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581.
582.
Comparative analysis of phytoplankton patterns in two modified lakes with contrasting hydrological features 总被引:1,自引:0,他引:1
Monica Tolotti Adriano Boscaini Nico Salmaso 《Aquatic Sciences - Research Across Boundaries》2010,72(2):213-226
Hydrological management represents one of the main factors controlling physical and chemical characteristics as well as biodiversity
and productivity of planktonic communities in artificial and modified lakes. In Alpine piedmont reservoirs, which often receive
large water inputs from high altitude watersheds, control operated by hydrological regime over ecological processes is also
mediated by other related variables such as water temperature and turbulence, and load of inorganic suspended solids. This
contribution reports on results obtained from a comparative study on the impact of hydrological regime on phytoplankton patterns
in two modified piedmont lakes of different size and hydrology located in the NE Italian Alps: Lake Santa Croce (V = 147 × 106 km3) and Lake Toblino (V = 5.7 × 106 km3). Phytoplankton of both lakes was characterised by a pronounced dominance of diatoms, accompanied by cryptophytes and green
algae. The mesotrophic Lake Santa Croce showed a typical seasonal succession of dominant groups, while phytoplankton growth
in the eutrophic Lake Toblino was variable and showed pronounced pulses in relation to dramatic changes in the hydrological
regime. The comparative study of phytoplankton, based on morpho-functional classification and application of multivariate
analyses (non-metric multidimensional scaling, principal components analysis, and redundancy analysis), showed that hydrological
regime affected phytoplankton growth in the two lakes both directly, i.e. through renewal time, and indirectly, i.e. regulating
thermal conditions in Lake Santa Croce and nutrient availability in both lakes. Nevertheless, effectiveness of hydrological
constraints largely depended on lake size and morphology, being more pronounced in the shallower and smaller Lake Toblino. 相似文献
583.
Robert Smith 《Astronomy& Geophysics》2010,51(1):1.13-1.17
M eeting report Mike Edmunds and Robert Smith draw together the wide-ranging scientific contributions made by Bernard Pagel, the theme of an RAS Specialist Discussion Meeting on 13 and 14 November 2008. 相似文献
584.
585.
Katharine A. Smith Elizabeth W. North Fengyan Shi Shih-Nan Chen Raleigh R. Hood Evamaria W. Koch Roger I. E. Newell 《Estuaries and Coasts》2009,32(4):748-757
Seagrass beds have declined in Chesapeake Bay, USA as well as worldwide over the past century. Increased seston concentrations,
which decrease light penetration, are likely one of the main causes of the decline in Chesapeake Bay. It has been hypothesized
that dense populations of suspension-feeding bivalves, such as eastern oysters (Crassostrea virginica), may filter sufficient seston from the water to reduce light attenuation and enhance seagrass growth. Furthermore, eastern
oyster populations can form large three-dimensional reef-like structures that may act like breakwaters by attenuating waves,
thus decreasing sediment resuspension. We developed a quasi-three-dimensional Seagrass-Waves-Oysters-Light-Seston (SWOLS)
model to investigate whether oyster reefs and breakwaters could improve seagrass growth by reducing seston concentrations.
Seagrass growth potential (SGP), a parameter controlled by resuspension-induced turbidity, was calculated in simulations in
which wave height, oyster abundance, and reef/breakwater configuration were varied. Wave height was the dominant factor influencing
SGP, with higher waves increasing sediment resuspension and decreasing SGP. Submerged breakwaters parallel with the shoreline
improved SGP in the presence of 0.2 and 0.4 m waves when sediment resuspension was dominated by wave action, while submerged
groins perpendicular to the shoreline improved SGP under lower wave heights (0.05 and 0.1 m) when resuspension was dominated
by along-shore tidal currents. Oyster-feeding activity did not affect SGP, due to the oysters’ distance from the seagrass
bed and reduced oyster filtration rates under either low or high sediment concentrations. Although the current implementation
of the SWOLS model has simplified geometry, the model does demonstrate that the interaction between oyster filtration and
along-shore circulation, and between man-made structures and wave heights, should be considered when managing seagrass habitats,
planning seagrass restoration projects, and choosing the most suitable methods to protect shorelines from erosion. 相似文献
586.
587.
