| In lakes and their river basin, sediments are the important home and accumulation library of nutrient and other contaminants. As researched, increase of nitrogen and phosphorus in water is a major cause of lake eutrophication. With long-term accumulation, excessive input of carbon, nitrogen and phosphorus, lake sediments turn to be endogenous load, which is hard to be cut. When environmental conditions of lake system get changed, the endogenous load would release upward to the overlying water through processes such as diffusion, convection and sediment resuspension water, and this would lead to "secondary pollution" phenomenon, then seriously influence the quality of overlying water. Sediment can indirectly reflect the water pollution situation, for controlling endogenous load and improving ecological system condition of lake water, it has important guiding significance to do a research on content and its distribution characteristics of nitrogen, phosphorus and organic matter in lake library sediment. NanSi Lake is the most important water source for eastern route project in the South-to-North Water Diversion Project, as well as the most important shipping section for the Beijing-Hangzhou Grand Canal, so it is particularly important to do a research on sediment distribution characteristics and their correlations of nitrogen, phosphorus and organic matter. This paper took four different lake areas of NanSi Lake as research object, columnar sediment sampler was utilized to obtain situ cylindrical sediments, then analyzed the lake library content of nitrogen, phosphorus and organic matter in sediments and their distribution characteristics. Meanwhile, peeper interstitial water collector and traditional centrifugation were used to obtain the sediment interstitial water, the distribution characteristic of PO43--P was analyzed, and the two methods compared. On the basis of the results above, the correlation between sediment phosphorus forms and interstitial water orthophosphate were analysed and explored. Through combination of wild field measurement and the indoor simulation experiment, this paper emphatically studied on physical and chemical process of complex system and nutrient exchange mechanism of NanSi Lake in soil and water sediment, interstitial water and overlying water, and obtained the main conclusion as followed:1.NanSi Lake sediments contain abundant nitrogen and have significant spatial difference. Generally, it presents a decreasing trend from north to south, in which Nanyang lake district (NSH1) contains the highest TN, its surface has30cm sediments with average content up to2471mg/kg, and the reason is that the north of NanSi Lake is close to Jining city and has been polluted seriously. The descending order of sediments TP content in NanSi Lake is NSH1> NSH2> NSH4> NSH3, among which the IP content is the highest, accounting for71-90%of TP. Sediments on the vertical distribution of the phosphorus form is more complex, and the regularity is not obvious.2. The average content of sediment organic matter (LOI) for four lakes of NanSi Lake is4.66-9.00%, and it has a significant correlation with TP, which shows that nitrogen and phosphorus from NanSi Lake sediments have a certain similarity in the deposition behavior, and the nitrogen and phosphorus in sediments might come mainly from organic matter mineralization of lake sediments. The correlation between TP and IP is obvious, while the correlation between TP and OP is indistinctive, indicating that the TP increase mainly comes from Fe/Al-P and Ca-P in inorganic phosphorus.3.In surface sediment, the sediment interstitial water content obtained by using NanSi Lake centrifugation presents a increasing tendency with depth, indicating that the gas-water interface of sediment has a higher concentration gradient and possesses upward releasing potential to overlying water. The maximum value of NSH1point interstitial water PO43--P is in7cm, reaching to1.98mg.L-1, and the average content is0.84mg.L-1. NSH1content is the highest in the four sampling points, and the interstitial water PO43--P content is significantly lower in the remaining three sampling points. In summer, NSH2maximum value appears to5cm,0.21mg.L-1, and its average value is0.15mg.L-1. NSH3maximum value appears to5cm,0.41mg.L-1, and its average value is0.2mg.L-1. NSH4maximum value appears to3cm,0.17mg.L-1, and its average value is0.11mg.L-1. The average contents of PO43--P interstitial water obtained by using Peeper method is about20%higher than that obtained by traditional centrifugation, and the correlation is quite well, and the results from two methods both indicate that sediments Fe/Al-P and Ca-P are positive correlated with PO43-P content in the pore water of Nansi Lake.4. Interstitial water from different lake districts are respectively obtained by using Peeper method and centrifugation method, then the release rate of NH4+-N and PO43--P are calculated by using molecular diffusion model, and the release rate respectively are3.69-4.51mg-(m2·d)-1,0.24-0.66mg-(m2·d)-1,2.54-4.16mg-(m2·d)-1and0.04-0.51mg·(m2·d)-1. For the same sampling point, the release rate got by using Peeper method is about20%higher than that got by using traditional centrifugation. In the spatial distribution, the release rate of NH4+-N and PO43--P obtained by static release experiments is consistent with the results calculated by interstitial water molecules diffusion model, but the former is significantly faster than the latter. Results of comparation analysis showed that R/F values of N and P is0.84,2.64and2.03,13.79respectively, indicating that the endogenous release rate estimated by original column sample static simulation experiment may be more close to the actual situation than that calculated by molecular diffusion model. |
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