The average negative trends for TNC and TNL are stronger in the east (32.2 μg l−1 yr−1, 7.4 kg km−2 yr−2) than in the west (8.7 μg l−1 yr−1, 1.6 kg km−2 yr−2) while positive trends are low in both the east and west (Table 2). On the contrary, positive trends for TPC and

TPL in the eastern catchments HIF inhibitor are stronger (2.5 μg l−1 yr−1, 0.39 kg km−2 yr−2) than in the west (0.5 μg l−1 yr−1, 0.12 kg km−2 yr−2) while negative trends are low in both the east and west. For the aggregated yearly time series, the Mann–Kendall trend test confirmed significant trends for TNC (both east and west), TNL (west), TPC (east) and TPL (east and west) (Fig. 1d, e, f and g). Clear differences were found between east and west (Fig. 3c) in terms of significant changes in the N:P ratio. 71% of the eastern catchment area showed a negative trend in the N:P ratio with an average decrease of 1.3 yr−1. 15% of the western catchment area exhibited a negative trend in the N:P ratio with an average decrease of 0.6 yr−1 while 37% of the western area has a positive trend of 0.4 yr−1. In the eastern catchments the N:P ratio declined over time from a ratio of almost 30 in 1970 to a ratio of almost 16 in 2000 (Fig. 1h). In the western catchments the N:P ratio appeared 5-Fluoracil in vitro stable at around 20. However, for the aggregated yearly time series, the Mann–Kendall

trend test confirmed significant trends for both the east and west. In order to gather more insight in whether the strength of the trend in one variable influences the strength of the trend in another variable, Kendall’s rank correlation analysis was carried out based on the slopes

of all significant trends in east and west (Table 3). In the east and west, as expected, a positive correlation (p < 0.05) was found between the increase in precipitation and the increase in discharge (τ = 0.4 for east and τ = 0.2 for west) as more precipitation will in general lead to more discharge ( Bae et al., 2008). However, a positive correlation (p < 0.05) was also found between TNC and discharge in the east (τ = 0.4), which was not expected as more click here discharge will in general dilute the concentration. In the west, a positive correlation (p < 0.05) was found between TNC and TPC (τ = 0.2), meaning that if the strength of the trend of one nutrient increases, the strength of the trend in the other nutrient will also increase (or vice versa). In the west, the strength of the trend in temperature has a positive correlation (p < 0.05) between TNC and TPC (both τ = 0.2). Hence, in western catchments where temperature increase is high, trends in TNC and TPC are also high. However, as expected, a negative correlation (p < 0.05) was found between temperature and discharge (τ = −0.3) as higher temperatures generally evaporate more water leading to decreased discharge. Please note that both temperature and discharge in most western catchments are increasing ( Fig. 2a and c).