Lakes are natural ecosystems that are daily exposed to pollution. The main culprits are the chemical
elements phosphorus and nitrogen. Thankfully lakes have the ability to be cleaned by itself to a certain
point. We call that the self-cleaning ability. Lake water pollution is caused by anthropogenic and natural
environmental influences. The quantities of nitrogen and phosphorus are affected by rainfall, type of
landscape, land use, level of urbanization, the number of households and the arrangement of drainage
and wastewater treatment.In this diploma work, I interpret and compare Lake Račeva in the
municipality of Logatec and Lake Divje jezero in Idrija. The aim was to calculate the indicative annual
amounts of nitrogen and phosphorus that lakes get from their own catchment areas. The calculations are
only indicative, because currently there are no analysis of water quality of lakes. On the web pages of
ARSO I first sought information of the ten-year average amount of rainfall on a few of meteorological
stations and determine the size and proportions of each land use in relation to the total surface
hydrological areas of both lakes. With the help of guidelines from various authors I determined the
quantities of two elements that contribute roads, hardened surfaces, household wastewater treatment
plants, industry and agricultural land. I acquired quantities for each reservoir separately and compared
the final results with each other.Because it is predominantly wooded area the forest also contributes the
largest amount of nitrogen and phosphorus. Among the major emitters we can count the road and
households which do not have drainage and cleaning waste water. The quantities of pollutants will be
significantly reduced when the waste water will be discharged to the treatment plant and when water
from busy roads will be retained in reservoirs.
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