文摘
Although it has been documented that waterfowl can cause water quality problems when their populations are large relative to the size or volume of the water body, the question as to how many waterbirds a wetland or a lake can support remains unanswered. A method to quantify the carrying capacity of a water body with regard to massive waterfowl was developed through the study of five wetlands that are used as the wintering ground by a large number of waterfowl in Japan. It takes into consideration water depth, retention time, and in-lake phosphorus concentration. For one of the sites, Sakata Lagoon, which is a registered Ramsar wetland in Japan, the assessment of its carrying capacity suggests that the number of waterfowl should be reduced by half to sustain the water quality of this wetland. Based on the comparison among the five wetlands, a simple indicator was proposed for quick diagnosis. Moreover, a general plot of permissible loading of phosphorus (kg/ha/year) by waterfowl was presented. Besides, this study shed some new light on potential toxicity and accumulation of waterfowl feces at lakebed. Finally, a proposal to increase the carrying capacity of Sakata Lagoon is discussed.