An integrated methodology to estimate the contribution of environmental factors controlling the spatial variation of total dissolved solids. Application on Jiu River Basin (Romania)

The variation of the total dissolved solids (TDS) in river water is highly dependent on the natural and anthropogenic features of the TDS source areas, namely the river basins upstream of the measurement points. Despite the significant theoretical knowledge on the factors governing the TDS variation in rivers’ waters, the quantification and modelling of the role of different environmental variables influencing the TDS has been less investigated. The objective of our work is to develop a methodology for estimating the contribution of the most significant natural and anthropic factors to the spatial variation of TDS, by integrating GIS and statistical tools. The methodology was applied on the Jiu River Basin (10,070 km2), located in SW Romania, covering different landforms (mountains, hills, plains) with diverse lithology, soils and land cover, as well as with various economic activities (one of which is coal mining). The study is based on TDS measurements on Jiu River and its main tributaries, performed during the summers of 2016, for the method setup, and of 2017, for the method validation, in periods of low and medium waters. The baseline factors considered in our analysis as primarily responsible for the TDS concentration were: rock types, vegetation cover, soil types, relevant human activities (types of industry and agricultural activities in the valleys and in the upstream river basins). For each catchment corresponding to the measurement points, we mapped the above-mentioned factors. Subsequently, using the principal component analysis (PCA) and a regression model, scores were assigned to calculate the importance of each class of influence factors, in order to quantify the contribution of these factors to the TDS. The results showed that lithology (the dominance of the marls) and soil texture (clayey soils) play the main role in explaining the TDS concentration measured during the 2016 field campaign, followed by the presence and type of industry (particularly coal extraction) and agriculture. Finally, we verified the regression model based on the measures performed in 2016, by running a sensitivity analysis on the TDS values measured in 2017. The development of an integrated methodology to improve the understanding of the relationship between the rivers’ TDS and the environmental drivers has reduced the uncertainty over the contribution of some factors to the TDS variation, which, until now, had been considered mostly theoretically.