Optimal allocation of agricultural water resources in Yanghe watershed considering blue water to green water ratio.

BACKGROUND: Yanghe Watershed has low annual rainfall, uneven spatial and temporal distribution, extreme shortage of water resources in some areas. The contradiction between supply and demand of water for agricultural production is prominent and the expected production value cannot be achieved. Therefore, it is necessary to investigate the supply and demand of agricultural water resources and the impact of green water on agricultural crops in Yanghe Watershed. RESULTS: This article proposes a new crop economic model for increasing the green-water footprint to blue-water footprint ratio (GWF:BWF) in accordance with the regional characteristics, alleviating agricultural water shortage in irrigation areas, optimizing water resource allocation, and achieving sustainable agricultural development. The proposition is based on a study of five crops in eight districts and counties in the Yanghe River watershed. By combining the economic model F with a crop water production function, we achieved 89.3%, 88.9%, 97.1%, 81.5%, and 87.0% of the optimal water demands of the five crops, respectively, and effectively improved the underground irrigation of crops and the water resource utilization efficiency. CONCLUSION: The GWF:BWF threshold interval was subsequently selected based on the temporal changes in the BWF and GWF in the study area. This enabled significant reduction of the planting area of blue-water crops and increase in the proportion of green-water crops, while also improving the agricultural economy of the Yanghe Watershed. The proposed model promises to afford enhanced management of agricultural irrigation areas that experience rainfall shortage. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

[Influence of Rainfall on the in situ Growth of Dominant Algae Species in Xiangxi River].

To understand the influence of rainfall on the in situ growth (in a culture cage) of dominant algae species in the Xiangxi River tributary of the Three Gorges Reservoir, culture experiments were carried out to measure the biomass of Microcystis aeruginosa, Chlorella vulgaris, and Chlorella aeruginosa before and after rainfall. The results showed that ① during the study period (October 4-18, 2017), there were significant differences in hydrodynamic conditions between the rainfall period and the non-rainfall period (ANOVA, P<0.05). Total Chl-a and the specific growth rate of the three main algae during rainfall period were significantly lower than during the non-rainfall period, which inhibited algae growth to some extent. The results of correlation analysis showed that the four hydrodynamic parameters characterizing vertical mixing had a highly significant negative correlation with the specific growth rate of the three dominant algae species. Meanwhile, the changes of shear force τ, the vertical turbulent viscosity coefficient Vr, and the vertical turbulent diffusion coefficient Vt were the key factors leading to the rapid decline of algae; ② the depth of the mixed layer was lower (1-2 m) before rainfall, but increased (>5 m) markedly after rainfall (October 10-18). At the same time, the concentration of Chl-a during the rainfall period was significantly lower than that during the non-rainfall period. The results of the correlation analysis showed that there was a highly significant positive correlation between the ratio of eutrophic depth to mixing depth (Zeu/Zmix) and the specific growth rate of the three dominant algae species. This indicated that the vertical disturbance of water was enhanced by rainfall, and mixing layer expanded continuously, which reduced the water temperature stratification and thus inhibited the growth and proliferation of algae; ③ there were significant differences in rainfall, water temperature, light intensity, total nitrogen, and dissolved total nitrogen between the rainfall period and non-rainfall period (ANOVA, P<0.05). Correlation analysis showed that changes in rainfall, water temperature, light intensity, total nitrogen, and dissolved total nitrogen caused by rainfall were the key environmental parameters affecting the in situ growth rate of three dominant algae.