Evaluation And Optimization Of Agricultural Ecosystem Services Of Jiajiyu Small Watershed

Study of agricultural ecosystem services (ESs) aims to guide and improve the management of agro-ecosystems, and to ensure conservation and sustainable utilization of agro-ecosystems. Analyzing agricultural ESs, studying the relations between ESs and small watershed management, and discussing the limiting factors of promotion and optimization effect of agricultural ESs under different management measures from small watershed scale, can provide reference for small watershed comprehensive management from the perspective of ESs.Jiajiyu is one of the typical small watersheds on the Loess Plateau region. This study select Jiajiyu small watershed as a case study area, and use three period land-use maps (1998,2006 and 2012), employ the valuation method of ESs, to obtain the value of ecosystem services (ESVs) for different period with different comprehensive management. On this basis, factors which affect the small watershed agricultural ESs and its influence for agricultural ESVs promotion were further analyzed. Then, the limiting factors that restrained the further enhancing of the agricultural ESVs of the study area were clarified. Moreover, the landscape patterns transfer method was used to optimize the agricultural landscape in the study area. Finally, the multi-objective linear programming method was employed to adjust the land use patterns, and compare different scenarios of trade-off between agricultural food production service and other ESs to optimize agricultural ESs in the study area. The main results are as follows:(1) ESVs assessment showed:ESVs of Jiajiyu small watershed were 13.5589 million yuan in 1998, among which agricultural ESVs were 12.6411 million yuan. After comprehensive managements through different periods, agricultural ESVs increased significantly, and the rate of increase was 48.12% in 2006 and 119.31% in 2012. During the 15 years, except that the ESVs of slope farmland declined, ESVs of other land use types increased. During 1998-2012, the largest contribution to the growth of agricultural ESVs was terrace, followed by arbor forest and economic forest. Comparing different ESVs of agricultural ecosystem showed that soil retention and biodiversity control dominated larger proportion, while proportion of food production, waste treatment and soil retention services continued to decline.(2) Affecting factors of the changes of agricultural ESVs showed:Serious soil and water loss, drought and water shortage, and poor quality of arable land are the important natural factors that restricted the ESs. To promotion the small watershed agricultural ESs have to solve those problems. Agricultural planting structure adjustment can effectively enhance the agricultural ESVs. While the most prominent effection of enhancing of the small watershed’s agricultural ESVs was the comprehensive management measures, such as transforming slope farmland into terrace, planting artificial grass, transforming slope farmland into forest, transforming waste-grassland into forest, etc. However, transforming slope farmland to waste-grassland can reduce the ESVs.(3) During 1998-2012, changes of agricultural landscape patterns of the small watershed were complex. The largest change was slope farmland transfer, which were transfered to unused land, terrace, forest, grassland and orchard, while some part of the unused land were transfered to forest, construction land and grassland. The number patchs (NP) of unused land and slope farmland decreased significantly, while NP of forest and grassland increased significantly. Advantage and dominant landscape types changed from slope farmland in 1998, to unused land in 2006, and to terraces in 2012. The larger change of mean patch size (MPS) were slope farmland and terrace, among which the largest rate of increase in MPS was terrace, and the largest rate of decline in MPS was slope farmland. While the MPS of forest and grassland increased gradually. Both Shannon diversity index (SHDI) of agricultural landscape and Shannon evenness index (SHEI) increased gradually, while dominance index (D) decreased gradually, and landscape fragmentation index (FN) was reduced after the increase in the first stage.According to the management measures conducted in the small watershed, the slope farmland and waste-grassland through landscape transfer were optimized, and its areas and spatial locations which are suitable for transfer were determined. Results of this part will provide constraint conditions for multi-objective linear programmingthat which will be used to optimize the agricultural ESs.(4) Agricultural ecosystem services optimization showed:Scenario 5 "other services optimization first" is the most suitable solution. In scenario 5, the agricultural ESVs will be 37.0621 million yuan in the planning year, with an increase rate of 33.68% compared to 2012. Besides, soil retention for unit area of agricultural ecosystem is 439.13 t/hm2/a, with an increase of 3.49% in the planning year compared to 2012. Furthermore, the total PN will decrease, while D index will increase, and fragmentation degree will reduce, and thus will result in more uniform of landscape distribution. On the whole, spatial patterns of agricultural landscape will be more reasonable, and the purpose of agricultural ESs optimization will be finally obtained.