Effects of iron and humic acid on competition between Microcystis aeruginosa and Scenedesmus obliquus revealed by HPLC analysis of pigments

Iron is a vital micronutrient for growth of bloom-forming Microcystis aeruginosa and competition with other algae,and its availability is affected by humic acid.The effect of iron and humic acid on growth and competition between M.aeruginosa and Scenedesmus obliquus was assessed.The results showed the growth of M.aeruginosa and S.obliquus in mono-cultures was inhibited by humic acid at low iron concentrations(0.01 mg/L);the maximum inhibition ratios were 67.84%and 38.31%,respectively.The inhibition of humic acid on the two species was significantly alleviated when iron concentrations were 1.00 mg/L,with the maximum inhibition rate reduced to 5.82%for M.aeruginosa and to 23.06%for S.obliquus.S.obliquus was the dominant species in mixed cultures,and the mutual inhibition between M.aeruginosa and S.obliquus at low iron concentration was greater than that at high iron concentration.The inhibition of S.obliquus on M.aeruginosa was reduced at low iron concentrations;it increased at high iron concentrations,as concentrations of humic acid rose.

Variations of soil organic carbon fractions in response to conservative vegetation successions on the Loess Plateau of China

Land use changes profoundly affect the equilibrium of soil organic carbon(soC)sequestration and greenhouse gas emissions.With the current global climatic changes,it is vital to understand the influence of ecological restoration and conservation management on the dynamics of soC under different land uses,especially in erosion-endangered Loess soils.Therefore,we investigated changes in soc through a suit of labile fractions,namely:light fraction organic C(LFOC),heavy fraction organic C(HFOC),coarse particulate organic C(CPOC),fine particulate organic C(FPOC),and dissolved organic C(DOC),from two forests i.e.,Robinia pseudoacacia(RP)and Platycladus orientalis(PO),with different ages,in comparison with farmland(FL).The SOC and STN contents significantly increased over 42 years in the RP forest where the contents of CPOC and FPOC were significantly higher than in the FL.Moreover,total SOC and its labile fractions,in the studied land use types,significantly correlated with soil CacO3,pH,and STN contents,indicating their key roles in SoC sequestration.The results reported here from different vegetation with different ages provide a better understanding of sOC and STN alterations at different stages of vegetation restoration.Our findings suggest that long-term natural vegetation restoration could be an effective approach for SoC sequestration and soil conservation on the Loess soil.

Stabilization of Cd and Pb in the contaminated soils by applying modified fly ash

This study investigated the stabilization of heavy metals by adding modified fly ash(FA)to contaminated soils,and two similar materials,NaOH-zeolite(ZE)and natural zeolite(ZO)were introduced into the soils for comparison.Column leaching tests were conducted to analyze the difference of stabilization effects between the three materials.Leaching columns were run for 6 months,and a considerable stabilization of heavy metals in the soils was observed.The concentration of cadmium(Cd)and lead(Pb)in the amended soil substantially decreased(p<0.05).The results indicated that after 11 weeks of column leaching,Cd and Pb concentrations in the soil leachate decreased to below the detection limit due to amendment stabilization.Among the three amendments,the ZE amendment showed the optimum capacity for heavy metal immobilisation in the soils.In addition,after 6 months of leaching,Pb and Cd concentrations in the soils with the three different amendments decreased to various degrees.The amendments of modified FA and ZE were better than those of natural ZO.Coal FA,after modification,is a useful amendment for the remediation of heavy metals in the contaminated soil.