# Preliminary Analysis of the Water Quality Status in an Urban Mediterranean River
## 2 Materials and Methods  
### Study Area and Sample Collection  
Kifisos river, including various spellings of the name (Kifisos, Cephissus, Kephisos), flows through Athens city and reaches the Saronic Gulf in the western part of Athens metropolitan area (~3.8 million inhabitants). It operates as major drainage channel for a large part of Athens. Its catchment area extends ~420 km\({}^{2}\) with the river main route length being approximately 29 km. Most of the year, water discharge is low (~3.2 m\({}^{3}\) s\({}^{-1}\)), but during flood events, the water fluxes may reach up to 1400 m\({}^{3}\) s\({}^{-1}\)[20]. According to a previous study [21], certain sections of the Kifisos drainage network, particularly in the central and north-western parts, are vulnerable to flood phenomena. Surface elevation differs between upland and low-land areas, ranging from 1350 m to sea level elevation in its estuary, while the mean elevation of the catchment area is 284.9 m. According to previous studies, approximately 65% of the geological formations are alpine, and the rest are meta-alpine formations [22]. Concerning land use, Kifisos catchment is characterized by multiple anthropogenic pressures, mainly industry, agricultural and residential use. The built-up areas (houses, roads, industries) cover most of the downstream parts of the catchment, and are estimated to exceed 70% while they are still increasing [23]. At two distinct parts along the Kifisos route, industries and manufacturing businesses have been operating on both sides of the river, functioning as unplanned and informal industrial zones. In the upstream areas, forests and shrubland are dominant, but have been significantly impacted by 2007 and 2019 wildfires. This is also where land used for agricultural and livestock use is located. Kifisos has undergone extensive river engineering in the last 13 km of its route, addressing issues of flood control, drainage system management and the road network; Kifisos river is canalized, alternating from fully boxed to open cross-section embankment. As a result, its riparian zone for this stretch was practically eliminated. Moreover, Kifisos Avenue a high-traffic-density road, and the central axis of Athens highway network was constructed over the canalized river. Five sampling locations were selected that are distributed along the drainage catchment from its upstream part, where limited pollution sources exist, to the river mouth (Figure 1). Monthly water surface collection was conducted in between 10:00 a.m. and 1:00 p.m. from May 2021 to April 2022 at five sampling sites (K Ekv, K 5, K 12, K 17, K MD). Physicochemical parameters such as dissolved oxygen (DO) (mg/L), electrical conductivity (EC) (\(\mu\)S/cm), temperature (T) (\({}^{\circ}\)C), pH and salinity (ppt) were measured on-site by a portable water quality multiparameter instrument (YSI ProDSS). Surface water samples were collected in sterile bottles, preserved by the addition of HgCl\({}_{2}\), stored in a cooler box and subsequently transferred to the Hellenic Centre for Marine Research (HCMR) laboratories to further analyze concentrations of NO\({}_{3}\)\({}^{-}\)-N (mg/L), NO\({}_{2}\)\({}^{-}\)-N (mg/L), DIN (mg/L), TN (mg/L) and TP (mg/L). Additionally, the output of the analyses was used to estimate the Hellenic Water Quality Index (HWQI) according to a Nutrient Classification System (NCS) initially developed by [18] and modified to include dissolved oxygen concentrations. Based on the values of five nutrient species along with dissolved oxygen levels, HWQI classifies water samples into five water quality categories: bad, poor, moderate, good and high, according to the requirements of the WFD (2000/60/EC). For microbiological analysis, water samples were collected separately in 1 L sterile containers for the quantification of _E. coli_ according to the International Organization for Standardization (ISO) method/protocol (ISO 9308-1:2014), which specifies the method for the enumeration of _Escherichia coli_ (_E. coli_).