Response of surface water quantity and quality to agricultural water use intensity in upstream Hutuo River Basin, China

A field hydrology survey was conducted to determine spatial variations in regional water yield and use intensity and clarify the main causes of the variation in upstream Hutuo River Basin (UHTB). The study showed that: 1) the spatial distribution of flow, salt and stable isotopes reflected variations in regional water yield and use intensity. Total Dissolved Solids (TDS) in river water were lower in Qingshui tributary and the headwater region of Hutuo River (HTR). The distributions of δD and δ18O of river water were nearly parallel to the Local Meteoric Water Line (LMWL), except for the middle reach. Intensive agricultural activities were responsible for the deviation of spatially stable isotopes from LMWL, the highest TDS and 0.85 evaporation fraction in the middle reach. 2) The spatial flow indicated that almost all the river water was used in agriculture (especially in the middle reach of UHTB) before inflow from Qingshui tributary. Based on the balance in monitored flow rate and isotopes, about 67.9% of the water flow (11.66 m3/s) was from upstream Shanxi province and discharged into the downstream of Hebei Province; 91.9% of which was from Qingshui tributary. 3) Irrigation function of upstream reservoirs was not fully reflected due to less storage of water along with low recharge and discharge events. Given the declining water yield and high water requirement, there was the need to overhaul agricultural water use strategies to ensure cross-border water availability. The research could lay the basis for designing cross-border agricultural water use strategies in UHTB and other basins with similar hydro-climatic conditions.