Planting Trees in Buffer Strips for Attenuating Phosphorus Runoff in Jiangsu Province, China

In the last four decades, the Jiangsu province, like the rest of China, has undergone rapid economic development coupled with a rapid increase in environmental pollution. Freshwater ecosystems have been particularly affected. In Lake Tai, China's third-largest freshwater lake by volume, water quality has been severely reduced. There is a renewed interest in establishing riparian buffer strips in China as a conservation practice for mitigating agricultural non-point source pollution. To study the effect of riparian buffers on phosphorus attenuation, eight 50 m x 20 m plots were established between a rice farm and the shore of Lake Tai in China, with the 20 m width facing the lake shore. They were planted with hybrid poplar (Populus deltoides x euramericana), hybrid cypress (Taxodium ascendens x mucronatum), or a mixture of both at densities of 2 m x 3 m, 2 m x 5 m, or 5 m x 5 m, while one plot was left as a control. Samples collected from soil, tree leaves, and groundwater during 2014-2018 were analyzed for multiple forms of phosphorus. Results indicated that riparian buffer width and time (year) were the most significant factors of phosphorus attenuation on all plots. Tree density had a minor effect, with medium density being the most effective, and we found negligible differences among hybrid tree species on attenuating phosphorus. Farmers should use densely vegetated buffer strips at least 15 m wide to ensure a significant reduction in nutrient runoff. Species selection should be based on market value and ecological benefits. Overfertilization of rice paddies is a systemic issue in China, with little incentive for farmers to change their practices. Riparian buffer strips can serve as an economically viable best management practice (BMP) for alleviating eutrophication on rice farms. A riparian buffer with a width of at least 15 m and medium tree density was found to be the most effective for attenuating phosphorus runoff.