Analysis of the Spatiotemporal Changes in Enclosed Aquaculture Areas in Hongze Lake, China, Over the Past 40 Years and Their Impact on the Water Environment

Enclosed aquaculture has brought about higher yields and better economic benefits, but it is undeniable that it has also led to the accumulation of excreta from fish, shrimp, and crabs in water bodies, posing challenges to the control of eutrophication and the protection of biodiversity in lakes. One of the challenges in assessing the impact of the extent of enclosed aquaculture areas on the water environment lies in the often difficulty of obtaining accurate measurements of the area of cage aquaculture areas. Here, we constructed an object-oriented extraction method, with an average accuracy of 92.96% on the validation dataset, based on random forest model using multi-period Landsat remote sensing images to identify enclosed aquaculture areas in Hongze Lake from 1984 to 2024. The regression analysis is conducted between the observed annual sequence values of water environmental factors, including TN, TP, SD, Chla, and the extracted area values of enclosed aquaculture areas. The results show that the area of enclosed aquaculture in Hongze Lake exhibited an evident increasing trend since 1992, reaching its peak in 2002 at approximately 600 km2. The increasing of the area of enclosed aquaculture led to higher concentrations of TN and Chla in the lake.