# PREFACE

".. when you can measure what,you are speaking about and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of science, whatever the matter may be."
Lord Kelvin
Biodiversity refers to the variety and variability among living organisms and the ecological complexes in which they occur. It encompasses different levels of biological organisation from regional landscapes; ecosystems, and habitats to species and genes, and their relative abundance. This shows a peculiar conception of tho significance of biodiversity. While, strictly speaking, it is correct that if new species are introduced into a region; e.g. by the introduction of cultivated poplars, or by change in water regime, biodiversity may have been increased, but this may be at the expense of the previous, may be more "natural", biodiversity that existed beforehand. Is such a increase of the biodiversity a useful result?

Biodiversity is an area related quantity which can be expressed e.g. by a variogram. This means that biodiversity, when using any classification, converges to a constant at some size of the monitoring area of characteristic biotope. To estimate the biodiversity of some characteristic area, the monitoring plot or a set of plots should be of proper, large enough, size. Statistically correct sampling methods and sampling distribution should be used to avoid a misinterpretation.

Biodiversity is also related to the water availability, temperature, morphology variability; ete: This should be understood when speaking about the location and extent of monitoring plots, stands, places, etc. and the use of the so called stationary monitoring plot system.

The use of stationary monitoring places is justified when monitoring the impact of large scale factors, as for ex- ample when long-term humidity or temperature changes are to be observed, or when stationary plots are statistically distributed over the whole area, characterising all the local but important factors as for example ground water level changes in connection with geomorphology. In some cases, as in monitoring the changes in the inundation area, monitoring in profiles across the inundation area is much more suitable. The reader of this publication should keep in mind that the monitoring of the Gabcikovo project is monitoring of the environmental impact of the engineering structures over the large area and not only monitoring of the changes on the specified plots or the stationary stands: The conclusions of the biota monitoring should be therefore based on the comparison with the results of the ground water monitoring and the soil moisture monitoring.

Monitoring of the ground water and the zone of aeration helps us to identify the real impact of the Gabcikovo structures on biota. The Gabcikovo structures are influencing the adjacent environment through changes in the ground water level in comparison to the ground water level without the impact of the structures: These changes are manifested through changes in the soil moisture in the zone of aeration. If there is an increase in the ground water level due to the construction of hydropower structures, then there is also an increase of moisture in the zone of aeration, occasionally the situation may remain unchanged at some depths, but there is in no case a decrease in the moisture caused by the engineering works. Reciprocally the same is valid. If there is a decrease in the ground water level due to the construction of the engineering structures, then there is also a decrease in fhe soil moisture in the zone of aeration, or the situation may be unchanged at some depths, but there is m no ceae an increase in soil moisture caused by the engineering works. Therefore, neither an increase of the moisture in the zone of aeration due to a decrease of the ground water level, nor a decrease of the moisture due to an increase of the ground water level, can happen. Similarly the other measures and impacts should be evaluated: One of the most important events is for example flooding of the inundation area.

Sustainable development is defiined as improving the quality of human life while living within the carrying capacity of the supporting ecosystems. Sustainable development can continue to develop only through improvements in knowledge, organisation, technical effciency and wisdom.

Monitoring of the Gabcikovo part of the Gabcikovo-Nagymaros Hydroelectric Power Project is aimed to improve knowledge, organisation, technical effiiciency and wisdom with the goal to ensure typical biodiversity the Danubian lowland, developed during the human symbiosis with the Danube in the past and to improve the development of the quality of human life in the country.

Igor Mucha