## 3 Results
### Hydrometeorological Conditions in the Catchment of the River Swierszcz
#### 3.2.3 Analysis of Selected Chemical Indicators  
Table 5 compares the descriptive statistics of the chemical parameters of rainwater with those of flowing water and groundwater. Figure 10 shows box plots of the chemical test results for the analysed types of water. There were no statistically significant differences in the distribution of water pH values (Kruskal-Wallis H = 4.59, \(p\) = 0.204) between the tested measurement points (Figure 10a). In most cases, rainwater, river water and water from the deep wells met the standard for pH in drinking water [36]. However, rainwater (sampled from points P1 and P2) had reduced pH values \(<6.5\) in several instances in August and September 2022 when there was relatively little precipitation, and the rain could have been \"acid rain\". Compliance with the drinking water standards for rainwater was 90% and 80% for P1 and P2, respectively. In the study, we found significant differences in the content of ammonium ions between the tested water groups (Kruskal-Wallis H = 18.05, \(p<0.001\)). Significantly higher differences in the content of ammonium ions were recorded at point P2 than at points P1, P3 (river water) and P4-P7 (deep well water). The acceptable ammonium ion limit of 0.5 mg/L for drinking water was only exceeded in rainwater collected at point P2 (Figure 10b). Compliance with drinking water standards for rainwater was 100% and 40% for P1 and P2, respectively. The increased content of ammonium ions in water samples taken at point P2, similar to the increased bacterial counts at 36 \({}^{\circ}\)C, could have been caused by the contamination of rainwater with bird droppings found on the surface of the roofs from which rainwater was collected. Previously, [PERSON] et al. [13] and [PERSON] et al. [10] also drew attention to this problem. Since these roofs are located in the Animal Breeding Centre in the very heart of the RNP, the number of birds in this place (P2) may be higher than in the town center of Zwierzyniec, where point P1 is located. In the case of nitrates (Figure 10a), no exceedance of the drinking water standard of 50 mg/L was recorded in any of the measuring points (P1-P7). The acceptable limit (0.5 mg/L) of nitrites, on the other hand, was exceeded only once at point P2 (Figure 10d). Compliance with drinking water standards for rainwater was 100% and 90% for P1 and P2, respectively. However, there were statistically significant differences in the content of nitrates and nitrites between the groups (nitrates: Kruskal-Wallis H = 10.44, \(p\) = 0.015; nitrites Kruskal-Wallis H = 14.80, \(p\) = 0.002). The highest contents of nitrates were found in groundwater (P4-P7), but the values were not significantly different from those recorded for rainwater (P1 and P2). In the case of nitrites, the lowest concentrations were recorded in groundwater, and they were significantly lower than those for rainwater sampled at P2 and river water (P3), but not significantly lower than those for rainwater from point P1. There were significant differences in the content of manganese in the tested waters (Kruskal-Wallis H = 20.26, \(p<0.001\)), which resulted mainly from the increased content of this element in the waters of the River Swierszcz (P3) (Figure 10e). At P3, the permissible limit of 0.05 mg/L of manganese in drinking water was exceeded for most of the study period. The limit was also exceeded twice in rainwater sampled at point P2. Compliance with the drinking water standards for rainwater was 100% and 80% for P1 and P2, respectively. Generally, however, no differences in manganese content were found between rainwater and groundwater. Significant differences were also found in the content of total iron between the tested water types (Kruskal-Wallis H = 18.90, \(p<0.001\)). The highest levels of iron, similar to manganese, were recorded in the waters of the River Swierszcz (P3) (Figure 10f). At P3, the permissible limit for iron in drinking water, namely, 0.2 mg/l, was exceeded throughout the study period.