Evaluation of Seasonal Changes in the Eutrophication Index and a Eutrophication Alleviation Technique in Osongji (Osong Pond), Jeonju-si, Korea

Excessive inflow of nitrate and phosphate is a major cause of eutrophication in surface water systems. Eutrophication induces the excessive growth of photosynthetic organisms, leading to the occurrence of algae blooms. Therefore, treating excessive nutrients can be an essential method to alleviate eutrophication. This study aimed to assess the seasonal changes in the eutrophication status in a lake and to evaluate the potential of using Ca-citrate complex for the simultaneous treatment of nitrate and phosphate in the lake environment. Osongji (Osong Pond), a small lake located in Jeonju-si, Korea, was selected as the study site, and the changes in physicochemical parameters and the Korean Eutrophication Index (TSI_KO) were used to evaluate the changes in the eutrophication status in the lake. In addition, a eutrophication alleviation technique using ca-citrate complex, was tested under three experimental conditions. The experiments included the application of Ca-citrate complex reagent every two weeks (T1; prevention) or one-time application (T2; one-time application). Closed (T3) and open (T4) controls (without application of the Ca-citrate complex) were also included for comparison. Analysis of seasonal changes in the eutrophication status was conducted every two months from November 2022 to September 2023, and the Ca-citrate complex experiments were conducted from June to September 2023. The results showed that Osongji had the eutrophic condition from November 2022 and the hypereutrophic condition from June to July 2023, and it returned to the eutrophic condition in August 2023. The evaluation of the eutrophication alleviation technique using ca-citrate complex indicated that, in T1 with periodic application, lower TSI_KO values maintained compared to the control groups without Ca-citrate complex. In the T2 condition with a one-time application, total phosphorous (T-P) and total nitrogen (T-N) decreased two weeks after application, and TSI_KO also decreased. In conclusion, the application of Ca-citrate complex reagent in the lake environment had effectiveness in preventing and alleviating eutrophication. This study can contribute to assessing the degree of eutrophication in a surface water system and developing management strategies for prevention or alleviation of eutrophication.