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New education and decision
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The river Mesta region (South-West Bulgaria)
In terms of the WFD 2000-60/EC (Annex XIA), the river Mesta is located in the eco-region 7 (Eastern Balkans). It s a transboundary river shared between Bulgaria and Greece.
In the Bulgarian territory, the Mesta River (named Nestos in Greece) is a mountain stream with 1318 m average altitude, 129 km length and having 2767 sq.km of catchment area and annual water discharge of 34 m3/s at the state border. At this point, the annual minimums (monthly and absolute) are estimated to be 1.55 (July 1993) and 0.851 (August 1993), respectively. The river system contains 25 tributaries; the largest of them (river Dospat) enters Mesta in the territory of Greece.
The catchments area of the Mesta is in the Continental-Mediterranean climatic zone, but the lower stretch (close to the state border) is influenced by purely Mediterranean climate. The typical feeding of the river is by snow (in high mountains) and rains (in lower stretches). There are two typical flow peaks – a primary in springs (shifted to the early summer) and a secondary in winters; low flow period may last 3-4 months (August-November).
There are no serious changes in the flow regime for the last 30years. Main water use is approached to irrigation of extensive agriculture along the river valley; there are several small hydropower stations on some of the tributaries. Industries in the watershed are in regress for the last 15 years.
The river Mesta has been intensively studied for the last 35 years due to the heavy organic pollution caused by yeast, cellulose and cardboard manufacturing in the town of Razlog (RAZL). The industrial wastewater production exceeded 90 000 m3 per day1; the average daily levels of BOD5 varied between 300-450 mg O2/dm3. Such an unfavorable ecological situation remained until 1990, when the operation of the plants – sources of great pollution, was banned by the respective authorities. Immediately, rapid improvements of the water quality and recovery of the affected ecosystem were registered.
By this way, the developments of the ecological status of the Mesta River could be defined in two large periods: until 1990, the period of heavy loading with organic matter of industrial origin, and after 1990, the period of recovery and stabilization of the ecological situation.
The available data base contains full set of data on hydro-morphological (incl. hydrological), physical (thermal conditions), chemical (oxygenation and nutrient conditions) and biological (mostly on macroinvertebrate species diversity, abundance/density, cenotic and trophic structures of bottom communities) and water quality assessments (saprobic, biotic and cenotic indices) since 1978 by 2005.