Stimulating effects of whooper swans’ behaviors on nutrient releasing from the sediments caused by different human feeding intensities in the swan Lake, China

Abstract

In many shallow water lakes of China, as the numbers of tourists observing waterflow increases, the amount of supplemental food provided to waterflow also increases. However, little attention has been paid to the role of waterfowl’s behavior perturbation in N and P nutrients releasing from the sediment. In this study, five feeding experiments were undertaken in the Swan Lake (Shandong Province, northern China) during the wintering season and a noticeable release of nutrients in all experiments was found by the disturbance of the swan behaviors. The release of TN and TP was through three stages including the non-release stage, the rapid release stage, and the stable release stage. Moreover, supplemental food also influenced the swan behavior changes and triggered the frequency of the swans’ grazing and aggression. The aggressive behaviors among the swans stirred nutrient (N & P) releasing from sediments and altered TN and TP concentrations in the water columns, indicating that the aggressive behaviors may be a significant factor in affecting the TN and TP releasing from the sediment. Human feeding intensity (HFI) suggested > 850 g of supplemental corn can be an optimal way to aid in avoiding foraging competition among the swans to control nutrient release by three levels of human feeding intensity assessment. Our findings demonstrate that under the swans’ optimal foraging need in natural versus artificial feeding scenarios, the swans acted as biological pumps to increase nutrient release. There is a need for a systematic and evidence-based feeding strategy for swans, with greater restrictions on the provision of small food items scattered by visitors. Our study provided novel insights into the release mechanism of N and P from bioturbation and could help to inform a whooper swan conservation strategy in coastal wetlands and nature reserves.