A heterogeneity of water and sediment nitrogen removal patterns in shallow lakes: implications for lake management

Large shallow lakes are strongly influenced by wind-induced wave disturbances, which lead to the transportation of nutrients from sediments into the water column, potentially facilitating more active nitrogen removal processes in the water column. However, the related rates and contributions remain unclear, prompting the present study. The results show that nitrogen removal in the water column of Taihu Lake contributes 43 % annually, with anammox being the dominant process in the water column, while denitrification dominates in the sediments. Significant spatiotemporal differences in nitrogen removal mechanisms were observed between the water column and sediments. The rate of anammox in the water column is relatively higher in spring and winter, while denitrification in the sediments is highest in spring. Further random forest analysis revealed that chlorophyll a is a significant factor influencing sediment denitrification, while NO₃^--N and NH₄⁺-N are key contributors to sediment anammox, water column denitrification and anammox. This study enhances our understanding of nitrogen removal mechanisms in both the water column and sediments of large shallow lakes.