Relation between nitrate concentration and water runoff in Lithuanian middle-sized river: the Šušvė case study

Abstract

The paper presents the study results and analysis of the relationship between nitrate concentration and water runoff in the river Šušvė within the period of 1992–2004. Both nitrate concentration and runoff changes during a year take a form of sinusoid curve. During the cold season of the year (November–April) the concentration was on the average 1.2–2.1 times higher than in the warm season (May–September). Dependence of the average nitrate concentration on the runoff is expressed by second degree polynomials. Maximum values of concentrations were observed when the annual average runoff was 12 l s-1 km-2 and the discharges during the cold and warm periods were 12 l s-1 km-2 and 8 l s-1 km-2 respectively. The annual distribution of nitrate concentrations is close to Weibull and corresponds to inherent distribution of water runoff from watershed. There exists a relationship between the runoff and nitrate concentration probability. Higher runoff predicts probability for higher concentration to occur. A mode of the concentration in river Šušve is 3–4 mg l-1. Based on the results from this study, river Šušvė pollution can be predicted on a basis of the river water discharge.