Gopina G, Mladenova S, Vŭdeva V
Probl Khig. 1992;17:35-42.
The present work gives the possibility to quality the waters of Maritsa, Iskŭr, Danube, Struma, Ogosta, Yantra and Tundzha rivers according to nitrate index, on the basis of monthly investigations for a period of 10 years, after the Unified national system. The rich content of the results and the sufficient period of time give grounds to calculate and draw the direction and rate of the tendency in the nitrate content changes, for this period, for the separate rivers--favourable for Struma, Iskŭr and Danube; with no changes for Ogosta and Yantra; pessimistic for Tundzha.
本研究基于统一国家系统，在10年的时间里每月进行调查，从而能够根据硝酸盐指数对马里查河、伊斯库尔河、多瑙河、斯特鲁马河、奥戈斯塔河、扬特拉河和通扎河的水质进行评估。丰富的调查结果和充足的时间跨度，使得我们有依据计算并描绘出这一时期各条河流硝酸盐含量变化的趋势方向和速率，其中斯特鲁马河、伊斯库尔河和多瑙河的趋势较为乐观；奥戈斯塔河和扬特拉河没有变化；通扎河的趋势则较为悲观。
