Three typical sites in eutrophical Donghu lake were selected to sample core sediment and pore water temporarily to investigate vertically spatial and temporal distributions of C、N and P in sediment,interstitial and pore water,as well as effects of trophic state and season on the changes in these nutrients content in different layers of sediment and pore water. The conclusions are listed as below:
1. The optimal experimental condition for pore water preparation was studied. 6000rad•min-1, 4℃ and 30min is a appropriate parameters for pore water preparation using centrifugation method.
2. Among the 3 sampling sites, the highest internal nutirtion loads occurred in the
most pollued Site 1 nearby Shuanghu bridge, sequently followed by Site 3 nearby
Moshan beauty spot and Site 2 in the center of Donghu lake with the lowest nutrition loads. The organic matters in the sediments have different sources: Site 1 owned much higher proportion of terrestrial sources,while the surface layer of Site 2 have both aquatic and terrestrial sources and the layer below were dominated by aquatic sources. In September,the organic matter of Site 3 were dominated by terrestrial sources and in the other months the surface layer have both aquatic and terrestrial sources and the layer below were dominated by aquatic sources.TN, TP, organic carbon, SRP, Al-P and Fe-P showed extensive accumulation in surface level of sediment for all sites, but ammonia and Ca-P increased initially with depth then decreased or stayed at stable levels. Different fractions of bound inorganic phosphorus excluding of O-P and Ca-P reached highest levels in summer, in winter for O-P and Ca-P contrarily. In addition, phosphorus fractions with high bioactivities such as Al-P and SRP showed a trend of transformation to low bioactive fractions such as Ca-P、O-P. TP of sediment changed not significantly in different season and showed significant correlativity with Fe-P.
3.By evaluation the changement of sediment with variation coefficient (C.V.),we knowed that there was good correlation between C.V. and pollution degree:while the pollution degree became worse ,the C.V. became less;with hard pollution of Side 1, the vetical variety of carbon,nitrogen and phosphorus in sediment showed less or middling variation and the variation of Side 2 was obvious;at Side 3, the vetical variety of sediment showed significant variation in June and December while it showed less variation in September.
4. By evaluating the sediment of Donghu lake with organic index and organic nitrogen,it is showed that the sediment of Side 1 was obviously polluted by organic matter of all season and at Side 2 and Side 3,the surface layer of sediment was polluted but the layer below was at the state of less clear excepting the sediment of Side 3 polluted in September ; With the increase of depth in vertical direction ,the organic index tended to decrease;most of the sediment of Donghu lake were polluted by organic nitrogen and except for the underlayer of sediment at Side 2 and Side 3 in December ,pollution of organic nitrogen existed at all other month of all Side.
5.The vertically spatial distributions of N、P in pore water is similar with that in the sediment, showed extensive accumulation in surface level of sediment, then decreased or stayed at stable levels. The major composition of TP in pore water is TDP and more than 65% TP make up of TDP in pore water. The concentrations of TN、TP in pore water have great difference in different seasons which are higher in summer and autumn then in spring and winter,but the diffenences are small in different sites. TN in the sediment showed significant correlativity with it in pore water but the correlativity between TP in the sediment and TP 、TDP in pore water is much lower.