# Integrated Assessment of Surface Water Quality in Danube River Chilia Branch
Management of water quality intended for various uses requires not only strict monitoring of its parameters and simple comparison of monitoring data with allowable values of hazardous chemicals stipulated by the instructions and the European Union (EU) Water Framework Directive (WFD) [18] imposed by EU member states, but also involves methods and mathematical instruments to interpret, group, and communicate information regarding the water quality status in a specific area within the wider context of human activity and use and the conservation of the natural environment [1; 19]. Thus, it is very important to build an integrated assessment model of each water body, using a water quality index (WQI), which is a useful tool that allows decision-makers and the public to receive simplified and reliable water quality information, assess tendencies for changes in water quality, and classify water according to various impairment categories [8; 20]. A quality index is an unitless number that ascribes a quality value to an aggregate set of measured parameters [21]. Over time, several WQIs have been developed, such as the NSF WQI-National Sanitation Foundation Water Quality Index (additive (AWQI) and multiplicative (MWQI) forms), CCME WQI-Canadian Council of Ministers of Environment Water Quality Index, BC WQI-British Columbia Water Quality Index, and OWQI-Oregon Water Quality Index. These have been extensively used for various assessment tasks in a particular region for a water body [1; 14; 22; 23; 24; 25; 26]. Detailed description of the main WQI calculations are reviewed in several synthetic works [1; 5; 20; 23; 24; 25; 26]. CCME WQI is the most popular index, with its applications presented in many journal papers, technical reports, and governmental agencies reports [20]. It allows flexibility for index users to select those water parameters which can be easily adapted for local conditions and issues, in the same time assuring a clear and intelligible diagnostic for managers and the general public [1; 20; 26; 27]. Moreover, the United Nations Environmental Program (UNEP) has endorsed the CCME WQI model as suitable for grading the quality of drinking waters worldwide [26]. In order to evaluate the water quality trends, the method could be coupled with Geographical Information System (GIS) techniques for building distribution maps [13; 28]. Information on the nutrient composition of Danube water in the Chilia branch in the last decade is very scarce [10; 13]. The main objectives of this study were two-fold: (1) to evaluate the water quality in the Chilia branch of the Danube River in terms of single indicators expressed in nutrient concentrations and in terms of CCME WQI integrated index, and (2) to represent, using GIS techniques, the distribution maps of the seven year (2013-2019) measurement datasets monitoring of the complex index, along the study area. The approach of the present study had as a premise the integration of the concentrations of a single class of compounds, nutrients, both at dissolved and total level, in a single complex indicator indicating the degree of eutrophication along the Chilia arm. In subsequent studies will be addressed the other classes of pollutants, namely oxygen regime, metals, salts, integrating their concentrations in complex quality indicators.