The pollutant spread and stream self-purification modelling with differential equations
2006
Purvinis, O. | Sidlauskas, V. | Sukys, P.
The paper analyses possibilities to model the concentration of DIN - a harmful pollutant from the eutrophication point of view-contained in the stream and self-purification processes of the stream. During the studies the data of a small right affluent of the river Musa (administrative district of Birzai) was used. The data comprised results of natural observations about the changes in DIN concentrations during the vegetation period and cold period of the year. The model of pollution dispersion through the stream is a parabolic differential equation with partial derivates, initial as well as boundary conditions. Constant DIN pollution in a stream stretch containing constant hydrological parameters and adequate environment conditions is proportional to the concentration of pollutants inflow. Further from the pollution source the constant pollution is exponentially decreasing. At the distance expressed by x (m) from the initial pollution concentration c0 measuring place, DIN concentration is expressed by C(x) = c0eE-0.00017x in the cold season of the year and by in C(x) = c0eE-0.00031x during the vegetation period. The stream polluted in the result of agricultural activity, further flowing through forest-covered area is significantly purified already at a 1.5 km stretch. Relatively, DIN concentration decreases about 3.8 times a day during the vegetation period and about 2.7 times a day during the cold season of the year.
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