Ikuho Yamada Barbara B. Brown Ken R. Smith Cathleen D. Zick Lori Kowaleski-Jones Jessie X. Fan 《The Professional geographer》2013,65(2):157-177
Obesity is a growing epidemic in the United States. Walkable neighborhoods, characterized as having the three Ds of walkability (population Density, land use Diversity, and pedestrian-friendly Design), have been identified as a potentially promising factor to prevent obesity for residents. Past studies examining the relationship between obesity and walkability vary in geographic scales of neighborhood definitions and methods of measuring the three Ds. To better understand potential influences of these sometimes arbitrary choices, we test how four types of alternative measures of land use diversity measured at three geographic scales relate to body mass index for 4,960 Salt Lake County adults. Generalized estimation equation models demonstrate that optimal diversity measures differed by gender and geographic scale and that integrating walkability measures at different scales improved the overall performance of models. 相似文献
588.
The past decade has seen what could reasonably be called an explosion in the number of food-related crises in China. Food safety issues represent a national crisis threatening the physical and psychological health of Chinese citizens, despite the repeated adoption of stringent food safety laws and regulations. This project, based on a stratified random sample of 337 households in Nanjing, assesses perceptions related to different food safety concerns and issues among urban residents and explores differences in perceptions across social strata as defined by socioeconomic and demographic variables using principal component analysis and standard statistical tests. 相似文献
589.
Joel W. Harrison Ralph E. H. Smith 《Aquatic Sciences - Research Across Boundaries》2013,75(3):399-411
Phytoplankton from Lake Ontario and six small Canadian lakes (Dorset Lakes) were supplemented with nitrogen (N) and phosphorus (P) to determine how nutrients affect Photosystem II (PSII) variable fluorescence and photoinhibition in natural freshwater communities. Susceptibility of PSII to photoinhibition by photosynthetically active radiation (PAR) and ultraviolet radiation (UVR), as well as recovery potential, was quantified using changes in variable fluorescence and compared between N- and P-supplemented (Nu+) and non-supplemented (Nu?) Lake Ontario phytoplankton. Nu+ communities exhibited slightly higher variable fluorescence than Nu? when dark-adapted (Fv:Fm) or under constant illumination (Fq′:Fm′). Rates of relative electron transport (rETR) were greater for Nu+ than Nu? phytoplankton, with higher non-photochemical quenching (NPQ) by Nu? samples. The initial slope of the rETR-irradiance curve (α) did not differ significantly between nutrient treatments, but the saturation irradiance (EK) was significantly higher for Nu+ samples than for Nu? samples. Nutrient supplementation increased rates of PAR- and UVR-dependent damage but also recovery, so that net PSII photoinhibition was equally severe as in the absence of added N and P. Additions of N, P, and N + P did not significantly alter Fv:Fm of Dorset Lakes phytoplankton. Compared to the range of variable fluorescence observable over the diel cycle of photoinhibition and recovery in Lake Ontario, the effects of supplemental nutrients observed in this study were minor. 相似文献
590.
Monica Riva Shlomo P. Neuman Alberto Guadagnini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):195-207
Earth and environmental variables are commonly taken to have multivariate Gaussian or heavy-tailed distributions in space and/or time. This is based on the observation that univariate frequency distributions of corresponding samples appear to be Gaussian or heavy-tailed. Of particular interest to us is the well-documented but heretofore little noticed and unexplained phenomenon that whereas the frequency distribution of log permeability data often seems to be Gaussian, that of corresponding increments tends to exhibit heavy tails. The tails decay as powers of ? $ \alpha $ where 1 < $ \alpha $ < 2 is either constant or grows monotonically toward an asymptote with increasing separation distance or lag. We illustrate the latter phenomenon on 1-m scale log air permeabilities from pneumatic tests in 6 vertical and inclined boreholes completed in unsaturated fractured tuff near Superior, Arizona. We then show theoretically and demonstrate numerically, on synthetically generated signals, that whereas the case of constant $ \alpha $ is consistent with a collection of samples from truncated sub-Gaussian fractional Lévy noise, a random field (or process) subordinated to truncated fractional Gaussian noise, the case of variable $ \alpha $ is consistent with a collection of samples from truncated sub-Gaussian fractional Lévy motion (tfLm), a random field subordinated to truncated fractional Brownian motion. Whereas the first type of signal is relatively regular and characterized by Lévy index $ \alpha $ , the second is highly irregular (punctuated by spurious spikes) and characterized by the asymptote of $ \alpha $ values associated with its increments. We describe a procedure to estimate the parameters of univariate distributions characterizing such signals and apply it to our log air permeability data. The latter are found to be consistent with a collection of samples from tfLm with $ \alpha $ slightly smaller than 2, which is easily confused with a Gaussian field (characterized by constant $ \alpha $ = 2). The irregular (spiky) nature of this signal is typical of observed fractured rock properties. We propose that distributions of earth and environmental variable be inferred jointly from measured values and their increments in a way that insures consistency between these two sets of data. 相似文献