Abstract: The eutrophication of urban lakes aggravates as the ecosystem function declines. Eutrophication of urban lakes is usually characterized by phosphorus limitation, while phosphorus mainly settles in sediments. Studying the content and distribution of phosphorus in lake sediments is of crucial significance to exploring its pollution status and controlling lake eutrophication. Yanglan Lake is a typical urban lake subjected to eutrophication in recent years. In this research, we took Yanglan Lake as a case study to probe into the content and spatial distribution of total phosphorus (TP) in surface sediments and assessed the status of phosphorus pollution by using single factor index method. Furthermore, we also examined the morphology and vertical distribution of phosphorus in sediments in three representative regions. We found that the TP concentration in surface sediments of Yanglan Lake ranged from 528 to 3 568 mg/kg, averaging 1 096 mg/kg. The west of the lake saw the highest TP concentration, averaging 1 362 mg/kg. The pollution index of TP in surface sediments ranged between 0.88 and 5.95, implying that the sediments in the whole lake area were polluted with phosphorus to different degrees. The lightly polluted area accounted for 9.38% of the whole lake area, moderately polluted area 32.81% and severely polluted area 57.81%. In addition, the proportion of exchangeable phosphorus was relatively small, whereas the proportion of Fe/Al bonded phosphorus in the sediments was the highest, which was the major source of phosphorus release in the sediments of Yanglan Lake.

Key words: urban lake, surface sediments, TP, distribution characteristics, pollution assessment, Yanglan Lake