Study On Evolution Of Ecosystem Services Of Jiajiyu Small Watershed

It is of vital importance to study the evolution mechanism of regional ecosystem services (ES) for regional ecological planning, policy development, ecological environment construction and economic development. Thus, it is practically significant to further understand the evolution mechanism of ES and its various function parts with the main components of the watershed, and the relationship between ES and regional elevation, distance from river and residents areas.Jiajiyu, a typical small watershed of the Loess Plateau, is the primary tributary of Jinghe River. This thesis selected Jiajiyu as case study area to carry out the temporal and spatial distribution and change characters of small watershed. First, land use distribution maps for the years1998,2006and2012were obtained by interpretation based on remote sensing images and field survey. Second, ecosystem service values (ESV) of the study area after being implemented various treatments over the three periods were valuated. Third, relationship between ESV of different periods and the three elements (elevation, distance from river and residents areas) were analyzed. The main results are as follows:1. Land use changes during the three periods shows: upstream part of Jiajiyu with higher elevation focused on transferring farmland to woodland and grassland; middle and lower stream had deep ravines and focused on planting woodland, artificial grass in the gully, and transforming slope farmland into terrace between the ravines; while downstream focused on developing woodland and orchard. From the point view of slope gradients, in all the land use transferred areas, those transferred to orchard distributed in the area with slope lower than15°; those transferred to woodland (arborous forest and economic forest), grassland (waste-grassland and artificial grassland) and terrace distributed in the area with slope lower than25°, mainly between15°and25°; in the slope between25°and35°, the main transformations were slope land transferred to waste-grassland, waste-grassland transferred to woodland (arborous forest and economic forest); in the area with slope over35°, the main transformation was slope land transferred to waste-grassland. 2. ESV valuation for the three periods shows: the ESV in1998,2006and2012vas990.05,1059.12and1300.13ten thousand Yuan, separately, which shows that ESV icreased with the passage of time. Compared to1998, ESV increased6.98%in006and31.32%in2012.From the point view of ESV of different land use types during the three periods, the sequence from high to low of ESV per unit area was orchard, arborous forest, economic forest, artificial grassland, terrace, waste-grassland, slope farmland, construction land, road and residential land, among which, ESV per unit area of orchard was2.22ten thousand Yuan per ha, while road and residential land was0.04ten thousand Yuan per ha. In1998, the sequence from high to low of ESV of different land use types was slope farmland, terrace, arborous forest, waste-grassland, orchard, artificial grassland, residential land, construction land and road, among which, ESV of the slope farmland was345.33ten thousand Yuan and the road was0.40ten thousand Yuan. In2006, the sequence is waste-grassland, terrace, arborous forest, slope farmland, orchard, economic forest, artificial grassland, residential land, construction land and road, among which, ESV of the waste-grassland is284.01ten thousand Yuan and the road is0.40ten thousand Yuan. In2012, the sequence was terrace, arborous forest, waste-grassland, economic forest, artificial grassland, orchard, slope farmland, residential land, construction land and road, among which, the terrace was363.32ten thousand Yuan and the road is0.40ten thousand Yuan. Besides, the trend of change of ESV was like that of area with four main change types, including ⅰ) increasing type (terrace, arborous forest, economic forest, artificial grassland, construction land), ⅱ) waving type (first increase and then keep the same value like orchard, first increase and then decrease like waste-grassland), ⅲ) keep the same value like road and residential land, ⅳ) decreasing type like slope farmland.From the point view of ES types, the sequence from high to low of ESV in1998was food production, soil conservation, nutrient cycling, carbon fixation and oxygen release, environment purification, water conservation. While in2006, the soil conservation rose to the first one and food production decreased to the second one. In2012, environment purification rose to the fourth one and nutrient cycling decreased to the fifth one.3. Spatial distribution of ESV shows: ESV of the middle stream, upstream and downstream was788.05,272.02and240.06ten thousand Yuan, separately.Gradients analysis of elevation, river buffer, residential areas buffer shows: the higher elevation, the higher ESV per unit area, and the highest ESV per unit area distributed in elevation1400-1500m with the value of0.55ten thousand Yuan per ha, while decreased first and then increased again when the elevation rose over1500m; the farther from river, the higher ESV per unit area, and the highest ESV per unit area was in the farthest distance from river of900-1000m with the value of1.37ten thousand Yuan per ha; with the distance increased from residential areas, ESV per unit area first increased and then decreased a little, and the highest value distributed in the second range of residential areas buffer (300-600m) with the value of0.54ten thousand Yuan per ha. 4. Dynamic change character of ESV during different periods shows: with the passage of time, percentage of changed area was42.23%, among which, increased part was accounted for41.01%with the transformation of slope farmland to grassland (waste-grassland and artificial grassland), and terrace, waste-grassland to woodland (arborous forest and economic forest), bare land to construction land. While the decrease part is1.22%with the transformation of waste-grassland to construction land.ESV of different periods with the gradients of elevation, river buffer and residential areas buffer shows: area increased first and then decreased with the increasing of elevation, while continuously decreased with the distance from river or residential areas increased. However, the change of ESV was like the trend of area change. As for ESV per unit area, the change was in contrast with the change of area in the sixth elevation gradient over1800m, or in the river buffer gradients (except the ESV per unit area in1998with the distance over800m from the river); In the residential areas gradients, the change of ESV per unit area was basically identical with the trend of area change.