Effect Of Dissolved Organic Matter On The Migration And Transformation Of Pb And As In Nansi Lake

The dissolved organic matter is important control over the biogeochemical behavior ang toxicity of heavy metals in natural waters. In recent years, Accumulation of heavy metals has improved significantly in Nansi Lake. Tributary pollution and human activities have lead to a degree of eutrophication problems. On the basis of field investigation, we have completed sample collection of 30 points of the wholoelake. We studied the influence of DOM in Nansi Lake on the species and more serious. Main contents of the thesis are listed as follow:(1)Physical and chemical properties of surface sediments tests show that Pb, As, Hg and Cd have significantenrichment in Nansi Lake. The whole lake was under moderaterisk of potential ecological. Shaoyang Lake which has the maximum value of RI was unfer high risk of potential ecological. By analyzing the correlation between heavy metal showed Cr, Cu, Zn and Ni was natural sedimentation, but in contrast, As, Hg, Cd and Pb was affected by human activities. The north half of the Nansi Lake overall pollution levels of heavy metals serious than thesouthern half oflake. The pollution rank(form high to low) of different water area was Shaoyang Lake(North half)>Nanyang Lake>Weishan Lake>Dushan Lake>Shaoyang Lake(South half).(2) Using the undisturbed water samples in Weishan Lake to conduct simulation experiments,to investigate the degradation process of DOM in light degradation and microbial degradation conditions.The results shows, the removal of DOM have a significant positive correlation with concentration of ammonia and SRP. Simultaneously, we used three-dimensional fluorescence spectroscopy to research the fluorescence spectra of DOM in the water. The three-dimensional fluorescence spectra appear four 0bvious fluorescence peaks.Peaks B and D were the protein peaks; Peaks A and C were referred to as fulvic-like fluorescence. By setting different lighting conditions,we explore the degradation process of DOM. The degree of DOM degradation were:UV>UL>DK; From the point of view of various components,protein substance to be degraded more easily, In particular, the aromatic ring is a protein amino acid structure substances most likely to be degraded;The fulvic acid macromolecule material more difficult to be degraded.(3)A series of adsorption experiments have studied the binding capacity of DOM and Pb and As in lake sediments,it turns out DOM can efficiently fix the Pb and As into the sediments.Desorption experiments show that DOM could easliy resolve the Pb and As from the adsorbent.Pb combined with DOM are better than As by comparison.The change of DOM and pH in adsorption process of Pb shows there are two stages,first ion exchange occurrs,then a precipitate generates by Pb combined with DOM of larger molecular weight compounds and the concentration of Pb ions decreases with the precipitate.A UV spectroscopy of DOM combined with Pb turns out that the unsaturation of DOM rise go up and the molecular weight reduced as the increase of initial concentration.(4)Balance permeation experiments showed that the molecular weight of surface sediments’ DOM in Nansi Lake is higher than that in Southern Lake.The molecular weight of DOM mainly concentrated in the range of 3.5 ~5.0ku in the North Lake,the one is in the range of 0.5 ~ 3.5ku in Southern Lake. There is no significant differences between the north and south area of Nansi Lake in the Pb binding capacity,but the North Lake is higher than the Southern Lake in As.It is indicated in three-dimensional fluorescence spectral characteristics that the fluorescence intensity after DOM combined with Pb is lager than the case of As.A caculation in binding capacity shows that the organic aggregation capability of As is bigger than Pb. Pb can easily combined with DOM with the molecular weight≤2.0ku,and As is with the molecular in 2.0 ~ 3.5ku.