Studies On Characteristics Of Dissolved Organic Matter And Organic Nitrogen In Lake Sediments

Eutrophication along with the blooms of blue-green algae became a global ecological problem, and eutrophication in Yunnan-Guizhou lakes was becoming increasingly evident. In order to understand the structure of dissolved organic matter (DOM) and distribution characteristics of soluble organic nitrogen (SON), DOM and SON of Yunnan-Guizhou lake sediments were studied using 3DEEM and UV-Vis Absorption Spectral. The results could provide theoretical references for preventive and rehabilitative measures against the eutrophication in Yunnan-Guizhou lakes. The main conclusions included:(1) Effects of submerged plants on characteristics of DOM in sediments under different doses of NH4+-N. Under the experimental conditions, different doses of NH4+-N had a little effect on the fluorescent intensity of DOM in sediments. The fluorescent intensity of DOM in sediments with submerged plants was stronger than that without submerged plants; Dose of NH4+-N enhanced the effect of submerged plants on DOM in sediments. The results indicated that the increase of the content of protein and amino acid resulting from extraneous NH4+-N submerged plants enhanced the bioavailability of dissolved organic nitrogen in sediments.(2) The difference of fluorescent characteristics of DOM in lake sediments. There were four fluorescent peaks in all samples, peak A, peak B, peak C and peak D. Because of the effect of submerged plants on DOM, the Peak D of DOM in 2# and 13# sediments in Erhai lakes was missing. In other lakes, the four fluorescent peaks had obvious central peaks. Moreover, the more polluted the lake was, the stronger fluorescent intensity of DOM was in sediments. The fluorescent intensity of peak A, peak C was stronger than that of peak B and peak D in Erhai lake sediment, and the intensity of peak D was the weakest one of all. And the contents of humic-like and fulvic-like substances were more than protein-like and amino-acid-like substances. For Chenhai, Fuxian and Xingyun lakes, the intensity of peak D was stronger than peak A, peak B and peak C. Namely, there were higher contents of humic-like substances than those of protein-like substances. Among all sediment samples, there were the highest contents of humic-like substances, and lowest contents of protein-like substances in DOM from Dianchi lake sediments.(3) UV-Vis absorption spectral character of DOM in Ehhai sediments. Distribution characteristic of DOM at 280nm was similar to DOC concentrations in sediment of Erhai Lake. The ratio (E3/E4) for the DOM in sediment was among 2.5 and 5.4 and most of them were between 3.5 and 5.4. The humification level of DOM was low and there were little aromatic rings in DOM structure. As for molecular weight distribution, it mainly based on fulvic acid contents which had small molecular weight, and the content of humic acid with big molecular weight was little.(4) The SON extraction method was studied by using salt solution, CaCl2, as extract. The stability of experimental data and repeatability of experimental results were satisfactory with this method. Though KCl also could draw same amount of SON as CaCl2, the experimental data were susceptible to minus values and the repeatability of experimental results was relatively poor. The antibacterial agent (HgCl2) can inhabit the decomposition reactions of SON in the experiments. Thus it was available to select 0.02 mol/L CaCl2 salt solution (with 10 mmol/LHgCl2) as extract.(5) The content distribution characteristics of SON in sediments was studied with 29 samples. Results indicated that SON contents varied greatly from 1.336 mg/kg to 136.897 mg/kg with a mean content of 47.511 mg/kg, and SON contents in Erhai lake samples varied greatly from 32.471 mg/kg to 75.887 mg/kg (mean content,47.216 mg/kg). The SON contents were highest in 9# which was in deep area and least in 7# where there were no plants. The SON contents were significantly correlated with their contents of TSN and TOC (R2 was 0.8969,0.8346 respectively), and SON were higher in the heavily polluted sediments than the light polluted ones. The distributions of SON were closely related to their lake pollution levels.