| In this paper,the sediments in three urban lakes was selected as research object,49samples werecollected in April,2013.18sampling sites were set in Longting Lake,20sampling sites were set inBaogong Lake,11sampling sites were set in Tieta Lake. Physicochemical properties of sediment,totalnitrogen,total phosphorus and heavy metals in the sediments of three urban lake were measured. The spatialdistribution of those were analyzed, two natural lakes of sediments such as Taihu Lake and Chaohu Lakewas choosed to make a comparative analysis. At the same time, physicochemical properties ofsediment,total nitrogen,total phosphorus and heavy metals in the sediments of three urban lake were madecorrelation analysis and their pollution assessment were carried out. The result showed that:(1)The sediments of three urban lakes are slightly alkaline; their grain size are so big, the mainpart of the sediment is powder sand fraction. The high contents of organic carbon in the sediment near thearea where is influenced by human activities greater than other areas. The grain size of sediments were inrange of4-63μm, little samples were bigger than63μm. The spatial distribution of organic carbon in thesediment of Longting Lake was gradually increased from the western lake northwest to the middle lakesoutheast, but Baogong Lake and Tieta Lake had no clear spatial distribution characteristics.(2)There are some differences between the physicochemical properties of sediment in three urbanlakes and natural lakes’.The sediment of Tai Lake’s average of pH values is6.6,it is belong tosubacidity,Chao Lake’s average of pH values is7.12,it is tend to neutral;their contents of sand and coarsesand composition are higher than natural lakes’; the contents of organic carbon in the sediment are higherthan natural lakes’. (3)The contens of total nitrogen and total phosphorus followed the order:Baogong Lake＞TietaLake＞Longting Lake. The high contents of total nitrogen and total phosphorus in the sediment near thearea where was influenced by human activities greater than others areas. Their spatial distribution of totalnitrogen were very similar to organic carbon; spatial distribution of total phosphorus and organic carbonhave different distribution characteristics in Longting Lake and Baogong Lake sediment, but spatialdistribution of total phosphorus are similar to organic carbon in Tieta Lake sediment.(4) The correlation of total nitrogen, total phosphorus and physicochemical properties showedthat organic nitrogen accounted a larger proportion of total nitrogen; the source of total nitrogen and totalphosphorus are different in Longting Lake, the total nitrogen and total phosphorus are homology inBaogong Lake and Tieta Lake. Their pH was negative correlated correlated with total nitrogen, totalphosphorus and organic carbon; the particle of above63μm was negative correlated with otal nitrogen, totalphosphorus and organic carbon in sediments of Longting Lake and Tieta Lake, however, the particle ofbelow4μm was positive correlated with them,but those correlation in the sediment of Baogong Lake wereopposed to those other lakes’.(5)By evaluating pollution situation with organic index and single factor appraisal methodshowed that there were little samples in Longting Lake and Tieta Lake belonged to clear category，anothersamples were belonged to organic nitrogen,all samples in Baogong Lake were belonged to organicpollution category. All samples of three urban lakes’ evaluation value of TN were higher than evaluationindex; all samples of Baogong Lake and Tieta Lake’s evaluation value of TP were higher than evaluationindex,77.8%of the samples in Longting Lake’s evaluation value of TP were higher than evaluationindex;this showed that their sediments were in a serious N and P pollution situation. (6)The contens of heavy metals in sediments of three urban lakes followed the order:BaogongLake＞Longting Lake＞Tieta Lake. The contents of heavy metals in the inflow river mouth areas weresignificantly lower than others areas,and the high contents of heavy metals was close to the lakefront wherewas influenced by human activities.(7)Cr, Ni, Cu, Zn, Cd in the sediment of Longting Lake were came from the same pollutionsource;the pollution source of Pb was same as Cr, Ni, Cu; Cr, Cu, Zn, Cd in the sediment of Baogong Lakewere came from the same pollution source and the pollution source of Pb was different from rest heavymetals; Cr, Ni, Cu, Zn, Cd in the sediment of Tieta Lake were came from the same pollution source and thepollution source of Pb was different from others heavy metals. With grain size from large to small,the negative correlation between heavy metals and particle size would became positive correlation, organiccarbon was significantly positive correlated with Cr, Ni, Cu, Zn, Cd, the pH was extremely significantnegative correlated with these heavy metals;heavy metals in the sediment of Baolong Lake were noobviously negative correlated with the particle of below4μm except Ni, organic carbon was significantlypositive correlated with Cr, Cu, Zn, Cd, the pH was significantly negative correlated with Cr, Cu, Zn, Cd,Pb;those heavy metals in the sediment of Tieta Lake were no obviously correlated with the particle ofbelow4μm except Cr and Ni, the organic carbon was extremely significant positive correlated with Cr, Ni,Cu, Zn, Cd, the pH was significantly negative correlated with Cu, Zn, Cd.(8)The evaluation of six kinds of heavy metals in sediments of three urban lakes with the methodof geoaccumulation assessment showed: six kinds of heavy metals in sediments of Longting Lake and TietaLake and five kinds of heavy metals in sediments of Baogong Lake were belonged to clear category whenreference value was choosed the highest background value of heavy metals in sediments beforeindustrialization; Cu element in sediment of Baogong Lake belonged to slight pollution. When the reference value was choosed the soil background value of Kaifeng, Cr,Ni,Cu,Zn in the sediment ofLongting Lake belonged to slight pollution, Cd element belonged to clear category and Pb elementbelonged to partial moderate pollution; Cr, Zn, Pb in the sediment of Baogong Lake belonged to partialmoderate pollution, Ni, Cd belonged to slight pollution and Cu element belonged to moderatelycontaminated; Cr, Cu,Zn in sediment of Tieta Lake belonged to slight pollution, Ni, Cd belonged to clearcategory and Pb element belonged to partial moderate pollution. The evaluation of six kinds of heavymetals in sediments of three urban lakes with the method of potential ecological risk assessment showed:when reference value was choosed the highest background value of heavy metals in sediments beforeindustrialization,their average of potential ecological risk indices for all heavy metals was low. When thereference value was choosed the soil background value of Kaifeng,the average of potential ecological riskindices for all heavy metals in sediments of Longting Lake and Tieta Lake was medium and BaogongLake’s was high. The average of potential ecological risk factor for heavy metals in sediments of LongtingLake was low except Cd element, Cd element’s average of potential ecological risk factor was medium; Cuand Cd average of potential ecological risk factor in the sediment of Baogong Lake was medium,rest kindsof heavy metals’ was low; Cd element’s average of potential ecological risk factor in the sediment of TietaLake was medium.(9)The contents of total nitrogen,total phosphorus and Pb element in sediments of three urbanlakes were higher than reference sediments of natural lakes’. The contents of total phosphorus was1.5-3times and the contents of total nitrogen was4times more than reference sediments of natural lakes’. Thecontents of Ni,Cd in sediments of three urban lakes were lower than reference sediments of natural lakes’. |
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