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71.
David P. Hamilton Katherine R. O’Brien Michele A. Burford Justin D. Brookes Chris G. McBride 《Aquatic Sciences - Research Across Boundaries》2010,72(3):295-307
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic
lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were
taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples
from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the
longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r
2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite
for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely
dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton
distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth
of the euphotic zone (z
eu) is consistently shallower than the depth of the surface mixed layer (z
SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear
to disrupt the annual cycle of maximum chlorophyll in winter. 相似文献
72.
Jonathan H. Sharp Kohei Yoshiyama Alexander E. Parker Matthew C. Schwartz Susan E. Curless Allison Y. Beauregard Justin E. Ossolinski Allen R. Davis 《Estuaries and Coasts》2009,32(6):1023-1043
The Delaware River and Bay Estuary is one of the major urbanized estuaries of the world. The 100-km long tidal river portion
of the estuary suffered from major summer hypoxia in the past due to municipal and industrial inputs in the urban region;
the estuary has seen remarkable water quality improvements from recent municipal sewage treatment upgrades. However, the estuary
still has extremely high nutrient loading, which appears to not have much adverse impact. Since the biogeochemistry of the
estuary has been relatively similar for the past two decades, our multiple year research database is used in this review paper
to address broad spatial and seasonal patterns of conditions in the tidal river and 120 km long saline bay. Dissolved oxygen
concentrations show impact from allochthonous urban inputs and meteorological forcing as well as biological influences. Nutrient
concentrations, although high, do not stimulate excessive algal biomass due to light and multiple nutrient element limitations.
Since the bay does not have strong persistent summer stratification, there is little potential for bottom water hypoxia. Elevated
chlorophyll concentrations do not exert much influence on light attenuation since resuspended bottom inorganic sediments dominate
the turbidity. Dissolved inorganic carbon and dissolved and particulate organic carbon distributions show significant variability
from watershed inputs and lesser impact from urban inputs and biological processes. Ratios of dissolved and particulate carbon,
nitrogen, and phosphorus help to understand watershed and urban inputs as well as autochthonous biological influences. Owing
to the relatively simple geometry of the system and localized anthropogenic inputs as well as a broad spatial and seasonal
database, it is possible to develop these biogeochemical trends and correlations for the Delaware Estuary. We suggest that
this biogeochemical perspective allows a revised evaluation of estuarine eutrophication that should have generic value for
understanding other estuarine and coastal waters. 相似文献
73.
Lakes are a prominent geographic feature in northern landscapes and play an important role in understanding regional climate systems. In order to better model changes within climate systems, it is important to study lake ice processes. Although the availability of records for lake ice through ground measurements has declined in recent years, the increased use of remote sensing provides an alternative to this. Using a preclassified snow and ice remote sensing product with a 500‐m resolution, based on images from the Moderate Resolution Imaging Spectroradiometer (MODIS/MOD10A1), and the use of measured and reanalysis temperature data, this study evaluated lake ice phenology dates in connection to recent trends in temperature and 0 °C isotherms within Ontario and Manitoba between 2001 and 2014. Temperature trends indicated both regional warming and cooling, with significant cooling observed in Southern Ontario (p < .05) and significant warming in Southern Manitoba (p < .1) during the fall. Spatial analysis of the trends in the lake ice data showed significant clustering of significant trends in ice on dates (p < .01). When analysing the trends in ice phenology in connection to the trends in temperature, it was found that 70% of lakes experienced a change in the ice on date with the expected change in temperature and 85% of lakes for ice off date. When shifting ice on and ice off dates are investigated in relation to 0 °C isotherms, it was seen that 80% of ice on dates and 100% of ice off dates shifted in sync with the isotherm dates. This demonstrates that the ice phenology of lakes in Ontario and Manitoba, Canada, is responding to short‐term variability in temperature. The MODIS product could be used to investigate ice phenology on a large scale and contribute towards expanding existing records of ice phenology. Establishing long‐term ice records could be a valuable asset for other research ranging from water balance studies to the response of lake biota under changing climate. 相似文献
74.
Small R. Justin DuVivier Alice K. Whitt Daniel B. Long Matthew C. Grooms Ian Large William G. 《Climate Dynamics》2021,56(1):299-327
Climate Dynamics - A shallow mixed layer depth bias in Austral winter in the Subantarctic Zone is a common feature of Coupled Model Intercomparison Project (CMIP5) models, including the Community... 相似文献
75.
