# Integrated Assessment of Surface Water Quality in Danube River Chilia Branch
## 2 Materials and Methods
### Chemical Analysis  
The surface water samples were taken from the water column (0-60 cm) according to European standards [29], preserved and properly stored in polypropylene containers. Dissolved nutrients (ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, orthophosphate) and nutrients in total forms (nitrogen and phosphorus) were analyzed at Danube Delta National Institute for Research and Development, Tulcea, Romania, in a chemistry laboratory accredited since 2005, according to the ISO/IEC 17025, by manual spectrophotometry, using a UV-VIS Lambda 10 Perkin Elmer spectrophotometer and ISO standards. The selected nutrients were converted by wet-chemical treatment into colored compounds with high molar absorptivity [30] that enabled low detection limits and low quantifications limits of each chemical indicator [31]. The quality assurance of chemical analysis was carried out using certified reference materials in flow charts. The parameters used in this work for nutrient analysis in Danube water samples are presented in Table 2.  
Method of Evaluation of Chilia Branch Water Quality, Using the Canadian Council of Ministers of Environment Water Quality Index (CCME WQI)  
In order to evaluate the water quality, after measuring the nutrient concentrations, another step is to report these values to quality standards, according to national legislation, Romanian Order MEWM 161/2006 [32], which transposes WFD and gives different quality classes, not a general quality. In addition, to achieve a general quality class for a selected surface water body, it is necessary to develop and to use integrated indices, that combine a sufficient number of chemical indicators in order to provide a single quality class for a water body. The Canadian Council of Ministers of Environment Water Quality Index, CCME WQI, is a suitable tool for surface water quality evaluation, from the chemical point of view, with no combination with other indicators or biological data, but with flexibility in the selection of input parameters (nutrients) and objectives. For computing this indicator, it is required to take into account at least four chemical indicators and four samples [22; 23; 26]. CCME \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sampling Point**} & \multirow{2}{*}{**Label**} & \multicolumn{2}{c}{**Geographical Coordinates**} \\ \cline{3-4}  & & **N** & **E** \\ \hline Ceatal Chilia & CC & 45\({}^{\circ}\)13.716\({}^{\prime}\) & 28\({}^{\circ}\)44.157\({}^{\prime}\) \\ Izmail Downstream & ID & 45\({}^{\circ}\)16.793\({}^{\prime}\) & 28\({}^{\circ}\)56.137\({}^{\prime}\) \\ Periproava & P & 45\({}^{\circ}\)24.051\({}^{\prime}\) & 29\({}^{\circ}\)33.867\({}^{\prime}\) \\ Bastroe Upstream & BU & 45\({}^{\circ}\)20.659\({}^{\prime}\) & 29\({}^{\circ}\)38.600\({}^{\prime}\) \\ Bastroe Downstream & BD & 45\({}^{\circ}\)19.975\({}^{\prime}\) & 29\({}^{\circ}\)39.337\({}^{\prime}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Geographical coordinates of sampling points from Chilia branch. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Nutrient**} & \multicolumn{4}{c}{**Parameters**} \\ \cline{2-5}  & **Detection Limit** & **Quantification Limit** & **Standard Limit** & **Analysis Standard** \\  & **[mg/L]** & **[mg/L]** & **[mg/L]** & **Analysis Standard** \\ \hline Ammonium nitrogen (N-NH\({}_{4}\)\({}^{+}\)) & 0.028 & 0.090 & 0.80 & SR ISO 7150–1: 2001 \\ Nitrite nitrogen (N-NO\({}_{2}\)\({}^{-}\)) & 0.0007 & 0.0024 & 0.03 & SR EN 26777: 2002 \\ Nitrate nitrogen (N-NO\({}_{3}\)\({}^{-}\)) & 0.006 & 0.021 & 3.00 & SR ISO 7890–3: 2000 \\ Total nitrogen (TN) & 0.030 & 0.0110 & 7.00 & SR EN ISO 11905-1:2003 \\ Orthophosphate (P-PO\({}_{4}\)\({}^{-}\)\({}^{3}\)) & 0.002 & 0.010 & 0.20 & SR EN ISO 6878: 2005 \\ Total phosphorus (TP) & 0.003 & 0.010 & 0.40 & SR EN ISO 6878: 2005 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Detection and quantification limits for nutrients.