Study On The Law Of Occurrence And Release Of Fe And S In Sediments Of Eutrophic Waterlogged Ponds In Guanzhong

Waterlogging pond is a small-scale water storage project to resist waterlogging and store flood in arid area of North China,which is similar to but different from small lake system.Waterlogging pond is very common in Guanzhong area of Shaanxi Province.The problem of eutrophication is becoming more and more serious,especially the problem of water body and sediment blackening caused by eutrophication,which has seriously affected the surrounding ecological environment and the health of residents.At present,there have been many researches done on the studying of blackening caused by eutrophication of rivers and lakes,but there are still insuficient researches to demonstrate this kind of problems faced by waterlogging pools.Therefore,this dissertation takes the waterlogging pools in Guanzhong district of Shaanxi Province as the research object.This research adopted a combined methods of field investigation,field sampling,indoor measurement and analysis,simulation test and mathematical simulation to study the blackening problem faced by waterlogged pond.The present work proved that the main blackening substance in Waterloo pond is FeS,and it was found that the main blackening substance is FES,the occurrence forms and stratification characteristics of Fe and S elements are explained,the main control factors affecting the release of Fe²⁺ and ΣS^2-are screened,the influence law of the main control factors on the release of Fe²⁺ and ΣS^2-was revealed,and the mathematical model of the release of Fe²⁺ andΣS^2-in the sediment of waterlogging pool was constructed.The main conclusions are as follows:（1）Through the determination and analysis of the TFe and sulfide in the domestic sewage,runoff and the soil around the waterlogging pond.It is determined that the main blackening pollutant in the waterlogging pond is suspended particulate matter in the overlying water,and the main blackening component is FeS,in which Fe mainly comes from the original soil and S possibly comes from domestic sewage（2）Residual iron is the main existing form of Fe in the sediments of waterlogged pond,accounting for 72.6%-81.2%of the total iron.Oxidized iron is the main form of available iron（the difference between total iron and residual iron）,accounting for 53.2%-58.2%of available iron.Exchangeable iron,oxidized iron,organic iron and residual iron all decrease first and then become stable with the increase of sediment profile depth,while carbonate bound iron increases with the increase of the depth of sediment profile,there is no obvious regularity of soluble iron in water.The proportion of reductive inorganic sulfur and organic sulfur in the total sulfur in the sediment of waterlogged pond is equal.Pyrite-s is the main existing form and the most stable form of total reductive inorganic sulfur,accounting for59.3%-68.6%of total reductive inorganic sulfur.AVS accounts for 26.4%-35.6%of total reductive inorganic sulfur.ES is the intermediate product in sulfur cycle process,so its content is only about 4%of total reductive inorganic sulfur.The FA-S is the main form of organic sulfur,accounting for 66.5%-68.9%of the total organic sulfur.The content of AVS first increases and then decreases with the increase of sediment depth,and finally stabilizes.The content of pyrote-s increases with the depth of the profile,the ES content first increases and then tends to be stable with the increase of profile depth.The FA-S decreases,then increases and finally stabilizes with the increase of depth.The HA-S content decreases slowly with the increase of depth.（3）Ten indexes of TN,TP,TOC,t,do,eh,pH,solar radiation energy and Fe²⁺,ΣS^2-at the sediment-water interface of Heiyu waterlogging pond were comprehensively analyzed by SPSS 25 stepwise regression analysis and structural equation modeling.The main controlling factors affecting the release of Fe²⁺ and ΣS^2-in sediments were determined to be eutrophic pollutants（TN,TP,TOC）and environmental factors（T,DO,pH）.The prediction equations of Fe²⁺ and ΣS^2-contents were obtained.（4）The contents of Fe²⁺ and ΣS^2-in the interface increase with the increase of PO43-in the overlying water.The higher the PO43-content,the higher the maximum Fe²⁺ and ΣS^2-contents and the faster the growth rate.When the content of PO43-increases from 0.03 mg/L to 1.1 mg/L,the maximum content of Fe²⁺ and ΣS^2-at the interface increases by 88.2%and 97.9%,respectively,and the growth rate increases by 51.2%and 34.8%,respectively.Increasing the content of PO43-has a greater impact on the growth rate of Fe²⁺content.NH4+-N is the main form of nitrogen in waterlogging pond.The increases of NH4+-N content in overlying water will cause the increase of Fe²⁺ and ΣS^2-contents at the interface.The higher the NH4+-N content,the greater the maximum Fe²⁺ and ΣS^2-contents at the interface and the faster the growth rate.There is no significant difference in the influence of NH4+-N content in overlying water on Fe²⁺ and ΣS^2-contents at the interface.Peptone,cysteine,methionine,glucose and starch can all promote the blackening of overlying water,and the sulfur-containing organic matter matrix（peptone,cysteine and methionine）can make the water blacken faster and more black than the non sulfur-containing organic matter matrix（glucose and starch）.No matter what kind of organic matrix,as long as its content reaches 0.8 g/L,it will cause water blackening.The type and content of organic matrix have more influence on the content of interface Fe²⁺ and ΣS^2-.（5）The content of Fe²⁺ and ΣS^2-at the sediment water interface increases with the increase of the ambient T.When the T is between 15℃ and 25℃,the content of Fe²⁺andΣS^2-at the interface increases rapidly,which makes the interface more prone to blackening.Do affects the content of Fe²⁺ and ΣS^2-by directly affecting the redox state of the interface.The contents of Fe²⁺ and ΣS^2-at the interface decrease with the increase of DO content.When DO≥^2-3 mg/L,the release of Fe²⁺ and the reduction of SO4^2-can be effectively inhibited.PH affects the content of Fe²⁺ and ΣS^2-by affecting the activity of sulphate-reducing bacteria and iron-reducing bacteria.PH=7 is the optimal pH for the coexistence of the two bacteria.At this time,the content of Fe²⁺ and ΣS^2-in the interface is higher,and the blackening phenomenon is more likely to occur.（6）Algae is one of the main inducements for the blackening of eutrophication waterlogging pool.The existence of algae is the main reason for the faster oxygen consumption rate and increase of the oxygen consumption at the sediment-water interface.After adding algae,the DO at the interface decreased rapidly to 0 mg/L within 70 min,and the Eh potential drooped to a negative value,the content of Fe²⁺ and ΣS^2-increased rapidly,and the blackening speed and degree increased.（7）Based on Fick’s law and the law of conservation of matter,a mathematical model for the release of Fe²⁺,ΣS^2-in sediments was established and its analytical solution was obtained.The reliability and accuracy of the mathematical model are verified by comparing the measured data with the predicted data.Three groups of parameters were given for three waterlogging pools with different service life,and the mathematical model was used to predict the changes of Fe²⁺ and ΣS^2-contents in Loudi waterlogging pond,Heiyu waterlogging pond and Xiaoziling waterlogging pond.