Examination Of The Ecohydrological Separation Hypothesis In Hillside, Mountain Foot And Flood Plain Of The Lanzhou City

The hypothesis of ecohydrological separation has attracted a lot of attention in the study of ecohydrology,which is of far-reaching significance to mechanical ecohydrological modeling and water resources management.The hypothesis of ecohydrological separation suggests that there are two unmixed water bodies in the soil,and plants are more inclined to absorb less mobile water,but less easily accessible mobile water.The existence of hypothesis has profound significance for mechanical ecological hydrological modeling and water resources management.At present,it is not clear when and where the ecohydrological separation phenomenon occurs,especially in the semi-arid continental monsoon marginal zone.In this paper,the characteristics of stable isotopes of hydrogen and oxygen of precipitation,soil water,plant stem water,groundwater,flowing soil water and river water in three geomorphologic units of hillside,mountain foot and floodplain of Lanzhou City are analyzed by four methods to judging the hypothesis of ecohydrological separation,and the phenomenon of ecological hydrological separation is discussed at different time scales.The results show as follows:(1)It was found that the seasonal variation characteristics of hydrogen and oxygen stable isotopes values in different water bodies are different and the spatial variation is remarkable.From April to October,the stable isotopes values of river water and groundwater did not change significantly and were relatively stable.The average values of hydrogen and oxygen stable isotopes of precipitation,soil water and plant stem water on the hillside show the rule of first increasing and then decreasing,which is the same as that of local temperature.The floodplain is affected by the river water,and the average variation of hydrogen and oxygen stable isotopes of precipitation,soil water and plant stem water are not obvious.(2)The ecological and hydrological separation degree of hillside,mountain foot and flood plain are different.In terms of the hillside,both the growing season and the monthly scale prove the existence of ecological and hydrological separation,and the evaporation of soil water on the hillside;Both the mountain foot and the floodplain in growing season existing obvious ecological hydrological separation,but in different months,the situation are different.The results of the mountain foot in June,July,August,September and October were more consistent,with ecological hydrological separation occurring,while the results in April and May were inconsistent.The judgments of floodplain in May,June and September were largely consistent,with full or partial separation perceived,while the April and October results were inconsistent.(3)Different growing environment,the degree of ecological hydrological separation is different,the more dry hillside without artificial irrigation has the phenomenon of ecological hydrological separation every month,the mountain foot and floodplain affected by artificial irrigation and river water are different degrees of ecological hydrological separation each month,some months have no ecological hydrological separation,and the results of different methods of judgment are inconsistent.