| Damming of rivers significantly alters the water-sediment regime,leading to changes in the transport of biogenic materials and causing significant ecological effects,among which phosphorus(P)is one of the important biogenic elements of interest,and its transport and transformation are closely related to the behavior of particulate matter under the changing water-sediment regime.The effects of dam construction on particulate transport are mainly manifested in 1)altering the concentration distribution of natural river particulate matter and 2)sorting of particulate matter,resulting in significant divergence of deposited particulate matter particle size in the river-reservoir spatial scale.The changes in particulate matter concentration and particle size lead to significant changes in the distribution of P between sedimentary particulate matter-water bodies,which in turn cause significant ecological and environmental effects,and this study is carried out in this context.The study selected the river-reservoir continuum in the Lancang River basin and the Yellow River basin,where large reservoirs were built,collected sediments,analyzed their physicochemical properties,selected representative sedimentary particulate matter,and investigated the response of the sedimentary particulate matter-water P distribution balance to the variation of five main factors,including particulate matter source,P load,particulate matter concentration,particle size,and p H,and established a surface complex model to scientifically assess their potential The surface complex model was developed to evaluate the potential ecological effects.The main research results are as follows:(1)The results of physicochemical property analysis showed that the median particle size(d50)of the river-reservoir continuum of the Lancang River Gongguoqiao and Jinghong basically showed a gradually decreasing trend from the upstream river to the end of the reservoir,and the d50 of the deposited particulate matter within the reservoir area of the Xiaolangdi Reservoir of the Yellow River was smaller compared with that of the deposited particulate matter outside the reservoir area,and the d50 of the deposited particulate matter within the reservoir area also showed a gradually decreasing trend.In the two major study areas,Fe/Al-adsorbed P and Fe/Al-bound P showed an increasing trend with decreasing particle size,and the contents of Fe/Al-P and Fe/Al-adsorbed P in the Yellow River reservoir area were higher than those in the points outside the reservoir area.(2)The results of P adsorption-desorption on the sediment-water showed that the equilibrium concentration of P increased gradually with the increase of p H(6-11)and showed an "S-shaped" variation pattern;the equilibrium concentration of P increased with the increase of P loading and decreased with the increase of sediment particle size;the equilibrium adsorption-desorption equilibrium of P in the samples from different areas of the Yellow River and Lancang River were significantly different.The adsorption-desorption equilibrium of P was significantly different between the samples of Yellow River and Lancang River,and the maximum adsorption capacity of P was higher than that of Lancang River.(3)A surface complexation model was further developed to analyze the partitioning mechanism and quantification of P on sediment particles-water.The results showed that the surface complexation model could simulate the experimental results well,and phosphorus loading,particle concentration,particle size and p H dominated the partitioning of P on sediment particles-water.The equilibrium constants(Log K)of the reactions in the Lancang River region ranged from 25.7 to 26.9,and the Log K values in the Yellow River region ranged from 25.3 to 26.4.Overall,the Log K values in the Lancang River region were larger than those in the Yellow River region.(4)After simulating the adsorption and desorption of sediment-particle-water P under the influence of multiple factors,it was found that the change of exogenous P load did not change the buffering capacity of sediment-particle P.Changing the concentration of sediment-particle and the percentage of fine particle size would affect the buffering capacity of sediment-particle P.Increasing the concentration and the percentage of fine particle size would enhance the buffering capacity of sediment-particle P.Decreasing the concentration of sediment-particle and the percentage of fine particle size would increase the buffering capacity of sediment-particle P.The buffering capacity of sedimentary particulate matter on P will be weakened by increasing the concentration and fine particle size ratio.The combined results show that the changes in river water-sediment conditions have a significant impact on the distribution of P between sedimentary particulate matter and water bodies,and their ecological effects are scientifically assessed. |
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