for NPH and PHN equivalents and a combustion source (e.g., automobile, ships) for BaP equivalents. The ratio BaP/PHN equivalents (0.05 ± 0.07, n = 37) confirms the predominance of petrogenic PACs for contamination by these chemicals in this region. 相似文献
243.
Alkenone paleothermometry: Biological lessons from marine sediment records off western South America
Fredrick G. Prahl Alan C. Mix Margaret A. Sparrow 《Geochimica et cosmochimica acta》2006,70(1):101-117
An empirical global core-top calibration that relates the alkenone unsaturation index to mean annual SST (maSST) is statistically the same as that defined for a subarctic Pacific strain of Emiliania huxleyi (CCMP1742) grown exponentially in batch culture under isothermal conditions. Although both equations have been applied widely for paleoSST reconstruction, uncertainty still stems from two key ecological factors: variability in the details of biosynthesis among genetically distinct alkenone-producing strains, and impacts of non-thermal physiological growth factors on . New batch culture experiments with CCMP1742 here reveal that diverge systematically from the core-top calibration in response to nutrient depletion and light deprivation, two physiological stresses experienced by phytoplankton populations in the real ocean. Other aspects of alkenone/alkenoate composition also respond to these stresses and may serve as signatures of such effects, providing an opportunity to detect, understand, and potentially correct for such impacts on the geologic record. A test case documents that sediments from the Southeast Pacific display the alkenone/alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation. Such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers. Late Pleistocene records in the Southeast Pacific yield plausible paleotemperature histories of ice-age cooling, but ice-age alkenone/alkenoate signatures fall outside the range of modern calibration samples of similar . They better match core-top samples deposited beneath waters characterized by much cooler maSST, suggesting key features of ice-age ecology for alkenone-producing haptophytes were different from today, and that the index taken alone may misgauge the total range of ice-age cooling at these locations. Analysis of the full spectrum of alkenone/alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple analysis and help resolve longstanding disagreements between various paleotemperature reconstruction methods. 相似文献
244.
Joseph G. Alfieri Dev Niyogi Hao Zhang Margaret A. LeMone Fei Chen 《Boundary-Layer Meteorology》2009,133(3):323-341
Spatial variability in the exchange of energy and moisture is a key control on numerous atmospheric, hydrologic, and environmental
processes. Using observations made on fair weather days during the 2002 International H2O Project, four methods for quantifying
the spatial variability of surface fluxes are investigated. The first two methods utilize applied statistical techniques to
describe the spatial variability of the surface fluxes, while the third method is a geostatistical technique rooted in variography.
Typically, the methods yield similar results, with median values of horizontal variability consistent to within 5%. The geostatistical
technique, however, provides much more information than the other statistical methods; it not only provides an estimate of
the spatial variability, but also provides estimates of the total variability, the non-spatial variability due to measurement
error, and the range of spatial correlation among the data points. The fourth method is based on the relationship between
the components of the surface energy budget. This method describes the variability in the fluxes in terms of the slope of
the best-fit line relating the time-averaged latent and sensible heat fluxes from different locations along the flight path.
The meaning of the slopes can also be interpreted in terms of the spatial variability in the available energy. For four of
the five days analyzed, the key control on the spatial variability in the turbulent heat fluxes was horizontal variability
in the soil heat flux. In turn, the soil heat flux varied as a function of surface properties including surface temperature,
soil moisture content, and leaf area index. On the remaining day, 25 May, the primary control was the variability in net radiation. 相似文献
245.
A method for estimating spatially variable seepage and hydraulic conductivity in channels with very mild slopes
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Margaret Shanafield Richard G. Niswonger David E. Prudic Greg Pohll Richard Susfalk Sorab Panday 《水文研究》2014,28(1):51-61
Infiltration along ephemeral channels plays an important role in groundwater recharge in arid regions. A model is presented for estimating spatial variability of seepage due to streambed heterogeneity along channels based on measurements of streamflow‐front velocities in initially dry channels. The diffusion‐wave approximation to the Saint‐Venant equations, coupled with Philip's equation for infiltration, is connected to the groundwater model MODFLOW and is calibrated by adjusting the saturated hydraulic conductivity of the channel bed. The model is applied to portions of two large water delivery canals, which serve as proxies for natural ephemeral streams. Estimated seepage rates compare well with previously published values. Possible sources of error stem from uncertainty in Manning's roughness coefficients, soil hydraulic properties and channel geometry. Model performance would be most improved through more frequent longitudinal estimates of channel geometry and thalweg elevation, and with measurements of stream stage over time to constrain wave timing and shape. This model is a potentially valuable tool for estimating spatial variability in longitudinal seepage along intermittent and ephemeral channels over a wide range of bed slopes and the influence of seepage rates on groundwater levels. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
246.
Margaret M. Skutsch 《Climate Policy》2013,13(4):433-443
Abstract The article considers the potential for community-based forest management (of existing forests) in developing countries, as a future CDM strategy, to sequester and mitigate carbon and to claim credits in future commitment periods. This kind of forestry is cost-effective, and should bring many more benefits to local populations than do afforestation and reforestation, thus contributing more strongly to sustainable development. However, community forest management projects are small-scale, and the transaction costs associated with justifying them as climate projects are likely to be high. A research project being carried out in five developing countries is testing carbon measurement and monitoring methods which can be carried out by community members with very little formal education, which should greatly reduce these transaction costs. Using hand-held computers with GIS capability and attached GPS, villagers with 4 years of primary education are able to accurately map their forest resource and input biomass data from sample plots into a program which calculates carbon values. 相似文献
247.
