The assessment of aquatic ecosystem services for polder in Taihu Basin

Today,the polder area,which is an important geographic unit in economically developed Taihu basin,comprise10,630. 91 km2,accounting for 28. 81% of the total basin area. A polder is an artificially created ecosystem in a low-lying zone of land adjoining a lake,river or other water body and enclosed by dikes. It can effectively prevent flooding and alleviate drought by controlling the influx of water with manually operated devices,thus ensuring the orderly development of industry and agriculture. Polder waters including river and pond are the lifeline of the polder ecosystem and maintain its overall stability,which directly affects other ecosystem functions. Therefore,quantitative estimation of polder aquatic ecosystem services is beneficial to deepening the understanding of its status in the basin ecosystem. This study has important theoretical and administrative significance for the optimal regulation of the ecosystem structure and reasonable allocation of water resources in the Taihu basin. The polder aquatic ecosystem services and their spatial variability in the Taihu basin were analyzed using the established evaluation index system based on the remote sensing image, meteorological,hydrological,and fieldwork data. The results showed that the polder aquatic ecosystem supplied 8. 61 × 108m3/ a of water,provided 58. 74 × 104 t / a of aquatic products,7. 17 × 108m3/ a of regulated water and 27. 12 × 108m3/ a of stored water,reduced 3. 62 × 104 t / a of nitrogen and 1. 10 × 104 t / a of phosphorous,controlled 4. 30 × 108m3/ a of flooding water,assimilated 129. 08 × 104 t / a of carbon and produced 153. 60 × 104 t / a of oxygen,maintained biodiversity at 1. 34 in terms of Shannon' s diversity index,and lowered summer temperature for 2. 27℃. The total value of polder ecosystemservices in Taihu basin was estimated at 325. 93 × 108 yuan / a. About 13. 93% of the estimated value came from the provisioning services including fresh water and aquatic products. About 83. 92% was contributed by regulation services including water regulation,water storage,water purification,flooding control,temperature regulation,carbon fixation,and oxygen production. Cultural services accounted for 1. 41% and supporting services including biodiversity maintenance made up 0. 74%. Thus,the regulating function predominated in the total value. The values of various services are in the ordered of: water storage water regulation aquatic products flood control carbon fixation oxygen production scientific research and culture water supply biodiversity maintenance nitrogen reduction phosphorus reduction temperature regulation. The value of the polder aquatic ecosystem services was dominated by the indirect value,which was 6. 18-fold larger than the direct value. Because of the different water surface area,the value of the total services of each subregion was as follows: Hangjiahu Yangchengdianmao Huxi Zhexi Wuchengxiyu Puxi Taihu Pudong. The average value of aquatic ecosystem services per unit area of the polder in the Taihu basin was 22. 73 yuan m- 2a- 1. Water supply,aquatic products,water regulation,water storage,nitrogen and phosphorus reduction,flood control,temperature regulation,carbon fixation,oxygen production,research culture,and biodiversity maintenance were worth 0.30,2. 87,3. 43,12. 96,0. 04,0. 02,1. 26,0. 02,0. 92,0. 43,0. 32,and 0. 17 yuan m- 2a- 1,respectively. The aquatic ecosystem service benefits per unit area of the Taihu basin were higher in the west and the south than in the east and the north. This paper provides scientific guidance for proper management of aquatic ecosystems and ecological restoration,which employ differentiated measures to address main environmental problems of each subregion.