Spatio-temporal dynamics and eco-hydrological controls of water and salt migration within and among different land uses in an oasis-desert system

摘要

Identifying the eco-hydrological processes associated with water-salt dynamics is important for the sustainable management of water resources and eco-environmental systems in groundwater-dependent ecosystems, especially across different land use types in salt-affected oasis-desert ecosystems. In this study, a typical cropland-shelterbelt-desert site at the oasis-desert system in the Sangong River watershed of northwestern China was selected to investigate the spatio-temporal variations of water-salt dynamics using the Spearman rank correlation analysis and water/mass balance analysis, and to identify the response of vegetation dynamics to water-salt variations based on a model framework for vegetation-salinity-groundwater interactions, within and among these land uses during crop growth period (CGP: April 1-June 28,2018) and non-crop-growth period (Non-CGP: June 29-October 31,2018). Results showed that the soil water content (SWC) and soil electrical conductivity (SEC) had clear vertical stratification, horizontal transition and seasonal fluctuation characteristics during both CGP and Non-CGP. Significant differences in groundwater depth and salinity were exhibited between both study periods. The water exchange flux (WEF) and salt exchange flux (SEF) in both the cropland and shel-terbelt were closely related to irrigation events and evidently higher than that in desert. The cropland maintained a salt accumulation state (especially at the ＞60-80 cm soil layer) during CGP. Hydrological links and salt transport processes among adjacent land uses have been weakened owing to the application of water-saving irrigation in cropland and the significantly declined of regional groundwater tables. Groundwater pumping and lateral groundwater flow (LGWF) were the most important media for water-salt exchange in the site. The interactions of vegetation with both the soil water-salt balance and groundwater dynamics may cause a discontinuous and irreversible ecosystem response to changes in land use or environmental conditions. Anthropogenic processes, especially the development of modern water-saving irrigation agriculture with groundwater-fed, are dominating the vegetation-salinity-groundwater interactions and its ecohydrological consequences in this ecosystem. Adaptive management of water and salt migration in soil and groundwater is essential for maintaining the coexistence of oasis-desert ecosystems in arid areas.