527 / 2024-06-30 15:39:44

The water quantity and quality characteristics of Four Lakes Main Channel and its response to the changes in agricultural cropping-breeding mode

agricultural cropping-breeding mode; Four Lakes Main Channel(FLMC); the water quantity and quality characteristics; nitrogen and phosphorus concentration; nitrogen and phosphorus flux

Subtheme 3: Eco-hydraulics and Environment > Topic 2: Water Eco-environment Monitoring and Simulation

 To explore the impact of the changes of agricultural cropping-breeding mode(ACBM) on the water quantity and quality of rivers, Four Lakes Main Channel(FLMC) in the Jianghan Plain was taken as the research object. Based on observation data from 2010 to 2023, the trend of annual water quantity and quality changes was analyzed. Remote sensing images and statistical yearbook data were used to identify the interannual area change characteristics of different land use types, and the characteristics of nitrogen(N) and phosphorus(P) point source load under the change of agricultural planting mode were analyzed, the influencing factors of N and P flux in FLMC were discussed，and redundancy analysis (RDA) was applied to explore the response of the main channel’s N and P concentration to the changes.The results indicate that: ①In the past 10 years, there has been a significant change in the water quantity and quality of the main channel, and the water quantity has shown an increasing trend. The N and P concentration in the water body first increases and then decreases before stabilizing; The seasonal changes in water quantity and quality within the year are significant, with water quantity and N and P concentration reaching peak in summer and autumn from May to September. ②The spatial differences in N and P concentrations in water are significant, with N and phosphorus concentrations increasing first and then decreasing from the beginning to the end of the main channel. ③The ACBM in the Four Lakes Basin has changed significantly, with the proportion of rice field cultivation increasing by 18.8%, and the N and P agricultural non-point source loads increasing by 4231t/a and 564t/a, respectively; dryland crops and freshwater aquaculture decreased by 14.7% and 2.1% respectively, while the N and P non-point source loads decreased by 2710t/a and 1634t/a , and the P decreased by 153t/a and 171t/a, respectively. ④The characteristics of N and P concentration changes in FLMC are significantly positively correlated with N and P non-point source load, with an explanatory power of 60.7% (*p<0.01). The freshwater aquaculture is the main sources of N and P non-point source load, with contribution rates of 50-60% and 6-30%, respectively. ⑤In addition, the N and P flux at typical cross-sections of FLMC is closely related with changes in agricultural cultivation patterns, the increase in N and P flux from 2010 to 2016 is related to the growth of freshwater aquaculture and rice field cultivation areas, while the decrease in N and P flux from 2016 to 2023 is related to the growth of freshwater aquaculture areas and dry crop.