The Sava Bohinjka River is a major tributary of the Sava River that is experiencing eutrophication
caused by high nutrient loading, leading to oxygen depletion. Determining the intensity of nutrient
pollution and identifying nutrient sources in the Sava Bohinjka catchment is desirable for understanding
nutrient dynamics and for informing water quality management strategies. This study analysed the
catchment using the Generalized Watershed Loading Functions (GWLF) model. The model was
calibrated and validated with measured hydrological and water quality data collected at the catchment
outlet. The calibrated GWLF model was used to simulate Discharge, total nitrogen (TN), and total
phosphorus (TP) at the outlet from the Sava Bohinjka River catchment till its confluence with the
Jezernica River (i.e., Sub-catchment 1), from 2007 to 2021. Model performance was evaluated using
statistical measures such as coefficient of determination (R2
), Nash Sutcliffe Efficiency (NSE), percent
bias (PBIAS), and Root Mean Standard Deviation Ratio (RSR). The normality of the residuals between
observed and simulated values was checked using Jarque-Bera (JB) test and Q-Q plot. All performance
ratings were within acceptable range. The results showed that the mean annual TN and TP from the Subcatchment 1 were 21.7 and 0.38 kg/ha, respectively. Groundwater was identified as the primary
contributor to the overall TN load, while pastures were the main source of TP load. Per unit surface area,
cropland contributed the highest nutrient loads, while forests had minimal nutrient export. Comparing
the nutrient loads from the Sub-catchment 1 and from Lake Bled, higher TN export was found in the
former, while the latter appeared to be a distinctive contributor of TP.
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