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.

Dissolved black carbon concentrations in suspended particulate matter from the Bohai Sea

Dissolved black carbon(DBC)includes the water-soluble component of black carbon and/or its degradation products.It is a hydrophobic organic compound due to its thick cyclic aromatic structure and can therefore be present as particulate DBC(PDBC)on suspended particulate matter or particulate organic matter.PDBC is not equivalent to particulate black carbon(PBC)and is thus often overlooked when researchers measure PBC in particulate matter using current conventional methods.Consequently,the amount of DBC in nature is likely underestimated in many studies and the reliability of current findings on the geochemical behavior of DBC is subject to challenge.In this study,we attempted to draw the solid-liquid partition coefficient(K_(d),PDBC/DBC)based on detailed data on PBC,DBC,particulate organic carbon,total suspended solids,dissolved polycyclic aromatic hydrocarbons,and particulate polycyclic aromatic hydrocarbons in the surface waters of the Bohai Sea.The obtained K_(d)was in the range of 0.018-0.072.Accordingly,the concentrations of PDBC were 1.637-6.449μg C L^(-1).The estimated inventory of PDBC on suspended particulate matter in the Bohai Sea was 2.049-8.194 Gg,which was lower than that of PBC(15.16 Gg)but of the same order of magnitude.These results indicate that PDBC is an important form of DBC in the Bohai Sea.Quantitative results of DBC fluxes between the dissolved and particulate phases will benefit our understanding of DBC transport and fates in the ocean.