Multi-scale Water Cycle Process Of Hani Rice Terraces Landscape Based On Stable Hydrogen And Oxygen Isotopes

In order to quantitatively trace the water cycle process and hydrological effect mechanism of typical watersheds in Hani terraced area under different landscape scales,and to clarify the key spatial-temporal heterogeneity models of water cycle processes in different scales and different water bodies,to realize the scientific management and efficient utilization and of water resources in the Mountain agricultural watershed,as well as the sustainable development of Hani terraced World Heritage under the premise of human-land coupling.This study takes the typical watershed of Hani terraced area as the research object,through the analysis of the multi-scale landscape pattern and the investigation of the intensity of human activities,the temporal and spatial variations of stable isotopic composition and effect of precipitation-groundwater-surface water in typical watersheds at different scales were analyzed.Combined with the simulation and analysis methods such as backward trajectory model,stable isotope mixing model,sub-cloud secondary evaporation model and groundwater recharge elevation analysis,96precipitation samples,168 groundwaterr samples and 228 surface wate samples collected in different landscape scales of Malizhai River Basin from May 2015 to April2016 were analyzed,and the following conclusions were drawn.（1）For the characteristics of multi-scale landscape pattern,at the large basin scale,the landscape of Malizhai is composed of paddy field,dry land,garden,forest land,grassland,village,water area and other land,with forest land（accounting for 42.95%）,and its vertical pattern is"Forest-Residential land-Paddy field-Forest-Garden-Dry land-Forest-Garden-Residential land".The landscape of Quanfuzhuang River watershed is also composed of 8 landscape types,with 56.31%forest land as the matrix.Its vertical pattern is"Grasslan-Forest-Village-Terrace".（2）For the composition of hydrogen and oxygen stable isotopes,the variation ranges ofδ¹⁸O andδD in precipitation,surface water and ground water are-15.46‰～4.06‰and-99.55‰～15.17‰,respectively,the relationship equations areδD=8.35δ¹⁸O+21.93（R²=0.97,n=96）,δD=5.18δ¹⁸O-13.85（R²=0.96,n=168）,δD=6.00δ¹⁸O-4.73（R²=0.88,n=228）.The relationships among the three types of water bodies show that precipitation is the main recharge source of surface water and groundwater,and surface water is recharged by both precipitation and groundwater.（3）In terms of water cycle at large basin scale,based on the recharge conversion of precipitation,groundwater and surface water among the upper,middle and lower reaches,there is significant temporal and spatial heterogeneity.Spatially,with the decrease of altitude,the recharge relationship between precipitation,groundwater and surface water in the three landscape types of the basin becomes more and more complex.The recharge ratio of atmospheric precipitation to groundwater and surface water in the upstream landscape is 95%and 62%,that in the midstream landscape is 71%and 55%,and that in the downstream landscape is 57%and 57%.In terms of time,atmospheric precipitation has three input modes,such as Dominant External Moisture（May to July）,Multiple External Moisture（August to November）and Local External Moisture（December to April of the next year）.Surface water has four recharge cycles,such as rain fed season（June to August）,spring fed season（September to November）,rain fed season（December to February of the next year）and spring fed season（February to May of the next year）".（4）In terms of water cycle process on the small watershed scale,based on the recharge conversion of precipitation,groundwater and surface water,there is significant spatial-temporal heterogeneity.First of all,the whole process of water cycle in the small watershed is significantly disturbed by local effects,such as sub-cloud secondary evaporation,over peak airflow on the south slope and human activities.Spatially,the process of water cycle in paddy field patches is more complex than that in forest patches,and the proportion of groundwater and surface water recharge in paddy field patches（74%and 33%）is higher than that in forest patches（22%and 39%）.Temporally,the input model of precipitation on the small watershed scale is basically consistent with that on the large basin scale,but for the recharge model of surface water,due to the influence of the local water cycle process,the precipitation recharge ratio of the two rain-fed seasons（more than 70%）is higher than that of the large basin scale（more than60%）,while the groundwater recharge ratio of the two spring seasons（more than 60%）is lower than that of the large basin scale（more than 60%）.（5）In terms of water cycle process on paddy field patch scale,based on the recharge conversion of precipitation,groundwater and surface water,there is also significant spatial-temporal heterogeneity in watershed water cycle.Spatially,there are two types of paddy field patches,such as rain fed terrace dominated by precipitation recharge and spring fed terrace dominated by groundwater recharge.Temporally,two different recharge periods existed:the rain-fed season（>70%recharge from precipitation）and the spring-fed season（>30%recharge from groundwater）.The temporally alternating recharge periods of spring-fed and rain-fed seasons and the interconnected spatial distribution of rain-fed and spring-fed types were essential to maintain stable water sources in the Hani terraces.Rice cultivation will be sustainable if the changes in monsoonal precipitation due to global climate change align with the anthropogenic agricultural cultivation cycle,including land preparation,planting,growing,and harvesting.This is the key reason that the mountainous rice cultivation systems of the Hani terraces have lasted for thousands of years under the influence of the East Asian monsoon.（6）Multi-scale water cycle is a key mechanism for the persistence of terrace landscape.The characteristics of water cycle at large scale determine the characteristics of water cycle at small scale;Similarly,water cycle at small scale can also affect water cycle at large scale.Under the interaction of water cycle,the stability of precipitation input on large basin scale and small watershed scale and distribution process of surface water on small watershed and patch scale are the core of the whole mechanism.The mechanism can provide important decision-making reference for mankind to deal with future climate change and improve the stability of food production and human well-being.In addition,future research should pay attention to the application of stable hydrogen and oxygen isotope tracing technology in mountainous rice terraces that lack of hydrological monitoring,and focus on the multi-scale coupling relationship between water cycle and eco-hydrological pattern in mountain rice agricultural areas greatly affected by human activities.Finally,based on the research results,suggestions and countermeasures are put forward to realize the sustainable development of the Hani Rice Terraces landscape.