Exploration of ecological compensation standard: Based on ecosystem service flow path

Ecosystem service flows are crucial links connecting ecosystems and human well-being. Clarifying the WEF (water-energy-food) service flow paths under the supply-demand balance has significant implications for regional ecosystems and sustainable human development. This study first identified the scale effect for the supply and demand areas of WEF in different periods. Then, this study innovatively used the supply-demand competition-based 2SFCA (two-step floating catchment area) and SPANs (service path attribution networks) model to simulate the WEF supply-demand service flow paths based on different service transport media. Finally, the study proposed a new ecological compensation strategy based on service flows for a WEF service flow after corrected the ecological compensation coefficient. The results showed that (1) The smaller the spatial scale, the more "fragmented" the supply-demand distribution. From 2000 to 2020, WEF services in Northeast China exhibited significant spatial and temporal dynamics. Water and food supplies increased substantially, with water supply average values between 1500 and 2000 t/hm2 across scales and food supply exceeding 4 t/hm2 by 2020, while energy supply slightly declined, and demand for all services showed spatial clustering linked to socio-economic patterns. (2) With the reduction of spatial scale, the WEF flow became intricate and showed dynamic changes. Water service flows mainly increased from north to south and east to west, with most flow ranges between 0 and 200 m3/hm2. Energy service flows moved chiefly from northeast to southwest, with most flows below 100 t/hm2. Food was primarily transported from east to central regions, with flows mainly within 0.3 t/hm2 (3) The spatial scale of ecological compensation schemes was directly related to the amount of compensation. At the municipal scale, water service flows showed a maximum compensation of 1285 million yuan in Harbin and Mudanjiang, while beneficiaries of energy services in western Liaoning received up to 492 million yuan. Due to sufficient supply, no food compensation was required. At the county scale, the highest water compensation was 83.7 billion yuan in Xinglongtai, while western counties generally received below 10 billion yuan. Energy and food compensation beneficiaries were concentrated in Jilin, Kuandian, and Yushu, with maximum amounts of 53.4 billion and 50 billion yuan, respectively, while the primary payers were in densely populated areas. At the subwatershed scale, high compensation payers for water services, such as the Hun and Taizi River watersheds, contributed amounts ranging from 50 million to 1.41 billion yuan, while energy compensation payments reached a maximum of 62 billion yuan. Food compensation beneficiaries concentrated in the downstream sub-watersheds of the Heilong and Woken Rivers, where amounts from 3 to 3.9 billion yuan. In the future, multi-scale collaborative management should be strengthened, and appropriate ecological compensation schemes should be formulated according to the regional development differences. This study provided a scientific reference for relevant departments to formulate WEF sustainable development management regulations and ecological compensation schemes at different scales.