Volume 3 - 2001

In the Mediterranean region, fire is a natural factor, which contributes in the shaping of landscape and
the preservation of a high degree of biodiversity. However, often repeated burning has negative impacts
on the forested landscapes. When the processes of natural or artificial regeneration are efficient and
the fire frequency is sufficiently low to enable the recovery of vegetation, recovery time T can be used
as a tool for setting priorities for the preservation of ecological and social functions of the forested
landsapes. Using a simple linear approach, we argue that their situation can be considered as acceptable,
when the percentage of the yearly burned area in relation to the total forested area is much lower
than 100/T (for practical purposes just lower than 10/T). This empirical rule was applied to the Greek
forested landscapes. In the case of pine forests of Pinus halepensis and Pinus brutia, it was found that
the condition implied by the rule was not satisfied and, therefore, a reduction of the yearly burned areas
of these lowland conifer forests is necessary. However, as far as the other types of forests, as well as
macchia and phrygana are concerned, the condition is satisfied.

Air pollution related problems, such as acidification, air quality and ground-level ozone, are recognized
as some of the important problems facing the people of the Czech Republic, whose health is damaged
by impacts of air pollutants. Also the impacts of these air pollutants on human health, forests and vegetation
are investigated. This paper presents evaluation of air pollution caused by sulfur dioxide, nitrogen
oxides, particulate matter and ozone, based on the readings of measuring site at Bílý Køíž for the
six-year period 1994-1999. The evaluation of the status of the ambient air pollution is based on air pollution
limit values as specified by the new European Directives. Concern has been expressed about the
possible effects of ozone, nitrogen oxides, sulfur dioxide and particulate matter exposures on forested
areas, materials and human health. The main objective of this study is to examine the evolution
observed in the concentrations of these air pollutants considered. The reduction is observed for winter
air pollutants as sulfur dioxide and particulate matter from 1996 to 1999. In contrary, the ozone concentrations
increase considerably for the same period.

Three hydrographic cruises were conducted during 1997-1999 in north Aegean Sea, in order to study the dissolved oxygen (DO) and nutrient distributions in Strymonikos Gulf impacted by the riverine waters of the Strymon River. The approaches used in this paper include a preliminary estimation of the nutrient load of Strymon River and the influence of the riverine waters upon the DO and nutrient distribution in Strymonikos Gulf. Nutrient levels recorded in Strymon River were similar with other international Rivers. The influence of Strymonas River on the DO and nutrient distributions was clearly detected during December 1997 and May 1998. On the contrary, during March 1999 the influence of Strymon River was not so clearly detected. High nutrient concentrations were recorded close to the mouth of the river. As mixing with offshore waters progressed, nutrient levels declined dramatically. Plots of atomic DIN:P (ratio of the total dissolved inorganic nitrogen to dissolved inorganic phosphorus), Si:P (ratio of dissolved silica to dissolved inorganic phosphorus) and Si:DIN ratios in Strymonikos Gulf, during the three sampling periods studied, indicated stoichiometric P-limitation in about 34%. Furthermore, the data indicated significant probable N-limitation (31.4%), while Si-limitation was not probable (2.9%). In particular, 31% of the data showed a defined P-limitation in December, whereas 30% of the data showed N-limitation. It is noteworthy that Si-limitation was not recorded. In May, the atomic DIN:P ratio indicated P-limitation in about 21% and N-limitation in about 46%. Si-limitation was not recorded. Finally, in March, the 51% of the data showed P-limitation, whereas only the 16% showed N-limitation and 8% showed Si-limitation.

The present study is performed with the aim to reduce the levels of polluting emissions from fuel combustion that produce acid rains and the greenhouse effect (NOx, CO2). The electric field effects on the processes of heat/mass transfer and propane combustion are studied in order to perform electric control of the levels of polluting emissions from the flame. The results of experimental studies show the direct influence of the electric field's enhanced mass transfer on local variations of the flame composition and fuel combustion. The related variations of the flame temperature, processes of soot formation, carbon capture and deposition along the flame channel flow are studied by varying the field strength and the equivalence ratio of the propane-air mixture. The results show that the electric field effect on soot for- mation, carbon capture and sequestration, for fuel-rich flame flow, can be used to reduce the levels of CO2 emissions from the flame. In addition, the field-enhanced heat/ mass transfer to the channel walls, for fuel-lean conditions, can be used to control the fuel combustion, flame temperature and temperature- sensitive levels of NOx emissions. The most pronounced electric field effects on fuel combustion and composition of the products are observed in the limit of the weak fields (U<1,2 kV, E<105 V m-1).