Studies on the migration,transformation and accumulation pattern of nitrogen and phosphorus in the vadose zone of coral islands
The migration and transformation of nitrogen and phosphorus in the vadose zone of coral islands have a direct impact on the groundwater quality and soil structure of the islands.Through XRD and SEM analyses,the unique CaCO3 phase composition and porous morphology of coral sand were elucidated.Static adsorption experiments were conducted to clarify the adsorption mechanism of N and P in coral sand;short-term continuous rainfall simulation column experiments were used to investigate the transport mechanism of N and P in coral sand,while long-term intermittent rainfall simulation column experiments examined the N transformation and P accumulation in different depth profiles.The results showed that the average adsorption amounts of NH4+and DIP in coral sand were 192mg/kg and 2051.75mg/kg,respectively,with adsorption models conforming to reversible linear adsorption and Freundlich isothermal adsorption models.The transport mechanism of NH4+was explicable by the linear equilibrium CDE model,while the transport process of low-concentration DIP followed a two-point chemical nonequilibrium model with an attenuation term.The transport of high-concentration DIP could not be modeled,and a dissolution and precipitation equilibrium reaction with CaCO3 was speculated in conjunction with the pH value.Under long-term rainfall conditions,microbial analysis indicated a nitrogen pathway N2→NH4+→NO2-→NO3-→N2/DON in the soil,posing a risk of nitrogen contamination to groundwater.Meanwhile,DIP was fixated in the form of insoluble phosphorus,potentially negatively impacting soil structure through long-term accumulation.In conclusion,the unique characteristics of N and P migration,transformation,and accumulation in the vadose zone of coral islands provide a scientific basis for environmental risk management in island ecological development.
coral sandstatic adsorptionnitrogen and phosphorus transporthydrus-1Dmicroorganisms
万方数据
维普
