Time-series analysis of long-term water quality records from Yantra River Basin, Bulgaria

The time-series analysis carried out has shown some specific features of th e Yantra river ecosystem. The trends for a relatively long period of observ ation (1980 - 1990) but influenced by local natural events (e.g. flooding i n 1984) and irregular data collection are not quite significant and, usuall y, are divided into two parts: until the event and afterwards. The influenc e of the natural events on the common trend is more distinct for urban regi ons without big industrial activity rather than for agricultural and heavil y industrialized areas. The latter two regions indicate a more clear trend of decrease of polluting species for the monitoring period. It is probably due to more strict environmental regulation of these activities as compared to the traditional attitude to everyday wastes. The seasonal data decomposition shows an almost equal pattern for the Yantr a river basin maximal values of pollutants in the spring season (mostly Mar ch), followed by a summer decrease. Only in typical urban areas summer peak s are observed (June). This is an indication for the different origin of th e pollutants for the different regions - urban wastes from one side and und erground waters, soil extracts, farming activities, on the other. This study gives also valuable directions for future studies of long-term w ater quality from the basin of Yantra river.