Effects of weather conditions on water quality in two small boreal rivers.
Arvola, Lauri; Hakala, Ilpo; Järvinen, Marko; Huitu, Eeva; Mäkelä, Suvi
Water chemistry data on two small boreal rivers in southern Finland were analysed in relation to local and regional (NAO) weather conditions. The data set was based on daily weather and runoff measurements and weekly chemical sampling. The data set started in autumn 1994 and continued until the end of 2000. The results indicated that air temperature and precipitation explained a high proportion of the annual and seasonal variability in water quality in these two rivers. However, the relationships between the weather and water quality variables were masked by time lags in hydrology, seasonality and complexity of the affecting factors. Based on the regression analyses of the different seasons, the seasonal and annual nutrient concentrations could be modelled adequately using hydrological data. This implies that weather conditions are among the most important driving forces in determining the nutrient concentrations of the out-flowing waters in these boreal drainage basins. The results indicate that, in terms of nutrient leaching from the drainage basins, the most sensitive periods of the year are late autumn and winter. At that time the regional and local weather conditions were highly correlated, as were the local weather and discharge. In the short-term, the most critical meteorological factors appear to be air temperature and precipitation, since they strongly affect nutrient leaching and transportation from the drainage basin.