floating treatment wetlands; shallow lake; eutrophication; nature-based solution; internal loading; biogeochemical cycling https://unilib.phaidrabg.rs/o:9833 doi:10.3390/w18121485 ISSN: 2073-4441 Abstract: Eutrophication remains a persistent water-quality problem in shallow lakes, where exter-nal inputs interact with internal loading and biogeochemical cycling. Although floating treatment wetlands (FTWs) are increasingly promoted as nature-based solutions for water remediation, their field-scale interpretation in hydrologically complex eutrophic lakes re-mains challenging. This study examined the spatial organization of water quality during the operation of a floating-island system in a eutrophic urban lake affected by polluted tributary inflow. The study was not designed to quantify isolated FTW removal efficiency, but to evaluate spatial water quality organization during FTW operation under real-use field conditions. Water quality was monitored over two growing seasons across six func-tionally defined zones, and spatial and temporal patterns were analyzed using descriptive statistics and linear mixed-effects models. The results showed parameter-specific spatial structuring rather than a uniform treatment response. The clearest inlet-lake contrasts were observed for electrical conductivity (EC), suspended matter (SM), and nitrate nitro-gen (NO3-N), whereas biochemical oxygen demand (BOD5), ammonium nitrogen (NH4-N), and total organic carbon (TOC) showed lower values at the inlet and higher values in downstream zones. Dissolved oxygen (DO), oxygen saturation (SO), chemical oxygen de-mand (COD), nitrite nitrogen (NO2-N), and orthophosphate phosphorus (PO4-P) showed moderate or non-robust zonal effects. These findings indicate that FTWs in shallow eu-trophic lakes should be evaluated through functional zoning and parameter-specific in-terpretation rather than as isolated units with uniform removal responses. Field-Scale Spatial Organization of Water Quality During Floating-Island Operation in a Eutrophic Urban Lake info:eu-repo/semantics/article 2026 application/pdf 1087965 bytes eng Multidisciplinary Digital Publishing Institute (MDPI) Water startpage: 1485 endpage: 1485 Čule, Nevena Lučić, Aleksandar Nešić, Marija Češljar, Goran Đorđević, Ilija Božović, Jelena Popović, Vladan http://creativecommons.org/licenses/by/4.0/legalcode