oa Chlorophyll and Water Quality Monitoring Results in the Zmiinyi Island Coastal Waters in 2004 – 2021

Purpose of the work. The study of the long-term changes in Chlorophyll a concentration and water quality in the Zmiinyi Island coastal waters. Data and Methods. Chlorophyll was determined using a standard spectrophotometry method. Water quality was assessed using the TRIX trophic index. The results of study. Chlorophyll a concentrations (0.02–28.03 μg/l) corresponded to the status of mesotrophic and eutrophic seawaters with maximal annual average values 1.87, 2.70, 2.05 μg/l in 2004, 2005, 2009 and minimal 0.62, 0.55 μg/l in 2019 and 2021 according. From 2004–2008 to 2018–2021 the average concentration of Chlorophyll decreased by a factor of 2 (surface) and 1.5 (bottom). The TRIX index range (3.0–7.2) covered trophic levels from oligotrophic to very hypertrophic, most corresponded to mesotrophic (43%) and eutrophic (43%) status with a tendency towards improvement of the condition in 2019–2021. Chlorophyll concentrations and TRIX index closely correlated with transparency, salinity, total nitrogen and phosphorus readings. Conclusions. The trophic state of seawaters in the Zmiinyi Island area corresponded to meso-eutrophic status (2004–2021), with a quality improvement in 2018–2021. Statistical interconnections between Chlorophyll and TRIX with physical and chemical characteristics indicated a priority contribution of the freshened Danube waters to the critically high trophic level of seawaters.