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Scaling concepts, related to basic physical transport and mixing processes and other ecological
aspects in lakes, are reviewed in an ecohydrodynamic perspective; the length and time scales as
well as the non-dimensional parameters governing the various flow regimes and relevant to these
processes are also presented, emphasizing the influence they have on lake ecosystems. The
hierarchy of length scales is very important in determining both the turbulence structure, and in
affecting the ecological processes occurring in lakes. Most of these scales are defined in terms of
several basic parameters which, when combined properly, yield important dimensionless numbers,
as: Rf, Ri, Pr, T, Ret, Frt, Grt, and Prt, the flux and gradient Richardson numbers, the Prandtl
number, a dimensionless time, and the turbulent Reynolds, Froude, Grasshof and Prandtl numbers,
respectively. A few more dimensionless numbers (as the Lake and Wedderburn numbers, LΝ, W,
etc.) are also useful in characterizing the general dynamic behavior of lakes. Ratios of length or time
scales may also provide similar useful parameters.

Many Public Aquaria have been designed and constructed all over the world during the last three
decades. The serial arrangement of relatively small, rectangular, concrete tanks has been replaced
by fewer large, irregularly shaped tanks, replicating habitats. The “taxonomic concept” of displaying
specimens in the old aquaria has now been succeeded by the more ecological, “community concept”
type of display. At the same time most of the “old aquaria” have been renovated. Aquarium missions
have also been broadened nowadays including research, conservation and education. Aquaria are
ideal places for research on husbandry, life cycles, reproduction, behavior, autoecology and fish
pathology. Collaboration with Universities and Research Centers increases the research potential in
scientific disciplines such as ecology, genetics, physiology and biochemistry. Collaboration also
provides mutual benefits in both infrastructure and personnel: The research background in aquaria
also forms a sound platform to materialize conservation projects, focusing either on the ex-situ
conservation of animals in the aquaria or on environmental protection of surrounding areas and reintroduction
of endangered species. In addition to formal educational opportunities, non formal
education to visitors, schools and undergraduates seems to become a major mission of aquaria.
Aquarium tank displays, preserved biological material, film projections, seminars / lectures and book
magazine publications enhance environmental awareness, encouraging people to adopt
Environmentally Responsible Behavior. All these missions are feasible because most public aquaria
are making a good profit mainly due to their high popularity. There are also benefits for the
community in the area; aquaria have enlivened declining water front areas and increased the income
of tourist resorts mainly by “stretching out” the tourist season. In the present work the objectives of a
public aquarium are reviewed and the main infrastructure subsystems and operational procedures
are described; Know how on aquarium systems can also be applied in research laboratories of
academic institutions if live organisms have to be kept for experimentation. Aquarium missions on
research, conservation and education are discussed.

In the present study seasonal changes of chlorophyll content and storage substances related to the
metabolic response of the widespread, evergreen plant oleander (Nerium oleander) to air pollution
were investigated. Mature leaves of oleander shrubs, grown at five sites of differing levels of air
pollution in the center and the suburbs of the Athens Metropolitan area, were examined during the
course of a year. Soluble sugars, starch and total lipid content of the leaves showed a peak at the
end of the cold season, while a decline was detected during the main growth period. Leaf
chlorophyll content was increased during spring. It seems likely that the level of air pollution in
Athens did not affect the concentration and the seasonal pattern of storage substances at the leaf
level. Elevated chlorophyll content was estimated in the polluted with oxides of nitrogen sites. In
contrast, leaf chlorophyll content declined in sites with ozone pollution.

The performance of electrocoagulation using iron electrodes for the removal of hexavalent chromium
from synthetic aqueous solutions and actual industrial electroplating wastewater was studied.
Parameters affecting the electrocoagulation process, such as initial pH, applied current density,
initial metal ion concentration, COD and time of electroprocessing were investigated. The optimum
pH was found to be in the range 4-8. Initial chromium concentrations of 200 – 800 mg L-1 did not
influence its removal rate. Higher concentrations were reduced significantly in relatively less time
than lower concentrations. Increased current density accelerated the electrocoagulation process,
however, on cost of higher energy consumption. Results revealed that best removal was achieved at
a current density 40 mA cm-2. The electrocoagulation process was successfully applied to the
treatment of an electroplating wastewater sample. Its Cr (VI) ion concentration and COD were
effectively reduced under the admissible limits in 50 minutes of electroprocessing.