# Integrated Assessment of Surface Water Quality in Danube River Chilia Branch
## 3 Results and Discussion  
The statistical analysis of the nutrient concentrations from the Chilia branch surface water requires methodologies that allow the evaluation of trends and a high degree of confidence. Combining spatial analysis by using GIS tools with nutrient concentration data, an easy-to-visualize product can be obtained, helpful for water quality management [28]. Ammonium nitrogen is present in the surface water of the Chilia branch at very low concentrations, which do not exceed the limit value corresponding to good ecological status [32]. With one exception (Periprava 2014), nitrite nitrogen does not exceed the standard quality. Nitrate nitrogen, phosphorus from orthophosphate, and total phosphorus also do not exceed the standard limits (Table 2). Due to organic nitrogen, total nitrogen has a different variation with highest values (over the maximum limit) in 2015 at sampling points and also in 2018 (Bastroe downstream). The high content of organic nitrogen, compared to the low content of inorganic nitrogen, is due to the fact that organic nitrogen seems to be assimilated by aquatic organisms at a much lower rate than inorganic forms of nitrogen [34]. In addition, some nitrogen contained in organic matter usually resists bacterial action and remains in water or sediment [35]. Analyzing the minimum and maximum values during the investigation period, the maximum values were observed as follows: Izmail downstream (ammonium nitrogen), Periprava (nitrite nitrogen and total nitrogen), and Ceatal Chilia (nitrate nitrogen, dissolved and total phosphorus). For the corresponding period, the minimum values were determined in surface water from Ceatal Chilia (ammonium nitrogen), Bastroe upstream (nitrite nitrogen), Izmail downstream (nitrate nitrogen and total nitrogen), and Periprava (dissolved and total phosphorus) (Table 5). Taking into account the negative values of flattening index, Kurtosis, of ammonium nitrogen concentrations (Ceatal Chilia, Periprava, Bastroe upstream and downstream), nitrite nitrogen concentrations (Izmail upstream), nitrate nitrogen concentrations (Izmail downstream, Bastroe upstream and downstream), total nitrogen (Izmail downstream, Bastroe upstream and downstream), dissolved phosphorus (Bastroe downstream), and total phosphorus (Izmail downstream, Bastroe upstream and downstream), the distributions are platykurtic, flat, which means that the values of their concentrations are very  
Figure 3: Grid processing steps: up—grid creation for the whole area, middle—altering the grid to the river flow, down—graduated quantile classes of the interpolated data. scattered compared to the average value expressed in mg/L and indicate a high degree of heterogeneity of the determined concentrations. For the other indicators, kurtosis index is positive, so the concentration distributions are leptokurtic, sharp, which means that the concentration values are very close to the average values, with a high degree of concentration homogeneity. According with asymmetry index, skewness, which is negative, the distributions of ammonium nitrogen concentration from Bastroe upstream and downstream and dissolved phosphorus concentration from Periprava are asymmetrical at the left, that means that the high concentrations predominate and the low concentrations are considered extreme concentrations. The positive values of Skewness index computed for the rest of the chemical indicators/sampling points, means that the concentration distributions are asymmetrical at the right; low concentrations predominate and high concentrations are considered extreme. At computing the CCM WQI using Equation (1) given in Table 3, the Romanian guidelines stipulated by Order MEWM 161/2006 ([PERSON], 2006) were taken into account in this work, using the standard limits for the \"good\" water quality class.