The paper reviews a number of challenges associated with reducing degradation and its related emissions through national approaches
to REDD+ under UNFCCC policy. It proposes that in many countries, it may in the short run be easier to deal with the kinds
of degradation that result from locally driven community over-exploitation of forest for livelihoods, than from selective
logging or fire control. Such degradation is low-level, but chronic, and is experienced over very large forest areas. Community
forest management programmes tend to result not only in reduced degradation, but also in forest enhancement; moreover they
are often popular, and do not require major political shifts. In principle these approaches therefore offer a quick start
option for REDD+. Developing reference emissions levels for low-level locally driven degradation is difficult however given
that stock losses and gains are too small to be identified and measured using remote sensing, and that in most countries there
is little or no forest inventory data available. We therefore propose that forest management initiatives at the local level,
such as those promoted by community forest management programmes, should monitor, and be credited for, only the net increase
in carbon stock over the implementation period, as assessed by ground level surveys at the start and end of the period. This
would also resolve the problem of nesting (ensuring that all credits are accounted for against the national reference emission
level), since communities and others at the local level would be rewarded only for increased sequestration, while the national
reference emission level would deal only with reductions in emissions from deforestation and degradation. 相似文献
248.
Eliška Rejmánková Ji?í Komárek Margaret Dix Jaroslava Komárková Nancy Girón 《Limnologica》2011,41(4):296-302
Lake Atitlan, one of the most important lakes not only in Central America but in the whole world, is facing serious problems with increasing water pollution. Over the last several decades, the uncontrolled nutrient input into the lake has lead to high P levels and low N:P ratios, initiating cyanobacterial blooms. The first bloom occurred in December of 2008, followed by more extensive bloom in October 2009. The blooms are formed by cyanobacteria from the rare planktic Lyngbya hieronymusii/birgei/robusta complex. Based on the species morphology, the Atitlan population corresponds to L. robusta and this is the first case of reported bloom of this species worldwide. Remote sensing images documented that at the maximum bloom development, 40% of the 137 km2 of the lake area were covered by dense patches of Lyngbya, with the chlorophyll a concentration reaching over 100 μg L−1. The only toxins detected in the 2009 bloom were trace levels of cylindrospermopsin and saxitoxin with 12 and 58 ng g−1, respectively. The nitrogen fixation followed a pattern expected in non-heterocytous cyanobacteria, i.e., the nitrogenase activity was minimal during the day, while during the night the activity reached 2.2 nmol C2H4 μg Ch a−1 h−1. Delta 15N of −0.86‰ was well in the range given for nitrogen fixing organisms. The cell C, N and P content was 36.7%, 5.9% and 0.9%, respectively, resulting in the molar ratio of 105:14.4:1. A well designed and executed lake monitoring program, strict control of nutrient input into the lake, and public education are the necessary prerequisites for potential prevention of even more severe blooms than the one from 2009. 相似文献
249.
250.
Michael J. Mottl Jeffrey S. Seewald Margaret K. Tivey Giora Proskurowski Eoghan Reeves C.-F. You Thomas Pichler 《Geochimica et cosmochimica acta》2011,75(4):1013-76
The Eastern Lau Spreading Center (ELSC) is the southernmost part of the back-arc spreading axis in the Lau Basin, west of the Tonga trench and the active Tofua volcanic arc. Over its 397-km length it exhibits large and systematic changes in spreading rate, magmatic/tectonic processes, and proximity to the volcanic arc. In 2005, we collected 81 samples of vent water from six hydrothermal fields along the ELSC. The chemistry of these waters varies both within and between vent fields, in response to changes in substrate composition, temperature and pressure, pH, water/rock ratio, and input from magmatic gases and subducted sediment. Hot-spring temperatures range from 229° to 363 °C at the five northernmost fields, with a general decrease to the south that is reversed at the Mariner field. The southernmost field, Vai Lili, emitted water at up to 334 °C in 1989 but had a maximum venting temperature of only 121 °C in 2005, due to waning activity and admixture of bottom seawater into the subseafloor plumbing system. Chloride varies both within fields and from one field to another, from a low of 528 mmol/kg to a high of 656 mmol/kg, and may be enriched by phase separation and/or leaching of Cl from the rock. Concentrations of the soluble elements K, Rb, Cs, and B likewise increase southward as the volcanic substrate becomes more silica-rich, especially on the Valu Fa Ridge. Iodine and δ7Li increase southward, and δ11B decreases as B increases, apparently in response to increased input from subducted sediment as the arc is approached. Species that decrease southward as temperature falls are Si, H2S, Li, Na/Cl, Fe, Mn, and 87Sr/86Sr, whereas pH, alkalinity, Ca, and Sr increase. Oxygen isotopes indicate a higher water/rock ratio in the three systems on Valu Fa Ridge, consistent with higher porosity in more felsic volcanic rocks. Vent waters at the Mariner vent field on the Valu Fa Ridge are significantly hotter, more acid and metal-rich, less saline, and richer in dissolved gases and other volatiles, including H2S, CO2, and F, than the other vent fields, consistent with input of magmatic gases. The large variations in geologic and geophysical parameters produced by back-arc spreading along the ELSC, which exceed those along mid-ocean ridge spreading axes, produce similar large variations in the composition of vent waters, and thus provide new insights into the processes that control the chemistry of submarine hot springs. 相似文献