Olivier Daillant David Boilley Martin Gerzabek Justin Porstendörfer Roland Tesch 《Journal of Atmospheric Chemistry》2004,49(1-3):329-341
Lichens are now well known for their potential as bio-indicators of environmental pollution, but less is known about their suitability as quantitative biomonitors for atmospheric emissions of tritium (mainly as tritiated water, HTO) and radiocarbon (as 14CO2) from nuclear facilities, although both radionuclides could result in non-trivial individual or collective radiation doses due to their high environmental mobility and their long half-lives. 3H and 14C are fixed in lichens mainly by the photosynthesis of the algal partner and then stored in the organic molecules of both alga and fungus. They have the advantage of allowing the monitoring of atmospheric water vapour without interference of soil water or soil organic substances as long as soil-inhabiting species are avoided. Lichens were collected in the surroundings of (military and civil) nuclear facilities, in areas away from any direct source of contamination and some were transplanted from a contaminated area to a non-contaminated one. The influence of the nuclear facilities can be clearly traced, sometimes in a spectacular way and the first results of analyses after transplants give a base for estimating the effective half-life of 3H in lichens. 相似文献
76.
77.
78.
Bleaching (whitening) of cnidarians such as corals and sea anemones has caused widespread degradation of coral reefs around the world and is therefore an urgent issue for coral reef science and conservation. Although cnidarians often bleach in aquaria, methods for experimental induction of bleaching in wild cnidarians are lacking, which impedes scientists’ ability to understand the ultimate effects of bleaching on the broader ecosystem. In this study, we investigated the utility of an in situ method for experimental induction of bleaching in the tropical sea anemone Heteractis crispa. Healthy, wild anemones were covered with opaque black plastic sheets, mesh cages or left undisturbed (controls) and tentacle colour and body size were monitored with a colour reference card and flexible tape, respectively, every 1–3 days for 15 days. Caged and control anemones remained unchanged for the duration of the experiment, but covered anemones commenced whitening after 4–6 days and were completely white after 7–14 days (mean time to bleaching ± SE = 10.1 ± 0.7 days). Experimental bleaching occurred without reduction in anemone body size and was visibly similar to natural bleaching seen previously in H. crispa. We hypothesize that light‐deprivation, reduced water flow, physical contact or some combination of these factors caused the bleaching. This study provides the basis for a simple and rapid method of inducing bleaching in situ, which releases scientists’ dependence on sporadic natural bleaching events or artificial aquarium experiments, and provides a means to investigate the effects of bleaching on other ecosystem components such as fishes. 相似文献
79.
Guotu Li Mohamed Iskandarani Matthieu Le Hénaff Justin Winokur Olivier P. Le Maître Omar M. Knio 《Computational Geosciences》2016,20(5):1133-1153
This study aims at analyzing the combined impact of uncertainties in initial conditions and wind forcing fields in ocean general circulation models (OGCM) using polynomial chaos (PC) expansions. Empirical orthogonal functions (EOF) are used to formulate both spatial perturbations to initial conditions and space-time wind forcing perturbations, namely in the form of a superposition of modal components with uniformly distributed random amplitudes. The forward deterministic HYbrid Coordinate Ocean Model (HYCOM) is used to propagate input uncertainties in the Gulf of Mexico (GoM) in spring 2010, during the Deepwater Horizon oil spill, and to generate the ensemble of model realizations based on which PC surrogate models are constructed for both localized and field quantities of interest (QoIs), focusing specifically on sea surface height (SSH) and mixed layer depth (MLD). These PC surrogate models are constructed using basis pursuit denoising methodology, and their performance is assessed through various statistical measures. A global sensitivity analysis is then performed to quantify the impact of individual modes as well as their interactions. It shows that the local SSH at the edge of the GoM main current—the Loop Current—is mostly sensitive to perturbations of the initial conditions affecting the current front, whereas the local MLD in the area of the Deepwater Horizon oil spill is more sensitive to wind forcing perturbations. At the basin scale, the SSH in the deep GoM is mostly sensitive to initial condition perturbations, while over the shelf it is sensitive to wind forcing perturbations. On the other hand, the basin MLD is almost exclusively sensitive to wind perturbations. For both quantities, the two sources of uncertainty have limited interactions. Finally, the computations indicate that whereas local quantities can exhibit complex behavior that necessitates a large number of realizations, the modal analysis of field sensitivities can be suitably achieved with a moderate size ensemble. 相似文献
80.
Alen Alexanderian Justin Winokur Ihab Sraj Ashwanth Srinivasan Mohamed Iskandarani William C. Thacker Omar M. Knio 《Computational Geosciences》2012,16(3):757-778
Polynomial chaos (PC) expansions are used to propagate parametric uncertainties in ocean global circulation model. The computations
focus on short-time, high-resolution simulations of the Gulf of Mexico, using the hybrid coordinate ocean model, with wind
stresses corresponding to hurricane Ivan. A sparse quadrature approach is used to determine the PC coefficients which provides
a detailed representation of the stochastic model response. The quality of the PC representation is first examined through
a systematic refinement of the number of resolution levels. The PC representation of the stochastic model response is then
utilized to compute distributions of quantities of interest (QoIs) and to analyze the local and global sensitivity of these
QoIs to uncertain parameters. Conclusions are finally drawn regarding limitations of local perturbations and variance-based
assessment and concerning potential application of the present methodology to inverse problems and to uncertainty management. 相似文献