A holistic approach to the spatio-temporal variability investigation of the main river water quality - The importance of tributaries

The surface water pollution can cause serious ecological disasters. An example is large-scale fish deaths due to excessive salinity, which is global problem. In order to prevent such situations, it is necessary to carry out regular monitoring of both main rivers and their tributaries. The current monitoring system is neither adapted to the variability associated with the diversified use of catchments nor to changing climatic conditions. The Bzura River is one of the most anthropogenically transformed Polish rivers. So far, no comprehensive assessment of the chemical status of its catchment has been carried out. The presented research is a continuation of the study of the spatio-temporal variability of the Bzura chemistry. It covered 19 tributaries within the boundaries of the L ' odz ' Voivodeship. Samples were collected once a month for one hydrological year. In total, 228 samples were obtained, in which 21 parameters were measured. Spatio-temporal variability of water quality on the basis of coefficients of variation (CVs) and water quality indices (WQIs) was evaluated. Principal component analysis (PCA) and cluster analysis (CA) were also performed. In addition, the datasets were visualized using geochemical maps. Combined monitoring with geospatial analysis brings benefits in terms of efficient control and management of water resources. The tributaries were divided according to the degree of their pollution. It was found that the electrical conductivity and concentrations of dissolved oxygen, nitrates, calcium and magnesium differentiated the tributaries in terms of pollution the most. The strong salinity from agricultural and geogenic sources was found. The WQIs were higher for the tributaries than for the Bzura. It suggests that the Bzura may be polluted by the tributaries under favorable climatic and hydrological conditions. Therefore, smaller watercourses should be included in monitoring and become more important in terms of an effective solution to global problem of surface water pollution.

Automated summary

Surface water pollution can lead to serious ecological disasters, such as large-scale fish deaths due to excessive salinity, which is a global problem. Regular monitoring of main rivers and their tributaries is necessary to prevent such situations. However, the current monitoring system is not adaptable to the variability associated with the diversified use of catchments and changing climatic conditions. This study focuses on the Bzura River and assesses the chemical status of its catchment. The results show that the water quality indices of the tributaries are higher than that of the Bzura River, indicating that the Bzura River may be polluted by its tributaries under favorable climatic and hydrological conditions. Therefore, smaller watercourses should be included in monitoring and become more important in addressing the global problem of surface water pollution.